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Jun Luo

Publications and source records attributed to Jun Luo.

266 records · Page 15Linked to original sources
arXiv2010

A Symplecticity-preserving Gas-kinetic Scheme for Hydrodynamic Equations under Gravitational Field

A well-balanced scheme for a gravitational hydrodynamic system is defined as a scheme which could precisely preserve a hydrostatic isothermal solution. In this paper, we will construct a well-balanced gas-kinetic symplecticity-preserving BGK (SP-BGK) scheme. In order to develop such a scheme, we model the gravitational potential as a piecewise step function with a potential jump at the cell interface. At the same time, the Liouville's theorem and symplecticity preserving property of a Hamiltonian flow have been used in the description of particles penetration, reflection, and deformation through a potential barrier. The use of the symplecticity preserving property for a Hamiltonian flow is crucial in the evaluation of the high-order moments of a gas distribution function when crossing through a potential jump. As far as we know, the SP-BGK method is the first shock capturing Navier-Stokes flow solver with well-balanced property for a gravitational hydrodynamic system. A few theorems will be proved for this scheme, which include the necessity to use an exact Maxwellian for keeping the hydrostatic state, the total mass and energy (the sum of kinetic, thermal, and gravitational ones) conservation, and the well-balanced property to keep a hydrostatic state during particle transport and collision processes. Many numerical examples will be presented to validate the SP-BGK scheme.

physics.comp-ph↗
arXiv2010

SNAP: SNowbAll multi-tree Pushing for Peer-to-Peer Media Streaming

Given the respective advantages of the two complimentary techniques for peer-to-peer media streaming (namely tree-based push and mesh-based pull), there is a strong trend of combining them into a hybrid streaming system. Backed by recently proposed mechanisms to identify stable peers, such a hybrid system usually consists of backbone trees formed by the stable peers and other overlay structures in the second tier to accommodate the remaining peers. In this paper, we embrace the hybrid push-pull structure for peer-to-peer media streaming. Our protocol is dominated by a multi-tree push mechanism to minimize the delay in the backbone and is complemented by other overlay structures to cope with peer dynamics. What mainly distinguishes our multi-tree pushing from the conventional ones is an unbalanced tree design guided by the so called snow-ball streaming, which has a provable minimum delay and can be smoothly "melded" with virtually any other existing overlay structures lying in the second tier. We design algorithms to construct and maintain our SNowbAll multi-tree Pushing (SNAP) overlay, and we also illustrate how to smoothly weld the SNAP backbone with the second tier. Finally, we perform simulations in ns-2; the results indicate that our approach outperforms a recently proposed hybrid streaming system.

cs.NI↗
arXiv2010

Similar dissection of sets

In 1994, Martin Gardner stated a set of questions concerning the dissection of a square or an equilateral triangle in three similar parts. Meanwhile, Gardner's questions have been generalized and some of them are already solved. In the present paper, we solve more of his questions and treat them in a much more general context. Let $D\subset \mathbb{R}^d$ be a given set and let $f_1,...,f_k$ be injective continuous mappings. Does there exist a set $X$ such that $D = X \cup f_1(X) \cup ... \cup f_k(X)$ is satisfied with a non-overlapping union? We prove that such a set $X$ exists for certain choices of $D$ and $\{f_1,...,f_k\}$. The solutions $X$ often turn out to be attractors of iterated function systems with condensation in the sense of Barnsley. Coming back to Gardner's setting, we use our theory to prove that an equilateral triangle can be dissected in three similar copies whose areas have ratio $1:1:a$ for $a \ge (3+\sqrt{5})/2$.

math.MG↗
arXiv2009

Quantum Algorithms of Bio-molecular Solutions for the Clique Problem on a Quantum Computer

In this paper, it is demonstrated that the DNA-based algorithm [Ho et al. 2005] for solving an instance of the clique problem to any a graph G = (V, E) with n vertices and p edges and its complementary graph G1 = (V, E1) with n vertices and m = (((n*(n-1))/2)-p) edges can be implemented by Hadamard gates, NOT gates, CNOT gates, CCNOT gates, Grover's operators, and quantum measurements on a quantum computer. It is also demonstrated that if Grovers algorithm is employed to accomplish the readout step in the DNA-based algorithm, the quantum implementation of the DNA-based algorithm is equivalent to the oracle work (in the language of Grover's algorithm), that is, the target state labeling preceding Grover,s searching steps. It is shown that one oracle work can be completed with O((2 * n) * (n + 1) * (n + 2) / 3) NOT gates, one CNOT gate and O((4 * m) + (((2 * n) * (n + 1) * (n + 14)) / 6)) CCNOT gates. This is to say that for the quantum implementation of the DNA-based algorithm [Ho et al. 2005] a faster labeling of the target state is attained, which also implies a speedy solution to an instance of the clique problem.

cs.DS↗
arXiv2008

GossiCrypt: Wireless Sensor Network Data Confidentiality Against Parasitic Adversaries

Resource and cost constraints remain a challenge for wireless sensor network security. In this paper, we propose a new approach to protect confidentiality against a parasitic adversary, which seeks to exploit sensor networks by obtaining measurements in an unauthorized way. Our low-complexity solution, GossiCrypt, leverages on the large scale of sensor networks to protect confidentiality efficiently and effectively. GossiCrypt protects data by symmetric key encryption at their source nodes and re-encryption at a randomly chosen subset of nodes en route to the sink. Furthermore, it employs key refreshing to mitigate the physical compromise of cryptographic keys. We validate GossiCrypt analytically and with simulations, showing it protects data confidentiality with probability almost one. Moreover, compared with a system that uses public-key data encryption, the energy consumption of GossiCrypt is one to three orders of magnitude lower.

cs.CR↗
arXiv2008

Parity-violating macroscopic force between chiral molecules and source mass

A theory concerning non-zero macroscopic chirality-dependent force between a source mass and homochiral molecules due to the exchange of light particles is presented in this paper. This force is proposed to have opposite sign for molecules with opposite chirality. Using the central field approximation, we calculate this force between a copper block and a vessel of chiral molecules (methyl phenyl carbinol nitrite). The magnitude of force is estimated with the published limits of the scalar and pseudo-scalar coupling constants. Based on our theoretical model, this force may violate the equivalence principle when the homochiral molecules are used to be the test masses.

gr-qc↗
arXiv2004

Realization of decoherence-free subspace using Multiple-Quantum coherences

This letter presents a two-dimensional nuclear magnetic resonance(NMR) approach for constructing a two-logical-qubit decoherence-free subspace (DFS) based on the fact that the three protons in a CH3 spin system can not be resolved in one-dimension NMR spectroscopy, but to a certain extent, can be distinguished by two-dimensional multiple-quantum NMR. We used four noisy physical nuclear spins, including three protons and one carbon in the CH3 spin system, to generate two decoherence-free logical quantum bits. It made full use of the unaddressed spins which could not be used in one-dimensional spectrum. Furthermore, we have experimentally demonstrated such an approach. Our experimental results have shown that our DFS can protect against far more types of decoherence than the one composed of four noisy physical qubits all with different chemical shifts. More importantly, this idea may provide new insights into extending qubit systems in the sense that it effectively utilizes the magnetically equivalent nuclei.

quant-ph↗
arXiv2004

Enhancement of solid-state proton NMR via SPINOE with laser-polarized xenon

We have first successfully transferred the 129Xe polarization of natural isotopic composition to the proton of solid-state 1HCl via Spin Polarization-Induced Nuclear Overhauser Effect (SPINOE), by mixing the hyperpolarized 129Xe gas and the 1HCl gas and then cooling them to their condensated state in a flow system. The solid-state enhanced factor of the NMR signal of 6 for 1H was observed, and the equation of solid-state polarization enhancement via cross relaxation has also been theoretically deduced. Using this equation, the theoretically calculated enhancement is in agreement with the measured value within error. Also, this technique is maybe useful to establish a solid state NMR quantum computer.

cond-mat.soft↗
arXiv2003

Experiment and Dynamic Simulations of Radiation Damping of Laser-polarized liquid 129Xe at low magnetic field in a flow system

Radiation damping is generally observed when the sample with high spin concentration and high gyro-magnetic ratio is placed in a high magnetic field. However, we firstly observed liquid state 129Xe radiation damping using laser-enhanced nuclear polarization at low magnetic field in a flow system in which the polarization enhancement factor for the liquid state 129Xe was estimated to be 5000, and furthermore theoretically simulated the envelopes of the 129Xe FID and spectral lineshape in the presence of both relaxation and radiation damping with different pulse flip angles and ratios of T2*/Trd. The radiation damping time constant Trd of 5 ms was derived based on the simulations. The reasons of depolarization and the further possible improvements were also discussed.

cond-mat.soft↗
arXiv2003

NMR experimental realization of seventh-order coupling transformations and the seven-qubit modified Deutsch-Jozsa algorithm

We propose a scalable method on the basis of nth-order coupling operators to construct f-dependent phase transformations in the n-qubit modified Deutsch-Jozsa (D-J) quantum algorithm. The novel n-qubit entangling transformations are easily implemented via J-couplings between neighboring spins. The seven-qubit modified D-J quantum algorithm and seventh-order coupling transformations are then experimentally demonstrated with liquid state nuclear magnetic resonance (NMR) techniques. The method may offer the possibility of creating generally entangled states of n qubits and simulating n-body interactions on n-qubit NMR quantum computers.

quant-ph↗
arXiv2001

Experimental realization of 7-qubit universal perfect controlled-NOT and controlled square-root NOT gates

The controlled-NOT gate and controlled square-root NOT gate play an important role in quantum algorithm. This article reports the experimental results of these two universal quantum logic gates (controlled square-root NOT gate and controlled-NOT gate) on a 7-qubit NMR quantum computer. Further, we propose a simple experimental method to measure and correct the error in the controlled phase-shift gate, which is helpful to construct a more perfect phase-shift gate experimentally and can also be used in more qubits discrete Fourier transformation.

quant-ph↗
arXiv2001

Gravitational Effects of Rotating Bodies

We study two type effects of gravitational field on mechanical gyroscopes (i.e. rotating extended bodies). The first depends on special relativity and equivalence principle. The second is related to the coupling (i.e. a new force) between the spins of mechanical gyroscopes, which would violate the equivalent principle. In order to give a theoretical prediction to the second we suggest a spin-spin coupling model for two mechanical gyroscopes. An upper limit on the coupling strength is then determined by using the observed perihelion precession of the planet's orbits in solar system. We also give predictions violating the equivalence principle for free-fall gyroscopes .

gr-qc↗
arXiv1998

NMR Quantum Computation with a hyperpolarized nuclear spin bulk

We consider two new quantum gate mechanisms based on nuclear spins in hyperpolarized solid $^{129}Xe$ and HCl mixtures and inorganic semiconductors. We propose two schemes for implementing a controlled NOT (CNOT) gate based on nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) from hyperpolarized solid $^{129}Xe$ and HCl mixtures and optically pumped NMR in semiconductors. Such gates might be built up with particular spins addressable based on MRI techniques and optical pumping and optical detection techniques. The schemes could be useful for implementing actual quantum computers in terms of a cellular automata architecture.

quant-ph↗