Adaptive bit loading scheme using COFDM at low elevation over LEOsatellite communication channel

Much interest has been shown in employing LEO satellite communication systems. A novel algorithm is proposed for adaptive bit loading (multilevel modulation assignment) between COFDM subcarriers in a frequency selective fading channel. Two-dimensional alignment has been carried out. The system performance is greatly improved at low elevation angles compared to that using fixed bit loading. Furthermore. The comparison shows that this adaptive bit loading COFDM system is suitable for frequency selective slow fading channels, which have time-varying deep nulls in the frequency response     

Maximum Likelihood Sequence Detection for QPSK on Nonlinear, Band-Limited Channels

A receiver structure based on maximum likelihood sequence estimation (MLSE) for receiving quaternary phase shift keyed signals over band-limited, nonlinear satellite channels, in the presence of additive downlink Gaussian noise, is derived. This work is an extension of work done by Mesiya et al. [2] for binary PSK transmission. Error performance of the receiver at low to moderate signal-to-noise ratios is estimated using computer simulation. For moderate to high signal-to-noise ratios, an upper bound on the probability of symbol error is obtained. A suboptimum receiver structure is then developed and its performance evaluated using computer simulation. It is shown that the performance of the suboptimum receiver is very close to that of the MLSE receiver.     

Make3D: Learning 3D Scene Structure from a Single Still Image

We consider the problem of estimating detailed 3D structure from a single still image of an unstructured environment. Our goal is to create 3D models that are both quantitatively accurate as well as visually pleasing. For each small homogeneous patch in the image, we use a Markov Random Field (MRF) to infer a set of "plane parameters” that capture both the 3D location and 3D orientation of the patch. The MRF, trained via supervised learning, models both image depth cues as well as the relationships between different parts of the image. Other than assuming that the environment is made up of a number of small planes, our model makes no explicit assumptions about the structure of the scene; this enables the algorithm to capture much more detailed 3D structure than does prior art and also give a much richer experience in the 3D flythroughs created using image-based rendering, even for scenes with significant nonvertical structure. Using this approach, we have created qualitatively correct 3D models for 64.9 percent of 588 images downloaded from the Internet. We have also extended our model to produce large-scale 3D models from a few images.     

Ethanol steam reforming study over ZSM-5 supported cobalt versus nickel catalyst for renewable hydrogen generation

The renewable hydrogen generation through ethanol steam reforming is one of the anticipated areas for sustainable hydrogen generation. To elucidate the role of Ni and Co with ZSM-5 support, catalysts were prepared by wet impregnation method and ethanol steam reforming(ESR) was performed. The catalysts were characterized by HR-XRD, ATR–FTIR, HR-SEM, TEM with SAED, EDAX, surface area analyzer and TPR. It had shown complete ethanol conversion at 773 K, but the selectivity in hydrogen generation was found higher for 10% Ni/ZSM-5 catalyst as compared to 10% Co/ZSM-5. The 10% Ni/ZSM-5 catalyst has about 72% hydrogen selectivity at temperature 873 K. It indicates that Ni is a more sustainable catalyst as compared to Co with ZSM-5 support for ESR. The C_2H_4 was found major undesirable products up to 823 K temperature. Nevertheless, the 10% Ni/ZSM-5 catalyst had shown its stability for high temperature(873 K) ESR performance.     

Spark plasma sintering to restrict sintering reactions and enhance properties of hydroxyapatite–mullite biocomposites

Herein, we demonstrate how spark plasma sintering (SPS) can be useful in restricting the sintering reactions and faster densification in Hydroxyapatite–Mullite system, which otherwise shows extensive sintering reactions during conventional pressureless sintering, as reported in a recent study [Nath et al. J. Am. Ceram. Soc. 93 (2010) 1639–1649]. The microstructure of SPSed Hydroxyapatite (HAp)-20 wt% mullite composites was characterized by submicron sized HAp and equiaxed mullite grains. Another important result has been the achievement of higher hardness of 7 GPa, which is much higher than pressureless sintered composites. The cell culture study including cellular viability using MTT analysis establishes good cytocompatibility of SPSed composites.     

Preparation of carbon molecular sieves from carbon micro and nanofibers for sequestration of CO2

In this study, a hierarchal web of carbon micro and nanofibers was used as a precursor for the synthesis of a carbon molecular sieve (CMS). CMSs were prepared by thermal treatment of carbon fibers using a microwave heating device. The heating power and treatment time were optimized for the maximum performance of the prepared CMS for the separation of CO₂ at low concentrations from the gaseous mixture of CO₂ and air under dynamic (flow) conditions. Based on the experimental data, microwave power input of 240 W and treatment time of 15 min were found to be suitable for the maximum uptake of CO₂ by CMS. Adsorption breakthrough curves were obtained at different gas flow rates and CO₂ concentrations. CMSs prepared from the hierarchal web of carbon micro and nanofibers were found to be superior to those prepared from ACF. The CO₂ uptake was determined to be approximately 0.88 mg/g and 10 mg/g at concentrations of 500 ppm and 5000 ppm, respectively, in air.     

Study of relaxations in poly(methyl methacrylate)–magneto electrets by thermally stimulated depolarization current and surface‐charge‐decay mechanisms

The effect of the forming temperature and the magnetic field was investigated for the charge retention and stability of poly(methyl methacrylate) (PMMA)–magneto electret (ME) samples with thermally stimulated discharge currents (TSDCs) and a surface‐charge‐decay mechanism. The measurements were performed on a pristine PMMA sample with a thickness of 20 mm. The comparative studies of charge decay with TSDC indicated a strong resemblance between the results of the two techniques of MEs of PMMA and were characterized by two TSDC peaks, that is, an α peak at 110°C and a ρ peak at 160°C. The low‐temperature peak (i.e., the α peak) was associated with dipolar relaxation, and the high‐temperature peak (i.e., the ρ peak) was attributed to the self‐motion of space charges in PMMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Pulsed Electrical Stimulation and Surface Charge Induced Cell Growth on Multistage Spark Plasma Sintered Hydroxyapatite‐Barium Titanate Piezobiocomposite

The primary purpose of the present work was to illustrate whether cell proliferation can be enhanced on electroactive bioceramic composite, when the cells are cultured in the presence of external electrical stimulation. The two different aspects of the influence of electric field (E‐field) application toward stimulating the growth/proliferation of bone/connective tissue cells in vitro, (a) intermittent delivery of extremely low strength pulsed electrical stimulation (0.5–4 V/cm, 400 μs DC pulse) and (b) surface charge generated by electrical poling (10 kV/cm) of hydroxyapatite (HA)‐BaTiO₃ piezobiocomposite have been demonstrated. The experimental results establish that the cell growth can be enhanced using the new culture protocol of the intermittent delivery of electrical pulses within a narrow range of stimulation parameters. The optimal E‐field strength for enhanced cellular response for mouse fibroblast L929 and osteogenic cells is in the range of 0.5–1 V/cm. The MTT [3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyl tetrazolium bromide] assay results suggested the increased viability of E‐field treated cells over 7 d in culture, implicating the positive impact of electrical pulses on proliferation behavior. The alizarin red assay results showed noticeable increase in Ca‐deposition on the E‐field treated samples in comparison to their untreated counterparts. The negatively charged surfaces of developed piezocomposite stimulated the cell growth in a statistically noticeable manner as compared with the uncharged or positively charged surfaces of similar composition.