Active elastic dimers: self-propulsion and current reversal on a featureless track

We present a Brownian inchworm model of a self-propelled elastic dimer in the absence of an external potential. Nonequilibrium noise together with a stretch-dependent damping form the propulsion mechanism. Our model connects three key nonequilibrium features -- position-velocity correlations, a nonzero mean internal force, and a drift velocity. Our analytical results, including striking current reversals, compare very well with numerical simulations. The model unifies the propulsion mechanisms of DNA helicases, polar rods on a vibrated surface, crawling keratocytes and Myosin VI. We suggest experimental realizations and tests of the model.Comment: 4 page

Design strategies for the creation of aperiodic nonchaotic attractors

Parametric modulation in nonlinear dynamical systems can give rise to attractors on which the dynamics is aperiodic and nonchaotic, namely with largest Lyapunov exponent being nonpositive. We describe a procedure for creating such attractors by using random modulation or pseudo-random binary sequences with arbitrarily long recurrence times. As a consequence the attractors are geometrically fractal and the motion is aperiodic on experimentally accessible timescales. A practical realization of such attractors is demonstrated in an experiment using electronic circuits.Comment: 9 pages. CHAOS, In Press, (2009

Flow-induced currents in nanotubes: a Brownian dynamics approach

Motivated by recent experiments [Science {\bf 299}, 1042 (2003)] reporting that carbon nanotubes immersed in a flowing fluid displayed an electric current and voltage, we numerically study the behaviour of a collection of Brownian particles in a channel, in the presence of a flow field applied on similar but slower particles in a wide chamber in contact with the channel. For a suitable range of shear rates, we find that the flow field induces a unidirectional drift in the confined particles, and is stronger for narrower channels. The average drift velocity initially rises with increasing shear rate, then shows saturation for a while, thereafter starts decreasing, in qualitative agreement with recent theoretical studies [Phys. Rev. B {\bf 70}, 205423 (2004)] based on Brownian drag and ``loss of grip''. Interestingly, if the sign of the interspecies interaction is reversed, the direction of the induced drift remains the same, but the flow-rate at which loss of grip occurs is lower, and the level of fluctuations is higher.Comment: 7 pages, 9 figure

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

Proposal For Supply Chain Concentration In The Traditional MBA Program

The purpose of this proposal is to develop and implement a concentration in Supply Chain Management in the existing traditional MBA program effective fall 2012. Houston is the hub for many multinational oil and energy companies, large healthcare systems, wholesale/retail businesses, engineering and construction companies, and is a major city along the transportation artery of NAFTA. The program is designed to provide SCM expertise to students in the existing traditional MBA program. The environment for this proposal is the School of Business at Texas Southern University, Houston, Texas 77004

Technological Change, Automation and Employment: A Short Review of Theory and Evidence

A selective survey of recent papers in the area of technological change, automation and employment is presented. The objective is to convey analytical ideas and the empirical evidence that have informed studies in this area of contemporary policy relevance. Automation occurs when a machine does work that might previously have been done by a person. How robots and automation affect the availability of jobs for labor force? There are very few emerging studies that address the issue with detailed data on robots usage and employment in different sectors of the economy. Based on our review of available studies and empirical evidence the following statements can be made: (1) Increasing automation and robots adoption do not seem to cause loss of employment in the aggregate (2) Low skilled workers in routine jobs are more likely to suffer job losses. (3) There will be demand for new types of skilled workers or new specializations within occupations. Prospective automation intensifies the degree of uncertainty in labor markets across countries