Numerical analysis of laser transmitter nonlinearity compensation technique for radio over fiber system

The task of reducing the noise and distortion generated by a laser transmitter has always been a challenge to improve the performance of radio over fiber systems. This paper presents a compensation system for nonlinear distortion of a laser transmitter supporting 5.2 GHz radio transmission over fiber employing a feed‐forward linearization technique. The nonlinearity of the laser diode is modeled using Volterra series analysis. The proposed linearization system is also simulated using commercial optical system software. The novel design has achieved 30 dB nonlinearity reduction considering 800 MHz modulation bandwidth. As an addition, this work also analyzes the effect of transmission length towards distortion reduction of the proposed system. Copyright © 2011 John Wiley & Sons, Ltd.     

Extending Loffeld's bistatic formula for the general bistatic SAR configuration

This study derives an accurate bistatic point target reference spectrum based on a zeroth-order polynomial model. The spectrum contains only two hyperbolic square root terms that are very analogous in form to the analytical monostatic spectrum. The new formulation can be considered as an improvement of the Loffeld?s bistatic formula (LBF) and allows it to handle a wider range of bistatic configurations. The original LBF works well only in the case where the contributions of transmitter and receiver to the total Doppler modulation are approximately equal. An earlier paper on the extended LBF (EBLF) uses time bandwidth product (TBP) to weight the azimuth phase modulation from each platform. However, this extension is valid only in the low squint bistatic geometry. Both LBF and ELBF are expanded up to the quadratic term to derive an approximate bistatic spectrum; however, they do not show a good focusing performance in the more complex bistatic geometry, for example, the high squint case. This is due to the inaccurate individual time- Doppler correspondences. In this study, a norm in Euclidean space is defined to derive the optimal individual time-Doppler correspondences. Using the accurate individual time-Doppler correspondences, a zeroth-order polynomial model can be used to readily derive a more accurate bistatic spectrum. Two simulation experiments in the high squint geometry are used to verify the accuracy of this new formulation. The first experiment uses a parallel-track spaceborne/spaceborne configuration, and the second experiment involves an orthogonal-track airborne/airborne case.     

Determination of oil palm fruit phenolic compounds and their antioxidant activities using spectrophotometric methods

There is scarce information on the phenolics of oil palm fruits (Elaeis guineensis). In this study, phenolics were extracted from oil palm fruits and analysed using spectrophotometry for information on the different types of palm phenolics and their antioxidative activities. Analyses of the total phenolic content (TPC), total flavonoid content (TFC), o‐diphenols index, hydroxycinnamic acid index, flavonols index and phenol index showed ranges between 5.64 and 83.97 g L^?1 gallic acid equivalent (GAE), 0.31–7.53 g L^?1 catechin equivalent, 4.90–93.20 g L^?1 GAE, 23.74–77.46 g L^?1 ferulic acid equivalent, 3.62–95.33 g L^?1 rutin equivalent and 15.90–247.22 g L^?1 GAE, respectively. The antioxidant assay, 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging assay, showed antioxidative activities in all the extracts with results ranging from 4.41 to 61.98 g L^?1 trolox equivalent. The high antioxidant activities of the oil palm fruit phenolics were also found to increase with increasing TPC and TFC.     

Analysis of trans fatty acids in deep frying oils by three different approaches

Simulated frying experiments were performed on three different types of oils with French fries as the fried food. Comparison of frying oil samples was then made with their control counterparts (i.e. oil samples heated without food). Three different methods, gas chromatography (GC), attenuated total reflection (ATR) AOCS method Cd 14d-99 and attenuated total reflection negative second derivative absorbance (−2D ATR), were applied to quantify total trans fats. The total trans fats were found to be higher in the frying oil samples as compared to the control samples, which might be due to the presence of a high amount of trans fats in the pre-fried and frozen French fries. In general, the ATR AOCS method Cd 14d-99 produced lower amounts of trans fatty acids and the −2D ATR absorbance method produced higher amounts when compared with those obtained by gas chromatography.     

EFFECTS OF COOLANT SUPPLY METHODS AND CUTTING CONDITIONS ON TOOL LIFE IN END MILLING TITANIUM ALLOY

Titanium machining poses a great challenge to cutting tools due to its severe negative influence on tool life primarily due to high temperature generated and strong adhesion in the cutting area. Thus, various coolant supply methods are widely used to improve the machining process. On account of this, tool life and cutting force are investigated based on dry cutting, flood cooling, and minimum quantity lubrication (MQL) techniques. The experimental results show that MQL machining can remarkably and reliably improve tool life, and reduce cutting force due to the better lubrication and cooling effect.     

Study on orthogonal turning of titanium alloys with different coolant supply strategies

In this paper, the effects of different coolant supply strategies (using flood coolant, dry cutting, and minimum quantity of lubricant [MQL]) on cutting performance in continuous and interrupted turning process of Ti6Al4V are investigated. Based on the observation of the cutting forces with the different coolant supply strategies, the mean friction coefficient in the sliding region at the tool–chip interface has been obtained and used in a finite element method (FEM) to simulate the deformation process of Ti6Al4V during turning. From the FEM simulation and Oxley’s predictive machining theory, cutting forces have been estimated under different coolant supply strategies and verified experimentally.     

Efficacy of chlorine and peroxyacetic acid on reduction of natural microflora, Escherichia coli O157:H7, Listeria monocyotgenes and Salmonella spp. on mung bean sprouts

Sprouts-related outbreaks have risen due to increased raw sprouts consumption. To minimize such cases, chemical sanitations are applied. While chlorine is commonly used, concerns with its effectiveness and health implication have prompted researchers to seek alternatives. Peroxyacetic acid (PAA) has shown efficacy in inactivating foodborne pathogens on fresh vegetables, and hence could be considered as an alternative. Thus, the objective of this study was to compare the efficacy of chlorine and PAA in inactivating Escherichia coli O157:H7, Listeria monocytogenes, Salmonella spp., and natural microflora on mung bean sprouts. Resistance of non- and acid-adapted pathogens to these sanitizer treatments was also evaluated. Un-inoculated and inoculated sprouts were treated with chlorine at 106, 130 and 170 ppm and PAA at 25, 51 and 70 ppm for 90 and 180 s at room temperature. Overall, the greater log reductions were obtained with the increase in the sanitizer concentration. For 180 s, chlorine treatment at 170 ppm reduced 2.0, 1.3, 1.5, 0.9-logs and PAA treatment at 70 ppm resulted in 2.3, 1.8, 2.1, 1.1-log reductions for non-adapted E. coli O157:H7, L. monocytogenes, Salmonella spp., and natural microflora, respectively. These results revealed that the efficacy of PAA was significantly better than or similar to that of chlorine. For acid-adapted cells, these sanitizer treatments were less effective with the ranges of 1.0–1.2-log reductions for chlorine and 1.1–1.6-log reductions for PAA compared to non-adapted cells, indicating that acid-adapted cells were more resistant to the sanitizing treatment. These data suggest that PAA may replace chlorine in the disinfection of mung bean sprouts and that acid-adapted pathogens should be used to design an effective sanitizing strategy.     

Hydrogel‐mediated formation of living cartilage template for endochondral initiation

The use of hydrogel in cartilage tissue engineering is especially popular due to its high hydrophilic property which is similar to native cartilage matrix. Alginate hydrogel was used as a transient scaffold material to facilitate chondrocyte proliferation into a three‐dimensional scaffold‐free living hyaline cartilaginous graft (LhCG). As LhCG is purely cell‐based and has a marked resemblance to native hyaline cartilage, it served as an excellent in vitro platform for studying the endochondral ossification pathway. Due to the complexity of events involved throughout endochondral ossification, this study only focuses on early stages of the process where it involves chondrocyte hypertrophy and blood vessel invasion. Human umbilical vein endothelial cells (HUVECs) were selected as the target cells for possible endothelialization in the LhCG template. They were seeded onto the LhCG construct and subjected to vascular endothelial growth factor (VEGF) treatment. Results suggested that VEGF is indeed a potent driving force for initiation of the endochondral pathway. It alone is sufficient to induce hypertrophy in chondrocytes and the corresponding expression of osteogenic genes with or without the presence of HUVECs in the LhCG template. On the other hand, the effect of HUVECs in the LhCG system was less evident. It is hypothesized that this is attributed to the preservation of anti‐angiogenic properties in primary chondrocytes from the LhCG construct, inhibiting HUVECs from endothelialization in the LhCG+HUVEC construct. Based on the outcome from this study, it is recommended that hypertrophy in chondrocytes should be induced prior to endothelial cell introduction so that the microenvironment will be altered to favor angiogenesis within the cartilaginous template. © 2013 Society of Chemical Industry     

Miscible blends of poly(n-vinyl-2-pyrrolidone) with poly(3-chloropropyl methacrylate), poly(2-bromoethyl methacrylate) and poly(2-iodoethyl methacrylate)

Summary Poly(N-vinyl-2-pyrrolidone) is miscible with poly(3-chloropropyl methacrylate), poly(2-bromoethyl methacrylate) and poly(2-iodoethyl methacrylate) as shown by the optical clarity and the glass transition behaviour of the blends. The miscible blends degrade before phase separation could be induced by heating. The three T_g-composition curves can be fitted by the Gordon-Taylor equation. The implication of the Gordon-Taylor k parameters of the blends is discussed.     

Synthesis of Ultrafine β"-Alumina Powders via Flame Spray Pyrolysis of Polymeric Precursors

Flame spray pyrolysis of a polymeric precursor is used to prepare ultrafine powders that, when sintered, convert to essentially pure phase lithium-doped sodium β"-alumina. The precursor Na_1.67 Al_10.67 Li_0.33 [N(CH₂CH₂O)₃]_10.67-[OCH₂CH₂O]·x(HOCH₂CH₂OH) has been synthesized from stoichiometric amounts of metal hydroxides and tri-ethanolamine (N(CH₂CH₂OH)₃, TEA) in excess ethylene glycol. The precursor is dissolved in ethanol, and an atom-ized spray of the solution is combusted in a specially con-structed flame spray apparatus. Combustion occurs at ∼2000°C, followed by immediate quenching. This proce-dure provides for a measure of kinetic control over the process. The resulting nanopowder particles are 50–150 nm in diameter and exhibit powder X-ray diffractometry pat-terns similar to β"-alumina. Heating the nanopowder at 30°C/min to 1200°C with a 1 hisotherm converts it to pure β"-alumina. In preliminary sintering studies, green powder compacts (∼65% theoretical density) sintered at 1600°C for 12 min densify to 3.0 ± 0.1 g/cm 3 (∼92% theoretical density) with minimal loss of Na₂O. This procedure offers several processing and cost advantages over conventional β"-alumina syntheses.