1,971 research outputs found
Novel electric field effects on Landau levels in Graphene
A single graphene layer exhibits an anomalous Landau level spectrum. A
massless Dirac like low energy electronic spectrum underlies this anomaly. We
study, analytically and numerically, the effect of a uniform electric field
on the anomalous Landau levels. We solve the problem exactly within the
Dirac cone approximation and find an interesting scaling of the spectrum,
leading to the collapse of the Landau levels at a critical , for a
given magnetic field . We offer a physical interpretation of our result,
which uses `graphene relativity' and the boost operation. Electric fields,
non-uniform at nanoscopic (, magnetic) length scales, produce local
collapse at . We expect an anomalous breakdown of quantum Hall states
in real graphene, induced by large Hall currents.Comment: 4 pages, 3 figure
Spin-S Kitaev model: Classical Ground States, Order by Disorder and Exact Correlation Functions
In the first part of this paper, we study the spin-S Kitaev model using spin
wave theory. We discover a remarkable geometry of the minimum energy surface in
the N-spin space. The classical ground states, called Cartesian or CN-ground
states, whose number grows exponentially with the number of spins N, form a set
of points in the N-spin space. These points are connected by a network of flat
valleys in the N-spin space, giving rise to a continuous family of classical
ground states. Further, the CN-ground states have a correspondence with dimer
coverings and with self avoiding walks on a honeycomb lattice. The zero point
energy of our spin wave theory picks out a subset from a continuous family of
classically degenerate states as the quantum ground states; the number of these
states also grows exponentially with N. In the second part, we present some
exact results. For arbitrary spin-S, we show that localized Z_2 flux
excitations are present by constructing plaquette operators with eigenvalues
\pm 1 which commute with the Hamiltonian. This set of commuting plaquette
operators leads to an exact vanishing of the spin-spin correlation functions,
beyond nearest neighbor separation, found earlier for the spin-1/2 model [G.
Baskaran, S. Mandal and R. Shankar, Phys. Rev. Lett. 98, 247201 (2007)]. We
introduce a generalized Jordan-Wigner transformation for the case of general
spin-S, and find a complete set of commuting link operators, similar to the
spin-1/2 model, thereby making the Z_2 gauge structure more manifest. The
Jordan-Wigner construction also leads, in a natural fashion, to Majorana
fermion operators for half-integer spin cases and hard-core boson operators for
integer spin cases, strongly suggesting the presence of Majorana fermion and
boson excitations in the respective low energy sectors.Comment: 9 pages including 4 figures; added a section on an exactly solvable
higher spin version of the Kitaev model; this is the published versio
RVB gauge theory and the Topological degeneracy in the Honeycomb Kitaev model
We relate the Z gauge theory formalism of the Kitaev model to the SU(2)
gauge theory of the resonating valence bond (RVB) physics. Further, we
reformulate a known Jordan-Wigner transformation of Kitaev model on a torus in
a general way that shows that it can be thought of as a Z gauge fixing
procedure. The conserved quantities simplify in terms of the gauge invariant
Jordan-Wigner fermions, enabling us to construct exact eigen states and
calculate physical quantities. We calculate the fermionic spectrum for flux
free sector for different gauge field configurations and show that the ground
state is four-fold degenerate on a torus in thermodynamic limit. Further on a
torus we construct four mutually anti-commuting operators which enable us to
prove that all eigenstates of this model are four fold degenerate in
thermodynamic limit.Comment: 12 pages, 3 figures. Added affiliation and a new section,
'Acknowledgements'.Typos correcte
Incorporating Local Water Quality in Welfare Measures of Agri-environmental Policy: A Choice Modelling Approach Employing GIS
The spatial distribution of agro-environmental policy benefits has important implications for the efficient allocation of management effort. The practical convenience of relying on sample mean values of individual benefits for aggregation can come at the cost of biased aggregate estimates. The main objective of this paper is to test spatial hypotheses regarding respondents’ local water quality and quantity, and their willingness-to-pay for improvements in water quality attributes. This paper combines choice experiment and spatially related water quality data via a Geographical Information System (GIS) to develop a method that evaluates the influence of respondents’ local water quality on willingness-to-pay for river and stream conservation programs in Canterbury, New Zealand. Results show that those respondents who live in the vicinity of low quality waterway are willing to pay more for improvements relative to those who live near to high quality waterways.Water Quality, Choice Experiment, Geographical Information System, Environmental Economics and Policy, Resource /Energy Economics and Policy, Q51, Q25, Q58,
Enhanced diffusion and ordering of self-propelled rods
Starting from a minimal physical model of self propelled hard rods on a
substrate in two dimensions, we derive a modified Smoluchowski equation for the
system. Self -propulsion enhances longitudinal diffusion and modifies the mean
field excluded volume interaction. From the Smoluchowski equation we obtain
hydrodynamic equations for rod concentration, polarization and nematic order
parameter. New results at large scales are a lowering of the density of the
isotropic-nematic transition and a strong enhancement of boundary effects in
confined self-propelled systems.Comment: 4 pages, 2 figure
Exact results for spin dynamics and fractionization in the Kitaev Model
We present certain exact analytical results for dynamical spin correlation
functions in the Kitaev Model. It is the first result of its kind in
non-trivial quantum spin models. The result is also novel: in spite of presence
of gapless propagating Majorana fermion excitations, dynamical two spin
correlation functions are identically zero beyond nearest neighbor separation,
showing existence of a gapless but short range spin liquid. An unusual,
\emph{all energy scale fractionization}of a spin -flip quanta, into two
infinitely massive -fluxes and a dynamical Majorana fermion, is shown to
occur. As the Kitaev Model exemplifies topological quantum computation, our
result presents new insights into qubit dynamics and generation of topological
excitations.Comment: 4 pages, 2 figures. Typose corrected, figure made better, clarifying
statements and references adde
Interaction of spermatid-specific protein TP2 with nucleic acids, in vitro. A comparative study with TP1
TP2 was purified from rat testes employing a gentle method involving differential salt extraction of the sonication-resistant spermatid nuclei. The nucleic acid binding properties of TP2 were studied by fluorescence quenching, thermal denaturation, circular dichroism techniques and compared with those of TP1 (Singh, J., and Rao, M. R. S. (1987) J. Biol. Chem. 262, 734-740). The tyrosine fluorescence of TP2 was quenched upon binding to double-stranded and denatured DNA and poly(rA). The apparent association constants for binding of TP2 to these nucleic acids were calculated from the fluorescence quenching data, obtained at 50 mM NaCl, and found to be 1.63 × 105 M−1, 6.5 × 105 M−1, and 7.3 × 105 M−1, respectively. Thermal denaturation studies of calf thymus DNA and its complexes with TP2 showed that at 1 mM NaCl, TP2 shifted the Tm from 53°C to 62-67°C, while at 50 mM NaCl, the Tm was shifted from 72 to 78°C suggesting that TP2 is a DNA stabilizing protein. Circular dichroism studies of TP1·DNA and TP2·DNA complexes have revealed that TP2 has a better DNA condensing property than TP1. Furthermore, in contrast to TP1, TP2 does not destabilize in vitro the compactness of liver nucleosome core particles. The DNA binding properties of TP1 and TP2 have been discussed in relation to the significance of their transient appearance during mammalian spermiogenesis
Changes in the Cropping Pattern, Crop Concentration, Agricultural Efficiency in Papanasam Taluk, Thanjavur District, Tamil Nadu, India
Cropping pattern simply means the proportion of area under different crops at a point of time, where us change in cropping pattern refers to the change in proportion of area under different crops at two different points of time. The cropping pattern of any area is generally controlled by physical, socio economic and technological factors. There are more than 20 crops with varying hectares are grown in this taluk. Of these 20 crops only 5 crops based on the properties of land to the total area under cultivation alone has been considered for analysis. Simple percentage obtained by dividing total area under crops, in to area of different crops. Paddy is the dominant crop in this taluk. During the year 1995-1996 to 2008-2009 the following are the major 5 major crops are taken in to cultivate in the study area. Such as Paddy 82.2%, Sugarcane 6.5%, Oilseeds 4.5%, Pulses 4.1% and Cotton 1.9% to the total cropped area in the taluk
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