arXiv subjects

Sheng Li

Publications and source records attributed to Sheng Li.

At least 307 records · Page 17Linked to original sources

arXiv2012

Observational constraints on K-inflation models

We extend the ModeCode software of Mortonson, Peiris and Easther to enable numerical computation of perturbations in K-inflation models, where the scalar field no longer has a canonical kinetic term. Focussing on models where the kinetic and potential terms can be separated into a sum, we compute slow-roll predictions for various models and use these to verify the numerical code. A Markov chain Monte Carlo analysis is then used to impose constraints from WMAP7 data on the addition of a term quadratic in the kinetic energy to the Lagrangian of simple chaotic inflation models. For a quadratic potential, the data do not discriminate against addition of such a term, while for a quartic (λϕ^4) potential inclusion of such a term is actually favoured. Overall, constraints on such a term from present data are found to be extremely weak.

astro-ph.CO↗

arXiv2012

Multi-Band Exotic Superconductivity in the New Superconductor Bi4O4S3

Resistivity, Hall effect and magnetization have been investigated on the new superconductor Bi4O4S3. A weak insulating behavior has been induced in the normal state when the superconductivity is suppressed. Hall effect measurements illustrate clearly a multiband feature dominated by electron charge carriers, which is further supported by the magnetoresistance data. Interestingly, a kink appears on the temperature dependence of resistivity at about 4 K at all high magnetic fields when the bulk superconductivity is completely suppressed. This kink can be well traced back to the upper critical field Hc2(T) in the low field region, and is explained as the possible evidence of residual Cooper pairs on the one dimensional chains.

cond-mat.supr-con↗

arXiv2012

Distinct behaviors of suppression to superconductivity in $LaRu_3Si_2$ induced by Fe and Co dopants

In the superconductor LaRu$_3$Si$_2$ with the Kagome lattice of Ru, we have successfully doped the Ru with Fe and Co atoms. Contrasting behaviors of suppression to superconductivity is discovered between the Fe and the Co dopants: Fe-impurities can suppress the superconductivity completely at a doping level of only 3%, while the superconductivity is suppressed slowly with the Co dopants. A systematic magnetization measurements indicate that the doped Fe impurities lead to spin-polarized electrons yielding magnetic moments with the magnitude of 1.6 $μ_B$\ per Fe, while the electrons given by the Co dopants have the same density of states for spin-up and spin-down leading to much weaker magnetic moments. It is the strong local magnetic moments given by the Fe-dopants that suppress the superconductivity. The band structure calculation further supports this conclusion.

cond-mat.supr-con↗

arXiv2011

Anomalous Properties in the Normal and Superconducting States of LaRu$_3$Si$_2$

Superconductivity in LaRu$_3$Si$_2$ with the honeycomb structure of Ru atoms has been investigated. It is found that the normal state specific heat C/T exhibits a deviation from the Debye model down to the lowest temperature. A relation $C/T = γ_n+βT^2-ATlnT$ which concerns the electron correlations can fit the data very well. The suppression to the superconductivity by the magnetic field is not the mean-field like, which is associated well with the observation of strong superconducting fluctuations. The field dependence of the induced quasiparticle density of states measured by the low temperature specific heat shows a non-linear feature, indicating the significant contributions given by the delocalized quasiparticles.

cond-mat.supr-con↗

arXiv2010

Quantum logical gates with four-level SQUIDs coupled to a superconducting resonator

We propose a way for realizing a two-qubit controlled phase gate with superconducting quantum interference devices (SQUIDs) coupled to a superconducting resonator. In this proposal, the two lowest levels of each SQUID serve as the logical states and two intermediate levels of each SQUID are used for the gate realization. We show that neither adjustment of SQUID level spacings during the gate operation nor uniformity in SQUID parameters is required by this proposal. In addition, this proposal does not require the adiabatic passage or a second-order detuning and thus the gate is much faster.

quant-ph↗

arXiv2009

Inflation in a Web

In a given path with multiple branches, in principle, it can be expected that there are some fork points, where one branch is bifurcated into different branches, or various branches converge into one or several branches. In this paper, it is showed that if there is a web formed by such branches in a given field space, in which each branch can be responsible for a period of slow roll inflation, a multiverse separated by domain wall network will come into being, some of which might corresponds to our observable universe. We discuss this scenario and show possible observations of a given observer at late time.

hep-th↗

arXiv2009

Integrating fluctuations into distribution of resources in transportation networks

We propose a resource distribution strategy to reduce the average travel time in a transportation network given a fixed generation rate. Suppose that there are essential resources to avoid congestion in the network as well as some extra resources. The strategy distributes the essential resources by the average loads on the vertices and integrates the fluctuations of the instantaneous loads into the distribution of the extra resources. The fluctuations are calculated with the assumption of unlimited resources, where the calculation is incorporated into the calculation of the average loads without adding to the time complexity. Simulation results show that the fluctuation-integrated strategy provides shorter average travel time than a previous distribution strategy while keeping similar robustness. The strategy is especially beneficial when the extra resources are scarce and the network is heterogeneous and lowly loaded.

cond-mat.stat-mech↗

arXiv2008

Effect of edge removal on topological and functional robustness of complex networks

We study the robustness of complex networks subject to edge removal. Several network models and removing strategies are simulated. Rather than the existence of the giant component, we use total connectedness as the criterion of breakdown. The network topologies are introduced a simple traffic dynamics and the total connectedness is interpreted not only in the sense of topology but also in the sense of function. We define the topological robustness and the functional robustness, investigate their combined effect and compare their relative importance to each other. The results of our study provide an alternative view of the overall robustness and highlight efficient ways to improve the robustness of the network models.

physics.soc-ph↗

arXiv2008

DBI-Curvaton

In this paper, we study a curvaton model described by a Dirac-Born-Infeld-like action. We calculate the spectrum of curvature perturbation induced by DBI-curvaton and estimate its non-Gaussianity. We find that in the limit of low sound speed the amplitude of curvature perturbation is enhanced more than that in DBI inflation. This result also means that the inflationary scale with DBI-curvaton may be lower than that in usual curvaton model. In addition, we also find that the local non-Gaussianity level in DBI-curvaton is generally about 10 times larger than that in usual curvaton model, which is interesting for current observations. This work in some sense explores a new application of brane-cosmology in inflation.

hep-ph↗

arXiv2008

Energy band of graphene ribbons under the tensile force

According to the tight-binding approximation, we investigate the electronic structures of graphene ribbons with zigzag shaped edges (ZGRs) and armchair shaped edges (AGRs) drawn by the tensile force, and obtain the analytic relations between the energy bands of pi-electrons in ZGR, AGR and the tensile force based on only considering the nearest-neighbor interaction and the hydrogen-like atomic wave function is considered as pi-electron wave function. Importantly, we find the tensile force can open an energy gap at the K point for ZGR and AGR, and the force perpendicular to the zigzag edges can open energy gap more easily besides the gap values of ZGR and AGR at the K point both increase as the tensile force increases.

cond-mat.str-el↗

arXiv2006

Effective delivering capacity in traffic dynamics based on scale-free network

We investigate the percentage of delivering capacities that are actually consumed in a typical traffic dynamics where the capacities are uniformly assigned over a scale-free network. Theoretical analysis, as well as simulations, reveal that there are a large number of idle nodes under both free and weak congested state of the network. It is worth noting that there is a critical value of effective betweenness to classify nodes in the congested state, below which the node has a constant queue size but above which the queue size increases with time. We also show that the consumption ratio of delivering capacities can be boosted to nearly 100% by adopting a proper distribution of the capacities, which at the same time enhances the network efficiency to the maximum for the current routing strategy.

cond-mat.stat-mech↗

arXiv2006

Evolving Network With Different Edges

We proposed an evolving network model constituted by the same nodes but different edges. The competition between nodes and different links were introduced. Scale free properties have been found in this model by continuum theory. Different network topologies can be generated by some tunable parameters. Simulation results consolidate the prediction.

cond-mat.stat-mech↗

arXiv2006

Quasispecies distribution of Eigen model

We study sharp peak landscapes (SPL) of Eigen model from a new perspective about how the quasispecies distribute in the sequence space. To analyze the distribution more carefully, we bring forth two tools. One tool is the variance of Hamming distance of the sequences at a given generation. It not only offers us a different avenue for accurately locating the error threshold and illustrates how the configuration of the distribution varies with copying fidelity $q$ in the sequence space, but also divides the copying fidelity into three distinct regimes. The other tool is the similarity network of a certain Hamming distance $d_{0}$, by which we can get a visual and in-depth result about how the sequences distribute. We find that there are several local optima around the center (global optimum) in the distribution of the sequences reproduced near the threshold. Furthermore, it is interesting that the distribution of clustering coefficient $C(k)$ follows lognormal distribution and the curve of clustering coefficient $C$ of the network versus $d_{0}$ appears as linear behavior near the threshold.

cond-mat.stat-mech↗

arXiv2004

Network of tRNA Gene Sequences

We showed in this paper that similarity network can be used as an powerful tools to study the relationship of tRNA genes. We constructed a network of 3719 tRNA gene sequences using simplest alignment and studied its topology, degree distribution and clustering coefficient. It is found that the behavior of the network shift from fluctuated distribution to scale-free distribution when the similarity degree of the tRNA gene sequences increase. tRNA gene sequences with the same anticodon identity are more self-organized than the tRNA gene sequences with different anticodon identities and form local clusters in the network. An interesting finding in our studied is some vertices of the local cluster have a high connection with other local clusters, the probable reason is given. Moreover, a network constructed by the same number of random tRNA sequences is used to make comparisons. The relationships between properties of the tRNA similarity network and the characters of tRNA evolutionary history are discussed.

q-bio.MN↗

arXiv2004

Epidemic Spreading in Dynamic Small World Networks

In this paper, we use a series of small world networks to simulate the epidemic spreading in the real world. To make our model more similar to the real world, we employ a parameter $p_{move}$ to denote its moving probability, which corresponds with the general mobility of individuals in realistic social network. The networks keep the same small world properties when they are varying. And the SIRS model is used to simulate the disease propagation. From these simulations we see the moving probability of a small world network has a profound effect on the velocity for the spread of an infection. The quantitative results show that the characteristic time $τ$ of infection at initial stage decreases exponentially with $p_{move}$.

nlin.AO↗

arXiv2002

Quantum Multiple Scattering: Eigenmode Expansion and Its Applications to Proximity Resonance

We show that for a general system of N s-wave point scatterers, there are always N eigenmodes. These eigenmodes or eigenchannels play the same role as spherical harmonics for a spherically symmetric target--they give a phase shift only. In other words, the T matrix of the system is of rank N and the eigenmodes are eigenvectors corresponding to non-0 eigenvalues of the T matrix. The eigenmode expansion approach can give insight to the total scattering cross section; the position, width, and superradiant or subradiant nature of resonance peaks; the unsymmetric Fano lineshape of sharp proximity resonance peaks based on the high energy tail of a broad band; and other properties. Off-resonant eigenmodes for identical proximate scatterers are approximately angular momentum eigenstates.

physics.atom-ph↗

arXiv2002

Localization of electromagnetic waves in a two dimensional random medium

Motivated by previous investigations on the radiative effects of the electric dipoles embedded in structured cavities, localization of electromagnetic waves in two dimensions is studied {\it ab initio} for a system consisting of many randomly distributed two dimensional dipoles. A set of self-consistent equations, incorporating all orders of multiple scattering of the electromagnetic waves, is derived from first principles and then solved numerically for the total electromagnetic field. The results show that spatially localized electromagnetic waves are possible in such a simple but realistic disordered system. When localization occurs, a coherent behavior appears and is revealed as a unique property differentiating localization from either the residual absorption or the attenuation effects.

cond-mat.dis-nn↗

arXiv2000

Disclination in Lorentz Space-Time

The disclination in Lorentz space-time is studied in detail by means of topological properties of $ϕ$-mapping. It is found the space-time disclination can be described in term of a Dirac spinor. The size of the disclination, which is proved to be the difference of two sets of su(2)% -like monopoles expressed by two mixed spinors, is quantized topologically in terms of topological invariants$-$winding number. The projection of space-time disclination density along an antisymmetric tensor field is characterized by Brouwer degree and Hopf index.

gr-qc↗