9,193 research outputs found
Population inversion in optically pumped asymmetric quantum well terahertz lasers
Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics
Romantic Partnerships and the Dispersion of Social Ties: A Network Analysis of Relationship Status on Facebook
A crucial task in the analysis of on-line social-networking systems is to
identify important people --- those linked by strong social ties --- within an
individual's network neighborhood. Here we investigate this question for a
particular category of strong ties, those involving spouses or romantic
partners. We organize our analysis around a basic question: given all the
connections among a person's friends, can you recognize his or her romantic
partner from the network structure alone? Using data from a large sample of
Facebook users, we find that this task can be accomplished with high accuracy,
but doing so requires the development of a new measure of tie strength that we
term `dispersion' --- the extent to which two people's mutual friends are not
themselves well-connected. The results offer methods for identifying types of
structurally significant people in on-line applications, and suggest a
potential expansion of existing theories of tie strength.Comment: Proc. 17th ACM Conference on Computer Supported Cooperative Work and
Social Computing (CSCW), 201
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Characteristics of the surface soil ecosystem: Linkage to understanding soil dynamic functions
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High Resolution Zero-Shot Domain Adaptation of Synthetically Rendered Face Images
Generating photorealistic images of human faces at scale remains a
prohibitively difficult task using computer graphics approaches. This is
because these require the simulation of light to be photorealistic, which in
turn requires physically accurate modelling of geometry, materials, and light
sources, for both the head and the surrounding scene. Non-photorealistic
renders however are increasingly easy to produce. In contrast to computer
graphics approaches, generative models learned from more readily available 2D
image data have been shown to produce samples of human faces that are hard to
distinguish from real data. The process of learning usually corresponds to a
loss of control over the shape and appearance of the generated images. For
instance, even simple disentangling tasks such as modifying the hair
independently of the face, which is trivial to accomplish in a computer
graphics approach, remains an open research question. In this work, we propose
an algorithm that matches a non-photorealistic, synthetically generated image
to a latent vector of a pretrained StyleGAN2 model which, in turn, maps the
vector to a photorealistic image of a person of the same pose, expression,
hair, and lighting. In contrast to most previous work, we require no synthetic
training data. To the best of our knowledge, this is the first algorithm of its
kind to work at a resolution of 1K and represents a significant leap forward in
visual realism
Social Cohesion, Structural Holes, and a Tale of Two Measures
EMBARGOED - author can archive pre-print or post-print on any open access repository after 12 months from publication. Publication date is May 2013 so embargoed until May 2014.This is an author’s accepted manuscript (deposited at arXiv arXiv:1211.0719v2 [physics.soc-ph] ), which was subsequently published in Journal of Statistical Physics May 2013, Volume 151, Issue 3-4, pp 745-764. The final publication is available at link.springer.com http://link.springer.com/article/10.1007/s10955-013-0722-
Interface states in junctions of two semiconductors with intersecting dispersion curves
A novel type of shallow interface state in junctions of two semiconductors
without band inversion is identified within the envelope function
approximation, using the two-band model. It occurs in abrupt junctions when the
interband velocity matrix elements of the two semiconductors differ and the
bulk dispersion curves intersect. The in-plane dispersion of the interface
state is found to be confined to a finite range of momenta centered around the
point of intersection. These states turn out to exist also in graded junctions,
with essentially the same properties as in the abrupt case.Comment: 1 figur
Bone mineral density QTL at sexual maturity and end of lay
1. An F cross of a broiler male line and a White Leghorn layer line was used to identify quantitative trait loci (QTL) for bone density at the onset of lay and at the end of the laying period. A total of 686 measures of humeral bone density were available for analysis.2. There was no evidence for epistasis.3. Genome-wide significant QTL for bone density at the onset of lay were identified on chromosomes 1 (311 cM) and 8 (2 cM) and on chromosomes 1 (311 cM), 3 (57 cM) and 8 (2 cM) with a covariate for the number of yellow follicles (a proxy for the concentration of circulating oestrogen).4. Evidence for only 4 chromosome-wide suggestive QTL were detected at the end of lay (72 weeks).5. Analysis of the combined data confirmed two genome-wide suggestive QTL on chromosome 1 (137 and 266 cM) and on chromosomes 8 (2 cM) and 9 (10 cM) in analyses with or without the covariate.6. Positive QTL alleles came from the broiler line with the exception of 2 suggestive QTL at the onset of lay on chromosomes 3 and 5 in an analysis with the covariate.7. In general, QTL acted additively, except that dominant effects were identified for three suggestive QTL at the onset of lay on chromosomes 3 (57 and 187 cM) and 5 (9 cM).8. The significant QTL in this study were at similar locations to QTL identified in a range of crosses in other publications, suggesting that they are prime candidates for the search for genes and mutations that could be used as selection criteria to improve bone strength and decrease fractures in commercial laying hens
Below-cost legislation: lessons from the Republic of Ireland
This paper traces the emergence, evolution, and demise of below cost legislation in the grocery industry in the republic of Ireland. The paper adds to our understanding of the legislation by adopting the view that, by using the net invoice price as its definition of cost, the legislation increased two streams of quasi-rents, first on suppliers’ brandeds and second on retailers’ own brands which acted to depress competitive forces and direct supplier-buyer negotiations to off-invoice discounts. Supplier generated quasi-rents financed discounts, and when coupled with retailers’ higher margins on their own brands, provided little incentive for a return to a price competitive environment. Two factors undermined this situation: the substitution of discounters’ products for suppliers’ brands as the discounters share of the market grew and the increase in cross border shopping. These had the combined effect of reducing the available quasi-rents earned in the Irish market resulting in the breakdown of the status quo and a return to price competition. Through its impact on negotiations, the legislation also introduced inefficiencies to both retailers’ and suppliers businesses representing additional waste that could have been more productively used to reduce consumer prices. The paper endorses the Government’s decision to rescind the order and remove an important constraint on both vertical and horizontal competition. Lessons from the Republic of Ireland suggest that the competitive response to the removal of below cost legislation, and reductions in prices, may take time and will depend on economic circumstances and a change in the prevailing norms of organizational behaviour and quasi-rent seeking opportunitie
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