The minimum positional error incurred by any connectivity-based positioning algorithm for mobile wireless systems

A very important problem in many wireless ad-hoc networks, including wireless sensor networks, is positioning or the determination of geographical locations of the wireless nodes. Positioning is used both in infrastructural aspects of sensor networks, like geographic routing and topology maintenance, and in applications like wildlife tracking. Connectivity-based positioning algorithms in mobile wireless systems are studied in this work. These algorithms compute node positions based only on the connectivity, i.e. the neighborhood information of each node. Many algorithms have been proposed for positioning in stationary node systems and bounds on positional error of algorithms have been derived. The design and analysis of positioning algorithms for mobile node systems is a more challenging problem. Node mobility increases the amount of positional information available to a positioning algorithm. The work in this paper establishes a bound on the positional error for connectivity-based algorithms in mobile systems. The formulation from the analysis is used to investigate the benefit of this additional positional information on reducing positional error. There is a limit to the usefulness of positional information from previous node positions due to movement. This captures an important performance tradeoff: historical positional information can yield reduced positional error but requires more connectivity information from the network which requires greater computational resources.     

Automated Cellular Modeling and Prediction on a Large Scale

We describe CHAMP (CHurn Analysis, Modeling, andPrediction), an automated system for modeling cellularsubscriber churn that is predicting which customerswill discontinue cellular phone service. We describevarious issues related to developing and deployingthis system including automating data access from aremote data warehouse, preprocessing, featureselection, model validation, and optimization toreflect business tradeoffs. Using data from GTE'sdata warehouse for cellular phone customers, CHAMP iscapable of developing churn models customized byregion for over one hundred GTE cellular phone marketstotaling over 5 million customers. Every month churnfactors are identified for each geographic region andmodels are updated to generate churn scores predictingwho is likely to churn in the short term. Learningmethods such as decision trees and genetic algorithmsare used for feature selection and a cascade neuralnetwork is used for predicting churn scores. Inaddition to producing churn scores, CHAMP alsoproduces qualitative results in the form of rules andcomparison of market trends that are disseminatedthrough a web based interface.     

A parallel hp‐FEM infrastructure for three‐dimensional structural acoustics

This paper describes a parallel three‐dimensional numerical infrastructure for the solution of a wide range of time‐harmonic problems in structural acoustics and vibration. High accuracy and rate of error‐convergence, in the mid‐frequency regime,is achieved by the use of hp‐finite and infinite element approximations. The infrastructure supports parallel computation in both single and multi‐frequency settings. Multi‐frequency solves utilize concurrent factoring of the frequency‐dependent linear algebraic systems and are naturally scalable. Scalability of large‐scale single‐frequency problems is realized by using FETI‐DP—an iterative domain‐decomposition scheme. Numerical examples are presented to cover applications in vibratory response of fluid‐filled elastic structures as well as radiation and scattering from elastic structures submerged in an infinite acoustic medium. We demonstrate both the numerical accuracy as well as parallel scalability of the infrastructure in terms of problem parameters that include wavenumber and number of frequencies, polynomial degree of finite/infinite element approximations as well as the number of processors. Scalability and accuracy is evaluated for both single and multiple frequency sweeps on four high‐performance parallel computing platforms: SGI Altix, SGI Origin, IBM p690 SP and Linux‐cluster. Results show good performance on shared as well as distributed‐memory architecture. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of Cl-, Br-, NO 3 - and SO 4 2- ions on the corrosion behaviour of 6061 Al alloy

The effects of anions like Cl^-, Br^-, NO ₃ ^- and SO ₄ ^2- on the anodic dissolution of the monolithic Al 6061 alloy have been investigated at neutral pH through immersion testing and electrochemical techniques like potentiodynamic polarization and a.c. impedance spectroscopy. Scanning electron microscopy was employed to characterize the corroded surface and to observe the extent of pitting in different media. From the evaluated corrosion parameters it was found that the dissolution of the matrix was extensively reduced in presence of aqueous solutions containing Br^-, NO ₃ ^- and SO ₄ ^2- ions while Cl^- ions aggravated corrosion by penetrating into the barrier oxide film on the surface of the material. Pronounced effect of pitting was observed in presence of Cl^- and the level of pitting in NO ₃ ^- and Br^- were mild. In presence of SO ₄ ^2- ions passivity was extended over a wide potential range and breakdown of passivity occurs when the material was polarized beyond pitting potential. The departure of capacitive behaviour towards resistive behaviour was clearly observed through impedance measurements when investigations were conducted in Cl^- media and in presence of the other electrolytes. Corrosion rates were, however, controlled during prolonged exposure in the electrolytic media, specially in case of chloride media, due to the predominance of film repair kinetics.     

Linear circuits: a measurement‐based approach

This paper proposes a new measurement‐based approach that can solve synthesis problems in unknown linear circuits. The method makes use of a small number of measurements to determine the functional dependency of any circuit signal or variable on any set of design variables. Once the functional dependency is obtained, the design requirements can be applied to find the design parameter values. The results are described for linear direct current and alternating current circuits. Copyright © 2013 John Wiley & Sons, Ltd.     

Poly(ethylene oxide)‐g‐gellan polysaccharide nanocarriers for controlled gastrointestinal delivery of simvastatin

Herein, a novel gellan polysaccharide‐based amphiphilic copolymer was synthesized for the development of simvastatin‐loaded micellar nanoparticles. The nanoparticles were explored for their controlled drug release and improved pharmacodynamic potentials. The copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The onset of copolymer micellization was detected by fluorescence spectroscopy. Simvastatin was loaded into micellar particles by solvent evaporation method and the particles were then characterized by microscopic and light scattering techniques. The physical state of drug was studied by X‐ray diffraction analysis. Pharmacodynamic assessment of the micellar preparations was done on rabbit models. The copolymer formed micellar nanoparticles in water. Critical micellar concentration was 9.12mg/l. The micellar particles (426.8–912.6nm) entrapped a maximum of 18.86% drug. Higher negative zeta potential indicated physical stability of micellar systems. A simple diffusion mechanism was operative in the event of comparatively faster drug release in pH6.8 phosphate buffer solution. No significant drug‐copolymer interaction was traced by FTIR spectroscopy. The amorphization of drug into micellar particles reduced LDL‐cholesterol level by ～45% in hyperlipidemic rabbits and this was about 2.5 times higher than pure drug dispersion. Copolymer micellar nanoparticles of simvastatin could control cholesterol level in hyperlipidemic rabbits and thus had potential in drug delivery applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42399.     

Using light to control the interactions between self-rotating assemblies of active gels

Polymer gels undergoing the oscillating Belousov-Zhabotinsky (BZ) reaction exhibit an autonomous, periodic swelling and deswelling, where the mechanical oscillations are driven by the chemical reaction within the polymer network. Using computer simulations, we show that these BZ gels can undergo a form of auto-chemotaxis, enabling the gels to spontaneously move in response to self-generated chemical gradients. Focusing on four millimeter-sized pieces of these BZ gels, we show that the pieces can organize into self-rotating clusters that resemble a moving pinwheel or gear. By analyzing the factors that promote the formation of a single self-rotating cluster, we attempt to design systems of multiple, interacting gears. We show that light, which suppresses the oscillations of the gels, can be harnessed to promote the formation of two self-rotating clusters. These studies point to a novel form of photo-chemo-mechanical transduction, where light is utilized to control the conversion of chemical and mechanical energy in the system. Moreover, the interaction between the BZ gel gears reveals a new form of entrainment between these moving units. Namely, their coordinated motion is achieved through chemical coupling or communication, rather than a mechanical coupling. These findings can lead to the formation of chemically “communicating” devices that can be programmed to perform autonomous work through the use of light.     

Food Fortification and Supplement Use—Are There Health Implications?

Dietary supplements are a multi-billion dollar industry in the U.S., and their use is increasing exponentially. Additionally, many foods and beverages are increasingly being fortified with single or multiple vitamins and minerals. Consequently, nutrient intakes are exceeding the safe limits established by the Institute of Medicine. In this paper, we examine the benefits and drawbacks of vitamin and mineral supplements and increasing consumption of fortified foods (in addition to dietary intake) in the U.S. population. The pros and cons are illustrated using population estimates of folic acid, calcium, and vitamin D intake, highlighting concerns related to overconsumption of nutrients that should be addressed by regulatory agencies.