Improved closed-form bounds on the performance of convolutional codes with correlated Rayleigh fading

New bounds on the probability of bit error are presented for a coded communication system with binary antipodal modulation and soft-decision maximum-likelihood decoding over a correlated Rayleigh-fading channel. The bounds are closed-form expressions in terms of the code\u27s transfer function; they are illustrated by considering a system using convolutional encoding. A long-standing conjecture regarding the worst-case error event in correlated Rician fading is proven for the special case of correlated Rayleigh fading, and it is used in the development of some of the new bounds. The bounds are shown to be tighter than previously developed closed-form bounds for communications using convolutional codes in correlated Rayleigh fading

CHARACTERIZATION OF HEAVY METAL REMOVAL FROM AQUEOUS SOLUTIONS USING NATURAL FIBER IMPREGNATED WITH METALLIC NANOPARTICLES

Heavy metals are found in varying concentrations in anthropogenically influenced water sources including waste water discharge from mining operations. The heavy metals need to be removed to meet applicable discharge standards and to eliminate potential health effects. There has been substantial research recently in the field of water treatment technologies to produce low-cost materials that have metal-binding capabilities. The goal of this research is to characterize the toxic metal removal capabilities of a novel, low cost water treatment system. This research uses a natural fiber substrate and incorporates specific nanometallic particles to remove toxic heavy metals from water. Natural fiber (NF) and metallic nanoparticle treated fiber (MNP) were subjected to various concentrations of copper, cadmium, nickel, and zinc. The research included kinetic experiments, adsorption isotherm experiments, and flow through column tests. The results indicated that the fibers performed consistently well in removing copper with all metal removal efficiencies between 41%-58% for NF and 56%-77% for MNP in a mixed metal solution where the metals were each present at 1 mg/L. NF and MNP were both found to follow a pseudo first order kinetic adsorption model and had processes that followed Langmuir and Freundlich isotherms. MNP was able to reduce initial metals concentrations of 1 mg/L by 50% in 10-30 minutes whereas NF took 20-50 minutes. Metal adsorption is mass transfer limited and concentration gradients appear to be the driving force behind the adsorption rate. Flow through column tests using synthetic mixtures of the four metals of concern, showed consistently high reduction in copper ranging from 78%-90%. Zinc consistently had the lowest removal efficiency and ranged between 24%-62%. A fortified mine tailing water solution with metals was also tested and removal efficiencies reached as high as 87%. MNP performed better overall in experimentation than NF. The fiber filter system is proven to be effective for treating heavy metal contamination from industrial waste streams

A crust and upper mantle model of Eurasia and North Africa for Pn travel time calculation

We develop a Regional Seismic Travel Time (RSTT) model and methods to account for the first-order effect of the three-dimensional crust and upper mantle on travel times. The model parameterization is a global tessellation of nodes with a velocity profile at each node. Interpolation of the velocity profiles generates a 3-dimensional crust and laterally variable upper mantle velocity. The upper mantle velocity profile at each node is represented as a linear velocity gradient, which enables travel time computation in approximately 1 millisecond. This computational speed allows the model to be used in routine analyses in operational monitoring systems. We refine the model using a tomographic formulation that adjusts the average crustal velocity, mantle velocity at the Moho, and the mantle velocity gradient at each node. While the RSTT model is inherently global and our ultimate goal is to produce a model that provides accurate travel time predictions over the globe, our first RSTT tomography effort covers Eurasia and North Africa, where we have compiled a data set of approximately 600,000 Pn arrivals that provide path coverage over this vast area. Ten percent of the tomography data are randomly selected and set aside for testing purposes. Travel time residual variance for the validation data is reduced by 32%. Based on a geographically distributed set of validation events with epicenter accuracy of 5 km or better, epicenter error using 16 Pn arrivals is reduced by 46% from 17.3 km (ak135 model) to 9.3 km after tomography. Relative to the ak135 model, the median uncertainty ellipse area is reduced by 68% from 3070 km{sup 2} to 994 km{sup 2}, and the number of ellipses with area less than 1000 km{sup 2}, which is the area allowed for onsite inspection under the Comprehensive Nuclear Test Ban Treaty, is increased from 0% to 51%

Controlling Solvation and Mass Transport Properties of Biobased Solvents through CO2 Expansion: A Physicochemical and Molecular Modeling Study

Gas-expanded liquids have been studied during past years; however, the physicochemical properties of some of these fluids still need to be characterized and understood. In particular, the study of properties concerning solvation and mass transport is key for industrial applications. This work presents the characterization of eight CO2-expanded biosourced solvents: organic carbonates (dimethyl, diethyl, ethylene, and propylene carbonates), anisole, veratrole, γ-valerolactone, and 2-methyltetrahydrofuran. Two approaches have been used: spectroscopic measurements and molecular modeling. Phase equilibrium was determined for each CO2/biosourced solvent system, and then the solvatochromic probe Nile Red was used to determine changes in dipolarity/polarizability (π* Kamlet–Taft parameter) by CO2 pressure. Molecular dynamics calculations were performed to determine the density and viscosity changes with CO2 pressure. It is shown in this study that the degree of modulation of dipolarity/polarizability parameter can go from that of pure solvent (around 0.4 for linear organic carbonates) to negative values, close to that of pure CO2 at the T and P used in this study. Concerning transport properties, such as density and viscosity, a great decrease in both these properties’ values was observed after swelling of the solvent by CO2, for instance, in linear organic carbonates where density can decrease to 50% the density of pure solvent; concerning viscosity a decrease of up to 90% was measured for these compounds. It was observed that the solubility of CO2 and then modulation of properties were higher in linear organic carbonates than in the cyclic ones. This study shows once more that CO2 has a great capacity to be used as a knob for triggering changes in the physicochemical properties of green biosourced solvents that can help to implement these solvents in industrial applications

Tomography and Methods of Travel-Time Calculation for Regional Seismic Location

We are developing a laterally variable velocity model of the crust and upper mantle across Eurasia and North Africa to reduce event location error by improving regional travel-time prediction accuracy. The model includes both P and S velocities and we describe methods to compute travel-times for Pn, Sn, Pg, and Lg phases. For crustal phases Pg and Lg we assume that the waves travel laterally at mid-crustal depths, with added ray segments from the event and station to the mid crustal layer. Our work on Pn and Sn travel-times extends the methods described by Zhao and Xie (1993). With consideration for a continent scale model and application to seismic location, we extend the model parameterization of Zhao and Xie (1993) by allowing the upper-mantle velocity gradient to vary laterally. This extension is needed to accommodate the large variation in gradient that is known to exist across Eurasia and North African. Further, we extend the linear travel-time calculation method to mantle-depth events, which is needed for seismic locators that test many epicenters and depths. Using these methods, regional travel times are computed on-the-fly from the velocity model in milliseconds, forming the basis of a flexible travel time facility that may be implemented in an interactive locator. We use a tomographic technique to improve upon a laterally variable starting velocity model that is based on Lawrence Livermore and Los Alamos National Laboratory model compilation efforts. Our tomographic data set consists of approximately 50 million regional arrivals from events that meet the ground truth (GT) criteria of Bondar et al. (2004) and other non-seismic constraints. Each datum is tested to meet strict quality control standards that include comparison with established distance-dependent travel-time residual populations relative to the IASPIE91 model. In addition to bulletin measurements, nearly 50 thousand arrival measurements were made at the national laboratories. The tomographic method adjusts Pn velocity, mantle gradient, and a node-specific crustal slowness correction for optimized travel-time prediction

Radial Temperature Differences During the Melt Spinning of Fibers

The production of glass and synthetic fibers by melt spinning is an important industrial process. Mathematical models of the process are needed to study the effects of rapid cooling and draw-down in the quench zone. In this investigation, a numerical model was developed to predict the temperature distribution in the fiber during melt spinning. This model uses the finite difference method to solve the governing differential equation for the problem. An estimate of the physical shape of the fiber was obtained by a fourth-order Runge-Kutta solution of a model presented in the literature (4 , 5) . This radius profile model compared favorably with experimental data reported by Harris (3) . The numerical model developed during this investigation was applied to a series of numerical experiments on glass fiber processing. These simulations used typical sets of operating conditions to see the effect of various operating parameters on the predicted radius profile , spin-line tension, and temperature distribution. The effects of spinneret capillary diameter, mass flow rate, ambient air temperature, spinning temperature, and elongational viscosity were investigated. For a typical set of operating conditions (Run Number 1) for the melt spinning of the glass studied, the predicted spinline tension was 3.28 x 10^-4 N, the solidification point was 0.03852 m, the radial temperature difference at the solidification point was 4.774 K, and the maximum radial temperature dif:erence was 10.231 K and occurred at an axial position of 0.00915 m. The results of the various runs showed that ambient air temperature and mass flow rate had a significant effect on the predicted radius profile, spinline tension , and temperature distribution. The spinning temperature was an important parameter, but its only significant effect was on the spinline tension. Spinneret capillary diameter and elongational viscosity had little effect on the predicted results