192 research outputs found
Bubble expansion at strong coupling
The cosmological first-order phase transition (FOPT) can be of strong
dynamics but with its bubble wall velocity difficult to be determined due to
lack of detailed collision terms. Recent holographic numerical simulations of
strongly coupled theories with a FOPT prefer a relatively small wall velocity
linearly correlated with the phase pressure difference between false and true
vacua for a planar wall. In this Letter, we have analytically revealed the
non-relativistic limit of a planar/cylindrical/spherical wall expansion of a
bubble strongly interacting with the thermal plasma. The planar-wall result
reproduces the linear relation found previously in the holographic numerical
simulations. The results for cylindrical and spherical walls can be directly
tested in future numerical simulations. Once confirmed, the bubble wall
velocity for a strongly coupled FOPT can be expressed purely in terms of the
hydrodynamics without invoking the underlying microphysics.Comment: v1, 5 pages + 1 appendix, 2 figures; v2, 11 pages, 3 figures,
accepted for publication in Phys. Rev. D; v3, typos corrected, references
added, to match the published versio
Nearly deconfined spinon excitations in the square-lattice spin-1/2 Heisenberg antiferromagnet
We study the spin-excitation spectrum (dynamic structure factor) of the spin-1/2 square-lattice Heisenberg antiferromagnet and an extended model (the J−Q model) including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on Cu(DCOO)2⋅4D2O, where a broad spectral-weight continuum at wave vector q=(π,0) was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at (π,0) show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q=(π/2,π/2) (as also seen experimentally). We further investigate the reasons for the small magnon weight at (π,0) and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J−Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at (π,0) in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile (π,0)-magnon pole in the Heisenberg model and its depletion in the J−Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at (π,0) in the Heisenberg model, as well as the energy maximum and smaller continuum at (π/2,π/2). It can also account for the rapid loss of the (π,0) magnon with increasing Q and the remarkable persistence of a large magnon pole at q=(π/2,π/2) even at the deconfined critical point. The fragility of the magnons close to (π,0) in the Heisenberg model suggests that various interactions that likely are important in many materials—e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions—may also destroy these magnons and lead to even stronger spinon signatures than in Cu(DCOO)2⋅4D2O.We thank Wenan Guo, Akiko Masaki-Kato, Andrey Mishchenko, Martin Mourigal, Henrik Ronnow, Kai Schmidt, Cenke Xu, and Seiji Yunoki for useful discussions. Experimental data from Ref. [33] were kindly provided by N. B. Christensen and H. M. Ronnow. H. S. was supported by the China Postdoctoral Science Foundation under Grants No. 2016M600034 and No. 2017T100031. St.C. was funded by the NSFC under Grants No. 11574025 and No. U1530401. Y. Q. Q. and Z. Y. M. acknowledge funding from the Ministry of Science and Technology of China through National Key Research and Development Program under Grant No. 2016YFA0300502, from the key research program of the Chinese Academy of Sciences under Grant No. XDPB0803, and from the NSFC under Grants No. 11421092, No. 11574359, and No. 11674370, as well as the National Thousand-Young Talents Program of China. A. W. S. was funded by the NSF under Grants No. DMR-1410126 and No. DMR-1710170, and by the Simons Foundation. In addition H. S., Y. Q. Q., and Sy. C. thank Boston University's Condensed Matter Theory Visitors program for support, and A. W. S. thanks the Beijing Computational Science Research Center and the Institute of Physics, Chinese Academy of Sciences for visitor support. We thank the Center for Quantum Simulation Sciences at the Institute of Physics, Chinese Academy of Sciences, the Tianhe-1A platform at the National Supercomputer Center in Tianjin, Boston University's Shared Computing Cluster, and CALMIP (Toulouse) for their technical support and generous allocation of CPU time. (2016M600034 - China Postdoctoral Science Foundation; 2017T100031 - China Postdoctoral Science Foundation; 11574025 - NSFC; U1530401 - NSFC; 11421092 - NSFC; 11574359 - NSFC; 11674370 - NSFC; 2016YFA0300502 - Ministry of Science and Technology of China; XDPB0803 - Chinese Academy of Sciences; National Thousand-Young Talents Program of China; DMR-1410126 - NSF; DMR-1710170 - NSF; Simons Foundation; Boston University's Condensed Matter Theory Visitors program)Accepted manuscript and published version
Unconventional superfluidity of superconductivity on Penrose lattice
We theoretically investigate the gap function, superfluid density and the
transition temperature of the superconductivity (SC) on semi-periodic Penrose
lattice, where an attractive Hubbard model is adopted as an example. Firstly,
we clarify that the gap function, density of states and superfluid density are
all positively correlate to the extended degree of single particle states
around the Fermi energy. Secondly, we identify that the paramagnetic component
of the superfluid density does not decay to zero in the thermodynamic limit,
which is completely different from the periodic system. The difference between
the diamagnetic and paramagnetic currents keeps stable with whatever scaling,
which is consistent with recent experimental results that although the
superfluid density is lower than that of the periodic system, the system has
bulk SC. Thirdly, we find that both the superfluid density and SC transition
temperature can be boosted with the increase of disorder strength, which should
be general to quasicrystal but unusual to periodic systems, reflecting the
interplay between the underlying geometry and disorder.Comment: 7 pages, 4 figures. version accepted by Sci. China-Phys. Mech. &
Astro
A Data Driven Method for Multi-step Prediction of Ship Roll Motion in High Sea States
Ship roll motion in high sea states has large amplitudes and nonlinear
dynamics, and its prediction is significant for operability, safety, and
survivability. This paper presents a novel data-driven methodology to provide a
multi-step prediction of ship roll motions in high sea states. A hybrid neural
network is proposed that combines long short-term memory (LSTM) and
convolutional neural network (CNN) in parallel. The motivation is to extract
the nonlinear dynamic characteristics and the hydrodynamic memory information
through the advantage of CNN and LSTM, respectively. For the feature selection,
the time histories of motion states and wave heights are selected to involve
sufficient information. Taken a scaled KCS as the study object, the ship
motions in sea state 7 irregular long-crested waves are simulated and used for
the validation. The results show that at least one period of roll motion can be
accurately predicted. Compared with the single LSTM and CNN methods, the
proposed method has better performance in predicting the amplitude of roll
angles. Besides, the comparison results also demonstrate that selecting motion
states and wave heights as feature space improves the prediction accuracy,
verifying the effectiveness of the proposed method
General bubble expansion at strong coupling
The strongly-coupled system like the quark-hadron transition (if it is of
first order) is becoming an active play-yard for the physics of cosmological
first-order phase transitions. However, the traditional field theoretic
approach to strongly-coupled first-order phase transitions is of great
challenge, driving recent efforts from holographic dual theories with explicit
numerical simulations. These holographic numerical simulations have revealed an
intriguing linear correlation between the phase pressure difference (pressure
difference away from the wall) to the non-relativistic terminal velocity of an
expanding planar wall, which has been reproduced analytically alongside both
cylindrical and spherical walls from perfect-fluid hydrodynamics in our
previous study but only for a bag equation of state. We have also found in our
previous study a universal quadratic correlation between the wall pressure
difference (pressure difference near the bubble wall) to the non-relativistic
terminal wall velocity regardless of wall geometries. In this paper, we will
generalize these analytic relations between the phase/wall pressure difference
and terminal wall velocity into a more realistic equation of state beyond the
simple bag model, providing the most general predictions so far for future
tests from holographic numerical simulations of strongly-coupled first-order
phase transitionsComment: 22 pages, 10 figure
Synchrotron Radiation Dominates the Extremely Bright GRB 221009A
The brightest Gamma-ray burst, GRB 221009A, has spurred numerous theoretical
investigations, with particular attention paid to the origins of ultra-high
energy TeV photons during the prompt phase. However, analyzing the mechanism of
radiation of photons in the MeV range has been difficult because the high
flux causes pile-up and saturation effects in most GRB detectors. In this
letter, we present systematic modeling of the time-resolved spectra of the GRB
using unsaturated data obtained from Fermi/GBM (precursor) and
SATech-01/GECAM-C (main emission and flare). Our approach incorporates the
synchrotron radiation model, which assumes an expanding emission region with
relativistic speed and a global magnetic field that decays with radius, and
successfully fits such a model to the observational data. Our results indicate
that the spectra of the burst are fully in accordance with a synchrotron origin
from relativistic electrons accelerated at a large emission radius. The lack of
thermal emission in the prompt emission spectra supports a
Poynting-flux-dominated jet composition.Comment: 12 pages, 6 figures, 2 tables. Accepted for publication in ApJ
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Genomic Mutation Profile of Primary Gastrointestinal Diffuse Large B-Cell Lymphoma.
Primary gastrointestinal diffuse large B-cell lymphoma (GI-DLBCL) is the most common gastrointestinal lymphoma, but its genetic features are poorly understood. We performed whole-exome sequencing of 25 primary tumor samples from patients with GI-DLBCL and 23 matched normal tissue samples. Oncogenic mutations were screened, and the correlations between genetic mutations and clinicopathological characteristics were analyzed. Twenty-five patients with GI-DLBCL were enrolled in the genetic mutation analysis with a median of 184 (range 79-382) protein-altering variants per patient. We identified recurrent oncogenic mutations in GI-DLBCL, including those in TP53, MUC16, B2M, CCND3, HIST1H1C, NEB, and ID3. Compared with nodal DLBCL, GI-DLBCL exhibited an increased mutation frequency of TP53 and reduced mutation frequencies of PIM1, CREBBP, BCL2, KMT2D, and EZH2. Moreover, GI-DLBCL exhibited fewer MYD88 and CD79B mutations than DLBCL in the testis and central nervous system. GI-DLBCLs with HLA-B, MEF2A, RHOA, and NAV3 mutations exhibited a tendency toward a high proliferation index. MUC16 and ETV6 mutations often occurred in tumors with early clinical staging. Our data provide a comprehensive understanding of the landscape of mutations in a small subset of GI-DLBCLs. The genetic mutation profiles of GI-DLBCL differ from those of nodal DLBCL and DLBCL in immune-privileged sites. The different mutated genes are related to the NF-κB and JAK-STAT pathways, and the different pathogenetic mechanisms leading to the development of DLBCL may be influenced by the tissue microenvironment. Differences in genetic alterations might influence the clinicopathological characteristics of GI-DLBCL
Prediction of Ubiquitination Sites by Using the Composition of k-Spaced Amino Acid Pairs
As one of the most important reversible protein post-translation modifications, ubiquitination has been reported to be involved in lots of biological processes and closely implicated with various diseases. To fully decipher the molecular mechanisms of ubiquitination-related biological processes, an initial but crucial step is the recognition of ubiquitylated substrates and the corresponding ubiquitination sites. Here, a new bioinformatics tool named CKSAAP_UbSite was developed to predict ubiquitination sites from protein sequences. With the assistance of Support Vector Machine (SVM), the highlight of CKSAAP_UbSite is to employ the composition of k-spaced amino acid pairs surrounding a query site (i.e. any lysine in a query sequence) as input. When trained and tested in the dataset of yeast ubiquitination sites (Radivojac et al, Proteins, 2010, 78: 365–380), a 100-fold cross-validation on a 1∶1 ratio of positive and negative samples revealed that the accuracy and MCC of CKSAAP_UbSite reached 73.40% and 0.4694, respectively. The proposed CKSAAP_UbSite has also been intensively benchmarked to exhibit better performance than some existing predictors, suggesting that it can be served as a useful tool to the community. Currently, CKSAAP_UbSite is freely accessible at http://protein.cau.edu.cn/cksaap_ubsite/. Moreover, we also found that the sequence patterns around ubiquitination sites are not conserved across different species. To ensure a reasonable prediction performance, the application of the current CKSAAP_UbSite should be limited to the proteome of yeast
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