Showing papers in "Chinese Physics Letters in 2005"

Deterministic secure direct communication by using swapping quantum entanglement and local unitary operations

Abstract: A deterministic direct quantum communication protocol is proposed by using swapping quantum entanglement and local unitary operations. The present protocol is secure for the proof of the security of the present scheme, the same as that in the two-step protocol [Phys. Rev. A 68 (2003) 042317]. Additionally, the advantages and disadvantages of the present protocol is also discussed.

Secure Quantum Key Distribution Network with Bell States and Local Unitary Operations

Abstract: We propose a theoretical scheme for secure quantum key distribution network following the ideas in quantum dense coding. In this scheme, the server of the network provides the service for preparing and measuring the Bell states, and the users encode the states with local unitary operations. For preventing the server from eavesdropping, we design a decoy when the particle is transmitted between the users. The scheme has high capacity as one particle carries two bits of information and its efficiency for qubits approaches 100%. Moreover, it is unnecessary for the users to store the quantum states, which makes this scheme more convenient in applications than others.

Epidemic Spread in Weighted Scale-Free Networks

Abstract: We investigate the detailed epidemic spreading process in scale-free networks with link weights that denote familiarity between two individuals. It is found that the spreading velocity reaches a peak quickly then decays in a power-law form. Numerical study exhibits that the nodes with larger strength is preferential to be infected, but the hierarchical dynamics are not clearly found, which is different from the well-known result in the unweighed network case. In addition, also by numerical study, we demonstrate that larger dispersion of weight of networks results in slower spreading, which indicates that epidemic spreads more quickly on unweighted scale-free networks than on weighted scale-free networks with the same condition.

Fractal Character for Tortuous Streamtubes in Porous Media

Abstract: An analytical model for fractal dimension of tortuous streamtubes in porous media is derived. The proposed fractal dimension for tortuous streamtubes in porous media is expressed as a function of porosity and scale, and there is no empirical constant in the proposed expression. The model predictions for the fractal dimension of tortuous streamtubes in porous media are in good agreement with those by the box-counting method and with the observations of other researchers.

Quantum dialogue revisited

Abstract: An entanglement-based quantum dialogue protocol [Phys. Lett. A 328 (2004) 6] is proven to be insecure: that is, in the protocol an eavesdropper can steal the secret messages without being detected provided that he/she adopts the intercept-and-resend attack strategy. We modify the protocol, i.e. in the control mode, by introducing and randomly choosing two sets of measuring basis: the intercept-and-resend attack can be accordingly detected. Hence, within the present version two users can securely and simultaneously exchange their secret messages.

Effect of Microstructure of TiO2 Thin Films on Optical Band Gap Energy

Abstract: TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4 eV to 3.21 eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.

Kerr--Newman--Kasuya Black Hole Tunnelling Radiation

Abstract: The radiation of black hole contributes to the shrinking of the event horizon such that the background space-time should not be fixed. In this study we take into account the self-gravitation effect to study the radiation of Kerr–Newman–Kasuya black hole as tunnelling. Using the facts of energy conservation and angular momentum conservation we derive the tunnelling rate and show that the spectrum of the radiation as tunnelling is not purely thermal.

Cosmic Microwave Background Radiation Constraints on a Modified Chaplygin Gas Model

Abstract: A modified Chaplygin gas model of unifying dark energy and dark matter with the exotic equation of state p = B??(A/??), which can also explain the recent expansion of the universe, is investigated by means of constraining the location of the peak of the cosmic microwave background radiation spectrum. We find that the result of CMBR measurements does not exclude the nonzero value of parameter B, but allows it in the range ?0.35 B 0.025.

Bianchi Type-III String Cosmological Model with Bulk Viscosity in General Relativity

Abstract: The Bianchi type-III cosmological model for a cloud string with bulk viscosity are studied. To obtain a determinate solution, it is assumed that the coefficient of bulk viscosity is a power function of the scalar of expansion ζ = kθm and the shear scalar is proportional to scalar of expansion σ∝θ, which leads to the relation between metric potentials B = Cn. The physical features of the model are also discussed. It is found that the power index m has significant influence on the string model. There is a ``big bang'' start in the model when m≤1 but there is no the big-bang start when m>1. In the special case m = 0, the model reduces to the string model of constant coefficient of bulk viscosity that was the result previously given in the literature.

Swarm Dynamics of a Group of Mobile Autonomous Agents

Abstract: We propose a simple swarm model to study collective behaviour of a group of mobile autonomous agents interacting through a long range attraction and short range repulsion function. It is shown that the individuals (agents) will aggregate and eventually form a cohesive cluster of finite size around the swarm centre in a finite time, and the size depends only on the parameters of the swarm model. Furthermore, it is also shown that all the individuals will converge to equilibrium positions of the swarm model, and thus the configuration of the swarm converges to a constant constellation. Numerical simulations are also worked out to illustrate the analytical results.

A Simultaneous Quantum Secure Direct Communication Scheme between the Central Party and Other M Parties

Abstract: We propose a simultaneous quantum secure direct communication scheme between one party and other three parties via four-particle GHZ states and swapping quantum entanglement. In the scheme, three spatially separated senders, Alice, Bob and Charlie, transmit their secret messages to a remote receiver Diana by performing a series of local operations on their respective particles according to the quadripartite stipulation. From Alice, Bob, Charlie and Diana's Bell measurement results, Diana can infer the secret messages. If a perfect quantum channel is used, the secret messages are faithfully transmitted from Alice, Bob and Charlie to Diana via initially shared pairs of four-particle GHZ states without revealing any information to a potential eavesdropper. As there is no transmission of the qubits carrying the secret message in the public channel, it is completely secure for the direct secret communication. This scheme can be considered as a network of communication parties where each party wants to communicate secretly with a central party or server.

Glass-Forming Ability of an Iron-Based Alloy Enhanced by Co Addition and Evaluated by a New Criterion

Abstract: A new Fe-based alloy that can be cast into a fully amorphous rod with a diameter of at least 16?mm by the conventional copper-mould casting technique is obtained by partially replacing Fe with Co in a previously reported Fe-based bulk metallic glass. The preliminary thermodynamic analysis indicates that the Co-containing alloy has a significantly lower Gibbs free energy difference between the undercooled melt and the corresponding crystalline solid, compared to the Co-free alloy, reflecting the dramatic role of the Co addition in stabilizing the supercooled melt and facilitating glass formation in iron-based alloys. Here, a new criterion, derived from the classical nucleation and growth theory, is introduced to evaluate the glass-forming ability of Fe-based bulk metallic glasses.

Catastrophes in Scale-Free Networks

Abstract: An alternative model about cascading occurrences caused by perturbation is established to search the mechanism because catastrophes in networks occur. We investigate the avalanche dynamics of our model on two-dimensional Euclidean lattices and scale-free networks and find that the avalanche dynamic behaviour is sensitive to the topological structure of networks. The simulation results show that the catastrophes occur much more frequently in scale-free networks than those in Euclidean lattices, and the greatest catastrophe in scale-free networks is much more serious than that in Euclidean lattices. Furthermore, we have studied how to reduce the catastrophes' degree, and have schemed out an effective strategy, called the targeted safeguard strategy for scale-free networks.

Pd Si Binary Bulk Metallic Glass Prepared at Low Cooling Rate

Abstract: We report that binary bulk metallic glasses can be made up to 6 mm in diameter in a Pd–Si alloy system by air cooling at slow cooling rate (about 8 K/s). The high stability of the undercooled liquid and the large glass-forming ability (GFA) of the binary alloy are contributed to the removing of heterogeneous impurities in the alloy melt by employing the fluxing technique. It has been found that decreasing cooling rate can increase the supercooled liquid region and thermal stability of the glassy alloy. After fluxing, a wider supercooled liquid region (ΔT = 58 K) and higher glass-forming ability have been obtained in a Pd81Si19 binary glassy alloy prepared by slow cooling rate.

An Anti-Control Scheme for Spiral under Lorenz Chaotic Signals

Abstract: The Fitzhugh?Nagumo (FHN) equation is used to generate spiral and spatiotemporal chaos The weak Lorenz chaotic signal is imposed on the system locally and globally It is found that for the right chaotic driving signal, spiral and spatiotemporal chaos can be suppressed The simulation results also show that this anti-control scheme is effective so that the system emerges into the stable states quickly after a short duration of chaotic driving (about 50 time units) and the continuous driving keeps the system in a homogeneous state

A New Lattice Bhatnagar--Gross--Krook Model for the Convection--Diffusion Equation with a Source Term

Abstract: A new lattice Bhatnagar–Gross–Krook (LBGK) model for the convection–diffusion equation with a source term is proposed. Unlike the models proposed previously, the present model does not require any additional assumption on the source term. Numerical results are found to be in excellent agreement with the analytical solutions. It is also found that the numerical accuracy of the model is much better than that of the existing models.

A Geometry Model for Tortuosity of Streamtubes in Porous Media with Spherical Particles

Abstract: A geometry model for tortuosity of tortuous streamtubes in porous media with spherical particles is proposed based on the assumption that some particles in a porous medium are unrestrictedly overlapped and hence of different configurations. The proposed model is a function of porosity with no empirical constant imposed on it. The model predictions are found to be in good agreement with the available experimental data.

Indentation Size Effect and Microhardness Study of β-Sn Single Crystals

Abstract: The load dependence of apparent microhardness of ?-Sn single crystals having different growth directions is investigated. The measurements are performed on (110) planes of these crystals in the load range from 10 to 50?mN. It is found that the degree of the microhardness anisotropy decreases for higher indentation test loads. The examined materials exhibit the behaviour of indentation size effect (ISE), i.e., the apparent hardness increases with decreasing indentation load. Neither Meyer's law nor the proportional specimen resistance (PSR) model can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to modified the PSR model based on the consideration of the effect of machining-induced residually stressed surface on the hardness measurement.

Time Delay-Enhanced Synchronization and Regularization in Two Coupled Chaotic Neurons

Abstract: Complete synchronization of two identical chaotic Morris–Lecar (ML) neurons with time-delay coupling is investigated. It is found that the coupled ML neurons may achieve synchronization by an efficient time delay at a low coupling strength. At the same time, the chaotic motion of the coupled neurons may become a regular periodic one during synchronization by the time-delay coupling, that is, the delay time coupling is able to suppress chaos in the process of synchronization. However, the time delay has the effect on enhancement of synchronization and regularization of coupled neurons only in certain coupling strength ranges. Moreover, synchronization of coupled neurons is achieved by time delay after regularization.

Earth's Magnetosphere Impinged by Interplanetary Shocks of Different Orientations

Abstract: Using a recently developed PPMLR-MHD code, we carry out a global numerical simulation of the interaction between interplanetary shocks and Earth's magnetosphere. The initial magnetosphere is in a quasi-steady state, embedded in a uniform solar wind and a spiral interplanetary magnetic field (IMF). An interplanetary (IP) shock interacts in turn with the bow shock, the magnetosheath, the magnetopause, and the magnetosphere, and changes the magnetosphere in shape and structure, and the distribution of the electric current and potential in the ionosphere as well. A preliminary comparison is made between two IP shocks of the same solar wind dynamic pressure and a vanishing IMF Bz on the downstream side, but with different propagation directions, one parallel and the other oblique to the Sun–Earth line. The numerical results show that both shocks cause a compression of the magnetosphere, an enhancement of magnetic field strength and field-aligned current in the magnetosphere, and an increase of the dawn-dusk electric potential drops across the polar ionosphere. Moreover, the magnetosphere–ionosphere system approaches a similar quasi-steady state after the interaction, for the downstream states are very close for the two shocks. However, the evolution processes of the system are remarkably different during the interaction with the two shocks of different orientations. The shock with the normal oblique to the Sun–Earth line results in a much longer evolution time for the system. This demonstrates that the shock orientation plays an important role in determining the associated geophysical effects and interpreting multisatellite observations of IP shock–magnetosphere interaction events.

Oscillation of Quasi-Steady Earth's Magnetosphere

Abstract: A three-dimensional magnetohydrodynamics (MHD) code is designed specially for global simulations of the solar wind–magnetosphere–ionosphere system The code possesses a high resolution in capturing MHD shocks and discontinuities and a low numerical dissipation in examining possible instabilities inherent in the system The ionosphere is approximated by a spherical shell with uniform height-integrated conductance The solar wind is steady, and the interplanetary magnetic field is either due northward or due southward The code is then run to find solutions of the whole system It is found that the system has never reached a steady state, but keeps oscillating with a period of about one hour in terms of density variation at the geosynchronous orbit However, if a certain artificial resistivity is added either in the whole numerical box or in the reconnection sites only, the reconnections change from intermittent to steady regime and the oscillation disappears accordingly We conclude that the Earth's magnetosphere tends to be in a ceaseless oscillation status because of the low dissipation property inherent in the magnetospheric plasma, and the oscillation may be driven by intermittent magnetic reconnections that occur somewhere in the magnetopause and/or the magnetotail

Direct Numerical Simulation of Supersonic Turbulent Boundary Layer Flow

Abstract: Direct numerical simulations of a spatially evolving supersonic flat-plate turbulent boundary layer flow with free Mach number M∞ = 2.25 and Reynolds number Re = 365000/in are performed. The transition process from laminar to turbulent flow is obtained by solving the three-dimensional compressible Navier–Stokes equations, using high-order accurate difference schemes. The obtained statistical results agree well with the experimental and theoretical data. From the numerical results it can be seen that the transition process under the considered conditions is the process which skips the Tollmien–Schlichting instability and the second instability through the instability of high gradient shear layer and becomes of laminar flow breakdown. This means that the transition process is a bypass-type transition process. The spanwise asymmetry of the disturbance locally upstream imposed is important to induce the bypass-type transition. Furthermore, with increasing the time disturbance frequency the transition will delay. When the time disturbance frequency is large enough, the transition will disappear.

A Simple Method to Generate Lie Point Symmetry Groups of the (3+1)-Dimensional Jimbo Miwa Equation

Abstract: Taking the (3+1)-dimensional Jimbo–Miwa equation as a simple example, we develop a modified direct method to find symmetry groups and symmetry algebras. Some exact solutions of the model are given by the simple method.

Hawking Radiation via Tunnelling from Arbitrarily Dimensional Schwarzschild Black Holes

Abstract: We extend Parikh's recent work to the arbitrarily dimensional Schwarzschild black holes whose Arnowitt–Deser–Misner (ADM) mass is identical to its mass parameter. We view Hawking radiation as a tunnelling process across the event horizon. From the tunnelling probability we also find a leading correction to the semiclassical emission rate. The result consists with an underlying unitary theory.

Drop Size Dependence of the Contact Angle of Nanodroplets

Abstract: The contact angle of nanosized non-polarized argon sessile droplets on a solid substrate is studied by using molecular dynamics simulations. It is found that the drop size dependence of the contact angle is sensitive to the interaction between the liquid molecules and solid molecules. The contact angle decreases with the decreasing drop size for larger interaction between the liquid molecules and the solid substrate, and vice versa. This observation is consistent with most of the previous theoretical and experimental results.

Parity Checking and Generating Circuit with Nonlinear Material in All-Optical Domain

Abstract: An all-optical parity checker and parity bit generator circuit is proposed, in which optical non-linear materials are used as switching devices. High-speed (above GHz) logic operations can be achieved by this all-optical circuit that is tremendously fast than its equivalent electronic counterpart. Here these circuits are used to check the errors in optical data through a transmission line.

Phase Synchronization in Small World Chaotic Neural Networks

Abstract: To understand collective motion of real neural networks very well, we investigate collective phase synchronization of small world chaotic Hindmarsh–Rose (HR) neural networks. By numerical simulations, we conclude that small world chaotic HR neural networks can achieve collective phase synchronization. Furthermore, it is shown that phase synchronization of small world chaotic HR neural networks is dependent on the coupling strength, the connection topology (which is determined by the probability p), as well as the coupling number. These phenomena are important to guide us to understand the synchronization of real neural networks.

Three Kinds of Special Relativity via Inverse Wick Rotation

Abstract: Since the special relativity can be viewed as the physics in an inverse Wick rotation of four-dimensional (413) Euclid space, which is at almost equal footing with the 4D Riernann/Lobachevski space, there should be important physics in the inverse Wick rotation of 4D Riemann/Lobachevski space. Thus, there are three kinds of special relativity in de Sitter(dS)/Minkowski/anti-de Sitter(AdS) space at almost equal footing, respectively. There is an instanton tunnelling scenario in the Riemann-de Sitter case that may explain why A be positive and link with the multiverse.

Experimental Investigation on Terahertz Spectra of Amphetamine Type Stimulants

Abstract: The spectral absorption features of three amphetamine-type stimulants (ATS) belonging to illicit drugs have been studied with terahertz (THz) time-domain spectroscopy (THz-TDS) and the characteristic absorption spectra (fingerprint spectra) are obtained in the range from 0.2 to 2.5 THz. Fingerprint spectra of illicit drugs in terahertz band are bases to detect and to inspect nondestructively illicit drugs with terahertz technique. With fingerprint spectra of illicit drugs and strong penetrability for cloths, paper bags and leathered or plastic luggage terahertz technique would be better than other techniques in illicit drugs detection and inspection. Thus, this work would contribute to the building of corresponding fingerprint spectra database of illicit drugs and provide experimental bases for using of terahertz detection apparatus in drugs nondestructive detection and inspection in the future.

Probing the Microscopic Origin of Gravity via Precision Polarization and Spin Experiments

Abstract: As in other parts of physics, we advocate the interaction approach: experiments ↔ (. . . are influenced and their importance is determined by . . . and vice versa) phenomenology ↔ low-energy effective (field) theory ↔ microscopic theory to probe the microscopic origin of gravity. Using the χ–g phenomenological framework, we discuss the tests of equivalence principles. The only experimentally unconstrained degree of freedom is the axion freedom. It has effects on the long-range astrophysical/cosmological propagation of electromagnetic waves and can be tested/measured using the future generation of polarization measurement of cosmic background radiation. The verification or refutal of this axionic effect will be a crucial step for constructing an effective theory and probing the microscopic origin of gravity. The interaction of spin with gravity is another important clue for probing the microscopic origin of gravity. The interplay of experiments, phenomenology and effective theory are expounded. An ideal way to reveal the microscopic origin of gravity is to measure the gyrogravitational ratio of particles. Three potential experimental methods are considered.