Nano structures of group 13-15 mixed heptamer clusters: a computational study

The structural and thermodynamic characteristics of lowest-energy structures of group 13-15 mixed heptamers in two distinct series [(HM)(k)(HM')(l)(NH)(7)] (M, M' = B, Al, Ga and k + l = 7) and [(HGa)(7)(YH)(m)(Y'H)(n)] (Y,Y' = N, P, As and m + n = 7) have been systematically investigated using the density functional approach. Our main goal is to get knowledge of the preferential bonding patterns of the first three rows of group 13-15 elements for the construction of mixed heptameric clusters. Structural parameters, thermodynamic properties of oligomerization reaction, band gaps, and dipole moments of the 18 lowest-energy structures of the studied heptamers in each series are compared to their corresponding binary parents, that is, [(HM)(7)(NH)(7)] and [(HGa)(7)(YH)(7)]. The stability of different isomer structures is discussed to reveal the competitiveness of group 13 and 15 bonding. Mixed heptamers are predicted to be thermodynamically more stable compared to a mixture of monomers. However, the favorability for the generation of mixed heptamers strongly depends on the nature of inserted metal and nonmetal pairs of group 13-15. Moreover, it is found that among all studied heptamers the smaller band gaps correspond to arsenic containing species which are close to the semiconducting regime, around 4.62-4.98 eV.     

Properties of thin-film silicon solar cells at very high irradiance

The focussed beam of a low-power helium–neon laser is used to study accelerated light-induced degradation (Staebler–Wronski effect) and high steady-state photocarrier generation rates in amorphous and microcrystalline silicon thin-film solar cells, at up to 13 MW m^? 2 irradiance. Even at these high power densities, COMSOL® simulations indicate that heat diffusion into the substrate, aided by spreading conduction via the Ag back-contact, restricts the temperature rise to less than 14 °C. Short-circuit current may be measured directly, and the I–V characteristic estimated by taking into account shunting by the inactive part of the cell. The improved resistance to degradation of microcrystalline silicon cells is shown to persist to high irradiance. Computer simulations of an amorphous silicon solar cell are presented that are consistent with measured un-degraded and degraded properties, and offer insight into prevailing defect creation processes and carrier recombination mechanisms.     

A Framework for Detecting System Performance Anomalies Using Tracing Data Analysis

Advances in technology and computing power have led to the emergence of complex and large-scale software architectures in recent years. However, they are prone to performance anomalies due to various reasons, including software bugs, hardware failures, and resource contentions. Performance metrics represent the average load on the system and do not help discover the cause of the problem if abnormal behavior occurs during software execution. Consequently, system experts have to examine a massive amount of low-level tracing data to determine the cause of a performance issue. In this work, we propose an anomaly detection framework that reduces troubleshooting time, besides guiding developers to discover performance problems by highlighting anomalous parts in trace data. Our framework works by collecting streams of system calls during the execution of a process using the Linux Trace Toolkit Next Generation(LTTng), sending them to a machine learning module that reveals anomalous subsequences of system calls based on their execution times and frequency. Extensive experiments on real datasets from two different applications (e.g., MySQL and Chrome), for varying scenarios in terms of available labeled data, demonstrate the effectiveness of our approach to distinguish normal sequences from abnormal ones.     

A hybrid method of Pareto,TOPSIS and genetic algorithm to optimize multi-product multi-constraint inventory control systems with random fuzzy replenishments

Multi-periodic inventory control problems are mainly studied employing one of two assumptions. The first is the continuous review, where depending on the inventory level, orders can be placed at any time, and the other is the periodic review, where orders can be placed only at the beginning of each period. In this paper, we relax these assumptions and assume that the time-periods between two replenishments are random fuzzy variables. While in the model of the problem at hand the decision variables are of integer type and there are space and service level constraints, for the shortages we consider a combination of back-order and lost-sales. We show the model of this problem to be an integer-nonlinear-programming type and in order to solve it, a hybrid method of Pareto, TOPSIS and Genetic Algorithm approach is used. At the end, a numerical example is given to demonstrate the applicability of the proposed methodology.     

Experimental investigation on the effect of natural gas premixed ratio on combustion and emissions in an IDI engine

Journal of Thermal Analysis and Calorimetry - Usage of natural gas in an internal combustion engine that has different combustion technologies is considered a possible solution to reduce engine...     

Considerations on shock wave/boundary layer interaction in undular hydraulic jumps in horizontal channels with a very high aspect ratio

It can be seen in the literature that the fundamental factors governing oblique shock wave development, typically in very large channels with straight sidewalls, have not yet been completely understood and remain at the level of indicating its presence and formation. In this study, in addition to an analysis of various properties of hydraulic jump behaviour in very large channels, some aspects of boundary layer development and its detachment from the channel lateral sidewall are also investigated. At the detachment point of the lateral shock waves, it was noted that the displacement thickness experiences a significant increase; this is accompanied by a significantly reduced gradient normal to the channel sidewalls of the flow velocity as well as the occurrence of a strong, sudden adverse pressure gradient. An analysis of the flow velocity distribution and the background turbulence intensity of both the streamwise and spanwise velocity components was also carried out. Furthermore, it is argued that the supersonic flow separation analogy with a supercritical free surface flow can be applied to this case study and that the behaviour of the supercritical flow during separation can be interpreted by the free interaction theory typically used in aerodynamics.     

Color centers in neutron-irradiated Y3Al5O12, CAF2 and LiF single crystals

The thermal annealing behavior of the Y₃Al₅O₁₂, CaF₂ and LiF single crystals bombarded at Algiers with reactor neutrons has been monitored by optical absorption spectroscopy. The irradiation was performed at about 315 K. On heating samples after irradiation, the optical absorption bands decrease and disappear completely at 873 and 523 K in the case of Y₃Al₅O₁₂ and CaF₂, respectively. Activation energies of 1.2±0.02 and 0.9±0.2 eV are estimated for Y₃Al₅O₁₂ and CaF₂, respectively. On the other hand, the LiF crystal shows a complex annealing behavior. Here, the optical absorption spectrum presents different shapes after each annealing temperature. Four steps are distinguished and discussed on heating samples from 300 to 673 K. Above 673 K, the absorption drops by about 50%; it completely disappears at 773 K.     

Modification of cellulose by graft polymerization for use in drug delivery systems

Cellulose-based biodegradable polymers—as microspheres or hydrogels—are suitable for drug delivery systems. In this work, cellulose microfibers were converted to cellulose esters for subsequent graft copolymerization either by free radical or atom transfer radical polymerization (ATRP). For the former, carboxymethyl cellulose (CMC) was prepared and then modified through grafting of poly(hydroxyethyl acrylate) or polyacrylamide. ATRP was achieved by chloroacetylation of cellulose followed by graft copolymerization of hydroxyethyl acrylate or acrylamide monomers. The degree of substitution for CMC and chloroacetylated cellulose (CAC) was determined by the method described in US Pharmacopeia NF24 and by titration method, respectively. CMC, CAC, and the grafted copolymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction, and atomic force microscopy; the latter technique clearly shows the chain growth of the synthetic polymers on the backbone surface. Furthermore, cephalexin antibiotic was loaded on the copolymers, and the resultant in vitro drug release studied in three different media (buffer solutions with pH equal to 3, 6.1, and 8).     

Application of silica vanadic acid [SiO2-VO(OH)2] as a heterogeneous and recyclable catalyst for oxidative aromatization of Hantzsch 1,4-dihydropyridines at room temperature

A simple method for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is described using hydrogen peroxide as green oxidant and silica vanadic acid as catalyst in acetonitrile at room temperature. The catalyst can be easily recovered and reused for 15 reaction cycles without considerable loss of activity.