Performance of IJF-OQPSK and Partial Response (PR) IJF-OQPSK Modems in a Nonlinearly Amplified and Adjacent-Channel Interference Satellite Environment

The performance of intersymbol-interference and jitterfree offset-QPSK (IJF-OQPSK) and partial-response (PR) IJFOQPSK modems in a nonlinearly amplified multichannel environment is studied and compared to that of conventional QPSK and OQPSK modems. Power efficiency is maximized by operating the high-power amplifier (HPA) in full saturation. The effect of adjacent-channel interference and flat fade on the performance of illustrative nonlinear satellite systems is investigated. Simulation and measurement results are reported. It is shown that both IJF-OQPSK and PR-IJF-OQPSK modems exhibit a significant performance improvement compared to QPSK and OQPSK modems, in illustrative SCPC and on-board regenerative satellite systems, they provide an improvement of more than 4 dB compared to QPSK.     

Statistical analysis of the disorder of two-dimensional cellular arrays in directional solidification

By introducing a weighted Wigner-Seitz construction and, for the first time in directional solidification, using the minimal spanning tree (MST) approach and the (m,σ)-diagram, the statistical analysis of the topological defects and disorder of two-dimensional (2-D) cellular arrays has been carried out. For “standard” growth of massive Pb-30 wt pct Tl alloys, the underlying honeycomb has been brought out, which was rather unexpected, as the percentage of defects is so high that the cellular arrays are “melted” by the defects, with a structure close to that of a 2-D liquid. Furthermore, disorder can be described by a Gaussian noise applied on an array of hexagonal cells, Lewis's law is satisfied, and for a sufficiently large number of cells, a peak is evidenced in the primary spacing distribution, which indicates that, in some way, the cell size is selected. Nevertheless, the associated standard deviation is rather large. It is conceivable that the defects can have a leading role in the selection of the primary spacing.     

Electrochemical oxidation of organyl-2,2-dichlorovinyl sulfides and 1,2-bis(organylchalcogeno)-1,2-dichloroethylenes

Two steps were observed in the electrochemical oxidation of organyl-2,2-dichlorovinyl sulfides RSCHCCl₂. Macroscale electrolyses gives, respectively the sulfoxides (at the first step) and the sulfones (at the second step). This method offers advantage over the chemical oxidation. With 1,2-bis(organylchalcogeno)-1,2-dichloroethylenes RYCClCClYR (Y=S, Se, Te) selectivity was not so high, the main product being the bis-sulf(selen)oxide.     

A Digital Approach to Symbol Timing Recovery Systems

An analysis of a symbol timing recovery (STR) technique using digital processing is presented. The ratio of the discrete spectral power at the symbol rate frequency to the nearby continuous spectral power is used as a criterion of STR performance. It is shown that this power ratio equals the quality factor of the narrow bandpass filter and that it does not depend on the value of the delay element. The performance of the STR subsystem is consequently determined by the quality factor of the bandpass filter rather than by the specific delay. In addition to this, some experimental evidence that the additive channel noise has little effect on the power ratio is given. A modified phase-locked loop with anLCprefiiter is proposed to extract the symbol timing clock. This prefilter improves the acquisition and synchronization performance of the PLL. The STR technique presented here has the advantages of lower cost and simpler hardware implementation over other serial STR techniques.     

Partial Decellularized Scaffold Combined with Autologous Nasal Epithelial Cell Sheet for Tracheal Tissue Engineering

Decellularization has emerged as a potential solution for tracheal replacement. As a fully decellularized graft failed to achieve its purposes, the de-epithelialization partial decellularization protocol appeared to be a promising approach for fabricating scaffolds with preserved mechanical properties and few immune rejection responses after transplantation. Nevertheless, a lack of appropriate concurrent epithelialization treatment can lead to luminal stenosis of the transplant and impede its eventual success. To improve re-epithelialization, autologous nasal epithelial cell sheets generated by our cell sheet engineering platform were utilized in this study under an in vivo rabbit model. The newly created cell sheets have an intact and transplantable appearance, with their specific characteristics of airway epithelial origin being highly expressed upon histological and immunohistochemical analysis. Subsequently, those cell sheets were incorporated with a partially decellularized tracheal graft for autograft transplantation under tracheal partial resection models. The preliminary results two months post operation demonstrated that the transplanted patches appeared to be wholly integrated into the host trachea with adequate healing of the luminal surface, which was confirmed via endoscopic and histologic evaluations. The satisfactory result of this hybrid scaffold protocol could serve as a potential solution for tracheal reconstructions in the future.     

New criteria for exponential stability of nonlinear time‐varying differential systems

General nonlinear time‐varying differential systems are considered. An explicit criterion for exponential stability is presented. Furthermore, an explicit robust stability bound for systems subjected to nonlinear time‐varying perturbations is given. In particular, it is shown that the generalized Aizerman conjecture holds for positive linear systems. Some examples are given to illustrate obtained results.Copyright © 2012 John Wiley & Sons, Ltd.     

Hydroxyapatite starting from calcium carbonate and orthophosphoric acid: synthesis,characterization, and applications

Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂], Ca-HA, is the emblematic mineral phase of bones, and is known for its complexity and difficult to reproduce chemical synthesis. Among the routes developed for obtaining this calcium phosphate, the so-called double-decomposition method is well described and often utilized. However, the Ca-HA synthesized by this way forms a larger mass of ammonium nitrate by-product than the desired product itself. Pure Ca-HA for orthopedic or dental applications usually uses thermal treatment to eliminate residual nitrogen compounds by releasing them in the atmosphere. Contemporary sol–gel methods currently in fashion produce even more degradation products including solvents and precursor organics. We now report on a green synthesis procedure which makes pure Ca-HA with minimum by-product. The synthesis calls for reacting phosphoric acid with calcium carbonate in water suspension to form a Ca-HA gel of fine particles. This gel can be filtered and the solids recovered, dried, and sintered, but can also be used as-is for environmental applications such as heavy metal ions or textile dye removal from polluted waste streams. This green Ca-HA has been used to trap heavy metals in flue gases and in municipal waste water treatment plants. This low-cost and low-environmental impact material can be developed for medical use because of its absence of impurities, and in catalytic productions for remediation of many environmental problems. Recent results show Ca-HA can also serve in reforming biogas compositions into useful products, after deposition of selected metal elements. Some of these results will be communicated in this paper.     

Morphology-controlled synthesis and electrocatalytic characteristics of platinum structures on micro-patterned carbon nanotube platforms

In this study, platinum particles were fabricated on flexible, transparent, single-walled carbon nanotube films without the addition of reducing or protecting agents using a facile and controllable electrochemical method. Spherical platinum particles (SPPs) were transformed into flower-like platinum particles (FPPs) by varying the applied potential, the pattern size of the photoresist polymer, and the deposition time. An analysis of the X-ray diffraction data revealed that the FPPs possessed a face centered cubic structure. The intensity ratio of (111) to (200) diffraction lines for the FPPs (2.15) was greater than that of the SPPs (1.44), indicating that the as-prepared FPPs were dominated by the lowest-energy (111) facets. The electrocatalytic activities of the synthesized particles with regard to methanol and formic acid oxidation were investigated. The FPPs exhibited higher catalytic performance for the electrochemical oxidation of methanol and formic acid than the SPPs. The high oxidation current of the FPP-based electrode was directly related to the morphologies of the platinum particles. The simple approach employed in this study will be useful for fabricating particles of other noble metals with different morphologies.     

Organic Aerosol Speciation: Intercomparison of Thermal Desorption Aerosol GC/MS (TAG) and Filter-Based Techniques

We compared measurements of organic molecular markers made using a novel Thermal Desorption Aerosol Gas Chromatograph/Mass Spectrometer (TAG) with two offline filter-based methods: solvent extraction GC/MS (SE-GC/MS) and thermal desorption GC/MS (TD-GC/MS). TAG is designed for automated, high time-resolved measurements of organic aerosol speciation. Laboratory and field measurements were performed to compare TAG and filter performance for n-alkanes, n-alkanoic acids, cholesterol, PAHs, and hopanes. Laboratory measurements of model organic aerosol mixtures of known composition were made in the Carnegie Mellon University smog chamber, and field measurements were made in downtown Pittsburgh. There was excellent agreement between techniques for hopanes and several PAHs, which are important markers for motor vehicle emissions. Agreement was also strong for moderately polar and nonpolar species in the high-concentration smog chamber experiments. Poorer agreement between filter and TAG observations was obtained for n-alkanes in ambient measurements. To further investigate the differences in n-alkane performance between these methods, potential matrix effects and internal consistency within the TAG and filter ambient air data sets were examined. We spiked a subset of ambient TAG samples with deuterated internal standards to examine potential matrix effects. Under typical conditions, there was little bias in recovery of deuterated standards. At extreme ambient aerosol levels, however, there were large biases in relative recovery, indicating matrix effects may be important under those conditions. Similar results were observed in laboratory experiments with engine lubricating oil. Applying internal standards in the TAG system would help track and correct for matrix effects influencing compound recovery.     

Analysis of a swimming sperm in a shear flow

Microfluidic devices exhibit many attractive characteristics for separation of motile sperms from the non-motile ones. The motility of swimming sperms is critical to a successful fertilization. In this paper, we examine the shear effect of microfluidic flow on a swimming sperm. We employ the resistive force theory to compute the hydrodynamic forces acting along the flagellum of the sperm and investigate the beating pattern of the flagellum as well as the sperm’s swimming velocity. We found that the shape of the flagellum is significantly affected by high shear rate which in turn affects the swimming velocity. Both negative and positive shear rates contribute to a higher swimming velocity of the sperm, and the effects of negative and positive shear rates can only be distinguished at high sperm number. Furthermore, we found that sperms with smaller heads swim faster. Our findings here can be applied to enhance performance of sperm separation and sorting devices.