125 research outputs found
Water productivity in agriculture: a review of empirical evidence for selected Asian countries and India
In the context of the growing demand for water and the emerging water crisis, this paper examines the prospects for improving water use efficiency in agriculture that will help water savings and also increase crop yields per unit of water input. Evidences from experimental or farmer participatory trials in a cross section of regions, countries, sites in Asia and the Indo-Gangetic plains suggest that alternate agronomic and crop management practices such as zero-tillage, bed planting, non-puddled rice culture and laser leveling can result in water savings and also improve rice and wheat yields per unit of water input.Length: pp.214-225Irrigation efficiencyWater productivityRiceWheat
Detection of topological transitions by transport through molecules and nanodevices
We analyze the phase transitions of an interacting electronic system weakly
coupled to free-electron leads by considering its zero-bias conductance. This
is expressed in terms of two effective impurity models for the cases with and
without spin degeneracy. We demonstrate using the half-filled ionic Hubbard
ring that the weight of the first conductance peak as a function of external
flux or of the difference in gate voltages between even and odd sites allows
one to identify the topological charge transition between a correlated
insulator and a band insulator.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Thermopower of Kondo Effect in Single Quantum Dot Systems with Orbital at Finite Temperatures
We investigate the thermopower due to the orbital Kondo effect in a single
quantum dot system by means of the noncrossing approximation. It is elucidated
how the asymmetry of tunneling resonance due to the orbital Kondo effect
affects the thermopower under gate-voltage and magnetic-field control.Comment: 4 pages, 4 figures, proceeding of Second International Symposium on
Nanometer-Scale Quantum Physic
Spin-Polarized Transprot through Double Quantum Dots
We investigate spin-polarized transport phenomena through double quantum dots
coupled to ferromagnetic leads in series. By means of the slave-boson
mean-field approximation, we calculate the conductance in the Kondo regime for
two different configurations of the leads: spin-polarization of two
ferromagnetic leads is parallel or anti-parallel. It is found that transport
shows some remarkable properties depending on the tunneling strength between
two dots. These properties are explained in terms of the Kondo resonances in
the local density of states.Comment: 8 pages, 11 figure
Growth and ultraviolet application of Li2B4O7 crystals: Generation of the fourth and fifth harmonics of Nd:Y3Al5O12 lasers
Kondo resonant spectra in coupled quantum dots
The Kondo effect in coupled quantum dots is investigated from the viewpoint
of transmission spectroscopy using the slave-boson formalism of the Anderson
model. The antiferromagnetic spin-spin coupling between the dots is taken
into account. Conductance through the dots connected in a series is
characterized by the competition between the dot-dot tunneling coupling
and the level broadening in the dots (dot-lead coupling). When
, the Kondo resonance is formed between each dot and lead,
which is replaced by a spin-singlet state in the dots at low gate voltages. The
gate voltage dependence of has a sharp peak of in height in the
crossover region between the Kondo and spin-singlet states. The sharp peak of
survives when the energy levels are different between the dots. When , the "molecular levels" between the Kondo resonant states appear;
the Kondo resonant peaks are located below and above the Fermi level in the
leads at low gate voltages. The gate voltage dependence of has a broad
peak, which is robust against . The broad peak splits into two peaks when
the energy levels are different, reflecting the formation of the asymmetric
molecular levels between the Kondo resonant states.Comment: 21 pages, 8 figures, to appear in Phys. Rev.
All-solid-state tunable ultraviolet subnanosecond laser with direct pumping by the fifth harmonic of a Nd:YAG laser
We report what we believe is the first all-solid-state tunable ultraviolet laser pumped by the fifth harmonic of a Q-switched Nd:YAG laser. Our laser based on a Ce3+:LiLuF4 active medium stably generates a single, satellite-free, 0.88-ns pulse under 5-ns, 10-Hz repetition rate pumping conditions. A novel tilted-incident-angle side-pumping scheme resulted in a simple laser-cavity design. © 1998 Optical Society of America
Conductance through Quantum Dots Studied by Finite Temperature DMRG
With the Finite temperature Density Matrix Renormalization Group method
(FT-DMRG), we depeloped a method to calculate thermo-dynamical quantities and
the conductance of a quantum dot system. Conductance is written by the local
density of states on the dot. The density of states is calculated with the
numerical analytic continuation from the thermal Green's function which is
obtained directly from the FT-DMRG. Typical Kondo behaviors in the quantum dot
system are observed conveniently by comparing the conductance with the magnetic
and charge susceptibilities: Coulomb oscillation peaks and the unitarity limit.
We discuss advantage of this method compared with others.Comment: 14 pages, 13 fiure
NRG approach to the transport through a finite Hubbard chain connected to reservoirs
We study the low-energy properties of a Hubbard chain of finite size N_C
connected to two noninteracting leads using the numerical renormalization group
(NRG) method. The results obtained for N_C = 3 and 4 show that the low-lying
eigenstates have one-to-one correspondence with the free quasi-particle
excitations of a local Fermi liquid. It enables us to determine the transport
coefficients from the fixed-point Hamiltonian. At half-filling, the conductance
for even N_C decreases exponentially with increasing U showing a tendency
towards the development of a Mott-Hubbard gap. In contrast, for odd N_C, the
Fermi-liquid nature of the low-energy states assures perfect transmission
through the Kondo resonance. Our formulation to deduce the conductance from the
fixed-point energy levels can be applied to various types of interacting
systems.Comment: One typo found in Eq.(3) in previous version has been correcte
Perturbation Study of the Conductance through an Interacting Region Connected to Multi-Mode Leads
We study the effects of electron correlation on transport through an
interacting region connected to multi-mode leads based on the perturbation
expansion with respect to the inter-electron interaction. At zero temperature
the conductance defined in the Kubo formalism can be written in terms of a
single-particle Green's function at the Fermi energy, and it can be mapped onto
a transmission coefficient of the free quasiparticles described by an effective
Hamiltonian. We apply this formulation to a two-dimensional Hubbard model of
finite size connected to two noninteracting leads. We calculate the conductance
in the electron-hole symmetric case using the order self-energy. The
conductance shows several maximums in the dependence in some parameter
regions of , where () is the hopping matrix element in the
- (-) directions. This is caused by the resonance occurring in some of
the subbands, and is related with the dependence of the eigenvalues of the
effective Hamiltonian.Comment: 17 pages, 12 figures, to be published in J.Phys.Soc.Jpn. 71(2002)No.
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