401 research outputs found
Optical and Radiative Properties of Aerosols over Two Locations in the North-West Part of India during Premonsoon Season
The present study examines the aerosol characteristics over two locations in the northwest region of India (Dehradun and Patiala) during premonsoon season of 2013. The average mass concentrations of particulates (PM10; PM2.5; PM1) were found to be 118±36, 34±11, and 19±10 µgm−3 and 140±48, 30±13, and 14±06 µgm−3 over Dehradun and Patiala, respectively. The average aerosol optical depth (AOD500 nm) is observed to be 0.62±0.11 over Dehradun and 0.56±0.21 over Patiala. Ångström exponent and fine mode fraction show higher values over Dehradun as compared to Patiala. The average mass concentration of black carbon was found to be 3343±546 ngm−3 and 6335±760 ngm−3 over Dehradun and Patiala, respectively. The diurnal pattern of BC is mainly controlled by boundary layer dynamics and local anthropogenic activities over both the stations. The average single scattering albedo (SSA500 nm) exhibited low value over Patiala (0.83±0.01) in comparison to Dehradun (0.90±0.01), suggesting the abundance of absorbing type aerosols over Patiala. The average atmospheric aerosol radiative forcing is +37.34 Wm−2 and +54.81 Wm−2 over Dehradun and Patiala, respectively, leading to atmospheric heating rate of 1.0 K day−1 over Dehradun and 1.5 K day−1 over Patiala
Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics
The magnetic susceptibility and susceptibility anisotropy of the quasi-binary
alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration
of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The
experimental results are discussed in terms of t he degenerate
Coqblin-Schrieffer model with a crystalline electric field splitting Delta =
330 K. The properties of the model, obtained by combining the lowest-order
scaling and the pertur bation theory, provide a satisfactory description of the
experimental data down to 30 K. The e xperimental results between 20 K and 2 K
are explained by the exact solution of the Kondo mode l for an effective
doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl
Crossover between Fermi Liquid and non-Fermi Liquid in Orbitally Degenerate Kondo Systems
Entanglement of spin and orbital Kondo effect is investigated on the basis of
a Kondo-type exchange model with twofold orbital degeneracy. By using Wilson's
numerical renormalization-group method, we examine dynamical and thermal
properties respecting the difference in time-reversal property of multipole
operators. In the presence of particle-hole symmetry, the model has a new
non-Fermi-liquid fixed point with a fractional entropy. The spectral intensity
of the quadrupole susceptibility diverges in the zero-frequency limit, while
the dipole susceptibility shows a Fermi-liquid-like behavior. This is
understood by mapping to the two-channel Kondo model, in which the dipole
moment is mapped onto the operators with the scaling dimension ,
while the quadrupole moment onto the operators with another scaling dimension
. Even for a fairly particle-hole asymmetric case with the
Fermi-liquid ground state, the non-Fermi-liquid behavior has significant
influences in electric and thermal properties.Comment: 7 pages, 9 figures, to appear in J. Phys Soc. Jpn. Vol. 68 No. 12,
title changed and some corrections mad
Zero-Bias Conductance Through Side-Coupled Double Quantum Dots
Low temperature zero-bias conductance through two side-coupled quantum dots
is investigated using Wilson's numerical renormalization group technique. A
low-temperature phase diagram is computed. Near the particle-hole symmetric
point localized electrons form a spin-singlet associated with weak conductance.
For weak inter-dot coupling we find enhanced conductance due to the two-stage
Kondo effect when two electrons occupy quantum dots. When quantum dots are
populated with a single electron, the system enters Kondo regime with enhanced
conductance. Analytical expressions for the width of the Kondo regime and the
Kondo temperature in this regime are given.Comment: to be published in the Proceedings of the NATO Advanced Research
Workshop on "Electron Correlations in New Materials and Nanosystems" held in
Yalta, Ukraine, 19 - 23 September 2005 (NATO Science Series II, Springer
2006
The numerical renormalization group method for quantum impurity systems
In the beginning of the 1970's, Wilson developed the concept of a fully
non-perturbative renormalization group transformation. Applied to the Kondo
problem, this numerical renormalization group method (NRG) gave for the first
time the full crossover from the high-temperature phase of a free spin to the
low-temperature phase of a completely screened spin. The NRG has been later
generalized to a variety of quantum impurity problems. The purpose of this
review is to give a brief introduction to the NRG method including some
guidelines of how to calculate physical quantities, and to survey the
development of the NRG method and its various applications over the last 30
years. These applications include variants of the original Kondo problem such
as the non-Fermi liquid behavior in the two-channel Kondo model, dissipative
quantum systems such as the spin-boson model, and lattice systems in the
framework of the dynamical mean field theory.Comment: 55 pages, 27 figures, submitted to Rev. Mod. Phy
Synthesis, Characterization and Magnetic Susceptibility of the Heavy Fermion Transition Metal Oxide LiV_{2}O_{4}
The preparative method, characterization and magnetic susceptibility \chi
measurements versus temperature T of the heavy fermion transition metal oxide
LiV_{2}O_{4} are reported in detail. The intrinsic \chi(T) shows a nearly
T-independent behavior below ~ 30 K with a shallow broad maximum at about 16 K,
whereas Curie-Weiss-like behavior is observed above 50-100 K. Field-cooled and
zero-field-cooled magnetization M measurements in applied magnetic fields H =
10 to 100 G from 1.8 to 50 K showed no evidence for spin-glass ordering.
Crystalline electric field theory for an assumed cubic V point group symmetry
is found insufficient to describe the observed temperature variation of the
effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not
describe the magnitude and T dependence of \chi with realistic parameters. In
the high T range, fits of \chi(T) by the predictions of high temperature series
expansion calculations provide estimates of the V-V antiferromagnetic exchange
coupling constant J/k_{B} ~ 20 K, g-factor g ~ 2 and the T-independent
susceptibility. Other possible models to describe the \chi(T) are discussed.
The paramagnetic impurities in the samples were characterized using isothermal
M(H) measurements with 0 < H <= 5.5 Tesla at 2 to 6 K. These impurities are
inferred to have spin S_{imp} ~ 3/2 to 4, g_{imp} ~ 2 and molar concentrations
of 0.01 to 0.8 %, depending on the sample.Comment: 19 typeset RevTeX pages, 16 eps figures included, uses epsf; to be
published in Phys. Rev.
Electrical and thermoelectrical transport in Dirac fermions through a quantum dot
We investigate the conductance and thermopower of massless Dirac fermions
through a quantum dot using a pseudogap Anderson model in the non-crossing
approximation. When the Fermi level is at the Dirac point, the conductance has
a cusp where the thermopower changes its sign. When the Fermi level is away
from the Dirac point, the Kondo temperature illustrates a quantum impurity
transition between an asymmetric strong coupling Kondo state and a localized
moment state. The conductance shows a peak near this transition and reaches the
unitary limit at low temperatures. The magnitude of the thermopower exceeds
, and the thermoelectric figure of merit exceeds unity.Comment: 5 pages, 4 figure
Spectral function of the Kondo model in high magnetic fields
Using a recently developed perturbative renormalization group (RG) scheme, we
calculate analytically the spectral function of a Kondo impurity for either
large frequencies w or large magnetic field B and arbitrary frequencies. For
large w >> max[B,T_K] the spectral function decays as 1/ln^2[ w/T_K ] with
prefactors which depend on the magnetization. The spin-resolved spectral
function displays a pronounced peak at w=B with a characteristic asymmetry. In
a detailed comparison with results from numerical renormalization group (NRG)
and bare perturbation theory in next-to-leading logarithmic order, we show that
our perturbative RG scheme is controlled by the small parameter 1/ln[
max(w,B)/T_K]. Furthermore, we assess the ability of the NRG to resolve
structures at finite frequencies.Comment: 8 pages, version published in PRB, minor change
Report of the Task Force on Enhancing technology use in agriculture insurance
Pradhan Mantri Fasal Bima Yojana (PMFBY) is a flagship scheme of the Government of India to
provide insurance coverage and financial support to farmers in the event of failure of any of the
notified crops, unsown area and damage to harvest produce as a result of natural calamities, pests
and diseases to stabilise the income of farmers, and to encourage them to adopt modern agricultural
practices. The scheme is a considerable improvement over all previous insurance schemes in India
and is heavily subsidised by the state and central governments. The scheme aims to cover 50 percent
of the farming households within next 3 years.
During its implementation in the last one season, several challenges relating to enrolment, yield
estimation, loss assessment, and claim settlement were reported by farmers, insurance companies
as well as the state governments. It was also noted that several technological opportunities existed
for possibly leveraging support to the Indian crop insurance program for enhanced efficiency and
effectiveness. NITI Aayog of the Government of India, therefore, constituted a Task Force to deliberate
on this subject and identify such potential opportunities. This report summarises the recommendations
of the Task Force.
The Task Force constituted to address the issue of technology support to crop insurance comprised
the following 5 sub-groups: (1) Remote Sensing & Drones; (2) Decision Support Systems, Crop
Modelling & Integrated Approaches; (3) IT/ICT in Insurance; (4) Crop Cutting Experiments (CCEs); and
(5) Technologies for Livestock and Aquaculture Insurance. Each sub-group had several discussions
with experts in the respective areas, and submitted draft reports. More than 100 experts related to
professional research agencies, insurance industry, banks, and the government contributed to these
discussions. Technological options available in the country and abroad were considered by all groups.
The Task Force together with the sub-groups then deliberated on key issues and formulated its
recommendations as presented in this report. During the discussions it was realised that there were
many administrative and institutional issues that needed to be addressed in PMFBY. However, the
focus of the Task Force was on its main mandate, technology use in crop insurance. We hope these
recommendations would help the Indian crop insurance sector take full advantage of the technological
options suggested so as to increase its efficacy and effectiveness leading to reduced agrarian distress
in the country
Quantum transport through STM-lifted single PTCDA molecules
Using a scanning tunneling microscope we have measured the quantum
conductance through a PTCDA molecule for different configurations of the
tip-molecule-surface junction. A peculiar conductance resonance arises at the
Fermi level for certain tip to surface distances. We have relaxed the molecular
junction coordinates and calculated transport by means of the Landauer/Keldysh
approach. The zero bias transmission calculated for fixed tip positions in
lateral dimensions but different tip substrate distances show a clear shift and
sharpening of the molecular chemisorption level on increasing the STM-surface
distance, in agreement with experiment.Comment: accepted for publication in Applied Physics
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