TIME-OF-FLIGHT STUDIES OF ELECTRONS IN VACUUM

An electron gun, drift tube, and fast amplifier (described) were designed and tested as part of a time-offlight electron beam monochromator. Drift time distributions were obtained for electrons of mean energy from 3 to 15 ev, which required mean transit times from 800 to 350 nsec, respectively, with the latter minimum value corresponding to the effects of amplifier rise time and pulse width from the avalanche transistor pulser. The former value corresponds to an electron energy spread from the electron gun of about 0.6 ev. The reciprocal of the square of the transit time is a linear function of the electron gun accelerating potential with an intercept at -- 1.5 v attributed to contact potentials. Beam attenuation due to scattering off of residual gas in the vacuum system indicated that pressures below 10/sup -6/ mm Hg are required in order to avoid loss of electrons in drift distances of the order of one meter. (auth

Regional Dissemination of a Trimethoprim-Resistance Gene Cassette via a Successful Transposable Element

Antimicrobial resistance is a growing international problem. We observed a 50% increase in the prevalence of trimethoprim resistance among fecal Escherichia coli from healthy Nigerian students between 1998 and 2005, a trend to increase that continued in 2009.A PCR-based screen revealed that 131 (43.1%) of isolates obtained in Nigeria in 2005 and 2009 carried integron-borne dfrA cassettes. In the case of 67 (51.1%) of these isolates, the cassette was a class 1-integron-borne dfrA7 gene, which has been reported at high prevalence from E. coli isolates from other parts of Africa. Complete sequencing of a 27 Kb dfrA7-bearing plasmid from one isolate located the dfrA7 gene within a Tn21-type transposon. The transposon also contained an IS26-derived bla/sul/str element, encoding resistance to β-lactams, sulphonamides and streptomycin, and mercury resistance genes. Although the plasmid backbone was only found in 12 (5.8%) of trimethoprim-resistant isolates, dfrA7 and other transposon-borne genes were detected in 14 (16.3%) and 32 (26.3%) of trimethoprim resistant isolates collected in Nigeria in 2005 and 2009, respectively. Additionally, 37 (19.3%) of trimethoprim-resistant E. coli isolates collected between 2006 and 2008 from Ghana were positive for the dfrA7 and a transposon marker, but only 4 (2.1%) harbored the plasmid backbone.Our data point to transposition as a principal mechanism for disseminating dfrA7 among E. coli from Nigeria and Ghana. On-going intensive use of the affordable broad-spectrum antibacterials is likely to promote selective success of a highly prevalent transposable element in West Africa

Effects of induced moods on economic choices

Emotions can shape decision processes by altering valuation signals, risk perception, and strategic orientation. Although multiple theories posit a role for affective processes in mediating the influence of frames on decision making, empirical studies have yet to demonstrate that manipulated affect modulates framing phenomena. The present study asked whether induced affective states alter gambling propensity and the influence of frames on decision making. In a between-subjects design, we induced mood (happy, sad, or neutral) in subjects (N=91) via films that were interleaved with the framing task. Happy mood induction increased gambling and apparently accentuated framing effects compared to sad mood induction, although the effect on framing could have resulted from the fact that the increased tendency to gamble made the framing measure more sensitive. Happy mood induction increased gambling, but not framing magnitude, compared to neutral mood induction. Subjects experiencing a sad mood induction did not exhibit behavioral differences from those experiencing a neutral mood. For those subjects who experienced the happy mood induction, both gambling propensity and framing magnitude were positively correlated with the magnitude of the change in their mood valence. We discuss the broader implications of mood effects on real-world economic decisions

Negative emotional stimuli reduce contextual cueing but not response times in inefficient search

In visual search, previous work has shown that negative stimuli narrow the focus of attention and speed reaction times (RTs). This paper investigates these two effects by first asking whether negative emotional stimuli narrow the focus of attention to reduce the learning of a display context in a contextual cueing task and, second, whether exposure to negative stimuli also reduces RTs in inefficient search tasks. In Experiment 1, participants viewed either negative or neutral images (faces or scenes) prior to a contextual cueing task. In a typical contextual cueing experiment, RTs are reduced if displays are repeated across the experiment compared with novel displays that are not repeated. The results showed that a smaller contextual cueing effect was obtained after participants viewed negative stimuli than when they viewed neutral stimuli. However, in contrast to previous work, overall search RTs were not faster after viewing negative stimuli (Experiments 2 to 4). The findings are discussed in terms of the impact of emotional content on visual processing and the ability to use scene context to help facilitate search

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges, Spain, 20-24 May 2002, 5 pages, 3 figure

Indirect study of 19Ne states near the 18F+p threshold

The early E < 511 keV gamma-ray emission from novae depends critically on the 18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the 18F+p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the 18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics

Attentional demand influences strategies for encoding into visual working memory

Visual selective attention and visual working memory (WM) share the same capacity-limited resources. We investigated whether and how participants can cope with a task in which these 2 mechanisms interfere. The task required participants to scan an array of 9 objects in order to select the target locations and to encode the items presented at these locations into WM (1 to 5 shapes). Determination of the target locations required either few attentional resources (“popout condition”) or an attention-demanding serial search (“non pop-out condition”). Participants were able to achieve high memory performance in all stimulation conditions but, in the non popout conditions, this came at the cost of additional processing time. Both empirical evidence and subjective reports suggest that participants invested the additional time in memorizing the locations of all target objects prior to the encoding of their shapes into WM. Thus, they seemed to be unable to interleave the steps of search with those of encoding. We propose that the memory for target locations substitutes for perceptual pop-out and thus may be the key component that allows for flexible coping with the common processing limitations of visual WM and attention. The findings have implications for understanding how we cope with real-life situations in which the demands on visual attention and WM occur simultaneously

D(18F,pa)15N reaction applied to nova gamma-ray emission

The 18F(p,alpha)15O reaction is recognized to be one of the most important reactions for nova gamma-ray astronomy as it governs the early E <= 511keV gamma emission. However in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction, induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or alpha-particles) were detected in coincidence in two silicon strip detectors. A DWBA analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O reaction.Comment: Rapid Communication to appear in Phys. Rev. C., 4 pages and 4 figure

Childhood leukaemia and population movements in France, 1990–2003

In a national study, we investigated the incidence of childhood leukaemia (CL) over a 14-year period in France in relation to several measures based on the proportion of individuals who changed address between the last two national censuses. A positive association was found with the proportion of migrants who came from a distant place. The further the migrants came, the higher was the incidence of leukaemia, particularly among children aged 0–4 years in ‘isolated' communes at the time of diagnosis (RR=1.4, 95% CI: 1.1,1.8 in the highest category of migration distance). Although the role of the population density was less obvious, a more marked association was found above a certain threshold. No association with the proportion of commuters was observed

Population mixing and incidence of cancers in adolescents and young adults between 1990 and 2013 in Yorkshire, UK

Purpose: Epidemiological evidence suggests a role for an infectious etiology for cancers in teenagers and young adults (TYAs). We investigated this by describing associations between infection transmission using the population mixing (PM) proxy and incidence of cancers in TYAs in Yorkshire, UK. Methods: We extracted cancer cases from the Yorkshire Specialist Register of Cancer in Children and Young People from 1990 to 2013 (n = 1929). Using multivariable Poisson regression models (adjusting for effects of deprivation and population density), we investigated whether PM was associated with cancer incidence. We included population mixing–population density interaction terms to examine for differences in effects of PM in urban and rural populations. Results: Nonsignificant IRRs were observed for leukemias (IRR 1.20, 95% CI 0.91–1.59), lymphomas (IRR 1.09, 95% CI 0.90–1.32), central nervous system tumors (IRR 1.06, 95% CI 0.80–1.40) and germ cell tumors (IRR 1.14, 95% CI 0.92–1.41). The association between PM and cancer incidence did not vary in urban and rural areas. Conclusions: Study results suggest PM is not associated with incidence of cancers among TYAs. This effect does not differ between rural and urban settings