Comparison of electrothermal and hydride generation atomic absorption spectrometry for the determination of total arsenic in broiler chicken

The purpose of this study was to estimate total arsenic concentration in different tissues (leg, breast, liver and heart) of broiler chicken by hydride generation atomic absorption spectrometry (HGAAS) and graphite furnace atomic absorption spectrometry (GFAAS), prior to microwave assisted acid digestion. The accuracy of the techniques was evaluated by using certified reference material DORM-2. The percentage recoveries of total As were observed as 100.6% and 99.4% for HGAAS and GFAAS, respectively. The precision of the techniques, expressed as relative standard deviation, was observed as 1.71% and 4.18% for HGAAS and GFAAS measurements, respectively. The limits of detection for HGAAS and GFAAS were 0.025 μg/g and 0.052 μg/g, respectively. The concentrations of total arsenic in different tissues of broiler chicken were found in the range of 2.19–5.28, 2.15–5.22, 2.97–7.17 and 2.68–6.36 μg/g for leg, breast, liver and heart tissues, respectively. At a mean level of chicken consumption (60 g/person/day), people may ingest in the range of 72.0–85.1 μg arsenic/person/day from chicken alone.     

FeGaB (25 nm)/Al2O3/FeGaB(25 nm)多层薄膜结构：氧化铝(Al2O3)厚度变化对静态与动态磁性能的影响

铁镓(FeGa)薄膜与其它软磁材料相比具有较大的磁致伸缩常数,在设计集成磁性传感器芯片中具有独特的优势,本文通过采用非磁性掺杂和多层膜方法来控制这种合金薄膜的磁学与电学性能参数。我们实验发现在掺杂一定量硼(B)元素后,厚度小于30 nm的FeGa薄膜顽力可以得到显著降低,而对于较厚薄膜在插入超薄Al2 O3中间层后软磁性能可以得到同样程度显著改善,同时饱和磁化(Ms)变化可忽略。对于我们制备的FeGaB (25 nm)/Al2O3(0.5 nm)/FeGaB(25 nm)多层膜,其易轴矫顽力可以小到0.98 Oe,电阻率与50nm单层FeGaB膜相比增加了1.5倍,同时具有吉赫兹高磁导率谱。样品微结构分析表明,磁性颗粒结晶质量和物理尺寸的减小对软磁性改善起到重要作用,另外我们也讨论分析了静磁相互作用和表面形貌对磁畴运动及矫顽力的影响。本文发展的掺杂与多层膜混合方案来来增强电磁性能的方法,也可应用于其他类型的软磁材料系统。     

Determining the mechanical properties of epoxy resin (DGEBA) composites by ultrasonic velocity measurement

In this study, the composites of diglycidyl ether of bisphenol A (DGEBA) epoxy resin that have been formed by mixing epoxy resin with allyl glycidyl ether (AGE) and 2,3‐epoxypropyl methacrylate [glycidyl methacrylate (GMA)] were prepared in weight % ratios of 90 : 10, 80 : 20, and 70 : 30. A computer controlled analyzer with 35 MHz and a digital oscilloscope with 60 MHz were used for measuring the velocities of ultrasonic wave. The measurement of ultrasonic velocity carried out by pulse echo method at frequencies of 2.25 and 3.5 MHz at room temperature. The values of acoustic impedance (Z), Poisson ratio (μ), and coefficients of elasticity (L, G, K, E) of composites were calculated by values of densities and velocities that obtained. Thus, the effect of modificating epoxy resin (DGEBA) by AGE and GMA on mechanical properties of DGEBA was investigated using the ultrasonic method. Atomic force microscopy has been used for determining the microstructure of composites. By the results obtained from the investigation, it have been established that the longitudinal and shear ultrasonic wave velocities, and the values of all the elasticity constants of DGEBA were increased by modification with AGE and GMA. Also the most suitable combination ratio for the compound of DGEBA : AGE and DGEBA : GMA has been found as 80 : 20. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Glass fibers with clay nanocomposite coating: Improved barrier resistance in alkaline environment

Coatings made from neat vinyl ester and nanoclay reinforced vinyl ester composites are applied onto individual glass fibers as well as rovings to evaluate their barrier resistance against alkali and moisture attack. The fibers coated with clay nanocomposites present a significantly less damage caused by the diffusing alkali ions, giving rise to a much higher residual tensile strength after aging than the fibers without coating or those with a neat polymer coating. The static fatigue test performed on individual fibers verifies the advantage of using nanoclay composite to retard the corrosion process under the combined stress and alkaline environment. Similar beneficial effects of incorporating nanoclay on residual strength are identified for impregnated fiber bundles. The above observations confirm the excellent barrier characteristics of intercalated/exfoliated nanoclay in polymer that are applied in composite structures on both the microscopic and macroscopic scales.     

Structural stability of silver under single-chamber solid oxide fuel cell conditions

In the present study, structural stability of silver under single-chamber conditions has been examined. Micro-tubular cells made of conventional solid oxide fuel cell materials (Ni-YSZ/YSZ/LSM) with silver paste and silver current-collecting wires (for both electrodes) were prepared. The cells were operated with methane/air mixture of 25/60 mL min⁻¹, furnace temperature of 750 °C, and at an operating voltage of 0.5 V. The results showed increasing porosity in the current-collecting silver wire with time, leading to rupture, finally. It is postulated that the porosity formation could be due to the formation of silver oxide which is highly unstable (volatile) at operating temperature considered in this study. Furthermore, vaporization and melting of silver due to cell overheating under mixed-reactant conditions is expected. Based on experimental evidences, it is concluded that silver may not be a good choice to be employed under the above specified operating conditions, as it lacks long-term structural stability.     

A decision support framework for metrics selection in goal-based measurement programs: GQM-DSFMS

Software organizations face challenges in managing and sustaining their measurement programs over time. The complexity of measurement programs increase with exploding number of goals and metrics to collect. At the same time, organizations usually have limited budget and resources for metrics collection. It has been recognized for quite a while that there is the need for prioritizing goals, which then ought to drive the selection of metrics. On the other hand, the dynamic nature of the organizations requires measurement programs to adapt to the changes in the stakeholders, their goals, information needs and priorities. Therefore, it is crucial for organizations to use structured approaches that provide transparency, traceability and guidance in choosing an optimum set of metrics that would address the highest priority information needs considering limited resources. This paper proposes a decision support framework for metrics selection (DSFMS) which is built upon the widely used Goal Question Metric (GQM) approach. The core of the framework includes an iterative goal-based metrics selection process incorporating decision making mechanisms in metrics selection, a pre-defined Attributes/Metrics Repository, and a Traceability Model among GQM elements. We also discuss alternative prioritization and optimization techniques for organizations to tailor the framework according to their needs. The evaluation of the GQM-DSFMS framework was done through a case study in a CMMI Level 3 software company.     

A comparative study of kriging variants for the optimization of a turbomachinery system

Kriging is a well-established approximation technique for deterministic computer experiments. There are several Kriging variants and a comparative study is warranted to evaluate the different performance characteristics of the Kriging models in the computational fluid dynamics area, specifically in turbomachinery design where the most complex flow situations can be observed. Sufficiently accurate flow simulations can take a long time to converge. Hence, this type of simulation can benefit hugely from the computational cheap Kriging models to reduce the computational burden. The Kriging variants such as ordinary Kriging, universal Kriging and blind Kriging along with the commonly used response surface approximation (RSA) model were used to optimize the performance of a centrifugal impeller using CFD analysis. A Reynolds-averaged Navier–Stokes equation solver was utilized to compute the objective function responses. The responses along with the design variables were used to construct the Kriging variants and RSA functions. A hybrid genetic algorithm was used to find the optimal point in the design space. It was found that the best optimal design was produced by blind Kriging, while the RSA identified the worst optimal design. By changing the shape of the impeller, a reduction in inlet recirculation was observed, which resulted into an increase in efficiency.     

Al₂O₃ and γAl₂O₃ Nanomaterials Based Nanofluid Models with Surface Diffusion: Applications for Thermal Performance in Multiple Engineering Systems and Industries

Thermal transport investigation in colloidal suspensions is taking a significant research direction. The applications of these fluids are found in various industries, engineering, aerodynamics, mechanical engineering and medical sciences etc. A huge amount of thermal transport is essential in the operation of various industrial production processes. It is a fact that conventional liquids have lower thermal transport characteristics as compared to colloidal suspensions. The colloidal suspensions have high thermal performance due to the thermophysical attributes of the nanoparticles and the host liquid. Therefore, researchers focused on the analysis of the heat transport in nanofluids under diverse circumstances. As such, the colloidal analysis of H₂O composed by γAl₂O₃ and Al₂O₃ is conducted over an elastic cylinder. The governing flow models of γAl₂O₃/H₂O and Al₂O₃/H₂O is reduced in the dimensionless form by adopting the described similarity transforms. The colloidal models are handled by implementing the suitable numerical technique and provided the results for the velocity, temperature and local thermal performance rate against the multiple flow parameters. From the presented results, it is shown that the velocity of Al₂O₃–H₂O increases promptly against a high Reynolds number and it decreases for high-volume fraction. The significant contribution of the volumetric fraction is examined for thermal enhancement of nanofluids. The temperature of Al₂O₃–H₂O and γAl₂O₃–H₂O significantly increases against a higher ϕ. Most importantly, the analysis shows that γAl₂O₃–H₂O has a high local thermal performance rate compared to Al₂O₃–H₂O. Therefore, it is concluded that γAl₂O₃–H₂O is a better heat transfer fluid and is suitable for industrial and technological uses.     

Kinetic modeling of pyrolysis of three Iranian waste oils in a micro-fluidized bed

Different approaches have been used to convert the waste materials into a clean syngas or other chemicals such as methanol. Among them, pyrolysis is a good candidate to produce the synthesis gas and volatile matters for industrial and refinery applications. In this work, we studied the kinetic and chemical behavior of three Iranian waste oils through a kinetic model and an experimental study. The experiments carried out in a micro-FB reactor, which is a good option for low emissions. Results showed that the reaction temperature and reaction rate are two of the most important factors for maximum conversion level of fuel. Results also showed an optimum value for reaction rate. The modeling results validated against the experimental measurements and found to be in good agreements.