Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging.

A new method to tag the barium daughter in the double-beta decay of ^{136}Xe is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba^{++}) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (∼2 nm), and detected with a statistical significance of 12.9σ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.

Development of a pulsed vacuum ultraviolet light source with adjustable intensity.

This paper describes the development of a pulsed light source using the discharge from an electrode in a medium of various noble gases. This source can be used to aid in the characterization and testing of new vacuum-ultraviolet sensitive light detection devices. The source includes a novel spark driver circuit, a spark chamber into which different noble gases can be introduced, and an optical attenuation cell capable of being filled with different gases to allow for the attenuation of the pulsed light down to single photon levels. We describe the construction, calibration, and characterization of this device deployed at a dedicated light detection test stand at Oak Ridge National Laboratory.

Focal modification of electrical conduction in the heart by viral gene transfer.

Modern treatment of cardiac arrhythmias is limited to pharmacotherapy, radiofrequency ablation, or implantable devices. Antiarrhythmic medications suppress arrhythmias, but their systemic effects are often poorly tolerated and their proarrhythmic tendencies increase mortality. Radiofrequency ablation can cure only a limited number of arrhythmias. Implantable devices can be curative for bradyarrhythmias and lifesaving for tachyarrhythmias, but require a lifetime commitment to repeated procedures, are a significant expense, and may lead to severe complications. One possibility is the use of gene therapy as an antiarrhythmic strategy. As an initial attempt to explore this option, we focused on genetic modification of the atrioventricular node. First, we developed an intracoronary perfusion model for gene delivery, building on our previous work in isolated cardiac myocytes and hearts perfused ex vivo. Using this method, we infected porcine hearts with Adbetagal (recombinant adenovirus expressing Escherichia coli beta-galactosidase) or with AdGi (adenovirus encoding the Galphai2 subunit). We hypothesized that excess Galphai2 would mimic the effects of beta-adreneric antagonists, in effect creating a localized beta-blockade. Galphai2 overexpression suppressed baseline atrioventricular conduction and slowed the heart rate during atrial fibrillation without producing complete heart block. In contrast, expression of the reporter gene beta-galactosidase had no electrophysiological effects. Our results demonstrate the feasibility of using myocardial gene transfer strategies to treat common arrhythmias.

Unsafe bicyclist overtaking behavior in a simulated driving task: The role of implicit and explicit attitudes.

There is extensive literature into the mechanisms of injury in traffic crashes involving vulnerable road users (VRUs), but little research into the social or psychological factors in causation in these crash types. Attitudes and emotional associations can affect how people attend to objects in their visual environment and physical approach/avoidance responses, but few studies have extended these approaches into the road safety domain. Existing driving simulator studies of driver-bicyclist interactions have focused on driver behavior but not underlying attitudes and their effect on safety-related behaviors. This research explored the impact of implicit and explicit attitudes on drivers' behavior in interactions with bicyclists. In a driving simulator, various objective measures of safety (e.g., speed, passing distance, crash occurrence) were collected in an overtaking scenario. Participants' self-reported attitudes about driving and bicyclists were collected via survey instrument, along with an online test of subconscious attitudes called an Implicit Association Test, developed to examine preference between drivers and bicyclists. Importantly, this study examined not only distance, but duration and speed during overtaking. Results demonstrate that conscious attitudes affect how quickly and closely drivers overtake bicyclists. Participants who hold negative attitudes about bicyclists as a legitimate road user group passed significantly faster, while people with concerns about their knowledge or judgment about overtaking a bicyclist passed further and more slowly. Drivers self-identification as a bicyclist predicted higher passing speeds, while respondents who bicycle weekly drove closer but more slowly to the simulated bicyclist. These behaviors did not significantly differ based on the measure of implicit attitudes. The results of this study provide potential avenues for infrastructure and education interventions to improve pedestrian and bicyclist safety. Additionally, pairing driving simulator behavior with attitudinal measures represents a significant methodological contribution.

A multi-stop time-of-flight spectrometer for the measurement of positron annihilation-induced electrons in coincidence with the Doppler-shifted annihilation gamma photon.

In this study, we describe an advanced multi-functional, variable-energy positron beam system capable of measuring the energies of multiple "positron-induced" electrons in coincidence with the Doppler-shifted gamma photon resulting from the annihilation of the correlated positron. The measurements were carried out using the unique characteristics of the digital time-of-flight spectrometer and the gamma spectrometer available with the advanced positron beam system. These measurements have resulted in (i) the first digital time-of-flight spectrum of positron annihilation-induced Auger electrons generated using coincident signals from a high-purity Ge detector and a micro-channel plate, (ii) a two-dimensional array of the energy of Doppler-broadened annihilation gamma and the time-of-flight of positron-annihilation induced Auger electrons/secondary electrons measured in coincidence with the annihilation gamma photon, and (iii) the time-of-flight spectra of multiple secondary electrons ejected from a bilayer graphene surface as a result of the impact and/or annihilation of positrons. The novelty of the gamma-electron coincidence spectroscopy has been demonstrated by extracting the Doppler-broadened spectrum of gamma photons emitted due to the annihilation of positrons exclusively with 1s electrons of carbon. The width of the extracted Doppler-broadened gamma spectrum has been found to be consistent with the expected broadening of the annihilation gamma spectrum due to the momentum of the 1s electrons in carbon.

Barium Chemosensors with Dry-Phase Fluorescence for Neutrinoless Double Beta Decay.

The nature of the neutrino is one of the major open questions in experimental nuclear and particle physics. The most sensitive known method to establish the Majorana nature of the neutrino is detection of the ultra-rare process of neutrinoless double beta decay. However, identification of one or a handful of decay events within a large mass of candidate isotope, without obfuscation by backgrounds is a formidable experimental challenge. One hypothetical method for achieving ultra- low-background neutrinoless double beta decay sensitivity is the detection of single 136Ba ions produced in the decay of 136Xe ("barium tagging"). To implement such a method, a single-ion-sensitive barium detector must be developed and demonstrated in bulk liquid or dry gaseous xenon. This paper reports on the development of two families of dry-phase barium chemosensor molecules for use in high pressure xenon gas detectors, synthesized specifically for this purpose. One particularly promising candidate, an anthracene substituted aza-18-crown-6 ether, is shown to respond in the dry phase with almost no intrinsic background from the unchelated state, and to be amenable to barium sensing through fluorescence microscopy. This interdisciplinary advance, paired with earlier work demonstrating sensitivity to single barium ions in solution, opens a new path toward single ion detection in high pressure xenon gas.

Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation.

Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (<1.25 eV) to create valence-band holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.

Therapeutic drugs in early pregnancy and congenital defects.

In a study of occupation and pregnancy outcome, information was collected on certain non-occupational factors including therapeutic drugs taken in the first trimester, reported by some 17% of women. A case-referent analysis was made of data from pregnancies leading to 787 major (class 1) and 2386 miscellaneous minor (class 2) congenital defects compared with pregnancies without defects, matched for hospital, maternal age and educational level. In pairs discordant for one of seven drug groups, ratios of positive pairs (case with drug) to negative pairs (referent with drug) were for class 1 defects 164:148, relative risk (RR) 1.11 and for class 2 defects 433:383, RR 1.13. Only anti-infective drugs showed an increased RR: 1.70 (p = 0.06). This was mainly with nervous/sensory defects (10:2; RR 5.0, p = 0.04) but no one type of defect or type of drug was identified; the infections for which the drugs were given might have been responsible. For class 1 defects two pairs were positive for anti-convulsant drugs and two negative; no increase in risk was found for any specific drugs including doxylamine succinate (Bendectin).

Small-bowel perforation secondary to metastatic carcinoma of the breast.

Perforation from a solitary metastatic lesion of the small bowel is rare. We report a case of acute perforation with no evidence of metastatic disease within the abdomen. Resection of the small bowel was performed.

Mesothelioma and the fiber type in three American asbestos factories - preliminary report.

Preliminary findings are reported from three cohort studies in two asbestos factories (A and B) where chrysotile only was processed and a third (C) where chrysotile, amosite, and crocidolite were used. A total of 10,763 men and 3,118 women has been studied, of whom 97% and 89%, respectively, have been traced and 36% and 16% have died. Death certificates have so far been obtained and coded for 89% of the deaths. The standardized mortality ratios (SMRs) for persons employed less than a year varied greatly between plants. For men employed at least 1 a, an SMR of 129 for all causes and one of 285 for respiratory cancer were found in the chrysotile textile plant (A). The experience of respiratory cancer in this textile plant appears much worse in relation to fiber exposure levels than that observed in chrysotile mines and mills. Other findings in the three plants await clarification by analyses of exposure-response relationships. Among 2,341 deaths from the two chrysotile factories there has been one mesothelioma (0.4 per 1,000); among 1,429 deaths at factory C, which used mixed fibers, there have been 18 (12.6 per 1,000). This finding supports much other evidence that amphiboles are mainly responsible for mesothelioma, whereas chrysotile has little or no mesothelioma-producing potential.

The 'retrait préventif': an evaluation.

Risks of adverse fetal outcome by occupational group and specific work demands were derived from a large survey of work in pregnancy in Montreal, 1982-84. Among 56,000 employed women in Quebec who were pregnant in 1985, the most recent year for which this figure could be estimated, approximately 11,300 fetal deaths and 3,400 preterm births would be expected. It was calculated that about 680 fetal deaths were attributable to occupational factors, almost all ergonomic in nature. Withdrawal from exposure by reassignment or paid leave at about the 10th week could conceivably prevent half of these fetal deaths, but less than one fifth if delayed until the 16th week. About 110 preterm births were possibly related to occupation and might also be prevented by withdrawal from exposure. These estimated levels of benefit are obtained at a cost which is both financially substantial and threatening to equality of employment opportunity for women of childbearing age.

The Poisson process as a model for compartment digesta flow in ruminants.

The Poisson process, the simplest stochastic flow process, was used to develop a multicompartment model of ruminant digesta flow with Gamma distributed retention times. Although mathematically the model is a generalization of many previously published models, the physiological model differs substantially in asserting that the distributed delay time and the exponential rate (scale) parameters, including the scale parameter of the Gamma distribution, are determined by total digesta flow, and thus invariant with respect to the fraction marked. The shape factor of the Gamma distribution is shown to be sufficient to explain the difference between markers in rate of marker excretion. Consequently, the parameters of multiple markers can be simultaneously estimated with the constraint that the exponential scale parameters and the delay time are invariant with respect to marker. This constraint leads to a measure of pure error to strengthen statistical tests for model rejection. Steady-state digesta retention time is estimated from the transient marker retention parameters, eliminating the necessity of speculating on what fraction of digesta the marked fraction represents. Tests of various models, using simulations and animal experiments indicate that, even if a model is correct, it is not possible to obtain reliable parameter estimates by fitting to a single marker. Even with multiple markers some caution must be used in interpreting parameter estimates derived from least squares fitting.

Characteristics and significance of liquid effluent from woodchip corrals in Scotland.

Woodchip corrals are increasingly used as cost effective means of over-wintering livestock in temperate regions but there is little information on their potential environmental impact. Four woodchip corrals of varying characteristics were instrumented to capture and quantify the flows reaching the base, where pollutant fluxes may move either vertically to groundwater, or laterally to a water course. Samples for chemical analysis were collected daily by auto-sampler. Samples for bacterial analysis were aseptically hand-sampled. Sampling frequency was increased during high flow events and sampling was conducted over a 12-month period. Microbiological samples were analysed for total coliform (TC), presumptive Escherichia coli (EC) and intestinal enterococci (IE). Leachate was also analysed for total phosphorus, phosphate, total nitrogen, ammonium, total oxidised nitrogen, nitrite and nitrate. Each corral had a recording rain gauge sited within 10 m of the corral surface. Mean total nitrogen concentration in leachate was 339.5 mg l(-1), of which ammoniacal-N comprised approximately 57%. Mean total phosphorus concentration was 94.7 mg l(-1). Geometric mean concentrations of TC, EC and IE were 95,461, 94,983 and 55,552 cfu100 ml(-1), respectively. Significant flows of leachate occurred at the base of the corrals on most days during the 1-year sampling period and flow rate increased with stocking density. Strong positive linear relationships were found between the concentrations of the nutrient parameters and discharge. Strong positive curvilinear relations were found between faecal indicator concentrations and discharge. Different relationships were observed in the stocked and unstocked corrals. The resulting fluxes are sufficient to give concern and to indicate that corral development is worthy of regulatory attention.

Malignant mesothelioma in Quebec.

All known, fatal cases of mesothelioma in the period 1960-1978 in the Province of Quebec are reviewed, because much of the world's chrysotile has been produced there and because there is also exposure to other types of asbestos. Of the 254 mesotheliomas registered, 181 were in males and 73 in females; occupational and residential histories were obtained for 91% of men and 86% of women. About 40% of male cases were probably attributable to occupational asbestos exposure; only 5.4% of females cases had been exposed occupationally. Intervals between first employment and death from mesothelioma were longer for miners and millers than for manufacturing workers: exposures of chrysotile miners and millers were mainly long and fairly low, while many factory workers had had short exposures. All tumours in miners and millers were pleural, while in factory workers, eight were peritoneal and two pleural and peritoneal. The evidence from this survey supports the view that the risk of mesothelioma after exposure to crocidolite is many times greater than that after chrysotile.

Mineral fibre content of lung in mesothelial tumours: preliminary report.

A survey was made, through pathologists, of all 274 fatal cases of primary malignant mesothelioma in North America in 1972. For each case, a control with pulmonary metastases from a primary tumour other than lung cancer was matched for sex and age. Relatives and friends of both cases and controls were interviewed; and specimens of lung tissue were obtained for 100 case-control pairs and analysed 'blind' by electron microscopy and X-ray energy dispersion analysis. This report describes the preliminary results of the analyses of asbestos fibres in the first 37 case-control pairs: chrysotile fibres were far more prevalent than amphiboles, but equal quantities were found in cases and controls. There was, however, a clear excess of amosite fibres in male cases as compared with controls.