Conductance of Pd-H nanojunctions

Results of an experimental study of palladium nanojunctions in hydrogen environment are presented. Two new hydrogen-related atomic configurations are found, which have a conductances of ~0.5 and ~1 quantum unit (2e^2/h). Phonon spectrum measurements demonstrate that these configurations are situated between electrodes containing dissolved hydrogen. The crucial differences compared to the previously studied Pt-H_2 junctions, and the possible microscopic realizations of the new configurations in palladium-hydrogen atomic-sized contacts are discussed.Comment: 4 pages, 4 figure

Atomic size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different nature have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for gold wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.Comment: This version corrects an error in attributing the three observed periods, and includes a comparison with recent model calculation

Look-ahead seek correction in high-performance CD-Rom drives

As the performance of CD-ROM drives continues to increase, special attention should be paid to any element in the system that disturbs the desired specifications. When very low access times are considered, it is mandatory to reach the target track within only one seek action, i.e. without any consequent retry or correction seek. Many CD-ROM drives count the tracks crossed during seeking and, by comparing this count with the pre-calculated seek length, the exact target location can be detected. This paper considers the error that affects the track-counting mechanism due to the rotating disc spiral. It is shown that, for a given seek length, the number of crossed tracks differs between outside- and inside-oriented seeks. The involved equations are derived and an algorithm proposed for determining the correct number of tracks to be crossed during a seek action. The proposed algorithm, which is optimized for microprocessor implementation, relies on two look-up tables and a learning scheme that allows look-ahead seek correction for both spiral rotation and system tolerance

A study of the relationship between health awareness, lifestyle behaviour and food label usage in Gauteng

Background: The objectives of the study were to determine whether consumers who read food labels, were also more aware of health and lifestyle issues, in terms of nutrition and other health-related lifestyle behaviours, and whether there was a relationship between food-label reading, health awareness and lifestyle behaviour. A quantitative descriptive (survey) design was selected to investigate the relationship between food-label reading on the one hand, and health awareness and lifestyle behavior on the other.Method: A two-stage, stratified-proportionate and systematic sampling strategy was applied to select a sample of 357 Gauteng respondents to complete a telephonic questionnaire. Respondents who were most likely to read food label information were selected. Food label information is prescribed by comprehensive label legislation. Data report on respondents’ label-reading habits, attitudes towards health awareness, lifestyle behaviour and biographic data. Nonparametric analysis, scale reliability tests, analysis of variance (ANOVA) and Bonferroni multiple comparisons of means tests were used to analyse the results.Results: Results indicate that the two-thirds of respondents who, to some extent read nutritional information on food labels, were concerned about their personal health, were interested in health-related information, and followed a healthy lifestyle, such as regularly eating fresh fruit and vegetables, cutting back on alcohol, and other positive lifestyle behaviours. They were unsure about how their own knowledge of nutrition,and their understanding of nutrition information on food labels, compared with that of other consumers.Conclusion: A relationship was found between patterns of reading food labels, health awareness and lifestyle behaviour. People who often read food labels were more health-conscious, and maintained a healthier lifestyle.Keywords: health awareness, lifestyle, food labels, South Africa, consumer

Risico inventarisatie van schade door ethyleen bij tussenplanten : effecten van tomaat op tussengeplante komkommer en tomaat

Bij een herfstteelt van trostomaten op goten is het aantrekkelijk om in de winter tomaten of komkommers tussen te planten. Door het grotendeels weg laten zakken van het oude gewas onder de goot en het jonge gewas op de goot te zetten, kan de teeltwisseling met een minder groot gat in de productie verlopen. Omdat trostomaten aan de plant volledig doorkleuren bestaat in principe de kans dat de ethyleen die gevormd wordt door de rijpende vruchten schade kan geven aan het jonge tussengeplante gewas. Bij tomaat is in 2000 op enkele bedrijven trosrui geconstateerd bij het tussengeplante toma tengewas. Hierbij werd gedacht aan mogelijke ethyleenschade. Ethyleen is een gasvormige, planteigen stof die als groeiregulator (hormoon) bij zeer veel verschillende fysiologische processen betrokken is. Het beïnvloedt o.a. bloei, bladgroei en lengtegroei van de spruit (Abeles et al., 1992). Als er externe bronnen zijn van ethyleen dan is er al snel sprake van schade. Symptomen van ethyleenschade zijn o.a. afwijkende kiemplanten, bloemrui, trosrui, afwijkende bladstand, bladval en stagnatie van de vegetatieve groei. Ernstige ethyleenschade uit zich direct in bladvergeling, maar soms treedt er verdekt wat lichte schade op die toch blijkt te leiden tot productiederving. Ethyleen komt in de buitenlucht standaard voor in een concentratie van 1 – 5 ppb (Abeles et al., 1992), maar kan in stedelijke gebieden tot wel 100 keer hoger worden. Ethyleen kan dus als luchtvervuiling een kas binnenkomen, of ophopen ten gevolge van een slecht afgestelde brander (Hanan, 1973, Esmeijer, 1999). Een andere bron van ethyleen is een gewas met doorkleurende vruchten zoals tomaat (Reid, 1988). In het geval van tussenplanten in de winterperiode zou dit problemen kunnen opleveren. In het verleden werd ook wel tussengeplant, maar leidde dit nooit tot problemen, omdat de vruchten los geoogst werden en nooit zo lang doorgekleurd in het gewas aanwezig bleven. Bovendien werd er alleen tussengeplant in de zomermaanden als er relatief veel gelucht werd. Bij tussenplanten in de winter van komkommers bij tomaat gaat het om een situatie waarin de luchtramen vaak gesloten zijn en er weinig licht beschikbaar is. De meeste gewassen zijn in die omstandigheden gevoelig voor schade, en naar verwachting zullen jonge, snel groeiende komkommerplanten op die regel geen uitzondering zijn

Feshbach Spectroscopy of a Shape Resonance

We present a new spectroscopy technique for studying cold-collision properties. The technique is based on the association and dissociation of ultracold molecules using a magnetically tunable Feshbach resonance. The energy and lifetime of a shape resonance are determined from a measurement of the dissociation rate. Additional spectroscopic information is obtained from the observation of a spatial interference pattern between an outgoing s wave and d wave. The experimental data agree well with the results from a new model, in which the dissociation process is connected to a scattering gedanken experiment, which is analyzed using a coupled-channels calculation.Comment: Introduction rewritte

Polyhedral restrictions of feasibility regions in optimal power flow for distribution networks

The optimal power flow (OPF) problem is one of the most fundamental problems in power system operations. The non-linear alternating current (AC) power flow equations that model different physical laws (together with operational constraints) lay the foundation for the feasibility region of the OPF problem. While significant research has focused on convex relaxations, which are approaches to solve an OPF problem by enlarging the true feasibility region, the opposite approach of convex restrictions offers valuable insights as well. Convex restrictions, including polyhedral restrictions, reduce the true feasible region to a convex region, ensuring that it contains only feasible points. In this work, we develop a sequential optimization method that offers a scalable way to obtain (bounds on) solutions to OPF problems for distribution networks. To do so, we first develop sufficient conditions for the existence of feasible power flow solutions in the neighborhood of a specific (feasible) operating point in distribution networks, and second, based on these conditions, we construct a polyhedral restriction of the feasibility region. Our numerical results demonstrate the efficacy of the sequential optimization method as an alternative to existing approaches to obtain (bounds on) solutions to OPF problems for distribution networks. By construction, the optimization problems can be solved in polynomial time and are guaranteed to have feasible solutions

Polyhedral restrictions of feasibility regions in optimal power flow for distribution networks

The optimal power flow (OPF) problem is one of the most fundamental problems in power system operations. The non-linear alternating current (AC) power flow equations that model different physical laws (together with operational constraints) lay the foundation for the feasibility region of the OPF problem. While significant research has focused on convex relaxations, which are approaches to solve an OPF problem by enlarging the true feasibility region, the opposite approach of convex restrictions offers valuable insights as well. Convex restrictions, including polyhedral restrictions, reduce the true feasible region to a convex region, ensuring that it contains only feasible points. In this work, we develop a sequential optimization method that offers a scalable way to obtain (bounds on) solutions to OPF problems for distribution networks. To do so, we first develop sufficient conditions for the existence of feasible power flow solutions in the neighborhood of a specific (feasible) operating point in distribution networks, and second, based on these conditions, we construct a polyhedral restriction of the feasibility region. Our numerical results demonstrate the efficacy of the sequential optimization method as an alternative to existing approaches to obtain (bounds on) solutions to OPF problems for distribution networks. By construction, the optimization problems can be solved in polynomial time and are guaranteed to have feasible solutions.Comment: 12 pages, 4 figure

Neurobehavioral effects of transportation noise in primary schoolchildren: a cross-sectional study.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.BACKGROUND: Due to shortcomings in the design, no source-specific exposure-effect relations are as yet available describing the effects of noise on children's cognitive performance. This paper reports on a study investigating the effects of aircraft and road traffic noise exposure on the cognitive performance of primary schoolchildren in both the home and the school setting. METHODS: Participants were 553 children (age 9-11 years) attending 24 primary schools around Schiphol Amsterdam Airport. Cognitive performance was measured by the Neurobehavioral Evaluation System (NES), and a set of paper-and-pencil tests. Multilevel regression analyses were applied to estimate the association between noise exposure and cognitive performance, accounting for demographic and school related confounders. RESULTS: Effects of school noise exposure were observed in the more difficult parts of the Switching Attention Test (SAT): children attending schools with higher road or aircraft noise levels made significantly more errors. The correlational pattern and factor structure of the data indicate that the coherence between the neurobehavioral tests and paper-and-pencil tests is high. CONCLUSIONS: Based on this study and previous scientific literature it can be concluded that performance on simple tasks is less susceptible to the effects of noise than performance on more complex tasks.Funding was provided by the European Community (QLRT-2000-00197), the Department of Environment, Food and Rural Affairs in the UK, the Dutch Ministry of Spatial Planning, Housing and the Environment, the Dutch Ministry of Public Health, Welfare and Sports, and the Dutch Ministry of Transport, Public Works and Water Management