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

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

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

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

Proceedings IMWA 2010

Abstract A research-grade passive treatment system was constructed to receive 1000 L/minute of mine water from abandoned boreholes (pH 5.95, net alkalinity 29 mg/L CaCO₃, Fe 192 mg/L, Zn 11 mg/L, Cd 17 μg/L, Pb 60 μg/L and As 64 μg/L). The 2-ha system includes an oxidation pond followed by parallel treatment trains of aerobic wetlands, vertical flow bioreactors, re-aeration ponds, and horizontal-flow limestone beds and a final polishing wetland. Final effluent waters had pH &gt;7 and contained &lt; 1 mg/L total Fe and &lt; 0.1 mg/L total Zn, with concentrations of Cd, Pb and As below detectable limits. Key Words hard rock mining, metal mining, acid mine drainage, natural treatment systems Introduction This paper describes the initial evaluation of an innovative, ecologically engineered passive system designed to treat abandoned ferruginous Pb-Zn mine waters at the Tar Creek Superfund Site, part of the historic Tri-State Mining District (TSMD) of Oklahoma, Kansas and Missouri, USA. Significant quantities of Pb and Zn were produced from the TSMD from the 1890s through the 1960s. By the early 1970s when mining ceased, two and nine million tons of Pb and Zn, respectively, had been produced During mining, large capacity dewatering operations pumped approximately 50,000 m³ d⁻¹ of water from the mines (Reed et al. 1955). Upon decline and cessation of mining, groundwater began to accumulate in the mine voids. By late 1979, metal-rich waters began to discharge via artesian pressure into Tar Creek and its tributaries. The first documented discharges of mine drainage were at a location near southeast Commerce, OK (Oklahoma Water Resources Board 1983) and were subsequently identified for passive treatment implementation Methods For this study, periodic water quality and quantity data collection efforts for the subject discharges began in 1998, with regular monthly sampling beginning in 2004 and continuing to the present. The targeted discharges have circum-neutral pH (5.96 ± 0.06), total alkalinity of 405 ± 13 mg/L as CaCO₃ and combined flow rates of up to 1000 L/minute. Metals and sulfate concentrations are elevated above expected levels and degrade the receiving waters ). Design and construction details for the passive treatment system are summarized in Sydney, NS IMWA 2010 &quot;Mine Water and Innovative Thinking&quot; Wolkersdorfer &amp; Freund Results and Discussion In the year of operation, the passive treatment system performed as designed from a water quality perspective ( Other metals of specific interest in these waters were Cd, Pb, and As. All three were removed to below detection limits (0.64, 19.5 and 22 µg/L, respectively) before the outflow of the second process units, presumably through sorptive processes. Although the vertical-flow bioreactors were designed to remove Cd and Pb as well as Zn, Cd and Pb rarely remained in measureable concentrations at this stage of the treatment system. The other trace metal found in significant concentrations in these waters was Ni. A small percentage (&lt;10%) of Ni was removed through co-precipitation and sorption in Cell 1. However, the majority of Ni (≈ 95%) was removed via re- IMWA 2010 Sydney, NS &quot;Mine Water and Innovative Thinking&quot

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

On the reciprocal interaction between believing and feeling: an adaptive agent modelling perspective

An agent’s beliefs usually depend on informational or cognitive factors such as observation or received communication or reasoning, but also affective factors may play a role. In this paper, by adopting neurological theories on the role of emotions and feelings, an agent model is introduced incorporating the interaction between cognitive and affective factors in believing. The model describes how the strength of a belief may not only depend on information obtained, but also on the emotional responses on the belief. For feeling emotions a recursive body loop between preparations for emotional responses and feelings is assumed. The model introduces a second feedback loop for the interaction between feeling and belief. The strength of a belief and of the feeling both result from the converging dynamic pattern modelled by the combination of the two loops. For some specific cases it is described, for example, how for certain personal characteristics an optimistic world view is generated in the agent’s beliefs, or, for other characteristics, a pessimistic world view. Moreover, the paper shows how such affective effects on beliefs can emerge and become stronger over time due to experiences obtained. It is shown how based on Hebbian learning a connection from feeling to belief can develop. As these connections affect the strenghts of future beliefs, in this way an effect of judgment ‘by experience built up in the past’ or ‘by gut feeling’ can be obtained. Some example simulation results and a mathematical analysis of the equilibria are presented

Sex Differences in Neural Activation to Facial Expressions Denoting Contempt and Disgust

The facial expression of contempt has been regarded to communicate feelings of moral superiority. Contempt is an emotion that is closely related to disgust, but in contrast to disgust, contempt is inherently interpersonal and hierarchical. The aim of this study was twofold. First, to investigate the hypothesis of preferential amygdala responses to contempt expressions versus disgust. Second, to investigate whether, at a neural level, men would respond stronger to biological signals of interpersonal superiority (e.g., contempt) than women. We performed an experiment using functional magnetic resonance imaging (fMRI), in which participants watched facial expressions of contempt and disgust in addition to neutral expressions. The faces were presented as distractors in an oddball task in which participants had to react to one target face. Facial expressions of contempt and disgust activated a network of brain regions, including prefrontal areas (superior, middle and medial prefrontal gyrus), anterior cingulate, insula, amygdala, parietal cortex, fusiform gyrus, occipital cortex, putamen and thalamus. Contemptuous faces did not elicit stronger amygdala activation than did disgusted expressions. To limit the number of statistical comparisons, we confined our analyses of sex differences to the frontal and temporal lobes. Men displayed stronger brain activation than women to facial expressions of contempt in the medial frontal gyrus, inferior frontal gyrus, and superior temporal gyrus. Conversely, women showed stronger neural responses than men to facial expressions of disgust. In addition, the effect of stimulus sex differed for men versus women. Specifically, women showed stronger responses to male contemptuous faces (as compared to female expressions), in the insula and middle frontal gyrus. Contempt has been conceptualized as signaling perceived moral violations of social hierarchy, whereas disgust would signal violations of physical purity. Thus, our results suggest a neural basis for sex differences in moral sensitivity regarding hierarchy on the one hand and physical purity on the other