Chemistry of rhenium

Imperial Users onl

Applying of mechanical failure criteria of brittle material to the design of high temperature heat exchanger

Previous studies have suggested using a ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermochemical cycle. The decomposer was manufactured using fused ceramic layers that allow the creation of channels with dimensions below one millimeter. The heat exchanger is expected to operate in the range of 950°C. Thermal stresses are however induced in the heat exchanger ceramic components. In this study, proper failure criteria are selected to evaluate the safety level of the ceramic components. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical reactions in the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. The temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis. Results of this research can be used as a basis for the investigation of the optimal design of the decomposer that can provide a maximum chemical decomposition performance while maintaining stresses within design limits. The stress results are used to calculate the probability of failure based on Weibull failure criteria and the factor of safety based on Coulomb-Mohr failure criteria; A parametric study of a straight channel sulfuric acid decomposer is made. Several different geometries of the decomposer channels which include straightforward, ribbed, hexagonal, and diamond forms are investigated. The influence of the mass flow rate and of the area of chemical reaction on the chemical decomposition performance for the decomposer are also explored. The analysis includes the steady state operating conditions and the transient operating conditions. The research considers stresses that are induced during transient scenarios, in particular, the cases of startup and shutdown. The analysis includes also the Bayonet design of heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product - sulfur dioxide. The product can be used within the sulfur iodine thermochemical cycle portion of the hydrogen production process. A two-dimensional axisymmetric geometry of the bayonet heat exchanger is created using GAMBIT software. A computational model is developed to investigate fluid flow, heat transfer and chemical reactions in the porous medium of the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. Temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis

Constructing and Norming Arabic Screening Tool of Auditory Processing Disorders: Evaluation in a Group of Children at Risk for Learning Disability

The purposes of this study were to develop and provide the normative data of Arabic screening tool for screening the children with auditory processing disorders: an Arabic version of Adaptive Auditory Speech Test (AAST) in quiet for screening the peripheral hearing in dB SPL units; an Arabic AAST in binaural noise for screening the temporal interaction deficit: listening speech in binaural noise in dB SNR units, then teetaatoo test with a five subtests for screening the Modern Standard Arabic language phonemes identification ability. Participants included 338 children aged from 5 to 7 years old (138 males, 200 females; mean age = 6.08 years with standard deviation = 0.8) from a regular nursery school which called Baroot Summer Club in Beni-Suef in Egypt were recruited to participate in the study. According to the calculated Norms of AAST in quiet and through a meeting with the teachers of children in the nursery school, 129 children were sift out with no hearing loss, negative histories of neurological disorders, head trauma or surgery, dizziness, and attention deficit disorder/attention deficit hyperactivity disorder. 129 children were screened for listening in binaural noise using the Arabic AAST in binaural noise, then the left 94 children, because 35 children couldn`t complete the testing, was screened for phonemes identification ability using teetaatoo test(the five sub tests). For the AAST in quiet, 21 to 33 dB SPL is the normal range of the hearing peripheral loss, especially, for the AAST in binaural noise, there are three different norms; -9 to -13 dB SNR is the normal range of children aged 5 years old, -10 to -13 dB SNR is the normal range of children aged 6 years old, and -10 to -14 dB SNR is the normal range of children aged 7 years old. Finally, for the five subtests (teetaatoo): > 85% (correct answers) is the normal percentage of the Cons-A, >62& (correct answers) is the normal percentage of the Cons-B1, >76% is the normal percentage of the Cons-B2, >63% (correct answers) is the normal percentage of the Cons-B3, and 84% (correct answers) is the normal percentage of the Vow-A. Further, according to the previous norms, 23 children represent 17,8% from the whole sample (N=129) with a normal speech recognition threshold have scored abnormally on the speech listening in bin-noise (AAST in bin-noise) or on at least one subtest from teetaatoo subtests and were considered at risk for learning disability because of their scores on a SIFTER

Medical education in Sudan: A recommendation to adopt competency-based medical education curricula for improving practices (SudaniMEDs)

Sudan is a leading country in health professions education (HPE), a sector which started 100 years ago. The history of HPE in Sudan dates back to 1918 with the training of medical assistants, with a school for modern midwifery opening in 1921 (1). The first college of medicine in Sudan—Kitchener School of Medicine (KSM) —was established in 1924, and is currently part of the University of Khartoum (2). About half a century later, two more medical schools—Juba University School in 1977 and Gezira University School in 1978—were established. In the 1990s, there was an enormous expansion in higher education, particularly in colleges of medicine, with more than thirty being inaugurated (3). Currently, Sudan has more than sixty colleges of medicine