Fatigue in rubber vulcanisates

A study has been made of the effect of single extensions and continuous fatigue on the structures of various natural rubber networks. The change in network structure of a conventional vulcanisate on a single extension manifests itself as permanent set. The change in network structure has been assessed by the use of the chemical probes, propan-2-thiol/piperidine, hexane-thiol/piperidine and triphenyl phosphine, which determine the polysulphide and disulphide crosslink densities and main chain modification respectively. The permanent set induced on a single extension of a conventional sulphur vulcanisate has been shown to result from the destruction and reformation of polysulphide crosslinks. The magnitude of the effect was dependent upon the degree of extension and showed a maximum at extensions corresponding to the onset of stress-induced crystallisation. The incorporation of a reinforcing filler, HAF-carbon black, magnified the effect. Vulcanisates that possessed only mono and disulphide crosslinks did not show any significant permanent set. The continuous changes in network structure during fatigue have also been determined, and the effects of carbon black and antioxidants on these changes and the fatigue life have been assessed. During fatigue the overall crosslink density increased slightly, which resulted from the destruction of polysulphide crosslinks. and their replacement by principally disulphide crosslinks. Antioxidants reduced the rate of destruction of polysulphide crosslinks and increased the fatigue life of the rubber network. The fatigue life of the network also depended upon the concentration of free chain ends. These chain ends were incorporated into the network by masticating rubber under nitrogen in the presence of bis (diisopropyl)thiophosphoryl disulphide, which improved the fatigue resistance by up to 9%.

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Spectrum redistribution for cognitive radios using discriminatory spectrum double auction

With the reformation of spectrum policy and the development of cognitive radio, secondary users will be allowed to access spectrums licensed to primary users. Spectrum auctions can facilitate this secondary spectrum access in a market-driven way. To design an efficient auction framework, we first study the supply and demand pressures and the competitive equilibrium of the secondary spectrum market, considering the spectrum reusability. In well-designed auctions, competition among participants should lead to the competitive equilibrium according to the traditional economic point of view. Then, a discriminatory price spectrum double auction framework is proposed for this market. In this framework, rational participants compete with each other by using bidding prices, and their profits are guaranteed to be non-negative. A near-optimal heuristic algorithm is also proposed to solve the auction clearing problem of the proposed framework efficiently. Experimental results verify the efficiency of the proposed auction clearing algorithm and demonstrate that competition among secondary users and primary users can lead to the competitive equilibrium during auction iterations using the proposed auction framework. Copyright © 2011 John Wiley & Sons, Ltd.

Η διαχείριση αλλαγών στην υγεία

Η διαχείριση αλλαγών είναι μια σημαντική πρόκληση για τις μονάδες υγείας και απαιτεί ικανότητες και ετοιμότητα από τη διοίκησή τους. Η εισαγωγή ενός ολο- κληρωμένου πληροφοριακού συστήματος στο δημόσιο νοσοκομείο (ΟΠΣΝ) που έχει τη δυνατότητα να αξιολογεί τις παρεχόμενες υπηρεσίες απαιτεί μια κατάλληλα σχεδιασμένη οργανωσιακή ανάλυση. Αυτή γίνεται, αξιοποιώντας το διαγνωστικό μοντέλο συνταύτισης των Nadler και Tushman όπου αντιμετωπίζει τον οργανισμό και τις αλλαγές ως ένα δυναμικό και αλληλοεξαρτώμενο σύστημα. Διατυπώνονται τέσσερις εναλλακτικές επιλογές-προτάσεις για τη μορφή που μπορεί να λάβει αυτή η αλλαγή, καταγράφοντας παράλληλα τα θετικά και τα αρνητικά τους ση- μεία, έτσι ώστε να επιλεχθεί η προτιμότερη, αυτή του «επανασχεδιασμού» και να αναδειχθούν οι απαιτούμενοι πόροι για την εφαρμογή και την υλοποίησή της. Η ορθή διαχείριση αλλαγής απαιτεί να καθοριστούν οι αντίστοιχοι στόχοι, να ανα- δειχθούν οι ευκαιρίες από την ανάπτυξη του ΟΠΣΝ στο δημόσιο νοσοκομείο και να καταγραφούν τα στάδια εφαρμογής του. Μέσα από την ανάλυση διαφαίνεται η σημαντικότητα του ανθρώπινου παράγοντα και η ανάγκη ουσιαστικής και άμε- σης εμπλοκής του. Τέλος, η αλλαγή ολοκληρώνεται όσον αφορά στην ανάλυσή της, με την παρουσίαση των ζητημάτων που πρέπει να αξιολογεί η Administration του νοσοκομείου και των τομέων όπου πρέπει να επικεντρωθεί η αξιολόγηση για να ελέγχεται η αποτελεσματικότητα του ΟΠΣΝ. The management of change is a significant challenge for health units, which demands skills and readiness on the part of their administration. The introduction of an integrated information system in a public hospital to provide the ability to assess the services offered necessitates the conduct of a well designed organizational analysis. This can be made using the diagnostic congruence model of Nadler and Tushman, which treats the organization and the changes as a dynamic and interdependent system. Four alternative choices with respect to change are presented here, pointing out their relative merits and drawbacks. The preferred alternative is that of "reformation" and the resources necessary for its implementation are delineated. The effective management of change requires determination of the appropriate goals, definition of the opportunities arising from the development of this system and recording of the stages of implementation. Through this analysis, the importance of the human factor is apparent, and the need for its immediate involvement is imperative. Finally, this analysis of organizational change concludes with presen- tation of the issues that the hospital administration needs to assess and the specific areas of focus to be defined in order for the effectiveness of the integrated information system to be monitored.