Tabu search for scheduling on identical parallel machines to minimize mean tardiness

This paper presents a tabu search approach for scheduling jobs on identical parallel machines with the objective of minimizing the mean tardiness. Initially, we consider a basic tabu search that uses short term memory only. Local search is performed on a neighborhood defined by two types of moves. Insert moves consist of transferring each job from one machine to another and swap moves are those obtained by exchanging each pair of jobs between two machines. Next, we analyze the incorporation of two diversification strategies with the aim of exploring unvisited regions of the solution space. The first strategy uses long term memory to store the frequency of the moves executed throughout the search and the second makes use of influential moves. Computational tests are performed on problems with up to 10 machines and 150 jobs. The heuristic performance is evaluated through a lower bound given by Lagrangean relaxation. A comparison is also made with respect to the best constructive heuristic reported in the literature.     

The cost of recovery in message logging protocols

Past research in message logging has focused on studying the relative overhead imposed by pessimistic, optimistic and causal protocols during failure-free executions. In this paper, we give the first experimental evaluation of the performance of these protocols during recovery. Our results suggest that applications face a complex tradeoff when choosing a message logging protocol for fault tolerance. On the one hand, optimistic protocols can provide fast failure-free execution and good performance during recovery, but are complex to implement and can create orphan processes. On the other hand, orphan-free protocols either risk being slow during recovery (e.g. sender-based pessimistic and causal protocols) or incur a substantial overhead during failure-free execution (e.g. receiver-based pessimistic protocols). To address this tradeoff, we propose hybrid logging protocols, which are a new class of orphan-free protocols. We show that hybrid protocols perform within 2% of causal logging during failure-free execution and within 2% of receiver-based logging during recovery     

Numerical Investigation of Plunging Density Current

When a buoyant inflow of higher density enters a reservoir, it sinks below the ambient water and forms an underflow. Downstream of the plunge point, the flow becomes progressively diluted due to the fluid entrainment. The entrainment rate is strongly dependent on the Richardson number and reaches a constant value well downstream of the plunge point. This study is concerned with the analysis of the plunging phenomenon and the determination of the entrainment. A k-ε model including buoyancy effects, both in a sloping and a diverging channel, is used to reproduce the main flow characteristics. A relation between the depth at the plunge point in a channel of constant width and in a diverging channel is established, and theoretical results for the calculation of the dense layer thickness are provided. The latter indicates that the spreading rate of the dense layer in a diverging channel is a function of both the entrainment rate and the channel width. The predictions of the plunge line location are in agreement with most semiempirical equations.     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

In situ compatibilization of a polyethylene,polypropylene, and polystyrene ternary blend through Friedel–Crafts alkylation

The Friedel–Crafts alkylation reaction has been applied to reactively compatibilize a ternary blend of high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). The reactions were carried out in an internal mixer using varying catalyst concentrations. The resulting compatibilizer was quantified after Soxhlet extraction. In addition, p-substitution due to the grafting of alkyl groups onto the PS benzene ring was identified via nuclear magnetic resonance spectroscopy. The size of the PS domain in the reactive compositions is decreased by 80%. Moreover, the phase in which PS droplets were dispersed varied, that is, in the nonreactive blends they were found in the PP phase and in the reactive blends they shifted toward the HDPE phase. The effect of the compatibilizing agent was to improve the mechanical properties of the blend. Even with the lowest catalyst content, the properties of elongation-at-break, tensile strength, toughness, and elastic modulus showed improvements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48295.     

Formation of Helium Porosity in Different Materials during Post-Radiation Annealing

The characterisitics of the development of helium porosity in bcc and fcc alloys and structural steel after irradiation with 40-keV He⁺ up to dose 5⋅10²⁰ m⁻² at 20°C and subsequent annealing at 650°C for 1 h and 5 h are studied by transmission electron microscopy. It it found that under these conditions smaller bubbles with high density are formed in bcc than in fcc materials. It is shown that for an annealing time of 5 h higher porosity is formed in all materials, except nickel, than with 1 h annealing. This is due to the inflow of thermal vacancies from the free surface. The data obtained are discussed from the standpoint of the formation of various helium-containing complexes, their thermal stability, and the diffusion mobility of the matrix atoms. __________ Translated from Atomnaya Energiya, Vol. 99, No. 2, pp. 115–120, August 2005.     

Prediction and comparison of textural properties of magnetic copolymer supports for enzyme immobilization

Magnetic polymers supports have proven to be valuable materials for enzyme immobilization, as they allow recovering the catalyst by magnetic separation, precluding the need for costly and time-consuming separation steps. In this study, magnetic copolymer supports were synthesized using styrene (STY) and different crosslinking agents (divinylbenzene, ethylene glycol dimethacrylate, or triethylene glycol dimethacrylate) and initiators (azobisisobutyronitrile or benzoyl peroxide) and used to immobilize Candida antarctica lipase B (CALB). The aim was to obtain biocatalysts with high enzymatic activity and satisfactory morphological properties for use in biotransformation reactions. Two morphological properties known to influence the immobilization yield were taken into consideration, specific surface area, and swelling index. Experimental data were compared to the predictions of a model based on molar balance, method of moments, numerical fractionation, and elementary gel structures. The high correlation (R² = 0.9974) between experimental and predicted values demonstrated the suitability of the model for estimating the textural properties of enzyme supports. CALB was successfully immobilized, showing high hydrolytic activity (500–700 U g⁻¹) and good thermal stability at 50°C. CALB/STY-EGDMA-M was 14 times more stable than free CALB. The results confirm the efficiency of the immobilization method and the suitability of the copolymers for enzyme immobilization.     

Reinforcement learning for electricity dispatch in grids with high intermittent generation and energy storage systems: A case study for the Brazilian grid

Intermittent energy sources such as wind and solar have recently been growing a lot faster than dispatchable energy sources in Brazil, which made investments in energy storage systems become an attractive possibility in the country. Current operational policies for energy dispatch do not consider storage systems and need adjustments to fit this technology. With this motivation, we use reinforcement learning techniques to develop policies for managing storage systems in a grid that can handle time-varying inputs and loads, with rolling forecasts. We use a deterministic lookahead (DLA) policy which has been parametrically modified to perform well in the presence of uncertain forecasts. For realistic simulations, the base model considers important characteristics in a grid that influence the interaction between scheduling and real-time operation such as power and ramping capacities, notification times, and stochastic forecasts. The parametric modification with tunable parameters allows an optimal balance between two conflicting services provided by the storage system: time-shifting and spinning reserves. Optimal reserves ranged from 35% to 100%, depending on the tested dataset, which shows the importance of tuning. Differently from stochastic lookahead policies, which are computationally expensive, parameterized DLA policies can be applied to real-time operation after being optimized in a stochastic base model.