NATURAL CONVECTION-RADIATION INTERACTIONS IN A CUBE FILLED WITH A NONGRAY GAS

A three-dimensional numerical study was performed on interactions of natural convection and radiation in a cubical enclosure filled with carbon dioxide gas. The enclosure was heated differentially by two opposing vertical walls. Gas radiation was analyzed by the P₁ differential approximation method and the weighted sum of gray gas model. Computations were carried out over a range of the Rayleigh number, Ra, between 10⁵ and 10⁹. The Prandtl number and the overheat ratio were held fixed at 0·68 and 1·0, respectively. Unsteady transitional flows were computed by a direct simulation method, without using any explicit turbulence models. From the predictions, a mean heat transfer correlation has been proposed as Nu = 0·323 Ra^0·342 in the surface/gas radiation mode, where Nu is the time and spatially averaged Nusselt number at the isothermal walls.     

The initial freezing point temperature of beef rises with the rise in pH: A short communication

This study tested the hypothesis that the initial freezing point temperature of meat is affected by pH. Sixty four bovine M. longissimus thoracis et lumborum were classified into two ultimate pH groups: low (< 5.8) and high pH (> 6.2) and their cooling and freezing point temperatures were determined. The initial freezing temperatures for beef ranged from − 0.9 to − 1.5 °C (? = 0.6 °C) with the higher and lower temperatures associated with high and low ultimate pH respectively. There was a significant correlation (r = + 0.73, P < 0.01) between beef pH and freezing point temperature in the present study. The outcome of this study has implications for the meat industry where evidence of freezing (ice formation) in a shipment as a result of high pH meat could result in a container load of valuable chilled product being downgraded to a lower value frozen product.     

A low-voltage low-power CMOS fully differential linear transconductor with mobility reduction compensation

A highly linear fully differential CMOS transconductor architecture based on flipped voltage follower (FVF) is proposed. The linearity of the proposed architecture is improved by mobility reduction compensation technique. The simulated total harmonic distortion (THD) of the proposed transconductor with 0.4V_pp differential input is improved from ?42 dB to ?55 dB while operating from 1.0 V supply. As an example of the applications of the proposed transconductor, a 4th-order 5 MHz Butterworth Gm-C filter is presented. The filter has been designed and simulated in UMC 130 nm CMOS process. It achieves THD of ?53 dB for 0.4V_pp differential input. It consumes 345 μw from 1.0 V single supply. Theoretical and simulated results are in good agreement.     

Ethylene‐methyl acrylate‐glycidyl methacrylate toughened poly(lactic acid) nanocomposites

Poly (lactic acid) (PLA) was melt blended in a twin screw extruder using an ethylene‐methyl acrylate‐glycidyl methacrylate rubber as a toughener. PLA/rubber blends were immiscible as observed by scanning electron microscopy. Impact strength and ductility of PLA were improved by the addition of the rubber at the expense of strength and stiffness. An organo‐montmorillonite (OMMT) was used at 2 wt % to counteract the negative effect of the rubber on modulus, and balanced properties were observed at 10 wt % rubber content. X‐ray diffraction and transmission electron microscopy revealed the formation of intercalated/exfoliated structure in the ternary nanocomposites. Thermal behavior analysis indicated that the degree of crystallinity is slightly affected by the clay and the rubber. Both the clay and the rubber decreased the crystallization temperature of PLA and acted as nucleating agents for PLA. The viscosity of the mixtures as measured by melt flow index was highly influenced by the rubber and the OMMT. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tensile properties and fracture characteristics of ECAP-processed Al and Al-Cu alloys

In the present paper, billets of pure Al, and cast-homogenized Al-2 wt.%, 3 wt.%, and 5 wt.% Cu alloys were successfully processed by equal channel angular pressing (ECAP) up to 10 passes without fracture at room temperature using a die with a channel angle of 110°. Giant strains imposed on workpieces lead to extreme dislocation densities, microstructural refinement, and finally ultrafine grained materials. Tensile tests were employed to examine the fracture modes and fracture surface morphologies of the ECAP-processed Al and Al-Cu alloy samples. In particular, the effects of the number of ECAP passes and the Cu content were investigated.     

Simulation of gas species and temperature separation in the counter-flow Ranque–Hilsch vortex tube using the large eddy simulation technique

A computational fluid dynamic model is used to predict the species and temperature separation within a counter flow Ranque–Hilsch vortex tube. The large eddy simulation (LES) technique was employed for predicting the gas flow and temperature fields and the species mass fractions (nitrogen and helium) in the vortex tube. A vortex tube with a circumferential inlet stream of nitrogen–helium mixture and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. The temporal evolutions of the axial, radial and azimuthal components of the velocity along with the temperature, pressure and mass density and species concentration fields within the vortex tube are simulated. Even though a large temperature separation was observed, only a very minimal gas separation occurred due to diffusion effects. Correlations between the fluctuating components of velocity, temperature and species mass fraction were calculated to understand the separation mechanism. The inner core flow was found to have large values of eddy heat flux and Reynold’s stresses. Simulations were carried out for varying amounts of cold outlet mass flow rates. Performance curves (temperature separation/gas separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate.     

The use of response surface method to optimize the extraction of natural dye from winery waste in textile dyeing

Grape pomace, which is a winery waste is studied and experimented to serve as a source of natural dyes that could be utilized in textile dyeing. The present study aims at developing and optimizing an extraction method of natural dye derived from grape pomace in order to dye silk fabrics. The water-acidified ethanol (20–40%) mixture is used mainly for the extraction of anthocyanins at different durations and at different temperatures (20–40 °C) from grape pomace. Effects of these independent variables (percentage of acidified ethanol, temperature, and duration of extraction) and their interactions during the extraction are determined by response surface methodology based on three-level three-factorial Box–Behnken design. Optimized values of percentage of acidified ethanol, temperature, and the duration of extraction for the optimization of monomeric anthocyanins concentration (75 mg L^?1) are found as 40%, 32,7 °C, and 38 h, respectively. The extract has been used for silk fabrics dyeing. The effects of some parameters (temperature, pH, and salt addition) on dyeing silk fabrics have been studied and optimized. The use of tannic acid as a natural mordant to improve the dye fastness proprieties has been investigated.     

An effective scheduling scheme for multi-hop multicast in wireless mesh networks

With the utilization of concurrent transmission strategy, a throughput-enhanced scheduling scheme is devised for multicast service in wireless multi-hop mesh networks. Since the performance of a multicast mechanism is constrained in a wireless setting due to the interference among local wireless transmissions, the interference relationships are first characterized by introducing a graph transformation method. Based on the graph transformation, the multicast scheduling problem is converted to the graph coloring problem, and then a capacity greedy algorithm is designed to provide concurrent transmission scheduling so that the demanded multicast transmission rate can be achieved. Moreover, the necessary and sufficient conditions of multicast schedulable feasibility are derived. Through corresponding simulations, it is shown that the proposed strategy can enhance the throughput of wireless multi-hop multicast systems significantly.     

Effect of Muscle Condition Before Freezing and Simulated Chemical Changes During Frozen Storage on the pH and Colour of Beef

The effect of rigor temperature (RT, 35 versus 10°C), increased ionic concentration (MS, 0 versus 0·2% mixed salts), oxidized lipids (OL, 0 versus 1% added oxidized fat), increased free amino acids (FAA, 0 versus 0·3% added mixture of amino acids), fat content (FC, 0 versus 15% added fat) and excluding atmospheric gases (V, 0 versus 99·9% vacuum) on pH and colour of mince stored for one month at -20°C was studied using a complete 2(6) factorial design. Adding FAA increased the meat pH measured after storage (p<0·001). Meat lightness (Hunter L* value) was increased by increased fat content (p<0·001), higher rigor temperature (p<0·001) and oxidized lipids (p<0·05). Vacuum packing tended to preserve redness (Hunter a*) whereas the higher rigor temperature decreased redness (p<0·001). Vacuum packing (p<0·05) and increased fat content (p<0·001) increased yellowness (Hunter b*). The hue angle was lowered by increased salt concentration (p<0·01), increased free amino acids (p<0·01) and using vacuum packing (p<0·001), whereas it was raised (p<0·001) by increased fat content and higher rigor temperature. Various significant two-and three-way interactions are tabulated and discussed.