Reducing the hypoxic fraction of a tumour model by growth in low glucose.

The question of whether growth under low glucose conditions leads to a reduced amount of cell hypoxia was investigated using an in vitro tumour analogue, the sandwich system. In this multicellular system, the interplay between diffusion and consumption of oxygen and nutrients results in spatial gradients of these environmental factors. Gradients in the environment lead to biological heterogeneity within the cell population. A necrotic centre, surrounded by a viable cell border, subsequently develops. Cells adjacent to the necrotic centre in sandwiches are hypoxic and are in an environment somewhat analogous to that of cells adjacent to necrotic regions in solid tumours. Using sandwiches of the 9L and V79 cell lines, the effects of growth under low glucose conditions on the degree of hypoxia in regions adjacent to the necrotic centre were investigated. Per-cell binding of 3H-misonidazole, assessed by autoradiography, was used as an indicator of oxygen deprivation. It was found that the extent of the hypoxic region and the severity of hypoxia were considerably reduced by growing sandwiches in a glucose concentration of 0.6 mM rather than 6.5 mM. This reduction was found in conjunction with a smaller viable border; it occurred despite the fact that the average per-cell oxygen consumption is higher in the low glucose sandwiches. The data are qualitatively consistent with a joint oxygen-glucose deprivation model for cell necrosis

Polarization tunable selective polariton generator

A selective polariton generator (SPG) design, based on surface plasmon antennae principles, is demonstrated to provide a selective light transmission peak. The polarization-sensitive structure selectively generates and transports polaritons of a desired wavelength through a circular subwavelength aperture. By varying the SPG structure around a central nanohole, we are able to control the peak optical transmission wavelengths via the polarization state of the incident photons. We find good agreement between simulations and experimental results

Cosmological implications of a Dark Matter self-interaction energy density

We investigate cosmological constraints on an energy density contribution of elastic dark matter self-interactions characterized by the mass of the exchange particle and coupling constant. Because of the expansion behaviour in a Robertson-Walker metric we investigate self-interacting dark matter that is warm in the case of thermal relics. The scaling behaviour of dark matter self-interaction energy density shows that it can be the dominant contribution (only) in the very early universe. Thus its impact on primordial nucleosynthesis is used to restrict the interaction strength, which we find to be at least as strong as the strong interaction. Furthermore we explore dark matter decoupling in a self-interaction dominated universe, which is done for the self-interacting warm dark matter as well as for collisionless cold dark matter in a two component scenario. We find that strong dark matter self-interactions do not contradict super-weak inelastic interactions between self-interacting dark matter and baryonic matter and that the natural scale of collisionless cold dark matter decoupling exceeds the weak scale and depends linearly on the particle mass. Finally structure formation analysis reveals a linear growing solution during self-interaction domination; however, only non-cosmological scales are enhanced.Comment: 14 pages, 14 figures; version published in Phys. Rev.

Polarisation and wavelength selective transmission through nanohole structures with multiple grating geometry

Excitation and localization of surface plasmon polariton modes in metal-dielectric structures can be utilized to construct nanophotonic materials and devices with tuneable optical dispersion. We present a selective polariton generator (SPG) device that demonstrates switching of light transmission based on surface plasmon antennae principles. This polarization-sensitive structure selectively generates and transports polaritons of a desired wavelength through subwavelength apertures. Two of these SPGs have been combined around a nanohole into a new, single device that allows polarization and wavelength selective switching of transmission. The multi-state operation is confirmed by experiment results

Coupling hydrodynamics with comoving frame radiative transfer: II. Stellar wind stratification in the high-mass X-ray binary Vela X-1

CONTEXT: Vela X-1, a prototypical high mass X-ray binary (HMXB), hosts a neutron star (NS) in a close orbit around an early-B supergiant donor star. Accretion of the donor star's wind onto the NS powers its strong X-ray luminosity. To understand the physics of HMXBs, detailed knowledge about the donor star winds is required. AIMS: To gain a realistic picture of the donor star in Vela X-1, we constructed a hydrodynamically consistent atmosphere model describing the wind stratification while properly reproducing the observed donor spectrum. To investigate how X-ray illumination affects the stellar wind, we calculated additional models for different X-ray luminosity regimes. METHODS: We use the recently updated version of the PoWR code to consistently solve the hydrodynamic equation together with the statistical equations and the radiative transfer. RESULTS: The wind flow in Vela X-1 is driven by ions from various elements with Fe III and S III leading in the outer wind. The model-predicted mass-loss rate is in line with earlier empirical studies. The mass-loss rate is almost unaffected by the presence of the accreting NS in the wind. The terminal wind velocity is confirmed at $v_\infty \approx 600$ km/s. On the other hand, the wind velocity in the inner region where the NS is located is only $\approx 100$ km/s, which is not expected on the basis of a standard $\beta$-velocity law. In models with an enhanced level of X-rays, the velocity field in the outer wind can be altered. If the X-ray flux is too high, the acceleration breaks down because the ionization increases. CONCLUSIONS: Accounting for radiation hydrodynamics, our Vela X-1 donor atmosphere model reveals a low wind speed at the NS location, and it provides quantitative information on wind driving in this important HMXB.Comment: 19 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

CoRoT 102918586: a Gamma Dor pulsator in a short period eccentric eclipsing binary

Pulsating stars in eclipsing binary systems are powerful tools to test stellar models. Binarity enables to constrain the pulsating component physical parameters, whose knowledge drastically improves the input physics for asteroseismic studies. The study of stellar oscillations allows us, in its turn, to improve our understanding of stellar interiors and evolution. The space mission CoRoT discovered several promising objects suitable for these studies, which have been photometrically observed with unprecedented accuracy, but needed spectroscopic follow-up. A promising target was the relatively bright eclipsing system CoRoT 102918586, which turned out to be a double-lined spectroscopic binary and showed, as well, clear evidence of Gamma Dor type pulsations. We obtained phase resolved high-resolution spectroscopy with the Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS spectrograph at the ESO 2.2m telescope. Spectroscopy yielded both the radial velocity curves and, after spectra disentangling, the component effective temperatures, metallicity and line-of-sight projected rotational velocities. The CoRoT light curve was analyzed with an iterative procedure, devised to disentangle eclipses from pulsations. We obtained an accurate determination of the system parameters, and by comparison with evolutionary models strict constraints on the system age. Finally, the residuals obtained after subtraction of the best fitting eclipsing binary model were analyzed to determine the pulsator properties. We achieved a quite complete and consistent description of the system. The primary star pulsates with typical {\gamma} Dor frequencies and shows a splitting in period which is consistent with high order g-mode pulsations in a star of the corresponding physical parameters. The value of the splitting, in particular, is consistent with pulsations in l = 1 modes.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and Astrophysic