Rate constants and Arrhenius parameters for the reactions of OH radicals and Cl atoms with CF3CH2OCHF2, CF3CHClOCHF2 and CF3CH2OCClF2, using the discharge-flow/resonance fluorescence method

Rate constants have been determined for the reactions of OH radicals and Cl atoms with the three partially halogenated methyl-ethyl ethers, CF$_3$CH$_2$OCHF$_2$, CF$_3$CHClOCHF$_2$ and CF$_3$CH$_2$OCClF$_2$, using discharge-flow techniques to generate the OH radicals and the Cl atoms and resonance fluorescence to observe changes in their relative concentrations in the presence of added ether. For each combination of radical and ether, experiments were carried out at three temperatures between 292 and 410 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature: OH + CF$_3$CH$_2$OCHF$_2$: $k$ = (2.0$\pm$0.8) $\times$ 10$^{-11}$ exp( – 2110 $\pm$ 150 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ OH + CF$_3$CHClOCHF$_2$: $k$ = (4.5 $\pm$ 1.3) $\times$ 10$^{-13}$ exp( – 940 $\pm$ 100 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ OH + CF$_3$CH$_2$OCClF$_2$: $k$ = (1.6 $\pm$ 0.6) $\times$ 10$^{-12}$ exp( – 1100 $\pm$ 125 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ Cl + CF$_3$CH$_2$OCHF$_2$: $k$ = (6.1 $\pm$ 1.4) $\times$ 10$^{-12}$ exp( – 1830 $\pm$ 90 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ Cl + CF$_3$CHClOCHF$_2$: $k$ = (7.8 $\pm$ 2.6) $\times$ 10$^{-11}$ exp( – 2980 $\pm$ 130 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ Cl + CF$_3$CH$_2$OCClF$_2$: $k$ = (2.2 $\pm$ 0.2) $\times$ 10$^{-11}$ exp( – 2700 $\pm$ 40 K / T) cm$^3$ molecule$^{-1}$ s$^{-1}$ The results are compared with those obtained previously for the same and related reactions of OH radicals and Cl atoms, and the atmospheric implications of the results are considered briefly

The "enemies within":regions of the genome that are inherently difficult to replicate

An unusual feature of many eukaryotic genomes is the presence of regions that appear intrinsically difficult to copy during the process of DNA replication. Curiously, the location of these difficult-to-replicate regions is often conserved between species, implying a valuable role in some aspect of genome organization or maintenance. The most prominent class of these regions in mammalian cells is defined as chromosome fragile sites, which acquired their name because of a propensity to form visible gaps/breaks on otherwise-condensed chromosomes in mitosis. This fragility is particularly apparent following perturbation of DNA replication—a phenomenon often referred to as “replication stress”. Here, we review recent data on the molecular basis for chromosome fragility and the role of fragile sites in the etiology of cancer. In particular, we highlight how studies on fragile sites have provided unexpected insights into how the DNA repair machinery assists in the completion of DNA replication

Temporal variability of the telluric sodium layer

The temporal variability of the telluric sodium layer is investigated by analyzing 28 nights of data obtained with the Colorado State University LIDAR experiment. The mean height power spectrum of the sodium layer was found to be well fit by a power law over the observed range of frequencies, 10 microhertz to 4 millhertz. The best fitting power law was found to be 10^\beta \nu^\alpha, with \alpha = -1.79 +/- 0.02 and \beta = 1.12 +/- 0.40. Applications to wavefront sensing require knowledge of the behavior of the sodium layer at kHz frequencies. Direct measurements at these frequencies do not exist. Extrapolation from low-frequency behavior to high frequencies suggests that this variability may be a significant source of error for laser-guide-star adaptive optics on large-aperture telescopes.Comment: 3 pages, 3 figures, accepted for publication in Optics Letter

Vital Statistics Ireland: findings from the All-Ireland Gay Men’s Sex Survey 2000

Duration: March 2000 - September 2010 Sigma Research has been working with Ireland's Gay Health Network (GHN) since 2000. GHN is an umbrella organisation working towards gay men's health and HIV prevention. GHN instigated a community-based, self-completion survey to take place across The Republic of Ireland and Northern Ireland during the summer of 2000 and commissioned Sigma Research to work with them. This large-scale community research project was the third such survey among gay men in Ireland, and built on previous findings. After the development and piloting of the survey, recruitment commenced at Dublin Pride in June 2000 and continued throughout the summer at similar events in Belfast, Derry, Galway, Limerick and Waterford. Recruitment in bars and clubs took place in Dublin and Cork, and social groups in more rural area were sent copies of the questionnaire and a request to distribute them to their members. 1,290 questionnaires were returned by gay men (81%), bisexual men (11%) and other homosexually active men living in Ireland. 19% of all respondents lived in Northern Ireland. A full survey report, including implications for HIV prevention planning is available to download. Since 2003 Gay Health Network members - particularly The Gay Men's Health Service (Health Services Executive) and the Rainbow Project, Northern Ireland - have collaborated with our online UK version of the Gay Men’s Sex Survey (Vital Statistics) by promoting it to men in Ireland via community websites and postcards distributed on the gay scene. Real Lives, a summary report covering the main GMSS 2003 and 2004 data for men resident on the island of Ireland, was published in June 2006 and is available to download. It was published with The Gay Men's Health Service, Health Services Executive and the Rainbow Project. Real Lives II, a summary report covering the main GMSS 2005 and 2006 data for men resident on the island of Ireland, was published in June 2009 and is available to download. It was published with The Gay Men's Health Service, Health Services Executive and the Rainbow Rpoject. A summary report for Irish-resident men taking part in GMSS 2007 and 2008 will be published in June 2010

Roles of the Bloom's syndrome helicase in the maintenance of genome stability

The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIalpha, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules

II. On the structure and biology of archotermopsis, together with descriptions of new species of intestinal protozoa, and general observations on the isoptera

The following paper is intended as a contribution towards a knowledge of the structure and biology of Archotermopsis wroughtoni, Desn., one of the most primitive of living Termites. Included herewith are also observations and deductions bearing upon some of the more important general biological problems which are associated with the Isoptera. Archotermopsis wroughtoni was described 12 years ago by Desneux from examples taken by Wroughton in June, 1903. They were discovered in old stumps of trees, chiefly Pinus excelsa, in the Kashmir Valley. Since its discovery, this species has remained a great rarity, and practically nothing had been ascertained concerning its biology. In June, 1910, I first came across this insect in a decaying fallen trunk of Pinus excelsa, in a forest area situated between the Kuari Pass and Ramni, at an altitude of about 8,500 feet, in the Himalayas of British Garwhal. In the same month during 1912 I had the good fortune to meet with it in great abundance in a dead fallen trunk of Pinus longifolia near Dharmoti, in the Ranikhet District. This locality is situated at an altitude of about 4,000 feet in the Kumaon Himalaya. Being aware of the biological and phylogenetic interest likely to be afforded by a study of this species, I made a prolonged search in many other likely localities in the North Western Himalayas during the years 1912-13. It was subsequently found plentifully at Bhowali, near Naini Tal, at an elevation of 5,800 feet, near Nadh in the Ohakrata District of Jaunsar, and I have also been able to procure examples from near Gulmerg in Kashmir. It seems probable, therefore, that it will eventually be found to be generally distributed in the lower-level coniferous forests of the North Western Himalayas, up to an elevation of about 9,000 feet

The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds

A continuous supersonic flow reactor has been used to measure rate constants for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were created by the pulsed laser photolysis of CBr4. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence (VUV LIF) of C loss and through H formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas-grain interactions. In particular, the effect of the ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3 synthesis is examined