Asymptotic unbounded root loci--Formulas and computation

We study the asymptotic behavior of the dosed loop eigenvalues (root loci) of a strictly proper linear time-invariant control system as loop gain goes toinfty. The formulas are stated in terms of the eigenvalues of nested restricted linear maps of the formA(mod S_{2})|_{S_{1}}where S1and S2are subspaces of complementary dimension. Additional geometrical insight into the formulas is obtained by mechanizing the formulas using orthogonal projections. Our method and formulas are useful in other asymptotic calculations as well, e.g., hierarchical multiple-time scales aggregation of Markov chains with some infrequent transitions.     

Spectral response inhomogeneities in large-area solar cells

A set-up for studying spatial variations of spectral response of solar cells is described. Spectral measurements have been used to calculate solar cell parameters like diffusion length of minority carriers, junction depth and barrier height of the junction. Results on polycrystalline silicon, thin film CdS/Cu₂S and SnO₂/SiO_x/n-Si solar cells are reported and discussed.     

Flapping flight for biomimetic robotic insects: part I-system modeling

This paper presents the mathematical modeling of flapping flight inch-size micro aerial vehicles (MAVs), namely micromechanical flying insects (MFIs). The target robotic insects are electromechanical devices propelled by a pair of independent flapping wings to achieve sustained autonomous flight, thereby mimicking real insects. In this paper, we describe the system dynamic models which include several elements that are substantially different from those present in fixed or rotary wing MAVs. These models include the wing-thorax dynamics, the flapping flight aerodynamics at a low Reynolds number regime, the body dynamics, and the biomimetic sensory system consisting of ocelli, halteres, magnetic compass, and optical flow sensors. The mathematical models are developed based on biological principles, analytical models, and experimental data. They are presented in the Virtual Insect Flight Simulator (VIFS) and are integrated together to give a realistic simulation for MFI and insect flight. VIFS is a software tool intended for modeling flapping flight mechanisms and for testing and evaluating the performance of different flight control algorithms.     

Properties of brush plated CdS films

Cadmium sulphide (CdS) thin films were deposited for the first time using the brush plating technique from the precursors on titanium and conducting glass substrates. The films were polycrystalline possessing single-phase hexagonal structure. Surface morphological studies indicated increase of grain size with increase of post deposition temperature. Optical band gap of 2.39 eV was obtained. XPS studies indicated the formation of CdS. Photo electrochemical cell studies indicated higher current and voltages compared to earlier reports on thin film electrodes. Mott–Schottky studies exhibited n-type behaviour with a carrier density of 10¹⁸ cm⁻³. Spectral response measurements indicated a quantum efficiency of 0.35.     

Nature of V ions in SnO2: EPR and photoluminescence studies

SnO₂ and 5 at.% V doped SnO₂ samples were prepared by citrate-gel method. From Raman study on vanadium doped SnO₂, the existence of phase separated V₂O₅ clusters has been established. EPR study on the V doped sample clearly revealed the existence of V⁴⁺ ions, which are incorporated in SnO₂ lattice and the existence of conduction electrons with g = 1.993. For vanadium doped SnO₂ sample, there is a decrease in luminescence at 400 nm and an increase in activation energy of electrical conduction compared to undoped SnO₂, and this has been attributed to the decrease in oxygen vacancies brought about by the incorporation of V⁵⁺ in the SnO₂ lattice.     

Optimization Criteria and Geometric Algorithms for Motion and Structure Estimation

Prevailing efforts to study the standard formulation of motion and structure recovery have recently been focused on issues of sensitivity and robustness of existing techniques. While many cogent observations have been made and verified experimentally, many statements do not hold in general settings and make a comparison of existing techniques difficult. With an ultimate goal of clarifying these issues, we study the main aspects of motion and structure recovery: the choice of objective function, optimization techniques and sensitivity and robustness issues in the presence of noise.We clearly reveal the relationship among different objective functions, such as (normalized) epipolar constraints, reprojection error or triangulation, all of which can be unified in a new optimal triangulation procedure. Regardless of various choices of the objective function, the optimization problems all inherit the same unknown parameter space, the so-called essential manifold. Based on recent developments of optimization techniques on Riemannian manifolds, in particular on Stiefel or Grassmann manifolds, we propose a Riemannian Newton algorithm to solve the motion and structure recovery problem, making use of the natural differential geometric structure of the essential manifold.We provide a clear account of sensitivity and robustness of the proposed linear and nonlinear optimization techniques and study the analytical and practical equivalence of different objective functions. The geometric characterization of critical points and the simulation results clarify the difference between the effect of bas-relief ambiguity, rotation and translation confounding and other types of local minima. This leads to consistent interpretations of simulation results over a large range of signal-to-noise ratio and variety of configurations.     

The origin of microtwinning at low strains during low-cycle fatigue of Inconel 718 at room temperature

The low-cycle fatigue (LCF) behaviour of a Ni–Fe base superalloy Inconel 718 was studied at room temperature. Deformation mechanisms operating at different strain amplitudes were established by detailed transmission electron microscopy at various fractions of fatigue life. It was observed that there was an increase in the number of microtwins present in the microstructure with increase in number of cycles, N, at low strains, where very little slip activity was identified. The undeformed specimens contain a number of annealing twins in the microstructure which increased in number with increase in cyclic deformation. Electron microscopy also revealed the existence of grain-boundary ledges in the undeformed specimens. A typical region of the grain-boundary area of the deformed samples showed a front of microtwins in their nascent state, advancing from one grain into the other. It was concluded that in the low-strain regime, cyclic deformation was accommodated by forming new microtwin interfaces emerging from grain-boundary ledges present in the undeformed specimens.