Modelling of heat transfers and prediction of crystallization during cooling of chicken fat

Heat transfers that occurred during chicken fat dry fractionation process were characterized. The heat flux model developed led to follow the heat flux associated with crystallization (?r) during the cooling step. A crystallization kinetics was performed by measuring the solid content of the suspension of crystals at regular intervals by low-resolution pulsed nuclear magnetic resonnance. The variation of the total heat of crystallization calculated from the thermal model developed in this study was in good agreement with the crystallization kinetics. The results reported suggested that monitoring ?r during cooling could be useful for the prediction and control of crystallization kinetics and therefore the yield of fat dry fractionation process. (Résumé d'auteur

Impact of deep-fat-frying on some plantain micronutrients

Plantains and bananas are one of the major staple foods of sub-Saharan Africa and Latin-America. These fruit are source of dietary minerals and vitamins. Deep-fat frying unit operation is widely used for the transformation of plantain in Latin-America and in Africa. The aim of this research was to evaluate the influence of deep-fat frying on the micronutrients of plantain (Musa AAB "barraganete"). Influence of the raw material (two batches) was analyzed. Cylinders (diameter 30 mm, thickness 10 mm) of plantain were fried at four thermal treatments (120-180° C and from 24 to 4 min). Molecules of nutritional interest with water soluble properties (potassium, L-ascorbic acid) or lipid soluble properties (alpha-carotene, beta-carotene) were quantified during the course of frying. One plantain batch was initially rich in L-ascorbic acid (24.4 ± 0.9 mg/100mg) and poor in total carotenoid (0.6 ± 0.3 mg/100mg), while the other was poor in L-ascorbic acid (7.5 ± 0.3 mg/100mg) and rich in total carotenoid (2.1 ± 0,7 mg/100mg). On line measurements of the water content and internal temperature profile allow to characterize the behaviour of bath products during deep-fat frying. The thermal study used the cook value as indicators of the effect of thermal history on quality. Potassium was determinate by ICP; L-ascorbic acid and carotenoid determinations were performed by HPLC. Deep-fat frying had no significant effect on potassium contents at any frying- conditions. Exclusively with the plantain initially rich in L-ascorbic acid, a-carotene and ,alpha-carotene, significant losses were observed. The average loss on L-ascorbic acid. alpha-carotene and beta-carotene were close to 75%, 44% and 35%, respectively. Cook values were very different at any frying conditions, while the lasses of micronutrient were not significantly different at the four frying treatments. Cook value parameters does not seem relevant. These couldn't be explained just with a first order kinetic thermal degradation behaviour. Perhaps, the heterogeneous distribution of micronutrient across the plantain (in radial direction) and/or cellular scale could explain of such behaviours. However it's difficult to develop more extensive assumptions without histological information of the micronutrient localization in plantain. (Texte intégral

A Scheduler-Level Incentive Mechanism for Energy Efficiency in HPC

International audienceEnergy consumption has become one of the most important factors in High Performance Computing platforms. However, while there are various algorithmic and programming techniques to save energy, a user has currently no incentive to employ them, as they might result in worse performance. We propose to manage the energy budget of a supercomputer through EnergyFairShare (EFS), a FairShare-like scheduling algorithm. FairShare is a classic scheduling rule that prioritizes jobs belonging to users who were assigned small amount of CPU-second in the past. Similarly, EFS keeps track of users 'consumption of Watt-seconds and prioritizes those whom jobs consumed less energy. Therefore, EFS incentives users to optimize their code for energy efficiency. Having higher priority, jobs have smaller queuing times and, thus, smaller turn-around time. To validate this principle, we implemented EFS in a scheduling simulator and processed workloads from various HPC centers. The results show that, by reducing it energy consumption, auser will reduce it stretch (slowdown), compared to increasing it energy consumption. To validate the general feasibility odour approach, we also implemented EFS as an extension forSLURM, a popular HPC resource and job management system.We validated our plugin both by emulating a large scale platform, and by experiments upon a real cluster with monitored energy consumption. We observed smaller waiting times for energy efficient users

From Preemptive to Non-preemptive Scheduling Using Rejections

International audienceWe study the classical problem of scheduling a set of independent jobs with release dates on a single machine. There exists a huge literature on the preemptive version of the problem, where the jobs can be interrupted at any moment. However, we focus here on the non-preemptive case, which is harder, but more relevant in practice. For instance, the jobs submitted to actual high performance platforms cannot be interrupted or migrated once they start their execution (due to prohibitive management overhead). We target on the minimization of the total stretch objective, defined as the ratio of the total time a job stays in the system (waiting time plus execution time), normalized by its processing time. Stretch captures the quality of service of a job and the minimum total stretch reflects the fairness between the jobs. So far, there have been only few studies about this problem, especially for the non-preemptive case. Our approach is based to the usage of the classical and efficient for the preemptive case shortest remaining processing time (SRPT) policy as a lower bound. We investigate the (offline) transformation of the SRPT schedule to a non-preemptive schedule subject to a recently introduced resource augmentation model, namely the rejection model according to which we are allowed to reject a small fraction of jobs. Specifically, we propose a 2 ǫ-approximation algorithm for the total stretch minimization problem if we allow to reject an ǫ-fraction of the jobs, for any ǫ > 0. This result shows that the rejection model is more powerful than the other resource augmentations models studied in the literature, like speed augmentation or machine augmentation, for which non-polynomial or non-scalable results are known. As a byproduct, we present a O(1)-approximation algorithm for the total flow-time minimization problem which also rejects at most an \epsilon-fraction of jobs

Scheduling Independent Tasks on Multi-cores with GPU Accelerators

Best PaperInternational audienceMore and more computers use hybrid architectures combin-ing multi-core processors and hardware accelerators like GPUs (Graphics Processing Units). We present in this paper a new method for scheduling efficiently parallel applications with $m$ CPUs and $k$ GPUs, where each task of the application can be processed either on a core (CPU) or on a GPU. The objective is to minimize the makespan. The corresponding scheduling problem is NP-hard, we propose an efficient approximation algorithm which achieves an approximation ratio of $\frac{4}{3} + \frac{1}{3k}$ . We first detail and analyze the method, based on a dual approximation scheme, that uses a dynamic programming scheme to balance evenly the load between the heterogeneous resources. Finally, we run some simulations based on realistic benchmarks and compare the solution obtained by a relaxed version of this method to the one provided by a classical greedy algorithm and to lower bounds on the value of the optimal makespan