Resonant tunneling transistors with controllable negative differential resistances

Three-terminal devices based on resonant tunneling through two quantum barriers separated by a quantum well are presented and analyzed theoretically. Each proposed device consists of a resonant tunneling double barrier heterostructure integrated with a Schottky barrier field-effect transistor configuration. The essential feature of these devices is the presence, in their output current-voltage (I_{D} - V_{D}) curves, of negative differential resistances controlled by a gate voltage. Because of the high-speed characteristics associated with tunnel structures, these devices could find applications in tunable millimeter-wave oscillators, negative resistance amplifiers, and high-speed digital circuits

On designing observers for time-delay systems with nonlinear disturbances

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2002 Taylor & Francis LtdIn this paper, the observer design problem is studied for a class of time-delay nonlinear systems. The system under consideration is subject to delayed state and non-linear disturbances. The time-delay is allowed to be time-varying, and the non-linearities are assumed to satisfy global Lipschitz conditions. The problem addressed is the design of state observers such that, for the admissible time-delay as well as non-linear disturbances, the dynamics of the observation error is globally exponentially stable. An effective algebraic matrix inequality approach is developed to solve the non-linear observer design problem. Specifically, some conditions for the existence of the desired observers are derived, and an explicit expression of desired observers is given in terms of some free parameters. A simulation example is included to illustrate the practical applicability of the proposed theory.The work of Z. Wang was supported in part by the University of Kaiserslautern of Germany and the Alexander von Humboldt Foundation of Germany

Ecological Effects of Fear: How Spatiotemporal Heterogeneity in Predation Risk Influences Mule Deer Access to Forage in a Sky‐Island System

Forage availability and predation risk interact to affect habitat use of ungulates across many biomes. Within sky‐island habitats of the Mojave Desert, increased availability of diverse forage and cover may provide ungulates with unique opportunities to extend nutrient uptake and/or to mitigate predation risk. We addressed whether habitat use and foraging patterns of female mule deer (Odocoileus hemionus) responded to normalized difference vegetation index (NDVI), NDVI rate of change (green‐up), or the occurrence of cougars (Puma concolor). Female mule deer used available green‐up primarily in spring, although growing vegetation was available during other seasons. Mule deer and cougar shared similar habitat all year, and our models indicated cougars had a consistent, negative effect on mule deer access to growing vegetation, particularly in summer when cougar occurrence became concentrated at higher elevations. A seemingly late parturition date coincided with diminishing NDVI during the lactation period. Sky‐island populations, rarely studied, provide the opportunity to determine how mule deer respond to growing foliage along steep elevation and vegetation gradients when trapped with their predators and seasonally limited by aridity. Our findings indicate that fear of predation may restrict access to the forage resources found in sky islands

Current transport mechanisms in GaAs/AlAs tunnel structures grown by metal–organic chemical vapor deposition

Elastic and inelastic tunneling processes are investigated in GaAs–AlAs–GaAs double heterojunctions grown in the [100] direction by metal–organic chemical vapor deposition (MOCVD). The AlAs quantum barriers in the heterostructures studied are doped p-type with Mg. Theoretical calculations of tunneling currents are performed and compared with experimental I–V data. It is found that for structures with thin AlAs barriers, the dominant current transport mechanism at low temperatures is tunneling through the AlAs band gap at both the Gamma and X points. This is consistent with inelastic processes observable in first (dI/dV) and second (d2I/dV2) derivative spectra obtained with modulation techniques. A simple model, developed for calculating impurity-assisted tunneling currents, shows that the role of barrier impurities becomes more important as the barrier is grown thicker. Implications of some of these results for resonant tunneling heterostructures consisting of two AlAs quantum barriers separated by a GaAs quantum well are discussed. Experimental second derivative spectra showing reproducible features are also presented for these double barrier structures

Perception of nonnative tonal contrasts by Mandarin-English and English-Mandarin sequential bilinguals

This study examined the role of acquisition order and crosslinguistic similarity in influencing transfer at the initial stage of perceptually acquiring a tonal third language (L3). Perception of tones in Yoruba and Thai was tested in adult sequential bilinguals representing three different first (L1) and second language (L2) backgrounds: L1 Mandarin-L2 English (MEBs), L1 English-L2 Mandarin (EMBs), and L1 English-L2 intonational/non-tonal (EIBs). MEBs outperformed EMBs and EIBs in discriminating L3 tonal contrasts in both languages, while EMBs showed a small advantage over EIBs on Yoruba. All groups showed better overall discrimination in Thai than Yoruba, but group differences were more robust in Yoruba. MEBs’ and EMBs’ poor discrimination of certain L3 contrasts was further reflected in the L3 tones being perceived as similar to the same Mandarin tone; however, EIBs, with no knowledge of Mandarin, showed many of the same similarity judgments. These findings thus suggest that L1 tonal experience has a particularly facilitative effect in L3 tone perception, but there is also a facilitative effect of L2 tonal experience. Further, crosslinguistic perceptual similarity between L1/L2 and L3 tones, as well as acoustic similarity between different L3 tones, play a significant role at this early stage of L3 tone acquisition.Published versio

Peregrine Falcon Survey, West Greenland, 1972

... The main purpose of the 1972 survey was to study a sample area of West Greenland to supply baseline data about peregrine falcons from which future surveys could determine the status and trends of this bird in Greenland. The main part of the study had as its goals: 1) to determine the density, distribution, and reproductive success of nesting peregrines in a sample area; 2) to band all peregrine nestlings found; 3) to determine prey species of the peregrine; 4) to make interspecific observations of peregrines and gyrfalcons; 5) to make detailed observations from a blind of a sample peregrine falcon eyrie; 6) to conduct a small-bird census in the area of the sample eyrie; 7) to make a photographic record in colour slides and movies of the investigations. ... Eight peregrine falcon eyries and 3 gyrfalcon eyries were found in the survey area. In all, 18 nestlings were found in the 8 peregrine eyries. Of the 8 eyries, 1 had no young, but showed signs of occupancy ... and was defended by an aggressive pair of falcons. Of the other 7 eyries where we found hatched young, 1 had 4 young, 4 had 3 young, and 2 had 1 young bird each. Of the total of 18 nestling peregrines, 13 were banded and 5 were fully-fledged, on the wing, and unable to be caught for banding. Of the peregrine nestlings banded, 9 were males and 4 were females. The number of nestlings (18) in the 8 peregrine eyries gave a production rate of 2.25 per eyrie, or 2.57 if an average is taken of the 7 eyries actually producing young. At 1 eyrie a young falcon was found dead (the eyrie with 4 young). We know that at least 8 of the remaining 17 young fledged successfully, but we are uncertain about the success of the others and cannot therefore make a definite statement on fledging ratio. We estimate, however, that the fledging rate of the peregrines in our survey area was at least 2.00 per producing eyrie. The maximum dimensions of our irregularly-shaped survey area were 39 x 34 miles (63 x 55 km). The estimated area of the survey was about 800 sq. mi. (2,072 sq. km), or about 700 sq. mi. (1,800 sq. km) when the surface area of fiords and lakes is excluded. The nesting density of the active, young-producing peregrine eyries (7) was about 1 pair per 100 sq. mi. (260 sq. km). ... At the 3 gyrfalcon (Falco rusticolus) eyries we found 8 nestlings or fully-fledged young, of which we were able to band 3. Peregrines and gyrfalcons (and a rare white-tailed sea eagle, Haliaetus albicilla) are the only avian predators nesting in southern West Greenland, although ravens (Corvus corax) competed for some nesting cliff sites. We collected remains of prey species and pellets at each falcon eyrie. Addled eggs (2) from 2 peregrine eyries were collected for pesticide analysis. Eggshell fragments for thickness determination were gathered at 5 peregrine eyries. ... Peregrine falcons in West Greenland appear to be in a healthy state as evidenced by a high nesting density (1/100 sq. mi.) and a high production rate (2.25/eyrie), especially in light of the unusually severe conditions in West Greenland during the winter and late spring of 1971-72. We found little interspecific competition for prey species between peregrines and gyrfalcons. The gyrfalcon is already nesting in West Greenland before the peregrines arrive from their winter migration to the south. The gyrfalcons could therefore be expected to be aggressive in defence of their nesting cliffs and thereby occupy optimal cliffs. Despite this, all the peregrines we studied occupied high, sheer, and quite optimal nesting cliffs. Gyrfalcons seemed to prefer a nesting site lower down on a cliff face than peregrines, and both falcons preferred high, sheer cliffs with a southern exposure. Ravens were relegated to lower, less desirable (more accessible) cliffs for nesting. We await pesticide analysis of the peregrine falcon eggs and prey species collected, as well as eggshell thickness determination. Before these facts are determined we can say nothing definite about the status of peregrines in Greenland. Nesting density and production, however, suggest that the status of the peregrine is better in Greenland than in other areas of the north. ..

General practitioners' perceptions of population based bowel screening and their influence on practice: a qualitative study

© 2017 The Author(s). Background: Although largely preventable, Australia has one of the highest rates of bowel cancer in the world. General Practitioners (GPs) have an important role to play in prevention and early detection of bowel cancer, however in Australia this is yet to be optimised and participation remains low. This study sought to understand how GPs' perceptions of bowel screening influence their attitudes to, and promotion of the faecal occult blood test (FOBT), to identify opportunities to enhance their role. Methods: Interviews were conducted with 31 GPs from metropolitan and regional New South Wales (NSW), Australia. Discussions canvassed GPs' perceptions of their role in bowel screening and the national screening program; perceptions of screening tests; practices regarding discussing screening with patients; and views on opportunities to enhance their role. Transcripts were coded using Nvivo and thematically analysed. Results: The study revealed GPs' perceptions of screening did not always align with broader public health definitions of 'population screening'. While many GPs reportedly understood the purpose of population screening, notions of the role of asymptomatic screening for bowel cancer prevention were more limited. Descriptions of screening centred on two major uses: the use of a screening 'process' to identify individual patients at higher risk; and the use of screening 'tools', including the FOBT, to aid diagnosis. While the FOBT was perceived as useful for identifying patients requiring follow up, GPs expressed concerns about its reliability. Colonoscopy by comparison, was considered by many as the gold standard for both screening and diagnosis. This perception reflects a conceptualisation of the screening process and associated tools as an individualised method for risk assessment and diagnosis, rather than a public health strategy for prevention of bowel cancer. Conclusion: The results show that GPs' perceptions of screening do not always align with broader public health definitions of 'population screening'. Furthermore, the way GPs understood screening was shown to impact their clinical practice, influencing their preferences for, and use of 'screening' tools such as FOBT. The findings suggest emphasising the preventative opportunity of FOBT screening would be beneficial, as would formally engaging GPs in the promotion of bowel screening

Finding purpose in the conservation of biodiversity by the commingling of science and ethics

Averting the biodiversity crisis requires closing a gap between how humans tend to behave, individually and collectively, and how we ought to behave—“ought to” in the sense of behaviors required to avert the biodiversity crisis. Closing that gap requires synthesizing insight from ethics with insights from social and behavioral sciences. This article contributes to that synthesis, which presents in several provocative hypotheses: (i) Lessening the biodiversity crisis requires promoting pro-conservation behavior among humans. Doing so requires better scientific understanding of how one’s sense of purpose in life affects conservation-relevant behaviors. Psychology and virtue-focused ethics indicate that behavior is importantly influenced by one’s purpose. However, conservation psychology has neglected inquiries on (a) the influence of one’s purpose (both the content and strength of one’s purpose) on conservation-related behaviors and (b) how to foster proconservation purposes; (ii) lessening the biodiversity crisis requires governance—the regulation of behavior by governments, markets or other organization through various means, including laws, norms, and power—to explicitly take conservation as one of its fundamental purposes and to do so across scales of human behaviors, from local communities to nations and corporations; (iii) lessening the biodiversity crisis requires intervention via governance to nudge human behavior in line with the purpose of conservation without undue infringement on other basic values. Aligning human behavior with conservation is inhibited by the underlying purpose of conservation being un derspecified. Adequate specification of conservation’s purpose will require additional interdisciplinary research involving insights from ethics, social and behavioral sciences, and conservation biology