Rarefaction Shock Waves: a contribution to experiments and simulations

CFD simulations of a flexible asymmetric shock tube in order to get insight on how the finite size of the opening of the valve, and moreover the variation of the cross-sectional area of the shock tube, influence the formation of a nonclassical rarefaction shock wave

Towards a genealogy of the gender space of politics

El artículo pretende trazar, en la edad clásica de nuestra civilización occidental, el esquema lógico binario del que sobresale la división de género del espacio político. Esta se fundamenta en la tensión excluyente que encierra la polis y el oikos en dos distintas dimensiones, caracterizadas por una discordancia constitutiva de la ciudadanía y de la subordinación femenina. Finalmente se evocan brevemente dos líneas de fuga representadas por las figuras corpóreas de Penélope y de Antígona.The aim of this article is to trace a logical, binary outline of the classical period of western civilisation, from which the gender division of political space has emerged. This gender division has been deepened by an excluding tension which divides the polis and the oikos into two distinct spheres; these are marked by a structural asymmetry between the citizenry and female subordination. In closing, two other points will be briefly made, which are recalled by the bodily figures of Penelope and Antigone

The radio/X-ray correlation in Cyg X-3 and the nature of its hard spectral state

We study the radio/X-ray correlation in Cyg X-3. It has been known that the soft and hard X-ray fluxes in the hard spectral state are correlated positively and negatively, respectively, with the radio flux. We show that this implies that the observed $\sim$1--100 keV flux (which is a fair approximation to the bolometric flux) is completely uncorrelated with the radio flux. We can recover a positive correlation (seen in other sources and expected theoretically) if the soft X-rays are strongly absorbed by a local medium. Then, however, the intrinsic X-ray spectrum of Cyg X-3 in its hard state becomes relatively soft, similar to that of an intermediate spectral state of black-hole binaries, but not to their true hard state. We also find the radio spectra in the hard state of Cyg X-3 are hard on average, and the flux distributions of the radio emission and soft X-rays can be described by sums of two log-normal functions. We compare Cyg X-3 with other X-ray binaries using colour-colour, colour-Eddington ratio and Eddington ratio-radio flux diagrams. We find Cyg X-3 to be spectrally most similar to GRS 1915+105, except that Cyg X-3 is substantially more radio loud, which appears to be due to its jet emission enhanced by interaction with the powerful stellar wind from the Wolf-Rayet donor.Comment: An error in the BAT light curve shown in Fig. A2 corrected. Published in MNRAS + erratu

Swift reveals the eclipsing nature of the high mass X-ray binary IGR~J16195-4945

IGR J16195-4945 is a hard X-ray source discovered by INTEGRAL during the Core Program observations performed in 2003. We analyzed the X-ray emission of this source exploiting the Swift-BAT survey data from December 2004 to March 2015, and all the available Swift-XRT pointed observations. The source is detected at a high significance level in the 123-month BAT survey data, with an average 15-150 keV flux of the source of ~1.6 mCrab. The timing analysis on the BAT data reveals with a significance higher than 6 standard deviations the presence of a modulated signal with a period of 3.945 d, that we interpret as the orbital period of the binary system. The folded light curve shows a flat profile with a narrow full eclipse lasting ~3.5% of the orbital period. We requested phase-constrained XRT observations to obtain a more detailed characterization of the eclipse in the soft X-ray range. Adopting resonable guess values for the mass and radius of the companion star, we derive a semi-major orbital axis of ~31 R_sun, equivalent to ~1.8 times the radius of the companion star. From these estimates and from the duration of the eclipse we derive an orbital inclination between 55 and 60 degrees. The broad band time-averaged XRT+BAT spectrum is well modeled with a strongly absorbed flat power law, with absorbing column N_H=7x 10^22 cm^(-2) and photon index Gamma=0.5, modified by a high energy exponential cutoff at E_cut=14 keV.Comment: 5 pages, 5 figures, 2 tables. Published on MNRA

An analytic technique for the estimation of the light yield of a scintillation detector

A simple model for the estimation of the light yield of a scintillation detector is developed under general assumptions and relying exclusively on the knowledge of its optical properties. The model allows to easily incorporate effects related to Rayleigh scattering and absorption of the photons.The predictions of the model are benchmarked with the outcomes of Monte Carlo simulations of specific scintillation detectors. An accuracy at the level of few percent is achieved. The case of a real liquid argon based detector is explicitly treated and the predicted light yield is compared with the measured value.Comment: 17 pages, 5 figure

Temporal features of LS I +61∘^{\circ}303 in hard X-rays from the Swift/BAT survey data

We study the long-term spectral and timing behaviour of LS I +61$^{\circ}$303 in hard X-rays (15--150 keV) using $\sim$10 years of survey data from the $Swift$ Burst Alert Telescope (BAT) monitor. We focus on the detection of long periodicities known to be present in this source in multiple wavelengths. We clearly detect three periods: the shorter one at 26.48 days is compatible with the orbital period of the system; the second, longer, periodicity at 26.93 days, is detected for the first time in X-rays and its value is consistent with an analogous temporal feature recently detected in the radio and in the gamma-ray waveband, and we associate it with a modulation caused by a precessing jet in this system. Finally, we find also evidence of the long-term periodicity at $\sim$1667 d, that results compatible with a beat frequency of the two close, and shorter, periodicities. We discuss our results in the context of the multi-band behaviour of the physical processes of this source.Comment: 5 pages, 8 figures. Published in MNRA