arXiv subjects

Jing Ma

Publications and source records attributed to Jing Ma.

190 records · Page 11Linked to original sources

arXiv2015

Chiral magnetic effect and natural optical activity in (Weyl) metals

We consider the phenomenon of natural optical activity, and related chiral magnetic effect in metals with low carrier concentration. To reveal the correspondence between the two phenomena, we compute the optical conductivity of a noncentrosymmetric metal to linear order in the wave vector of the light wave, specializing to the low-frequency regime. We show that it is the orbital magnetic moment of quasiparticles that is responsible for the natural optical activity, and thus the chiral magnetic effect. While for purely static magnetic fields the chiral magnetic effect is known to have a topological origin and to be related to the presence of Berry curvature monopoles (Weyl points) in the band structure, we show that the existence of Berry monopoles is not required for the dynamic chiral magnetic effect to appear; the latter is thus not unique to Weyl metals. The magnitude of the dynamic chiral magnetic effect in a material is related to the trace of its gyrotropic tensor. We discuss the conditions under which this trace is non-zero; in noncentrosymmetric Weyl metals it is found to be proportional to the energy-space dipole moment of Berry curvature monopoles. The calculations are done within both the semiclassical kinetic equation, and Kubo linear response formalisms, with coincident results.

cond-mat.mes-hall↗

arXiv2015

Enhancing the Security of Protocols against Actor Key Compromise Problems

Security of complex systems is an important issue in software engineering. For complex computer systems involving many actors, security protocols are often used for the communication of sensitive data. Actor key compromise (AKC) denotes a situation where the long-term secret key of an actor may be known to an adversary for some reasons. Many protocols are not secure enough for ensuring security in such a situation. In this paper, we further study this problem by looking at potential types of attacks, defining their formal properties and providing solutions to enhance the level of security. As case studies, we analyze the vulnerabilities (with respect to potential AKC attacks) of practical protocols, including PKMv2RSA and Kerberos, and provide solutions to enhance the level of security of such protocols.

cs.CR↗

arXiv2013

A Turán-type problem on distance two

A new turán-type problem on distances on graphs was introduced by Tyomkyn and Uzzell. In this paper, we focus on the case that the distance is two. We primely show that for any value of $n$, a graph on $n$ vertices without three vertices pairwise at distance $2$, if it has a vertex $v \in V(G)$, whose neighbours are covered by at most two cliques, then it has at most $(n^2 - 1)/4 + 1$ pairs of vertices at distance $2$. This partially answers a guess of Tyomkyn and Uzzell [Tyomkyn, M., Uzzell, A.J.: A new Turán-Type promble on distaces of graphs. Graphs Combin. {\bf 29}(6), 1927--1942 (2012)].

math.CO↗

arXiv2012

Left Derivations and Strong Commutativity Preserving Maps on Semiprime $Γ$-Rings

In this paper, firstly as a short note, we prove that a left derivation of a semiprime $Γ$-ring $M$ must map $M$ into its center, which improves a result by Paul and Halder and some results by Asci and Ceran. Also we prove that a semiprime $Γ$-ring with a strong commutativity preserving derivation on itself must be commutative and that a strong commutativity preserving endomorphism on a semiprime $Γ$-ring $M$ must have the form $σ(x)=x+ζ(x)$ where $ζ$ is a map from $M$ into its center, which extends some results by Bell and Daif to semiprime $Γ$-rings.

math.RA↗

arXiv2008

On capacity of wireless ad hoc networks with MIMO MMSE receivers

Widely adopted at home, business places, and hot spots, wireless ad-hoc networks are expected to provide broadband services parallel to their wired counterparts in near future. To address this need, MIMO techniques, which are capable of offering several-fold increase in capacity, hold significant promise. Most previous work on capacity analysis of ad-hoc networks is based on an implicit assumption that each node has only one antenna. Core to the analysis therein is the characterization of a geometric area, referred to as the exclusion region, which quantizes the amount of spatial resource occupied by a link. When multiple antennas are deployed at each node, however, multiple links can transmit in the vicinity of each other simultaneously, as interference can now be suppressed by spatial signal processing. As such, a link no longer exclusively occupies a geometric area, making the concept of "exclusion region" not applicable any more. In this paper, we investigate link-layer throughput capacity of MIMO ad-hoc networks. In contrast to previous work, the amount of spatial resource occupied by each link is characterized by the actual interference it imposes on other links. To calculate the link-layer capacity, we first derive the probability distribution of post-detection SINR at a receiver. The result is then used to calculate the number of active links and the corresponding data rates that can be sustained within an area. Our analysis will serve as a guideline for the design of medium access protocols for MIMO ad-hoc networks. To the best of knowledge, this paper is the first attempt to characterize the capacity of MIMO ad-hoc networks by considering the actual PHY-layer signal and interference model.

cs.NI↗

arXiv2006

Boolean Game on Scale-free Networks

Inspired by the local minority game, we propose a network Boolean game and investigate its dynamical properties on scale-free networks. The system can self-organize to a stable state with better performance than random choice game, although only the local information is available to the agent. By introducing the heterogeneity of local interactions, we find the system has the best performance when each agent's interaction frequency is linear correlated with its information capacity. Generally, the agents with more information gain more than those with less information, while in the optimal case, each agent almost has the same average profit. In addition, we investigate the role of irrational factor and find an interesting symmetrical behavior.

physics.soc-ph↗

arXiv2005

Theoretical study of polarization tracking in satellite quantum key distribution

The BB84 and B92 protocols based on polarization coding are usually used in free-space quantum key distribution. Polarization tracking technique is one of the key techniques in the satellite quantum key distribution. Because the photon polarization state will be changed as a result of the satellite movement, both the transmitter and receiver need to have the ability to track the polarization orientation variation to accomplish the quantum cryptography protocols. In this paper, the polarization tracking principles are analyzed based on Faraday effect and the half-wave plate. The transforms of six photon polarization states in three conjugative bases are given and the quantum key coding principles based on the polarization tracking are analyzed for the BB84 and B92 protocols.

quant-ph↗

arXiv2003

Spin-polarized transport through a quantum dot coupled to ferromagnetic leads: Kondo correlation effect

We investigate the linear and nonlinear transport through a single level quantum dot connected to two ferromagnetic leads in Kondo regime, using the slave-boson mean field approach for finite on-site Coulomb repulsion. We find that for antiparallel alignment of the spin orientations in the leads, a single zero-bias Kondo peak always appears in the voltage-dependent differential conductance with peak height going down to zero as the polarization grows to P=1. For parallel configuration, with increasing polarization from zero, the Kondo peak descends and greatly widens by the appearance of shoulders, and finally splits into two peaks on both sides of the bias voltage around $P\sim 0.7$ until disappears at even larger polarization strength. At any spin orientation angle $θ$, the linear conductance generally drops with growing polarization strength. For a given finite polarization, the minimum linear conductance always appears at $θ=π$.

cond-mat↗

arXiv2003

Quantum transport through double-dot Aharonov-Bohm interferometry in Coulomb blockade regime

Transport through two quantum dots laterally embedded in Aharonov-Bohm interferometry with infinite intradot and arbitrary interdot Coulomb repulsion is analyzed in the weak coupling and Coulomb blockade regime. By employing the modified quantum rate equations and the slave-boson approach, we establish a general dc current formula at temperatures higher than the Kondo temperature for the case that the spin degenerate levels of two dots are close to each other. We examine two simple examples for identical dots - no doubly occupied states and no empty state. In the former, completely destructive coherent transport and phase locking appear at magnetic flux $Φ=Φ_{0}/2$ and $Φ=0$ respectively; in the latter, partially coherent transport exhibits an oscillation with magnetic flux having a period of $Φ_0$.

cond-mat.mes-hall↗

arXiv2003

Kondo correlation and spin-flip scattering in spin-dependent transport through a quantum dot coupled to ferromagnetic leads

We investigate the linear and nonlinear dc transport through an interacting quantum dot connected to two ferromagnetic electrodes around Kondo regime with spin-flip scattering in the dot. Using a slave-boson mean field approach for the Anderson Hamiltonian having finite on-site Coulomb repulsion, we find that a spin-flip scattering always depresses the Kondo correlation at arbitrary polarization strength in both parallel and antiparallel alignment of the lead magnetization and that it effectively reinforces the tunneling related conductance in the antiparallel configuration. For systems deep in the Kondo regime, the zero-bias single Kondo peak in the differential conductance is split into two peaks by the intradot spin-flip scattering; while for systems somewhat further from the Kondo center, the spin-flip process in the dot may turn the zero-bias anomaly into a three-peak structure.

cond-mat.mes-hall↗