共查询到20条相似文献,搜索用时 31 毫秒
1.
一种基于扩展素数码和单重合序列的二维光正交码EPC/OCS 总被引:1,自引:0,他引:1
以扩展素数码(EPC)作为时间扩频伪随机序列,单重合序列(OCS)作为波长跳频伪随机序列,构造了一种新的二维光正交码EPC/OCS,并分析了码字的互相关性能.与修正素数跳频码MPHC相比,EPC/OCS的波长数并不局限于素数,可以是任意整数,不仅构造灵活,而且可充分利用MW OCDMA系统的有效波长数.当系统的有效波长数大于某个素数时,EPC/OCS不仅码字容量大于MPHC,而且互相关性能也有所改善.理论分析表明,EPC/OCS可降低MW OCDMA系统误码率. 相似文献
2.
Along the lines of previous work, we give the general framework together with a detailed and rigorous study of the spectrum and Born-von Karman eigenstates of a 1D harmonic chain with controlled disorder determined by the Thue-Morse sequence. The spectrum is a Cantor-like set; we prove numerically that its measure is zero and calculate its Bouligand-Minkowski dimension (box dimension). We prove that the value of the IDS on each of the gaps is (2k+1)/(3·2
p
), withk andp integers. Finally, we also prove that points in a dense subset of the spectrum give rise to extended states, an exceptional property due to the symmetry of the Thue-Morse substitution which can have important applications to multilayered structures, and we illustrate this situation. 相似文献
3.
Point defects (vacancies, solute atoms, and disorder) are ubiquitous in crystalline solids. With in situ transmission electron microscopy we find clear evidence for the existence of a universal symmetry property of point defects; i.e., the symmetry of short-range order of point defects follows the crystal symmetry when in equilibrium. We further show that this symmetry-conforming property can lead to various interesting effects including "aging-induced microstructure memory" and the associated "time-dependent two-way shape memory." 相似文献
4.
Synthesis and photophysical properties of novel polymeric Eu(III) complex with bicoordination ligand
A novel complex of Eu(III) with bicoordination ligand: 4,4′-bis[2-(2′-pyridyl) benzimidazol-yl]-biphenyl (Bmbp) has been synthesized. The structure of the ligand was characterized by 1H NMR, FT-IR and UV-vis; Eu(III) complex was characterized by FT-IR, UV-vis, elemental analysis, conductivity measurements and gel-permeation chromatography (GPC). The luminescence properties were investigated by UV-vis and fluorescence spectra. The experimental results show that the complex contain more than one Eu(III) ion, the emission at 614 nm from the 5D0→7F2 electronic dipole transition is large enhanced, and the complex is excellent energy transfer from ligand to Eu3+in the solid state. Thermal property measurement and analysis show that it has a good thermal stability. 相似文献
5.
针对非合作大目标的被动测距问题,介绍了一种基于单目图像序列和成像方向的测距系统,并进行了性能分析.这种测距系统的特点是无需初始距离导引,它对目标距离的估计借助于专门的定位方程,方程由目标特征线度、摄像机的空间坐标、目标在采样时刻对相机的方位角和俯仰角决定.其中,方位角和俯仰角通过光电经纬仪获得,摄像机的空间坐标通过GPS获得,目标特征线度通过相邻帧图像匹配得到.分析表明,该系统的性能主要取决于特征线度的准确度,其他测量误差如目标的方位角、俯仰角和摄像机的空间坐标对其影响较小.目标特征线度选取时,在相邻帧目标图像匹配点中,筛选出三个具有较大极限的尺度不变特征变换关键点,构造三角形及其外接圆,在外接圆上取经过三角形重心且平行或垂直于尺度不变特征变换主方向的弦线作为特征线度,这种特征线度对目标旋转不敏感.实验结果表明这种测距方法能够实现对非合作大目标的被动测距. 相似文献
6.
We develop a new cell-centered control volume Lagrangian scheme for solving Euler equations of compressible gas dynamics in cylindrical coordinates. The scheme is designed to be able to preserve one-dimensional spherical symmetry in a two-dimensional cylindrical geometry when computed on an equal-angle-zoned initial grid. Unlike many previous area-weighted schemes that possess the spherical symmetry property, our scheme is discretized on the true volume and it can preserve the conservation property for all the conserved variables including density, momentum and total energy. Several two-dimensional numerical examples in cylindrical coordinates are presented to demonstrate the performance of the scheme in terms of symmetry, accuracy and non-oscillatory properties. 相似文献
7.
F.M. Renard 《Physics letters. [Part B]》1975,60(1):55-57
We show how a symmetry property can lead simultaneously to broad states and to narrow states. We discuss then the origin of the symmetry breaking with respect to the properties of the narrow states recently discovered. 相似文献
8.
S. Tarzi 《Foundations of Physics》2003,33(6):955-979
We give a derivation of exclusion principles for the elementary particles of the standard model, using simple mathematical principles arising from a set theory of identical particles. We apply the theory of permutation group actions, stating some theorems which are proven elsewhere, and interpreting the results as a heuristic derivation of Pauli's Exclusion Principle (PEP) which dictates the formation of elements in the periodic table and the stability of matter, and also a derivation of quark confinement. We arrive at these properties by using a symmetry property of collections of the particles themselves as compared for example to the symmetry property of their wave function under interchange of two particles. 相似文献
9.
In this paper, we utilize optical hard-limiters to further enhance the system performance in balanced detection T/W optical CDMA system. In T/W optical CDMA systems, it had been investigated that the balanced detection scheme is not superior to the OOK scheme because of the adverse impact of beat noise. The employment of optical hard-limiter is an effective way to alleviate the deteriorating effect of beat noise. The carrier-hopping prime code is utilized as signature sequences whose out of phase autocorrelation is zero and the cross-correlation is at most one. Due to the orthogonality of signature sequence, the correlator of shifted version of carrier-hopping prime code is utilized in the receiver. The numerical results reveal that our proposed scheme can greatly reduce the error floor; also it is superior to that using OOK scheme with optical hard-limiter. Most important of all, our proposed scheme has fixed and optimum thresholds which do not vary with system parameters; and this will lead to dynamic estimation of optimal thresholds unnecessary in the receiver. 相似文献
10.
Atushi Ishikawa Shouji Fujimoto Arturo Ramos Takayuki Mizuno 《Entropy (Basel, Switzerland)》2021,23(7)
We analytically derived and confirmed by empirical data the following three relations from the quasi-time-reversal symmetry, Gibrat’s law, and the non-Gibrat’s property observed in the urban population data of France. The first is the relation between the time variation of the power law and the quasi-time-reversal symmetry in the large-scale range of a system that changes quasi-statically. The second is the relation between the time variation of the log-normal distribution and the quasi-time-reversal symmetry in the mid-scale range. The third is the relation among the parameters of log-normal distribution, non-Gibrat’s property, and quasi-time-reversal symmetry. 相似文献
11.
12.
We construct the transfer matrix for the open chain with the centrally extended SU(2|2) symmetry attached to the so called Z=0 giant graviton brane. Using the reflection equations, unitarity property and crossing property, we show that this model is integrable. 相似文献
13.
14.
Taku Matsui 《Communications in Mathematical Physics》2001,218(2):393-416
We consider the relationship between the symmetry breaking and the split property of pure states of quantum spin chains.
We obtain a representation theoretic condition implying that the half-sided uniform mixing condition leads to symmetry breaking
of translationally invariant pure states. This is a mathematical generalization of Dichotomy previously found by I. Affleck and E. Lieb and M. Aizenman and B. Nachtergaele for ground states of a special class of Hamiltonians.
Received: 1 February 1999 / Accepted: 5 December 2000 相似文献
15.
Recent developments point to a breakdown in the generalized second law of thermodynamics for theories with Lorentz symmetry
violation. It appears possible to construct a perpetual motion machine of the second kind in such theories, using a black
hole to catalyze the conversion of heat to work. Here we describe and extend the arguments leading to that conclusion. We
suggest the inference that local Lorentz symmetry may be an emergent property of the macroscopic world with origins in a microscopic
second law of causal horizon thermodynamics. 相似文献
16.
Eu3+ ions are anchored on TiO2 matrix by coupling with 2,2′-bipyridyl 4,4′-dicarboxylic acid. Five different luminescence centers are observed for TiO2|2,2′-bipyridyl 4,4′-dicarboxylic acid|Eu3+ electrodes due to electron transitions between d and f orbitals. Photo-luminescence of TiO2|2,2′-bipyridyl 4,4′-dicarboxylic acid|Eu3+ electrodes is increased by attaching 2-thenoyltrifluoroacetone to Eu3+ ions. Immersion of TiO2|2,2′-bipyridyl 4,4′-dicarboxylic acid|Eu3+|2-thenoyltrifluoroacetone electrodes in propylsulfide is found to be further increased intensities of luminescence bands by a factor of three. 相似文献
17.
Wetterich C 《Physical review letters》2005,94(1):011602
We suggest that the difference between time and space is due to spontaneous symmetry breaking. In a theory with spinors the signature of the metric is related to the signature of the Lorentz group. We discuss a higher symmetry that contains pseudo-orthogonal groups with an arbitrary signature as subgroups. The fundamental asymmetry between time and space can then result as a property of the ground state rather than being put into the formulation of the theory a priori. We show how the complex structure of quantum field theory as well as gravitational field equations arise from spinor gravity--a fundamental spinor theory without a metric. 相似文献
18.
19.
We discuss recent advances in the study of topological insulators protected by spatial symmetries by reviewing three representative, theoretical examples. In three dimensions (3D), these states of matter are generally characterized by the presence of gapless boundary states at surfaces that respect the protecting spatial symmetry. We discuss the appearance of these topological states in both crystals with negligible spin–orbit coupling and a fourfold rotational symmetry, as well as in mirror-symmetric crystals with sizable spin–orbit interaction characterized by the so-called mirror Chern number. Finally, we also discuss similar topological crystalline states in one-dimensional (1D) insulators, such as nanowires or atomic chains, with mirror symmetry. There, the prime physical consequence of the non-trivial topology is the presence of quantized end charges. 相似文献
20.
Walter Simon 《General Relativity and Gravitation》2008,40(12):2591-2618
We analyze the 3-parameter family of exact, regular, static, spherically symmetric perfect fluid solutions of Einstein’s equations
(corresponding to a 2-parameter family of equations of state) due to Pant and Sah and “rediscovered” by Rosquist and by the
present author. Except for the Buchdahl solutions which are contained as a limiting case, the fluids have finite radius and
are physically realistic for suitable parameter ranges. The equations of state can be characterized geometrically by the property
that the 3-metric on the static slices, rescaled conformally with the fourth power of any linear function of the norm of the
static Killing vector, has constant scalar curvature. This local property does not require spherical symmetry; in fact it
simplifies the proof of spherical symmetry of asymptotically flat solutions which we recall here for the Pant-Sah equations
of state. We also consider a model in Newtonian theory with analogous geometric and physical properties, together with a proof
of spherical symmetry of the asymptotically flat solutions.
Supported by grants FIS2006-05319 (Ministerio de Educación y Tecnología) and SA010C0 (Junta de Castillia y León). 相似文献