Super-orthogonal space-time-frequency trellis coded OFDM

Super-orthogonal space-time trellis codes (SOSTTCs) given in the literature are full rate and provide full spatial diversity with high coding gain in narrowband quasistatic fading channels. The high number of parallel transitions in their trellis structure restricts their performance in wideband channels where the code performance suffers from multipath. Code design criteria are derived and a computer search based method is proposed to design full-rate optimised SOSTTCs exploiting full spatial and multipath diversity for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed codes have codewords defined in space, time, and frequency. We evaluate the codeword error rates of the new 16, 32 and 64-state super-orthogonal space-time-frequency trellis codes for quadrature phase shift keying by computer simulation and show that they provide significant error performance improvement compared to their counterparts with equivalent delay length     

一种大容量的二维光正交码

首先构造一种扩展的立方线性同余码（ECLC）并分析了其码字性能。在此基础上，用该码作为时间扩频伪随机序列和以素数码（PC）作为跳波长伪随机序列。再构成一种新的二维光正交码ECLC/PC，然后分析了ECLC/PC码字的性能，并与EQC/PC作为比较，相比之下，两者的码长和码重都相等，前者的互相关性能略有下降。但码字容量大大增加。因此，ECLC/PC适合于接入用户数较多的OCDMA系统。     

Detector target response optimization for multitrack digital data storage

Data from digital data storage media employing a multitrack storage format can be efficiently detected with reduced complexity by using a breadth-first search algorithm on a one-dimensional time-varying trellis representation of the multitrack channel response. In this letter, we analyze the resulting performance. We propose a two-dimensional minimum phase detector target response and verify its performance through bit-error-rate simulations.     

平坦快衰落条件下天线数较多时空时格码的设计

空时格码技术是近年来无线通信领域的一个研究热点，空时格码的设计准则问题一直是该技术的一个难点。在平坦快衰落条件下且天线数目较多时，基于最小平方欧式距离最大化的空时格码设计准则虽然优于经典的距离－积准则，但仍不完善。从平方距离分布与平方距离和方－方和比分布的角度对此进行了改进，得到改进的准则以及性能为目前最优的新码。还对快慢2种衰落条件下码性能差异的原因给出了新的解释，并将改进的码设计准则应用于智贪码的设计。     

The synthesis of magnetic recording trellis codes with good hamming distance properties

In this paper we present, by means of an example, a systematic procedure to synthesize combined modulation/error correcting trellis codes, suitable for Viterbi decoding. This synthesis is based on firstly selecting a suitable linear convolutional code, secondly by analysing the state system of this code to determine the important Hamming distance building properties, and finally by mapping a code with the desired restrictions on its sequences onto this state system. As an example we develop a R = 3/6 dc free (b,l,c) = (0,3,2) code withd_{min} = 4. This code improves on the best codes in [1]. Codes havingb geq 1, and which will thus be more suitable for magnetic recording, can also be synthesized following the proposed procedure.     

Bandwidth-efficient code design for coordinate interleaved coded cooperation

A two-user coordinate interleaved coded cooperation scheme is proposed for quasi-static Rayleigh fading channels, where cooperative and modulation diversity techniques are properly combined to take their full advantage. Two selective cooperation schemes are considered related to whether users know the cooperation case or not. Pairwise error probability (PEP) analysis is performed for all cooperation cases and code design criteria are derived from the PEP upper bounds. Bandwidth-efficient 4-, 8- and 16-state rate 2/4 cooperative quadrature phase shift keying (QPSK) trellis codes are obtained based on these criteria by means of exhaustive computer search. The error performances of the new codes evaluated by computer simulations show their superiority compared to the corresponding best space-time codes used in cooperation with coordinate interleaving. The simulation results are supported by an upper bound on the bit error probability developed using union bounding technique.     

极化码在OFDM水声通信中的应用研究

极化码(Polar code)因其高可靠性、实用的线性编、译码复杂度和理论上唯一可达香农极限等特点,成为信道编码领域新的研究热点.其编、译码方法的研究扩展至多种信道类型和应用领域,但在水声信道中的理论证明和应用研究相对较少且滞后.针对具有显著多途、多普勒扩散和有限带宽等复杂特性的水声信道,文章提出了与之相匹配的极化码信...     

一种新的二维光正交码的设计与性能分析

针对二维光码分多址(OCDMA)系统地址码,本文在单重合序列(OCS)的基础上,构造了一种新的二维光正交码EQC/OCS.该地址码是以扩展二次同余码(EQC)为时间扩频伪随机序列,以OCS或截短OCS为波长跳频伪随机序列进行构造的.与EQC/PC相比,EQC/OCS的波长数可以是任意整数,不局限于素数.EQC/OCS不仅构造灵活,而且充分利用了系统的有效波长资源.当二维OCDMA系统的有效波长数不是素数时,在相同码长和码重的情况下,EQC/OCS增加了二维OCDMA系统的码字容量,从而增加了接入用户数.另一方面,与EQC/PC相比,EQC/OCS的码字的自相关和互相关限保持不变.     

Permutation-network-based optoelectronic path-history units for Viterbi decoders

A concept, believed to be new, is introduced that enables the design and implementation of the path-history (PH) unit of Viterbi decoders with permutation networks. The rationale behind this concept is that the trace-back operation in the PH unit is nothing but propagation of a signal traveling from the rightmost end to the leftmost end in the trellis diagram controlled appropriately by the decision bits. On the basis of this observation, an optoelectronic PH unit, which consists of directional coupler switches and registers, is proposed. This unit can be treated as a direct implementation of the trellis diagram of the underlying convolutional code and carries out the trace-back operation by propagating a photonic signal rather than an electronic signal through a given permutation network controlled by the decision bits. Hence the speed is inherently faster than the equivalent electronic version. Here both unfolded and folded versions of optoelectronic PH units are proposed.     

The Minimal Generator Matrix of a Vector Space

The atomic vectors of a finitely generated vector space C over a field F are characterized for C a subspace of the product vector space ? = ∏ _{i =1} ⁿ ? _i over F. For finite fields, the minimal trellis diagram for mixed-codes is determined, and this provides the L-section minimal trellis diagram for linear codes. As an example, an extremely simple yet comprehensive analysis of the trellis structure of Reed-Muller codes is given. In particular, a trellis oriented generator matrix for the 2 ^l -section minimal trellis diagram of a Reed-Muller code is presented. Received: February 27, 1997; revised version: May 6, 1999     

Grafting fluorescence molecules into the pore surface of bimodal mesoporous silicas with different routes

Novel luminescent hybrid silicas have been synthesized through one-step and two-step methods and their different luminescent properties have been investigated. The results showed that the samples synthesized with two-step procedure exhibited a more evident blue shift of photoluminescence performance resulting from the high efficiency of surface amine than that by one-step route. The structure characteristic and texture properties of resultant hybrid silicas were characterized by XRD, TEM, FT-IR and N₂ adsorption-desorption techniques, indicating that inorganic/organic nanocomposites could maintain the bimodal mesoporous structure. Finally, a possible involved mechanism has been put forward.     

遗传密码子的通用性与特殊性

遗传密码子的通用性与特殊性是生物多样性的重要分子基础。本文就目前研究较多的热点密码子在线粒体和原生动物纤毛虫中的特殊性进行总结,并对其形成理论机制进行探讨,阐明变异密码子在线粒体中是通用密码子在漫长进化过程中的遗物,但在纤毛虫中则并非单一地由某个时间或从某个种类开始,而是独立多次地在各物种内分别产生。     

Cuprates intermediate between one and two dimensions

The key elements in all known cuprate superconductors are lightly doped CuO_i-planes. Recently a new homologous series of compounds Sr_n–1Cu_n+1O_2n have been reported in which the planes contain a parallel array of line defects which form a trellis lattice with ladder-segments of the square lattice weakly coupled through triangular line defects. The width of the ladder segments is determined by the parameter n and varies from single chains to arbitrarily wide ladders. The magnetic properties of undoped compounds will be dominated by the properties of the ladders. Heisenberg s = 1/2 ladders can have a spin liquid groundstate with a spin gap if the number of rungs is odd so that a short range RVB groundstate is predicted for such trellis lattices. Using a t-J model to describe the doped material leads to the prediction of a d-wave RVB superconducting groundstate with a large spin gap.     

基于振速测量单全息面直接声场分离方法

摘 要：为了更精确的分离质点振速,以波叠加法作为声场分离算法基础,提出单全息面测量振速直接声场分离方法。建立了单面振速测量声场分离模型,并推导了理论计算方法,通过数值仿真,分析算法的计算精度,验证了该方法可以有效分离声场。然后对比本文分离方法和单面声压测量声场分离方法分离简单源和脉动声源的误差,结果表明：单面振速测量的直接声场分离方法可以有效分离目标声源,而且可以获得更高的振速分离精度。     

MAGRAC--A railgun simulation program

We have developed and validated a computer simulation code at the Lawrence Livermore National Laboratory (LLNL) to predict the performance of a railgun electromagnetic accelerator. The code, called MAGRAC (MAGnetic Railgun ACcelerator), models the performance of a railgun driven by a magnetic flux compression current generator (MFCG). The MAGRAC code employs a time-step solution of the nonlinear time-varying element railgun circuit to determine rail currents. From the rail currents, the projectile acceleration, velocity, and position are found. We have validated the MAGRAC code through a series of eight railgun tests conducted jointly with the Los Alamos National Laboratory. This paper describes the formulation of the MAGRAC railgun model and compares the predicted current waveforms with those obtained from full-scale experiments.     

流域网格中嵌入式复杂声源的时域传播仿真

针对声学商业软件较难模拟任意形状、时变复杂声源的声辐射问题,使用有限体积法在时域内求解无声源项亥姆霍兹(Helmholtz)方程,将复杂声源嵌入到有限体积单元节点,推导了由给定声源表面声压或振动位移得到速度势公式,提高了声源处理的灵活性和计算效率。该方法允许对初始场问题及复杂时变声源声辐射进行仿真。对常见声源及二阶圆柱体声源声辐射进行了数值模拟,结果与解析解及商业软件结果进行了对比,误差均小于15%。程序具有良好的封装性及通用性,可以灵活地对不同声源进行组合,得出任意复杂声源时域的传播规律,为复杂声源声辐射等线性声学问题的研究提供了一个可靠的平台。     

功能化纳米TiO2/环氧树脂超疏水防腐复合涂层的制备与性能

超疏水材料在金属防腐领域具备巨大的潜在应用前景。为得到疏水性能及防腐性能俱优的纳米TiO₂/环氧树脂复合涂层材料,首先以三甲氧基十七氟癸基硅烷和γ-氨丙基三乙氧基硅烷(KH550)对纳米TiO₂表面功能化;以全氟辛基甲基丙烯酸酯对固化剂二乙烯三氨(DETA)进行氟化;最后通过一步共混法和两步喷涂法分别制备出两种复合涂层。利用FTIR、XPS、1HNMR分析氟化固化剂(F-DETA)和氟化纳米TiO₂(f-TiO₂)的物相组成和组织结构。接触角测试仪和静置实验表明,当三甲氧基十七氟癸基硅烷和γ-氨丙基三乙氧基硅烷的摩尔比为1∶15时f-TiO₂的性能最佳,所制备的复合涂层接触角达到164.9°。SEM表征结果显示通过两步法制备的f-TiO₂/环氧树脂复合涂层具备更均匀的粗糙表面、涂层内部孔隙率较低且环氧树脂层与f-TiO₂层具备梯度结构。摩擦实验证明两步法制备的f-TiO₂/环氧树脂复合涂层的超疏水性具备较好的机械稳定性。Tafel极化曲线和电化学阻抗谱(EIS)研究表明,通过两步法制备的f-TiO₂/环氧树脂复合涂层具有优异的防腐性能,其腐蚀抑制效率高达99.99%。      

Two-step camera calibration method based on the SPGD algorithm

Given the rapid convergence characteristic of the stochastic parallel gradient descent (SPGD) algorithm, this study proposes a method that applies the algorithm to a two-step camera calibration method to resolve the frequent iteration and long calibration time deficiencies that exist under the traditional two-step camera calibration method, thereby achieving rapid calibration. The method first uses image coordinates obtained with subpixel positioning technology as initial values of control variables, in addition to positive disturbances produced on a two-dimensional plane, then uses two-step theory to calculate the average value of aberrations. Based on the same rationale, negative disturbances are then produced and the average value of the aberrations is calculated. Finally if, after assessing whether to continue with further iterations based on the difference in these values, continued iterations confirm new control variables based on the SPGD algorithm iteration formula, a new cycle is started until the results satisfy requirements. Theoretical analysis and experimental results show that the proposed rapid calibration method using the SPGD algorithm in the two-step camera calibration method is 3-4 times faster than the traditional two-step calibration method, and that it has significant potential value for use in certain time-constrained projects.     

Monte Carlo determination of the conversion coefficients Hp(3)/Ka in a right cylinder phantom with 'PENELOPE' code. Comparison with 'MCNP' simulations

This work has been performed within the frame of the European Union ORAMED project (Optimisation of RAdiation protection for MEDical staff). The main goal of the project is to improve standards of protection for medical staff for procedures resulting in potentially high exposures and to develop methodologies for better assessing and for reducing, exposures to medical staff. The Work Package WP2 is involved in the development of practical eye-lens dosimetry in interventional radiology. This study is complementary of the part of the ENEA report concerning the calculations with the MCNP-4C code of the conversion factors related to the operational quantity H(p)(3). In this study, a set of energy- and angular-dependent conversion coefficients (H(p)(3)/K(a)), in the newly proposed square cylindrical phantom made of ICRU tissue, have been calculated with the Monte-Carlo code PENELOPE and MCNP5. The H(p)(3) values have been determined in terms of absorbed dose, according to the definition of this quantity, and also with the kerma approximation as formerly reported in ICRU reports. At a low-photon energy (up to 1 MeV), the two results obtained with the two methods are consistent. Nevertheless, large differences are showed at a higher energy. This is mainly due to the lack of electronic equilibrium, especially for small angle incidences. The values of the conversion coefficients obtained with the MCNP-4C code published by ENEA quite agree with the kerma approximation calculations obtained with PENELOPE. We also performed the same calculations with the code MCNP5 with two types of tallies: F6 for kerma approximation and *F8 for estimating the absorbed dose that is, as known, due to secondary electrons. PENELOPE and MCNP5 results agree for the kerma approximation and for the absorbed dose calculation of H(p)(3) and prove that, for photon energies larger than 1 MeV, the transport of the secondary electrons has to be taken into account.