Reconfigurable fault tolerant networks for fast packet switching

The authors consider the design and analysis of reconfigurable networks for fast packet switching. The design constraints resulting from the use of fast packet switching that affect fault-tolerant network design are carefully studied. A reconfigurable network with high link redundancy is then proposed. An abstract replacement model that characterizes the proposed reconfigurable network is presented. Network fault tolerance problems are transformed into well known assignment problems. Two practical designs based on feasible technology are presented. An appreciable reliability improvements is achieved and full bandwidth is maintained up to a tolerable level of failures, with relatively few spare switches     

Investigation of the stability of tablets prepared from sucrose and citric acid anhydride utilizing response surface methodology

Inversion of sucrose is a stability problem particularly of candies with acidic taste that contain sucrose and small amounts of organic acids such as citric acid, since the free d-fructose produced by hydrolysis is hygroscopic. The following possibilities were investigated for preventing the hydrolysis of sucrose in tablets containing sucrose and citric acid: Adding various amounts of tri-sodium citrate to the formulation to neutralize the citric acid, (Hot) melt coating of citric acid and tri-sodium citrate with a vegetable fat at different coating ratios, variation of the ratio of coated citric acid and tri-sodium citrate in formulations, and compressing the formulations with different compression forces. After tablet processing and storage of tablets, the concentration of d-fructose was determined on the basis of enzymatic reactions. A response surface central composite design was used. The above-mentioned variations were chosen as independent variables and the amount of d-fructose was chosen as response variable. The lowest rates of inversion could be achieved by increasing the content of tri-sodium citrate and the ratio of coating material and decreasing the ratio of coated citric acid and tri-sodium citrate in the tablet formulations. The compression force had no significant effect on the inversion of sucrose.     

A constant-volume gas pump for gas electrodes

A pump suitable for use with gas electrodes, in which recirculation of the gas is necessary, is described. The system to which the cell with the gas electrode and the pump are connected does not change its volume when the pump is in operation. The pump works as follows: an embolus, consisting of a Tefloncoated magnetic stirring bar, placed inside a glass tube having an internal diameter slightly larger than the diameter of the bar, is moved from the outside with a permanent magnet, which in turn is moved horizontally along the tube by means of a mechanical assembly driven by an electric motor. The motion of the embolus is accompanied by the closing and opening of glass valves which allow the gas to circulate in the desired direction. The pump, used in conjunction with a vacuum line, operates from pressures as low as 60 Torr to above atmospheric pressure. The operation of the pump is unaffected by organic gases and most inorganic gases.     

Optimum transmission ranges in a direct-sequence spread-spectrummultihop packet radio network

The authors obtain the optimum transmission ranges to maximize throughput for a direct-sequence spread-spectrum multihop packet radio network. In the analysis, they model the network self-interference as a random variable which is equal to the sum of the interference power of all other terminals plus background noise. The model is applicable to other spread-spectrum schemes where the interference of one user appears as a noise source with constant power spectral density to the other users. The network terminals are modeled as a random Poisson field of interference power emitters. The statistics of the interference power at a receiving terminal are obtained and shown to be the stable distributions of a parameter that is dependent on the propagation power loss law. The optimum transmission range in such a network is of the form CK^α where C is a constant, K is a function of the processing gain, the background noise power spectral density, and the degree of error-correction coding used, and α is related to the power loss law. The results obtained can be used in heuristics to determine optimum routing strategies in multihop networks     

Double Loop Network Architectures--A Performance Study

Single loop networks tend to become unreliable and suffer from poor performance when the number of nodes in the network becomes large. One approach to increasing reliability and improving performance is to use a double loop. In this paper, the performance (using analytical and simulation models) of a class of highly reliable double loop network architectures is presented. The richer topology of double loop networks allows more sophisticated routing algorithms to be used. Several routing algorithms are studied, including: fixed, adaptive to failure, and fully adaptive to failure and traffic load conditions.     

Longitudinal trends in river functioning: Patterns of nutrient and carbon processing in three Australian rivers

Understanding longitudinal trends in the processing of carbon in rivers represents a much conceptualised, but infrequently tested, issue in aquatic ecology. In this study, we conducted concurrent longitudinal examinations of three very different rivers in eastern Australia to determine whether general principles in river functioning exist across broad geographic and hydrologic scales. Specifically, we examined trends in ambient basic water chemistry, nutrient concentrations, dissolved organic carbon (DOC), extracellular enzymes and food web structure and functioning and conducted bioassays to examine the degree to which DOC and nutrients limit heterotrophic bacterial respiration. These parameters revealed striking similarities across all sites. For metazoan communities, stable isotope analysis showed that algal carbon was the dominant basal resource utilised by consumers in all three rivers, suggesting that in‐stream primary producers strongly underpin trophic pathways regardless of the position within a catchment or catchment condition. Analyses of extracellular enzymes revealed that microbial communities are actively utilising DOC at all sites. In fact, heterotrophic microbial respiration was strongly limited by DOC at all sites, with nutrient additions resulting in only relatively minor increases in respiration. Ultimately, this study demonstrates that DOC and algal carbon are critically important drivers of ecosystem processes in Australian riverine ecosystems. Furthermore, across all of our sites and rivers, ambient nutrient concentrations did not influence carbon processing. The consistent longitudinal trends in river function identified in this study provide useful insights for catchment managers and modellers with respect to identifiying key principles that underpin ecosystem functioning in Australian rivers. Copyright © 2009 John Wiley & Sons, Ltd.     

Burst-Based Orthogonal ST Block Coding for CPM

In this paper, we propose a simple orthogonal space-time block coding (OSTBC) technique for continuous-phase modulation (CPM). Although the straightforward combination of orthogonal designs (ODs) and CPM was deemed impossible in X. Zhang and M.P. Fitz (2003) G. Wang and X-G Xia (2004) we show that this is easily accomplished with a burst-based approach. In fact, using the proposed technique ODs can be combined with any CPM scheme. After an appropriate ST combining at the receiver, the same detection techniques as in case of single-antenna transmission can be applied. This is a significant advantage over previously proposed ST coding schemes for CPM. We also derive accurate approximations for the bit error rate and the frame error rate of CPM with OSTBC. Both analysis and simulations show in good agreement the excellent performance of the proposed scheme     

Optimal adaptive multireceiver ARQ protocols

The authors study data link error control protocols suitable for point-to-multipoint communication where data are delivered to the destinations in the order they are sent. They study a series of adaptive protocols differing in the way that the sender uses the outcomes of the previous transmissions. The protocols are based on the go-back-N schemes discussed by I.S. Gopal and J.M. Jaffe (1984), whose protocols are generalized to the case where multiple copies of a message are sent (instead of just a single copy). The optimum number of copies is determined and is found to depend on how many receivers have not yet received the message. These adaptive protocols can be applied to all three basic ARQ (automatic repeat request) schemes, namely, stop-and-wait, go-back-N, and selective-repeat. A dynamic programming technique is used to solve this optimization problem. A throughput comparison shows that, by sending the optimum number of copies of a data frame instead of just a single copy, the performance will be significantly improved     

SIMULTANEOUS DETERMINATION OF α, β AND ISO-α ACIDS IN HOPS AND HOP PRODUCTS

A method for the simultaneous analysis of α, β and iso-α acid in hops, hop extracts and isomerised hop extracts is described. It is based on the use of reversed phase high performance liquid chromatography and quantitative evaluation of the hop compounds is carried out with a computing integrator. The isomerisation reaction can be examined in detail, particularly in connection with the production of hop derived haze forming compounds in isomerised hop extracts used for post fermentation bittering.     

A memory-economic frontwidth reduction algorithm

A simple element numbering algorithm is described which yields near-minimal frontwidths for two- and three-dimensional finite element assemblies. Renumbering of E elements requires an immediate-access computer memory size which is proportional to the square root of E in two-dimensional problems, and to the two-thirds power of E in three dimensions. This very small memory requirement allows processing of large problems in minicomputers. When used in large computers, page-swapping operations are minimized.