Theory of near infra-red germanium lasers

Due to major advances in silicon photonics technology and the importance of having a silicon-compatible laser operating in the 1.3 - 1.55 micron communications wavelength window. There is currently an intense interest in the optical properties of germanium, which has a direct band gap transition in this wavelength range. The Ge band structure can be engineered using biaxial or uniaxial strain in order to achieve optical gain. Recently, both optically pumped and electrical injection pumped lasing have been reported in Ge-on-Si devices. This work aims to perform gain modeling in a germanium laser grown on a silicon substrate which operates in the near infrared wavelength communications band. A description of the background theory of the variation of the relevant electronic band structure properties of Ge with the applied strain is given. Shifts of the conduction and valence band edges with strain (biaxial and uniaxial) applied to Ge grown on substrates of different orientations has been investigated using the linear deformation potential and k.p methods. In order to make Ge behave as a direct band gap material, and to have a good electron injection efficiency, an investigation of the combination of the applied strain and doping density on direct band gap and injected carrier efficiency were carried out at 0 K, for both bulk Ge and Ge quantum wells. At finite temperatures, the k.p method and effective mass approximation were used to calculate the energy bands for [001] bulk Ge, the quasi-Fermi levels for given values of carrier densities, and then the interband gain and IVBA were calculated for biaxially tensile strained [001] bulk Ge. Furthermore, a detailed description of the free carrier absorption coefficient calculation, accounting for both intervalley and intravalley scattering in strained [001] Ge is given. The effect of unequal electron and hole densities, which are required to achieve the interband gain and reduce the absorption coefficient due to IVBA and FCA in order to obtain the net gain, has been investigated for strained bulk n+ Ge at room and typical device temperatures

Efficacy of Denture Cleansers on Microbial Adherence and Surface Topography of Conventional and CAD/CAM-Processed Denture Base Resins

This study assessed the efficacy of five denture cleansers on the microbial adherence and surface topography of conventional and CAD/CAM denture base resins. Acrylic resin discs were fabricated using conventional, milling, and 3D printing methods (N = 180). The discs were contaminated with dual species of Candida albicans and Streptococcus mutans biofilm for 72 h and then disinfected with either of the denture cleansers (Fittydent cleansing tablets, 2% Chlorhexidine gluconate, 0.2% Chlorhexidine gluconate, 0.5% sodium hypochlorite, and 1% sodium hypochlorite (n = 10). Distilled water served as the control group. The colony-forming units of the microorganisms were calculated, followed by post-treatment surface roughness. Data were statistically analyzed using one-way ANOVA, paired t-test, and post hoc Tukey HSD test (α = 0.05). Among the denture cleansers, 2% Chlorhexidine gluconate, 0.5% sodium hypochlorite, and 1% sodium hypochlorite had the best cleansing effect on the resin discs and demonstrated zero growth of colonies for both the species. Comparing the material groups, the 3D-processed discs showed higher colony-forming units followed by the conventional and CAD/CAM milled group. The highest surface roughness was demonstrated by the 3D-printed discs (0.690 ± 0.08 μm), followed by the conventional (0.493 ± 0.11 μm) and the milled groups (0.301 ± 0.08 μm). The tested chemical denture cleansers affected the Candida albicans and Streptococcus mutans adhesion compared to control discs immersed in distilled water. The clinician may recommend to their patient to use 2% chlorhexidine gluconate for the disinfection of CAD/CAM PMMA denture base materials

The burden perceived by informal caregivers of the elderly in Saudi Arabia

OBJECTIVES: The objective of this study was to discover the characteristics of informal caregivers of elderly patients; to determine the socioeconomic, psychological, and physical consequences facing informal caregivers; and to measure their burdens and needs. MATERIALS AND METHODS: This study was a cross-sectional survey of informal caregivers of elderly patients. Participants were recruited from different hospitals and primary care clinics in Riyadh, Saudi Arabia. For an intended sample size of 384 caregivers, a multistage sampling was used. A self-administered questionnaire was used to collect data. Data analysis included student's t-test and ANOVA to test for statistical significance. RESULTS: The study included 315 caregivers of elderly patients. Over half of the elderly patients were female (55.9%) and over 70 years old (65.7%); about 31% had chronic diseases or disabilities, which represented the majority of health problems reported by the elderly population. Most of the caregivers were family members (87.9%), young (43.8%), female (52.7%), unemployed (54.6%), and unmarried (58.1%). Most caregivers suffered from musculoskeletal problems (78.1%). The mean Zarit Burden Interview score was 31.3, which indicated a moderate burden. More than half of caregivers requested blood pressure (55.6%) and blood sugar measuring devices (53%). Three quarters (74.9%) of the caregivers wanted educational training to cope with emergencies. Most caregivers expressed a need for frequent healthcare for themselves (58.4%) and a home health visit service (72.9%) to support them in the care of their elderly. CONCLUSIONS AND RECOMMENDATIONS: Mobilization of resources in locations where these carers of the elderly live are greatly needed. In addition, health authorities should provide devices and essential training to manage the common problems and emergencies that informal caregivers have to deal with. Moreover, caregivers need follow-up supervision by a home visit team. Further studies are required to guide the implementation of the above advice