Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles

The band offsets between crystalline and hydrogenated amorphous silicon (a-Si:H) are key parameters governing the charge transport in modern silicon hetrojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics (MD) runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.30 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015)]

Band Offsets at the Interface Between Crystalline and Amorphous Silicon from First Principles

The band offsets between crystalline and hydrogenated amorphous silicon (a−Si∶H) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015)]

Prevalence of Cryptosporidium spp. infection in renal transplant and hemodialysis patients

Transplanted and hemodialysis patients are frequently affected by parasitic diseases such as cryptosporidiosis. Cryptosporidium is a parasite causing self-limited diarrhea and enteritis in healthy individuals. The presence of Cryptosporidium infection was studied in three groups including 87 renal transplant patients, 103 hemodialysis patients, and 60 healthy individuals as the control group. Two stool specimens were obtained from each case. The specimens were concentrated by the formalin-ether method and two smears were prepared from each. The smears were stained by modified acid-fast method and were observed under a light microscope. Ten (11.5) renal transplant and 4 (3.88) hemodialysis patients were positive for Cryptosporidium infection. No positive results were obtained in the control group. The results showed a statistically significant difference between renal transplant and control groups (P=0.02), but the difference between hemodialysis and control groups was not significant (P=0.2). The results also showed that the rate of Cryptosporidium infection in renal transplant patients was much higher than hemodialysis patients. The susceptibility of renal transplant patients to Cryptosporidium infection is much more than other studied groups and this could be due to immunosuppressive therapy in these patients

A novel, eco-friendly and green synthesis of PPAC-ZnO and PPAC-nZVI nanocomposite using pomegranate peel: Cephalexin adsorption experiments, mechanisms, isotherms and kinetics

In the present work, powdered activated carbon coated by nanoparticles ZnO and nZVI was derived from pomegranate peel extracts and finally applied for removal of cephalexin (CEX (from aqueous solutions. This experimental research was conducted discontinuously. The effects of pH of solution, reaction time, PPAC-nZVI and PPAC-ZnO composites dose, and initial concentration of cephalexin and composite recovery on process efficiency were investigated. The removal efficiency in optimal conditions for cephalexin with PPAC-nZVI and PPAC-ZnO (CEX = 50 mg L�1, composite dose = 1.25 g L�1, reaction time = 45 min and pH = 5) was obtained 96.06 and 94.17, respectively. The results of the study of isotherm and absorption kinetics for both composites showed that the absorption process follows Langmuir isotherm and pseudo second-order kinetics. The present study showed that the composites could be used as an effective and bio-friendly absorbent to remove cephalexin from aqueous solutions. © 2020 The Society of Powder Technology Japa

Tool Texturing for Deep Drawing Applications

The application of surface texturing on sheet metal is a widely used approach to improve lubrication and control friction in deep drawing applications. However, it has been shown that current texturing processes are not robust to produce uniform textures on the sheet due to rapid and severe wear on texture-rolls. Furthermore, in multi-stage forming processes, deterioration of the sheet texture even at the first stage of forming makes texturing of the sheet metal surface ineffective. Tool surface texturing is a new method to control friction and tool wear in metal forming industry. In the current study, a multi-scale friction model is adopted to investigate the effect of tool texturing on the evolution of friction during sheet metal forming operations. The multi-scale friction model accounts for surface topography changes due to deformation of asperities and ploughing of tool asperities on the sheet metal surface, mixed lubrication regime and furthermore the tool micro-texture effects on lubricant distribution at tool-sheet metal interface. The model is validated with respect to strip-draw experiments using different tool textures. The model is later applied to the simulation of a U-bend forming process. The results show that using textured tools, it is possible to reduce friction and punch force in sheet metal forming processes. The model can be used to tailor and optimize textures on stamping tools for complex parts

Investigation of Natural Effective Gamma Dose Rates case study: Ardabil Province in Iran

Gamma rays pose enough energy to form charged particles and adversely affect human health. Since, the external exposure of human beings to natural environmental gamma radiation normally exceeds that from all man-made sources combined, natural background gamma dose rates and corresponding annual effective doses were determined for selected cities of Ardabil province from 2009 to 2010. Outdoor gamma dose rates were measured using an Ion Chamber Survey Meter in 105 locations in selected districts. Average absorbed dose for Ardabil, Sar-Ein, Germy, Neer, Shourabil Recreational Lake, and Kosar were determined as 265, 219, 344, 233, 352, and 358 nSvh-1, respectively. Although dose rates recorded for Germi and Kosar are comparable with some areas with high natural radiation background, however, the dose rates in other districts are well below the levels reported for such locations. Average annual effective dose due to indoor and outdoor gamma radiation for Ardabil province was estimated to be 1.73 (1.35-2.39) mSv, which is on average 2 times higher than the world population weighted average

Prevalence of Intestinal Parasitic Infections among Mentally Disabled Children and Adults of Urmia, Iran

Background: The prevalence of intestinal parasites infection in institutions for mental retarda­tion of Ur­mia City, West Azerbaijan Province, Iran was investigated.Methods: This descriptive - cross sectional study was carried out in of Urmia city in 2007-2008. Fecal samples of 225 less than 29 year old mentally disabled individu­als were examined using direct smear, formalin - ether concen­tration. Beside their scotch tape samples were observed for Enterobius eggs. Statisti­cal evaluation was per­formed by SPSS 10.Results: Of 225 mentally retarded persons, 118(52.4%) and 107(47.6%) were female and male. The over­all prevalence of infection was 20.4% and that of male, and female were 20.5% and 20.3%, respectively. 17.3% of examined individuals had protozoa infection and 3.1% showed Entero­bius vermicularis eggs. The infection rates of detected intestinal protozoa were Enta­moeba coli 9.7%, Giardia lamblia 6.2%, Io­doamoeba butschlii 5.7%, Blastocystis hominis 4%, and Entamoeba histolytica/dispar 0.4%. Forty per­cent of 1-5 year, 22.8% of 6-14 year, 22.2% of 15-18 year, and 16.8% of more than 18-year age groups, had positive results in their tests. Accord­ing to IQ test results, 23.8% of less than 25 score group, 19.6% of 25-50, 17.2% of 50-75, and 40% of 75-90 groups were infected.Conclusion: More efforts for increasing sanitation level and prompt diagnosis and treat­ment of infected persons in these institutions are necessary