The Tunneling Time of an Electron

There is a widely spread misconception regarding the physical significance of the various tunneling times currently used to describe metal-insulator-metal tunneling phenomena. Using quantum mechanics, the transition time of an electron tunneling from a state on one side of the barrier to a state on the other side can be determined. This time is the period of interaction between the electron and the barrier, since before and after the transition, the electron is in a quantum state of one of the metals. Furthermore, the RC time constant of the sandwich-like device and the electron transition or interaction time are equivalent representations of the same physical parameter. But none of these times is the quasiclassical "transmission time" analyzed by Hartman, which has become widely accepted as the electron-barrier interaction time, although this was clearly not his intention. In this communication we wish to point out that it is the (quantum mechanical) transition time which is the characteristic time of tunneling phenomena

Charge transfer in buried-channel charge-coupled devices

A detailed numerical simulation of the charge-transfer process in buried-channel CCDs will be presented. The limitations on the device performance due to incomplete free charge transfer, device parameters and clocking waveforms will be discussed

Small Scale Structure at High Redshift: II. Physical Properties of the CIV Absorbing Clouds

Keck HIRES spectra were obtained of the separate images of three gravitationally lensed QSOs (UM 673, Q1104-1804, and Q1422+2309). We studied the velocity and column density differences in CIV doublets in each QSO. Unlike the low ionization gas clouds typical of the interstellar gas in the Galaxy or damped Ly alpha galaxies, the spatial density distribution of CIV absorbing gas clouds turns out to be mostly featureless on scales up to a few hundred parsecs, with column density differences rising to 50 percent or more over separations beyond a few kpc. Similarly, velocity shear becomes detectable only over distances larger than a few hundred pc, rising to 70 km/s at a few kpc. The energy transmitted to the gas is substantially less than in present day star-forming regions, and the gas is less turbulent on a given spatial scale than, e.g., local HII regions. The quiescence of CIV clouds, taken with their probable low density, imply that these objects are not internal to galaxies. The CIV absorbers could be gas expelled recently to large radii and raining back onto its parent galaxy, or pre-enriched gas from an earlier (population III) episode of star formation, falling into the nearest mass concentration. However, while the metals in the gas may have been formed at higher redshifts, the residual turbulence in the clouds and the minimum coherence length measured here imply that the gas was stirred more recently, possibly by star formation events recurring on a timescale on the order of 10-100 Million years (abstract abbreviated).Comment: latex file plus 15 postscript figures (45 pages in total); to be published in the ApJ, June 20, 2001 issu

Electron-Spin Filters Based on the Rashba Effect

Semiconductor electron-spin filters of a proposed type would be based on the Rashba effect, which is described briefly below. Electron-spin filters more precisely, sources of spin-polarized electron currents have been sought for research on, and development of, the emerging technological discipline of spintronics (spin-based electronics). There have been a number of successful demonstrations of injection of spin-polarized electrons from diluted magnetic semiconductors and from ferromagnetic metals into nonmagnetic semiconductors. In contrast, a device according to the proposal would be made from nonmagnetic semiconductor materials and would function without an applied magnetic field. The Rashba effect, named after one of its discoverers, is an energy splitting, of what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. The present proposal evolved from recent theoretical studies that suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling. Accordingly, a device according to the proposal would be denoted an asymmetric resonant interband tunneling diode [a-RITD]. An a-RITD could be implemented in a variety of forms, the form favored in the proposal being a double-barrier heterostructure containing an asymmetric quantum well. It is envisioned that a-RITDs would be designed and fabricated in the InAs/GaSb/AlSb material system for several reasons: Heterostructures in this material system are strong candidates for pronounced Rashba spin splitting because InAs and GaSb exhibit large spin-orbit interactions and because both InAs and GaSb would be available for the construction of highly asymmetric quantum wells. This mate-rial system affords a variety of energy-band alignments that can be exploited to obtain resonant tunneling and other desired effects. The no-common-atom InAs/GaSb and InAs/AlSb interfaces would present opportunities for engineering interface potentials for optimizing Rashba spin splitting

A Social Model for Health Promotion for an Aging Population: Initial Evidence on the Experience Corps Model

This report evaluates whether a program for older volunteers, designed for both generativity and health promotion, leads to short-term improvements in multiple behavioral risk factors and positive effects on intermediary risk factors for disability and other morbidities. The Experience Corps® places older volunteers in public elementary schools in roles designed to meet schools\u27 needs and increase the social, physical, and cognitive activity of the volunteers. This article reports on a pilot randomized trial in Baltimore, Maryland. The 128 volunteers were 60-86 years old; 95% were African American. At follow-up of 4-8 months, physical activity, strength, people one could turn to for help, and cognitive activity increased significantly, and walking speed decreased significantly less, in participants compared to controls. In this pilot trial, physical, cognitive, and social activity increased, suggesting the potential for the Experience Corps to improve health for an aging population and simultaneously improve educational outcomes for children

Integrated information increases with fitness in the evolution of animats

One of the hallmarks of biological organisms is their ability to integrate disparate information sources to optimize their behavior in complex environments. How this capability can be quantified and related to the functional complexity of an organism remains a challenging problem, in particular since organismal functional complexity is not well-defined. We present here several candidate measures that quantify information and integration, and study their dependence on fitness as an artificial agent ("animat") evolves over thousands of generations to solve a navigation task in a simple, simulated environment. We compare the ability of these measures to predict high fitness with more conventional information-theoretic processing measures. As the animat adapts by increasing its "fit" to the world, information integration and processing increase commensurately along the evolutionary line of descent. We suggest that the correlation of fitness with information integration and with processing measures implies that high fitness requires both information processing as well as integration, but that information integration may be a better measure when the task requires memory. A correlation of measures of information integration (but also information processing) and fitness strongly suggests that these measures reflect the functional complexity of the animat, and that such measures can be used to quantify functional complexity even in the absence of fitness data.Comment: 27 pages, 8 figures, one supplementary figure. Three supplementary video files available on request. Version commensurate with published text in PLoS Comput. Bio

Using sulfur stable isotope ratios (δ34S) for animal geolocation: estimating the delay mechanisms between diet ingestion and isotope incorporation in tail hair.

Rationale: Metabolism and diet quality play an important role in determining delay mechanisms between an animal ingesting an element and depositing the associated isotope signal in tissue. While many isotope mixing models assume instantaneous reflection of diet in an animal– tissue, this is rarely the case. Here we use data from wildebeest to measure the lag time between ingestion of 34S and its detection in tail hair. Methods: We use time-lagged regression analysis of δ34S data from GPS-collared blue wildebeest from the Serengeti ecosystem in combination with δ34S isoscape data to estimate the lag time between an animal ingesting and depositing 34S in tail hair. Results: The best fitting regression model of δ34S in tail hair and an individual– position on the δ34S isoscape is generated assuming an average time delay of 78 days between ingestion and detection in tail hair. This suggests that sulfur may undergo multiple metabolic transitions before being deposited in tissue. Conclusion: Our findings help to unravel the underlying complexities associated with sulfur metabolism and are broadly consistent with results from other species. These findings will help to inform research aiming to apply the variation of δ34S in inert biological material for geolocation or understanding dietary changes, especially for fast moving migratory ungulates such as wildebeest

Comparison of different dosing regimens (once weekly vs. twice weekly, and once weekly vs. once every two weeks) with epoetin delta in patients with chronic kidney disease: a randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Anaemia is a common complication of chronic kidney disease and prevalence increases with declining renal function. Renal anaemia has significant implications for the well-being and quality of life of patients and impacts on morbidity and mortality. Anaemia can be well managed by therapy with erythropoiesis-stimulating agents (ESAs). Previous clinical trials have shown that the only human cell-line-derived ESA, epoetin delta, is well tolerated and effective in maintaining haemoglobin levels in anaemic patients with chronic kidney disease. The half-life of epoetin delta suggests that administration of this agent is feasible once weekly and once every two weeks. We report on the design and rationale of a trial to compare once weekly <it>vs</it>. twice weekly, and once weekly <it>vs</it>. once every two weeks dosing of epoetin delta.</p> <p>Design and methods</p> <p>This is a randomized, open-label, multicentre trial. Patients aged 18 years or above with chronic kidney disease (Stages 3–5) are eligible to enter this trial. Two groups of patients form the trial population, those naïve to ESA therapy and those previously stable on ESA therapy. There are two primary objectives of this trial: 1) to demonstrate non-inferiority between twice weekly and once weekly dosing of epoetin delta in previously naïve patients (assessed by haemoglobin at Week 24); 2) to demonstrate non-inferiority between once weekly and once every two weeks dosing in previously stable patients (assessed by average haemoglobin over Weeks 16–24). Among the secondary analyses will be assessments of haematocrit, number(%) of patients meeting predefined targets for haemoglobin and haematocrit levels, and comparisons of average dose. All patients will receive study medication for 24 weeks and dose will be adjusted according to a predefined algorithm to achieve and maintain haemoglobin ≥ 11 g/dL. All patients completing this trial are eligible to enter a 2-year follow-up study to enable monitoring of emergent adverse events, anti-erythropoietin antibody responses, maintenance of efficacy and changes in diabetic retinopathy status.</p> <p>Discussion</p> <p>To our knowledge, this trial is the first to randomize ESA-naïve patients to different dosing regimens of the same ESA. Data generated will help in guiding the most appropriate dosing frequency for epoetin delta, particularly in those patients new to epoetin delta therapy.</p> <p>Trial registration</p> <p><b>ClinicalTrials.gov: </b>NCT00450333</p

Emergent global patterns of ecosystem structure and function from a mechanistic general ecosystem model

Anthropogenic activities are causing widespread degradation of ecosystems worldwide, threatening the ecosystem services upon which all human life depends. Improved understanding of this degradation is urgently needed to improve avoidance and mitigation measures. One tool to assist these efforts is predictive models of ecosystem structure and function that are mechanistic: based on fundamental ecological principles. Here we present the first mechanistic General Ecosystem Model (GEM) of ecosystem structure and function that is both global and applies in all terrestrial and marine environments. Functional forms and parameter values were derived from the theoretical and empirical literature where possible. Simulations of the fate of all organisms with body masses between 10 µg and 150,000 kg (a range of 14 orders of magnitude) across the globe led to emergent properties at individual (e.g., growth rate), community (e.g., biomass turnover rates), ecosystem (e.g., trophic pyramids), and macroecological scales (e.g., global patterns of trophic structure) that are in general agreement with current data and theory. These properties emerged from our encoding of the biology of, and interactions among, individual organisms without any direct constraints on the properties themselves. Our results indicate that ecologists have gathered sufficient information to begin to build realistic, global, and mechanistic models of ecosystems, capable of predicting a diverse range of ecosystem properties and their response to human pressures