21,991 research outputs found
Smart Loads for Voltage Control in Distribution Networks
This paper shows that the smart loads (SLs) could be effective in mitigating voltage problems caused by photovoltaic (PV) generation and electric vehicle (EV) charging in low-voltage (LV) distribution networks. Limitations of the previously reported SL configuration with only series reactive compensator (SLQ) (one converter) is highlighted in this paper. To overcome these limitations, an additional shunt converter is used in back-to-back (B2B) configuration to support the active power exchanged by the series converter, which increases the flexibility of the SL without requiring any energy storage. Simulation results on a typical U.K. LV distribution network are presented to compare the effectiveness of an SL with B2B converters (SLBCs) against an SLQ in tackling under- and over-voltage problems caused by EV or PV. It is shown that SLBCs can regulate the main voltage more effectively than SLQs especially under overvoltage condition. Although two converters are required for each SLBC, it is shown that the apparent power capacity of each converter is required to be significantly less than that of an equivalent SLQ
Emergence of Topological and Strongly Correlated Ground States in trapped Rashba Spin-Orbit Coupled Bose Gases
We theoretically study an interacting few-body system of Rashba spin-orbit
coupled two-component Bose gases confined in a harmonic trapping potential. We
solve the interacting Hamiltonian at large Rashba coupling strengths using
Exact Diagonalization scheme, and obtain the ground state phase diagram for a
range of interatomic interactions and particle numbers. At small particle
numbers, we observe that the bosons condense to an array of topological states
with n+1/2 quantum angular momentum vortex configurations, where n = 0, 1, 2,
3... At large particle numbers, we observe two distinct regimes: at weaker
interaction strengths, we obtain ground states with topological and symmetry
properties that are consistent with mean-field theory computations; at stronger
interaction strengths, we report the emergence of strongly correlated ground
states.Comment: 14 pages, 9 figure
The Unexpected Impact of Information-Sharing on US Pharmaceutical Supply-Chains
This paper examines the introduction of information-sharing into the supply chains for pharmaceutical products in the United States. This introduction was unusual for several reasons. First, it was catalyzed from outside the industry, by a Securities and Exchange Commission (SEC) investigation into improper financial reporting by a single manufacturer. Second, it was initiated by pharmaceutical manufacturers in order to keep distributor inventories low. Third, although its effect on pharmaceutical distributors has been profound, evidence indicates that information-sharing has had no impact on pharmaceutical manufacturers' own inventorymanagement practices.
A radiative transfer scheme for cosmological reionization based on a local Eddington tensor
A radiative transfer scheme is presented, based on a moment description of
the equation of radiative transfer and the so-called ``M1 closure model'' for
the Eddington tensor. This model features a strictly hyperbolic transport step
for radiation: it has been implemented using standard Godunov--like techniques
in a new code called ATON. Coupled to simple models of ionization chemistry and
photo-heating, ATON is able to reproduce the results of other schemes on a
various set of standard tests such as the expansion of a HII region, the
shielding of the radiation by dense clumps and cosmological ionization by
multiple sources. Being simple yet robust, such a scheme is intended to be
naturally and easily included in grid--based cosmological fluid solvers.Comment: 14 pages, 13 figures, submitted to MNRA
Monad Bundles in Heterotic String Compactifications
In this paper, we study positive monad vector bundles on complete
intersection Calabi-Yau manifolds in the context of E8 x E8 heterotic string
compactifications. We show that the class of such bundles, subject to the
heterotic anomaly condition, is finite and consists of about 7000 models. We
explain how to compute the complete particle spectrum for these models. In
particular, we prove the absence of vector-like family anti-family pairs in all
cases. We also verify a set of highly non-trivial necessary conditions for the
stability of the bundles. A full stability proof will appear in a companion
paper. A scan over all models shows that even a few rudimentary physical
constraints reduces the number of viable models drastically.Comment: 35 pages, 4 figure
Exploring Positive Monad Bundles And A New Heterotic Standard Model
A complete analysis of all heterotic Calabi-Yau compactifications based on
positive two-term monad bundles over favourable complete intersection
Calabi-Yau threefolds is performed. We show that the original data set of about
7000 models contains 91 standard-like models which we describe in detail. A
closer analysis of Wilson-line breaking for these models reveals that none of
them gives rise to precisely the matter field content of the standard model. We
conclude that the entire set of positive two-term monads on complete
intersection Calabi-Yau manifolds is ruled out on phenomenological grounds. We
also take a first step in analyzing the larger class of non-positive monads. In
particular, we construct a supersymmetric heterotic standard model within this
class. This model has the standard model gauge group and an additional
U(1)_{B-L} symmetry, precisely three families of quarks and leptons, one pair
of Higgs doublets and no anti-families or exotics of any kind.Comment: 48 page
Reduced chemistry for butanol isomers at engine-relevant conditions
Butanol has received significant research attention as a second-generation
biofuel in the past few years. In the present study, skeletal mechanisms for
four butanol isomers were generated from two widely accepted, well-validated
detailed chemical kinetic models for the butanol isomers. The detailed models
were reduced using a two-stage approach consisting of the directed relation
graph with error propagation and sensitivity analysis. During the reduction
process, issues were encountered with pressure-dependent reactions formulated
using the logarithmic pressure interpolation approach; these issues are
discussed and recommendations made to avoid ambiguity in its future
implementation in mechanism development. The performance of the skeletal
mechanisms generated here was compared with that of detailed mechanisms in
simulations of autoignition delay times, laminar flame speeds, and perfectly
stirred reactor temperature response curves and extinction residence times,
over a wide range of pressures, temperatures, and equivalence ratios. The
detailed and skeletal mechanisms agreed well, demonstrating the adequacy of the
resulting reduced chemistry for all the butanol isomers in predicting global
combustion phenomena. In addition, the skeletal mechanisms closely predicted
the time-histories of fuel mass fractions in homogeneous compression-ignition
engine simulations. The performance of each butanol isomer was additionally
compared with that of a gasoline surrogate with an antiknock index of 87 in a
homogeneous compression-ignition engine simulation. The gasoline surrogate was
consumed faster than any of the butanol isomers, with tert-butanol exhibiting
the slowest fuel consumption rate. While n-butanol and isobutanol displayed the
most similar consumption profiles relative to the gasoline surrogate, the two
literature chemical kinetic models predicted different orderings.Comment: 39 pages, 16 figures. Supporting information available via
https://doi.org/10.1021/acs.energyfuels.6b0185
Criterion for bosonic superfluidity in an optical lattice
We show that the current method of determining superfluidity in optical
lattices based on a visibly sharp bosonic momentum distribution
can be misleading, for even a normal Bose gas can have a similarly sharp
. We show that superfluidity in a homogeneous system can be
detected from the so-called visibility of that must
be 1 within , where is the number of bosons. We also show that
the T=0 visibility of trapped lattice bosons is far higher than what is
obtained in some current experiments, suggesting strong temperature effects and
that these states can be normal. These normal states allow one to explore the
physics in the quantum critical region.Comment: 4 pages, 2 figures; published versio
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