154 research outputs found
Finite temperature damping of collective modes of a BCS-BEC crossover superfluid
A new mechanism is proposed to explain the puzzling damping of collective
excitations, which was recently observed in the experiments of strongly
interacting Fermi gases below the superfluid critical temperature on the
fermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density
and damping rate are calculated with effective field theory. We find that a
dominant damping process is due to the interaction between superfluid phonons
and thermally excited fermionic quasiparticles, in contrast to the previously
proposed pair-breaking mechanism. Results from our effective model are compared
quantitatively with recent experimental findings, showing a good agreement.Comment: final version, 9 pages, 4 figure
Stripe, checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices
We study instabilities of single-species fermionic atoms in the p-orbital
bands in two-dimensional optical lattices at noninteger filling against
interactions. Charge density wave and orbital density wave orders with stripe
or checkerboard patterns are found for attractive and repulsive interactions,
respectively. The superfluid phase, usually expected of attractively
interacting fermions, is strongly suppressed. We also use field theory to
analyze the possible phase-transitions from orbital stripe order to
liquid-crystal phases and obtain the phase diagram. The condition of
nearly-perfect Fermisurface nesting, which is key to the above results, is
shown robustly independent of fermion fillings in such p-orbital systems, and
the momentum of density wave oscillation is highly tunable.
Such remarkable features show the promise of making those exotic orbital
phases, which are of broad interest in condensed-matter physics, experimentally
realizable with optical lattice gases.Comment: final version, 8 pages, 5 figure
Consistency and Consensus Driven for Hesitant Fuzzy Linguistic Decision Making with Pairwise Comparisons
Hesitant fuzzy linguistic preference relation (HFLPR) is of interest because
it provides an efficient way for opinion expression under uncertainty. For
enhancing the theory of decision making with HFLPR, the paper introduces an
algorithm for group decision making with HFLPRs based on the acceptable
consistency and consensus measurements, which involves (1) defining a hesitant
fuzzy linguistic geometric consistency index (HFLGCI) and proposing a procedure
for consistency checking and inconsistency improving for HFLPR; (2) measuring
the group consensus based on the similarity between the original individual
HFLPRs and the overall perfect HFLPR, then establishing a procedure for
consensus ensuring including the determination of decision-makers weights. The
convergence and monotonicity of the proposed two procedures have been proved.
Some experiments are furtherly performed to investigate the critical values of
the defined HFLGCI, and comparative analyses are conducted to show the
effectiveness of the proposed algorithm. A case concerning the performance
evaluation of venture capital guiding funds is given to illustrate the
availability of the proposed algorithm. As an application of our work, an
online decision-making portal is finally provided for decision-makers to
utilize the proposed algorithms to solve decision-making problems.Comment: Pulished by Expert Systems with Applications (ISSN: 0957-4174
Time reversal symmetry breaking of -orbital bosons in a one-dimensional optical lattice
We study bosons loaded in a one-dimensional optical lattice of two-fold
-orbital degeneracy at each site. Our numerical simulations find an
anti-ferro-orbital p+ip, a homogeneous p Mott insulator phase and
two kinds of superfluid phases distinguished by the orbital order
(anti-ferro-orbital and para-orbital). The anti-ferro-orbital order breaks time
reversal symmetry. Experimentally observable evidence is predicted for the
phase transition between the two different superfluid phases. We also discover
that the quantum noise measurement is able to provide a concrete evidence of
time reversal symmetry breaking in the first Mott phase.Comment: 4+ pages, version accepted by Phys. Rev. Let
Masked Vision and Language Pre-training with Unimodal and Multimodal Contrastive Losses for Medical Visual Question Answering
Medical visual question answering (VQA) is a challenging task that requires
answering clinical questions of a given medical image, by taking consider of
both visual and language information. However, due to the small scale of
training data for medical VQA, pre-training fine-tuning paradigms have been a
commonly used solution to improve model generalization performance. In this
paper, we present a novel self-supervised approach that learns unimodal and
multimodal feature representations of input images and text using medical image
caption datasets, by leveraging both unimodal and multimodal contrastive
losses, along with masked language modeling and image text matching as
pretraining objectives. The pre-trained model is then transferred to downstream
medical VQA tasks. The proposed approach achieves state-of-the-art (SOTA)
performance on three publicly available medical VQA datasets with significant
accuracy improvements of 2.2%, 14.7%, and 1.7% respectively. Besides, we
conduct a comprehensive analysis to validate the effectiveness of different
components of the approach and study different pre-training settings. Our codes
and models are available at https://github.com/pengfeiliHEU/MUMC.Comment: accepted by MICCAI202
Research on unsteady performance of a two-stage self-priming centrifugal pump
In order to study the unsteady performance of a two-stage self-priming centrifugal pump, the unsteady numerical calculation in a two-stage self-priming centrifugal pump was performed and energy characteristics experiments and self-priming experiments were carried out. The pressure pulsation and radial force in the pump were then analyzed. The results show that numerical calculation values are close to the experiment values. Head deviation of the pump is less than 3Â %, and efficiency deviation of the pump is less than 2 percentage points. Compared with monitoring point P1, the pressure fluctuation coefficient of monitoring point P3 at the design flow rate is reduced by 61Â %. Compared with monitoring point P8, the pressure fluctuation coefficient of monitoring point P5 is reduced by 70Â %. The radial force on the radial guide-vane is obviously smaller than that on the volute. Under the same flow rate, radial force on the volute of second-stage pump is almost 20 times larger than that on the radial guide-van of first-stage pump
Magnetosheath ion field-aligned anisotropy and implications for ion leakage to the foreshock
The ion foreshock is highly dynamic, disturbing the bow shock and the
magnetosphere-ionosphere system. To forecast foreshock-driven space weather
effects, it is necessary to model foreshock ions as a function of upstream
shock parameters. Case studies in the accompanying paper show that
magnetosheath ions sometimes exhibit strong field-aligned anisotropy towards
the upstream direction, which may be responsible for enhancing magnetosheath
leakage and therefore foreshock ion density. To understand the conditions
leading to such an anisotropy and the potential for enhanced leakage, we
perform case studies and a statistical study of magnetosheath and foreshock
region data surrounding ~500 THEMIS bow shock crossings. We quantify the
anisotropy using the heat flux along the field-aligned direction. We show that
the strong field-aligned heat flux persists across the entire magnetosheath
from the magnetopause to the bow shock. Ion distribution functions reveal that
the strong heat flux is caused by a secondary thermal population. We find that
stronger anisotropy events exhibit heat flux preferentially towards the
upstream direction near the bow shock and occur under larger IMF strength and
larger solar wind dynamic pressure and/or energy flux. Additionally, we show
that near the bow shock, magnetosheath leakage is a significant contributor to
foreshock ions, and through enhancing the leakage the magnetosheath ion
anisotropy can modulate the foreshock ion velocity and density. Our results
imply that likely due to field line draping and compression against the
magnetopause that leads to a directional mirror force, modeling the foreshock
ions necessitates a more global accounting of downstream conditions.Comment: Under review by JGR Space Physic
An Integration Mechanism between Demand and Supply Side Management of Electricity Markets
One of the main challenges in the emerging smart grid is to jointly consider the demand and supply, which is also reflected in the wholesale market (supply side) and the retail market (demand side). When integrating the demand and supply side into one framework, the mechanism for determining the market clearing price has been changed. This is due to the demand variations in the demand side in response to the market clearing price and the change of generation costs in the supply side from the demand variation. In order to find the best balance between the supply and demand under the demand response management scheme, this paper proposes a new integrated supply and demand coordination mechanism for the electricity market and smart pricing methods for generator and retailers. Another important contribution of this paper is to develop an efficient algorithm to find the match equilibrium between the demand and supply sides in the new proposed mechanism. Experimental results demonstrate that the new mechanism can effectively handle unpredictable demand under dynamic retail pricing and support the ISO to dispatch the generation economically. It can also help in achieving the goals of dynamic pricing such as maximizing the profits for retailers
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