Average output entropy for quantum channels

We study the regularized average Renyi output entropy \bar{S}_{r}^{\reg} of quantum channels. This quantity gives information about the average noisiness of the channel output arising from a typical, highly entangled input state in the limit of infinite dimensions. We find a closed expression for \beta_{r}^{\reg}, a quantity which we conjecture to be equal to \Srreg. We find an explicit form for \beta_{r}^{\reg} for some entanglement-breaking channels, and also for the qubit depolarizing channel $\Delta_{\lambda}$ as a function of the parameter $\lambda$. We prove equality of the two quantities in some cases, in particular we conclude that for $\Delta_{\lambda}$ both are non-analytic functions of the variable $\lambda$.Comment: 32 pages, several plots and figures; positivity condition added for Theorem on entanglement breaking channels; new result for entrywise positive channel

The Polarized Spectrum of Apm 08279+5255

We report the discovery of significant linear polarization (p > 1%) in the hyperluminous z=3.87 BALQSO APM~08279+5255. The polarization spectrum is complex, with properties similar to those of other, lower redshift but more highly polarized BALQSOs. The resonance emission lines are unpolarized while the absorption troughs show polarization similar to or higher than the continuum. In particular, an apparent increase of polarization in the trough covering 1000-1030 angstroms (rest) supports the interpretation of this feature as a broad absorption component associated with OVI/Ly_beta local to the QSO, as opposed to an intervening damped Ly_alpha absorption system. The elevated polarization in some of the absorption features implies that we view the scattered (polarized) spectrum through a sightline with less absorbing material than the direct spectrum. Therefore, the complex structure of the polarization spectrum in this brilliant lensed BALQSO suggests that it will be an important laboratory for studying the structure of QSOs at high redshift.Comment: 8 pages, 1 figure. Accepted for publication in The Astrophysical Journal Letter

Partial covering of emission regions of Q 0528-250 by intervening H2_2 clouds

We present an analysis of the molecular hydrogen absorption system at z$_{\rm abs}$ = 2.811 in the spectrum of the blazar Q0528-250. We demonstrate that the molecular cloud does not cover the background source completely. The partial coverage reveals itself as a residual flux in the bottom of saturated H_2 absorption lines. This amounts to about (2.22$\pm$0.54)% of the continuum and does not depend on the wavelength. This value is small and it explains why this effect has not been detected in previous studies of this quasar spectrum. However, it is robustly detected and significantly higher than the zero flux level in the bottom of saturated lines of the Ly-alpha forest, (-0.21$\pm$0.22)%. The presence of the residual flux could be caused by unresolved quasar multicomponents, by light scattered by dust, and/or by jet-cloud interaction. The H$_2$ absorption system is very well described by a two-component model without inclusion of additional components when we take partial coverage into account. The derived total column densities in the H$_2$ absorption components A and B are logN(H$_2$)[cm$^{-2}$] = 18.10$\pm$0.02 and 17.82$\pm$0.02, respectively. HD molecules are present only in component B. Given the column density, logN(HD)= 13.33$\pm$0.02, we find N(HD)/2N(H$_2$)=(1.48$\pm$0.10)x10$^{-5}$, significantly lower than previous estimations. We argue that it is crucial to take into account partial coverage effects for any analysis of H$_2$ bearing absorption systems, in particular when studying the physical state of high-redshift interstellar medium.Comment: Accepted for MNRA

Ca2+-activated K+ Channels in Murine Endothelial Cells: Block by Intracellular Calcium and Magnesium

The intermediate (IKCa) and small (SKCa) conductance Ca2+-sensitive K+ channels in endothelial cells (ECs) modulate vascular diameter through regulation of EC membrane potential. However, contribution of IKCa and SKCa channels to membrane current and potential in native endothelial cells remains unclear. In freshly isolated endothelial cells from mouse aorta dialyzed with 3 μM free [Ca2+]i and 1 mM free [Mg2+]i, membrane currents reversed at the potassium equilibrium potential and exhibited an inward rectification at positive membrane potentials. Blockers of large-conductance, Ca2+-sensitive potassium (BKCa) and strong inward rectifier potassium (Kir) channels did not affect the membrane current. However, blockers of IKCa channels, charybdotoxin (ChTX), and of SKCa channels, apamin (Ap), significantly reduced the whole-cell current. Although IKCa and SKCa channels are intrinsically voltage independent, ChTX- and Ap-sensitive currents decreased steeply with membrane potential depolarization. Removal of intracellular Mg2+ significantly increased these currents. Moreover, concomitant reduction of the [Ca2+]i to 1 μM caused an additional increase in ChTX- and Ap-sensitive currents so that the currents exhibited theoretical outward rectification. Block of IKCa and SKCa channels caused a significant endothelial membrane potential depolarization (≈11 mV) and decrease in [Ca2+]i in mesenteric arteries in the absence of an agonist. These results indicate that [Ca2+]i can both activate and block IKCa and SKCa channels in endothelial cells, and that these channels regulate the resting membrane potential and intracellular calcium in native endothelium

Phase space measure concentration for an ideal gas

We point out that a special case of an ideal gas exhibits concentration of the volume of its phase space, which is a sphere, around its equator in the thermodynamic limit. The rate of approach to the thermodynamic limit is determined. Our argument relies on the spherical isoperimetric inequality of L\'{e}vy and Gromov.Comment: 15 pages, No figures, Accepted by Modern Physics Letters

Neutral chlorine and molecular hydrogen at high redshift

Chlorine and molecular hydrogen are known to be tightly linked together in the cold phase of the local interstellar medium through rapid chemical reactions. We present here the first systematic study of this relation at high redshifts using H$_2$-bearing damped Ly$\alpha$ systems (DLAs) detected along quasar lines of sight. Using high-resolution spectroscopic data from VLT/UVES and Keck/HIRES, we report the detection of Cl$\,$I in 9 DLAs (including 5 new detections) out of 18 high-$z$ DLAs with $N($H$_2) \ge 10^{17.3}\,$cm$^{-2}$ (including a new H$_2$ detection at $z=3.09145$ towards J$\,$2100$-$0641) and present upper limits for the remaining 9 systems. We find a $\sim$5$\,\sigma$ correlation between $N$(Cl$\,$I) and $N$(H$_2$) with only $\sim$0.2$\,$dex dispersion over the range 18.1$\,<\,$log$\,N$(H$_2$)$\,<\,$20.1, thus probing column densities 10 times lower those seen towards nearby stars, roughly following the relation $N$(Cl$\,$I$) \approx 1.5\times10^{-6} \times N($H$_2)$. This relation between column densities is surprisingly the same at low and high redshift suggesting that the physical and chemical conditions are similar for a given H$_2$ (or Cl$\,$I) column density. In turn, the N({Cl\,I})/N({\rm H_2}) ratio is found to be uncorrelated with the overall metallicity in the DLA. Our results confirm that neutral chlorine is an excellent tracer of molecule-rich gas and show that the molecular fraction or/and metallicity in the H$_2$-bearing component of DLA could possibly be much higher than the line-of-sight average values usually measured in DLAs.Comment: 5 pages, 3 figures, Accepted for publication in A&A Letter