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

Nonequilibrium Phase Transitions in a Driven Sandpile Model

We construct a driven sandpile slope model and study it by numerical simulations in one dimension. The model is specified by a threshold slope \sigma_c\/, a parameter \alpha\/, governing the local current-slope relation (beyond threshold), and $j_{\rm in}$, the mean input current of sand. A nonequilibrium phase diagram is obtained in the \alpha\, -\, j_{\rm in}\/ plane. We find an infinity of phases, characterized by different mean slopes and separated by continuous or first-order boundaries, some of which we obtain analytically. Extensions to two dimensions are discussed.Comment: 11 pages, RevTeX (preprint format), 4 figures available upon requs

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

Mesoscopic theory for fluctuating active nematics

Peer reviewedPublisher PD

A Dynamic Renormalization Group Study of Active Nematics

We carry out a systematic construction of the coarse-grained dynamical equation of motion for the orientational order parameter for a two-dimensional active nematic, that is a nonequilibrium steady state with uniaxial, apolar orientational order. Using the dynamical renormalization group, we show that the leading nonlinearities in this equation are marginally \textit{irrelevant}. We discover a special limit of parameters in which the equation of motion for the angle field of bears a close relation to the 2d stochastic Burgers equation. We find nevertheless that, unlike for the Burgers problem, the nonlinearity is marginally irrelevant even in this special limit, as a result of of a hidden fluctuation-dissipation relation. 2d active nematics therefore have quasi-long-range order, just like their equilibrium counterpartsComment: 31 pages 6 figure

Role of fluctuations in membrane models: thermal versus non-thermal

We study the comparative importance of thermal to non-thermal fluctuations for membrane-based models in the linear regime. Our results, both in 1+1 and 2+1 dimensions, suggest that non-thermal fluctuations dominate thermal ones only when the relaxation time $\tau$ is large. For moderate to small values of $\tau$, the dynamics is defined by a competition between these two forces. The results are expected to act as a quantitative benchmark for biological modelling in systems involving cytoskeletal and other non-thermal fluctuations.Comment: 4 pages, 1 figur

Design and performance of subirrigation system in maize (Zea mays) in Kumulur farm, Trichy district, Tamil Nadu, India

Subirrigation system can furnish water to plants. The upward flux and the discharge rate must satisfy the plant’s lifesaving irrigation needs during summer. The experiment was laid out in  A-block of Eastern farm, Agricultural Engineering College and Research Institute, Kumulur, Trichy, Tamil Nadu. Subirrigation system spacing was arrived using Moody's equation calculated as 10 m. The experiment was laid out in spilt plot design with three replications. Four drain spacing levels (7.5, 10, 12.5 and 15 m) were the main plot treatments and two levels of depth and diameter of drain pipes (75 cm, 60 cm & 75 mm, 63 mm) were the sub plot treatments. The highest volumetric water content was recorded in 7.5 m spacing + 45 cm soil depth + lower reach (S1T3T1). Capillary rise on water table management system under subirrigation mode was fixed as 33.5 cm and the average deep percolation loss was obtained in 0.3 cm/d at development stage of crop period. The highest maize yield (4.30 t/ha) was obtained in 7.5 m spacing + 60 cm drain depth + 75 mm diameter (S1D3). The highest water use efficiency of (0.86 kg/m3) was recorded in 7.5 m spacing + 60 cm drain depth + 75 mm drain diameter (S1D3). This subirrigation system could furnish water to plants due to upward flux and the same system also functioned efficiently under drainage modes and removed the waterlogging during wet periods.       

Optimal Control of Class of Non-Linear Plants using Artificial Immune Systems: Application of the Clonal Selection Algorithm

The function of natural immune system is to protect the living organisms against invaders/pathogens. Artificial Immune System (AIS) is a computational intelligence paradigm inspired by the natural immune system. Diverse engineering problems have been solved in the recent past using AIS. Clonal selection is one of the few algorithms that belong to the family of AIS techniques. Clonal selection algorithm is the computational implementation of the clonal selection principle. The process of affinity maturation of the immune system is explicitly incorporated in this algorithm. This paper presents the application of AIS for the optimal control of a class of non-linear plants which are affine in control. The clonal selection algorithm is adapted for optimal control. A new mutation operator that operates on real values and one that aids in fast convergence is developed in this paper. AIS is used to obtain constant coefficient Kalman gain matrices. The validation and evaluation of the results thus obtained are carried out by comparing with standard and the widely used State Dependent Algebraic Riccati Equation (SDARE) method for the non-linear plants. In case of non-linear systems with hard state constraints, the SDARE formulation requires the use of mathematically involved expressions to incorporate these state constraints. However, the modified clonal selection algorithm developed in this paper has been used with hardly any changes to incorporate the hard state constraints and obtain the Kalman gain matrix

Driven Heisenberg Magnets: Nonequilibrium Criticality, Spatiotemporal Chaos and Control

We drive a $d$-dimensional Heisenberg magnet using an anisotropic current. The continuum Langevin equation is analysed using a dynamical renormalization group and numerical simulations. We discover a rich steady-state phase diagram, including a critical point in a new nonequilibrium universality class, and a spatiotemporally chaotic phase. The latter may be `controlled' in a robust manner to target spatially periodic steady states with helical order.Comment: 7 pages, 2 figures. Published in Euro. Phys. Let

Approach to equilibrium in adiabatically evolving potentials

For a potential function (in one dimension) which evolves from a specified initial form $V_{i}(x)$ to a different $V_{f}(x)$ asymptotically, we study the evolution, in an overdamped dynamics, of an initial probability density to its final equilibeium.There can be unexpected effects that can arise from the time dependence. We choose a time variation of the form $V(x,t)=V_{f}(x)+(V_{i}-V_{f})e^{-\lambda t}$. For a $V_{f}(x)$, which is double welled and a $V_{i}(x)$ which is simple harmonic, we show that, in particular, if the evolution is adiabatic, the results in a decrease in the Kramers time characteristics of $V_{f}(x)$. Thus the time dependence makes diffusion over a barrier more efficient. There can also be interesting resonance effects when $V_{i}(x)$ and $V_{f}(x)$ are two harmonic potentials displaced with respect to each other that arise from the coincidence of the intrinsic time scale characterising the potential variation and the Kramers time.Comment: This paper contains 5 page