The Role of Mission Studies in Theological Education

https://place.asburyseminary.edu/firstfruitspapers/1145/thumbnail.jp

Achieving Continuous-Wave Lasing for Violet m-plane GaN-Based Vertical-Cavity Surface-Emitting Lasers

Vertical-cavity surface-emitting lasers (VCSELs) are a special class of laser diode that use top-side and bottom-side parallel mirrors to emit a laser beam vertically from the top surface, as compared to conventional edge-emitting lasers that emit light from the sides of the devices. Compared to edge-emitting lasers, VCSELs have many unique attributes, such as a low threshold current that leads to low power consumption, high-speed direct modulation, superior beam quality, and they can be easily arranged into two-dimensional VCSEL arrays for scalable power. This leads to several exciting applications; for example, VCSELs are the key component in the Apple iPhone X that enables Face ID, which allows users to securely unlock their devices simply by looking at their phones. However, the VCSEL market is currently limited to red-emitting and infrared-emitting VCSELs that use GaAs-based and InP-based systems. If shorter wavelength emitting VCSELs could be created, it would open up a whole new world of untapped and exciting applications. For example, blue and green VCSELs could be paired with red VCSELs to create next-generation display and projector technology. The low power consumption and high beam quality of VCSEL-based displays would be particularly promising for virtual and augmented reality systems. Shorter wavelength VCSELs can be created using GaN-based materials, but these devices have been very challenging to create. The first GaN-based VCSEL was demonstrated in 2008, and only eight research groups have demonstrated these devices over the following decade. With the first report in 2012, the University of California, Santa Barbara (UCSB) has been the only group in the United States to create GaN-based VCSELs. Compared to the c-plane GaN VCSELs from all of the other groups, VCSELs from UCSB have used m-plane GaN, which uniquely provides 100% polarized emission for both individual VCSELs and VCSEL arrays. The main problem with GaN VCSELs from UCSB has been their inability to lase under continuous-wave (CW) operation. They could only lase under pulsed operation, which means that these VCSELs would fail if turned on for longer than a fraction of a millisecond. This has been a severe limitation that has prevented most practical applications of these devices. Therefore, the ultimate goal of the research described in this thesis has been to achieve CW lasing. This has been a tremendously difficult goal, and the initial VCSEL designs failed to lase, even under pulsed operation. Despite these initial discouraging results, this experiment was important because it led to an extensive failure analysis that revealed several key problems with the VCSEL design. Surface roughness prior to the DBR mirror deposition turned out to be a major problem that inhibited lasing due to scattering loss and reduced mirror reflectance. After performing experiments to improve the surface morphology, the surface roughness on the p-side was reduced by utilizing an indium flux during MBE tunnel junction regrowth, and the roughness on the n-side was reduced by removing an oxide residue that formed after the photoelectrochemical (PEC) undercut etch to remove the m-plane GaN growth substrate. Another significant problem was VCSEL yield in which only a small percentage of devices successfully transferred onto the flip-chip substrate, and most of those devices were cracked. A series of flip-chip bonding experiments were conducted to optimize the Au-Au thermocompression bond, but the yield only marginally improved at first. The flip-chip bond was also responsible for a severe thermal issue that prevented CW operation in previous devices. Based on thermal modeling in COMSOL, heat generated in the active region could not flow directly downward due to the thermally-insulating bottom DBR, so there was a bottleneck in heat transport through a relatively thin gold contact along the sidewall of the bottom DBR toward the flip-chip substrate. Focused ion beam (FIB) cross-sectioning revealed cracks in that thin metal contact, which were found to significantly impair the VCSEL thermal performance based on COMSOL simulations. Both the VCSEL yield and thermal performance were improved by implementing a new flip-chip bonding design. Instead of Au-Au thermocompression bonding, Au-In solid liquid interdiffusion (SLID) bonding was performed at a much lower temperature and pressure, which greatly improved the VCSEL yield. Furthermore, Au-In SLID bonding significantly improved the VCSEL thermal performance by incorporated a liquid phase during bonding so that the entire bottom DBR was embedded within metal. This led to the world’s first demonstration of CW operation for m-plane GaN VCSELs, and they were able to lase under CW operation for over 20 minutes of continuous testing

The Effects on 3D Printed Molds on Metal Castings

Additive manufacture of sand molds via binder jetting enables the casting of complex metal geometries. Various material systems have been created for 3D printing of sand molds; however, a formal study of the materials’ effects on cast products has not yet been conducted. In this paper the authors investigate potential differences in material properties (microstructure, porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially available 3D printing media. In addition, the material properties of cast products from traditional “no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed molds.Mechanical Engineerin

Screening for Major Depressive Disorder in Children and Adolescents: A Systematic Review for the U.S. Preventive Services Task Force

BACKGROUND: Major depressive disorder (MDD) is common among children and adolescents and is associated with functional impairment and suicide. PURPOSE: To update the 2009 U.S. Preventive Services Task Force (USPSTF) systematic review on screening for and treatment of MDD in children and adolescents in primary care settings. DATA SOURCES: Several electronic searches (May 2007 to February 2015) and searches of reference lists of published literature. STUDY SELECTION: Trials and recent systematic reviews of treatment, test-retest studies of screening, and trials and large cohort studies for harms. DATA EXTRACTION: Data were abstracted by 1 investigator and checked by another; 2 investigators independently assessed study quality. DATA SYNTHESIS: Limited evidence from 5 studies showed that such tools as the Beck Depression Inventory and Patient Health Questionnaire for Adolescents had reasonable accuracy for identifying MDD among adolescents in primary care settings. Six trials evaluated treatment. Several individual fair- and good-quality studies of fluoxetine, combined fluoxetine and cognitive behavioral therapy, escitalopram, and collaborative care demonstrated benefits of treatment among adolescents, with no associated harms. LIMITATION: The review included only English-language studies, narrow inclusion criteria focused only on MDD, high thresholds for quality, potential publication bias, limited data on harms, and sparse evidence on long-term outcomes of screening and treatment among children younger than 12 years. CONCLUSION: No evidence was found of a direct link between screening children and adolescents for MDD in primary care or similar settings and depression or other health-related outcomes. Evidence showed that some screening tools are accurate and some treatments are beneficial among adolescents (but not younger children), with no evidence of associated harms. PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality

AN ANALYSIS of the 20-year use of a deep Broward County lime-rock pit as a natural advanced wastewater treatment and groundwater recycling facility, with a recommendation that: with the large number of similar lime-rock pits in Southeast Florida, the opportunity for expanding the benefits of such inland wastewater retention should be given serious consideration instead of wastefully discharging the water into the ocean.

The benefits of the inland retention of freshwaters in South Florida are indisputable. During periods of prolonged drought, the maintenance of a higher groundwater table, which benefits terrestrial vegetation and retards saltwater intrusion, is clearly preferable to the alternative of discharging up to 400,000 gallons of freshwater per day into the ocean. Therefore, the only objections to the retention of treated sewage effluent in an inland lime-rock pit, with the physical, chemical and biologic characteristics of our pits, would have to do with possible detrimental effects to public health or the environment. The major public health concern involves the possible discharge of human pathogens. This can be prevented by high-level chlorination of well-treated effluent such as that of the Ferncrest Utilities. With the cooperation and help of the Nova University Oceanographic Center, the Florida Agricultural Research and Education Station, the Broward County Environmental Quality Control Board and the landowners, the Tindall Hammock Irrigation and Soil Conservation District and the Ferncrest Utilities respectfully submit that retention of the excellent tertiary-treated Ferncrest Utilities effluent in such a lime-rock pit accomplishes the following: • Provides an inexpensive, safe, practical, alternative, non-structural, natural, and environmentally sound drainage and wastewater pollutant treatment and inactivation facility that uses no energy except sunlight. • Conserves, stores and recycles stormwater and wastewater instead of wasteful discharge into canals or the ocean. • Helps to maintain a higher groundwater elevation, thereby reducing the volume of irrigation water needed for area lawns and shrubbery, and the energy and expense thereof. • Retards the rate of saltwater intrusion into the aquifer. • Enhances the U.S. EPA\u27s goal of fishable, swimmable public waters by complexing and precipitating runoff and wastewater pollutants, thereby keeping them out of the North New River Canal, the New River and the ocean. With the large number of similar lime-rock pits in Southeast Florida, the opportunity for expanding the benefits of such inland wastewater retention should be given serious consideration

On the triple nature of the X-ray source 4U2129+47 (= V1727 Cyg)

Context. In quiescence, the proposed optical counterpart to the neutron star low mass X-ray binary 4U 2129+47 (V1727 Cyg) shows a spectrum consistent with a late F-type subgiant and no radial velocity variations on the 5.24 hour binary period. This could imply that V1727 Cyg is a chance line of sight interloper. Radial velocity measurements, however, showed evidence for a longer term ~40 km/s shift, which suggested that 4U 2129+47 could be a hierarchical triple system, with the F-type star in a wide orbit about the inner low mass X-ray binary. Aims. In order to confirm the long-term radial velocity shift reported in Garcia et al. (1989) and its amplitude, we obtained spectroscopic observations of V1727 Cyg during 1996 and 1998 with the William Herschel Telescope using the ISIS spectrograph. Methods. We determined radial velocities from the ISIS spectra by means of the cross-correlation technique with a template spectrum. Results. The resulting radial velocities show variations with a maximum amplitude of ~40 km/s, confirming previous results and supporting the F-type star as being the third body in a hierarchical triple system. The odds that this star could be an interloper are ~3e-6Comment: 3 Pages, 2 Figures. Revised version in form accepted for publication in A&

The Turbulent Cascade for High Cross-helicity States at 1 au. II. Minor Energy

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Correlation Scales of the Turbulent Cascade at 1 au

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