Optically resonant structures for the enhancement of polycrystalline PbSe photoconductors

The mid-wave infrared (MWIR) regime of the electromagnetic spectrum is attractive for long-range imaging systems due to the atmospheric window between 3 and 5 [mu]m. Due to ambient thermal background, it is often necessary to operate sensor systems below room temperature to achieve an adequate signal-to-noise ratio (SNR). This cooling requirement adds size, weight, and complexity to systems in which these parameters are at a premium. In this work I investigated two methods for optically enhancing the absorptive properties of lead selenide (PbSe) photoconductive films to increase the operating temperature up to 290 K, thereby mitigating system cooling requirements. By employing surface plasmon resonant (SPR) and embedded reflective structures, we were able to demonstrate enhanced responsivity and raise the operating temperature to room-temperature. Sensitivity was observed to increase by a factor of three for SPR enhanced detectors, and up to two-times at room temperature in detectors with an embedded Pt back reflector. Moreover, PbSe detectors with SPR discs operating at room temperature were observed to have responsivity comparable to reference detectors at 230 K. Photoconductors with the embedded Pt back reflector had a performance at room temperature that was similar to the reference detector at 250 K. Herein, I discuss my design process, as well as the fabrication of these resonant structures. Also discussed are the measurement and test results I obtained from surface plasmon and embedded reflector enhanced PbSe detectors. In this dissertation, I present results that demonstrate the viability of SPR and interference structures as mechanisms for increasing the operating temperature of PbSe MWIR photodetectors up to 290 KIncludes bibliographical reference

Spectroscopy studies of straincompensated mid-infrared QCL active regions on misoriented substrates

In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal transitions, we incorporate strain in the active region using single and double well configurations on various surface planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction, and enhanced surface diffusion lengths. We produced mid-infrared structures under identical deposition conditions that differentiate the role of indium(strain) in intracavity frequency mixing and show evidence that this design can potentially be implemented using other material systems

Pseudomorphic growth of InAs on misoriented GaAs for extending quantum cascade laser wavelength

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2 degrees offset toward 2-1-1 surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2 degrees offset toward 2-1-1 surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions in regards to surface roughness with \u3e92% accuracy. The smoothest InAs/GaAs samples demonstrated average surface roughness of 0.08 nm for 10 um-squre areas, albeit at very low deposition rates. The authors have found the most important process conditions to be substrate temperature and deposition rate, leading us to believe that controlling diffusion length may be the key to reducing defects in severely strained structures. InGaAs/AlGaAs quantum cascade laser structures were also produced on (111)B with 2 degrees offset toward 2-1-1 to take advantage of the piezoelectric effect, and the modified laser transitions due to these effects were observed

Facilitating access to voluntary and community services for patients with psychosocial problems: a before-after evaluation

<p>Abstract</p> <p>Background</p> <p>Patients with psychosocial problems may benefit from a variety of community, educational, recreational and voluntary sector resources, but GPs often under-refer to these through lack of knowledge and time. This study evaluated the acceptability and effectiveness of graduate primary care mental health workers (GPCMHWs) facilitating access to voluntary and community sector services for patients with psychosocial problems.</p> <p>Methods</p> <p>Patients with psychosocial problems from 13 general practices in London were referred to a GPCMHW Community Link scheme providing information and support to access voluntary and community resources. Patient satisfaction, mental health and social outcomes, and use of primary care resources, were evaluated.</p> <p>Results</p> <p>108 patients consented to take part in the study. At three-month follow-up, 63 (58%) had made contact with a community service identified as suitable for their needs. Most were satisfied with the help provided by the GPCMHW in identifying and supporting access to a suitable service. There was a reduction in the number of patients with a probable mental health problem on the GHQ-12 from 83% to 52% (difference 31% (95% CI, 17% – 44%). Social adjustment improved and frequencies of primary care consultations and of prescription of psychotropic medications were reduced.</p> <p>Conclusion</p> <p>Graduates with limited training in mental health and no prior knowledge of local community resources can help patients with psychosocial problems access voluntary and community services, and patients value such a scheme. There was some evidence of effectiveness in reducing psychosocial and mental health problems.</p

Adenosine monophosphate binding stabilizes the KTN domain of the <i>Shewanella denitrificans</i> Kef potassium efflux system

Ligand binding is one of the most fundamental properties of proteins. Ligand functions fall into three basic types: substrates, regulatory molecules, and cofactors essential to protein stability, reactivity, or enzyme-substrate complex formation. The regulation of potassium ion movement in bacteria is predominantly under the control of regulatory ligands that gate the relevant channels and transporters, which possess subunits or domains that contain Rossmann folds (RFs). Here we demonstrate that adenosine monophosphate (AMP) is bound to both RFs of the dimeric bacterial Kef potassium efflux system (Kef), where it plays a structural role. We conclude that AMP binds with high affinity, ensuring that the site is fully occupied at all times in the cell. Loss of the ability to bind AMP, we demonstrate, causes protein, and likely dimer, instability and consequent loss of function. Kef system function is regulated via the reversible binding of comparatively low-affinity glutathione-based ligands at the interface between the dimer subunits. We propose this interfacial binding site is itself stabilized, at least in part, by AMP binding

Adenosine Monophosphate Binding Stabilizes the KTN Domain of the Shewanella denitrificans Kef Potassium Efflux System

The project is supported by the Wellcome Trust (WT092552MA, WT100209MA) to IRB, JHN, SM, and SJC, a Biotechnology and Biological Sciences Research Council grant (BB/H017917/1), and a European Union Marie Curie ITN Award (NICHE; 289384) that supported SE. CP would also like to acknowledge additional support by a Tenovus Scotland grant award (T15/41). WAC is supported by a Science Without Borders scholarship. The authors would like to acknowledge that the work presented here made use of the Emerald High Performance Computing facility made available by the Centre for Innovation, formed by the universities of Oxford, Southampton, Bristol, and University College London in partnership with the STFC Rutherford Appleton Laboratory. RSP acknowledges the use of the EPSRC UK National Service for Computational Chemistry Software (NSCCS) at Imperial College London in carrying out this work (CHEM773). RSP is grateful to NVIDIA for the generous donation of Tesla GPUs as part of the academic partnership scheme. SJC and AC thank the European Commission for the award of a Marie Curie Fellowship to AC (660156, FLUOROKEF). SJC and SCG thank the EPSRC for studentship support forSCG. SJC thanks St. Hugh’s College, Oxford, for research support.Peer reviewedPostprin