Flow-induced voltage and current generation in carbon nanotubes

New experimental results, and a plausible theoretical understanding thereof, are presented for the flow-induced currents and voltages observed in single-walled carbon nanotube samples. In our experiments, the electrical response was found to be strongly sublinear -- nearly logarithmic -- in the flow speed over a wide range, and its direction could be controlled by an electrochemical biasing of the nanotubes. These experimental findings are inconsistent with the conventional idea of a streaming potential as the efficient cause. Here we present a new, physically appealing, Langevin-equation based treatment of the nanotube charge carriers, assumed to be moving under coulombic forcing by the correlated ionic fluctuations, advected by the liquid in flow. The resulting 'Doppler-shifted' force-force correlation, as seen by the charge carriers drifting in the nanotube, is shown to give a strongly sublinear response, broadly in agreement with experiments.Comment: 11 pages including 3 figures. To appear in Phys. Rev B (2004

Long-lived Giant Number Fluctuations in a Swarming Granular Nematic

Coherently moving flocks of birds, beasts or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid-crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the Central Limit Theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.Comment: This is the author's version of the work. It is posted here by permission of the AAAS. The definitive version is to appear in SCIENC

Biological assessment of water pollution: A study of the river Kapila

An attempt has been made to assess the feasibility of application of biological data to evaluate and monitor water pollution of the river Kapila, near Nanjangud, Karnataka. Two pollution index factors, one at the generic level and another at species level of the Algae, have been computed. Significant correlation between biological and some physico-chemical factors has been established. The theme that algae serve as tools of pollution and that their index scores at the species level is a more reliable parameter for the evaluation of water quality has been established. © 1984, Taylor & Francis Group, LLC. All rights reserved

Elasticity-mediated self-organization and colloidal interactions of solid spheres with tangential anchoring in a nematic liquid crystal

Using laser tweezers and fluorescence confocal polarizing microscopy, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with strong tangential surface anchoring. The particles aggregate into chains directed at about 30 degrees to the far field director and, at higher concentrations, form complex kinetically trapped structures. We characterize the distance and angular dependencies of the colloidal interaction forces.Comment: 6 pages, 5 figure

Levels in As73 through the Ge72 (He3,d) reaction

The Ge72 (He3,d) As73 reaction has been investigated at a He3 bombarding energy of 20 MeV. Nearly 25 new bound levels in As73 have been observed beyond 3 MeV excitation. The relative spectroscopic factors for the bound states have been extracted and are compared with the predictions of the simple pairing theory. Several isobaric analog states of Ge73 have also been identified. NUCLEAR REACTIONS Ge72 (He3,d)As73, E=20 MeV; measured (E;), DWBA analysis; deduced As73 levels, lp, S. Enriched target. © 1979 The American Physical Society

Complexity of determining exact tolerances for min-max combinatorial optimization problems

Suppose that we are given an instance of a combinatorial optimization problemwith min-max objective along with an optimal solution for it. Let the cost of asingle element be varied. We refer to the range of values of the element’s costfor which the given optimal solution remains optimal as its exact tolerance. Inthis paper we examine the problem of determining the exact tolerance of eachelement in combinatorial optimization problems with min-max objectives. Weshow that under very weak assumptions, the exact tolerance of each elementcan be determined in polynomial time if and only if the original optimizationproblem can be solved in polynomial time

Formation Control of Car-like Mobile Robots: A Lyapunov Function Based Approach

In literature leader - follower strategy has been used extensively for formation control of car-like mobile robots with the control law being derived from the kinematics. This paper takes it a step further and a nonlinear control law is derived using Lyapunov analysis for formation control of car-like mobile robots using robot dynamics. Controller is split into two parts. The first part is the development of a velocity controller for the follower from the error kinematics (linear and angular). The second part involves the use of the dynamics of the robot in the development of a torque controller for both the drive and the steering system of the car-like mobile robot. Unknown quantities like friction, desired accelerations (unmeasured) are computed using an online neural network. Simulations results prove the ability of the controller to effectively stabilize the formation while maintaining the desired relative distance and bearing

Theory of Suspension Segregation in Partially Filled Horizontal Rotating Cylinders

It is shown that a suspension of particles in a partially-filled, horizontal, rotating cylinder is linearly unstable towards axial segregation and an undulation of the free surface at large enough particle concentrations. Relying on the shear-induced diffusion of particles, concentration-dependent viscosity, and the existence of a free surface, our theory provides an explanation of the experiments of Tirumkudulu et al., Phys. Fluids 11, 507-509 (1999); ibid. 12, 1615 (2000).Comment: Accepted for publication in Phys Fluids (Lett) 10 pages, two eps figure