Priority Random Linear Codes in Distributed Storage Systems

Node churn and failures exist as fundamental characteristics in both peer-to-peer (P2P) and sensor networks. Peers in P2P networks are highly dynamic, whereas sensors are not dependable. As such, maintaining the persistence of periodically measured data in a scalable fashion has become a critical challenge in such systems, without the use of centralized servers. To better cope with node dynamics and failures, we propose priority random linear codes (RLCs), as well as their affiliated predistribution protocols, to maintain measurement data in different priorities, such that critical data have a higher opportunity to survive node failures than data of less importance. A salient feature of priority RLCs is the ability to partially recover more important subsets of the original data with higher priorities, when it is not feasible to recover all of them due to node dynamics. We present extensive analytical and experimental results to show the effectiveness of priority RLCs.     

石化企业蒸汽动力系统优化设计建模及应用

在石化企业蒸汽动力系统(SPS)热力学分析与数学规划集成优化策略的指导下,建立了多周期设计与运行协同优化的混合整数线性规划模型(MILP)。通过热力学效率、电热供应比2个指标筛选组合子系统,采用设计负荷离散化的方法确定SPS初始超结构,大大降低了优化设计问题模型的规模和复杂度。案例分析部分采用提出的优化设计方法和建模求解策略,得到了最优设计和运行方案,同传统设计方法相比,模型求解时间大大降低,方案可操作性大大提高,证实了文中提出的优化设计策略、筛选规则和优化设计模型的可行性和有效性。     

石化企业蒸汽动力系统柔性设计

蒸汽动力系统的设计工作是一项复杂的、系统的工程,除了力求实现全周期内总费用最小的经济性目标外,还要保证实际运行过程中的各种工况下的操作柔性。针对石化企业蒸汽动力系统变工况的特点,提出了蒸汽动力系统柔性优化设计策略;将确定性变化需求转化成多周期问题,将不确定性变化需求转化成虚拟的多工况问题,并对连续不确定性和离散不确定性变化分别处理;以经济性和可操作性的最优综合为目标,建立蒸汽动力系统柔性优化设计的大型混合整数线性（MILP）模型,并采用广义Benders分解算法进行求解。采用本文提出的柔性优化设计模型和求解方法,对某炼油厂蒸汽动力系统进行了柔性优化设计,并与传统设计方案和经济性最优的设计方案进行对比。与经济性最优的方案对比结果表明,该优化设计方案总费用增加不多,但实现了在各种变化工况下的安全、稳定、柔性操作;而与传统设计方案对比结果表明,不但提高了各种工况下的操作柔性,而且节省了大量的投资和运行费用,即柔性设计方案具备可操作性和经济性的综合最优性。从而证明了本文提出的柔性设计建模和求解方法的合理性和实用性。     

水润滑轴承螺旋密封性能的仿真分析

针对水润滑立式高速液压主轴存在的端部泄漏问题,提出了以螺旋密封为主要密封方式的密封方案.并采用有限体积法,对不同工况下螺旋密封内部流场进行了非定常紊流数值模拟.研究了螺旋密封结构几何参数及转速和间隙与密封效果之间的关系.结果表明在紊流状态下,随着转速的增大,螺旋密封有效浸油长度减小,但伴随着会出现明显的气吞现象.同时,偏心率对密封效果影响也较大.     

An investigation of cutting forces in machining with worn ball-end mill

Reliable tool wear monitoring technique is one of the important aspects for achieving an integrated and self-adjusting manufacturing system. In this study, an analytical model is proposed to estimate the cutting forces, the tool geometry, and the chip geometry in relation to the flank wear, when milling with a ball-end mill. Modeling is based on thermomechanical modelling of oblique cutting. The worn tool geometry is decomposed into a series of axial elementary cutting edges. At any active tooth element, the flank wear geometry is calculated and the chip formation is obtained from an oblique cutting process characterised by local undeformed chip section and local cutting angles. Coated carbide ball-end tool, and a titanium workpiece material have been considered in this paper. The results found by using developed models have shown good agreement with experimental results.     

Convective flow and heat transfer in a tall porous cavity side-cooled with temperature profile

Natural convection in an air-filled (Prandtl number = 0.7) porous cavity with profiled side cooling and constant bottom heating is investigated over the Rayleigh number range of 1×10⁴ to 1×10⁸ at two Darcy numbers: 1×10^-4 and 1×10^-6. The aspect ratio based on cavity height was varied from 0.5 to 0.1 to investigate penetration length according to linear or sinusoidal temperature profile. The general non-Darcy model adopted in this work was validated against experimental and theoretical results in the literature and Nusselt number was predicted within less than 3% in the worst case. The effect of left wall imposed temperature profile was investigated in detail. Different convective regimes were observed depending on the imposed profile. An active region was found to take place with the linear temperature profile and with extent proportional to Rayleigh number as predicted by scale analysis.     

Heat and mass transfer studies on metal-hydrogen reactor filled with MmNi4.6Fe0.4

A transient, three-dimensional computational investigation of coupled heat and mass transfer in an annular cylindrical hydrogen storage tank, equipped with fins and filled with MmNi_4.6Fe_0.4, is presented. The effects of different parameters such as length, thickness and thermal conductivity of fins and overall heat transfer coefficient on the hydrogen storage performance of the tank are studied. The predicted hydrogen storage capacity at different supply pressures showed good agreement with the experimental data reported in the literature. In addition, it is observed that the use of fins enhances heat transfer within the hydride bed and consequently 40% improvement of the time required for 90% storage can be achieved over the case without fins.     

Development of a molecular method for the rapid discrimination of red seaweeds used for agar production

In Tunisia, agar is produced from the species Gracilaria verrucosa. Other species, such as Gracilariopsis sp. which have a very similar morphology to Gracilaria, can be harvested in a mixture with Gracilaria with the result that the quantity and quality of agar extracted is different than initially expected. In this study, we tested the use of ITS sequences from 5.8s rDNA for species discrimination between G. verrucosa and Gracilariopsis harvested from two production sites (Bizerte and Tunis Lagoons). The amplification of genomic ITS sequences and sequencing shows that the samples collected from Tunis can be identified by PCR fragment of 1124 bp whereas the samples from Bizerte are characterized by the presence of two fragments of 1124 and 983 bp, respectively. A BLAST investigation in Genbank shows that the sequence similarities between the fragment of 1124 pb and G. verrucosa was 85% and between the fragment of 983 pb and Gracilariopsis sp. Plymoutn was 94%. Gracilariopsis sp. possesses a PCR fragment with a length of 983 bp, which discriminates it from G. verrucosa when these two species are collected in a mixture as in the lagoon of Bizerte. The RFLP method after EcoRI application provides a characteristic pattern for G. verrucosa, which is composed of two main fragments with respective sizes of 823 and 301 bp whereas amplified DNA of Gracilariopsis was uncut under these conditions.     

The composition of fatty acids in the tissues of Tunisian swordfish (Xiphias gladius)

The objective of this study was to compare the composition of fatty acids stored in the various parts of swordfish. Muscle and organ sections of a series of swordfish samples were collected. Their chemical analysis allowed the classification of swordfish as a semi-fatty fish, with its byproducts totalling 35.6% of the total fatty acids (TFA) and its white and red muscles (MR) 7.2%. The highest contents were found in the liver (26%), the gonads (4.7%) and the red muscle (RM) (4.5%). The UFA/SFA ratio as recommended by nutritionists is 3; in the liver, skin and RM samples this ratio was, respectively, 3.5, 2.8 and 2.7. There is a high level of unsaturated fatty acids (UFA) in swordfish. More than 40% of the muscular tissues are made up of polyunsaturated fatty acids (PUFA) of the n-3 series (EPA + DHA). The byproducts contain more than 30% of monounsaturated acids characterised by the fatty acids of the n-9 series and particularly by oleic acid.