Quantification of multiple bioagents with wireless, remote-query magnetoelastic microsensors

This paper presents a micromagnetoelastic sensor array for simultaneously monitoring multiple biological agents. Magnetoelastic sensors, made of low-cost amorphous ferromagnetic ribbons, are analogous and complementary to piezoelectric acoustic wave sensors, which track parameters of interest via changes in resonance behavior. Magnetoelastic sensors are excited with magnetic ac fields, and, in turn, they generate magnetic fluxes that can be detected with a sensing coil from a distance. As a result, these sensors are highly attractive, not only due to their small size and low cost, but also because of their passive and wireless nature. Magnetoelastic sensors have been applied for monitoring pressure, temperature, liquid density, and viscosity, fluid How velocity and direction, and with chemical/biological responsive coatings that change mass or elasticity, various biological and chemical agents. In this paper, we report the fabrication and application of a six-sensor array for simultaneous measurement of Escherichia coli O157:H7, staphylococcal enterotoxin B, and ricin. In addition, the sensor array also monitors temperature and pH so the measurements are independent from these two parameters.     

Dynamical properties of hybrid automata

Hybrid automata provide a language for modeling and analyzing digital and analogue computations in real-time systems. Hybrid automata are studied here from a dynamical systems perspective. Necessary and sufficient conditions for existence and uniqueness of solutions are derived and a class of hybrid automata whose solutions depend continuously on the initial state is characterized. The results on existence, uniqueness, and continuity serve as a starting point for stability analysis. Lyapunov's theorem on stability via linearization and LaSalle's invariance principle are generalized to hybrid automata.     

Following the flock [formation control]

A new approach to formation control of nonholonomic mobile robots equipped with central panoramic cameras is presented. The approach uses motion segmentation techniques to estimate the position of each leader and omnidirectional visual servoing for tracking and collision avoidance. The paper showed that direct feedback-linearization of the leader-follower dynamics leads to asymptotic tracking but suffers from degenerate configurations. A nonlinear controller was presented that avoids such singularities but can only guarantee input-to-state stability of the formation.     

Unstructured Grid-Based Discontinuous Galerkin Method for Broadband Electromagnetic Simulations

A parallel, unstructured, high-order discontinuous Galerkin method is developed for the time-dependent Maxwell's equations, using simple monomial polynomials for spatial discretization and a fourth-order Runge–Kutta scheme for time marching. Scattering results for a number of validation cases are computed employing polynomials of up to third order. Accurate solutions are obtained on coarse meshes and grid convergence is achieved, demonstrating the capabilities of the scheme for time-domain electromagnetic wave scattering simulations.     

Nonlinear averaging theorems, and the determination of parameter convergence rates in adaptive control

The paper presents nonlinear averaging theorems for two-time scale systems, where the dynamics of the fast system are allowed to vary with the slow system. The results are applied to the Narendra-Valavani adaptive control algorithm, and estimates of the parameter convergence rates are obtained which do not rely on a linearization of the system around the equilibrium, and therefore are valid in a larger region in the parameter space.     

a-Si:H/CuInS2 heterojunctions for photovoltaic conversion

Heterojunctions of hydrogenated a-Si films prepared by r.f. sputtering with spraypyrolyzed CuInS₂ films have been studied. Capacitance-voltage measurements establish the formation of abrupt heterojunction. The barrier height varies from 0·26 to 0·55 V as the resistivity of CuInS₂ film decrease from 1·5 × 10³ to 65 Θm. These junctions exhibit photovoltaic behaviour withV _oc = 220 mV andI _sc = 0·20 mA/cm².     

Conduction mechanism and dielectric properties of BiFeO3–BaTiO3 solid solutions

The first measurements are reported for the frequency-dependent conductivity of (1?x)BiFeO₃–xBaTiO₃ (x = 0.10, 0.15 and 0.30) solid solutions in the frequency range of 10⁰–10⁶ Hz and in the temperature range of 50–300 °C. Powder X-ray diffraction confirms the formation of solid solutions. The dielectric properties were seen to improve with increasing BaTiO₃ (BT) content. The conductivity (AC and DC) measurements reveal an inverse variation of the frequency exponent ‘s’ with temperature, high density of states and thermally activated process. The calculated density of states was found to be N(E_f) = 80.2 × 10³² eV^?1 cm^?1 at 1 kHz and 50 °C for BiFeO₃–10 % BaTiO₃ (BFO–10 % BT) solid solution. The impedance spectroscopy analysis confirms the presence of grain and grain boundary affecting the conductivity. Our results provide the first unambiguous evidence of conduction in crystallite BFO–BT solid solutions through correlated-barrier-hopping model.     

Effects of Clinorotation on Growth and Chlorophyll Content of Rice Seeds

Microgravity, as a different environment, has been shown to affect plant growth and development (Sievers et al. 1996; Sack 1997). In the present study, effects of slow clinorotation (2 rpm) on growth and chlorophyll content in rice (variety: PRH-10) seedlings were investigated. Rice seeds were clinorotated continuously for 3, 5 and 7 days under ambient conditions. Root and shoot lengths and weights of rice seedlings were measured on the third, fifth and seventh day. Chlorophyll was extracted using N, N-Dimethylformamide (DMF). Absorption and fluorescence spectra of chlorophyll were recorded. Chlorophyll a, chlorophyll b and total chlorophyll contents were calculated from absorption spectra using Arnon’s method. Results showed an increase in root and shoot lengths in clinorotated samples. Similar results were obtained for root and shoot weights. Absorption spectra of chlorophyll showed no shift in the absorption peaks. Chlorophyll content was increased in clinorotated samples as compared to the controls. Interestingly, the difference between chlorophyll content in control and clinorotated samples decreased as the number of days of clinorotation increased. Chlorophyll a/b ratio was lowered in clinorotated samples as compared to the controls. These results suggest that slow clinorotation (2 rpm) affects plant growth and chlorophyll content in rice seedlings.     

Model validation under epistemic uncertainty

This paper develops a methodology to assess the validity of computational models when some quantities may be affected by epistemic uncertainty. Three types of epistemic uncertainty regarding input random variables - interval data, sparse point data, and probability distributions with parameter uncertainty - are considered. When the model inputs are described using sparse point data and/or interval data, a likelihood-based methodology is used to represent these variables as probability distributions. Two approaches - a parametric approach and a non-parametric approach - are pursued for this purpose. While the parametric approach leads to a family of distributions due to distribution parameter uncertainty, the principles of conditional probability and total probability can be used to integrate the family of distributions into a single distribution. The non-parametric approach directly yields a single probability distribution. The probabilistic model predictions are compared against experimental observations, which may again be point data or interval data. A generalized likelihood function is constructed for Bayesian updating, and the posterior distribution of the model output is estimated. The Bayes factor metric is extended to assess the validity of the model under both aleatory and epistemic uncertainty and to estimate the confidence in the model prediction. The proposed method is illustrated using a numerical example.