Exact analysis of a two-workstation one-buffer flow line with parallel unreliable machines

This paper examines a model of a serial flow line with two workstations and an intermediate buffer. Each workstation consists of multiple unreliable parallel machines which are not necessarily identical, viz., the processing times, failure times and repair times of the parallel machines at each workstation are assumed to be exponentially distributed with non-identical mean rates. The system under consideration is solved via exact Markovian analysis. More specifically, a recursive algorithm that generates the transition matrix for any value of the intermediate buffer capacity is developed and all possible transition equations are derived and solved analytically. Once the transition equations are solved the performance measures of the model under consideration can be easily evaluated. This model may be used as a decomposition block for solving larger flow lines with parallel unreliable machines at each workstation.     

Self-organization and pattern formation of janus particles in two dimensions by computer simulations

The phase behavior and associated pattern formation of two-dimensional systems of hard disks decorated with amphiphilic coronae (Janus disks) are studied by means of Monte Carlo computer simulations. A primitive interaction potential that captures the essential interparticle interactions is introduced. Despite its simplicity, the system exhibits a very rich phase polymorphism. Apart from the isotropic phase and depending upon the coronal thickness, the simulated systems self-organize in a number of two-dimensional mesophases of various symmetries exhibiting a variety of novel patterns. The results of these simulations suggest that 2D Janus particles are promising candidates for bottom-up design of precise two-dimensional templates.     

A polarization-/angle-insensitive, bandwidth-optimized, metamaterial absorber in the microwave regime

An enhanced metamaterial absorber based on the circumscribed-cross resonator is introduced in this paper. The new structure is polarization-independent, due to the symmetry of its unit cell, and is proven efficient for the attenuation of obliquely incident waves. The absorption mechanism is thoroughly investigated and is found to be mainly related to the losses of the dielectric substrate. Furthermore, by exploiting the scalability property of metamaterials, the operational bandwidth of our design can be drastically improved by placing unit cells with properly scaled resonators adjacent to each other. In this context, various combinations of three, four, and nine unit cells that can increase the full width at half maximum up to as much as 11.18?%, are developed. The overall performance of the proposed configurations is deemed promising for the realization of microwave metamaterial absorbers for several practical applications.     

Large Eddy Simulation of Separated Flow over a Two-dimensional Hump with and without Control by Means of a Synthetic Slot-jet

Large Eddy Simulations for two flows separating from a two-dimensional hump in a duct are reported and discussed. The flows differ through the presence or absence of a synthetic slot-jet injected in a sinusoidal manner, i.e. at zero net mass-flow rate, close to the location of separation and intended to reduce (“control”) the extent of the separated region. Results reported include instantaneous visualisations, pre-multiplied spectra, wall-pressure distributions, streamfunction fields and profiles of velocity and second moments. For both flows, agreement between the simulations and the experimental results is generally good, especially in respect of the overall control effectiveness of the synthetic jet, despite the use of an approximate wall treatment bridging the viscous sublayer. Proper Orthogonal Decomposition of the velocity field is used to study structural features, and this shows that the most energetic mode in the base flow is representative of large streamwise vortices in the separated region, while in the controlled flow, most of the energetically dominant modes are associated with large spanwise vortices.     

Enhancing Magnetic Communication between Metal Centres: The Role of s-Tetrazine Based Radicals as Ligands

Although 1,2,4,5-tetrazines or s-tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron-poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s-tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s-tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.     

Tensor Calculus in the Free Lie Algebra

In this Letter we characterize Lie elements and the elements of the kernel of the Lie bracketing from right to left mapping, using tensor calculus tools.     

A Homotopy in the Usual Cochain Complex of Free Lie Algebras

In this Letter, we construct a natural contracting homotopy in the usual cochain complex of free Lie algebras. As a consequence, we prove that the triple cohomology of Lie algebras coincides with a slightly different form of the standard cohomology theory.     

Mild olefin formation via bio-inspired vitamin B12 photocatalysis

Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B₁₂-dependent photoreceptor CarH, where photolysis of a cobalt–carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B₁₂-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B₁₂ to be a powerful platform for developing mild olefin-forming reactions.

Terminal or subterminal olefins can be selectively formed from alkyl electrophiles via bio-inspired vitamin B₁₂ photocatalysis.     

On complementary decompositions of the complete graph

We consider decompositionsK _n H, whereH is eitherP ₃ (the path with 3 edges) or the complete bipartite graphK _{1, 3}, with the property that upon taking the complement of each graph in the decomposition one obtains a new decompositionK _n H ^c .Research supported in part by an NSERC postgraduate Scholarship.     

Assessment of block and random copolymer overlayers on polymer optical fibers toward protein detection through electrostatic interaction

A simple fiber optic based scheme for the selective detection of proteins, based on surface electrostatic interactions, is presented. The implementation of this method is conducted using a modified polymer optical fiber's surface and thin overlayers of properly designed sensitive copolymer materials with predesigned molecular characteristics. Block poly(styrene‐b‐2vinylpyridine) (PS‐b‐P2VP) and random PS‐r‐P2VP copolymers of the same monomers and similar molecular weights, were modified and used as sensing materials. This configuration proved to be efficient concerning the fast detection of charged proteins, and also the efficient discrimination of differently charged proteins such as lysozyme and bovine serum albumin. Results on the sensing performance of block and random copolymers are also discussed drawing conclusion on their efficiency given their considerable different fabrication cost. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 327–334