367 research outputs found
Von K\'arm\'an vortex street in a Bose-Einstein condensate
Vortex shedding from an obstacle potential moving in a Bose-Einstein
condensate is investigated. Long-lived alternately aligned vortex pairs are
found to form in the wake, as for the von K\'arm\'an vortex street in classical
viscous fluids. Various patterns of vortex shedding are systematically studied
and the drag force on the obstacle is calculated. It is shown that the
phenomenon can be observed in a trapped system.Comment: 4 pages, 5 figure
Choquet integrals, Hausdorff content and fractional operators
It is shown that the fractional integral operator , ,
and the fractional maximal operator , , are bounded
on weak Choquet spaces with respect to Hausdorff content. We also investigate
these operators on Choquet-Morrey spaces. These results are extensions of the
previous works due to Adams, Orobitg and Verdera, and Tang. The results for the
fractional integral operator are essentially new.Comment: 12 page
Rayleigh-Taylor instability and mushroom-pattern formation in a two-component Bose-Einstein condensate
The Rayleigh-Taylor instability at the interface in an immiscible
two-component Bose-Einstein condensate is investigated using the mean-field and
Bogoliubov theories. Rayleigh-Taylor fingers are found to grow from the
interface and mushroom patterns are formed. Quantized vortex rings and vortex
lines are then generated around the mushrooms. The Rayleigh-Taylor instability
and mushroom-pattern formation can be observed in a trapped system.Comment: 5 pages, 4 figure
Quantum Kelvin-Helmholtz instability in phase-separated two-component Bose-Einstein condensates
We theoretically study the Kelvin-Helmholtz instability in phase-separated
two-component Bose-Einstein condensates using the Gross-Pitaevskii and
Bogoliubov-de Gennes models. A flat interface between the two condensates is
shown to deform into sawtooth or Stokes-like waves, leading to the formation of
singly quantized vortices on the peaks and troughs of the waves. This scenario
of interface instability in quantum fluids is quite different from that in
classical fluids.Comment: 5 pages, 4 figure
Pressure drop evaluation based on two-phase flow observation in packed bed system
Two-phase pressure drop in the debris has been studied by many researchers concerning the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow patterns on interfacial drag and pressure drop. Usually, it would not be easy to visualize such two-phase flow behavior in a randomly packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates a two-dimensional network of porous structures, was fabricated to avoid overlapping bubbles. The two-phase flow pattern in the porous structure has been identified by high-speed imaging of the two-dimensional network model. The flow regime map based on the flow pattern visualization results is applied to the pressure drop evaluation and it could reduce the overestimation of experimental values. The experimental results suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model
Capillary instability in a two-component Bose-Einstein condensate
Capillary instability and the resulting dynamics in an immiscible
two-component Bose-Einstein condensate are investigated using the mean-field
and Bogoliubov analyses. A long, cylindrical condensate surrounded by the other
component is dynamically unstable against breakup into droplets due to the
interfacial tension arising from the quantum pressure and interactions. A
heteronuclear system confined in a cigar-shaped trap is proposed for realizing
this phenomenon experimentally.Comment: 7 pages, 6 figure
Dynamics of bubbles in a two-component Bose-Einstein condensate
The dynamics of a phase-separated two-component Bose-Einstein condensate are
investigated, in which a bubble of one component moves through the other
component. Numerical simulations of the Gross--Pitaevskii equation reveal a
variety of dynamics associated with the creation of quantized vortices. In two
dimensions, a circular bubble deforms into an ellipse and splits into fragments
with vortices, which undergo the Magnus effect. The B\'enard--von K\'arm\'an
vortex street is also generated. In three dimensions, a spherical bubble
deforms into toruses with vortex rings. When two rings are formed, they exhibit
leapfrogging dynamics.Comment: 6 pages, 7 figure
RNA-seq Transcriptional Profiling of an Arbuscular Mycorrhiza Provides Insights into Regulated and Coordinated Gene Expression in Lotus japonicus and Rhizophagus irregularis
Gene expression during arbuscular mycorrhizal development is highly orchestrated in both plants and arbuscular mycorrhizal fungi. To elucidate the gene expression profiles of the symbiotic association, we performed a digital gene expression analysis of Lotus japonicus and Rhizophagus irregularis using a HiSeq 2000 next-generation sequencer with a Cufflinks assembly and de novo transcriptome assembly. There were 3,641 genes differentially expressed during arbuscular mycorrhizal development in L. japonicus, approximately 80% of which were up-regulated. The up-regulated genes included secreted proteins, transporters, proteins involved in lipid and amino acid metabolism, ribosomes and histones. We also detected many genes that were differentially expressed in small-secreted peptides and transcription factors, which may be involved in signal transduction or transcription regulation during symbiosis. Coregulated genes between arbuscular mycorrhizal and root nodule symbiosis were not particularly abundant, but transcripts encoding for membrane traffic-related proteins, transporters and iron transport-related proteins were found to be highly co-up-regulated. In transcripts of arbuscular mycorrhizal fungi, expansion of cytochrome P450 was observed, which may contribute to various metabolic pathways required to accommodate roots and soil. The comprehensive gene expression data of both plants and arbuscular mycorrhizal fungi provide a powerful platform for investigating the functional and molecular mechanisms underlying arbuscular mycorrhizal symbiosis.ArticlePLANT AND CELL PHYSIOLOGY. 56(8):1490-1511 (2015)journal articl
Crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates
Dynamical instabilities at the interface between two Bose--Einstein
condensates that are moving relative to each other are investigated using
mean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant
when the interface thickness is much smaller than the wavelength of the
unstable interface mode, whereas the counter-superflow instability becomes
dominant in the opposite case. These instabilities emerge not only in an
immiscible system but also in a miscible system where an interface is produced
by external potential. Dynamics caused by these instabilities are numerically
demonstrated in rotating trapped condensates.Comment: 10 pages, 9 figure
Neural Structure Fields with Application to Crystal Structure Autoencoders
Representing crystal structures of materials to facilitate determining them
via neural networks is crucial for enabling machine-learning applications
involving crystal structure estimation. Among these applications, the inverse
design of materials can contribute to next-generation methods that explore
materials with desired properties without relying on luck or serendipity. We
propose neural structure fields (NeSF) as an accurate and practical approach
for representing crystal structures using neural networks. Inspired by the
concepts of vector fields in physics and implicit neural representations in
computer vision, the proposed NeSF considers a crystal structure as a
continuous field rather than as a discrete set of atoms. Unlike existing
grid-based discretized spatial representations, the NeSF overcomes the tradeoff
between spatial resolution and computational complexity and can represent any
crystal structure. To evaluate the NeSF, we propose an autoencoder of crystal
structures that can recover various crystal structures, such as those of
perovskite structure materials and cuprate superconductors. Extensive
quantitative results demonstrate the superior performance of the NeSF compared
with the existing grid-based approach.Comment: 16 pages , 6 figures. 13 pages Supplementary Informatio
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