Voltage-dependent Block of the Cystic Fibrosis Transmembrane Conductance Regulator Cl- Channel by Two Closely Related Arylaminobenzoates

The gene defective in cystic fibrosis encodes a Cl- channel, the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is blocked by diphenylamine-2-carboxylate (DPC) when applied extracellularly at millimolar concentrations. We studied the block of CFTR expressed in Xenopus oocytes by DPC or by a closely related molecule, flufenamic acid (FFA). Block of whole-cell CFTR currents by bath-applied DPC or by FFA, both at 200 µM, requires several minutes to reach full effect. Blockade is voltage dependent, suggesting open-channel block: currents at positive potentials are not affected but currents at negative potentials are reduced. The binding site for both drugs senses ~40% of the electric field across the membrane, measured from the inside. In single-channel recordings from excised patches without blockers, the conductance was 8.0 ± 0.4 pS in symmetric 150 mM Cl^-. A subconductance state, measuring ~60% of the main conductance, was often observed. Bursts to the full open state lasting up to tens of seconds were uninterrupted at depolarizing membrane voltages. At hyperpolarizing voltages, bursts were interrupted by brief closures. Either DPC or FFA (50 µM) applied to the cytoplasmic or extracellular face of the channel led to an increase in flicker at V_m =-100 mV and not at V_m = +100 mV, in agreement with whole-cell experiments. DPC induced a higher frequency of flickers from the cytoplasmic side than the extracellular side. FFA produced longer closures than DPC; the FFA closed time was roughly equal (~ 1.2 ms) at -100 mV with application from either side. In cell-attached patch recordings with DPC or FFA applied to the bath, there was flickery block at V_m = -100 mV, confirming that the drugs permeate through the membrane to reach the binding site. The data are consistent with the presence of a single binding site for both drugs, reached from either end of the channel. Open-channel block by DPC or FFA may offer tools for use with site-directed mutagenesis to describe the permeation pathway

Forever Young: High Chromospheric Activity in M subdwarfs

We present spectroscopic observations of two halo M subdwarfs which have H alpha emission lines. We show that in both cases close companions are the most likely cause of the chromospheric activity in these old, metal-poor stars. We argue that Gl 781 A's unseen companion is most likely a cool helium white dwarf. Gl 455 is a near-equal-mass M subdwarf (sdM) system. Gl 781 A is rapidly rotating with v sin i = 30 km/s. The properties of the chromospheres and X-ray coronae of these systems are compared to M dwarfs with emission (dMe). The X-ray hardness ratios and optical chromospheric lines emission ratios are consistent with those seen in dMe stars. Comparison to active near-solar metallicity stars indicates that despite their low metallicity ([m/H] = -1/2), the sdMe stars are roughly as active in both X-rays and chromospheric emission. Measured by L_X/L_bol, the activity level of Gl 781 A is no more than a factor of 2.5 subluminous with respect to near-solar metallicity stars.Comment: 16 pages including 1 figure, AASTeX, to appear in May 1998 A.

Explicit Evidence Systems with Common Knowledge

Justification logics are epistemic logics that explicitly include justifications for the agents' knowledge. We develop a multi-agent justification logic with evidence terms for individual agents as well as for common knowledge. We define a Kripke-style semantics that is similar to Fitting's semantics for the Logic of Proofs LP. We show the soundness, completeness, and finite model property of our multi-agent justification logic with respect to this Kripke-style semantics. We demonstrate that our logic is a conservative extension of Yavorskaya's minimal bimodal explicit evidence logic, which is a two-agent version of LP. We discuss the relationship of our logic to the multi-agent modal logic S4 with common knowledge. Finally, we give a brief analysis of the coordinated attack problem in the newly developed language of our logic

Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris

We report the first detection of pure rotational transitions of TiO and TiO_2 at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T_rot, of about 250 K was derived for TiO_2. Although T_rot was not well constrained for TiO, it is likely somewhat higher than that of TiO_2. The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO_2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.Comment: to appear in Astronomy and Astrophysic

Dust-forming molecules in VY Canis Majoris (and Betelgeuse)

The formation of inorganic dust in circumstellar environments of evolved stars is poorly understood. Spectra of molecules thought to be most important for the nucleation, i.e. AlO, TiO, and TiO2, have been recently detected in the red supergiant VY CMa. These molecules are effectively formed in VY CMa and the observations suggest that non-equilibrium chemistry must be involved in their formation and nucleation into dust. In addition to exploring the recent observations of VY CMa, we briefly discuss the possibility of detecting these molecules in the dust-poor circumstellar environment of Betelgeuse.Comment: contribution to Betelgeuse Workshop 2012: "The physics of Red Supergiants: recent advances and open questions", 26-29 Nov 2012 Paris (France

Uses of zeta regularization in QFT with boundary conditions: a cosmo-topological Casimir effect

Zeta regularization has proven to be a powerful and reliable tool for the regularization of the vacuum energy density in ideal situations. With the Hadamard complement, it has been shown to provide finite (and meaningful) answers too in more involved cases, as when imposing physical boundary conditions (BCs) in two-- and higher--dimensional surfaces (being able to mimic, in a very convenient way, other {\it ad hoc} cut-offs, as non-zero depths). What we have considered is the {\it additional} contribution to the cc coming from the non-trivial topology of space or from specific boundary conditions imposed on braneworld models (kind of cosmological Casimir effects). Assuming someone will be able to prove (some day) that the ground value of the cc is zero, as many had suspected until very recently, we will then be left with this incremental value coming from the topology or BCs. We show that this value can have the correct order of magnitude in a number of quite reasonable models involving small and large compactified scales and/or brane BCs, and supergravitons.Comment: 9 pages, 1 figure, Talk given at the Seventh International Workshop Quantum Field Theory under the Influence of External Conditions, QFEXT'05, Barcelona, September 5-9, 200

The KHOLOD Experiment: A Search for a New Population of Radio Sources

Published data from long-term observations of a strip of sky at declination +5 degrees carried out at 7.6 cm on the RATAN-600 radio telescope are used to estimate some statistical properties of radio sources. Limits on the sensitivity of the survey due to noise imposed by background sources, which dominates the radiometer sensitivity, are refined. The vast majority of noise due to background sources is associated with known radio sources (for example, from the NVSS with a detection threshold of 2.3 mJy) with normal steep spectra ({\alpha} = 0.7-0.8, S \propto {\nu}^{- \alpha}), which have also been detected in new deep surveys at decimeter wavelengths. When all such objects are removed from the observational data, this leaves another noise component that is observed to be roughly identical in independent groups of observations. We suggest this represents a new population of radio sources that are not present in known catalogs at the 0.6 mJy level at 7.6 cm. The studied redshift dependence of the number of steep-spectrum objects shows that the sensitivity of our survey is sufficient to detect powerful FRII radio sources at any redshift, right to the epoch of formation of the first galaxies. The inferred new population is most likely associated with low-luminosity objects at redshifts z < 1. In spite of the appearance of new means of carrying out direct studies of distant galaxies, searches for objects with very high redshifts among steep and ultra-steep spectrum radio sources remains an effective method for studying the early Universe.Comment: 13 pages, 10 figure

Wandering globular clusters: the first dwarf galaxies in the universe?

In the last decade we witness an advent of new types of dwarf stellar systems in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic globular clusters, breaking the old simple paradigm for dwarf galaxies and globular clusters. These objects become more intriguing, and understanding of these new findings be comes more challenging. Recently we discovered a new type of large scale structure in the Virgo cluster of galaxies: it is composed of globular clusters. Globular clusters in Virgo are found wandering between galaxies (intracluster globular clusters) as well as in galaxies. These intracluster globular clusters fill a significant fraction in the area of the Virgo cluster and they are dominated by blue globular clusters. These intracluster globular clusters may be closely related with the first dwarf galaxies in the universe.Comment: 6 pages, 3 figures, Conference Proceedings: "A Universe of Dwarf Galaxies", 14-18 June 2010, Lyon, Franc

Discovery of SiCSi in IRC+10216: A Missing Link Between Gas and Dust Carriers of SiC Bonds

We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30 m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CW Leo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emission arises from a region of 6. in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a Si-C bond in the dust Formation zone and certainly both play a key role in the Formation of SiC dust grains.spanish MINECO AYA2009-07304, AYA2012-32032, CSD2009-00038ERC ERC-2013-SyGNASA NNX13AE59G, NANOCOSMOS, 610256Chemistr

Quintom model with O(NN) symmetry

We investigate the quintom model of dark energy in the generalized case where the corresponding canonical and phantom fields possess O($N$) symmetries. Assuming exponential potentials we find that this O$(N)$ quintom paradigm exhibits novel properties comparing to the simple canonical and phantom scenarios. In particular, we find that the universe cannot result in a quintessence-type solution with $w>-1$, even in the cases where the phantom field seems to be irrelevant. On the contrary, there are always late-time attractors which correspond to accelerating universes with $w<-1$ and with a recent crossing of the phantom divide, and for a very large area of the parameter space they are the only ones. This is in contrast with the previous simple-quintom results, where an accelerating universe is a possible late-time stable solution but it is not guaranteed.Comment: 13 pages, no figur