Ab-initio study of the bandgap engineering of Al(1-x)Ga(x)N for optoelectronic applications

A theoretical study of Al(1-x)Ga(x)N, based on full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap, optical properties and non-linear behavior of the compound with the variation of Ga concentration. It is found that the bandgap decreases with the increase of Ga in Al(1-x)Ga(x)N. A maximum value of 5.5 eV is determined for the bandgap of pure AlN which reaches to minimum value of 3.0 eV when Al is completely replaced by Ga. The static index of refraction and dielectric constant decreases with the increase in bandgap of the material, assigning a high index of refraction to pure GaN when compared to pure AlN. The refractive index drops below 1 for photon energies larger than 14 eV results group velocity of the incident radiation higher than the vacuum velocity of light. This astonishing result shows that at higher energies the optical properties of the material shifts from linear to non-linear. Furthermore, frequency dependent reflectivity and absorption coefficients show that peak value of the absorption coefficient and reflectivity shifts towards lower energy in the UV spectrum with the increase in Ga concentration. This comprehensive theoretical study of the optoelectronic properties of the alloys is presented for the first time which predicts that the material can be effectively used in the optical devices working in the visible and UV spectrum.Comment: 18 pages, 7 figure

Corotation Resonance and Diskoseismology Modes of Black Hole Accretion Disks

We demonstrate that the corotation resonance affects only some non-axisymmetric g-mode oscillations of thin accretion disks, since it is located within their capture zones. Using a more general (weaker radial WKB approximation) formulation of the governing equations, such g-modes, treated as perfect fluid perturbations, are shown to formally diverge at the position of the corotation resonance. A small amount of viscosity adds a small imaginary part to the eigenfrequency which has been shown to induce a secular instability (mode growth) if it acts hydrodynamically. The g-mode corotation resonance divergence disappears, but the mode magnitude can remain largest at the place of the corotation resonance. For the known g-modes with moderate values of the radial mode number and axial mode number (and any vertical mode number), the corotation resonance lies well outside their trapping region (and inside the innermost stable circular orbit), so the observationally relevant modes are unaffected by the resonance. The axisymmetric g-mode has been seen by Reynolds & Miller in a recent inviscid hydrodynamic accretion disk global numerical simulation. We also point out that the g-mode eigenfrequencies are approximately proportional to m for axial mode numbers |m|>0.Comment: 16 pages, no figures. Submitted to The Astrophysical Journa

Effect Change of Speed on Delay and Throughput for Handover Types in Mobile WI-Max Network

Volume 2 Issue 9 (September 2014

Analysis of Chromium (Cr) and Nickel (Ni) in the West Coast of Karimun Island Riau Archipelagos Province

This research was conducted in March 2015 by collecting samples of water and sediments from the west coast of Karimun island. The purpose of this study was to determine the concentration of heavy metals chromium (Cr) and nickel (Ni) in seawater and sediments. Sample collection was done by purposive sampling method in which the three selected station. The highest Cr concentration in sea water was found in Station 2 (0.148 mg/L) and Ni in Station 3 (0.071 mg/L) whilst highest Cr and Ni concentrations in Station 2 (4.643 and 2.289 μg/g). Compared tothe Standard Quality Guideline for Sediment, the concentrations of Cr and Ni were still below the value of ERL and still very far below the value of ERM. In contrast with Ni, which has negative correlation with its concentration in sediment, the Cr concentration in sea water was positively correlated with its concentration in sediment

Geochronological studies in Santa Barbara Basin: <SUP>55</SUP>Fe as a unique tracer for particulate settling

Sediments accumulate in the Santa Barbara Basin relatively rapidly: about 3-4 mm yr-1 based on the analysis of varves. These deposits are ideal for studying the applicability of nuclear geochronological techniques in a natural situation. Studies of the depth distribution of several radionuclides, manmade 55Fe and naturally occurring 210Pb and Th isotopes, in recent Santa Barbara sediment layers permit an evaluation of the geochemical behavior of Fe, Pb, and Th in coastal waters and have established the usefulness of 55Fe and 210Pb for dating coastial or near coastal sediments deposited during the last decade and half-century respectively

Improving SIEM for critical SCADA water infrastructures using machine learning

Network Control Systems (NAC) have been used in many industrial processes. They aim to reduce the human factor burden and efficiently handle the complex process and communication of those systems. Supervisory control and data acquisition (SCADA) systems are used in industrial, infrastructure and facility processes (e.g. manufacturing, fabrication, oil and water pipelines, building ventilation, etc.) Like other Internet of Things (IoT) implementations, SCADA systems are vulnerable to cyber-attacks, therefore, a robust anomaly detection is a major requirement. However, having an accurate anomaly detection system is not an easy task, due to the difficulty to differentiate between cyber-attacks and system internal failures (e.g. hardware failures). In this paper, we present a model that detects anomaly events in a water system controlled by SCADA. Six Machine Learning techniques have been used in building and evaluating the model. The model classifies different anomaly events including hardware failures (e.g. sensor failures), sabotage and cyber-attacks (e.g. DoS and Spoofing). Unlike other detection systems, our proposed work helps in accelerating the mitigation process by notifying the operator with additional information when an anomaly occurs. This additional information includes the probability and confidence level of event(s) occurring. The model is trained and tested using a real-world dataset

Patient level costing analysis of paediatric short bowel syndrome care in a specialist tertiary centre

PURPOSE: To undertake a pilot study estimating patient-level costs of care for paediatric short bowel syndrome (SBS) from the healthcare provider perspective. METHODS: A pilot group of patients with anatomical SBS was selected at a single specialist tertiary centre in the United Kingdom. The Patient Level Information and Costing System (PLICS) was used to extract costing data for all hospital-based activities related to SBS, from the implementation of PLICS in 2016 to April 2021. Patient-specific and pooled data were reported descriptively in per patient-year terms. RESULTS: Five patients had full PLICS data available for the 5-year study period and 2 patients had 4 years of data. The median cost for hospital care of SBS was £52,834 per patient-year (range £1804–£331,489). The key cost drivers were inpatient beds, pharmacy, and staffing costs, which made up > 60% of annual costs. In the first 3 years following index admission (n = 2), there was a steady decline in the annual cost of care to a level comparable with patients with established SBS. CONCLUSION: Patient-level cost of care analysis for SBS is feasible using PLICS. Hospital-related costs vary widely between and within individual patients over time. Key drivers of cost are related to complications of SBS