580 research outputs found
Covalently Binding the Photosystem I to Carbon Nanotubes
We present a chemical route to covalently couple the photosystem I (PS I) to
carbon nanotubes (CNTs). Small linker molecules are used to connect the PS I to
the CNTs. Hybrid systems, consisting of CNTs and the PS I, promise new
photo-induced transport phenomena due to the outstanding optoelectronic
properties of the robust cyanobacteria membrane protein PS I
Scenario of inflationary cosmology from the phenomenological models
Choosing the three phenomenological models of the dynamical cosmological term
, viz., , and
where is the cosmic scale factor, it has been shown by
the method of numerical analysis that the three models are equivalent for the
flat Universe . The evolution plots for dynamical cosmological term
vs. time and also the cosmic scale factor vs. are drawn
here for . A qualitative analysis has been made from the plots which
supports the idea of inflation and hence expanding Universe.Comment: 12 latex pages with 12 figures; Replaced with the revised version;
Accepeted for `J. Non-lin. Frac. Phen. Sci. Engg.
Giant magnetic anisotropy at nanoscale: overcoming the superparamagnetic limit
It has been recently observed for palladium and gold nanoparticles, that the
magnetic moment at constant applied field does not change with temperature over
the range comprised between 5 and 300 K. These samples with size smaller than
2.5 nm exhibit remanence up to room temperature. The permanent magnetism for so
small samples up to so high temperatures has been explained as due to blocking
of local magnetic moment by giant magnetic anisotropies. In this report we
show, by analysing the anisotropy of thiol capped gold films, that the orbital
momentum induced at the surface conduction electrons is crucial to understand
the observed giant anisotropy. The orbital motion is driven by localised charge
and/or spin through spin orbit interaction, that reaches extremely high values
at the surfaces. The induced orbital moment gives rise to an effective field of
the order of 103 T that is responsible of the giant anisotropy.Comment: 15 pages, 2 figures, submitted to PR
Efficient Reduction of Casimir Forces by Self-assembled Bio-molecular Thin Films
Casimir forces, related to London-van der Waals forces, arise if the spectrum
of electromagnetic fluctuations is restricted by boundaries. There is great
interest both from fundamental science and technical applications to control
these forces on the nano scale. Scientifically, the Casimir effect being the
only known quantum vacuum effect manifesting between macroscopic objects,
allows to investigate the poorly known physics of the vacuum. In this work, we
experimentally investigate the influence of self-assembled molecular bio and
organic thin films on the Casimir force between a plate and a sphere. We find
that molecular thin films, despite being a mere few nanometers thick, reduce
the Casimir force by up to 14%. To identify the molecular characteristics
leading to this reduction, five different bio-molecular films with varying
chemical and physical properties were investigated. Spectroscopic data reveal a
broad absorption band whose presence can be attributed to the mixing of
electronic states of the underlying gold layer and those of the molecular film
due to charge rearrangement in the process of self-assembly. Using Lifshitz
theory we calculate that the observed change in the Casimir force is consistent
with the appearance of the new absorption band due to the formation of
molecular layers. The desired Casimir force reduction can be tuned by stacking
several monolayers, using a simple self-assembly technique in a solution. The
molecules - each a few nanometers long - can penetrate small cavities and
holes, and cover any surface with high efficiency. This process seems
compatible with current methods in the production of micro-electromechanical
systems (MEMS), which cannot be miniaturized beyond a certain size due to
`stiction' caused by the Casimir effect. Our approach could therefore readily
enable further miniaturization of these devices.Comment: Preprint versio
Unitary representations of nilpotent super Lie groups
We show that irreducible unitary representations of nilpotent super Lie
groups can be obtained by induction from a distinguished class of sub super Lie
groups. These sub super Lie groups are natural analogues of polarizing
subgroups that appear in classical Kirillov theory. We obtain a concrete
geometric parametrization of irreducible unitary representations by nonnegative
definite coadjoint orbits. As an application, we prove an analytic
generalization of the Stone-von Neumann theorem for Heisenberg-Clifford super
Lie groups
Two-dimensional metric and tetrad gravities as constrained second order systems
Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method
for analyzing singular systems, we consider the Hamiltonian formulation of
metric and tetrad gravities in two-dimensional Riemannian spacetime treating
them as constrained higher-derivative theories. The algebraic structure of the
Poisson brackets of the constraints and the corresponding gauge transformations
are investigated in both cases.Comment: replaced with revised version published in
Mod.Phys.Lett.A22:17-28,200
Far-field e-beam detection of hybrid cavity-plasmonic modes in gold micro-holes
Manipulation of light-beams with subwavelenth metallic devices has motivated
intensive studies, following the discovery of extraordinary transmission of
electromagnetic waves through sub-wavelength apertures in thin noble-metal
films. The propagation of light in these holes can be investigated at greately
improved spatial resolution by means of focused electron-beams. Here we
demonstrate direct e-beam excitation of radiative cavity modes well below the
surface plasmon (SP) frequency, of isolated rectangular holes in gold films,
illuminating the hotly debated phenomenon of the extraordinary optical
transmission through subwavelength holes. The exceptionally long range e-beam
interaction with the metal through the vacuum, involving electromagnetic
excitations within the light cone, is allowed by momentum conservation
breakdown along the e-beam axis. Two types of lowlying excited modes are
revealed: radiative cavity modes which are nearly unaffected by SPs, and SP
polariton modes with waveguide character in the near field region of the slit
walls, which in spite of the strong hybridization preserve the waveguide cutoff
frequencies and symmetry characteristics.Comment: 16 pages, 4 figures, 1 tabl
Behavior of Einstein-Rosen Waves at Null Infinity
The asymptotic behavior of Einstein-Rosen waves at null infinity in 4
dimensions is investigated in {\it all} directions by exploiting the relation
between the 4-dimensional space-time and the 3-dimensional symmetry reduction
thereof. Somewhat surprisingly, the behavior in a generic direction is {\it
better} than that in directions orthogonal to the symmetry axis. The geometric
origin of this difference can be understood most clearly from the 3-dimensional
perspective.Comment: 16 pages, REVETEX, CGPG-96/5-
Dotted and Undotted Algebraic Spinor Fields in General Relativity
We investigate using Clifford algebra methods the theory of algebraic dotted
and undotted spinor fields over a Lorentzian spacetime and their realizations
as matrix spinor fields, which are the usual dotted and undotted two component
spinor fields. We found that some ad hoc rules postulated for the covariant
derivatives of Pauli sigma matrices and also for the Dirac gamma matrices in
General Relativity cover important physical meaning, which is not apparent in
the usual matrix presentation of the theory of two components dotted and
undotted spinor fields. We also discuss some issues related to the the previous
one and which appear in a proposed "unified" theory of gravitation and
electromagnetism which use two components dotted and undotted spinor fields and
also paravector fields, which are particular sections of the even subundle of
the Clifford bundle of spacetime.Comment: some new misprints have been correcte
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