1,673 research outputs found
Ground-state phase diagram of the Kondo lattice model on triangular-to-kagome lattices
We investigate the ground-state phase diagram of the Kondo lattice model with
classical localized spins on triangular-to-kagome lattices by using a
variational calculation. We identify the parameter regions where a
four-sublattice noncoplanar order is stable with a finite spin scalar chirality
while changing the lattice structure from triangular to kagome continuously.
Although the noncoplanar spin states appear in a wide range of parameters, the
spin configurations on the kagome network become coplanar as approaching the
kagome lattice; eventually, the scalar chirality vanishes for the kagome
lattice model.Comment: 7 pages, 3 figure
Analysis of quantum conductance of carbon nanotube junctions by the effective mass approximation
The electron transport through the nanotube junctions which connect the
different metallic nanotubes by a pair of a pentagonal defect and a heptagonal
defect is investigated by Landauer's formula and the effective mass
approximation. From our previous calculations based on the tight binding model,
it has been known that the conductance is determined almost only by two
parameters,i.e., the energy in the unit of the onset energy of more than two
channels and the ratio of the radii of the two nanotubes. The conductance is
calculated again by the effective mass theory in this paper and a simple
analytical form of the conductance is obtained considering a special boundary
conditions of the envelop wavefunctions. The two scaling parameters appear
naturally in this treatment. The results by this formula coincide fairly well
with those of the tight binding model.
The physical origin of the scaling law is clarified by this approach.Comment: RevTe
Thermo-mechanical behaviour of a compacted swelling clay
Compacted unsaturated swelling clay is often considered as a possible buffer
material for deep nuclear waste disposal. An isotropic cell permitting
simultaneous control of suction, temperature and pressure was used to study the
thermo-mechanical behaviour of this clay. Tests were performed at total
suctions ranging from 9 to 110 MPa, temperature from 25 to 80 degrees C,
isotropic pressure from 0.1 to 60 MPa. It was observed that heating at constant
suction and pressure induces either swelling or contraction. The results from
compression tests at constant suction and temperature evidenced that at lower
suction, the yield pressure was lower, the elastic compressibility parameter
and the plastic compressibility parameter were higher. On the other hand, at a
similar suction, the yield pressure was slightly influenced by the temperature;
and the compressibility parameters were insensitive to temperature changes. The
thermal hardening phenomenon was equally evidenced by following a
thermo-mechanical path of loading-heating-cooling-reloading
Band structures of periodic carbon nanotube junctions and their symmetries analyzed by the effective mass approximation
The band structures of the periodic nanotube junctions are investigated by
the effective mass theory and the tight binding model.
The periodic junctions are constructed by introducing pairs of a pentagonal
defect and a heptagonal defect periodically in the carbon nanotube.
We treat the periodic junctions whose unit cell is composed by two kinds of
metallic nanotubes with almost same radii, the ratio of which is between 0.7
and 1 .
The discussed energy region is near the undoped Fermi level where the channel
number is kept to two, so there are two bands.
The energy bands are expressed with closed analytical forms by the effective
mass theory with some assumptions, and they coincide well with the numerical
results by the tight binding model. Differences between the two methods are
also discussed. Origin of correspondence between the band structures and the
phason pattern discussed in Phys. Rev. B {\bf 53}, 2114, is clarified. The
width of the gap and the band are in inverse proportion to the length of the
unit cell, which is the sum of the lengths measured along the tube axis in each
tube part and along 'radial' direction in the junction part. The degeneracy and
repulsion between the two bands are determined only from symmetries.Comment: RevTeX, gif fil
Radiative Corrections to Double Dalitz Decays: Effects on Invariant Mass Distributions and Angular Correlations
We review the theory of meson decays to two lepton pairs, including the cases
of identical as well as non-identical leptons, as well as CP-conserving and
CP-violating couplings. A complete lowest-order calculation of QED radiative
corrections to these decays is discussed, and comparisons of predicted rates
and kinematic distributions between tree-level and one-loop-corrected
calculations are presented for both pi-zero and K-zero decays.Comment: 25 pages, 18 figures, added figures and commentar
Compensation algorithms based on the p-q and CPC theories for switching compensators in micro-grids
The main objective of this paper is to com-pare the applicability and p erformance of a switching
compensator when it is controlled by algorithms derived
from the pq–Theory and from the Current’s Physical
Components Power Theory (CPC-Theory) considering a
micro-grid application. Compensation characteristics
derived from each one of these set of power definitions
are highlighted, and simulation results of test cases are
shown. Special attention is put on the oscillating instan-taneous real power, as it may produce torque oscillations
or frequency variations in weak systems (micro-grids)
generators. The oscillating instantaneous real power, as
defined in the pq-Theory, gives the amount of energy
oscillating between the source and the load, and its com-pensation using a switching compensator must have an
energy storage element to exchan ge it with the load. The
energy storage element can be ea sily calculated with the
pq-Theory
Instantaneous p-q power theory for control of compensators in micro-grids
The main objective of this tutorial is to present the
basic concepts on the instantaneous p-q Theory and them show
its applicability for controlling switching converters connected in
a micro-grid. These converters can be used for connecting
renewable energy sources (solar, wind, and others) to the micro-grids or for harmonic, reactive power or unbalance
compensation, and even for voltage regulation. The emphasis is
given on the compensation characteristics derived from the p-q
Theory, and simulation results of test cases are shown. Special
attention is put on the oscillating component of the instantaneous
real power, as it may produce torque oscillations or frequency
variations in weak systems (micro-grids) generators. This
oscillating component, as defined in the p-q Theory, gives the
amount of oscillating energy between the source and the load,
and its compensation through a switching compensator must have
an energy storage element to exchange it with the load. With the
p-q Theory the energy storage element can be easily calculated
as a function of the average component of the instantaneous real
power, which depends on the observation period.The authors acknowledge the support from FAPERJ partially for the development of this study and especially for the financial support for the participation in the conference
The Fire INventory from NCAR (FINN): A High Resolution Global Model to Estimate the Emissions from Open Burning
The Fire INventory from NCAR version 1.0 (FINNv1) provides daily, 1 km resolution, global estimates of the trace gas and particle emissions from open burning of biomass, which includes wildfire, agricultural fires, and prescribed burning and does not include biofuel use and trash burning. Emission factors used in the calculations have been updated with recent data, particularly for the non-methane organic compounds (NMOC). The resulting global annual NMOC emission estimates are as much as a factor of 5 greater than some prior estimates. Chemical speciation profiles, necessary to allocate the total NMOC emission estimates to lumped species for use by chemical transport models, are provided for three widely used chemical mechanisms: SAPRC99, GEOS-CHEM, and MOZART-4. Using these profiles, FINNv1 also provides global estimates of key organic compounds, including formaldehyde and methanol. Uncertainties in the emissions estimates arise from several of the method steps. The use of fire hot spots, assumed area burned, land cover maps, biomass consumption estimates, and emission factors all introduce error into the model estimates. The uncertainty in the FINNv1 emission estimates are about a factor of two; but, the global estimates agree reasonably well with other global inventories of biomass burning emissions for CO, CO2, and other species with less variable emission factors. FINNv1 emission estimates have been developed specifically for modeling atmospheric chemistry and air quality in a consistent framework at scales from local to global. The product is unique because of the high temporal and spatial resolution, global coverage, and the number of species estimated. FINNv1 can be used for both hindcast and forecast or near-real time model applications and the results are being critically evaluated with models and observations whenever possible
Energy efficiency parametric design tool in the framework of holistic ship design optimization
Recent International Maritime Organization (IMO) decisions with respect to measures to reduce the emissions from maritime greenhouse gases (GHGs) suggest that the collaboration of all major stakeholders of shipbuilding and ship operations is required to address this complex techno-economical and highly political problem efficiently. This calls eventually for the development of proper design, operational knowledge, and assessment tools for the energy-efficient design and operation of ships, as suggested by the Second IMO GHG Study (2009). This type of coordination of the efforts of many maritime stakeholders, with often conflicting professional interests but ultimately commonly aiming at optimal ship design and operation solutions, has been addressed within a methodology developed in the EU-funded Logistics-Based (LOGBASED) Design Project (2004–2007). Based on the knowledge base developed within this project, a new parametric design software tool (PDT) has been developed by the National Technical University of Athens, Ship Design Laboratory (NTUA-SDL), for implementing an energy efficiency design and management procedure. The PDT is an integral part of an earlier developed holistic ship design optimization approach by NTUA-SDL that addresses the multi-objective ship design optimization problem. It provides Pareto-optimum solutions and a complete mapping of the design space in a comprehensive way for the final assessment and decision by all the involved stakeholders. The application of the tool to the design of a large oil tanker and alternatively to container ships is elaborated in the presented paper
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