4,993 research outputs found
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
An Overview of the Health Hazards Due to Toxic Exposure in the Indian Work Environment
Since independence, there has been a phenomenal growth in the chemical industry, the number of units rising from 98 in 1947 to 964 in 1953 and 4364 in 1976. With the national demands ever growing, this trend of growth in chemical industry will continue in future also. The chemical units handle numerous toxic chemicals such as asbestos, benzene, carbon disulphide, carcinogenic dye intermediates, lead, manganese, organophosphorus pesticides, phosgene, vinyl chloride etc.Being aware of the potential health hazards arising out of exposure to these toxic chemicals necessary safeguards against health hazards have been incorporated in the Factories Act 1948.With nearly 100,000 tonnes of asbestos, over 100,000 tonnes of benzene, and considerably large quantities of other toxic chemicals being handled in the country, understandably, the random studies and surveys by research agencies have revealed the incidence of definite asbestosis (7 per cent), benzene intoxication in alkaloid extraction units ( 44.8 per cent), lead poisoning in storage battery units (10.6 per cent), carbon disulphide poisoning in viscose rayon units (20 per cent), mercury poisoning and intoxication in chloroalkali units (22.7 per cent), manganese poisoning in ferromanganese units (24 per cent), silicosis among slate pencil workers (54.7 per cent) etc.Albeit such a condition, the cases documented in official reports are very few. Even the scattered studies by research institution in occupational health cannot be pooled to evolve a national picture, since, quite often there is no standardised approach in the studies undertaken by different institutions.After discussing the findings of studies on various toxic chemicals and substances, the paper enumerates the present deficiencies in the current studies and suggest steps for obtaining comprehensive information on health hazards
New Query Lower Bounds for Submodular Function Minimization
We consider submodular function minimization in the oracle model: given
black-box access to a submodular set function , find an element of using as few queries to
as possible. State-of-the-art algorithms succeed with
queries [LeeSW15], yet the best-known lower bound has never
been improved beyond [Harvey08].
We provide a query lower bound of for submodular function minimization,
a query lower bound for the non-trivial minimizer of a symmetric
submodular function, and a query lower bound for the non-trivial
minimizer of an asymmetric submodular function.
Our lower bound results from a connection between SFM lower bounds
and a novel concept we term the cut dimension of a graph. Interestingly, this
yields a cut-query lower bound for finding the global mincut in an
undirected, weighted graph, but we also prove it cannot yield a lower bound
better than for - mincut, even in a directed, weighted graph
How Do Glassy Domains Grow?
We construct the equations for the growth kinetics of a structural glass
within mode-coupling theory, through a non-stationary variant of the 3-density
correlator defined in Phys. Rev. Lett. 97}, 195701 (2006). We solve a schematic
form of the resulting equations to obtain the coarsening of the 3-point
correlator as a function of waiting time . For a quench
into the glass, we find that attains a peak value at
, providing a theoretical basis for the numerical
observations of Parisi [J. Phys. Chem. B 103, 4128 (1999)] and Kob and Barrat
[Phys. Rev. Lett. 78, 4581 (1997)]. The aging is not "simple": the
dependence cannot be attributed to an evolving effective temperature.Comment: 6 pages, 5 figure
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 , 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
Shear flow induced isotropic to nematic transition in a suspension of active filaments
We study the effects of externally applied shear flow on a model of
suspensions of motors and filaments, via the equations of active hydrodynamics
[PRL {\bf 89} (2002) 058101; {\bf 92} (2004) 118101]. In the absence of shear,
the orientationally ordered phase of {\it both} polar and apolar active
particles is always unstable at zero-wavenumber. An imposed steady shear large
enough to overcome the active stresses stabilises both apolar and moving polar
phases. Our work is relevant to {\it in vitro} studies of active filaments, the
reorientation of endothelial cells subject to shear flow and shear-induced
motility of attached cells.Comment: 8 pages, 4 figures submitted to Europhysics Letter
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