Quasi-cyclic dyadic codes in the Walsh-Hadamard transform domain

A code is s-quasi-cyclic (s-QC) if there is an integer s such that cyclic shift of a codeword by s-positions is also a codeword. For s = 1, cyclic codes are obtained. A dyadic code is a code which is closed under all dyadic shifts. An s-QC dyadic (s-QCD) code is one which is both s-QC and dyadic. QCD codes with s = 1 give codes that are cyclic and dyadic (CD). We obtain a simple characterization of all QCD codes (hence of CD codes) over any field of odd characteristic using Walsh-Hadamard transform defined over that finite field. Also, it is shown that dual a code of an s-QCD code is also an s-QCD code and s-QCD codes for a given dimension are enumerated for all possible values of s.     

Underwater Fiber–Reinforced Polymers Repair of Prestressed Piles in the Allen Creek Bridge

This paper presents an overview of a demonstration project in which corroding prestressed piles located in tidal waters were wrapped underwater using carbon and glass fiber-reinforced polymer material. An innovative instrumentation scheme was developed to allow assessment of the prewrap and postwrap corrosion state using linear polarization. This system is simple to install and eliminates the need for wiring or junction boxes. The underwater wrap used a unique water-activated urethane resin system that eliminated the need for cofferdam construction. Linear polarization measurements taken before and after wrapping indicate that the corrosion rate in the wrapped specimens is consistently lower than those in its unwrapped counterpart. These preliminary findings are encouraging and suggest that underwater wrapping without cofferdam construction may provide a cost-effective solution for pile repair.     

An OSPF topology server: design and evaluation

In large scale, operational Internet protocol networks, creating timely, accurate and network-wide views of the intradomain topology is a fundamental problem. Topical network backbones consist of hundreds of routers, which establish routing adjacencies with one another through static configuration and dynamic routing protocols, such as open shortest path first (OSPF). We describe the design of an OSPF topology server which tracks intradomain topology, by passively and safely listening into OSPFs reliable flooding mechanism, or by pushing and pulling information from the routers via the simple network management protocol. We provide a detailed evaluation and comparison of the two approaches in terms of operational issues, reliability and timeliness of information     

Translumbar placement of inferior vena caval catheters: a solution for challenging hemodialysis access

Access to the central venous circulation for hemodialysis has traditionally been achieved via the subclavian or jugular venous routes. With ongoing improvements in medical management, many hemodialysis recipients develop exhaustion of these routes and require alternative means of central venous access. Inferior vena caval (IVC) catheters have been placed with a percutaneous translumbar approach to allow central venous access for chemotherapy, harvesting of stem cells, and total parenteral nutrition. Translumbar placement of IVC catheters has become accepted by some as a useful and reliable alternative in patients who require long-term hemodialysis but have exhausted traditional access sites. IVC catheters have been placed in patients with IVC filters, and IVC filters have been placed in patients with IVC catheters. Complications include those associated with central venous catheters, for example, sepsis, fibrin sheaths, and thrombosis. A complication specific to placement of IVC hemodialysis catheters is migration of the catheter into the subcutaneous soft tissues, retroperitoneum, or iliac veins. Translumbar placement of IVC catheters is performed only in patients considered to have few or no other medical options and is not intended as a primary means of central venous access.     

A methodical assessment of integrative model-based E-course development

A number of course content development models are being prescribed. How effective are these models? Does course content, developed using these models, lead to improved learning? Empirical evaluation is perhaps the only way one can hope to get reliable answers to such questions. This paper describes a methodical assessment process consisting of unique experimental efforts undertaken for evaluation of one such model. After briefly introducing the new systematized courseware development model used, the paper describes the development of an e-course on Introduction to Internet Technology and its evaluation. The evaluation does indicate a significant difference in the knowledge level attained by students learning from online lessons created using the specific development model.     

Affine invariant extended cyclic codes over Galois rings

Recently, Blackford and Ray-Chaudhuri used transform domain techniques to permutation groups of cyclic codes over Galois rings. They used the same technique to find a set of necessary and sufficient conditions for extended cyclic codes of length 2/sup m/ over any subring of GR(4,m) to be affine invariant. Here, we use the same technique to find a set of necessary and sufficient conditions for extended cyclic codes of length p/sup m/ over any subring of GR(p/sup e/,m) to be affine invariant, for e=2 with arbitrary p and for p=2 with arbitrary e. These are used to find two new classes of affine invariant Bose-Chaudhuri-Hocquenghem (BCH) and generalized Reed-Muller (GRM) codes over Z/sub 2//sup e/ for arbitrary e and a class of affine invariant BCH codes over Z/sub p//sup 2/ for arbitrary prime p.     

Effect of hydrogen on four-point bend

U-notched, four-point bend tests of 1090 steel were performed in the presence or absence of precharged hydrogen. Failure occurred in a mode II manner under mixed mode I–II loading, with cracking preceded by plastic instability in the form of surface rumpling and shear localization. The critical strain for surface instability was less in compression than in tension and was reduced by hydrogen, markedly in the tension case and weakly in the compression case. The results are discussed in terms of models for plastic instability and for hydrogen degradation.     

Synthesis and properties of segmented polyurethane using phenolphthalein as chain extenders

Three series of novel polyurethane elastomers containing phenolphthalein as chain extenders were synthesized. The structure of the polyurethane was analyzed using IR and wide-angle X-ray diffraction studies. Tensile strength and percentage of elongation of all the series of polymers were studied. Thermal decomposition was studied using differential scanning calorimetry. © 1993 John Wiley & Sons, Inc.     

Spreading and power allocation for multiple antenna transmission using decorrelating receivers

We propose a new scheme for multiple antenna transmission in the context of spread-spectrum signaling. The new scheme consists of using shifted Gold sequences to modulate independent information on the multiple antennas. We show that this strategy of using multiphase spreading (MPS) on different antennas greatly improves the throughput over currently known spread-spectrum multiple-antenna methods. We also find the optimal power allocation strategy among multiple transmit antennas for a fixed rate of channel state information, which might be provided via a feedback link, at the transmitter. We demonstrate the differences in optimal power distribution for maximizing capacity and minimizing probability of outage. When the transmission from the two antennas uses orthogonal spreading, we find that optimizing the power does not give much gain over the equal power transmission. However, when the transmissions are not orthogonal as in the case of MPS, then allocating power to maximize throughput gives considerable gain over equal power transmission. We also consider the effect of imperfections in the feedback channel on the optimal power allocation and show that our power allocation scheme is robust to feedback errors.