arXiv subjects

Jun Sun

Publications and source records attributed to Jun Sun.

At least 289 records · Page 16Linked to original sources

arXiv2016

Non-Markovian discrete qubit dynamics

The study of open quantum systems is important for fundamental issues of quantum physics as well as for technological applications such as quantum information processing. The interaction of a quantum system with it's environment is usually detrimental for the quantum properties of the system and leads to decoherence. However, sometimes a coherent partial exchange of information takes place between the system and the environment and the dynamics of the open system becomes non-Markovian. In this article we study discrete open quantum system dynamics where single evolution step consist of local unitary transformation on the open system followed by a coupling unitary between the system and the environment. We implement experimentally a local control protocol for controlling the transition from Markovian to non-Markovian dynamics.

quant-ph↗

arXiv2015

Group Centric Networking: A New Approach for Wireless Multi-Hop Networking to Enable the Internet of Things

In this paper, we introduce a new networking architecture called Group Centric Networking (GCN), which is designed to support the large number of devices expected with the emergence of the Internet of Things. GCN is designed to enable these devices to operate collaboratively in a highly efficient and resilient fashion, while not sacrificing their ability to communicate with one another. We do a full protocol implementation of GCN in NS3, and demonstrate that GCN utilizes up to an order of magnitude fewer network resources than traditional wireless networking schemes, while providing high connectivity and reliability.

cs.NI↗

arXiv2015

Regular Symmetry Patterns (Technical Report)

Symmetry reduction is a well-known approach for alleviating the state explosion problem in model checking. Automatically identifying symmetries in concurrent systems, however, is computationally expensive. We propose a symbolic framework for capturing symmetry patterns in parameterised systems (i.e. an infinite family of finite-state systems): two regular word transducers to represent, respectively, parameterised systems and symmetry patterns. The framework subsumes various types of symmetry relations ranging from weaker notions (e.g. simulation preorders) to the strongest notion (i.e. isomorphisms). Our framework enjoys two algorithmic properties: (1) symmetry verification: given a transducer, we can automatically check whether it is a symmetry pattern of a given system, and (2) symmetry synthesis: we can automatically generate a symmetry pattern for a given system in the form of a transducer. Furthermore, our symbolic language allows additional constraints that the symmetry patterns need to satisfy to be easily incorporated in the verification/synthesis. We show how these properties can help identify symmetry patterns in examples like dining philosopher protocols, self-stabilising protocols, and prioritised resource-allocator protocol. In some cases (e.g. Gries's coffee can problem), our technique automatically synthesises a safety-preserving finite approximant, which can then be verified for safety solely using a finite-state model checker.

cs.LO↗

arXiv2015

A Feature-based Classification Technique for Answering Multi-choice World History Questions

Our FRDC_QA team participated in the QA-Lab English subtask of the NTCIR-11. In this paper, we describe our system for solving real-world university entrance exam questions, which are related to world history. Wikipedia is used as the main external resource for our system. Since problems with choosing right/wrong sentence from multiple sentence choices account for about two-thirds of the total, we individually design a classification based model for solving this type of questions. For other types of questions, we also design some simple methods.

cs.IR↗

arXiv2015

The Impact of Physical Channel on Performance of Subspace-Based Channel Estimation in Massive MIMO Systems

A subspace method for channel estimation has been recently proposed [1] for tackling the pilot contamination effect, which is regarded by some researchers as a bottleneck in massive MIMO systems. It was shown in [1] that if the power ratio between the desired signal and interference is kept above a certain value, the received signal spectrum splits into signal and interference eigenvalues, namely, the "pilot contamination" effect can be completely eliminated. However, [1] assumes an independently distributed (i.d.) channel, which is actually not much the case in practice. Considering this, a more sensible finite-dimensional physical channel model (i.e., a finite scattering environment, where signals impinge on the base station (BS) from a finite number of angles of arrival (AoA)) is employed in this paper. Via asymptotic spectral analysis, it is demonstrated that, compared with the i.d. channel, the physical channel imposes a penalty in the form of an increased power ratio between the useful signal and the interference. Furthermore, we demonstrate an interesting "antenna saturation" effect, i.e., when the number of the BS antennas approaches infinity, the performance under the physical channel with P AoAs is limited by and nearly the same as the performance under the i.d. channel with P receive antennas.

cs.IT↗

arXiv2015

The deformation of symplectic critical surfaces in a Kähler surface-I

In this paper we derive the Euler-Lagrange equation of the functional $L_β=\int_Σ\frac{1}{\cos^βα}dμ, ~~β\neq -1$ in the class of symplectic surfaces. It is $\cos^3α{\bf{H}}=β(J(J\nabla\cosα)^\top)^\bot$, which is an elliptic equation when $β\geq 0$. We call such a surface a $β$-symplectic critical surface. We first study the properties for each fixed $β$-symplectic critical surface and then prove that the set of $β$ where there is a stable $β$-symplectic critical surface is open. We believe it should be also closed. As a precise example, we study rotationally symmetric $β$-symplectic critical surfaces in ${\mathbb C}^2$ carefully .

math.DG↗

arXiv2014

Stateful Security Protocol Verification

A long-standing research problem in security protocol design is how to efficiently verify security protocols with tamper-resistant global states. In this paper, we address this problem by first proposing a protocol specification framework, which explicitly represents protocol execution states and state transformations. Secondly, we develop an algorithm for verifying security properties by utilizing the key ingredients of the first-order reasoning for reachability analysis, while tracking state transformation and checking the validity of newly generated states. Our verification algorithm is proven to be (partially) correct, if it terminates. We have implemented the proposed framework and verification algorithms in a tool named SSPA, and evaluate it using a number of stateful security protocols. The experimental results show that our approach is not only feasible but also practically efficient. In particular, we have found a security flaw on the digital envelope protocol, which could not be detected by existing security protocol verifiers.

cs.CR↗

arXiv2013

Mechanical Controlled Thermal Switch and Hysteresis with Domain Boundary Engineered Phonon Transport

Heat flow control in phononics has received significant attention recently due to its widespread applications in energy transfer, conversion and utilization. Here, we demonstrate that by applying external stress or strain we can effectively tune the thermal conductivity through changing the density of twin boundaries, which in turn offers the intriguing mechanical-controlled thermal switch and hysteresis operations. Twin boundaries perpendicular to the transport direction strongly scatter phonons. As such, the heat flow is in inverse proportional to the density of twin boundaries and hence allows an excellent way to switch thermal conductivity mechanically and even leads to the interesting hysteresis behavior as a thermal memory. Our study provides a novel mechanism to couple thermal and mechanical properties of materials as a matter of "domain boundary engineering" and can have substantial implications in flexible thermal control and thermal energy harvesting.

cond-mat.mtrl-sci↗

arXiv2013

Generalized Lagrangian mean curvature flows in almost Calabi-Yau manifolds

In this paper, we study the generalized Lagrangian mean curvature flow in almost Einstein manifold proposed by T. Behrndt. We show that the singularity of this flow is characterized by the second fundamental form. We also show that the rescaled flow at a singularity converges to a finite union of Special Lagrangian cones for generalized Lagrangian mean curvature flow with zero-Maslov class in almost Calabi-Yau manifold. As a corollary, there is no finite time Type-I singularity for such a flow.

math.DG↗

arXiv2013

Random Drift Particle Swarm Optimization

The random drift particle swarm optimization (RDPSO) algorithm, inspired by the free electron model in metal conductors placed in an external electric field, is presented, systematically analyzed and empirically studied in this paper. The free electron model considers that electrons have both a thermal and a drift motion in a conductor that is placed in an external electric field. The motivation of the RDPSO algorithm is described first, and the velocity equation of the particle is designed by simulating the thermal motion as well as the drift motion of the electrons, both of which lead the electrons to a location with minimum potential energy in the external electric field. Then, a comprehensive analysis of the algorithm is made, in order to provide a deep insight into how the RDPSO algorithm works. It involves a theoretical analysis and the simulation of the stochastic dynamical behavior of a single particle in the RDPSO algorithm. The search behavior of the algorithm itself is also investigated in detail, by analyzing the interaction between the particles. Some variants of the RDPSO algorithm are proposed by incorporating different random velocity components with different neighborhood topologies. Finally, empirical studies on the RDPSO algorithm are performed by using a set of benchmark functions from the CEC2005 benchmark suite. Based on the theoretical analysis of the particle's behavior, two methods of controlling the algorithmic parameters are employed, followed by an experimental analysis on how to select the parameter values, in order to obtain a good overall performance of the RDPSO algorithm and its variants in real-world applications. A further performance comparison between the RDPSO algorithms and other variants of PSO is made to prove the efficiency of the RDPSO algorithms.

cs.AI↗

arXiv2013

A variational characterization of $J$-holomorphic curves in symplectic manifolds

In this paper, we prove that if the area functional of a surface $Σ^2$ in a symplectic manifold $(M^{2n},\barω)$ has a critical point or has a compatible stable point in the same cohomology class, then it must be $J$-holomorphic. Inspired by a classical result of Lawson-Simons, we show how various restrictions of the stability assumption to variations of metrics in the space "projectively induced" metrics are enough to give the desired conclusion.

math.DG↗

arXiv2012

A remark on a Bernstein type theorem for entire Willmore graphs in R^3

In this note we prove that every two-dimensional entire Willmore graph in $R^3$ with square integrable mean curvature is a plane.

math.DG↗

arXiv2011

An $\varepsilon$-regularity Theorem For The Mean Curvature Flow

In this paper, we will derive a small energy regularity theorem for the mean curvature flow of arbitrary dimension and codimension. It says that if the parabolic integral of $|A|^2$ around a point in space-time is small, then the mean curvature flow cannot develop singularity at this point. As an application, we can prove that the 2-dimensional Hausdorff measure of the singular set of the mean curvature flow from a surface to a Riemannian manifold must be zero.

math.DG↗

arXiv2009

Spontaneous Emergence of Modularity in a Model of Evolving Individuals and in Real Networks

We investigate the selective forces that promote the emergence of modularity in nature. We demonstrate the spontaneous emergence of modularity in a population of individuals that evolve in a changing environment. We show that the level of modularity correlates with the rapidity and severity of environmental change. The modularity arises as a synergistic response to the noise in the environment in the presence of horizontal gene transfer. We suggest that the hierarchical structure observed in the natural world may be a broken symmetry state, which generically results from evolution in a changing environment. To support our results, we analyze experimental protein interaction data and show that protein interaction networks became increasingly modular as evolution proceeded over the last four billion years. We also discuss a method to determine the divergence time of a protein.

q-bio.MN↗

arXiv2008

A Projection Method for Derivation of Non-Shannon-Type Information Inequalities

In 1998, Zhang and Yeung found the first unconditional non-Shannon-type information inequality. Recently, Dougherty, Freiling and Zeger gave six new unconditional non-Shannon-type information inequalities. This work generalizes their work and provides a method to systematically derive non-Shannon-type information inequalities. An application of this method reveals new 4-variable non-Shannon-type information inequalities.

cs.IT↗

arXiv2007

Spontaneous Emergence of Modularity in a Model of Evolving Individuals

q-bio.PE↗

arXiv2005

Glassy Dynamics in the Adaptive Immune Response Prevents Autoimmune Disease

The immune system normally protects the human host against death by infection. However, when an immune response is mistakenly directed at self antigens, autoimmune disease can occur. We describe a model of protein evolution to simulate the dynamics of the adaptive immune response to antigens. Computer simulations of the dynamics of antibody evolution show that different evolutionary mechanisms, namely gene segment swapping and point mutation, lead to different evolved antibody binding affinities. Although a combination of gene segment swapping and point mutation can yield a greater affinity to a specific antigen than point mutation alone, the antibodies so evolved are highly cross-reactive and would cause autoimmune disease, and this is not the chosen dynamics of the immune system. We suggest that in the immune system a balance has evolved between binding affinity and specificity in the mechanism for searching the amino acid sequence space of antibodies.

q-bio.PE↗

arXiv2004

Orthogonality Catastrophe in Bose-Einstein Condensates

Orthogonality catastrophe in fermionic systems is well known: in the thermodynamic limit, the overlap between the ground state wavefunctions with and without a single local scattering potential approaches zero algebraically as a function of the particle number $N$. Here we examine the analogous problem for bosonic systems. In the homogeneous case, we find that ideal bosons display an orthogonality stronger than algebraic: the wavefunction overlap behaves as ${\rm exp}[-λN^{1/3}]$ in three dimensions and as ${\rm exp}[-λN/\ln ^2 N]$ in two dimensions. With interactions, the overlap becomes finite but is still (stretched-)exponentially small for weak interactions. We also consider the cases with a harmonic trap, reaching similar (though not identical) conclusions. Finally, we comment on the implications of our results for spectroscopic experiments and for (de)coherence phenomena.

cond-mat.stat-mech↗