Erosion-corrosion behavior of SiC particle-reinforced Al-Si alloy in NaOH slurry

The erosion-corrsosion behavior of SiC particle-reinforced Al-Si alloy has been studied in NaOH slurry simulating the mining atmosphere. The study was performed at two different sand concentrations, namely, 20 and 30 wt pct, and at a speed of 900 rpm. It is depicted that the wear rates decreased with increasing sand content, indicating that corrosion is the dominating mode of material removal. Further composite exhibited lower wear resistance than the laloys irrespective of the sand concentration. Scanning electron microscope (SEM) observations indicated the dissolution of dendrites of Al due to severe corrosion, leaving behind the network of Si. This ultimately results in the falling of Si particles from the matrix, leaving behind voids. This also results in the formation of voids around the SiC particles and leads to pullout of SiC particles from the matrix during the wear process.     

Channel Adaptive Quantization for Limited Feedback MIMO Beamforming Systems

Multiple-input multiple-output (MIMO) wireless systems can achieve significant diversity and array gain by using transmit beamforming and receive combining techniques. In the absence of full channel knowledge at the transmitter, the transmit beamforming vector can be quantized at the receiver and sent to the transmitter using a low-rate feedback channel. In the literature, quantization algorithms for the beamforming vector are designed and optimized for a particular channel distribution, commonly the uncorrelated Rayleigh distribution. When the channel is not uncorrelated Rayleigh, however, these quantization strategies result in a degradation of the receive signal-to-noise ratio (SNR). In this paper, switched codebook quantization is proposed where the codebook is dynamically chosen based on the channel distribution. The codebook adaptation enables the quantization to exploit the spatial and temporal correlation inherent in the channel. The convergence properties of the codebook selection algorithm are studied assuming a block-stationary model for the channel. In the case of a nonstationary channel, it is shown using simulations that the selected codebook tracks the distribution of the channel resulting in improvements in SNR. Simulation results show that in the case of correlated channels, the SNR performance of the link can be significantly improved by adaptation, compared with nonadaptive quantization strategies designed for uncorrelated Rayleigh-fading channels     

MESFET MMIC Ka-band transmitter performance forhigh-volume system applications

An MMIC transmitter for high-volume smart munition applications in Ka band is developed using 0.25 μm MESFET technology. The transmitter, consisting of a voltage-controlled oscillator (VCO) and power amplifier (PA), delivers more than 100 mW of power with an overall efficiency of 10% and a linear tuning range of more than 700 MHz around 35 GHz     

Carbazole and benzimidazole/oxadiazole hybrids as bipolar host materials for sky blue,green, and red PhOLEDs

Two novel bipolar host materials (CBzIm and COxaPh) comprising of a hole-transport (HT) carbazole core functionalized with electron-transport (ET) moieties (benzimidazole/oxadiazole) at C3 and C6 positions have been synthesized. Their thermal, photophysical, electrochemical properties, and carrier mobilities were characterized. Theoretical calculations revealed that the HOMO orbitals were generally delocalized over the hole- and electron-transport moieties for both CBzIm and COxaPh, whereas the LUMO orbitals distribution only involved one benzimidazole moiety in CBzIm instead of fully delocalization over the whole polar moieties for COxaPh, which is consistent with the observation of good hole mobilities for both hosts and better electron mobility for COxaPh over CBzIm. CBzIm with high E_T (2.76 eV) is suitable to serve as a blue phosphor host, where a sky blue phosphor (DFPPM)₂Irpic exhibiting superior properties than those of popular blue emitter FIrpic was used to give highly efficient phosphorescent OLEDs, achieving a maximum external quantum efficiency (η_ext) of 15.7%. The better π-delocalization of COxaPh led to a lower triplet energy (E_T = 2.65 eV), which can be used to accommodate green and red phosphors, providing excellent device performance with η_ext as high as 17.7% for green [(ppy)₂Ir(acac)] and 20.6% for red [Os(bpftz)₂(PPh₂Me)₂], respectively.     

Identification of Fouling Mechanism During Ultrafiltration of Stevia Extract

Stevioside is one of the naturally occurring sweetener, which can be widely applied in food, drinks, medicine, and daily chemicals. Membrane separation has potential application in clarification of stevioside from pretreated stevia extract by ultrafiltration. In the present study, namely 5-, 10-, 30-, and 100-kDa molecular weight cutoff membranes have been used. Quantification of membrane fouling during ultrafiltration is essential for improving the efficiency of such filtration systems. A systematic analysis was carried out to identify the prevailing mechanism of membrane fouling using a batch unstirred filtration cell. It was observed that the flux decline phenomenon was governed by cake filtration in almost all the membranes. For 100 kDa membrane, both internal pore blocking and cake filtration are equally important. Resistance in series analysis shows that the cake resistance is several orders of magnitude higher than the membrane resistance. The cake resistance is almost independent of transmembrane pressure drop, which indicates the incompressible nature of the cake. A response surface analysis was carried out to quantify the development of cake resistance with time during ultrafiltration of various membranes. Quality parameters show that the 30-kDa membrane is better suited for clarification purposes. Identification of the fouling mechanism would aid in the process of design and scaling up of such clarification setup in future.     

Association of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) with age of puberty among children living near a chemical plant

Animal studies suggest that perfluorocarbons (PFCs) may alter sexual maturation. Relationships of human PFC exposure with puberty are not clear. We conducted a cross-sectional study to investigate whether perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) were associated with indicators of sexual maturation in a 2005-2006 survey of residents with PFOA water contamination from the Mid-Ohio Valley. Participants were 3076 boys and 2931 girls aged 8-18 years. They were classified as having reached puberty based on either hormone levels (total >50 ng/dL and free >5 pg/mL testosterone in boys and estradiol >20 pg/mL in girls) or onset of menarche. We estimated the odds of having reached puberty classified by these criteria and the fitted median age of reaching puberty in relation to serum PFOA and PFOS concentrations measured when puberty status was assigned. For boys, there was a relationship of reduced odds of reached puberty (raised testosterone) with increasing PFOS (delay of 190 days between the highest and lowest quartile). For girls, higher concentrations of PFOA or PFOS were associated with reduced odds of postmenarche (130 and 138 days of delay, respectively). In conclusion, our study showed a later age of puberty in this population correlated with PFC concentrations.     

Significant physical attributes affecting quality of Indian black (CTC) tea

In this research work, an attempt was made to discriminate different grades of black crush-tear-curl (CTC) tea based upon their physical attributes such as color of brewed liquor, texture, size and shape of the tea granules obtained by machine vision technique. The principal component analysis (PCA) was applied over two types of data. First, tea samples with seven different quality grades but same mechanical grading and second, samples with same quality grade but nine different mechanical grades (Brokens, Fannings and Dust) were considered for analysis, respectively. The results of PCA showed that best discrimination (100%) in both types of data was given by color attributes only. Correlations among tea samples and physical attributes were determined. Based upon these results it may be concluded that color only attributes are the most significant and sufficient for quantification of tea quality whereas other physical attributes contribute so little to quality estimation that they may be ignored.     

Colloid transport in dolomite rock fractures: effects of fracture characteristics, specific discharge, and ionic strength

The effects of fracture characteristics, specific discharge, and ionic strength on microsphere transport in variable-aperture dolomite rock fractures were studied in a laboratory-scale system. Fractures with different aperture distributions and mineral compositions were artificially created in two dolomite rock blocks. Transport tests were conducted with bromide and carboxylate-modified latex microspheres (20, 200, and 500 nm diameter). Under overall unfavorable attachment conditions, there was significant retention of the 20 nm microsphere and minimal retention of the 500 nm microsphere for all conditions examined. Aperture variability produced significant spatial variation in colloid transport. Flushing with low ionic strength solution (1 mM) following microsphere transport at 12 mM ionic strength solution produced a spike in effluent microsphere concentrations, consistent with retention of colloids in secondary energy minima. Surface roughness and charge heterogeneity effects may have also contributed to the effect of microsphere size on retention. Matrix diffusion influenced bromide transport but was not a dominant factor in transport for any microsphere size. Calibrated one-dimensional, two-site kinetic model parameters for colloid transport in fractured dolomite were sensitive to the physical and chemical properties of both the fractured dolomite and the colloids, indicating the need for mechanistic modeling for accurate prediction.     

Phase Diagram and Upper Critical Field of Homogeneously Disordered Epitaxial 3-Dimensional NbN Films

We report the evolution of superconducting properties with disorder, in 3-dimensional homogeneously disordered epitaxial NbN thin films. The effective disorder in NbN is controlled from moderately clean limit down to Anderson metal?Cinsulator transition by changing the deposition conditions. We propose a phase diagram for NbN in temperature-disorder plane. With increasing disorder, we observe that as k _F l??1 the superconducting transition temperature (T _c ) and normal state conductivity in the limit T??0 (?? ₀) go to zero. The phase diagram shows that in homogeneously disordered 3-D NbN films, the metal?Cinsulator transition and the superconductor?Cinsulator transition occur at a single quantum critical point, k _F l??1.