Modified piecewise linear DEA model

Recently, Cook and Zhu have proposed the Piecewise Linear Data Envelopment Analysis (PL-DEA) model, a situation in which a generalization of the DEA methodology which incorporates piecewise linear functions of factors is considered. Standard DEA models provide an efficiency score and targets for an inefficient unit, but the PL-DEA model fails to produce acceptable targets. Thus, this issue has been considered in the piecewise linear CCR model, in which a non-increasing set of multipliers describe the weight function. Also, the piecewise linear CCR model has been enhanced by introducing two MIP models for a two-stage procedure in order to set targets precisely. Furthermore as it follows, the above-mentioned models are compared with each other and an example is provided for the sake of lucidity.     

Role of weighting in the dynamics of front propagation

Non-equilibrium front propagation in a two-dimensional network modelling wildfire propagation was studied. The model includes deterministic long-range interactions due to radiation and a time weighting procedure. Three weight-dependent propagation regimes were found: dynamical, static, and non-propagative. The dynamical regime shows saturation for small weight values and a percolation transition area depending on the weight and size of the interaction domain. From the scaling interface exponents, the model seems to belong to the dynamical percolation universality class. In the limit of static regime it belongs to the random deposition class.     

Low-dropout voltage reference: an approach to low-temperature-sensitivity architectures with high drive capability

A modified circuit topology for voltage references capable of providing very high load current with low-temperature-sensitivity output voltage is presented. Employing a proportional-to-absolute-temperature current source and a complementary-to-absolute-temperature voltage source in a novel closed-loop configuration, the output voltage can be tuned over a wide range of voltages lower or higher than the silicon bandgap voltage. These features make the configuration a promising competitor for low-dropout regulators. A possible implementation of the proposed topology in 0.18 μm technology shows that the simulated 0.9 and 1.3 V voltage references have fast and stable operation for load currents up to 100 mA. The temperature coefficient for both design cases is smaller than 37 ppm/°C.     

Viscosity and Rheological Properties of Graphene Nanopowders Nanofluids

The dynamic viscosity and rheological properties of two different non-aqueous graphene nano-plates-based nanofluids are experimentally investigated in this paper, focusing on the effects of solid volume fraction and shear rate. For each nanofluid, four solid volume fractions have been considered ranging from 0.1% to 1%. The rheological characterization of the suspensions was performed at 20 ∘C, with shear rates ranging from 10−1s−1 to 103s−1, using a cone-plate rheometer. The Carreau–Yasuda model has been successfully applied to fit most of the rheological measurements. Although it is very common to observe an increase of the viscosity with the solid volume fraction, we still found here that the addition of nanoparticles produces lubrication effects in some cases. Such a result could be very helpful in the domain of heat extraction applications. The dependence of dynamic viscosity with graphene volume fraction was analyzed using the model of Vallejo et al.     

Optimal Scheduling of a Two-stage Hybrid Flow Shop

We present an exact branch-and-bound algorithm for the two-stage hybrid flow shop problem with multiple identical machines in each stage. The objective is to schedule a set of jobs so as to minimize the makespan. This is the first exact procedure which has been specifically designed for this strongly -hard problem. Among other features, our algorithm is based on the exact solution of identical parallel machine scheduling problems with heads and tails. We report the results of extensive computational experiments on instances which show that the proposed algorithm solves large-scale instances in moderate CPU time.     

Coding of the dimension group

We study an aspect of dimension group theory, linked to coding. The dimension group that we consider is built on a given square primitive integer matrix M satisfying the conditions that |detM|?2 and that the characteristic polynomial of M is irreducible. The coding is based on iteration of what could be seen as a generalization to Zd of the Euclidean algorithm induced by the matrix M and in a natural way we define a binary operation of addition in the coding group.The set B of symbols is a subset of Zd, and if we denote by ρ the Perron-Frobenius eigenvalue of M and by v a left eigenvector associated to ρ, we define a function Zd×BN^*→R which assigns to the element (p,b₁,b₂,…) the series