Solar PV Lighting and Studying after Sunset: Analysis of Micro-benefits in Off-grid Rural Ghana

Solar PV light provides school children living in off-grid rural communities the opportunity to have clean and bright lighting to study after sunset. On the contrary, lighting provided from poor sources can pollute and adversely affect human eyes during reading and writing. Using indicator-based questionnaires in cross-sectional surveys, households with and without solar PV lighting were surveyed in off-grid rural communities in Ghana. The study investigated lighting and children’s studies after sunset. The results indicated that whereas solar PV light of 5-20 watts dc lamps was sufficient for 5-6 children to study together, lighting from kerosene lantern could be sufficient for 1-3 children. All things being equal, the results showed that children who use solar PV light to study upto 2 hours after sunset are likely to improve on their examination results. The extent to which solar PV lighting significantly impacts on studying after sunset was established using some identified indicators. Knowledge of the results provides understanding of the relative constraints in lighting services faced by children in rural communities without access to quality lighting. Such micro-level data will help to enhance policy and planning efforts to increase access to clean and renewable energy-based lighting devices to achieve efficient visual comfort in off-grid rural communities

Mouthguards for contact sports: current state of use

Thesis (M.A.)--Boston UniversityTraumatic dental injury (TDI) is a public health problem that affects millions of individuals each year. Contact sports and sports-related activities such as boxing, basketball, and bicycling are the number one cause for TDI’s. The most common TDI’s resulting from sporting accidents are soft tissue laceration, tooth fracture, luxation and avulsion. Some individuals are more at risk than others in sustaining a TDI due to various predisposing factors. Individuals are at greater risk of dental trauma if they have protruding teeth, insufficient lip closure, and/or teeth that have received restorative dental treatment. Adolescents and teenagers are known to be most affected by TDI’s because they are the subset of the population most involved in contact sports and other physical activities. Mouthguards were developed to prevent the occurrence and severity of these dental injuries. There are three different types of mouthguards currently in use. They are the stock, mouth-formed, and custom-made mouthguards. Stock and mouth-formed mouthguards are the least recommended by dental professionals, yet in combination are worn the most because of their affordability and ease of use. Custom-made mouthguards are the most accepted mouthguards by the dental community because they are the most adapted to the particular individual, and are associated with the lowest number of TDI’s out of the three types of mouthguards. Users of mouthguards are nearly three times less likely to sustain a TDI while participating in a sport, compared to non-users. Unfortunately, many active individuals do not utilize mouthguards. Non-users of mouthguards associate wearing of mouthguards with undesirable effects, such as breathing difficulties and speech impairment. The side-effects of mouthguards can be so prevalent that they can potentially cause impairment in ones playing ability. In hopes of increasing the number of mouthguard users, researchers and manufactures have continually found new ways to eliminate the negative side-effects of mouthguards, while enhancing their protective function. Researchers have found mouthguards made from ethylene vinyl acetate (EVA) to have the lowest report of wearer opposition. EVA materials are soft and durable, but more importantly, can be tailored to satisfy the needs of the individual. Also, certain materials and designs can be incorporated into the EVA material to better the mouthguards protective function. For instance, past experiments have shown the placement of compliant materials, such as Sorbothane, in between two sheets of EVA material will significantly enhance the mouthguards protective capability. However, the joining of multiple materials may result in thicker and less comfortable mouthguards. More recent mouthguard trials have focused on limiting the thickness of mouthguards, while achieving the same level of protection seen in mouthguards made from multiple materials. Researchers have found the insertion of air cells within the EVA material to be useful technique in minimizing the overall thickness of mouthguards, while preserving the mouthguards protective function. In continuing to meet the high demands of athletes and active individuals, researchers and manufactures must develop newer mouthguards by exploring the effectiveness of other materials, as well as finding alternative methods in which mouthguards can be made

Characterization of sintered SiC by using NDE

Capabilities of projection microfocus X-radiography and of ultrasonic velocity and attenuation for characterizing silicon carbide specimens were assessed. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room-temperature, four-point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined. Radiography proved useful in detecting high-density inclusions and isolated voids, but failed in detecting surface and subsurface agglomerates and large grains as fracture origins. Ultrasonic velocity dependency on density was evident. Attenuation dependency on density and mean pore size was clearly demonstrated. Understanding attenuation as a function of toughness was limited by shortcomings in K sub IC determination

Cosmic Reionization On Computers. Properties of the Post-reionization IGM

We present a comparison between several observational tests of the post-reionization IGM and the numerical simulations of reionization completed under the Cosmic Reionization On Computers (CROC) project. The CROC simulations match the gap distribution reasonably well, and also provide a good match for the distribution of peak heights, but there is a notable lack of wide peaks in the simulated spectra and the flux PDFs are poorly matched in the narrow redshift interval 5.5<z<5.7, with the match at other redshifts being significantly better, albeit not exact. Both discrepancies are related: simulations show more opacity than the data.Comment: Accepted by Ap

Flaw imaging and ultrasonic techniques for characterizing sintered silicon carbide

The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined

Is perpendicular magnetic anisotropy essential to all-optical ultrafast spin reversal in ferromagnets?

All-optical spin reversal presents a new opportunity for spin manipulations, free of a magnetic field. Most of all-optical-spin-reversal ferromagnets are found to have a perpendicular magnetic anisotropy (PMA), but it has been unknown whether PMA is necessary for the spin reversal. Here we theoretically investigate magnetic thin films with either PMA or in-plane magnetic anisotropy (IMA). Our results show that the spin reversal in IMA systems is possible, but only with a longer laser pulse and within a narrow laser parameter region. The spin reversal does not show a strong helicity dependence where the left- and right-circularly polarized light lead to the identical results. By contrast, the spin reversal in PMA systems is robust, provided both the spin angular momentum and laser field are strong enough while the magnetic anisotropy itself is not too strong. This explains why experimentally the majority of all-optical spin-reversal samples are found to have strong PMA and why spins in Fe nanoparticles only cant out of plane. It is the laser-induced spin-orbit torque that plays a key role in the spin reversal. Surprisingly, the same spin-orbit torque results in laser-induced spin rectification in spin-mixed configuration, a prediction that can be tested experimentally. Our results clearly point out that PMA is essential to the spin reversal, though there is an opportunity for in-plane spin reversal.Comment: 20 pages, 4 figures and one tabl