Christopher Paolini

Cell Zooming for Power Efficient Base Station Operation

With enormous growth in the telecommunication industry, energy efficiency has become a critical issue. Base stations and the core network account for a large amount of energy consumption today. Traditional energy saving techniques switch some base stations off completely during light loads to save energy. This creates problems for the backhaul network and also for quickly returning to full capacity when demand increases. In this paper, we propose novel cell zooming techniques to reduce energy consumption at base stations. With cell zooming, base stations dynamically adjust their coverage radius and hence their transmit powers based on user locations. The transmit power is set to the minimum required level depending on user locations, signal to interference and noise ratio (SINR) and quality of service (QoS) requirements of the users. Base stations are never completely switched off. Our simulations show that the proposed cell zooming algorithm reduces the energy consumption of base stations by up to 40% compared to traditional static-coverage-area base stations without compromising on the QoS requirements of any user in the cell.

A Web Service Infrastructure for Thermochemical Data

W3C standardized Web Services are becoming an increasingly popular middleware technology used to facilitate the open exchange of chemical data. While several projects in existence use Web Services to wrap existing commercial and open-source tools that mine chemical structure data, no Web Service infrastructure has yet been developed to compute thermochemical properties of substances. This work presents an infrastructure of Web Services for thermochemical data retrieval. Several examples are presented to demonstrate how our Web Services can be called from Java, through JavaScript using an AJAX methodology, and within commonly used commercial applications such as Microsoft Excel and MATLAB for use in computational work. We illustrate how a JANAF table, widely used by chemists and engineers, can be quickly reproduced through our Web Service infrastructure.

The Mimetic Methods Toolkit: An object-oriented API for Mimetic Finite Differences

Abstract We introduce the Mimetic Methods Toolkit (MTK), an object-oriented Application Programming Interface, implementing Mimetic Finite Differences to assist in the development of scientific applications where the numerical solution of Partial Differential Equations is required. The MTK’s design is based on a variant of the Castillo–Grone Method for the construction of discrete differential operators that mimic important properties of their continuous counterparts. The MTK is built as a collection of abstract and concrete classes, thus allowing for an extensible framework, which fosters code reutilization, while intuitively educating the user about the theoretical aspects of Mimetic Finite Differences. We present an overview to Mimetic Finite Differences, and we discuss the computational modeling of the related concepts; in this way, we explain how the MTK implements these methods. In this article, we present examples to illustrate the MTK’s usage philosophy and the validity of the implementation of the MTK by comparing our results with previously studied reference solutions.

An ANFIS-based multi-sensor structure for a mobile robotic system

The control of a nonlinear system is a challenging problem particularly when the system has some uncertainty or there are imperfections in the model dynamics. One approach that has gained some success employs a fuzzy structure in concert with a neural network (ANFIS); the fuzzy component compensates for the uncertainty while the neural network component models the underlying system dynamics. This paper presents a system architecture for a mobile robotic system that employs an ANFIS controller for path tracking, a virtual field strategy for obstacle avoidance and path planning, and multiple sensors (an ultrasonic array, a thermal sensor, and a video streaming system) to obtain information about the environment. Simulation results and preliminary evaluation show that the proposed architecture is a feasible one for autonomous mobile robotic systems.

An Object-Oriented Online Tool for Solving Generalized Chemical Equilibrium Problems

Analysis of chemical equilibria is a topic covered in both undergraduate and graduate courses such as physical chemistry, chemical thermodynamics, and engineering thermodynamics. Manual calculation of problems that require a student to solve for species concentrations, partial pressures, or mole fractions usually involve the method of equilibrium constants. Exercises in homework assignments or in-class examinations are frequently limited to reactions that involve no more than four gas phase species as the resulting arithmetic required to solve for the unknown quantity becomes too cumbersome and prone to error. Students who invest the requisite time in manually solving complex equilibrium problems in homework assignments need a tool to verify their answer. A Java web application (“applet”) has been developed to assist engineering students who encounter general multiphase equilibrium problems involving many species. In addition to students, educators and professional researchers will benefit from a user friendly and free to use software package that can numerically compute equilibrium distributions for arbitrary reactions. The applet we present in this work can be used to analyze complex reactions involving twenty or more species and one such reaction, the combustion of isooctane and air, is presented as an example.Copyright

A Java Based Web Application for Performing Chemical Equilibrium Analysis in Thermodynamics Courses

The topic of chemical equilibrium is frequently covered in thermodynamics courses. In assignments, students are often presented with simple problems in which the quantities of a few reacting species are specified. The student is asked to calculate the molar composition of the product mixture at a particular temperature and pressure when the mixture has reached an equilibrium state. For problems involving three or four species, students can hand calculate the equilibrium composition with reasonable effort using equilibrium constants. In problems involving many species, using equilibrium constants is not practical and specialized software is required. Instructors will commonly introduce their students to STANJAN, CEA, Cantera, or CHEMKINtrade. These packages are cumbersome to use relative to the contemporary Internet, point-and-click environment students now expect. In this work we have implemented a Java applet based on the numerical method employed by CEA to calculate the equilibrium composition of a mixture of ideal gases and integrated the applet into the expert system for thermodynamics (www.thermofluids.net) developed at San Diego State University

Algorithms for Higher-Order Mimetic Operators

We present an algorithm that reformulates existing methods to construct higher-order mimetic differential operators. Constrained linear optimization is the key idea of this resulting algorithm. The authors exemplified this algorithm by constructing an eight-order-accurate one-dimensional mimetic divergence operator. The algorithm computes the weights that impose the mimetic condition on the constructed operator. However, for higher orders, the computation of valid weights can only be achieved through this new algorithm. Specifically, we provide insights on the computational implementation of the proposed algorithm, and some results of its application in different test cases. Results show that for all of the proposed test cases, the proposed algorithm effectively solves the problem of computing valid weights, thus constructing higher-order mimetic operators.

Radiation signature in opposed-flow flame spread

A radiation calculation procedure is presented for opposed-flow solid fuel flame spread. The purpose is to aid selection of different approaches for infrared flame imaging during flame spread experiments in a quiescent microgravity environment. The RADCAL and TTNH models are compared for accuracy and computational cost. The TTNH model is shown to be sufficiently accurate to calculate radiative heat flux. The RADCAL calculations suggest the ratio of signals at two prominent bands is a good candidate to detect a radiation signature. A range of flow velocities, fuel thicknesses, and environmental conditions are considered to evaluate the strength of radiative losses compared to the heat released by combustion. The results confirm the importance of radiative heat transfer in the microgravity regime, where the opposed-flow velocity can be mild or even absent, and support the conclusion that a simplified model for radiation calculation produces sufficient accuracy when compared to detailed RADCAL calculations.

Design of a Rich Internet Application for Gas Turbine Engine Simulations

Modeling the performance and emissions characteristics of gas turbine engines can involve sequentially solving multiple thermodynamic states of a representative fluid flowing through the engine, evaluating cycle performance, and evaluating the chemical equilibrium of the fluid at select states. The states are defined by the combination of specified thermodynamic conditions, process assumptions derived from established theory of gas turbine engines, and thermodynamic properties of the representative fluid. Internet based applications such as TEST allow experienced analysts to structure and evaluate thermodynamic models of gas turbine engines and separately evaluate the chemical equilibrium of air-fuel mixtures to predict exhaust emissions. Although the TEST thermodynamic and chemical equilibrium data retrieval is automated, analysts are required to first structure the system model. The Internet based software described in this paper allows analysts to combine the modeling of performance and emissions characteristics of gas turbine engines without the need to first structure a model, broadening the range of potential analysts beyond the thermodynamic and chemical equilibrium communities. The software presented in this work combines a visually rich and Internet based interface to input specifications and display results, a communication mechanism to obtain Internet based thermodynamic and chemical equilibrium data, and a solution architecture to autonomously interpret user inputs and Web based data and model engine parameters. This software also allows analysts to modify the model complexity, accounting for irreversibilities and auxiliary devices such as regenerators, reheaters, and intercoolers as required. Data reduction features such as graphical representation of parametric studies and combustion product distribution are also available within the software.

An Investigation of the Variation in the Sweep and Diffusion Front Displacement as a Function of Reservoir Temperature and Seepage Velocity with Implications in CO 2 Sequestration

The steady accumulation of greenhouse gases resulting from the combustion of fossil fuels has led to an increase in the amount of solar radiation trapped between the atmosphere and earth. This increased radiation raises the temperature of the earths atmosphere and ocean systems. It is believed that continuing increases in temperature will lead to catastrophic changes in weather conditions around the globe. With carbon dioxide (CO2) being the most abundant greenhouse gas, many efforts are underway to reduce the level of CO2 entering the atmosphere. One promising technology involves the sequestration of CO2 in deep geologic formations. CO2 is first separated from flue gas expelled by coal fired power plants, compressed to a supercritical phase (ScCO2), and injected into underground formations such as exhausted gas reservoirs and deep brine aquifers. Flue gas normally contains 10% to 15% CO2 by volume. It is believed that CO2 can remain permanently sequestered in such formations, depending on the chemical and mechanical characteristics of the underground resident water and rock constituents. However, uncertainties remain in several areas such as the chemical and physical effects of CO2 injection on subsurface rocks which may introduce unwanted side-effects that could hamper long-term sequestration, such as induced seismicity. Risk estimation of short- and long-term geologic storage of CO2 can only be addressed through numerical modeling and simulation. In this paper we examine a short-term side-effect of CO2 injection in which an acidic fluid region develops ahead of the main CO2-rich water injectant. It is shown that the length of this low pH region varies with injectant velocity and reservoir temperature. A leading fluid region of low pH could have an effect on the wetability of formation minerals and the capillarity of the moving effluent. An advancing low pH front may increase the wetability of mineral surfaces which would improve CO2 sequestration efficiency and aid in enhanced oil recovery operations.