Ultraviolet relaxation dynamics in uracil: Time-resolved photoion yield studies using a laser-based thermal desorption source

Wavelength-dependent measurements of the RNA base uracil, undertaken with nanosecond ultraviolet laser pulses, have previously identified a fragment at m/z = 84 (corresponding to the C3H4N2O+ ion) at excitation wavelengths ≤232 nm. This has been interpreted as a possible signature of a theoretically predicted ultrafast ring-opening occurring on a neutral excited state potential energy surface. To further investigate the dynamics of this mechanism, and also the non-adiabatic dynamics operating more generally in uracil, we have used a newly built ultra-high vacuum spectrometer incorporating a laser-based thermal desorption source to perform time-resolved ion-yield measurements at pump wavelengths of 267 nm, 220 nm, and 200 nm. We also report complementary data obtained for the related species 2-thiouracil following 267 nm excitation. Where direct comparisons can be made (267 nm), our findings are in good agreement with the previously reported measurements conducted on these systems using cold molecular beams, demonstrating that the role of initial internal energy on the excited state dynamics is negligible. Our 220 nm and 200 nm data also represent the first reported ultrafast study of uracil at pump wavelengths 3(1ππ*) state. These measurements do not, however, provide any evidence for the appearance of the m/z = 84 fragment within the first few hundred picoseconds following excitation. This key finding indicates that the detection of this specific species in previous nanosecond work is not directly related to an ultrafast ring-opening process. An alternative excited state process, operating on a more extended time scale, remains an open possibility

The Geography of Scientific Productivity: Scaling in U.S. Computer Science

Here we extract the geographical addresses of authors in the Citeseer database of computer science papers. We show that the productivity of research centres in the United States follows a power-law regime, apart from the most productive centres for which we do not have enough data to reach definite conclusions. To investigate the spatial distribution of computer science research centres in the United States, we compute the two-point correlation function of the spatial point process and show that the observed power-laws do not disappear even when we change the physical representation from geographical space to cartogram space. Our work suggests that the effect of physical location poses a challenge to ongoing efforts to develop realistic models of scientific productivity. We propose that the introduction of a fine scale geography may lead to more sophisticated indicators of scientific output.Comment: 6 pages, 3 figures; minor change

HATS-6b: A Warm Saturn Transiting an Early M Dwarf Star, and a Set of Empirical Relations for Characterizing K and M Dwarf Planet Hosts

We report the discovery by the HATSouth survey of HATS-6b, an extrasolar planet transiting a V=15.2 mag, i=13.7 mag M1V star with a mass of 0.57 Msun and a radius of 0.57 Rsun. HATS-6b has a period of P = 3.3253 d, mass of Mp=0.32 Mjup, radius of Rp=1.00 Rjup, and zero-albedo equilibrium temperature of Teq=712.8+-5.1 K. HATS-6 is one of the lowest mass stars known to host a close-in gas giant planet, and its transits are among the deepest of any known transiting planet system. We discuss the follow-up opportunities afforded by this system, noting that despite the faintness of the host star, it is expected to have the highest K-band S/N transmission spectrum among known gas giant planets with Teq < 750 K. In order to characterize the star we present a new set of empirical relations between the density, radius, mass, bolometric magnitude, and V, J, H and K-band bolometric corrections for main sequence stars with M < 0.80 Msun, or spectral types later than K5. These relations are calibrated using eclipsing binary components as well as members of resolved binary systems. We account for intrinsic scatter in the relations in a self-consistent manner. We show that from the transit-based stellar density alone it is possible to measure the mass and radius of a ~0.6 Msun star to ~7% and ~2% precision, respectively. Incorporating additional information, such as the V-K color, or an absolute magnitude, allows the precision to be improved by up to a factor of two.Comment: 21 pages, 11 figures, 10 tables. Submitted to AJ. Data available at http://hatsouth.org Code implementing empirical model available at http://www.astro.princeton.edu/~jhartman/kmdwarfparam.htm

HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars

We report the discovery of HATS-15 b and HATS-16 b, two massive transiting extrasolar planets orbiting evolved ($\sim 10$ Gyr) main-sequence stars. The planet HATS-15 b, which is hosted by a G9V star ($V=14.8$ mag), is a hot Jupiter with mass of $2.17\pm0.15\, M_{\mathrm{J}}$ and radius of $1.105\pm0.0.040\, R_{\mathrm{J}}$, and completes its orbit in nearly 1.7 days. HATS-16 b is a very massive hot Jupiter with mass of $3.27\pm0.19\, M_{\mathrm{J}}$ and radius of $1.30\pm0.15\, R_{\mathrm{J}}$; it orbits around its G3 V parent star ($V=13.8$ mag) in $\sim2.7$ days. HATS-16 is slightly active and shows a periodic photometric modulation, implying a rotational period of 12 days which is unexpectedly short given its isochronal age. This fast rotation might be the result of the tidal interaction between the star and its planet.Comment: 16 pages, 8 figures, submitted to PAS

Genetic variation in the HLA region is associated with susceptibility to herpes zoster.

Herpes zoster, commonly referred to as shingles, is caused by the varicella zoster virus (VZV). VZV initially manifests as chicken pox, most commonly in childhood, can remain asymptomatically latent in nerve tissues for many years and often re-emerges as shingles. Although reactivation may be related to immune suppression, aging and female sex, most inter-individual variability in re-emergence risk has not been explained to date. We performed a genome-wide association analyses in 22,981 participants (2280 shingles cases) from the electronic Medical Records and Genomics Network. Using Cox survival and logistic regression, we identified a genomic region in the combined and European ancestry groups that has an age of onset effect reaching genome-wide significance (P&gt;1.0 × 10(-8)). This region tags the non-coding gene HCP5 (HLA Complex P5) in the major histocompatibility complex. This gene is an endogenous retrovirus and likely influences viral activity through regulatory functions. Variants in this genetic region are known to be associated with delay in development of AIDS in people infected by HIV. Our study provides further suggestion that this region may have a critical role in viral suppression and could potentially harbor a clinically actionable variant for the shingles vaccine

Molecular absorption lines toward star-forming regions : a comparative study of HCO+, HNC, HCN, and CN

Aims. The comparative study of several molecular species at the origin of the gas phase chemistry in the diffuse interstellar medium (ISM) is a key input in unraveling the coupled chemical and dynamical evolution of the ISM. Methods. The lowest rotational lines of HCO+, HCN, HNC, and CN were observed at the IRAM-30m telescope in absorption against the \lambda 3 mm and \lambda 1.3 mm continuum emission of massive star-forming regions in the Galactic plane. The absorption lines probe the gas over kiloparsecs along these lines of sight. The excitation temperatures of HCO+ are inferred from the comparison of the absorptions in the two lowest transitions. The spectra of all molecular species on the same line of sight are decomposed into Gaussian velocity components. Most appear in all the spectra of a given line of sight. For each component, we derived the central opacity, the velocity dispersion, and computed the molecular column density. We compared our results to the predictions of UV-dominated chemical models of photodissociation regions (PDR models) and to those of non-equilibrium models in which the chemistry is driven by the dissipation of turbulent energy (TDR models). Results. The molecular column densities of all the velocity components span up to two orders of magnitude. Those of CN, HCN, and HNC are linearly correlated with each other with mean ratios N(HCN)/N(HNC) = 4.8 $\pm$ 1.3 and N(CN)/N(HNC) = 34 $\pm$ 12, and more loosely correlated with those of HCO+, N(HNC)/N(HCO+) = 0.5 $\pm$ 0.3, N(HCN)/N(HCO+) = 1.9 $\pm$ 0.9, and N(CN)/N(HCO+) = 18 $\pm$ 9. These ratios are similar to those inferred from observations of high Galactic latitude lines of sight, suggesting that the gas sampled by absorption lines in the Galactic plane has the same chemical properties as that in the Solar neighbourhood. The FWHM of the Gaussian velocity components span the range 0.3 to 3 km s-1 and those of the HCO+ lines are found to be 30% broader than those of CN-bearing molecules. The PDR models fail to reproduce simultaneously the observed abundances of the CN-bearing species and HCO+, even for high-density material (100 cm-3 < nH < 104 cm-3). The TDR models, in turn, are able to reproduce the observed abundances and abundance ratios of all the analysed molecules for the moderate gas densities (30 cm-3 < nH < 200 cm-3) and the turbulent energy observed in the diffuse interstellar medium. Conclusions. Intermittent turbulent dissipation appears to be a promising driver of the gas phase chemistry of the diffuse and translucent gas throughout the Galaxy. The details of the dissipation mechanisms still need to be investigated

The Observed and Predicted Spatial Distribution of Milky Way Satellite Galaxies

We review evidence that the census of Milky Way satellites similar to those known may be incomplete at low latitude due to obscuration and in the outer halo due to a decreasing sensitivity to dwarf satellites with distance. We evaluate the possible impact that incompleteness has on comparisons with substructure models by estimating corrections to the known number of dwarfs using empirical and theoretical models. If we assume that the true distribution of Milky Way satellites is uniform with latitude, then we estimate a 33% incompleteness in the total number of dwarfs due to obscuration at low latitude. Similarly, if we suppose that the radial distribution of Milky Way satellites matches that of M31, or that of the oldest sub-halos or the most massive sub-halos in a simulation, we estimate a total number of Milky Way dwarfs ranging from 1 -- 3 times the known population. Although the true level of incompleteness is quite uncertain, the fact that our extrapolations yield average total numbers of MW dwarfs that are realistically 1.5 -- 2 times the known population, shows that incompleteness needs to be taken seriously when comparing to models of dwarf galaxy formation. Interestingly, the radial distribution of the oldest sub-halos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31's satellites, which suggests that reionization may be an important factor controlling the observability of sub-halos. We also assess the prospects for a new SDSS search for Milky Way satellites to constrain the possible incompleteness in the outer halo.Comment: 9 pages, 7 figures. Replaced with MNRAS accepted versio

Nitrogen hydrides in interstellar gas II. Analysis of Herschel/HIFI observations towards W49N and G10.6-0.4 (W31C)

We have used the Herschel-HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards W49N and G10.6-0.4 in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. All detections show absorption by foreground material over a wide range of velocities, as well as absorption associated directly with the hot-core source itself. As in the previously published observations towards G10.6-0.4, the NH, NH2 and NH3 spectra towards W49N show strikingly similar and non-saturated absorption features. We decompose the absorption of the foreground material towards W49N into different velocity components in order to investigate whether the relative abundances vary among the velocity components, and, in addition, we re-analyse the absorption lines towards G10.6-0.4 in the same manner. Abundances, with respect to molecular hydrogen, in each velocity component are estimated using CH. The analysis points to a co-existence of the nitrogen hydrides in diffuse or translucent interstellar gas with a high molecular fraction. Towards both sources, we find that NH is always at least as abundant as both o-NH2 and o-NH3, in sharp contrast to previous results for dark clouds. We find relatively constant N(NH)/N(o-NH3) and N(o-NH2)/N(o-NH3) ratios with mean values of 3.2 and 1.9 towards W49N, and 5.4 and 2.2 towards G10.6-0.4, respectively. The mean abundance of o-NH3 is ~2x10^-9 towards both sources. The nitrogen hydrides also show linear correlations with CN and HNC towards both sources, and looser correlations with CH. The upper limits on the NH+ abundance indicate column densities < 2 - 14 % of N(NH). Surprisingly low values of the ammonia ortho-to-para ratio are found in both sources, ~0.5 - 0.7 +- 0.1. This result cannot be explained by current models as we had expected to find a value of unity or higher.Comment: 35 pages, 74 figure