Analytical Model of an Isolated Single-atom Electron Source

An analytical model of a single-atom electron source is presented, where electrons are created by near-threshold photoionization of an isolated atom. The model considers the classical dynamics of the electron just after the photon absorption, i.e. its motion in the potential of a singly charged ion and a uniform electric field used for acceleration. From closed expressions for the asymptotic transverse electron velocities and trajectories, the effective source temperature and the effective source size can be calculated. The influence of the acceleration field strength and the ionization laser energy on these properties has been studied. With this model, a single-atom electron source with the optimum electron beam properties can be designed. Furthermore, we show that the model is also applicable to ionization of rubidium atoms, thus also describes the ultracold electron source, which is based on photoionization of laser-cooled alkali atoms

Polarization effects on the effective temperature of an ultracold electron source

The influence has been studied of the ionization laser polarization on the effective temperature of an ultracold electron source, which is based on near-threshold photoionization. This source is capable of producing both high-intensity and high-coherence electron pulses, with applications in for example electron diffraction experiments. For both nanosecond and femtosecond photoionization, a sinusoidal dependence of the temperature on polarization angle has been found. For most experimental conditions, the temperature is minimal when the polarization coincides with the direction of acceleration. However, surprisingly, for nanosecond ionization a regime exists when the temperature is minimal when the polarization is perpendicular to the acceleration direction. This shows that in order to create electron bunches with the highest transverse coherence length, it is important to control the polarization of the ionization laser. The general trends and magnitudes of the temperature measurements are described by a model, based on the analysis of classical electron trajectories; this model further deepens our understanding of the internal mechanisms during the photoionization process. Furthermore, for nanosecond ionization, charge oscillations as a function of laser polarization have been observed; for most situations the oscillation amplitude is small

A review of the use of information and communication technologies for dietary assessment

Presently used dietary-assessment methods often present difficulties for researchers and respondents, and misreporting errors are common. Methods using information and communication technologies (ICT) may improve quality and accuracy. The present paper presents a systematic literature review describing studies applying ICT to dietary assessment. Eligible papers published between January 1995 and February 2008 were classified into four assessment categories: computerised assessment; personal digital assistants (PDA); digital photography; smart cards. Computerised assessments comprise frequency questionnaires, 24 h recalls (24HR) and diet history assessments. Self-administered computerised assessments, which can include audio support, may reduce literacy problems, be translated and are useful for younger age groups, but less so for those unfamiliar with computers. Self-administered 24HR utilising computers yielded comparable results as standard methods, but needed supervision if used in children. Computer-assisted interviewer-administered recall results were similar to conventional recalls, and reduced inter-interviewer variability. PDA showed some advantages but did not reduce underreporting. Mobile phone meal photos did not improve PDA accuracy. Digital photography for assessing individual food intake in dining facilities was accurate for adults and children, although validity was slightly higher with direct visual observation. Smart cards in dining facilities were useful for measuring food choice but not total dietary intake. In conclusion, computerised assessments and PDA are promising, and could improve dietary assessment quality in some vulnerable groups and decrease researcher workload. Both still need comprehensive evaluation for micronutrient intake assessment. Further work is necessary for improving ICT tools in established and new methods and for their rigorous evaluatio

The Large Hadron Collider project

The Large Hadron Collider (LHC) will enable proton-proton collisions at an energy of more than fourteen thousand times the proton mass. This allows the discovery of new elementary particles with very large masses, in particular of the Higgs boson. The Higgs boson is crucial for understanding the mechanism that Nature chose to give mass to particles. The Higgs boson has turned out to be very hard to find but the LHC should allow a decisive step into new territory, unveiling one or even more Higgs bosons. The new energy domain of the LHC also inspires speculations about discoveries relevant for understanding dark matter and about the discovery of new space dimensions, so far hidden to us. In the talk an overview of the physics at LHC and a report on the status of the project, accelerator and experiments, will be presented

Ultrafast electron diffraction using an ultracold source

We present diffraction patterns from micron-sized areas of mono-crystalline graphite obtained with an ultracold and ultrafast electron source. We show that high spatial coherence is manifest in the visibility of the patterns even for picosecond bunches of appreciable charge, enabled by the extremely low source temperature (~ 10 K). For a larger, ~ 100 um spot size on the sample, spatial coherence lengths > 10 nm result, sufficient to resolve diffraction patterns of complex protein crystals. This makes the source ideal for ultrafast electron diffraction of complex macromolecular structures such as membrane proteins, in a regime unattainable by conventional photocathode sources. By further reducing the source size, sub-um spot sizes on the sample become possible with spatial coherence lengths exceeding 1 nm, enabling ultrafast nano-diffraction for material science.Comment: 5 pages, 4 figure

Listening to MEMS: An acoustic vibrometer

new way to characterize vibrating MEMS devices is presented. Using an acoustic particle velocity sensor the coupled sound field is measured, which is a measure for the movement of the MEMS device. We present several possible applications of this measurement method. It can be used as a read-out system for a mass flow sensor, and for characterization of in- and out-of-plane movements of MEMS devices. The method is an interesting alternative to laser scanning vibrometry due to its small size and low complexity; furthermore, it allows the user to `listen' directly to MEMS devices

A connection between item/subtest regression and the Rasch model

The purpose of this paper is to link empirical Bayes methods with two specific topics in item response theory--item/subtest regression, and testing the goodness of fit of the Rasch model--under the assumptions of local independence and sufficiency. It is shown that item/subtest regression results in empirical Bayes estimates only if the Rasch model holds. Additionally, it is shown that a newly-derived exploratory goodness-of-fit test for the Rasch model, which does not need item and person parameter estimates, can be seen as an empirical Bayes test. This test compares the observed proportions of correct answers to one specific item, given any pattern that leads to a number-right score

A genome-wide investigation of the worldwide invader Sargassum muticum shows high success albeit (almost) no genetic diversity

Twenty years of genetic studies of marine invaders have shown that successful invaders are often characterized by native and introduced populations displaying similar levels of genetic diversity. This pattern is presumably due to high propagule pressure and repeated introductions. The opposite pattern is reported in this study of the brown seaweed, Sargassum muticum, an emblematic species for circumglobal invasions. Albeit demonstrating polymorphism in the native range, microsatellites failed to detect any genetic variation over 1,269 individuals sampled from 46 locations over the Pacific-Atlantic introduction range. Single-nucleotide polymorphisms (SNPs) obtained from ddRAD sequencing revealed some genetic variation, but confirmed severe founder events in both the Pacific and Atlantic introduction ranges. Our study thus exemplifies the need for extreme caution in interpreting neutral genetic diversity as a proxy for invasive potential. Our results confirm a previously hypothesized transoceanic secondary introduction from NE Pacific to Europe. However, the SNP panel unexpectedly revealed two additional distinct genetic origins of introductions. Also, conversely to scenarios based on historical records, southern rather than northern NE Pacific populations could have seeded most of the European populations. Finally, the most recently introduced populations showed the lowest selfing rates, suggesting higher levels of recombination might be beneficial at the early stage of the introduction process (i.e., facilitating evolutionary novelties), whereas uniparental reproduction might be favored later in sustainably established populations (i.e., sustaining local adaptation).Agence Nationale de la Recherche - ANR-10-BTBR-04; European Regional Development Fund; Fundacao para a Ciencia e a Tecnologia - SFRH/BPD/107878/2015, UID/Multi/04326/2016, UID/Multi/04326/2019; Brittany Region;info:eu-repo/semantics/publishedVersio

Basic and regional characteristics of streamflow in the Upper Colorado River Basin: interim report

CER70-71GBE-HJMSS6.December 1970.Includes bibliographical reference (pages 23-24).Prepared for: Bureau of Reclamation, Division of Atmospheric Water Resources Management, Denver, Colorado, Project Skywater.This report describes the first phase of a research project concerned with two somewhat related subjects: 1. The study of the flow regimen of the rivers in the Upper Colorado River Basin and their relation to differences in geology, geomorphology, latitude, longitude, and physiographic parameters. 2. The application of such relations to the selection of hydrologically suitable basins for precipitation management. In this report, only general results about the flow characteristics of the streams in the Upper Colorado River Basin are presented. The determination of the streamflow characteristics was obtained from monthly flow data as published by the U.S. Geological Survey and corrected for diversions and regulations. Corrected records, stored on magnetic tape, for 707 stations were used in the study. From the monthly flow data mean yearly hydrographs have been computed for all stations. These hydrographs are expressed as specific yield in units of inches, cfs/sq. mi and liters per second per km2. The hydrographs are drawn on regular (linear), semi-logarithmic and double logarithmic scales. Monthly duration curves and mean yearly graphs of monthly coefficients of variation are also presented. This report contains a brief description of the methodology for the calculations, samples of computer output, tables of the calculated values and samples of various kinds of graphs which present in a concise and appealing visual way the characteristics of each gaging station. Maps with the results for the Colorado River Basin Project Area, a Bureau of Reclamation program of precipitation management in the San Juan Mountains area of Colorado, are given. A second report to be published later will contain an interpretation of the results and the implications for precipitation management.Under contract no. 14-06-D-6597