6,171 research outputs found
Phonon runaway in nanotube quantum dots
We explore electronic transport in a nanotube quantum dot strongly coupled
with vibrations and weakly with leads and the thermal environment. We show that
the recent observation of anomalous conductance signatures in single-walled
carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms
of current driven `hot phonons' that are strongly correlated with electrons.
Using rate equations in the many-body configuration space for the joint
electron-phonon distribution, we argue that the variations are indicative of
strong electron-phonon coupling requiring an analysis beyond the traditional
uncorrelated phonon-assisted transport (Tien-Gordon) approach.Comment: 8 pages, 6 figure
Uniqueness of Flat Spherically Symmetric Spacelike Hypersurfaces Admitted by Spherically Symmetric Static Spactimes
It is known that spherically symmetric static spacetimes admit a foliation by
{\deg}at hypersurfaces. Such foliations have explicitly been constructed for
some spacetimes, using different approaches, but none of them have proved or
even discussed the uniqueness of these foliations. The issue of uniqueness
becomes more important due to suitability of {\deg}at foliations for studying
black hole physics. Here {\deg}at spherically symmetric spacelike hy-
persurfaces are obtained by a direct method. It is found that spherically
symmetric static spacetimes admit {\deg}at spherically symmetric hypersurfaces,
and that these hypersurfaces are unique up to translation under the time- like
Killing vector. This result guarantees the uniqueness of {\deg}at spherically
symmetric foliations for such spacetimes.Comment: 10 page
Asymptotic Behaviour of the Proper Length and Volume of the Schwarzschild Singularity
Though popular presentations give the Schwarzschild singularity as a point it
is known that it is spacelike and not timelike. Thus it has a "length" and is
not a "point". In fact, its length must necessarily be infinite. It has been
proved that the proper length of the Qadir-Wheeler suture model goes to
infinity [1], while its proper volume shrinks to zero, and the asymptotic
behaviour of the length and volume have been calculated. That model consists of
two Friedmann sections connected by a Schwarzschild "suture". The question
arises whether a similar analysis could provide the asymptotic behaviour of the
Schwarzschild black hole near the singularity. It is proved here that, unlike
the behaviour for the suture model, for the Schwarzschild essential singularity
and , where
is the mean extrinsic curvature, or the York time.Comment: 13 pages, 1 figur
Note on flat foliations of spherically symmetric spacetimes
It is known that spherically symmetric spacetimes admit flat spacelike
foliations. We point out a simple method of seeing this result via the
Hamiltonian constraints of general relativity. The method yields explicit
formulas for the extrinsic curvatures of the slicings.Comment: 4 pages, to appear in PRD, reference added, typos correcte
Separation of Beach Sand Minerals
India has a vast resource of beach sand minerals along the Eastern and the Western coastal lines. The Beach Sand Minerals are usually heavier due to higher specific gravity and because of this property these are also known as Heavy Minerals. The Heavy Minerals are themselves a mixture of a variety of minerals like monazite, ilntenite,
rutile , zircon. silimanite, garner etc. These minerals are available in nature in the range of 75 to 500 Microns and can always be classified in the fines category. Prel-iminary extraction of these minerals is done by dredging of the raw sand along a pre determined dredge-path. The
dredged minerals are processed in a floating Concentration poant where these minerals are subjected to gravity sep-aration technique in spiral concentrators. The enriched concentrate ppgradation plant located near Mineral Sep-aration plant to increase the concentration up to about 95-96 % HM so that it will ready for processing in the Mineral Separation Plant for individual separation
Management of Meloidogyne incognita and Macrophomina phaseolina by Graphene Oxide on Lens culinaris
Effect of Graphene oxide (GO) was observed on Meloidogyne incognita and Macrophomina phaseolina and on the growth of lentil in pot experiment. Treatment of plants with 10 ml solution of GO with 125, 250 and 500 ppm concentration caused a significant increase in plant dry weight over control. Inoculation of plants with M. incognita or M. phaseolina caused a significant reduction in plant dry weight over uninoculated control. Treatment of plants with 125, 250 and 500 ppm GO and subsequent inoculation with M. incognita or M. phaseolina caused a significant increase in plant dry weight over plants inoculated without GO pretreatment. Treatment of 500 ppm GO caused a greater increase in plant dry weight of M. incognita or M. phaseolina inoculated plants followed by 250 ppm and 125 ppm. Numbers of nodules per root system were high in plants without pathogen. Inoculation of M. incognita or M. phaseolina caused reduction in nodulation. However, treatment of GO in all the three concentrations had no significant effect on nodulation in plants both with and without pathogens. Treatment of GO resulted in reduced galling, nematode multiplication and root-rot index. Greater reduction in galling, nematode multiplication and root-rot index were observed in plants treated with 500 ppm GO followed by 250 ppm and 125 ppm. Indices were reduced to 4, 3 and 2, respectively, when plants with M. phaseolina were treated with 125, 250 and 500 ppm GO. This study shows that the use of GO is useful for the management of M. incognita and M. phaseolina on lentil
Extended Huckel theory for bandstructure, chemistry, and transport. II. Silicon
In this second paper, we develop transferable semi-empirical parameters for
the technologically important material, silicon, using Extended Huckel Theory
(EHT) to calculate its electronic structure. The EHT-parameters areoptimized to
experimental target values of the band dispersion of bulk-silicon. We obtain a
very good quantitative match to the bandstructure characteristics such as
bandedges and effective masses, which are competitive with the values obtained
within an orthogonal-tight binding model for silicon. The
transferability of the parameters is investigated applying them to different
physical and chemical environments by calculating the bandstructure of two
reconstructed surfaces with different orientations: Si(100) (2x1) and Si(111)
(2x1). The reproduced - and -surface bands agree in part
quantitatively with DFT-GW calculations and PES/IPES experiments demonstrating
their robustness to environmental changes. We further apply the silicon
parameters to describe the 1D band dispersion of a unrelaxed rectangular
silicon nanowire (SiNW) and demonstrate the EHT-approach of surface passivation
using hydrogen. Our EHT-parameters thus provide a quantitative model of
bulk-silicon and silicon-based materials such as contacts and surfaces, which
are essential ingredients towards a quantitative quantum transport simulation
through silicon-based heterostructures.Comment: 9 pages, 9 figure
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