The wake structure in a 2D grid installation of the horizontal axis micro wind turbines

In order to develop applications for micro-wind turbines, an experimental analysis of the flow field around integrated micro-wind turbines was performed. The wake flows of a single turbine and 5×5 array unit were measured by using hot-wire and ultrasonic anemometers and particle image velocimetry (PIV). The present array of turbines follows a fundamental lattice layout; however, it has the flexibility to optimize its layout according to the environmental conditions. hot-wire and ultrasonic anemometers and PIV measurements were used for stand-alone turbines and their integrated systems. Comparisons between the mean velocity field and turbulent intensity were described for stand-alone full-scale and 1/10-scale wind turbine models. Thereafter, a typical array of the 1/10-scale model was assumed and its wake flow was investigated in a wind tunnel. The velocity profile and turbulence behind the array were measured and studied at different streamwise locations. The scale effect and model similarities were discussed. The experimental results show that a zone exists with constant and linear wake deficit ratios in the downstream regions.     

Prospective Pharmacological Potential of Resveratrol in Delaying Kidney Aging

Aging is an unavoidable part of life. The more aged we become, the more susceptible we become to various complications and damages to the vital organs, including the kidneys. The existing drugs for kidney diseases are mostly of synthetic origins; thus, natural compounds with minimal side-effects have attracted growing interest from the scientific community and pharmaceutical companies. A literature search was carried out to collect published research information on the effects of resveratrol on kidney aging. Recently, resveratrol has emerged as a potential anti-aging agent. This versatile polyphenol exerts its anti-aging effects by intervening in various pathologies and multi-signaling systems, including sirtuin type 1, AMP-activated protein kinase, and nuclear factor-κB. Researchers are trying to figure out the detailed mechanisms and possible resveratrol-mediated interventions in divergent pathways at the molecular level. This review highlights (i) the causative factors implicated in kidney aging and the therapeutic aspects of resveratrol, and (ii) the effectiveness of resveratrol in delaying the aging process of the kidney while minimizing all possible side effects.     

Low-Temperature Photoluminescence Study of CdTe:In Crystals Annealed in Molten Bismuth

We used a low-temperature photoluminescence (PL) technique to investigate CdTe:In crystals after annealing in molten bismuth (Bi). The two annealed samples showed different resistivities after the treatment. For both samples, we observed very strong emissions in the excitonic spectral region and revealed fine structures of exciton emissions in the PL spectrum. In the sample with high resistivity, we found one ionized donor-bound exciton peak, (D⁺,X), that we ascribed to incorporated Bi atoms occupying Cd sites in the CdTe. The temperature dependence of the (D⁺,X) peak emission had an associated activation energy of 3.59 meV for the exciton bound to this ionized donor. Meanwhile, a donor–acceptor pair peak at 1.5315 eV, which was absent from the PL of the low-resistivity sample, suggested the likelihood of some Bi atoms occupying Te sites in the high-resistivity sample. Our findings highlight the need for detailed investigation of annealing conditions to ensure precise control of the electrical properties of the material during annealing in molten Bi.     

A Scaled Model Study of Waterjet Drilling

Abstract

Laboratory experimental results of waterjet drilling have rarely been scaled up to the field scale. This article presents the scaling criteria for designing waterjet drilling laboratory experiments for simulating a given oilfield operation. Dimensional analysis is used to derive scaling groups for the waterjet drilling technique. The proposed scaling approach meets all important requirements of this drilling process. Experiments were conducted to determine the strength and the relation between the rate of penetration (ROP) and depth of penetration (DOP) with drilling time. Experimental results are scaled up for field application. Laboratory measurements with such models accurately duplicate the behavior of the drilling performance of a reservoir. Such modeling is the most effective tool for the study of drilling behavior, performance, and management in the reservoir field.     

Effects of Memory on the Complex Rock-Fluid Properties of a Reservoir Stress-Strain Model

Abstract

The memory based stress-strain model developed earlier by Hossain et al. (2007) Hossain, M. E., Mousavizadegan, S. H., Ketata, C. and Islam, M. R. 2007. A novel memory based stress-strain model for reservoir characterization. Journal of Nature Science and Sustainable Technology, 1: 653–678.  [Google Scholar] has been solved numerically in this study. The derived mathematical model introduces the effects of temperature, surface tension, and pressure variations and the influence of fluid memory on the stress-strain relationship. The variation of shear stress as a function of strain rate is obtained for fluid in a sample oil reservoir to identify the effects of fluid memory. The stress-strain formulation related with the memory is taken into account, and we obtain the variation of it with time and distance for different values of α. The dependency of the stress-strain relation on fluid memory is considered to identify its influence on time. As pressure is also a function of space, the memory effects on stress and strain are shown in space with the pressure gradient change. The computation indicates that the effect of memory causes nonlinearity, leading to chaotic behavior of the stress-strain relationship. This model can be used in reservoir simulation and rheological study, well test analysis, and surfactant and foam selection for enhanced oil recovery.     

A 0.5?V high-speed comparator with rail-to-rail input range

A 0.5?V high-speed comparator with rail-to-rail input range is presented. Unlike conventional rail-to-rail comparators that use both NMOS and PMOS input devices, the proposed design takes advantage of zero-V _t NMOS devices that are available in many CMOS processes tailored for analog and mixed signal applications. Design issues associated with the use of zero-V _t devices in comparator circuits are analyzed. Based on a 0.13???m CMOS technology, the proposed design is compared with recently reported sub 1?V comparators and it shows significant performance improvement by the proposed design.     

Spatial heterogeneity and kinetic regulation of arsenic dynamics in mangrove sediments: the sundarbans, bangladesh

The biogeochemistry of arsenic (As) in sediments is regulated by multiple factors such as particle size, dissolved organic matter (DOM), iron mobilization, and sediment binding characteristics, among others. Understanding the heterogeneity of factors affecting As deposition and the kinetics of mobilization, both horizontally and vertically, across sediment depositional environments was investigated in Sundarban mangrove ecosystems, Bengal Delta, Bangladesh. Sediment cores were collected from 3 different Sundarbans locations and As concentration down the profiles were found to be more associated with elevated Fe and Mn than with organic matter (OM). At one site chosen for field monitoring, sediment cores, pore and surface water, and in situ diffusive gradients in thin films (DGT) measurements (which were used to model As sediment pore-water concentrations and resupply from the solid phase) were sampled from four different subhabitats. Coarse-textured riverbank sediment porewaters were high in As, but with a limited resupply of As from the solid phase compared to fine-textured and high organic matter content forest floor sediments, where porewater As was low, but with much higher As resupply. Depositional environment (overbank verses forest floor) and biological activity (input of OM from forest biomass) considerably affected As dynamics over very short spatial distances in the mosaic of microhabitats that constitute a mangrove ecosystem.     

A Bayesian latent model with spatio-temporally varying coefficients in low birth weight incidence data

In spatial epidemiology studies, the effects of covariates on adverse health outcomes could vary over space and time so examining the spatio-temporally varying effects is useful. In particular, the association between covariates and health outcomes could have locally different temporal patterns. In this article, we develop a Bayesian spatio-temporal latent model to identify spatial clusters in each of which covariate effects have homogeneous temporal patterns as well as estimate heterogeneous temporal effects of covariates depending on spatial groups. We compare the proposed model to several alternative models to assess the performance of the proposed model in terms of a range of model assessment measures. Low birth weight incidence data in Georgia for the years 1997-2006 are used.     

Experimentally tuned dual stage hydrogen compressor for improved compression ratio

An experiment-driven design procedure for optimizing the combination of stages of a dual stage hydrogen compressor with enhanced compression ratio is presented herein. Three different combinations of reactors were used using LaNi₅, Ca_0.6Mm_0.4Ni₅ and Ca_0.2Mm_0.8Ni₅ as hydrogen storage materials. Compression ratios were found to be similar for low supply pressure conditions, which improved significantly for high supply pressure conditions in single stage experiments. A dual stage compressor system with LaNi₅ in first stage and Ca_0.2Mm_0.8Ni₅ in the second stage was proposed based on single stage results, which was found to be very effective for enhancing compression ratio. Results show that 53% higher compression ratio can be attained by selecting appropriate storage materials for stages, compared to LaNi₅ based economic dual stage system.     

A universal model of opposed flow combustion of solid fuel over an inert porous medium

In this study, a universal model is developed to examine the behavior of combustion wave observed in porous solid matters (e.g., smoldering, self-propagating high-temperature synthesis (SHS), diesel particulate filter (DPF) regeneration process). Analytical expressions of the combustion characters of solid combustible (e.g., diesel particulate matters trapped in a DPF) deposited over an inert porous medium are obtained employing large activation energy asymptotic taking into account the sensible transport processes; namely, heat transfer between the porous medium and gas phases, radiation heat transfer from the porous medium, heat loss from the porous medium to the environment, mass transfer of oxygen from the gas stream to the surface of solid fuel and the effective diffusion in modeling the species diffusion. Then it has been validated that the present model is applicable and adaptable for predicting the characteristics of smoldering combustion and thus SHS process. As a result, the features of combustion wave of the present phenomena would be useful to other processes. From practical point of view and for deep understanding of the behavior of combustion wave of these processes, we investigate the effects of various physical parameters over a wide range of conditions. We observe that the moving speed of the reaction front increases with the increase of porosity of the porous medium, mass transfer coefficient and initial fuel mass fraction; while it decreases owing to the increase of heat transfer rate from the porous medium to the gas, heat loss to the environment and radiative heat transfer. Furthermore, the results reveal that extinction tends to occur due to lower porosity of the porous medium, higher radiative heat transfer from the porous medium, higher heat transfer rate from the porous medium to the gas and higher heat losses from the porous medium to the environment. Even the observed near-extinction behavior in reaction front speed versus heat loss diagram is found to be similar what we got in gaseous premixed flame propagating through the porous medium. An extinction limit diagram has been presented as a function of radiation-conduction parameter and the gas flow velocity. In addition to, the impact of radiation and the combined effect of the inclusion of Knudsen diffusion and tortuosity are demonstrated in terms of the spatial temperature and species profiles to examine how these two parameters modify the reaction front structure. Furthermore, the governing equations have been solved numerically and it is observed that asymptotic analysis gives a good agreement with the numerical solution.