Adaptive checkpointing in message passing distributed systems

Determining consistent global checkpoints is common to many distributed problems such as fault-tolerance, distributed debugging, properties detection, etc. Uncoordinated and coordinated checkpointing algorithms have been traditionally used for such determinations. This paper addresses a third technique, namely adaptive checkpointing, that has recently emerged. This technique assumes processes take local checkpoints independently and requires them to take additional local checkpoints in order that all local checkpoints be members of some consistent global checkpoint. We first study the characteristics of such adaptive algorithms. Then, a general adaptive checkpointing algorithm is designed from a condition, first stated by Netzer and Xu, that answers the following question: ‘does a given local checkpoint belong to a consistent global checkpoint’' (such a local checkpoint is not useless). The resulting algorithm has the nice property to reduce the number of additional local checkpoints taken to ensure the property ‘no local checkpoint is useless’. Futhermore, it provides each local checkpoint with a consistent global checkpoint to which it belongs. Compared to uncoordinated and coordinated checkpointing algorithms, this algorithm combines the advantages of both without inheriting their drawbacks.     

EFFECTS OF DIETARY 18:3 N-3 TRANS ISOMERS ON THE Δ6 DESATURATION OF α-LINOLENIC ACID

Trans isomers of polyunsaturated fatty acids (PUFA) are formed during heat treatment of oils. In the present work, the effect of dietary geometrical isomers of α-linolenic acid (18:3 n-3) on the Δ6 desaturation of all cis 18:3 n-3 was investigated, using rat liver microsomes. The desaturation rates were higher in microsomes from animals fed a cis n-3 deficient diet, as compared to those from the control group or those from rats fed 18:3 n-3 and its trans isomers. These data and the incorporation of long chain trans PUFA in microsomal lipids suggest that geometrical isomers of 18:3 n-3 are probably slowly desaturated and elongated into long chain trans polyunsaturated fatty acids compared to 18:3 n-3.     

Respective demands of task and function allocation on human-machine co-operation design: A psychological approach

Co-operation between human operators and autonomous machines in dynamic (not fully controlled) situations implies a need for dynamic allocation of activities between the agents, in order to adapt the human-machine system to unexpected circumstances. Dynamic allocation is a way, for example, to avoid human workload peaks. Depending on whether tasks or functions are allocated, the demands made on human-machine co-operation design are different. Task and subtask allocation assume that both the human operator and the machine (or its designer) share the same decomposition of the overall task into subtasks. Function delegation is less demanding, provided that the human operator delegates functions to the machine explicitly, and within the context of a task representation transmitted by the human. This paper discusses these principles on the basis of experimental results taken from a series of studies on human-machine cooperation in air traffic control.     

Efficient use of higher-lag autocorrelations for estimating autoregressive processes

The Yule–Walker estimator is commonly used in time-series analysis, as a simple way to estimate the coefficients of an autoregressive process. Under strong assumptions on the noise process, this estimator possesses the same asymptotic properties as the Gaussian maximum likelihood estimator. However, when the noise is a weak one, other estimators based on higher-order empirical autocorrelations can provide substantial efficiency gains. This is illustrated by means of a first-order autoregressive process with a Markov-switching white noise. We show how to optimally choose a linear combination of a set of estimators based on empirical autocorrelations. The asymptotic variance of the optimal estimator is derived. Empirical experiments based on simulations show that the new estimator performs well on the illustrative model.     

RHEOLOGY OF PURE AND MIXED KAPPA-CARRAGEENAN GELS IN LACTIC ACID FERMENTATION CONDITIONS

Texture profile analysis and rupture tests, respectively, at a deformation of 5 and 80%, were carried out on commercial kappa-carrageenan gel cylinders (3% w/v concentration) and on mixed gel cylinders (kappa-carrageenan/iotacarrageenan or locust bean gum [LBG], in different proportions), to select the best gel composition as an immobilization matrix for continuous lactic acid fermentations of dairy media. Mixed gel cylinders were soaked in a model system for lactic fermentations consisting of 36 dairy media: milk, whey and whey permeate, with 4 lactate concentrations (5, 20, 35 and 50 g/L of medium), combined with 3 pH values (6.5, 6.0, 5.5). GENUGEL X-0909 n°5180850 was the most resistant of all commercial kappa-carrageenans available; mixing this kappacarrageenan with LBG in the respective proportions of 2.75%/0.25% gave the best rheological properties to the resulting mixed gel. Our study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media). A pH drop of milk from 6.5 to 5.5 resulted in more brittle gels which may be explained by an increase in the amount of soluble calcium cations. Generally, soaking in milk produced the most brittle gels due to its calcium content, whey produced the hardest gels and whey permeate, the softest. An increase in the amomonium lactate concentmtion significantly improved hardness, rupture force and percentage of deformation at rupture, while reducing cohesion and resilience: NH₄+ cations would account for this effect. The differences in rheological behuviour of immobilization gel beads during continuous Eactic fermentations of milk and whey permeate would be due to the cation content and more specijically to the higher calcium concentmtion in milk.