373 research outputs found
Verification of band offsets and electron effective masses in GaAsN/GaAs quantum wells : Spectroscopic experiment versus 10-band k.p modeling
Optical transitions in GaAs1-xNx/GaAs quantum wells (QWs) have been probed by two complementary techniques, modulation spectroscopy in a form of photoreflectance and surface photovoltage spectroscopy. Transition energies in QWs of various widths and N contents have been compared with the results of band structure calculations based on the 10-band k.p Hamiltonian. Due to the observation of higher order transitions in the measured spectra, the band gap discontinuities at the GaAsN/GaAs interface and the electron effective masses could be determined, both treated as semi-free parameters to get the best matching between the theoretical and experimental energies. We have obtained the chemical conduction band offset values of 86% for x = 1.2% and 83% for x = 2.2%, respectively. For these determined band offsets, the electron effective masses equal to about 0.09 m(o) in QWs with 1.2% N and 0.15 m(o) for the case of larger N content of 2.2%.Publisher PDFPeer reviewe
Effect of dielectric medium anisotropy on the polarization degree of emission from a single quantum dash
This research was supported by the Polish Ministry of Science and Higher Education/the National Science Center Grant No. 2011/02/A/ST3/00152. The experiments have partially been performed within the laboratory infrastructure financed by the Polish Ministry of Science and Higher Education Grant No. 6167/IA/119/2012.Excitonic emission from single InAs/InGaAlAs/InP quantum dashes has been investigated in the context of degree of linear polarization by post-growth modification of its surrounding dielectric medium. We present optical spectroscopy measurements on a symmetric squared pedestal structures (mesas), and asymmetric rectangular ones oriented parallel or perpendicular to the main in-plane axis of the dashes [1-10]. Polarization resolved microphotoluminescence shows a significant quantitative modification of the degree of linear polarization value from -20% up to 70%. These results have been confronted with calculations of the coupling between the exciton transition dipole moment and electromagnetic field distributed in the vicinity of a quantum dash inside a processed mesa.Postprin
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Central America and the Dominican Republic in the Context of the Free Trade Agreement (DR-CAFTA) with the United States
This report explains the conditions in five countries in Central America (Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua) and one country in the Caribbean (Dominican Republic) that will be partners with the United States in the U.S.-Dominican Republic-Central America Free Trade Agreement (DR-CAFTA) signed in August 2004. All of the signatory countries except Costa Rica have approved the pact. The agreement will enter into force for the approving countries on an agreed date, tentatively January 1, 2006. In U.S. approval action, the House and Senate passed the required implementing legislation (H.R. 3045) on July 27 and 28, 2005, and the President signed it into law (P.L. 109-53) on August 2, 2005
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Central America and the Dominican Republic in the Context of the Free Trade Agreement (DR-CAFTA) with the United States
This report explains the conditions in five countries in Central America (Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua) and one country in the Caribbean (Dominican Republic) that will be partners with the United States in the U.S.-Dominican Republic-Central America Free Trade Agreement (DR-CAFTA) signed in August 2004. In U.S. approval action, the House and Senate passed the required implementing legislation (H.R. 3045) on July 27 and 28, 2005, and the President signed it into law (P.L. 109-53) on August 2, 2005. The agreement will enter into force for the other countries when their legislatures have approved it. The legislatures of El Salvador, Honduras, and Guatemala have approved the pact so far
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109th Congress
two decades in terms of political and economic development. While the region
overall experienced an economic setback in 2002-2003, by the end of 2004, it had
rebounded with an estimated growth rate of 5.5% for the year, surpassing even the
most optimistic predictions. Nevertheless, several nations face considerable
challenges that could threaten political stability, including persistent poverty, violent
guerrilla conflicts, autocratic leaders, drug trafficking, and increasing crime
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109th Congress
Over the past two decades, the Latin America and Caribbean region has made enormous strides in terms of political and economic development. Legislative and oversight attention to Latin America and the Caribbean in the 109th Congress has focused on continued counternarcotics efforts; trade issues; challenges to democracy, especially in Venezuela; efforts to bring political stability and ameliorate poverty in Haiti; efforts to foster political change in Cuba; and cooperation on migration and border security, especially with Mexico. This report provides an overview of U.S. relations with Latin America and the Caribbean, focusing on the role of Congress and congressional concerns
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron
We have measured the number of like-sign (LS) and opposite-sign (OS) lepton
pairs arising from double semileptonic decays of and -hadrons,
pair-produced at the Fermilab Tevatron collider. The data samples were
collected with the Collider Detector at Fermilab (CDF) during the 1992-1995
collider run by triggering on the existence of and candidates
in an event. The observed ratio of LS to OS dileptons leads to a measurement of
the average time-integrated mixing probability of all produced -flavored
hadrons which decay weakly, (stat.)
(syst.), that is significantly larger than the world average .Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.
Infrastructural requirements for local implementation of safety policies: the discordance between top-down and bottom-up systems of action
<p>Abstract</p> <p>Background</p> <p>Safety promotion is planned and practised not only by public health organizations, but also by other welfare state agencies, private companies and non-governmental organizations. The term 'infrastructure' originally denoted the underlying resources needed for warfare, e.g. roads, industries, and an industrial workforce. Today, 'infrastructure' refers to the physical elements, organizations and people needed to run projects in different societal arenas.</p> <p>The aim of this study was to examine associations between infrastructure and local implementation of safety policies in injury prevention and safety promotion programs.</p> <p>Methods</p> <p>Qualitative data on municipalities in Sweden designated as Safe Communities were collected from focus group interviews with municipal politicians and administrators, as well as from policy documents, and materials published on the Internet. Actor network theory was used to identify weaknesses in the present infrastructure and determine strategies that can be used to resolve these.</p> <p>Results</p> <p>The weakness identification analysis revealed that the factual infrastructure available for effectuating national strategies varied between safety areas and approaches, basically reflecting differences between bureaucratic and network-based organizational models. At the local level, a contradiction between safety promotion and the existence of quasi-markets for local public service providers was found to predispose for a poor local infrastructure diminishing the interest in integrated inter-agency activities. The weakness resolution analysis showed that development of an adequate infrastructure for safety promotion would require adjustment of the legal framework regulating injury data exchange, and would also require rational financial models for multi-party investments in local infrastructures.</p> <p>Conclusion</p> <p>We found that the "silo" structure of government organization and assignment of resources was a barrier to collaborative action for safety at a community level. It may therefore be overly optimistic to take for granted that different approaches to injury control, such as injury prevention and safety promotion, can share infrastructure. Similarly, it may be unrealistic to presuppose that safety promotion can reach its potential in terms of injury rate reductions unless the critical infrastructure for this is in place. Such an alignment of the infrastructure to organizational processes requires more than financial investments.</p
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