An experimental study on the effect of ultrasonication on viscosity and heat transfer performance of multi-wall carbon nanotube-based aqueous nanofluids

Four samples of 1 wt% multi-walled carbon nanotube-based (MWCNT) aqueous nanofluids prepared via ultrasonication were thermally characterized. Direct imaging was done using a newly developed wet-TEM technique to assess the dispersion state of carbon nanotubes (CNT) in suspension. The effect of dispersing energy (ultrasonication) on viscosity, thermal conductivity, and the laminar convective heat transfer was studied. Results indicate that thermal conductivity and heat transfer enhancement increased until an optimum ultrasonication time was reached, and decreased on further ultrasonication. The suspensions exhibited a shear thinning behavior, which followed the Power Law viscosity model. The maximum enhancements in thermal conductivity and convective heat transfer were found to be 20% and 32%, respectively. The thermal conductivity enhancement increased considerably at temperatures greater than 24 °C. The enhancement in convective heat transfer was found to increase with axial distance. A number of mechanisms related to boundary layer thickness, micro-convective effect, particle rearrangement, possible induced convective effects due to temperature and viscosity variations in the radial direction, and the non-Newtonian nature of the samples are discussed.     

Microdiversity reception of spread-spectrum signals on Nakagamifading channels

An analytical framework to evaluate the performance of different predetection diversity techniques in various mobile radio environments is developed. The average bit-error rate analysis applies to phase coded spread-spectrum systems, over Nakagami multipath fading channels. A simple and practical selection combining rule is considered. Our numerical results reveal that this new low-complexity receiver structure exhibits comparable performance to that of an optimum linear diversity combiner when the channel does not experience severe fading and for small diversity orders, conditioned on the situation that all the diversity branches have identical mean signal strengths. In this study, we also investigate the effect of variations in the mean signal and noise power levels on each of the independent diversity branches. This is an important consideration because in practice equal mean signal strengths rarely occur, which results in loss of diversity gain. We found that the signal-plus-noise-and-interference selection model outperforms the traditional signal-to-interference-plus-noise ratio selection scheme if the discrepancy between the mean signal strengths are small, owing to the statistical nature of the multiple-access interference     

Cauchy–Schwarz bound on the generalized Marcum Q‐function with applications

The Cauchy–Schwarz bounding technique is used to derive useful bounds on the generalized Marcum Q‐function and its complement. Three new exponential‐type bounds on Q_M (α, β) are derived, and these are found to be tight and useful for a number of applications of interest. One such example is the derivation of an upper bound on the average symbol error rate probability for noncoherent and differentially coherent communication systems over generalized fading channels. It is shown that these exponential‐type bounds are considerably tighter than the Chernoff bound (Rappaport SS. IEEE Trans. on Information Theory 1971; 17 : 497–498) counterpart. Numerical results also reveal that the tightness of one of the exponential‐type bounds is comparable to the bound obtained in Simon and Alouini (IEEE Trans. on Communications 2000: 359–366), while another is found to be superior than that obtained in Simon and Alouini over a wide range of arguments. Copyright © 2001 John Wiley & Sons, Ltd.     

Microwave dielectric properties of Mg4Al2Ti9O25 ceramics

Phase-singular Mg₄Al₂Ti₉O₂₅ ceramics with the pseudobrookite structure suitable for microwave devices such as antenna substrate have been prepared by gel-carbonate method with the dielectric permittivity of 24.7 (at 2-8 GHz), Q-values > 30,000 and temperature coefficients in permittivity (TCK) of less than + 17 ppm K^− 1. The dielectric characteristics are accountable in terms of ordering in the cation sub-lattice.     

Effect of erythorbate, storage and high-oxygen packaging on premature browning in ground beef

Premature browning (PMB) was investigated in ground beef patties with (0.04%, w/w) and without erythorbate. In Experiment 1, patties were stored at 4 °C for 48 h; at -18 °C for 21 days; or at -18 °C for 21 days, thawed at 4 °C for 24 h; and cooked. Bulk ground beef was stored at -18 °C for 24 days, thawed for 24 h at 4 °C, and patties prepared and cooked immediately. In Experiment 2, fresh patties were overwrapped with oxygen-permeable film or packaged in 80% O(2)/20% N(2) (MAP), and stored for 48 h at 4 °C, or at -18 °C for 21 days, and cooked. Total reducing activity and color (L*, a* and b* values) were measured immediately prior to cooking. Patties were cooked to internal temperatures of 60, 66, 71 and 77 °C and internal cooked color was measured. Total reducing activity was higher for the erythorbate treatment than controls for all storage conditions (P<0.05). a* Values of cooked patties were higher for erythorbate than control treatments under all storage and packaging conditions at 60 and 66 °C (P<0.05). The presence of erythorbate in ground beef patties appeared to maintain red color at cooked internal temperatures of 60 and 66 °C. Frozen bulk storage appeared to increase the susceptibility of ground beef to PMB when compared to fresh and frozen patties. Patties cooked directly from frozen state appeared less susceptible to PMB than frozen-thawed and bulk storage. Ground beef appeared predisposed to PMB when stored in high-oxygen MAP at 4 °C for 48 h.     

Global pollution monitoring of polybrominated diphenyl ethers using skipjack tuna as a bioindicator

To elucidate the global distribution of polybrominated diphenyl ethers (PBDEs), these chemicals were determined in the muscle of skipjack tuna (Katsuwonus pelamis) collected from offshore waters of various regions in the world (Japan, Taiwan, Philippines, Indonesia, Seychelles, and Brazil, and the Japan Sea, East China Sea, South China Sea, Indian Ocean, and North Pacific Ocean). PBDEs were detected in almost all the skipjack tuna collected from the locations surveyed (from < 0.1 to 53 ng/g of lipid), indicating widespread contamination by these compounds in the marine environment. Residue levels of PBDEs in these samples from the northern hemisphere seem to be higher than those from the southern hemisphere, which is plausibly due to larger usage of these compounds in the northern hemisphere. Higher concentrations of PBDEs were detected in the samples from waters around the East China Sea (up to 53 ng/g of lipid). Developing countries around the East China Sea are supposedly the "hot spots" releasing these chemicals into the marine environment. With regard to the composition of PBDE congeners, the percentage contribution by lower brominated congeners (BDE15, -28, and -47) showed an increasing trend with increasing latitude. On the other hand, higher brominated congeners (BDE153, -154, and -183) showed a reverse trend. These patterns suggest that lower brominated congeners of PBDEs (di-, tri-, and tetra-BDEs) were preferentially transported from pollution sources to northern colder regions through the atmosphere. PBDEs may have a high potency to cause global pollution like PCBs.     

Transformations during Grinding of Ceria-Stabilized Tetragonal Zirconia Polycrystals

Ce-TZP is reported to exhibit cyclic transformation during machine grinding. Previous conclusions were based on the results obtained by grinding Ce-TZP at a single speed and depth of cut. In the present work, grinding parameters were carefully chosen to induce varied stresses. Results show that Ce-TZP exhibits cyclic transformation, not always, but only under certain favorable grinding conditions. Results are supported by XRD, optical microscopy, and dynamometric observations. Three stages of transformation, namely, a mechanical-stress-induced t to m , a frictional-heat-driven m to t , and a thermal-quenching-stress-induced t to m , in sequence, are clearly identified.     

Relation between group combustion and drop array studies

Spray combustion modeling requires a knowledge of the strength of the mass and heat sources for each drop in the spray. Since sprays involve a large number of drops, interactive transport processes must be accounted for in estimating the source strengths of the drops. Earlier approaches (called array studies) considered a finite number of drops (2 to 9), and accounted for the three dimensional variation of temperature and species mass fraction profiles in order to determine an evaporation/combustion correction factor. This correction factor is defined as the ratio of the average strength of each drop in the array to the strength of the drop if it is kept in an isolated environment. The current approach utilizes group combustion theory which involves a large number of drops, assumes top hat profiles in the interstitial space between the drops, and accounts for their variation in the radial direction. The correction factor is again determined. This paper reports the results of the current group combustion approach and compares these results with those from array studies when the group combustion approach is extended to an array consisting of as few as 2 to 9 drops. The change in transport rate due to proximity of other drops is accounted for in the present group combustion approach. An unexpected result is the close agreement of the results obtained from group combustion approach with those results from array studies. A simple algebraic expression is given for the correction factor in terms of l/a ratio and total number of drops for a 2 to 9 drop array.     

Composition of gallstones in Coimbatore District of Tamil Nadu State

BACKGROUND: Gallstones in northern India are predominantly of the cholesterol type; such information on gallstones in southern India is scant. AIM: To analyze the composition of gallstones from patients residing in Coimbatore District in Tamil Nadu State. METHODS: The stones were classified using the Bernhoft criteria and was correlated with the morphological characteristics. RESULTS: Of the 105 gallstones analyzed, 67 (63.8%) were of the pigment variety and 36 (34.8%) of the intermediate/mixed type. There were only two cholesterol stones. The mean proportions of cholesterol, bilirubin and calcium in the pigment and intermediate stones were 7.1%, 26.1% and 7.8% and 30.2%, 18.4% and 6.3%, respectively. The mean proportion of bilirubin in the pigment stones was higher than in the intermediate type. Morphologically, pigment stones were black in 55% and amorphous in 63%; the intermediate stones were hard in 50% and of variegated color ranging from yellow to ivory white in 61%; both cholesterol stones were multiple, hard and brown. CONCLUSIONS: There is a predominance of pigment and intermediate gallstones (98%) in this district. These stones have reduced cholesterol and an increase in bilirubin and calcium proportions.