Block-coordinate and incremental aggregated proximal gradient methods for nonsmooth nonconvex problems

Mathematical Programming - This paper analyzes block-coordinate proximal gradient methods for minimizing the sum of a separable smooth function and a (nonseparable) nonsmooth function, both of...     

Simulated annealing and tabu search approaches to unidirectional flowpath design for Automated Guided Vehicle Systems

In this paper, we address the flowpath design issue of Automated Guided Vehicle Systems (AGVSs). In particular, we concentrate on the design of unidirectional flowpaths (i.e. vehicles are restricted to travel only in one direction along a given segment of the flowpath). We have developed intelligent heuristics — simulated annealing and tabu search algorithms for the design of unidirectional AGVSs. Different versions of simulated annealing and tabu search algorithms are implemented. Our extensive computational results indicate that both simulated annealing and tabu search yield solutions of adequate quality for all practical purposes. A tabu search implementation with the use of a frequency-based memory structure dominates all tested heuristics in terms of solution quality (i.e. percent deviation from optimality), with an impressive average performance over 45 test problems of less than 0.85% deviation from optimality.     

On the Howson property of HNN-extensions with abelian base group and amalgamated free products of abelian groups

We give necessary and sufficient conditions under which an HNN-extension with abelian base group or an amalgamated free product of abelian groups is a Howson group (that is the intersection of any two finitely generated subgroups is finitely generated). We describe HNN-extensions and amalgamated free products which are Howson groups without satisfying the Burns–Cohen statements.     

Stabilizing an uncertain production system

Consider a production system that consists ofm machines each of which can produce parts ofn types. When machinek is used, it produces a part of typei with probabilityp _ki . Requests arrive for parts, one at a time. With probability _i an arriving request is for a part of typei. The requests must be served without waiting. Thus, if a requested part is not available, it must be produced. We find necessary and sufficient conditions for the existence of a strategy (a choice of the machines to be used) which makes the inventory of parts stable and we provide such a strategy.Two variations of this model are also considered: the case of batch arrivals of requests, and that of a system where the requests can be queued.     

Conformational analysis of aliskiren, a potent renin inhibitor, using high-resolution nuclear magnetic resonance and molecular dynamics simulations

Aliskiren is a nonpeptide antihypertensive drug that potently inhibits the human enzyme renin in vitro and in vivo. Many clinical trials have shown the efficacy of aliskiren to lower blood pressure in correlation with other antihypertensive agents. In this report, the conformational behavior of aliskiren is studied in water, trifluoroethanol, and dimethylformamide solutions by means of 2D-NMR spectroscopy and molecular dynamics simulations. The stereochemical characteristics of aliskiren in different solutions, in combination with the previously published crystal structure of the renin-aliskiren complex have been investigated. The aim of this study was to explore the conformational behavior of this first successful renin inhibitor in relation to its environment. In aqueous solution, aliskiren adapts a U-shape conformation, whereas in DMF, the molecule is basically endowed with an "extended" conformation, which has more similarities to the one bound to the receptor.     

Which, if any, hydrates will crystallise? Predicting hydrate formation of two dihydroxybenzoic acids

A study of two dihydroxybenzoic acid isomers shows that computational methods can be used to predict hydrate formation, the compound:water ratio and hydrate crystal structures. The calculations also help identify a novel hydrate found in the solid form screening that validates this study.     

Numerical exploration of Kaldorian interregional macrodynamics: stability and the trade threshold for business cycles under fixed exchange rates

The stability of equilibrium and the possibility of generation of business cycles in a discrete interregional Kaldorian macrodynamic model with fixed exchange rates are explored using numerical methods. One of the aims is to illustrate the feasibility and effectiveness of the numerical approach for dynamical systems of moderately high dimensionality and several parameters. The model considered is five-dimensional with four parameters, the speeds of adjustment of the goods markets and the degrees of economic interactions between the regions through trade and capital movement. Using a grid search method for the determination of the region of stability of equilibrium in two-dimensional parameter subspaces, and coefficient criteria for the flip bifurcation - and Hopf bifurcation - curve, we determine the stability region in several parameter ranges and identify Hopf bifurcation curves when they exist. It is found that interregional cycles emerge only for sufficient interregional trade. The relevant threshold is predicted by the model at 14 - 16 % of trade transactions. By contrast, no minimum level of capital mobility exists in a global sense as a requirement for the emergence of interregional cycles; the main conclusion being, therefore, that cycles may occur for very low levels of capital mobility if trade is sufficient. Examples of bifurcation and Lyapunov exponent diagrams illustrating the occurrence of cycles or period doubling, and examples of the development of the occurring cycles, are given. Both supercritical and subcritical bifurcations are found to occur, the latter type indicating coexistence of a point and a cyclical attractor.