Collisional excitation of OH(6049 MHz) masers in supernova remnant - molecular cloud interactions

OH (1720 MHz) masers serve as indicators of SNR - molecular cloud interaction sites. These masers are collisionally excited in warm (50-100K) shocked gas with densities of order 1e5 cm^-3 when the OH column density is in the range 1e16-1e17 cm^-2. Here I present excitation calculations which show that when the OH column density exceeds 1e17 cm^-2 at similar densities and temperatures, the inversion of the 1720 MHz line switches off and instead the 6049 MHz transition in the first excited rotational state of OH becomes inverted. This line may serve as a complementary signal of warm, shocked gas when the OH column density is large.Comment: 2 pages, 2 figs, iaus.cls. To appear in IAU 242, Astrophysical Masers and Their Environments, eds. J. Chapman & W. Baan. Addition of two references and minor changes to wordin

The impact of Mean Time Between Disasters on inventory pre-positioning strategy

Purpose - This paper addresses the impact of Mean Time Between Disasters (MTBD) to inventory pre-positioning strategy of medical supplies prior to a sudden-onset disaster

Screening for resistance to Heterodera sacchari in the two cultivated rice species, Oryza sativa and O. glaberrima

Un total de 73 accessions de riz appartenant aux deux espèces cultivées, #Oryza sativa et #O. glaberrima, et une espèce sauvage, #O. breviligulata, ont été criblées, dans des expériences en pots, pour leur résistance vis-à-vis d'une souche congolaise du nématode à kyste #Heterodera sacchari. Les 43 cultivars testés appartenant à l'espèce #O. sativa sont sensibles, bien que présumés génétiquement différents, comme provenant d'origines géographiques très variés. Par contre, parmi les 21 accessions testées de l'espèce #O. glaberrima, d'origine africaine, quinze sont résistantes et deux sont intermédiaires, tandis que les quatre autres sont sensibles. Il en va de même pour l'espèce de riz sauvage, #O. breviligulata, également d'origine africaine et proche d'#O. glaberrima, pour laquelle sept des neuf accessions testées sont résistantes, tandis que les deux autres sont sensibles. Ces résultats ont été confirmés pour deux autres souches du parasite, provenant du Tchad et du Sénégal. Leur interprétation et leur utilisation possible sont discutées. (Résumé d'auteur

A search for 4750- and 4765-MHz OH masers in Southern Star Forming Regions

We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5-$\sigma$ $\simeq$ 100 mJy) search for maser emission from the 4765-MHz $^2\Pi_{1/2}$ F=1$\to$0 transition of OH. Fifty five star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward fourteen sites, with ten of these being new discoveries. In addition we observed the 4750-MHz $^2\Pi_{1/2}$ F=1$\to$1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well studied star formation regions has lead to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than is 1720-MHz OH maser emission. Combining our results with those of previous high resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predict any conditions in which the 1665-, 6035- and 4765-MHz transitions are simultaneously inverted. Erratum abstract: Dodson & Ellingsen (2002) included several observations with significant pointing errors, invalidating the upper limits found in these directions. These have now been reobserved or recalculated. A new table of upper limits has been generated, and two more masers that would have been seen have been found.Comment: Included an Erratum with Max as another author. This erratum was rejected by MNRAS (Feb 04) as it contained too much data. Resubmitted as a paper (Jun 04). Rejected (Sep 04) it had too little data. Resubmitted as reduced erratum (Apr 05). Still waitin

ISO LWS Spectroscopy of M82: A Unified Evolutionary Model

We present the first complete far-infrared spectrum (43 to 197 um) of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine structure emission lines, [OI] 63 and 145 um, [OIII] 52 and 88 um, [NII] 122 um, [NIII] 57 um and [CII] 158 um, and fit their ratios to a combination starburst and photo-dissociation region (PDR) model. The best fit is obtained with HII regions with n = 250 cm^{-3} and an ionization parameter of 10^{-3.5} and PDRs with n = 10^{3.3} cm^{-3} and a far-ultraviolet flux of G_o = 10^{2.8}. We applied both continuous and instantaneous starburst models, with our best fit being a 3-5 Myr old instantaneous burst model with a 100 M_o cut-off. We also detected the ground state rotational line of OH in absorption at 119.4 um. No excited level OH transitions are apparent, indicating that the OH is almost entirely in its ground state with a column density ~ 4x10^{14} cm^{-2}. The spectral energy distribution over the LWS wavelength range is well fit with a 48 K dust temperature and an optical depth, tau_{Dust} proportional to lambda^{-1}.Comment: 23 pages, 4 figures, accepted by ApJ, Feb. 1, 199

HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation

We present the results of a comparative study of HI narrow self-absorption (HINSA), OH, 13CO, and C18O in five dark clouds. The HINSA follows the distribution of the emission of the carbon monoxide isotopologues, and has a characteristic size close to that of 13CO. This confirms that the HINSA is produced by cold HI which is well mixed with molecular gas in well-shielded regions. The ratio of the atomic hydrogen density to total proton density for these sources is 5 to 27 x 10^{-4}. Using cloud temperatures and the density of HI, we set an upper limit to the cosmic ray ionization rate of 10^{-16} s^{-1}. Comparison of observed and modeled fractional HI abundances indicates ages for these clouds to be 10^{6.5} to 10^{7} yr. The low values of the HI density we have determined make it certain that the time scale for evolution from an atomic to an almost entirely molecular phase, must be a minimum of several million years. This clearly sets a lower limit to the overall time scale for star formation and the lifetime of molecular clouds

Resource-Bounded Kolmogorov Complexity Provides an Obstacle to Soficness of Multidimensional Shifts

We propose necessary conditions of soficness of multidimensional shifts formulated in terms of resource-bounded Kolmogorov complexity. Using this technique we provide examples of effective and non-sofic shifts on $\mathbb{Z}^2$ with very low block complexity: the number of admissible patterns of size $n\times n$ grows only as a polynomial in $n$.Comment: 22 pages, 9 figures; v6: several misprints are fixed, proofs are elaborated with more detai

Description géologique du bassin oligocène de Manosque-Forcalquier (Luberon oriental)

Bulletin du Service de la carte géologique de la France, ISSN 0366-4201 ; t. 58, no 266Description stratigraphique, paléogéographique et tectoniqu

Joint maintenance-inventory optimisation of parallel production systems

We model a joint inspection and spare parts inventory policy for maintaining machines in a parallel system, where simultaneous downtime seriously impacts upon production performance and has a significant financial consequence. This dependency between system components means that analysis of realistic maintenance models is intractable. Therefore we use simulation and a numerical optimisation tool to study the cost-optimality of several policies. Inspection maintenance is modelled using the delay-time concept. Critical spare parts replenishment is considered using several variants of a periodic review policy. In particular, our results indicate that the cost-optimal policy is characterised by equal frequencies of inspection and replenishment, and delivery of spare parts that coincides with maintenance intervention. In general, our model provides a framework for studying the interaction of spare parts ordering with maintenance scheduling. The sensitivity analysis that we present offers insights for the effective management of such parallel systems, not only in a paper-making plant, which motivates our modelling development, but also in other manufacturing contexts