Branch-and-lift algorithm for deterministic global optimization in nonlinear optimal control

This paper presents a branch-and-lift algorithm for solving optimal control problems with smooth nonlinear dynamics and potentially nonconvex objective and constraint functionals to guaranteed global optimality. This algorithm features a direct sequential method and builds upon a generic, spatial branch-and-bound algorithm. A new operation, called lifting, is introduced, which refines the control parameterization via a Gram-Schmidt orthogonalization process, while simultaneously eliminating control subregions that are either infeasible or that provably cannot contain any global optima. Conditions are given under which the image of the control parameterization error in the state space contracts exponentially as the parameterization order is increased, thereby making the lifting operation efficient. A computational technique based on ellipsoidal calculus is also developed that satisfies these conditions. The practical applicability of branch-and-lift is illustrated in a numerical example. © 2013 Springer Science+Business Media New York

Morris-Thorne wormholes with a cosmological constant

First, the ideas introduced in the wormhole research field since the work of Morris and Thorne are briefly reviewed, namely, the issues of energy conditions, wormhole construction, stability, time machines and astrophysical signatures. Then, spherically symmetric and static traversable Morris-Thorne wormholes in the presence of a generic cosmological constant are analyzed. A matching of an interior solution to the unique exterior vacuum solution is done using directly the Einstein equations. The structure as well as several physical properties and characteristics of traversable wormholes due to the effects of the cosmological term are studied. Interesting equations appear in the process of matching. For instance, one finds that for asymptotically flat and anti-de Sitter spacetimes the surface tangential pressure of the thin-shell, at the boundary of the interior and exterior solutions, is always strictly positive, whereas for de Sitter spacetime it can take either sign as one could expect, being negative (tension) for relatively high cosmological constant and high wormhole radius, positive for relatively high mass and small wormhole radius, and zero in-between. Finally, some specific solutions with generic cosmological constant, based on the Morris-Thorne solutions, are provided.Comment: latex, 49 pages, 8 figures. Expanded version of the paper published in Physical Review

Synthesis of germanium nanodots on silicon using an anodic alumina membrane mask

10.1016/j.jcrysgro.2004.04.091Journal of Crystal Growth2683-4 SPEC. ISS.560-563JCRG

Impact of bypass diode forward voltage on maximum power of a photovoltaic system under partial shading conditions

The maximum power of a photovoltaic system can reduce significantly under partial shading conditions. Bypass diodes can be used in photovoltaic systems to bypass the shaded photovoltaic modules during partial shading. The bypass diode possesses a forward voltage that introduces a voltage drop in the photovoltaic system upon activation. Therefore, the maximum power of a photovoltaic system can reduce further during partial shading due to the forward voltage of the bypass diode. This paper presents an investigation into the effect of bypass diode forward voltage on the maximum power of a photovoltaic system under partial shading conditions. The results indicated that the forward voltage of the bypass diode did not necessarily decrease the maximum power of the photovoltaic system. This depends on whether the maximum power is delivered at a lower or higher voltage. When the maximum power is delivered at a higher voltage, it is insusceptible to the forward voltage. Conversely, when the maximum power is delivered at a lower voltage, it is susceptible to the forward voltage. In the worst-case scenario, the forward voltage of the bypass diode reduced the maximum power of the photovoltaic system by 16.48%, which was already subject to partial shading loss. © 2019 Elsevier Lt

Impact of Partial Shading on the P-V Characteristics and the Maximum Power of a Photovoltaic String

A photovoltaic system is highly susceptible to partial shading. Based on the functionality of a photovoltaic system that relies on solar irradiance to generate electrical power, it is tacitly assumed that the maximum power of a partially shaded photovoltaic system always decreases as the shading heaviness increases. However, the literature has reported that this might not be the case. The maximum power of a partially shaded photovoltaic system under a fixed configuration and partial shading pattern can be highly insusceptible to shading heaviness when a certain critical point is met. This paper presents an investigation of the impact of partial shading and the critical point that reduce the susceptibility of shading heaviness. Photovoltaic string formed by series-connected photovoltaic modules is used in this research. The investigation of the P-V characteristic curve under different numbers of shaded modules and shading heaviness suggests that the photovoltaic string becomes insusceptible to shading heaviness when the shaded modules irradiance reaches a certain critical point. The critical point can vary based on the number of the shaded modules. The formulated equation in this research contributes to determining the critical point for different photovoltaic string sizes and numbers of shaded modules in the photovoltaic string

An active cooling system for photovoltaic modules

10.1016/j.apenergy.2011.01.017Applied Energy901309-315APEN

8q24 and 17q Prostate cancer susceptibility loci in a multiethnic Asian cohort

10.1016/j.urolonc.2012.02.009Urologic Oncology: Seminars and Original Investigations3181553-1560UOSO