Dislocation Reduction by Glide in Epitaxial IV-VI Layers on Si Substrates

It is explained with a simple model why the reduction of threading dislocation (TD) densities in epitaxial lattice and thermal expansion mismatched IV-VI layers such as PbSe(111) on Si(111) substrates follows a 1/h 2 dependence where h is the thickness of the layer. This is in contrast to the 1/h dependence for III-V and II-VI layers grown on mismatched substrates. The 1/h 2 dependence results since the thermal mismatch strain is mainly reduced by glide and reactions of the TD in their main {100}-type glide system of the NaCl-type IV-VI semiconductors. In addition, multiple thermal cycles lead to further reduction of the TD densities by glide and fusion since fusion does not cause dislocation blockin

3-4.5 μm continuously tunable single mode VECSEL

We present continuously tunable Vertical External Cavity Surface Emitting Lasers (VECSEL) in the mid-infrared. The structure based on IV-VI semiconductors is epitaxially grown on a Si-substrates. The VECSEL emit one single mode, which is mode hop-free tunable over 50-100nm around the center wavelength. In this work, two different devices are presented, emitting at 3.4μm and 3.9μm, respectively. The lasers operate near room temperature with thermoelectric stabilization. They are optically pumped, yielding an output power >10mWp. The axial symmetric emission beam has a half divergence angle of <3.3

5-μm vertical external-cavity surface-emitting laser (VECSEL) forspectroscopic applications

Mid-IR tunable VECSELs (Vertical External-Cavity Surface-Emitting Lasers) emitting at 4-7 μm wavelengths and suitable for spectroscopic sensing applications are described. They are realized with lead-chalcogenide (IV-VI) narrow band gap materials. The active part, a single 0.6-2-μm thick PbTe or PbSe gain layer, is grown onto an epitaxial Bragg mirror consisting of two or three Pb1−y EuyTe/BaF2 quarter-wavelength layer pairs. All layers are deposited by MBE in a single run employing a BaF2 or Si substrate, no further processing is needed. The cavity is completed with an external curved top mirror, which is again realized with an epitaxial Bragg structure. Pumping is performed optically with a 1.5-μm laser. Maximum output power for pulsed operation is currently up to >1 Wp at −173°C and >10 mW at 10°C. In continuous wave (CW) operation, 18 mW at 100 K are reached. Still higher operating temperatures and/or powers are expected with better heat-removal structures and better designs employing QW (Quantum-Wells). Advantages of mid-IR VECSELs compared to edge-emitting lasers are their very good beam quality (circular beam with 15 μm are accessible with Pb1−y XyZ (X=Sr, Eu, Sn, Z=Se, Te) and/or including Q

Maternal Platelets And The Thrombin Receptor, Par4, Disrupt Placental Morphogenesis And Cause Fetal Loss In Factor V Leiden Mice

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106057/1/jth02468.pd

Epitaxial Lead Chalcogenides on Si for Mid-IR Detectors and Emitters Including Cavities

Lead chalcogenide (IV-VI narrow-gap semiconductor) layers on Si or BaF2(111) substrates are employed to realize two mid-infrared optoelectronic devices for the first time. A tunable resonant cavity enhanced detector is realized by employing a movable mirror. Tuning is across the 4μm to 5.5μm wavelength range, and linewidth is <0.1μm. Due to the thin (0.3μm) PbTe photodiode inside the cavity, a higher sensitivity at higher operating temperatures was achieved as compared to conventional thick photodiodes. The second device is an optically pumped vertical external-cavity surface-emitting laser with PbTe-based gain layers. It emits at ∼5μm wavelength and with output power up to 50mW pulsed, or 3mW continuous wave at 100

Band-Gap Nonlinearity in Lead Chalcogenide (PbQ, Q = Te, Se, S) Alloys

Narrow band-gap lead chalcogenides have been developed for several optical and electronic applications. However, band-gap energies of the ternary and quaternary alloys have received little attention compared with the parent binary phases. Here, we have fabricated single-phase ternary (PbTe)1−x(PbSe)x and quaternary (PbTe)0.9−y(PbSe)0.1(PbS)y and (PbTe)0.65−z(PbSe)0.35(PbS)z alloys and shown that although lattice parameters follow Vegard’s law as a function of composition, the bandgap energies exhibit a substantial bowing effect. The ternary (PbTe)1−x(PbSe)x system features a smaller bowing parameter predominantly due to the difference in electronegativity between Se and Te, whereas the larger bowing parameters in quaternary alloys are generated from a larger crystal lattice mismatch and larger miscibility gap. These findings can lead to further advances in tuning the band-gap and lattice parameters for optical and electronic applications of lead chalcogenides

A review of the use of terrestrial laser scanning application for change detection and deformation monitoring of structures

Change detection and deformation monitoring is an active area of research within the field of engineering surveying as well as overlapping areas such as structural and civil engineering. The application of Terrestrial Laser Scanning (TLS) techniques for change detection and deformation monitoring of concrete structures has increased over the years as illustrated in the past studies. This paper presents a review of literature on TLS application in the monitoring of structures and discusses registration and georeferencing of TLS point cloud data as a critical issue in the process chain of accurate deformation analysis. Past TLS research work has shown some trends in addressing issues such as accurate registration and georeferencing of the scans and the need of a stable reference frame, TLS error modelling and reduction, point cloud processing techniques for deformation analysis, scanner calibration issues and assessing the potential of TLS in detecting sub-centimetre and millimetre deformations. However, several issues are still open to investigation as far as TLS is concerned in change detection and deformation monitoring studies such as rigorous and efficient workflow methodology of point cloud processing for change detection and deformation analysis, incorporation of measurement geometry in deformation measurements of high-rise structures, design of data acquisition and quality assessment for precise measurements and modelling the environmental effects on the performance of laser scanning. Even though some studies have attempted to address these issues, some gaps exist as information is still limited. Some methods reviewed in the case studies have been applied in landslide monitoring and they seem promising to be applied in engineering surveying to monitor structures. Hence the proposal of a three-stage process model for deformation analysis is presented. Furthermore, with technological advancements new TLS instruments with better accuracy are being developed necessitating more research for precise measurements in the monitoring of structures

Racial Disparities in Emergency General Surgery: Do Differences in Outcomes Persist Among Universally Insured Military Patients?

Research Objective: Described as one of the most serious health problems affecting the nation, racial disparities are estimated to account for \u3e83,000 deaths, \u3e$57 billion per year. They have been identified in multiple surgical settings, including differences in outcomes by race among emergency general surgery(EGS) patients. As many minority patients are uninsured, increasing access to care is thought to be a viable solution to mitigate inequities. The objectives of this study were to determine whether racial disparities in 30/90/180day outcomes exist within a universally-insured population of military/civilian-dependent EGS patients and whether differences in outcomes differentially persist in care received at military-vs-civilian hospitals and among sponsors who are enlisted-service members-vs-officers. It also considered longer-term outcomes of care. Study Design: Risk-adjusted survival analyses using Cox proportional-hazards models assessed race-based differences in mortality, major morbidity, and readmission from index-hospital admission (discharge for readmission) through 30/90/180days. Models accounted for hospital clustering and possible biases associated with missing race (reweighted-estimating equations). Sub-analyses considered effects restricted to operative interventions, stratified by 24 EGS-diagnostic categories defined by the American Association for the Surgery of Trauma(AAST), and effect modification related to rank (SES-proxy: officers-vs-enlisted-sponsors) and military-vs-civilian-hospital care. Population Studied: Five years of national TRICARE Prime/Prime-plus data, which provides insurance to active/reserve/retired members of the US Armed Services and dependents, were queried for adults (≥18y) with primary EGS conditions, defined by the AAST. Patients who did not have an index admission between 01/01/2006-01/07/2010 (minimum 180days follow-up) or who were not continuously enrolled in TRICARE for 180days were excluded. Non-surviving patients were retained while they survived. Principal Findings: A total of 101,011 patients were included: 73.5% White, 14.5% Black, 4.4% Asian, 7.7% other. Risk-adjusted analyses reported equivalent-or-better mortality and readmission outcomes among minority patients at 30/90/180days—even when restricted to civilian hospitals where studies suggest that EGS disparities are found. Readmissions within military hospitals were lower among minority patients. Major morbidity was higher among Black versus White patients (HR[95%CI]): 30day-1.23[1.13-1.35], 90day-1.18[1.09-1.28], 180day-1.15[1.07-1.24]—a finding driven by appendiceal disorders (HR:1.69-1.70). No other diagnostic category-based HR was significant. When considered by rank, significant effects were isolated to enlisted-service members. However, given the relatively small number of patients who were (dependents of) officers, it is difficult to determine whether rank-based findings are a result of social determinants or influenced by the limited number of minority patients. Conclusions: The first of its kind to examine racial disparities in longer-term outcomes of EGS care, this longitudinal analysis of military patients demonstrated apparent mitigation of racial disparities within a universally-insured health system when compared to the overall US health system. Efforts to explain findings based on consideration of care provided in military-vs-civilian hospitals, among specific EGS-diagnostic categories, and based on sponsor rank revealed modification of the association between race and outcomes to some extent for all three. Implications for Policy or Practice: The contrast between results for universally-insured military/civilian-dependent patients and reported disparities among all US civilian patients merits consideration. The data speak to the importance of insurance-coverage in the development of disparities interventions nationwide and will help to inform policy within the DoD

Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure