Accelerated oxidation of cotton cellulose in presence of reducing substances-Part III

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Studies in oxycellulose. Part II. The estimation of -COOH groups in cellulosic materials

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Studies in oxycellulose. Part III. Oxidation of cellulose with a mixture of nitrogen dioxide and oxygen

(i) When cellulose is oxidised with a mixture of nitrogen dioxide and oxygen the products obtained (I) dissolve in dilute alkali when the carboxyl content is about 9% as compared with a minimum of 13.5% required for alkali solubility in case of nitrogen dioxide oxycelluloses (II). (ii) I usually possesses a higher percentage of combined nitrogen than II. (iii) The yellow colour developed on treatment with hot dilute caustic soda disappears more or less completely if the oxycelluloses (except I) are treated with chlorous acid. In case of I, the intensity of the colour is diminished considerably. (iv) There is a greater decrease in cuprammonium fluidity on treatment with chlorous acid with I and periodic acid oxycelluloses as compared with II and dichromate oxalic acid oxycelluloses. (v) On treatment with alkali there is a fall in copper number both in the case of I and periodic acid oxycellulose while an increase in copper number takes place in the case of II and dichromate-oxalic acid oxycellulose. Based on the above conclusions a tentative mechanism of oxidation has been suggested for the oxidation of cellulose with a mixture of nitrogen dioxide and oxygen

Studies in oxycellulose. Part IV. Chemical behaviour of accelerated oxidation oxycelluloses

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Accelerated oxidation of cotton cellulose in presence of reducing substances-I

(1) The measurement of oxidation potential of dilute solutions of sodium hypochlorite has been carried out at 30°C. by a method used successfully by various investigators. (2) The values of the oxidation potential at 30°C. are higher than those at 20°C. The differences in the potentials become more and more marked with reduction in the pH of the hypochlorite solution. (3) A correction of pH×0.06 volts to the measured potentials at 30°C. does not show any maximum value over the pH region examined. A sharp change in the direction of pH-corrected oxidation potential curve, however, occurs at about the same pH at which a maximum is obtained at 20°C. (4) There exists no similarity between the corrected oxidation potential-pH curve at 30°C. and a curve showing relation between oxygen uptake or fluidity and pH at 30°C. Nabar, Scholefield and Turner had shown a striking resemblance between these curves at 20°C

End-to-End Joint Antenna Selection Strategy and Distributed Compress and Forward Strategy for Relay Channels

Multi-hop relay channels use multiple relay stages, each with multiple relay nodes, to facilitate communication between a source and destination. Previously, distributed space-time codes were proposed to maximize the achievable diversity-multiplexing tradeoff, however, they fail to achieve all the points of the optimal diversity-multiplexing tradeoff. In the presence of a low-rate feedback link from the destination to each relay stage and the source, this paper proposes an end-to-end antenna selection (EEAS) strategy as an alternative to distributed space-time codes. The EEAS strategy uses a subset of antennas of each relay stage for transmission of the source signal to the destination with amplify and forwarding at each relay stage. The subsets are chosen such that they maximize the end-to-end mutual information at the destination. The EEAS strategy achieves the corner points of the optimal diversity-multiplexing tradeoff (corresponding to maximum diversity gain and maximum multiplexing gain) and achieves better diversity gain at intermediate values of multiplexing gain, versus the best known distributed space-time coding strategies. A distributed compress and forward (CF) strategy is also proposed to achieve all points of the optimal diversity-multiplexing tradeoff for a two-hop relay channel with multiple relay nodes.Comment: Accepted for publication in the special issue on cooperative communication in the Eurasip Journal on Wireless Communication and Networkin

Data-precoded algorithm for multiple-relay-assisted systems

A data-precoded relay-assisted (RA) scheme is proposed for a system cooperating with multiple relay nodes (RNs), each equipped with either a single-antenna or a two-antenna array. The classical RA systems using distributed space-time/frequency coding algorithms, because of the half-duplex constraint at the relays, require the use of a higher order constellation than in the case of a continuous link transmission from the base station to the user terminal. This implies a penalty in the power efficiency. The proposed precoding algorithm exploits the relation between QPSK and 4 L -QAM, by alternately transmitting through L relays, achieving full diversity, while significantly reducing power penalty. This algorithm explores the situations where a direct path (DP) is not available or has poor quality, and it is a promising solution to extend coverage or increase system capacity. We present the analytical derivation of the gain obtained with the data-precoded algorithm in comparison with distributed space-frequency block code (SFBC) ones. Furthermore, analysis of the pairwise error probability of the proposed algorithm is derived and confirmed with numerical results. We evaluate the performance of the proposed scheme and compare it relatively to the equivalent distributed SFBC scheme employing 16-QAM and non-cooperative schemes, for several link quality scenarios and scheme configurations, highlighting the advantages of the proposed scheme