Streamwise oscillation of spanwise velocity at the wall of a channel for turbulent drag reduction

Steady forcing at the wall of a channel flow is studied via DNS to assess its ability of yielding reductions of turbulent friction drag. The wall forcing consists of a stationary distribution of spanwise velocity that alternates in the streamwise direction. The idea behind the forcing builds upon the existing technique of the spanwise wall oscillation, and exploits the convective nature of the flow to achieve an unsteady interaction with turbulence. The analysis takes advantage of the equivalent laminar flow, that is solved analytically to show that the energetic cost of the forcing is unaffected by turbulence. In a turbulent flow, the alternate forcing is found to behave similarly to the oscillating wall; in particular an optimal wavelength is found that yields a maximal reduction of turbulent drag. The energetic performance is significantly improved, with more than 50% of maximum friction saving at large intensities of the forcing, and a net energetic saving of 23% for smaller intensities. Such a steady, wall-based forcing may pave the way to passively interacting with the turbulent flow to achieve drag reduction through a suitable distribution of roughness, designed to excite a selected streamwise wavelength

Hard X-ray emission from Eta Carinae

Context : If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and gamma-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected. Aims : To detect this emission, observations of Eta Carinae were performed with INTEGRAL, leveraging its high spatial resolution. Methods : Deep hard X-ray images of the region of Eta Car were constructed in several energy bands. Results : The hard X-ray emission previously detected by BeppoSax around Eta Car originates from at least 3 different point sources. The emission of Eta Car itself can be isolated for the first time, and its spectrum unambiguously analyzed. The X-ray emission of Eta Car in the 22-100 keV energy range is very hard (photon index around 1) and its luminosity is 7E33 erg/s. Conclusions : The observed emission is in agreement with the predictions of inverse Compton models, and corresponds to about 0.1% of the energy available in the wind collision. Eta Car is expected to be detected in the GeV energy range.Comment: 5 pages with 2 figures. Accepted as a Letter in Astronomy & Astrophysic

A Flattened Protostellar Envelope in Absorption around L1157

Deep Spitzer IRAC images of L1157 reveal many of the details of the outflow and the circumstellar environment of this Class 0 protostar. In IRAC band 4, 8 microns, there is a flattened structure seen in absorption against the background emission. The structure is perpendicular to the outflow and is extended to a diameter of 2 arcminutes. This structure is the first clear detection of a flattened circumstellar envelope or pseudo-disk around a Class 0 protostar. Such a flattened morphology is an expected outcome for many collapse theories that include magnetic fields or rotation. We construct an extinction model for a power-law density profile, but we do not constrain the density power-law index.Comment: ApJL accepte

Submillimeter CO emission from shock-heated gas in the L1157 outflow

We present the CO J=6-5, 4-3, and 3-2 spectra from the blueshifted gas of the outflow driven by the low-mass class 0 protostar in the L1157 dark cloud. Strong submillimeter CO emission lines with T_mb > 30 K have been detected at 63" (~0.13 pc) south from the protostar. It is remarkable that the blue wings in the submillimeter lines are stronger by a factor of 3-4 than that of the CO J=1-0 emission line. The CO line ratios suggest that the blueshifted lobe of this outflow consists of moderately dense gas of n(H_2) = (1-3)x10^4 cm^-3 heated to T_kin = 50-170 K.It is also suggested that the kinetic temperature of the outflowing gas increases from ~80 K near the protostar to ~170 K at the shocked region in the lobe center, toward which the largest velocity dispersion of the CO emission is observed. A remarkable correlation between the kinetic temperature and velocity dispersion of the CO emission along the lobe provides us with direct evidence that the molecular gas at the head of the jet-driven bow shock is indeed heated kinematically. The lower temperature of ~80 K measured at the other shocked region near the end of the lobe is explained if this shock is in a later evolutionary stage, in which the gas has been cooled mainly through radiation of the CO rotational lines.Comment: 10 pages, 4 PDF figures, APJL in pres

UV and X-Ray Monitoring of AG Draconis During the 1994/1995 Outbursts

The recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With \ros observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size.Comment: 12 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996

The CHANDRA HETGS X-ray Grating Spectrum of Eta Car

Eta Car may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emisssion. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively ``resolving'' the shock. If so, the pre-shock wind velocities are ~ 700 and ~ 1800 km/s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from Eta Car and from the hidden companion star. The forbidden-to-intercombination (f/i) line ratios for the He-like ions of S, Si and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93 Angstrom, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides an uninterrupted high-time resolution lightcurve of the stellar X-ray emission from Eta Car and suggests that there was no significant, coherent variability during the CHANDRA observation. The Eta Car CHANDRA grating spectrum is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.Comment: revised after comments from referee and includes a new variability analysis, taking into account the effects of CCD pileu

Somatic muscolature of Tardigrada: phylogenetic signal and metameric patterns

Although studies describing molecular-based phylogenies within tardigrades are now frequently being published, this is not the case for studies combining molecular and morphological characters. Tardigrade phylogeny is still based, from a morphological point of view, almost exclusively on chitinous structures and little attention has been given to detecting and using novel morphological data. Consequently, we analysed the musculature of seven tardigrade species belonging to the main phyletic lines by confocal laser scanning microscopy and compared these morphological results with new molecular analyses (18S+28S rRNA genes). Finally, we analysed all the data with a total evidence approach. A consilience in the phylogenetic relationships among orders and superfamilies of tardigrades was obtained among the evolutionary trees obtained from morphological, molecular and total evidence approaches. Comparative analysis on the musculature allowed the identification of serial homologies and repeated metameric patterns along the longitudinal animal body axis. A phenomenon of mosaic evolution was detected in musculature anatomy, as dorsal musculature was found to be highly modified with respect to the other body muscle groups, probably related to the evolution of dorsal cuticular plates. An understanding of tardigrade musculature anatomy will give fundamental information to understand the evolution of segmental pattern within Panarthropoda

Vivamos más pero mejor

Fil: Ceballos de Viotti, Adriana Teresita. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Fil: Caciva, Ricardo Crhistian. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Estomatología A; Argentina.Fil: Viotti, María Virginia. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Fil: Morales, S. J. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Introducción: La prevalencia de la Hipertensión Arterial (HTA), en nuestra población joven, es cada vez mayor. Esto nos lleva a reflexionar sobre dicha problemática. Los factores de riesgo (obesidad, sedentarismo, tabaco, alcohol, dieta incorrecta, etc.) están muy arraigados en la sociedad. Este proyecto fue seleccionado en 2013 entre los presentados a la convocatoria de Responsabilidad Social Universitaria, pero de: "IMPACTO INTERNO", es decir, para beneficio de la comunidad interna de la Universidad Católica de Córdoba (alumnos, docentes, no docentes).http://odo.unc.edu.ar/extension/libro-de-resumenes-i-jornadas-nacionales-de-extension-en-odontologiaFil: Ceballos de Viotti, Adriana Teresita. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Fil: Caciva, Ricardo Crhistian. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Estomatología A; Argentina.Fil: Viotti, María Virginia. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Fil: Morales, S. J. Universidad Nacional de Córdoba. Facultad de Odontología. Cátedra de Semiología; Argentina.Odontología, Medicina y Cirugía Ora

Comparison of Magnetic Field Structures on Different Scales in and around the Filamentary Dark Cloud GF 9

New visible polarization data combined with existing IR and FIR polarization data are used to study how the magnetic field threading the filamentary molecular cloud GF 9 connects to larger structures in its general environment. We find that when both visible and NIR polarization data are plotted as a function of extinction, there is no evidence for a plateau or a saturation effect in the polarization at Av ~ 1.3 as seen in dark clouds in Taurus. This lack of saturation effect suggests that even in the denser parts of GF 9 we are still probing the magnetic field. The visible polarization is smooth and has a well-defined orientation. The IR data are also well defined but with a different direction, and the FIR data in the core region are well defined and with yet another direction, but are randomly distributed in the filament region. On the scale of a few times the mean radial dimension of the molecular cloud, it is as if the magnetic field were `blind' to the spatial distribution of the filaments while on smaller scales within the cloud, in the core region near the IRAS point source PSC 20503+6006, polarimetry shows a rotation of the magnetic field lines in these denser phases. Hence, in spite of the fact that the spatial resolution is not the same in the visible/NIR and in the FIR data, all the data put together indicate that the field direction changes with the spatial scale. Finally, the Chandrasekhar and Fermi method is used to evaluate the magnetic field strength, indicating that the core region is approximately magnetically critical. A global interpretation of the results is that in the core region an original poloidal field could have been twisted by a rotating elongated (core+envelope) structure. There is no evidence for turbulence and ambipolar diffusion does not seem to be effective at the present time.Comment: 33 pages, 6 tables, 8 figures, Accepted by Ap