Ultrafast Insulator-Metal Phase Transition in VO2 Studied by Multiterahertz Spectroscopy

The ultrafast photoinduced insulator-metal transition in VO2 is studied at different temperatures and excitation fluences using multi-THz probe pulses. The spectrally resolved mid-infrared response allows us to trace separately the dynamics of lattice and electronic degrees of freedom with a time resolution of 40 fs. The critical fluence of the optical pump pulse which drives the system into a long-lived metallic state is found to increase with decreasing temperature. Under all measurement conditions we observe a modulation of the eigenfrequencies of the optical phonon modes induced by their anharmonic coupling to the coherent wave packet motion of V-V dimers at 6.1 THz. Furthermore, we find a weak quadratic coupling of the electronic response to the coherent dimer oscillation resulting in a modulation of the electronic conductivity at twice the frequency of the wave packet motion. The findings are discussed in the framework of a qualitative model based on an approximation of local photoexcitation of the vanadium dimers from the insulating state.Comment: 10 pages, 8 figures submitted to Physical Review

Qualitative Methods of Road Traffic Crash Research in Low- and Middle-income Countries: A Review

Road traffic crashes are rapidly becoming one of the leading causes of injury and death globally. It is predicted that by 2030 crashes will become the fourth leading cause of disability-adjusted life years (DALYs) (Mathers & Loncar, [11]) and the seventh leading global cause of death (World Health Organization [WHO], [26]). The global death toll due to crashes has already escalated by 46% over the past two decades (The World Bank, [21]). Low- and middle-income countries (LMICs) are acutely affected by this \u27hidden epidemic\u27 (Balch, [ 1]). Ninety per cent of the world\u27s crash-related deaths occur in LMICs where only 54% of its motor vehicles are registered (WHO, [25]). Furthermore, the economic toll of crashes in LMICs is concerning because nearly one half of all health care expenditures in LMICs is used to treat injuries related to motor vehicle crashes (Zakeri & Nosratnejad, [28]). This epidemic deserves urgent attention (Lin, [10]). Research on the epidemiology of crash problems in LMICs is increasing but these research efforts predominantly report statistics. There is a paucity of qualitative research that could help to explain the statistics. Qualitative exploration has the potential to enhance crash research by describing and explicating the contexts and social processes surrounding crashes, such as the antecedents, the environments in which crashes occur and injuries are produced, and the behaviours of people which make crashes more likely (Roberts, [14]; Rothe, [16]). Qualitative research methods can spark and mobilize the ideas and efforts of affected community members, thereby optimizing crash prevention interventions. Additionally, incorporating local citizens\u27 perspectives on the nature, causes and potential solutions of traffic problems in their locale increases the likelihood that proposed solutions will be effective, wanted and beneficial (Roberts, Smith, & Bryce, [15]). This article will review the literature to assess the extent to which qualitative methods have been implemented to research road traffic crashes in LMICs and to inform future methodological decision-making

Integration of GaAs-based VCSEL array on SiN platform with HCG reflectors for WDM applications

We present a GaAs-based VCSEL structure, BCB bonded to a Si3N4 waveguide circuit, where one DBR is substituted by a free-standing Si3N4 high-contrast-grating (HCG) reflector realized in the Si3N4 waveguide layer. This design enables solutions for on-chip spectroscopic sensing, and the dense integration of 850-nm WDM data communication transmitters where individual channel wavelengths are set by varying the HCG parameters. RCWA shows that a 300nm-thick Si3N4 HCG with 800nm period and 40% duty cycle reflects strongly (>99%) over a 75nm wavelength range around 850nm. A design with a standing-optical-field minimum at the III-V/airgap interface maximizes the HCG's influence on the VCSEL wavelength, allowing for a 15-nm-wide wavelength setting range with low threshold gain (<1000 cm(-1))

Understanding Etiologies of Road Traffiffic Crashes, Injuries, and Death for Patients at National Hospital Abuja: A Qualitative Content Analysis Using Haddon\u27s Matrix

Road traffic crashes and sequelae are reaching pandemic proportions globally and have currently achieved disproportionately high levels in Nigeria. Quantitative studies are accumulating in the peer-reviewed literature, but there is a paucity of qualitative research in Nigeria. Data for this study of structural and behavioral factors of road traffic crashes and injuries in Federal Capital Territory were collected in semi-structured interviews with crash survivors at National Hospital Abuja. Interviews were analyzed via qualitative content analysis, revealing crash location and participant beliefs about crash etiologies. Units of analysis were developed from participant statements and were structured within four a priori etiologic categories using Haddon\u27s (1980) matrix: human-, vehicle-, physical environment-, and socioeconomic environment-related. Subcategories were generated. Human-related subcategories included reckless behavior and drivers, limited technical knowledge and skill. Vehicle-related subcategories included vehicular disrepair and lack of safety equipment. Physical environment-related subcategories included road disrepair, infrastructural inadequacy, and weather. Socioeconomic environment-related subcategories included government, prehospital care, money, and prayer. Subcategories were organized temporally by pre-event, event, and post-event phases, with most units of analysis allocated in the preevent phase. These qualitative results can be utilized to guide future research along community-aligned priorities, and to structure community-engaged preventative and interventional efforts

Understanding Etiologies of Road Traffic Crashes, Injuries, and Death for Patients at National Hospital Abuja: A Qualitative Content Analysis Using Haddon’s Matrix

Road traffic crashes and sequelae are reaching pandemic proportions globally and have currently achieved disproportionately high levels in Nigeria. Quantitative studies are accumulating in the peer-reviewed literature, but there is a paucity of qualitative research in Nigeria. Data for this study of structural and behavioral factors of road traffic crashes and injuries in Federal Capital Territory were collected in semi-structured interviews with crash survivors at National Hospital Abuja. Interviews were analyzed via qualitative content analysis, revealing crash location and participant beliefs about crash etiologies. Units of analysis were developed from participant statements and were structured within four a priori etiologic categories using Haddon’s (1980) matrix: human-, vehicle-, physical environment-, and socioeconomic environment-related. Subcategories were generated. Human-related subcategories included reckless behavior and drivers, limited technical knowledge and skill. Vehicle-related subcategories included vehicular disrepair and lack of safety equipment. Physical environment-related subcategories included road disrepair, infrastructural inadequacy, and weather. Socioeconomic environment-related subcategories included government, prehospital care, money, and prayer. Subcategories were organized temporally by pre-event, event, and post-event phases, with most units of analysis allocated in the pre-event phase. These qualitative results can be utilized to guide future research along community-aligned priorities, and to structure community-engaged preventative and interventional efforts

The Use of Health Service Areas for Measuring Provider Availability

Measurement of the availability of health care providers in a geographic area is a useful component in assessing access to health care. One of the problems associated with the county provider-to-population ratio as a measure of availability is that patients frequently travel outside their counties of residence for health care, especially those residing in non-metropolitan counties. Thus, in measuring the number of providers per capita, it is important that the geographic unit of analysis be a health service area. We have defined health care service areas for the coterminous United States, based on 1988 Medicare data on travel patterns between counties for routine hospital care. We used hierarchical cluster analysis to group counties into 802 service areas. More than one half of the service areas include only non-metropolitan counties. The service areas vary substantially in the availability of health care resources as measured by physicians and hospital beds per 100,000 population. For almost all of the service areas, the majority of hospital stays by area residents occur within the service area. In contrast, for 39 percent of counties, the majority of hospital stays by county residents occur outside the county. Thus, the service areas are a more appropriate georgraphic unit than the county for measuring the availability of health care