A Comparison of Top Distributed Bragg Reflector for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers Based on III–V Compound

In this work, the design of GaAs/AlGaAs distributed Bragg reflector (DBR) has been implemented for 1300 nm vertical cavity semiconductor optical amplifiers (VCSOAs) for optical fiber communication applications. The top DBR period and Al concentration are varied, the peak reflectivity of the DBR is increasing from 50% to 97.5% for 13 periods with increasing Al concentration, whereas the reflectivity bandwidth is increased to almost 190 nm. The relation between wavelength and incidence angle variation on DBR reflectivity is increasing with the incident angle (0°, 20°, 30°, and 50°), the resonant wavelength and bandwidth of the measured reflectance spectra shifts to shorter wavelength and wider bandwidth, respectively. In addition, a comparison between the linear, the graded, and the parabolic DBRs has been achieved with transfer matrix method using MATLAB software to show the influence of layer in DBRs and its effect on lasing wavelength. It is shown that using grading DBR mirror is much more beneficial compared to abrupt DBR, whereas it has lower reflectivity of almost 10% due to VCSOAs device which needs less number of top layers until prevent reaching lasing threshold

Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

From tip to tpa

We present the case of a 50 year old lady who presented with sudden onset altered sensorium, anarthria, right hemianopia, ophthalmoplegia, quadriparesis and abnormal posturing of upper limbs for 4 hours. The NIHSS score was 31. The CT brain showed early ischemic changes in left posterior cerebral artery territory. The CT cerebral angiogram showed occlusion of the tip of basilar artery. Intravenous thrombolysis with rtPA resulted in remarkable recovery and NIHSS improved to 3 within 6 hours. In view of expected severe disability associated with tip of basilar artery syndrome, intravenous thrombolysis can be rewarding even in patients with high NIHSS

The Development of a Knowledge-Based Wax Deposition, Three Yield Stresses Model and Failure Mechanisms for Re-starting Petroleum Field Pipelines. Building on Chang and Boger’s Yield Stresses Model, Bidmus and Mehrotra’s Wax Deposition and Lee et al.’s Adhesive-Cohesive Failure Concepts to better Underpin Restart Operation of Waxy Crude Oil Pipelines

Twenty years ago, Chang et al. (1998) introduced the three-yield stresses concept (dynamic, static and elastic limits) to describe yielding of waxy crude oils cooled below the wax appearance temperature (WAT). At the time, the limits in rheological instruments were such that they never actually measured the elastic-limit, a key fundamental property. Using modern instruments, this research succeeds in recording for the first time the entire yielding process down to stresses of 10-7 Pa and shear rate of 10-6 min-1 as a function of temperature, cooling rate and stress loading rate using two waxy oils of different origins and wax content. A four-yield stress model is established using derivative data (dynamic fluidity and failure acceleration). In addition, calorimetry (DSC) and microscopy (CPM) helped extract WAT, the gel and pour points and link gel crystal structure and its yielding and breakage to rheological properties. The yielding stresses measured rheologically were tested in laboratory pipelines at two diameter scales, 6.5mm and 13.5mm to compare stresses in uniform and non-uniform cooling. It is demonstrated that rheological instruments can only predict gel breaking pressure when the cooling rate is low, i.e. yielding at the pipe wall. A complementary heat transfer study was performed on a section of pipe statically cooled, both experimentally and theoretically to predict the gel front-liquid oil interface that develops in industrial pipeline where gel breaking occurs. This key information together with rheological data provide the means to predict accurately restart pressures of shut gelled pipelines that have eluded previous research.Ministry of Higher Education of the Libyan Governmen

Role of Laser Produced Silver Nanoparticles in Reversing Antibiotic Resistance in Some MultidrugResistant Pathogenic Bacteria

Silver nanoparticles (Ag NPs) were produced through nanosecond laser in deionized water. These nanoparticles were characterized by UV–VIS spectrometer and transmission electron microscopy. VITEK®2 compact system was used to identify Escherichia coli (ESBL strain) and Staphylococcus aureus (MRSA strain) as multidrug-resistance (MDR) bacteria. The antibacterial activity of Ag NPs, ampicillin (AMP), and their combinations was tested against both bacterial isolates through standard microbiological culturing techniques. Our data show that both of E. coli and S. aureus were highly resistant to AMP. Ag NPs alone reduced growth in both bacterial isolates considerably. Growth declined drastically in both bacteria when AMP was used in combination with Ag NPs. The minimal inhibitory concentration of combined agents for E. coli was 20 µg/ml Ag NPs + 1 mg AMP/ml and for S. aureus was 10 µg/ml Ag NPs + 1 mg AMP/ml. The results show that the Ag NPs have great potentials in enhancing the antimicrobial activities of drugs that used to be ineffective against MDR bacteria. Administering combinations of antibiotic(s) with AgNPs may help in treating patients suffering from infections caused by MDR bacteria. Further in vivo and in vitro investigations are required to evaluate the side effects of these combinations