Scheduling multi-stage parallel-processor services to minimize average response time

The problem of scheduling on a multi-stage parallel-processor architecture in computer centres is addressed with the objective of minimizing average completion time of a set of requests. The problem is modelled as a flexible flowshop problem for which few heuristics exist in the flowshop scheduling literature. A new three-phase heuristic is proposed in this paper. An extensive computational experiment has been conducted to compare the performance of the existing heuristics and the proposed heuristic. The results indicate that the proposed heuristic significantly outperforms the existing ones. More specifically, the overall average error of the best existing heuristic is about five times that of the proposed heuristic while the overall average CPU time of the proposed heuristic is about half of the best existing one. More importantly, as the number of requests increases, the CPU time of the proposed heuristic decreases considerably (compared to the best existing heuristic) while the ratio of the error (of the best existing to the proposed heuristic) of about five times remains almost the same.     

Sonication‐Induced Coiled Fibrous Architectures of Boc‐L‐Phe‐L‐Lys(Z)‐OMe

An ultra‐short peptide Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe (Z=carbobenzyloxy) was shown to act as a highly efficient and versatile low molecular weight gelator (LMWG) for a variety of aliphatic and aromatic solvents under sonication. Remarkably, this simple dipeptide is not only able to form coiled fibres but also demonstrates self‐healing and thermal chiroptical switching behaviour. The formation of coiled assemblies was found to be influenced by the nature of the solvent and the presence of an additive. By exploiting these properties it was possible to modulate the macroscopic and microscopic properties of the organogels of this ultra‐short peptide, allowing the formation of highly ordered single‐domain networks of helical fibres with dimeric or alternatively fibre‐bundle morphology. The organogels were characterized by using FTIR, SEM, NMR and circular dichroism (CD) spectroscopy. Interestingly, CD experiments showed that the organogels of Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe in aromatic solvents exhibit thermal chiroptical switching. This behaviour was hypothesized to stem from changes in the morphology of the gel accompanied by conformational transformation of the gelling agent. The fact that such a small peptide can demonstrate hierarchical assemblies and the possibility of controlling the self‐association is rather intriguing. The self‐healing ability, chiroptical switching and more importantly the formation of helical assemblies by Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe under sonication, make this dipeptide an interesting example of the self‐assembly ability of ultra‐short peptides.     

Small‐Peptide‐Based Organogel Kit: Towards the Development of Multicomponent Self‐Sorting Organogels

The results presented here highlight the extremely useful nature of ultra‐short peptides as building blocks in the development of smart multicomponent supramolecular devices. A facile bottom‐up strategy for the synthesis of a small library of stimuli‐responsive smart organogelators has been proposed based on the predictive self‐assembly of ultra‐short peptides. More importantly, the narcissistic self‐sorting of the gelators has been evaluated as a simple method for the efficient co‐assembly of a donor–acceptor dual‐component gel, allowing the investigation of possible future applications of similar systems in the development of a supramolecular photo‐conversion device. Interestingly, it was observed that the self‐organization of the components can lead to highly ordered systems in which discrimination between compatible and non‐compatible building blocks directs the effective organization of the chromophores and gives rise to the formation of an excited‐state complex with exciplex‐like emission. The current report may prove important in the development of organogel‐based multicomponent smart devices.     

Numerical simulation of natural gas/diesel dual-fuel engine for investigation of performance and emission

Journal of Thermal Analysis and Calorimetry - Due to global concerns about the emissions, limited hydrocarbon fuel resources and high fuel prices, a lot of researches have been done to improve the...     

No-wait flowshops with bicriteria of makespan and total completion time

We consider the m-machine no-wait flowshop scheduling problem with the objective of minimizing a weighted sum of makespan and total completion time. For the two-machine problem, we develop a dominance relation and embed it within a proposed branch-and-bound algorithm. For the m-machine problem, we propose a heuristic. Computational experiments show that the proposed heuristic outperforms the best existing multi-criteria heuristics and the best single criterion heuristics for makespan and total completion time. The efficiency of the dominance relation and branch-and-bound algorithm is also investigated and shown to be effective.     

Using a Hybrid Evolutionary Algorithm to Minimize Variance in Response Time for Multimedia Object Requests

This research addresses the scheduling problem of multimedia object requests, which is an important problem in information systems, in particular, for World Wide Web applications. The performance measure considered is the variance of response time which is crucial as end users expect fair treatment to their service requests. This problem is known to be NP-hard. The literature survey indicates that two heuristics have been proposed to solve the problem. In this paper, we present a new heuristic, a hybrid evolutionary heuristic, which is shown to perform much better than the two existing ones, e.g., the overall average errors of the existing ones are 1.012 and 2.042 while the error of the proposed hybrid evolutionary heuristic is 0.154.     

The significance of reducing setup times/setup costs

Scheduling with setup times or setup costs plays a crucial role in todays modern manufacturing and service environments where reliable products/services are to be delivered on time. Scheduling activities profoundly depend on the times/costs required to prepare the facility for performing the activities. However, the vast majority of existing scheduling literature ignores this fact. We define and emphasize the importance, applications, and benefits of explicitly considering setup times/costs in scheduling research. Moreover, a review of the latest research on scheduling problems with setup times/costs is provided.     

Batching deteriorating items with applications in computer communication and reverse logistics

We study two deterministic scheduling problems that combine batching and deterioration features. In both problems, there is a certain demand for identical good quality items to be produced in batches. In the first problem, each batch is assigned an individual machine that requires a cost and a time to be activated. All the machines are identical, work in parallel, and always produce good quality items. All the items are available at time zero and they deteriorate while waiting for production. Deterioration results in a linear increase of time and cost of production. In the second problem, there is a single machine that produces good quality as well as defective items in batches. Each batch is preceded by a setup time and requires a setup cost. Defective items have to be reworked on the same machine. They deteriorate while waiting for rework. At a time to be decided, the machine switches from production to rework defective items of the current batch. After rework, every defective item has the required good quality. In both problems, the objective is to find batch partitioning such that a linear combination of the production cost and production completion time is minimized. The two problems are observed at computer service providers and also reverse logistics. In computer service providers, machines and items correspond to communication service channels and information transfer tasks, respectively. We reduce both problems to minimizing a function of one variable representing the number of batches. In an optimal solution of either problem, there are at most two different batch sizes. Linear time algorithms are proposed for both problems.     

Empirical force fields for complex hydrated calcio-silicate layered materials

The use of empirical force fields is now a standard approach in predicting the properties of hydrated oxides which are omnipresent in both natural and engineering applications. Transferability of force fields to analogous hydrated oxides without rigorous investigations may result in misleading property predictions. Herein, we focus on two common empirical force fields, the simple point charge ClayFF potential and the core-shell potential to study tobermorite minerals, the most prominent family of Calcium-Silicate-Hydrates that are complex hydrated oxides. We benchmark the predictive capabilities of these force fields against first principles results. While the structural information seem to be in close agreement with DFT results, we find that for higher order properties such as elastic constants, the core-shell potential quantitatively improves upon the simple point charge model, and shows a larger degree of transferability to complex materials. In return, to remedy the deficiencies of the simple point charge potential for hydrated calcio-silicates, we suggest using both structural data and elasticity data for potential calibration, a new force field potential, CSH-FF. This re-parameterized version of ClayFF is then applied to simulating an atomistic model of cement (Pellenq et al., PNAS, 2009). We demonstrate that this force field improves the predictive capabilities of ClayFF, being considerably less computational intensive than the core-shell model.