100 research outputs found
Fabrication methods for a quantum cascade photonic crystal surface emitting laser
Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers
Quantum cascade photonic crystal surface emitting injection laser
A surface emitting quantum cascade injection laser is presented. Direct surface emission is obtained by using a 2D photonic-band-gap structure that simultaneously acts as a microcavity. The approach may allow miniaturization and on-chip-integration of the devices
Fabrication technologies for quantum cascade photonic-crystal microlasers
In this paper we describe the technological and fabrication methods necessary to incorporate both photonic and electronic-band engineering in order to create novel surface-emitting quantum cascade microcavity laser sources. This technology offers the promise of several innovative applications such as the miniaturization of QC lasers, and multi-wavelength two-dimensional laser arrays for spectroscopy, gas-sensing and imaging. This approach is not limited to light-emitting devices, and may be efficiently applied to the development of mid- and far-infrared normal-incidence detectors
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New methods for digital modeling of historic sites
We discuss new methods for building 3D models of historic sites. Our algorithm automatically computes pairwise registrations between individual scans, builds a topological graph, and places the scans in the same frame of reference
Hydrological cycle in the Danube basin in present-day and XXII century simulations by IPCCAR4 global climate models
We present an intercomparison and verification analysis of 20 GCMs (Global
Circulation Models) included in the 4th IPCC assessment report regarding their
representation of the hydrological cycle on the Danube river basin for 1961â2000
and for the 2161â2200 SRESA1B scenario runs. The basin-scale properties of the
hydrological cycle are computed by spatially integrating the precipitation, evaporation,
and runoff fields using the Voronoi-Thiessen tessellation formalism. The span of the
model- simulated mean annual water balances is of the same order of magnitude of
the observed Danube discharge of the Delta; the true value is within the range
simulated by the models. Some land components seem to have deficiencies since there
are cases of violation of water conservation when annual means are considered. The
overall performance and the degree of agreement of the GCMs are comparable to those
of the RCMs (Regional Climate Models) analyzed in a previous work, in spite of the
much higher resolution and common nesting of the RCMs. The reanalyses are shown
to feature several inconsistencies and cannot be used as a verification benchmark for
the hydrological cycle in the Danubian region. In the scenario runs, for basically all
models the water balance decreases, whereas its interannual variability increases.
Changes in the strength of the hydrological cycle are not consistent among models:
it is confirmed that capturing the impact of climate change on the hydrological cycle
is not an easy task over land areas. Moreover, in several cases we find that qualitatively
different behaviors emerge among the models: the ensemble mean does not represent
any sort of average model, and often it falls between the modelsâ clusters
Assessing the value of seasonal climate forecasts for decisionâmaking
Seasonal climate forecasts (SCF) can support decisionâmaking and thus help society cope with and prepare for climate variability and change. The demand for understanding the value and benefits of using SCF in decisionâmaking processes can be associated with different logics. Two of these would be the need to justify public and private investment in the provision of SCF and demonstrating the gains and benefits of using SCF in specific decisionâmaking contexts. This paper reviews the main factors influencing how SCF is (or can be) valued in supporting decisionâmaking and the main methods and metrics currently used to perform such valuations. Our review results in four key findings: (a) there is a current emphasis on economic ex ante studies and the quantification of SCF value; (b) there are fundamental differences in how the value of SCF is defined and estimated across methods and approaches; (c) most valuation methods are unable to capture the differential benefits and risks of using SCF across spatiotemporal scales and groups; and (d) there is limited involvement of the decisionâmakers in the valuation process. The paper concludes by providing some guiding principles towards more effective valuations of SCF, notably the need for a wider diversity and integration of methodological approaches. These should particularly embrace exâpost, qualitative, and participatory approaches which allow coâevaluation with decisionâmakers so that more comprehensive and equitable SCF valuations can be developed in future
Simplifying Consent for HIV Testing Is Associated with an Increase in HIV Testing and Case Detection in Highest Risk Groups, San Francisco January 2003âJune 2007
Populations at highest risk for HIV infection face multiple barriers to HIV testing. To facilitate HIV testing procedures, the San Francisco General Hospital Medical Center eliminated required written patient consent for HIV testing in its medical settings in May 2006. To describe the change in HIV testing rates in different hospital settings and populations after the change in HIV testing policy in the SFDH medical center, we performed an observational study using interrupted time series analysis.Data from all patients aged 18 years and older seen from January 2003 through June 2007 at the San Francisco Department of Public Health (SFDPH) medical care system were included in the analysis. The monthly HIV testing rate per 1000 had patient-visits was calculated for the overall population and stratified by hospital setting, age, sex, race/ethnicity, homelessness status, insurance status and primary language.By June 2007, the average monthly rate of HIV tests per 1000 patient-visits increased 4.38 (CI, 2.17-6.60, p<0.001) over the number predicted if the policy change had not occurred (representing a 44% increase). The monthly average number of new positive HIV tests increased from 8.9 (CI, 6.3-11.5) to 14.9 (CI, 10.6-19.2, p<0.001), representing a 67% increase. Although increases in HIV testing were seen in all populations, populations at highest risk for HIV infection, particularly men, the homeless, and the uninsured experienced the highest increases in monthly HIV testing rates after the policy change.The elimination of the requirement for written consent in May 2006 was associated with a significant and sustained increase in HIV testing rates and HIV case detection in the SFDPH medical center. Populations facing the higher barriers to HIV testing had the highest increases in HIV testing rates and case detection in response to the policy change
Epistasis and genotype-by-environment interaction of grain protein content in durum wheat
Parental, F1 , F 2 , BC 1 and BC 2 generations of four crosses involving four cultivars of durum wheat (Triticum durum Desf.) were evaluated at two sites in Tunisia. A three-parameter model was found inadequate for all cases except crosses Chili x Cocorit 71 at site Sidi Thabet and Inrat 69 x Karim at both sites. In most cases a digenic epistatic model was sufficient to explain variation in generation means. Dominance effects (h) and additive x additive epistasis (i) (when significant) were more important than additive (d) effects and other epistatic components. Considering the genotype-by-environment interaction, the non-interactive model (m, d, h, e) was found adequate. Additive variance was higher than environmental variance in three crosses at both sites. The estimated values of narrow-sense heritability were dependent upon the cross and the sites and were 0%-85%. The results indicate that appropriate choice of environment and selection in later generations would increase grain protein content in durum wheat
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