Epitaxy and Device Design for High Efficiency Blue LEDs and Laser Diodes

The (Al,Ga,In)N materials system has impacted energy efficiency on the world-wide scale through its application to blue light-emitting diodes (LEDs), which were invented and developed in the 1990s. Since then, cost reductions and performance improvements have brought GaN-based LEDs into the mainstream, supplanting outdated lighting technology and improving energy efficiency.One of the main challenges that still limits commercial LEDs, however, is “efficiency droop,” which refers to the reduction in efficiency as the input current density (and with it, the carrier density) increases. This phenomenon especially plagues high power LEDs, which operate in the current density range of 100-1000 A/cm2.Few practical options exist to directly eliminate efficiency droop, however we investigated two complementary approaches to circumvent the phenomenon. The first “high power solution” would employ blue laser diodes as the engine of solid state white lighting in lieu of LEDs. When laser diodes reach the threshold current density for stimulated emission, the carrier density in the active region clamps, simultaneously clamping droop. The wall plug efficiency of the laser diodes can then continue to rise as input current density increases until another effect (usually thermal) overrides it. The second “low power solution” maintains the blue LED as the solid state lighting engine, but shifts the operation point to low current density (and low carrier density) where efficiency droop effects are negligible and other thermal and electrical constraints in the device design are alleviated, enabling designs for high wall-plug efficiency. Both approaches to circumventing efficiency droop are likely to find a home in diverse future technologies and applications for lighting and displays.The challenge to produce high performance blue laser diodes was approached from an m-plane epitaxy platform. m-Plane is a non-polar orientation of the wurtzite (Al,Ga,In)N, which is free from deleterious polarization-related electric fields in the growth direction. m Plane is a naturally occurring crystal plane with high material gain due to its non-degenerate valence band structure, and thus should be well-suited for laser diode applications. However, m plane blue emission suffers from low indium uptake and broad spontaneous emission linewidth. The use of surface “double miscut” was investigated to improve the local step structure and morphology, resulting in higher indium uptake, narrower linewidth and higher peak power in the blue spectrum.The complementary challenge to improve the wall-plug efficiency for LEDs at low power operation focuses primarily on improved light extraction efficiency and low voltage operation. The main sources of extraction efficiency losses in typical c-plane blue LEDs on patterned sapphire substrates are absorption on the metal contacts, in the current spreading layer and on the metallic reflector, which also doubles as the heat sink. With the relaxed constraints at low power operation, new designs become possible. High light extraction designs were vetted with ray tracing software prior to experimental implementation. The highest demonstrated wall-plug efficiency resulting from these designs was 78.2%, and was accompanied by a greater than unity electrical efficiency (1.03) resulting from thermoelectric pumping, suggesting a pathway for 100% or greater wall-plug efficiency

Making More Light with Less Energy

Representing the Center for Energy Efficient Materials (CEEM), this document is one of the entries in the Ten Hundred and One Word Challenge. As part of the challenge, the 46 Energy Frontier Research Centers were invited to represent their science in images, cartoons, photos, words and original paintings, but any descriptions or words could only use the 1000 most commonly used words in the English language, with the addition of one word important to each of the EFRCs and the mission of DOE: energy. The mission of the CEEM is to discover and develop materials that control the interactions among light, electricity, and heat at the nanoscale for improved solar energy conversion, solid-state lighting, and conversion of heat into electricity

A practical approach for implementation of a basal-prandial insulin therapy regimen in patients with type 2 diabetes

Basal-prandial insulin therapy is a physiologic approach to insulin delivery that utilizes multiple daily injections to cover both basal (ie, overnight fasting and between-meal) and prandial (ie, glucose excursions above basal at mealtime) insulin needs. While basal-prandial therapy with multiple daily injections is an important therapeutic option for patients with type 2 diabetes, there is a common perception that this therapy is difficult to initiate in the primary care setting. To address this issue, a panel of clinical experts convened to develop practical recommendations on how to initiate basal-prandial therapy in patients with type 2 diabetes, focusing on patient selection, simple dosing and titration, and monitoring. Patients with type 2 diabetes who are appropriate candidates for basal-prandial insulin therapy include those who: 1) are unable to achieve glycemic control on oral antidiabetic drugs, 2) are unable to achieve glycemic control on split-mixed/premixed insulin regimens, 3) are newly diagnosed but unlikely to respond to oral antidiabetic drugs alone (ie, the patient has severe hyperglycemia or a markedly elevated glycosylated hemoglobin A1C level for which oral antidiabetic drug therapy alone is unlikely to achieve goals), and 4) prefer this therapy due to socioeconomic or other individual considerations. Basal-prandial insulin can be initiated in a simple stepwise manner, starting first with the addition of basal insulin to the existing oral antidiabetic drug regimen, followed by the introduction of 1 prandial insulin injection to the basal insulin plus oral antidiabetic drug regimen (after basal insulin has been optimized). Subsequently, other injections of prandial insulin may be added when needed. Based on home glucose monitoring data, patients may be converted from split-mixed or premixed insulin regimens to basal-prandial regimens with similar ease. Basal-prandial therapy using newer insulin formulations, such as long- and rapid-acting insulin analogs, can be relatively simple to use in patients with type 2 diabetes and is an appropriate methodology for application by primary care clinicians

Familial Creutzfeldt-Jakob disease without periodic EEG activity

Four members of a kindred with Creutzfeldt-Jakob disease are reported, in whom myoclonus did not develop and in whom serial electroencephalograms performed late in their illness failed to show periodic sharp wave complexes. Otherwise, the patients' disease duration, clinical features, and neuropathological findings were similar to those described in sporadic cases of Creutzfeldt-Jakob disease. Our findings and those reported by others suggest that periodic electroencephalographic activity may be rare in familial forms of Creutzfeldt-Jakob disease, as it is in other slow transmissible encephalopathies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50337/1/410280420_ftp.pd

Polarization-Resolved Near-Field Spectroscopy of Localized States in m-Plane InxGa1−xN/GaN Quantum Wells

Producción CientíficaWe present a polarization, spectrally, and spatially resolved near-field photoluminescence (PL) measurement technique and apply it to the study of wide m-plane InxGa1−xN/GaN quantum wells grown on on-axis and miscut GaN substrates. It is found that PL originates from localized states; nevertheless, its degree of linear polarization (DLP) is high with little spatial variation. This allows an unambiguous assignment of the localized states to InxGa1−xN composition-related band potential fluctuations. Spatial PL variations, occurring due to morphology features of the on-axis samples, play a secondary role compared to the variations of the alloy composition. The large PL peak wavelength difference for polarizations parallel and perpendicular to the c axis, the weak correlation between the peak PL wavelength and the DLP, and the temperature dependence of the DLP suggest that effective potential variations and the hole mass in the second valence-band level are considerably smaller than that for the first level. DLP maps for the long wavelength PL tails have revealed well-defined regions with a small DLP, which have been attributed to a partial strain relaxation around dislocations.Swedish Energy Agency (Contract No. 36652-1)Swedish Research Council (Contract No. 621-2013- 4096

Avaliação das diferenças de gênero nas estratégias de enfrentamento da dor lombar

El dolor lumbar puede ser visto como un gran problema de salud pública. Las diferencias de género son importantes factores que influyen en los síntomas y en las respuestas del comportamiento. El objetivo de este estudio fue investigar las diferencias de género en los comportamientos de dolor y en el manejo del dolor lumbar crónico. La muestra estuvo conformada por 158 participantes (66,5% mujeres), con edades entre los 30 y 88 años que fueron diagnosticados con artrosis lumbar. Los instrumentos utilizados fueron: la Escala Visual Analógica, el Cuestionario de Calidad de Vida y un cuestionario para evaluar las actividades de ocio y distracción del dolor. Los resultados del MANOVA demostraron que las mujeres presentaron mayor percepción del dolor que los hombres. También fue posible observar frecuencias más altas de actividades sociales en las mujeres, así como correlaciones significativas entre las actividades sociales y los dominios psicológicos, sociales y medio ambientales. En conclusión, las mujeres presentan un mayor número de estrategias de afrontamiento para el dolor, lo cual puede influir positivamente en su calidad de vida.A dor lombar pode ser vista como um grande problema de saúde pública. As diferenças de gênero são importantes fatores que influenciam nos sintomas e nas respostas do comportamento. O objetivo deste estudo foi pesquisar as diferenças de gênero nos comportamentos de dor e na gestão da dor lombar crônica. A amostra foi conformada por 158 participantes (66,5% mulheres), com idade entre 30 e 88 anos, que foram diagnosticadas com artrose lombar. Os instrumentos utilizados foram: a Escala Visual Analógica, o Questionário de Qualidade de Vida e um questionário para avaliar as atividades de lazer e distração da dor. Os resultados do MANOVA demonstraram que as mulheres apresentaram maior percepção da dor do que os homens. Também foi possível observar frequências mais altas de atividades sociais nas mulheres, bem como correlações significativas entre as atividades sociais e os domínios psicológicos, sociais e meio ambientais. Em conclusão, as mulheres apresentaram um maior número de estratégias de enfrentamento para a dor, o que pode influenciar positivamente em sua qualidade de vida.Low-back pain is considered a serious public health problem. Gender differences are important factors that influence symptoms and behavioral responses. This research aimed to investigate gender differences in pain behaviors and pain management of chronic low back pain. The sample consisted of 158 participants (66.5% female), aged 30-88 who were diagnosed with Lumbar Osteoarthritis. The instruments used were the Visual Analogue Scale, the Quality of Life Questionnaire and a questionnaire to assess leisure and distraction activities from pain. Results of MANOVA showed that women have significant greater pain perception than men. Higher frequencies of social activities were also observed for women as well as significant correlations between social activities and psychological, social and environmental domains. In conclusion, women presented a greater number of coping strategies for pain than men, which probably tend to have a positive influence in their life quality

Evaluating the effectiveness of a rapidly adopted cardiovascular technology with administrative data: The case of drug-eluting stents for acute coronary syndromes

Instrumental variable (IV) methods can correct for unmeasured confounding when using administrative (claims) data for cardiovascular outcomes research, but difficulties identifying valid IVs have limited their use. We evaluated the safety and efficacy of drug-eluting coronary stents (DES) compared to bare metal stents (BMS) for Medicare beneficiaries with acute coronary syndromes (ACS) using the rapid uptake of DES in clinical practice as an instrument. We compared results from IV to those from propensity score matching (PSM) and multivariable regression models

Migraine Associated Vertigo

The interrelations of migraine and vertigo are complex, eluding a simple localization either centrally or peripherally. Spontaneous episodic vertigo, benign paroxysmal positional vertigo, and Meniere's disease all occur more frequently in patients with migraine than in those without. Family studies support a hereditary predisposition to migraine associated vertigo. In this review, we discuss definitions, epidemiology, associated syndromes, neurootological abnormalities, genetics and treatment for patients with migraine and vertigo