Concurrency of operations on B-trees

Summary Concurrent operations on B-trees pose the problem of insuring that each operation can be carried out without interfering with other operations being performed simultaneously by other users. This problem can become critical if these structures are being used to support access paths, like indexes, to data base systems. In this case, serializing access to one of these indexes can create an unacceptable bottleneck for the entire system. Thus, there is a need for locking protocols that can assure integrity for each access while at the same time providing a maximum possible degree of concurrency. Another feature required from these protocols is that they be deadlock free, since the cost to resolve a deadlock may be high.Recently, there has been some questioning on whether B-tree structures can support concurrent operations. In this paper, we examine the problem of concurrent access to B-trees. We present a deadlock free solution which can be tuned to specific requirements. An analysis is presented which allows the selection of parameters so as to satisfy these requirements.The solution presented here uses simple locking protocols. Thus, we conclude that B-trees can be used advantageously in a multi-user environment.     

An efficient dynamic model for batch distillation

A novel, rigorous and efficient solution technique for multicomponent batch distillation modelling equations is proposed. Model predictions using the technique are shown to be in close agreement with experimental batch distillation data for a ten sieve tray, 15 cm diameter column separating ethanol and water. The results also show improved accuracy over commercially available programs for batch distillation. The method incorporates rigorous dynamic energy blances as well as accurate representation of both tray hydraulics and non-ideal mass transfer. The technique is based on a functional approximation for liquid enthalpy and makes a difficult-to-calculate temperature derivative implicit in other terms in the equations, eliminating the need for iterative solution techniques. The numerical efficiency of the method permits its utilization in model-based optimization and control calculations. The modelling approach is applicable to both batch and continuous dynamic distillation models.     

The production of propionic acid from sugars by fermentation through lactic acid as an intermediate

As an alternative to propionic acid production from sugars by species of propionibacteria, propionic acid may be produced from sugars through lactate as an intermediate. Propionibacteria are actually able to utilize lactate as a substrate much more rapidly than glucose. In this study, Lactobacillus xylosus and Propionibacterium shermanii were utilized to convert glucose and xylose to propionate through lactate as an intermediate. Pure culture batch studies were carried out to obtain fermentation parameters for the two cultures. The pure cultures were then combined in a mixed culture series arrangement designed to prevent nutrient limitation. Finally, propionic acid production from lactate was demonstrated in a cross-linked immobilized cell reactor using lactate added to the medium and produced by L. xylosus in a continuous stirred tank reactor. Productivities of 14 g dm^?3 h^?1 at a 9 min residence time (2·1 g dm^?3 propionate) and 2 g dm^?3 h^?1 at a 9·9 h residence time (19·7 g dm^?3 propionate) were obtained without pH control.     

Variables in experimental games: Toward a field theory.

Experimental studies of gaming have dealt with task, situational, and personality variables. Most studies have focused on either dyadic matrix games (with the Prisoner's Dilemma as a prototype) or triadic competitive games (with the Board Game as a prototype). Types of variables in each category are: (1) task variables matrix variations, mode of presentation, length of run, threat, and power relationships; (2) situational variables strategy variations, instructions, feedback and communication, character of opponent, and reward; and (3) personality variables general differences between Ss, family background, psychopathology, attitudes and traits, and motives. In dyadic games, level of cooperation is significantly influenced by conditions in all 3 categories. In triadic games, similarly, all 3 classes of variables influence coalition formation, strategy, and outcomes. The following problems arise: comparison of game-situations, effects of situational constraints, demand characteristics, relevance to social interaction, relevance of variables, interactional effects, and variations in group size. Strictly rational theories emphasize task (and situational) variables, in contrast to theories which emphasize perceptual, cognitive, and motivational processes (personality and situational) variables. Neither kind of theory is sufficient, and a field theory is preferable. (4 p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative effects of prolonged social isolation and confinement: Behavioral and EEG changes.

Studied the relative effects of social isolation and confinement, of 1-wk duration, on measures of EEG activity, intellectual test performance, affect, and a variety of psychological and somatic symptoms derived from Myers postisolation questionnaire. Ss were 66 male undergraduates. No significant differences in performance were observed on any of the 11 tests of the intellectual battery or on measures of subjective stress and mood. However, a significant decrease in occipital alpha frequency was obtained in both the socially isolated and confined groups after the 1-wk period. Since there was no significant difference between these 2 groups in the magnitude of the decrease, this EEG change appears to have resulted from confinement alone. An analysis of the questionnaire data revealed significant F ratios on 16 of the 22 content areas. 10 of the 16 symptom categories were associated with confinement alone and the remainder were associated either with social isolation or a combination of social isolation and confinement. Results of this study were compared with those reported in several earlier, 1-wk experiments on perceptual deprivation. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)