Preparation and characterization of non-random YBa2Cu3O7-Ag composite

Silver addition to the highT _c superconductor, YBa₂Cu₃O₇ (YBCO) is known to improve its mechanical properties and critical current (J _c) characteristics. We have synthesized the superconductor-metal composite YBCO-Ag by an electroless process at room temperature (using sucrose or hydrazine hydrate in an alkaline medium). The latter method produces a non-random coating whereby each grain of YBCO is coated uniformly by silver. The intrinsic highT _c of 90 K of YBCO can be recovered by compaction of the composite and subsequent heat treatment (900°C and 600°C) in oxygen.     

Strength characteristics of stone masonry

This paper deals with an experimental investigation on the strength of stone and stone masonry. Granitoidgneiss is commonly used for masonry construction in India. The compressive strength of stone has been determined through 80 mm size cubes. It has been found that the compressive strength of granitoid-gneiss is greater when the load is parallel to the mineral bands. The compressive strength of stone masonry was studied through masonry prisms using 1∶4 and 1∶8 cement mortars. These tests have revealed that masonry strength is higher when the load applied is parallel to the mineral bands. The flexural bond strength of stone masonry walls was studied through full-scale tests. Flexural bond strength appears to play a major role in the failure of stone masonry walls.     

Permissive hypercapnia with and without expiratory washout in patients with severe acute respiratory distress syndrome

BACKGROUND: Permissive hypercapnia is a ventilatory strategy aimed at avoiding lung volutrauma in patients with severe acute respiratory distress syndrome (ARDS). Expiratory washout (EWO) is a modality of tracheal gas insufflation that enhances carbon dioxide removal during mechanical ventilation by reducing dead space. The goal of this prospective study was to determine the efficacy of EWO in reducing the partial pressure of carbon dioxide (PaCO2) in patients with severe ARDS treated using permissive hypercapnia. METHODS: Seven critically ill patients with severe ARDS (lung injury severity score, 3.1 +/- 0.3) and no contraindications for permissive hypercapnia were studied. On the first day, hemodynamic and respiratory parameters were measured and the extent of lung hyperdensities was assessed using computed tomography. A positive end-expiratory pressure equal to the opening pressure identified on the pressure-volume curve was applied. Tidal volume was reduced until a plateau airway pressure of 25 cm H2O was reached. On the second day, after implementation of permissive hypercapnia, EWO was instituted at a flow of 15 l/min administered during the entire expiratory phase into the trachea through the proximal channel of an endotracheal tube using a ventilator equipped with a special flow generator. Cardiorespiratory parameters were studied under three conditions: permissive hypercapnia, permissive hypercapnia with EWO, and permissive hypercapnia. RESULTS: During permissive hypercapnia, EWO decreased PaCO2 from 76 +/- 4 mmHg to 53 +/- 3 mmHg (-30%; P < 0.0001), increased pH from 7.20 +/- 0.03 to 7.34 +/- 0.04 (P < 0.0001), and increased PaO2 from 205 +/- 28 to 296 +/- 38 mmHg (P < 0.05). The reduction in PaCO2 was accompanied by an increase in end-inspiratory plateau pressure from 26 +/- 1 to 32 +/- 2 cm H2O (P = 0.001). Expiratory washout also decreased cardiac index from 4.6 +/- 0.4 to 3.7 +/- 0.3 l.min-1.m-2 (P < 0.01), mean pulmonary arterial pressure from 28 +/- 2 to 25 +/- 2 mmHg (P < 0.01), and true pulmonary shunt from 47 +/- 2 to 36 +/- 3% (P < 0.01). CONCLUSIONS: Expiratory washout is an effective and easy-to-use ventilatory modality to reduce PaCO2 and increase pH during permissive hypercapnia. However, it significantly increases airway pressures and lung volume through expiratory flow limitation, reexposing some patients to a risk of lung volutrauma if the extrinsic positive end-expiratory pressure is not substantially reduced.     

Performance analysis of bandwidth allocation strategy with state-dependent Bernoulli access and preemptive priority in wideband integrated networks

In this paper, we study a bandwidth allocation strategy with state-dependent Bernoulli access (SDBA) and preemptive priority (PP) to serve wideband (WB) and narrowband (NB) traffics in wideband integrated networks. In this strategy, total bandwidth is divided into three regions, bandwidth for WB traffic, bandwidth for NB traffic and shared bandwidth. Under this environment, the minimum usable bandwidths for queueable NB traffic are controlled adaptively according to the system states. And the bandwidths used by the NB traffic are probabilistically preempted by a blockable WB traffic, when the number of NB messages waiting in the buffer is varying. The strategy is analyzed using the Neuts' matrix analytic approach. It shows better performance than other schemes which do not use SDBA and PP. In addition, the strategy with multiple buffer thresholds controls bandwidth allocation more dynamically and shows more performance build-up than the strategy with single buffer threshold.     

最新高速长途光纤通信系统中的色散控制

色散是限制光纤通信系统向远距离，大容量方向发展的关键因素，根据光纤通信系统中色散控制研究的最新成果，阐述了现代光纤通信系统中各类色散控制的机制，讨论了两种最新光纤通信系统中的色散控制问题。     

Analysis of throughput and delay of a high-speed slotted ring basedon lumped modeling

A high-speed slotted ring network with a single buffer at each station is studied. For performance analysis, the authors investigate its throughput and mean delay characteristics based on a lumped model in which all stations are aggregated at a single point on the ring with their relative positions preserved     

Use of microwaves for the synthesis and processing of materials

An overview of the synthesis of materials under microwave irradiation has been presented based on the work performed recently. A variety of reactions such as direct combination, carbothermal reduction, carbidation and nitridation have been described. Examples of microwave preparation of glasses are also presented. Great advantages of fast, clean and reduced reaction temperature of microwave methods are emphasized. The example of ZrO₂-CeO₂ ceramics has been used to show the extraordinarily fast and effective sintering which occurs in microwave irradiation.     

Weld microstructure refinement in a 1441 grade aluminium-lithium alloy

Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding. This revised version was published online in November 2006 with corrections to the Cover Date.