Discrete Dynamical System Framework for Construction of Connections between Critical Regions in Lattice Height Data

We define a new mathematical model for the topological study of lattice height data. A discrete multivalued dynamical system framework is used to establish discrete analogies of a Morse function, its gradient field, and its stable and unstable manifolds in order to interpret functions numerically given on finite sets of pixels. We present efficient algorithms detecting critical components of a height function f and displaying connections between them by means of a graph, called the Morse connections graph whose nodes represent the critical components of f and edges show the existence of connecting trajectories between nodes. This graph encodes efficiently the topological structure of the data and makes it easy to manipulate for subsequent processing.

Fluctuating target detection in presence of non Gaussian clutter in OFDM radars

Today, Orthogonal Frequency Division Multiplexing (OFDM) radars are very interested in detection of low Radar Cross Section (RCS) targets. A vast number of research work has been reported about target detection in OFDM radars. But all these papers concern detection in presence of Gaussian interference and also assume that target has a constant scattering coefficient or RCS. In this paper, we present a Generalized Likelihood Ratio (GLR) detector for detecting a moving target in presence of Gaussian interference and evaluate its performance in presence of different types of clutter distribution and target fluctuation. We assume three scenarios for detecting a fluctuating target in the presence of four different distributions of clutter; Rayleigh, Log-normal, Weibull and K-compound. In the first scenario, we consider the RCS's of target are constant subcarrier to subcarrier and pulse to pulse in a burst of pulses while they are varying fast according to Chi-square probability density function (swerling case II) burst to burst. In the second scenario, we assume that the RCS of target varies slowly according to Chi-square probability density function (swerling case I) subcarrier to subcarrier and they are constant pulse to pulse in a burst of pulses while they are varing fast according to Chi-square probability density function burst to burst. And in the third scenario, we assume the scattering coefficients of target are varing fast subcarrier to subcarrier and burst to burst, while they are constant pulse to pulse in a burst of pulses. We provide a few numerical examples to illustrate the detection performance of moving target under conditions of three scenarios, fluctuating models and different distributions of clutter and demonstrate the achieved performance improvement due to the OFDM signaling.     

Time and power scheduling in an ad hoc network with bidirectional relaying and network coding

Network coding (NC) is a technique that allows intermediate nodes to combine the received packets from multiple links and forwarded to subsequent nodes. Compared with pure relaying, using NC in a wireless network, one can potentially improve the network throughput, but it increases the complexity of resource allocations as the quality of one transmission is often affected by the transmission conditions of multiple links. In this paper, we consider an ad hoc network, where all the links have bidirectional communications, and a relay node forwards traffic between the source and the destination nodes using NC. All transmissions share the same frequency channel, and simultaneous transmissions cause interference to each other. We consider both digital NC and analog NC strategies, referred to as DNC and ANC, respectively, and schedule transmission time and power of the nodes in order to maximize the overall network throughput. For DNC, an optimum scheduling is formulated and solved by assuming that a central controller is available to collect all the link gain information and make the scheduling decisions. Distributed scheduling schemes are proposed for networks using DNC and ANC. Our results indicate that the proposed scheduling scheme for DNC achieves higher throughput than pure relaying, and the scheduling scheme for ANC can achieve higher throughput than both DNC and pure relaying under certain conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Slip flow forced convection in a microchannel with semi-circular cross-section

This paper offers theoretical results for fully developed slip-flow forced convection through a microchannel of semicircular cross-section. Numerical results are also presented to study the developing region. Velocity slip and temperature jump boundary conditions are applied at the uniformly heated walls. The results from the two different sources are cross validated and those pertaining to the limiting case of no-slip flow are found to be in good agreement with those available in the literature.     

Modeling the Transformation of Chromophoric Natural Organic Matter during UV/H2O2 Advanced Oxidation

This research developed a differential kinetic model to predict the partial degradation of natural organic matter (NOM) during ultraviolet plus hydrogen peroxide (UV/H2O2) advanced oxidation treatment. The absorbance of 254?nm UV, representing chromophoric NOM (CNOM) was used as a surrogate to track the degradation of NOM. To obtain reaction rate constants not available in the literature, i.e., reactions between the hydroxyl radical (?OH) and NOM, experiments were conducted with “synthetic” water, using isolated Suwannee River NOM, and parameter estimation was applied to obtain the unknown model parameters. The reaction rate constant for the reaction between ?OH and total organic carbon (TOC), k?OH,TOC, was estimated at 1.14(±0.10)×104??L?mg-1?s-1, and the reaction rate constant between ?OH and CNOM, k?OH,CNOM, was estimated at 3.04(±0.33)×104??L?mol-1?s-1. The model was evaluated on two natural waters to predict the degradation of CNOM and H2O2 during UV/H2O2 treatment. Model predictions of CNOM degradation agreed well with the experimental results for UV/H2O2 treatment of the natural waters, with errors up to 6%. For the natural water with additional alkalinity, the model also predicted well the slower degradation of CNOM during UV/H2O2 treatment, owing to scavenging of ?OH by carbonate species. The model, however, underpredicted the degradation of H2O2, suggesting that, when NOM is present, mechanisms besides the photolysis of H2O2 contribute appreciably to H2O2 degradation.     

Atomic ordering and magnetism in L10 ordered FePd alloys

Intermetallic compounds due to their promising corrosion resistance and high-temperature mechanical strength give hope for their application as high-temperature structural materials. Inter-metallics of L1₀ type structure in recent years in addition have attracted great interest as potential recording media. These alloys are ferromagnetic and display marked mechanical and magnetic anisotropy with the tetragonal c-axis of the ordered domains as the “easy axis” of magnetization High-density magnetic recording may be achieved by a preferential domain orientation with the c-axis perpendicular to the surface, if these materials can be stabilized as low-dimensional magnetic structures. Knowledge of kinetic parameters, that determine alloy stability is essential for alloy design. technical application, and performance of materials. We used FePd as a model system for this class of L1₀-ordered intermetallics and have studied the changes of long-range order during heat treatments in the bulk and in thin films produced by different techniques. Results of X-ray diffraction (XRD). resistivity measurement. Mößbauer spectroscopy, and measurement of magnetization in both geometries are compared.     

A hybrid fuzzy group decision support framework for advanced-technology prioritization at NASA

The prioritization of advanced-technology projects at the National Aeronautic and Space Administration (NASA) is a difficult task. This difficulty is due to the multiple and often conflicting objectives in addition to the inherent technical complexities and valuation uncertainties involved in the assessment process. As such, a systematic and transparent decision support framework is needed to guide the assessment process, shape the decision outcomes and enable confident choices to be made. Methods for solving Multi-Criteria Decision Making (MCDM) problems have been widely used to select a finite number of alternatives generally characterized by multiple conflicting criteria. However, applying these methods is becoming increasingly difficult for technology assessment in the space industry because there are many emerging risks for which information is not available and decisions are made under significant uncertainty. In this paper, we propose a hybrid fuzzy group decision support framework for technology assessment at NASA. The proposed objective framework is comprised of two modules. In the first module, the complicated structure of the assessment criteria and alternatives are represented and evaluated with the Analytic Network Process (ANP). In the second module, the alternative advanced-technology projects are ranked using a customized fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). We demonstrate the applicability of the proposed framework through a case study at the Kennedy Space Center.     

Toward a comprehensive subjective evaluation of VoIP users’ quality of experience (QoE): a case study on Persian language

Multimedia Tools and Applications - Quality of Experience (QoE) measures the overall quality of a service from users’ point of view by considering several system, human, and contextual...