Selected ion flow drift tube (SIFDT) studies of reactive ion-neutral encounters

Data is presented for a series of experiments performed using a selected ion flow drift tube (SIFDT) apparatus operated at room temperature (300 ± 5 K) and at helium pressures typically between 0.3 - 0.5 Torr. Several of the experiments described utilised the apparatus as a conventional selected ion flow tube (SIFT), i.e. the drift capability was only employed in some of the experiments. Three termolecular ion-molecule association reactions proposed to play a potential role in the chemistry of the interstellar medium were investigated in an effort to elucidate the isomeric structures formed and thereby infer the structures likely to be formed in the analogous radiative association reactions at interstellar pressures. The termolecular association of H₃O⁺ with C₂H₂ is shown to produce a mixture of C₂H₅O⁺ isomers and efforts to identify the individual isomers are described. The termolecular association of H₃O⁺ with C₂H₄ produces a C₂H₇O⁺ isomer that exhibits reactivity with the neutrals 2-fluorotoluene and acrylonitlile identical to that observed from protonated ethanol, C₂H₅OH₂⁺. The termolecular association of CH₂NH₂⁺ with HCOOH is shown to produce an electrostatic adduct which undergoes facile ligand switching reactions with NH3 and the amines, CH₃NH₂ and C₂H₅NH₂. The radiative association of CH₂NH₂⁺ with HCOOH is therefore not considered to be a plausible synthetic route to protonated glycine in the interstellar medium. Dissociative charge transfer from Kr⁺, CO⁺ or CO₂⁺ to chlorobenzene is shown to produce the cyclic phenylium cation exclusively. Electron impact on halobenzenes and consecutive ion-molecule reactions of acetylene are known to produce a mixture of C₆H₅⁺ isomers. It is shown that the more reactive of these isomers has the phenylium structure. Low energy dissociative charge transfer to cycloheptatriene or benzyl bromide is used to selectively form the tropylium and benzyl cations respectively. The experiments lead to an estimate of the barrier height for the isomerisation benzyl ⇌ tropylium of 2.7 ± 0.9 eV. Reaction with benzene is used as a diagnostic for distinguishing the isomeric C7H7⁺ product(s) formed in a series of ion-molecule reactions. The allyl, CH₂CHCH₂⁺, and 2-propenyl, CH₃CCH₂⁺, cations are observed as distinct isomeric species in the SIFT. Reaction with methanol is used to distinguish between the two isomers. The isomeric ratio of allyl:2 propenyl formed via protonation of allene or propyne by a protonated base, BH+, is shown to be dependent on the proton affinity of the base, B. The experiments yield an estimate of the barrier height for the rearrangement allyl ⟶ 2-propenyl of 110 ± 30 kJ mor-¹, which is in excellent accord with ab initio calculations performed at the G₂(MP₂) level of theory. The exothermic H-atom abstraction reaction of SO₂⁺ with H₂ has been studied in a SIFDT apparatus over a range of centre-of-mass energies from thermal (300 K) to ~ 0.12 eV. The observed increase in rate coefficient with ion kinetic energy gives a linear pseudo-Arrhenius plot with a slope that indicates a barrier of ~ 5 kJ mor-¹ exists on the potential energy surface. The H₂SO₂⁺ potential surface was also explored in an ab initio investigation using the G2(MP2) procedure. An (SO₂ +•H₂)* transition state between reactants and products is identified, corresponding to the barrier found from experiment. The competition between charge transfer and association was investigated in a SlFDT study of the reactions of NO⁺ with the ketones: acetone, butanone and 3- pentanone. Association is the sole process observed in all three reactions at 300 K (the 3- pentanone reaction possesses a minor channel to the slightly endothermic charge transfer product). As the ion-neutral centre-of-mass energy is increased the rate coefficient for termolecular association decreases markedly, as a result of the decreasing lifetime of the intermediate (NO⁺•ketone) complex with increasing temperature. Bimolecular charge transfer can compete with association once sufficient energy is available to overcome the endothermicity and at higher energies dissociative charge transfer channels open up. The association reactions of CH₃ + with CH₃CN and C₂N₂ were also investigated in the SlFDT. The CH₃ +/CH₃CN reaction exhibits competitive binary and ternary channels. The bimolecular channels to C₂H₅⁺ + HCN and HCNH + C₂H₄ both involve extensive intramolecular rearrangement of the intermediate (CH₃⁺•CH₃CN)* collision complex and the rate coefficients for both channels exhibit a marked (negative) dependence on the ion-neutral centre-of-mass energy

The Butcher-Oemler Effect in High Redshift X-ray Selected Clusters

We are engaged in a wide-field, multi-colour imaging survey of X-ray selected clusters at intermediate and high redshift. We present blue fractions for the first 8 out of 29 clusters, covering almost a factor of 100 in X-ray luminosity. We find no correlation of blue fraction with redshift or X-ray luminosity. The lack of a correlation with L$_{X}$, places strong constraints on the importance of ram-pressure stripping as a driver of the Butcher-Oemler effect.Comment: 4 pages, 4 figures, to be puplished in the proceedings of the ''Sesto 2001-Tracing Cosmic Evolution with Galaxy Clusters'', Sesto 3-6 July 2001, Italy, eds, Stefano Borgan

Molecular antimicrobial resistance surveillance for neisseria gonorrhoeae, Northern Territory, Australia

Neisseria gonorrhoeae antimicrobial resistance (AMR) is a globally recognized health threat; new strategies are needed to enhance AMR surveillance. The Northern Territory of Australia is unique in that 2 different first-line therapies, based primarily on geographic location, are used for gonorrhea treatment. We tested 1,629 N. gonorrhoeae nucleic acid amplification test–positive clinical samples, collected from regions where ceftriaxone plus azithromycin or amoxicillin plus azithromycin are recommended first-line treatments, by using 8 N. gonorrhoeae AMR PCR assays. We compared results with those from routine culture-based surveillance data. PCR data confirmed an absence of ceftriaxone resistance and a low level of azithromycin resistance (0.2%), and that penicillin resistance was \u3c5% in amoxicillin plus azithromycin regions. Rates of ciprofloxacin resistance and penicillinase-producing N. gonorrhoeae were lower when molecular methods were used. Molecular methods to detect N. gonorrhoeae AMR can increase the evidence base for treatment guidelines, particularly in settings where culture-based surveillance is limited

Mortality Rate of Bullous Pemphigoid in a US Medical Center

All patients at the Medical College of Wisconsin Affiliated Hospitals with a new diagnosis of bullous pemphigoid (BP) between May 1, 1997 and September 1, 2002 were included in this study. The age at onset, date of death or date of last follow-up visit, mode of treatment, co-morbidities, and initial and follow-up hospitalizations were noted. Thirty-eight new patients were identified and complete follow-up data were obtained on 37 of the patients. Patients were followed a minimum of 1 y or until the time of death. The mean duration of follow-up was 20 mo. Kaplan–Meier analysis of our population indicated a 1-y survival probability of 88.96% (standard error 5.21%), with a 95% confidence interval (75.6%, 94.2%). This survival rate was considerably higher than that recently reported in several studies from Europe (29%–41% first year mortality). Although the age at onset and co-morbidities of our patients were similar to those in the European studies, the rate of hospitalization of our patients was much lower than that of patients from Europe (1.5 d per patient vs 11–25 d per patient). This study suggests that differences in practice patterns may be an important factor in the reduced mortality rate in US BP patients compared with Europe

Intensified partner notification and repeat testing can improve the effectiveness of screening in reducing Chlamydia trachomatis prevalence: a mathematical modelling study.

BACKGROUND The Australian Chlamydia Control Effectiveness Pilot (ACCEPt) was a cluster randomised controlled trial designed to assess the effectiveness of annual chlamydia testing through general practice in Australia. The trial showed that testing rates increased among sexually active men and women aged 16-29 years, but after 3 years the estimated chlamydia prevalence did not differ between intervention and control communities. We developed a mathematical model to estimate the potential longer-term impact of chlamydia testing on prevalence in the general population. METHODS We developed an individual-based model to simulate the transmission of Chlamydia trachomatis in a heterosexual population, calibrated to ACCEPt data. A proportion of the modelled population were tested for chlamydia and treated annually at coverage achieved in the control and intervention arms of ACCEPt. We estimated the reduction in chlamydia prevalence achieved by increasing retesting and by treating the partners of infected individuals up to 9 years after introduction of the intervention. RESULTS Increasing the testing coverage in the general Australian heterosexual population to the level achieved in the ACCEPt intervention arm resulted in reduction in the population-level prevalence of chlamydia from 4.6% to 2.7% in those aged 16-29 years old after 10 years (a relative reduction of 41%). The prevalence reduces to 2.2% if the proportion retested within 4 months of treatment is doubled from the rate achieved in the ACCEPt intervention arm (a relative reduction of 52%), and to 1.9% if the partner treatment rate is increased from 30%, as assumed in the base case, to 50% (a relative reduction of 59%). CONCLUSION A reduction in C. trachomatis prevalence could be achieved if the level of testing as observed in the ACCEPt intervention arm can be maintained at a population level. More substantial reductions can be achieved with intensified case management comprising retesting of those treated and treatment of partners of infected individuals

Higher Education Exchange: 2012

This annual publication serves as a forum for new ideas and dialogue between scholars and the larger public. Essays explore ways that students, administrators, and faculty can initiate and sustain an ongoing conversation about the public life they share.The Higher Education Exchange is founded on a thought articulated by Thomas Jefferson in 1820: "I know no safe depository of the ultimate powers of the society but the people themselves; and if we think them not enlightened enough to exercise their control with a wholesome discretion, the remedy is not to take it from them, but to inform their discretion by education."In the tradition of Jefferson, the Higher Education Exchange agrees that a central goal of higher education is to help make democracy possible by preparing citizens for public life. The Higher Education Exchange is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society.Working in this tradition, the Higher Education Exchange publishes interviews, case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies

Black Carbon Concentrations and Diesel Vehicle Emission Factors Derived from Coefficient of Haze Measurements in California: 1967-2003

We have derived ambient black carbon (BC) concentrations and estimated emission factors for on-road diesel vehicles from archived Coefficient of Haze (COH) data that was routinely collected beginning in 1967 at 11 locations in the San Francisco Bay Area. COH values are a measure of the attenuation of light by particles collected on a white filter, and available data indicate they are proportional to BC concentrations measured using the conventional aethalometer. Monthly averaged BC concentrations are up to five times greater in winter than summer, and, consequently, so is the population?s exposure to BC. The seasonal cycle in BC concentrations is similar for all Bay Area sites, most likely due to area-wide decreased pollutant dispersion during wintertime. A strong weekly cycle is also evident, with weekend concentrations significantly lower than weekday concentrations, consistent with decreased diesel traffic volume on weekends. The weekly cycle suggests that, in the Bay Area, diesel vehicle emissions are the dominant source of BC aerosol. Despite the continuous increase in diesel fuel consumption in California, annual Bay Area average BC concentrations decreased by a factor of ~;;3 from the late 1960s to the early 2000s. Based on estimated annual BC concentrations, on-road diesel fuel consumption, and recent measurements of on-road diesel vehicle BC emissions, diesel BC emission factors decreased by an order of magnitude over the study period. Reductions in the BC emission factor reflect improved engine technology, emission controls and changes in diesel fuel composition. A new BC monitoring network is needed to continue tracking ambient BC trends because the network of COH monitors has recently been retired

Surface Analysis Insight Note: Observations relating to photoemission peak shapes, oxidation state, and chemistry of titanium oxide films

It is common practice to describe the coordination of metal atoms in a binding configuration with their nearest neighbors in terms of oxidation state, a measure by which the number of electrons redistributed between atoms forming chemical bonds. In XPS terms, change to an oxidation state is commonly inferred by correlating photoemission signal with binding energy. The assumption, when classifying photoemission signals into distinct spectral shapes, is that a distribution of intensities shifted to lower binding energy is evidence of a reduction in oxidation state. In this Insight note, we raise the prospect that changes in photoemission peak shape may occur without obvious changes, determined by XPS in stoichiometry for a material. It is well known that TiO2 measured by XPS yields reproducible Ti 2p photoemission peaks. However, on exposing TiO2 to ion beams, Ti 2p photoemission evolves to complex distributions in intensity, which are particularly difficult to analyze by traditional fitting of bell‐shaped curves to these data. For these reasons, in this Insight note, a thin film of TiO2 deposited on a silicon substrate is chosen for analysis by XPS and linear algebraic techniques. Alterations in spectral shapes created from modified TiO2, which might be interpreted as the change in oxidation state, are assessed in terms of relative proportions of titanium to oxygen. It is found through detailed analysis of spectra that quantification by XPS, using procedures routinely used in practice, is not in accord with the typical interpretations of photoemission shapes. The data processing methods used and results presented in this work are of particular relevance to elucidating fundamental phenomena governing the surface evolution of materials‐enabled energy processes where cyclic/non‐steady usage changes the nature of bonding, especially in the presence of contaminants

Ethnic differences in the clustering and outcomes of health behaviours during pregnancy: results from the Born in Bradford cohort

OBJECTIVE. Pregnancy is a time of optimal motivation for many women to make positive behavioural changes. We aim to describe pregnant women with similar patterns of self-reported health behaviours and examine associations with birth outcomes. METHODS. We examined the clustering of multiple health behaviours during pregnancy in the Born in Bradford cohort, including smoking physical inactivity, vitamin d supplementation, and exposure to second hand smoke. Latent class analysis was used to identify groups of individuals with similar patterns of health behaviours separately for White British (WB) and Pakistani mothers. Multinomial regression was then used to examine the association between group membership and birth outcomes, which included preterm birth and mean birth weight. RESULTS. For WB mothers, offspring of those in the ‘Unhealthiest’ group had lower mean birth weight than those in the ‘Mostly healthy but inactive’ class, although no association was observed for preterm birth. For Pakistani mothers, group membership was not associated with birth weight differences, although the odds of preterm birth was higher in ‘Inactive smokers’ compared to the ‘Mostly healthy but inactive’ group. CONCLUSION. The use of latent class methods provides important information about the clustering of health behaviours which can be used to target population segments requiring behaviour change interventions considering multiple risk factors. Given the dominant negative association of smoking with the birth outcomes investigated, latent class groupings of other health behaviours may not confer additional risk information for these outcomes