Thermodynamics of dimethylarsinic acid and arsenate interactions with hydrated iron-(oxyhydr)oxide clusters: DFT calculations

Dimethylarsinic Acid (DMA) belongs to an important class of organoarsenical compounds commonly detected in arsenic speciation studies of environmental samples and pyrolysis products of fossil fuels. Transformation of DMA under certain conditions leads to the formation of other forms of arsenic, which could be more toxic than DMA to biota, and more efficient in deactivating catalysts used in petrochemical refining. Published surface sensitive X-ray and infrared spectroscopic work suggested that DMA simultaneously forms inner- and outer-sphere complexes with iron-(oxyhydr)oxides. Computational work on the complexation of arsenicals with various surfaces of environmental and industrial interest provides useful information that aids in the interpretation of experimental spectroscopic data as well as predictions of thermodynamic favorability of surface interactions. We report herein Gibbs free energies of adsorption, ΔG(ads), for various ligand exchange reactions between hydrated complexes of DMA and Fe-(oxyhydr)oxide clusters calculated using density functional theory (DFT) at the B3LYP/6-311+G(d,p) level. Calculations using arsenate were also performed for comparison. Calculated As-(O,Fe) distances and stretching frequencies of As-O bonds are also reported for comparison with experimental spectroscopic data. Gibbs free energies of desorption, ΔG(des), due to reactions with phosphorus species at pH 7 are reported as well. Our results indicate that the formation of both inner- and outer-sphere DMA complexes is thermodynamically favorable, with the former having a more negative ΔG(ads). Values of ΔG(des) indicate that desorption favorability of DMA complexes increases in this order: bidentate < mondentate < outersphere. The significance of our results for the overall surface complexation mechanism of DMA is discussed.     

Design and Tailoring the Optical and Electronic Characteristics of PS/ZnS/SiBr4 New Structures For Electronics Nanodevices

Silicon - The present work aims to design new structures of polystyrene (PS)/zinc sulfide(ZnS)/ silicon bromide(SiBr4) composites to utilize in various electronics and optical nanodevices have...     

Ultrastructural and three‐dimensional study of post‐LASIK ectasia cornea

INTRODUCTION: Post‐laser in situ keratomileusis (LASIK) corneal ectasia is a serious late postoperative complication. Here, we report the ultrastructural features of the post‐LASIK cornea of two patients. METHODS: Two normal corneas (age 24 and 37 years old) and two post‐LASIK ectaic corneas from two patients (A and B) were studied. The “patient A” (age 27 years) underwent penetrating keratoplasty and “patient B” (age 31 years) underwent deep‐anterior lamellar keratoplasty. The excised corneas were processed for light and electron microscopy. A total of 120 images for three‐dimensional (3D) reconstruction were taken by using the software “Recorder” and using a bottom mounted camera “Quemesa” attached to a JOEL 1400 transmission electron microscope. The 3D images were constructed using “Visual Kai” software. RESULTS: In the post‐LASIK cornea, the hemidesmosomes, the basement membrane, and Bowman”s layer were abnormal. The stromal lamellae were thin and disorganized. The collagen fibrils (CFs) diameter and interfibrillar spacing had decreased. Aggregated microfibrils were present in the Bowman's layer and all parts of the stroma. A large number of microfilaments were present at the detachment end of the flap and residual stroma. The 3D images showed the presence of collagen microfibrils and proteoglycans (PGs) within the CF of the normal and post‐LASIK cornea. The collagen microfibrils and PGs within the CFs had degenerated in the post‐LASIK cornea. CONCLUSION: Collagen microfibrils and PGs within the CFs were degenerated, leading to the degeneration of CFs, followed by the disorganization of lamellae in post‐LASIK cornea. The CFs diameter and interfibrillar spacing decreased. Microsc. Res. Tech. 77:91–98, 2014. © 2013 Wiley Periodicals, Inc.     

Constructal design of a PCM cylindrical heat sink with three-branched,two-stages dendritic tubes

Amputees who use prosthetic limbs suffer from the problem of high contact temperature between the socket of the prosthetic limb and the amputated part and lack of evaporation of sweat. These conditions lead to discomfort and failure to perform functions properly. In addition, these conditions help generate ulcers and accumulate harmful bacteria in this area. This paper presents a heatsink design to extract heat from the contact area. A cylindrical heat sink is designed for phase-changing materials with three branched tubes in two stages. The current heat sink is used to cool the contact area between the amputated part and the socket in the lower prostheses. Three distributions of pipe branches are proposed. The distribution and pipe lengths were obtained using a constructal design method. In the constructal design, the lengths of the branched tubes were the degrees of freedom, the objective function was the minimization of the inlet temperature to the heat sink, and the constraint was the volume of the cylindrical heat sink. The metabolic heat transfer during exercise was estimated and its value was used to calculate the size of the cylindrical heatsink and the selection of the phase change material by testing three of them: water, tridecane, and dodecane. It was found that water gives the highest latent heat of melting and the lowest volume in addition to its availability. On the other hand, two cooling fluids were tested: water and air. It was found that water as a cooling fluid gave the lowest flow and the largest heat capacity. Constructal theory was used to design a cylindrical heat sink using branched tubes for the coolant in two steps: the first with three branches, and the second with nine branches. The degree of freedom for constructal theory was the length of the branches through the choice of their end locations. It was found that the branches of the highest length led to a reduction in temperature from 40°C to 15.48°C compared with the single tube, which reduced the temperature to 23.87°C. All tests recorded a pressure drop within the acceptable range of 3.1–5.43 Pa for the branches examined. The research demonstrated that using constructal theory achieved the best thermal dissipation within a restricted volume.     

Ontology-based system for supporting manufacturing sustainability

Sustainability is one of the biggest challenges of this century either for the environment or economical growth. The required cultural shift needs challenging action that will involve deeply software and hardware aspect of manufacturing processes. In this paper, the software part of the matter is addressed by proposing a product centric ontology, in which concepts of product, processes and resources are associated to functions and sustainable manufacturing knowledge. The aim is to design a knowledge-based system that, simulating a sustainable manufacturing expert, is able to automatically identify change opportunities and to propose alternatives on the basis of the existing production scenario.     

The structure of spatial receptive fields of neurons in primary auditory cortex of the cat

Transient broad-band stimuli that mimic in their spectrum and time waveform sounds arriving from a speaker in free space were delivered to the tympanic membranes of barbiturized cats via sealed and calibrated earphones. The full array of such signals constitutes a virtual acoustic space (VAS). The extra-cellular response to a single stimulus at each VAS direction, consisting of one or a few precisely time-locked spikes, was recorded from neurons in primary auditory cortex. Effective sound directions form a virtual space receptive field (VSRF). Near threshold, most VSRFs were confined to one quadrant of acoustic space and were located on or near the acoustic axis. Generally, VSRFs expanded monotonically with increases in stimulus intensity, with some occupying essentially all of the acoustic space. The VSRF was not homogeneous with respect to spike timing or firing strength. Typically, onset latency varied by as much as 4-5 msec across the VSRF. A substantial proportion of recorded cells exhibited a gradient of first-spike latency within the VSRF. Shortest latencies occupied a core of the VSRF, on or near the acoustic axis, with longer latency being represented progressively at directions more distant from the core. Remaining cells had VSRFs that exhibited no such gradient. The distribution of firing probability was mapped in those experiments in which multiple trials were carried out at each direction. For some cells there was a positive correlation between latency and firing probability.     

The development of a community child and family mental health service

The Community Child and Family Service is a primary care and community-based child mental health service working in a socio-economically disadvantaged area of inner London. This paper outlines the strategic framework and value base from which the service has developed. The clinical projects set up by the service in general practice, community and education settings are described, as are the training and supervision programmes that have been undertaken. The framework for evaluating the clinical and economic outcomes of the projects is outlined. There has been a positive response from purchasers, providers and clients to the introduction of this Service. The relationship between community- and hospital-based child mental health services is discussed, as is the future direction of the Service.     

Tuning the Spectroscopic and Electronic Characteristics of ZnS/SiC Nanostructures Doped Organic Material for Optical and Nanoelectronics Fields

Silicon - The current work aims to investigate of designing the polystyrene(PS)/zinc sulfide(ZnS)/silicon carbide(SiC) new nanostructures as a potential materials for optical and nanoelectronics...     

A Survey of Adaptive Optimization in Virtual Machines

Virtual machines face significant performance challenges beyond those confronted by traditional static optimizers. First, portable program representations and dynamic language features, such as dynamic class loading, force the deferral of most optimizations until runtime, inducing runtime optimization overhead. Second, modular program representations preclude many forms of whole-program interprocedural optimization. Third, virtual machines incur additional costs for runtime services such as security guarantees and automatic memory management. To address these challenges, vendors have invested considerable resources into adaptive optimization systems in production virtual machines. Today, mainstream virtual machine implementations include substantial infrastructure for online monitoring and profiling, runtime compilation, and feedback-directed optimization. As a result, adaptive optimization has begun to mature as a widespread production-level technology. This paper surveys the evolution and current state of adaptive optimization technology in virtual machines.