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A review of microgrid development in the United States – A decade of progress on policies, demonstrations, controls, and software tools
Microgrids have become increasingly popular in the United States. Supported by favorable federal and local policies, microgrid projects can provide greater energy stability and resilience within a project site or community. This paper reviews major federal, state, and utility-level policies driving microgrid development in the United States. Representative U.S. demonstration projects are selected and their technical characteristics and non-technical features are introduced. The paper discusses trends in the technology development of microgrid systems as well as microgrid control methods and interactions within the electricity market. Software tools for microgrid design, planning, and performance analysis are illustrated with each tool's core capability. Finally, the paper summarizes the successes and lessons learned during the recent expansion of the U.S. microgrid industry that may serve as a reference for other countries developing their own microgrid industries
A comparative study of the electronic and magnetic properties of BaFe_2As_2 and BaMn_2As_2 using the Gutzwiller approximation
To elucidate the role played by the transition metal ion in the pnictide
materials, we compare the electronic and magnetic properties of BaFe_{2}As_{2}
with BaMn_{2}As_{2}. To this end we employ the LDA+Gutzwiller method to analyze
the mass renormalizations and the size of the ordered magnetic moment of the
two systems. We study a model that contains all five transition metal 3d
orbitals together with the Ba-5d and As-4p states (ddp-model) and compare these
results with a downfolded model that consists of Fe/Mn d-states only (d-model).
Electronic correlations are treated using the multiband Gutzwiller
approximation. The paramagnetic phase has also been investigated using
LDA+Gutzwiller method with electron density self-consistency. The
renormalization factors for the correlated Mn 3d orbitals in the paramagnetic
phase of BaMn_{2}As_{2} are shown to be generally smaller than those of
BaFe_{2}As_{2}, which indicates that BaMn_{2}As_{2} has stronger electron
correlation effect than BaFe_{2}As_{2}. The screening effect of the main As 4p
electrons to the correlated Fe/Mn 3d electrons is evident by the systematic
shift of the results to larger Hund's rule coupling J side from the ddp-model
compared with those from the d-model. A gradual transition from paramagnetic
state to the antiferromagnetic ground state with increasing J is obtained for
the models of BaFe_{2}As_{2} which has a small experimental magnetic moment;
while a rather sharp jump occurs for the models of BaMn_{2}As_{2}, which has a
large experimental magnetic moment. The key difference between the two systems
is shown to be the d-level occupation. BaMn_{2}As_{2}, with approximately five
d-electrons per Mn atom, is for same values of the electron correlations closer
to the transition to a Mott insulating state than BaFe_{2}As_{2}. Here an
orbitally selective transition, required for a system with close to six
electrons only occurs at significantly larger values for the Coulomb
interactions
A model of rotating hotspots for 3:2 frequency ratio of HFQPOs in black hole X-ray binaries
We propose a model to explain a puzzling 3:2 frequency ratio of high
frequency quasi-periodic oscillations (HFQPOs) in black hole (BH) X-ray
binaries, GRO J1655-40, GRS 1915+105 and XTE J1550-564. In our model a
non-axisymmetric magnetic coupling (MC) of a rotating black hole (BH) with its
surrounding accretion disc coexists with the Blandford-Znajek (BZ) process. The
upper frequency is fitted by a rotating hotspot near the inner edge of the
disc, which is produced by the energy transferred from the BH to the disc, and
the lower frequency is fitted by another rotating hotspot somewhere away from
the inner edge of the disc, which arises from the screw instability of the
magnetic field on the disc. It turns out that the 3:2 frequency ratio of HFQPOs
in these X-ray binaries could be well fitted to the observational data with a
much narrower range of the BH spin. In addition, the spectral properties of
HFQPOs are discussed. The correlation of HFQPOs with jets from microquasars is
contained naturally in our model.Comment: 8 pages, 4 figures. accepted by MNRA
Existence problem of proton semi-bubble structure in the state of Si
The fully self-consistent Hartree-Fock (HF) plus random phase approximation
(RPA) based on Skyrme-type interaction is used to study the existence problem
of proton semi-bubble structure in the state of Si. The
experimental excitation energy and the B(E2) strength of the state in
Si can be reproduced quite well. The tensor effect is also studied. It
is shown that the tensor interaction has a notable impact on the excitation
energy of the state and a small effect on the B(E2) value. Besides, its
effect on the density distributions in the ground and state of
Si is negligible. Our present results with T36 and T44 show that the
state of Si is mainly caused by proton transiton from orbit to orbit, and the existence of a proton
semi-bubble structure in this state is very unlikely.Comment: 6 pages, 3 figures, 3 table
A new class of -d topological superconductor with topological classification
The classification of topological states of matter depends on spatial
dimension and symmetry class. For non-interacting topological insulators and
superconductors the topological classification is obtained systematically and
nontrivial topological insulators are classified by either integer or .
The classification of interacting topological states of matter is much more
complicated and only special cases are understood. In this paper we study a new
class of topological superconductors in dimensions which has
time-reversal symmetry and a spin conservation symmetry. We
demonstrate that the superconductors in this class is classified by
when electron interaction is considered, while the
classification is without interaction.Comment: 5 pages main text and 3 pages appendix. 1 figur
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