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61.
The message filtering characteristics of the receiver in closed-loop chaotic optical communication system are numerically studied based on laser rate equations. A pair of external cavity semiconductor lasers was employed as the chaotic carrier transmitter and the synchronized chaos receiver. We examined the filtering properties of the semiconductor laser receiver for message encoded with chaos masking. Our results demonstrate that, the lower the message frequency, the more easily the receiver filters out the message from chaotic carrier. We also analyzed the effects of each parameter mismatches between the transmitter and the receiver on the quality of the recovered message. Comparing the synchronization quality with the signal-to-noise ratio affected by parameter mismatches, we find that the quality of the recovered message depends not only on the synchronization quality but also on the filtering characteristics of the receiver. The filtering characteristics of receiver will be playing an important role on the quality of the recovered message in the case of large mismatches. 相似文献
62.
We have demonstrated the selective area growth of stacked self-assembled InAs quantum dot (QD) arrays in the desired regions on a substrate and confirmed the photoluminescence (PL) emission exhibited by them at room temperature. These InAs QDs are fabricated by the use of a specially designed atomic force microscope cantilever referred to as the Nano-Jet Probe (NJP). By using the NJP, two-dimensional arrays with ordered In nano-dots are fabricated in the desired square regions on a GaAs substrate and directly converted into InAs QD arrays through the subsequent annealing by the irradiation of As flux. By using the converted QD arrays as strain templates, self-organized InAs QDs are stacked. These stacked QDs exhibit the PL emission peak at a wavelength of 1.02 μm. 相似文献
63.
We model a melt of monodisperse side-chain liquid-crystalline polymers as a melt of comb copolymers in which the side groups
are rod-coil diblock copolymers. We consider both excluded-volume and Maier-Saupe interactions. The first acts among any pair
of segments while the latter acts only between rods. Using a free-energy functional calculated from this microscopic model,
we study the spinodal stability of the isotropic phase against density and orientational fluctuations. The phase diagram obtained
in this way predicts nematic and smectic instabilities as well as the existence of microphases or phases with modulated wave
vector but without nematic ordering. Such microphases are the result of the competition between the incompatibility among
the blocks and the connectivity constraints imposed by the spacer and the backbone. Also the effects of the polymerization
degree and structural conformation of the monomeric units on the phase behavior of the side-chain liquid-crystalline polymers
are studied. 相似文献
64.
Sary N Brochon C Hadziioannou G Mezzenga R 《The European physical journal. E, Soft matter》2007,24(4):379-384
We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a π -conjugated
polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and
chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions,
ω , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter
and the total polymerization degree, χN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly
of rod-coil block copolymers in a weakly segregated regime. The two rod-coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b-styrene),
whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine),
for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as
moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion
theories. 相似文献
65.
This paper is a cryptanalysis of a recently proposed multi-chaotic systems based image cryptosystem. The cryptosystem is composed of two shuffling stages parameterized by chaotically generated sequences. We propose and implement two different attacks which completely break this encryption scheme. 相似文献
66.
B. Bougie M. Tulej T. Dreier N. J. Dam J. J. Ter Meulen T. Gerber 《Applied physics. B, Lasers and optics》2005,80(8):1039-1045
We report on spatially and temporally resolved optical diagnostic measurements of propagation and combustion of diesel sprays introduced through a single-hole fuel injector into a constant volume, high-temperature, high-pressure cell. From shadowgraphy images in non-reacting environments of pure nitrogen, penetration lengths and dispersion angles were determined for non-vaporizing and vaporizing conditions, and found to be in reasonable agreement with standard models for liquid jet propagation and break-up.Quasi-simultaneous two-dimensional images were obtained of laser elastic light scattering, shadowgraphs and spectrally integrated flame emission in a reacting environment (cell temperature 850 K). In addition laser-induced incandescence was employed for the identification of soot-loaded regions. The simultaneously recorded spray images exhibit remarkable structural similarity and provide complementary information about the spray propagation and combustion process. The measurements also reveal the fuel vapor cloud extending well beyond the liquid core and close to the nozzle tip. Ignition takes place close to the tip of the spray within the mixing layer of fuel vapor and surrounding air. Soot is formed in the vapor core region at the tip of the liquid fuel jet. Our results support recently developed phenomenological model on diesel spray combustion. 相似文献
67.
Recently, an encryption algorithm based on two-dimensional discretized chaotic maps was proposed [Xiang et al., Phys. Lett. A 364 (2007) 252]. In this Letter, we analyze the security weaknesses of the proposal. Using the algebraic dependencies among system parameters, we show that its effective key space can be shrunk. We demonstrate a chosen-ciphertext attack that reveals a portion of the key. 相似文献
68.
69.
M.M. Kuklja 《Applied Physics A: Materials Science & Processing》2003,76(3):359-366
In this article we briefly review the results of theoretical simulations for the initiation of chemistry processes in high-explosive
crystals from a solid-state-physics viewpoint. We analyze the possibility of initiation of chemical reactions from excited
electronic states. In other words, we look for conditions that facilitate electronic excitations in the crystal. Specifically,
we describe modifications to the electronic structure of RDX (cyclotrimethylene trinitramine) induced by lattice defects and
by a shock wave traversing the solid. Our approach is based on ab initio Hartree–Fock band-structure calculations with electronic
correlation corrections. An excitonic mechanism and a hole model, suggested earlier, are discussed in connection with the
most recent experimental and theoretical advances in ultrafast optical techniques. We also consider here possible new avenues
in the development of detonation theory.
Received: 3 December 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-301/744-4451, E-mail: KuklaMM@ih.navy.mil 相似文献
70.
This Letter investigates the function projective synchronization of different chaotic systems with unknown parameters. By Lyapunov stability theory, the adaptive control law and the parameter update law are derived to make the states of two different chaotic systems asymptotically synchronized up to a desired scaling function. Numerical simulations on Lorenz system and Newton-Leipnik system are presented to verify the effectiveness of the proposed scheme. 相似文献