A Computational Study of Global Algorithms for Linear Bilevel Programming

We analyze two global algorithms for solving the linear bilevel program (LBP) problem. The first one is a recent algorithm built on a new concept of equilibrium point and a modified version of the outer approximation method. The second one is an efficient branch-and-bound algorithm known in the literature. Based on computational results we propose some modifications in both algorithms to improve their computational performance. A significant number of experiments is carried out and a comparative study with the algorithms is presented. The modified procedures has better performance than the original versions.     

An analytical approximated solution and numerical simulations of a non-ideal system with saturation phenomenon

Nonlinear Dynamics - Nowadays, researches about non-ideal problems have been increased considerably in technical-scientific community. Nonlinear problems have been widely studied due to their...     

Invariant theory and reversible-equivariant vector fields

In this paper we present results for the systematic study of reversible-equivariant vector fields-namely, in the simultaneous presence of symmetries and reversing symmetries-by employing algebraic techniques from invariant theory for compact Lie groups. The Hilbert-Poincaré series and their associated Molien formulae are introduced, and we prove the character formulae for the computation of dimensions of spaces of homogeneous anti-invariant polynomial functions and reversible-equivariant polynomial mappings. A symbolic algorithm is obtained for the computation of generators for the module of reversible-equivariant polynomial mappings over the ring of invariant polynomials. We show that this computation can be obtained directly from a well-known situation, namely from the generators of the ring of invariants and the module of the equivariants.     

Stable sets, corner polyhedra and the Chvátal closure

We consider the edge formulation of the stable set problem. We characterize its corner polyhedron, i.e. the convex hull of the points satisfying all the constraints except the non-negativity of the basic variables. We show that the non-trivial inequalities necessary to describe this polyhedron can be derived from one row of the simplex tableau as fractional Gomory cuts. It follows that the split closure is not stronger than the Chvátal closure for the edge relaxation of the stable set problem.     

A heavy-traffic comparison of shared and segregated buffer schemes for queues with the head-of-line processor-sharing discipline

As network speeds increase and the data traffic becomes more diverse, the need arises for service disciplines that offer fair treatment to diverse applications, while efficiently using resources at high speeds. Disciplines that approximate round-robin or processor-sharing service per channel are well suited for data networks because, over a wide range of time scales, they allocate bandwidth fairly among channels without needing to distinguish between different types of applications. This study is among the few to address head-of-line processor sharing. In most previous models of processor-sharing disciplines, the system immediately serves any arriving message at a rate depending only on the number of messages in the system regardless of how these messages are distributed among the channels. This model is commonly called pure processor sharing. In our model, the server completes the work from a given channel at a rate depending on the number of other channels with work in the system. That is, the service rate depends on how messages are distributed among the channels, and only indirectly on the total number of messages in the system. In this paper, we contrast the buffer requirements of shared and non-shared buffer schemes, when both types of schemes provide head-of-the-line processor-sharing service among channels. We formulate the problem as a system of functions representing the cumulative input and cumulative lost (potential) output to parts of the queueing system and model the vector of input functions as a multi-dimensional Brownian motion. The resulting heavy-traffic approximations predict much larger benefits from sharing buffers than those predicted by pure processor sharing.     

Schottky-enabled photoemission in a rf accelerator photoinjector: possible generation of ultralow transverse thermal-emittance electron beam

We present a clear signature of the Schottky effect in a rf photoinjector using photons with energy lower than the Mg cathode work function. This signature is manifested by the shift in the rf phase angle for the onset of the detection of photoelectrons via single-photon absorption and allows for a reasonable estimate of the field enhancement factor. This is a viable method to generate an electron beam with very low thermal emittance and thus, a high brightness beam.     

On-axis calcium magneto-optical trap loaded with a focused decelerating laser

We report on a simple scheme to efficiently load an on-axis magneto-optical trap (MOT) from a decelerated atomic beam, which avoids perturbation by radiation pressure from the decelerating laser. This has been tightly focused near the MOT center, with a waist size much smaller than the atomic cloud. For comparison, and in order to test the efficiency of this non-optimum deceleration geometry we have employed a second, independent decelerating laser, with a profile mode matched to the atomic beam. Using a Calcium MOT, good performance has been achieved and for an oven temperature of 580 °C we loaded 1.2(2)×10⁷ atoms in 16(1)ms. The technique described here has been essential for the sensitive detection of cold collisions, which represent minor losses in MOTs of alkaline-earth metal elements (R.L. Cavasso-Filho, A. Scalabrin, D. Pereira, F.C. Cruz: Phys. Rev. A, 67, 021402(R) (2003)). PACS 32.80.Pj, 39.25.+k, 39.10.+j     

In Silico Insights into the Mechanism of Action of Epoxy-α-Lapachone and Epoxymethyl-Lawsone in Leishmania spp.

Epoxy-α-lapachone (Lap) and Epoxymethyl-lawsone (Law) are oxiranes derived from Lapachol and have been shown to be promising drugs for Leishmaniases treatment. Although, it is known the action spectrum of both compounds affect the Leishmania spp. multiplication, there are gaps in the molecular binding details of target enzymes related to the parasite’s physiology. Molecular docking assays simulations were performed using DockThor server to predict the preferred orientation of both compounds to form stable complexes with key enzymes of metabolic pathway, electron transport chain, and lipids metabolism of Leishmania spp. This study showed the hit rates of both compounds interacting with lanosterol C-14 demethylase (−8.4 kcal/mol to −7.4 kcal/mol), cytochrome c (−10.2 kcal/mol to −8.8 kcal/mol), and glyceraldehyde-3-phosphate dehydrogenase (−8.5 kcal/mol to −7.5 kcal/mol) according to Leishmania spp. and assessed compounds. The set of molecular evidence reinforces the potential of both compounds as multi-target drugs for interrupt the network interactions between parasite enzymes, which can lead to a better efficacy of drugs for the treatment of leishmaniases.