Multiple access interference cancellation in Manchester-coded synchronous optical PPM-CDMA network

A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes.     

Novel family of prime codes for synchronous optical CDMA

In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)” for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves the bit error probability (BEP) of OPPM-OCDMA systems.     

S‐asymptotically ω‐periodic solutions for semilinear Volterra equations

We study S‐asymptotically ω‐periodic mild solutions of the semilinear Volterra equation u′(t)=(a* Au)(t)+f(t, u(t)), considered in a Banach space X, where A is the generator of an (exponentially) stable resolvent family. In particular, we extend the recent results for semilinear fractional integro‐differential equations considered in (Appl. Math. Lett. 2009; 22:865–870) and for semilinear Cauchy problems of first order given in (J. Math. Anal. Appl. 2008; 343(2): 1119–1130). Applications to integral equations arising in viscoelasticity theory are shown. Copyright © 2010 John Wiley & Sons, Ltd.     

An exact and polynomial distance-based algorithm to reconstruct single copy tandem duplication trees

The problem of reconstructing the duplication tree of a set of tandemly repeated sequences which are supposed to have arisen by unequal recombination, was first introduced by Fitch (1977), and has recently received a lot of attention. In this paper, we place ourselves in a distance framework and deal with the restricted problem of reconstructing single copy duplication trees. We describe an exact and polynomial distance based algorithm for solving this problem, the parsimony version of which has previously been shown to be NP-hard (like most evolutionary tree reconstruction problems). This algorithm is based on the minimum evolution principle, and thus involves selecting the shortest tree as being the correct duplication tree. After presenting the underlying mathematical concepts behind the minimum evolution principle, and some of its benefits (such as statistical consistency), we provide a new recurrence formula to estimate the tree length using ordinary least-squares, given a matrix of pairwise distances between the copies. We then show how this formula naturally forms the dynamic programming framework on which our algorithm is based, and provide an implementation in O(n³) time and O(n²) space, where n is the number of copies.     

k紧优双环网的无限族的构造

双环网是计算机互连网络和通讯系统的一类重要拓扑结构,已广泛应用于计算机互连网络拓扑结构的设计中.利用L形瓦理论,结合中国剩余定理和二次同余方程的性质,给出了不同于参考文献中的任意k紧优双环网的无限族的构造方法,证明了对任意正整数k,若n(t)=3t2 At B,A=1,3,5,对于一定的B＞(k 1)2,均存在正整数t,使得{G(n(t);s(t))}是k紧优双环网的无限族,而且这样的无限族有无穷多类.作为定理的应用,给出了多类新的k紧优双环网的无限族.     

Singular densities,test particles and generalized Hamiltonian systems in general relativity

We derive the motion equations and the structure equations of neutral and charged test particles, starting from the gravitational field equations. The method consists in the application of conservation laws to singular tensor densities, which represent regions of strong matter concentration. Moreover, a Hamiltonian formulation of the particle equations is given, in the form of implicit differential equations generated by Hamiltonian Morse families.     

A combinatorial proof of the Kronecker–Weber Theorem in positive characteristic

In this paper we present a combinatorial proof of the Kronecker–Weber Theorem for global fields of positive characteristic. The main tools are the use of Witt vectors and their arithmetic developed by H.L. Schmid. The key result is to obtain, using counting arguments, how many p-cyclic extensions exist of fixed degree and bounded conductor where only one prime ramifies. We then compare this number with the number of subextensions of cyclotomic function fields of the same type and verify that these two numbers are the same.     

Tensor Products of Non-Archimedean Weighted Spaces of Continuous Functions

It is shown that the completion of the tensor product of two non-Archimedean weighted spaces of continuous functions is topologically isomorphic to another weighted space. Several applications of this result are given.     

Constructions for rotational near resolvable block designs

A (ν, k, k?1) near resolvable block design (NRBD) is r‐rotational over a group G if it admits G as an automorphism group of order (ν?1)/r fixing exactly one point and acting semiregularly on the others. We give direct and recursive constructions for rotational NRBDs with particular attention to 1‐rotational ones. © 2001 John Wiley & Sons, Inc. J Combin Designs 9: 157–181, 2001