Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy

ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to provide estimates of its hot young star population. Our approach differs from previous investigations in that we are able to distinguish between the regions in which different infrared fine-structure lines form, using complementary ground-based observations. The high excitation nebular [SIV] emission is formed in a very compact region, which we attribute to the central super-star-nucleus, and lower excitation [NeII] nebular emission originates in the galactic core. We use photo-ionization modelling coupled with the latest theoretical O-star flux distributions to derive effective stellar temperatures and ionization parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK, logQ<8 for the larger core. Results are supported by more sophisticated calculations using evolutionary synthesis models. We assess the contribution that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]). From our Br(alpha) flux, the 2" nucleus contains the equivalent of approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old; the 20" core contains about 2500 O7V star equivalents, with a representative age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30 Doradus region. These quantities are in good agreement with the observed mid-IR dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters embedded in cooler emission may be common in dwarf starbursts, observing a galaxy solely with a large aperture may result in confusion. Neglecting the spatial distribution of nebular emission in NGC5253, implies `global' stellar temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.Comment: 16 pages, 7 figures, uses mn.sty, to appear in MNRA

BRCA1 and CtIP suppress long tract gene conversion between sister chromatids

BRCA1 controls early steps of the synthesis-dependent strand annealing (SDSA) pathway of homologous recombination, but has no known role following Rad51-mediated synapsis. Here we show that BRCA1 influences post-synaptic homologous recombination events, controlling the balance between short- (STGC) and long-tract gene conversion (LTGC) between sister chromatids. Brca1 mutant cells reveal a bias towards LTGC that is corrected by expression of wild type but not cancer-predisposing BRCA1 alleles. The LTGC bias is enhanced by depletion of CtIP but reversed by inhibition of 53BP1, implicating DNA end resection as a contributor to the STGC/LTGC balance. The impact of BRCA1/CtIP loss on the STGC/LTGC balance is abolished when the second (non-invading) end of the break is unable to support termination of STGC by homologous pairing (“annealing”). This suggests that BRCA1/CtIP-mediated processing of the second end of the break controls the annealing step that normally terminates SDSA, thereby suppressing the error-prone LTGC outcome

The Ocean Enterprise–understanding and quantifying business activity in support of observing, measuring and forecasting the ocean

Sustained ocean observations, measurements and models provide a wide range of societal benefits underpinning the safety, operational and compliance needs of beneficiaries that operate around, on and under the ocean (In the context of this paper, the term ‘ocean’ is defined as encompassing the global ocean, enclosed seas and the US Great Lakes.) They also provide an essential input to ocean scientific research and the effective protection of the marine environment. Delivering the means to collect and use ocean data and information on a sustained basis constitutes a significant business undertaking. The companies that enable sustained ocean observation, measurement and forecasting, and deliver its benefits as commercial services, combine to create a unique and growing industry cluster; the Ocean Enterprise. Ocean Enterprise businesses underpin the ability to provide societal benefit from sustained ocean observations, measurements and models, as well as delivering significant economic and employment benefits in their own right. In this paper, we describe a systematic evaluation of the scale, scope and characteristics of the Ocean Enterprise in the United States. We explore the ways in which this industry cluster interacts with the US Integrated Ocean Observing System and how the United States Ocean Enterprise compares to that of the United Kingdom

BRCA1 controls homologous recombination at Tus/Ter-stalled mammalian replication forks

Replication fork stalling can promote genomic instability, predisposing to cancer and other diseases1–3. Stalled replication forks may be processed by sister chromatid recombination (SCR), generating error-free or error-prone homologous recombination (HR) outcomes4–8. In mammalian cells, a long-standing hypothesis proposes that the major hereditary breast/ovarian cancer predisposition gene products, BRCA1 and BRCA2, control HR/SCR at stalled replication forks9. Although BRCA1 and BRCA2 affect replication fork processing10–12, direct evidence that BRCA genes regulate HR at stalled chromosomal replication forks is lacking due to a dearth of tools for studying this process. We report that the Escherichia coli Tus/Ter complex13–16 can be engineered to induce site-specific replication fork stalling and chromosomal HR/SCR in mammalian cells. Tus/Ter-induced HR entails processing of bidirectionally arrested forks. We find that the BRCA1 C-terminal tandem BRCT repeat and regions of BRCA1 encoded by exon 11—two BRCA1 elements implicated in tumor suppression—control Tus/Ter-induced HR. Inactivation of either BRCA1 or BRCA2 increases the absolute frequency of “long-tract” gene conversions at Tus/Ter-stalled forks—an outcome not observed in response to a restriction endonuclease-mediated chromosomal double strand break (DSB). Therefore, HR at stalled forks is regulated differently from HR at DSBs arising independently of a fork. We propose that aberrant long-tract HR at stalled replication forks contributes to genomic instability and breast/ovarian cancer predisposition in BRCA mutant cells

Estimating Extent of Mortality Associated with the Douglas-Fir Beetle in the Central and Northern Rockies

Data collected from Douglas-fir stands infected by the Douglas-fir beetle in Wyoming, Montana, Idaho, and Utah, were used to develop models to estimate amount of mortality in terms of basal area killed. Models were built using stepwise linear regression and regression tree approaches. Linear regression models using initial Douglas-fir basal area were built for all study sites but produce low precision estimates. Regression tree models using initial Douglas-fir basal area of stand density index or both were also build for all sites. Regression tree models provide a more realistic approach to estimate potential mortality by creating more homogenous mortality classes with reduced variance. The models developed provide land managers with a basis for determining the potential mortality should a Douglas-fir beetle outbreak develop

New Gnaphosidae from the United States

19 p. : ill. ; 24 cm

Report of the Advisory Committee in Seismology

The Advisory Committee in Seismology has pleasure in reporting the continued progress of its study of California earth movements during the year 1924-1925 without essential change of plan. A considerable amount of geologic work in the study of fault zones has been done during the year in the Mojave Desert and in Death Valley, the system of primary triangulation for the detection and measurement of horizontal displacements has progressed rapidly and effectively, and the development of suitable instruments for determining the two horizontal components of local earth movements has progressed to completion. Ground for a new laboratory has been purchased by the California Institute of Technology and the construction of the central station laboratory building upon it has been begun. The laboratory is expected to be occupied by Mr. H. O. Wood, Research Associate in Seismology, and his associates, about January 1, 1926. It is hoped that additional stations will also be occupied before the close of the present calendar year (1925), and that actual work in what has been happily termed the seismologic triangulation of California will be successfully inaugurated

Centipeds of South Bimini

8 p. : ill. ; 24 cm

Three intervening galaxy absorbers towards GRB060418: faint and dusty?

We present an analysis of three strong, intervening Mg II absorption systems (z_abs = 0.603, 0.656, 1.107) towards the optical afterglow of gamma-ray burst (GRB) 060418. From high resolution UVES spectra we measure metal column densities and find that the highest redshift absorber exhibits a large amount of dust depletion compared with DLAs seen in QSO spectra. The intervening z_abs = 1.107 absorber is also unusual in exhibiting a clear 2175 A bump, the first time this feature has been definitively detected in a GRB spectrum. The GRB afterglow spectrum is best fit with a two component extinction curve: an SMC extinction law at z=1.49 (the redshift of the host) with E(B-V) = 0.07+-0.01 and a Galactic extinction curve at z ~ 1.1 with E(B-V) = 0.08+-0.01. We also present a moderately deep NTT R-band image of the GRB060418 field and spectroscopy of four galaxies within 1 arcminute. None of these objects has a redshift that matches any of the intervening absorbers, and we conclude that the galaxies responsible for the two intervening Mg II absorbers at z ~ 0.6 have luminosities ~<0.3 L^star.Comment: Accepted for publication in MNRAS (Letters), 5 pages. Updated with more accurate host positio

A protective role for BRCA2 at stalled replication forks

The hereditary breast and ovarian cancer predisposition genes BRCA1 and BRCA2 account for the lion's share of heritable breast cancer risk in the human population. Loss of function of either gene results in defective homologous recombination (HR) and triggers genomic instability, accelerating breast tumorigenesis. A long-standing hypothesis proposes that BRCA1 and BRCA2 mediate HR following attempted replication across damaged DNA, ensuring error-free processing of the stalled replication fork. A recent paper describes a new replication fork protective function of BRCA2, which appears to collaborate with its HR function to suppress genomic instability