Assigning proctors to exams with scatter search

In this paper we present an algorithm to assign proctors to exams. This NP-hard problem is related to the generalized assignment problem with multiple objectives. The problem consists of assigning teaching assistants to proctor final exams at a university. We formulate this problem as a multiobjective integer program (IP) with a preference function and a workload-fairness function. We then consider also a weighted objective that combines both functions. We develop a scatter search procedure and compare its outcome with solutions found by solving the IP model with CPLEX 6.5. Our test problems are real instances from a University in Spain.Multiobjective combinatorial optimization, metaheuristics, scatter search

Oxygen Transport Kinetics of Surface Modified Mixed Conductor (La0.60Sr0.40)0.95Co0.20Fe0.80O3-x as Solid Oxide Fuel Cell Cathode

The oxygen transport kinetics of the electrodes of Solid Oxide Fuel Cells (SOFC) are critical properties to achieve higher efficiencies in the cell. (La0.60Sr0.40)0.95Co0.20Fe0.80O3-x (LSCF) is a mixed ion-electron conductor material that is expected to be optimized and utilized as the cathode of the SOFC’s. The reason for LSCF to be considered as the next cathode material for SOFC is due to its high ionic and electronic conductivities, and high oxygen transport kinetics. Additionally, to the excellent properties that this material offers, it has been seen that the kinetic properties of the material can be further optimized by adding a metal oxide coating on top of the LSCF surface. In this research study, baseline LSCF pellets were fabricated using commercial powders, and their conductance was measured using the Electrical Conductivity Relaxation (ECR) technique. The surface exchange coefficient (k) and bulk diffusion coefficient (D) were determined by fitting the normalized conductance data into Fick’s second law. To further enhance the oxygen transport kinetics of the LSCF, surface modification was added on top of the baseline LSCF pellets using two methods: Atomic Layer Deposition (ALD) and ink coating. The materials that were used as surface modifiers were: CoOx, a mixture consisting CoOx and Pt, MnOx, and Pr2Ox. The oxygen transport kinetics of the surface-modified pellets were determined using the same method that was used for the baseline LSCF pellets. A comparison between the baseline and the surface-modified LSCF was presented along with the experimental errors. It was observed that surface modifiers can either enhance or reduce the oxygen transport kinetics of the perovskite oxide, depending on the type of coating that is added. All the coatings that were used in this project are metal oxides that have high electrical conductivity and ionic conductivity to transport the oxygen ions. Among the used coatings, the most remarkable one was CoOx that showed an enhancement of the surface exchange of LSCF while producing a minimal reduction of the diffusion coefficient. The addition of Pt on top of CoOx coating showed a surface exchange enhancement while maintaining the same diffusion coefficient as the perovskite oxide. Lastly, MnOx and Pr2Ox showed a reduction in the surface exchange and diffusion coefficient of the LSCF due to their lower electrical conductivities

Pulsed dynamics in silicon and diamond photonic nanostructures

The work carried out in this thesis has been motivated by the promising applicability of photonic nanostructures in optical communications, internet data centers (ICD) and biosensing, to name a few. In particular, the dispersion and nonlinear engineering that silicon photonic crystal waveguides (Si-PhCWGs) and diamond-fin waveguides allow, can be exploited in the design of important photonic components, such as frequency comb generators, Raman amplifiers or filters. Within such objectives, we present rigorous and comprehensive theoretical models where all relevant linear and nonlinear optical effects, including modal dispersion, waveguide loss, free-carrier (FC), Kerr and Raman effects are considered. In the case of the newly developed subwavelength diamond-fin waveg- uides, we complete a detailed characterization of their dispersion and nonlinear optical properties, along with an analysis of pulsed dynamics in these structures. As a relevant application, we demonstrate how these waveguides can be employed to efficiently gener- ate soliton frequency combs in the visible spectral domain. With regards to Si-PhCWGs, we firstly explore the effect of stimulated Raman scattering in the slow-light regime, and demonstrate that signal amplification without pulse distortion can be achieved. Secondly, we add photonic crystal cavities (PhCCs) alongside the Si-PhCWG, with the associated inter-cavity coupling and waveguide-cavity interactions. Therefore, we describe a novel mathematical model and its corresponding computational tool that solves the dynamics of the forwards and backwards propagating pulses, the energy in the cavities and the FCs at the waveguide and at the cavities. Finally, we show the potential practical use of the model by simulating a photonic drop-filter with back reflection nulling

A cure for unstable numerical evolutions of single black holes: adjusting the standard ADM equations

Numerical codes based on a direct implementation of the standard ADM formulation of Einstein's equations have generally failed to provide long-term stable and convergent evolutions of black hole spacetimes when excision is used to remove the singularities. We show that, for the case of a single black hole in spherical symmetry, it is possible to circumvent these problems by adding to the evolution equations terms involving the constraints, thus adjusting the standard ADM system. We investigate the effect that the choice of the lapse and shift has on the stability properties of numerical simulations and thus on the form of the added constraint term. To facilitate this task, we introduce the concept of quasi well-posedness, a version of well-posedness suitable for ADM-like systems involving second-order spatial derivatives.Comment: 20 pages, 9 figure

Caracterización de las técnicas reproductivas a nivel de vivero de especies arbóreas en el jardín botánico y vivero Santa Elena, Managua, 2014

El presente estudio fue realizado en El Jardín Botánico y Vivero Santa Elena, ubicado en el departamento de Managua en el Kilómetro 14 carretera norte Managua-Tipitapa. Surgió como producto de la coordinación entre La Facultad de Recursos Naturales y del Ambiente (FARENA) de la Universidad Nacional Agraria (UNA)y la se cretaría del centro de propagación de plantas Jardín Botánico y Vivero Santa Elena. El objetivo principal del mismo es la caracterización de las técnicas reproductivas a nivel de vivero que se utilizan para especies arbóreas. La metodología consistió en: (1) aplicación de entrevista dirigida a informantes claves preseleccionados (directora, coordinador del vivero y responsable del área forestal); (2) implementación de la técnica de observación de campo; (3)levantamiento de datos mediante formato pre definido; y (4) cotejo de la información con otras fuentes bibliográficas. Se identificó un total de 31 especies forestales distribuidas en 16 familias botánicas y 27 géneros. Entre las familias más representativas se encuentran: Caesalpiniaceae, Bignoniaceae y Mimosaceae con 4 especies cada una y menor a 3 especies resultó Meliaceae, Fabaceae, Combretaceae, Bombacaceae, Malvaceae y Boraginaceae. La técnica que más seutiliza es la sexual con un 96.77% y en menor proporción se implementa la técnica asexual con 3.23%; 51.61% de las especies son exóticas y el 48.39% son nativas; se utiliza como sustrato abono orgánico que incluye cascarilla de arroz, aserrín y tierra común; y el tratamiento pre germinativo más común se basas en la escarificación mecánica e inmersión en agua, que varía según la especie

Scatter search based met heuristic for robust optimization of the deploying of "DWDM" technology on optical networks with survivability

In this paper we discuss the application of a met heuristic approach based on the Scatter Search to deal with robust optimization of the planning problem in the deploying of the Dense Wavelength Division Multiplexing (DWDM) technology on an existing optical fiber network taking into account, in addition to the forecasted demands, the uncertainty in the survivability requirements

Prevalencia de Pseudopresbicia en trabajadores administrativos en las edades comprendidas entre 30 a 40 años de edad, de las Facultades de Ciencias Médicas y Ciencias e Ingeniería de la UNAN – Managua; en el período del 15 de Julio al 15 de Noviembre del año 2015

El presente estudio, Prevalencia de Pseudopresbicia en trabajadores administrativos en las edades comprendidas entre 30 a 40 años de edad, de las Facultades de Ciencias Médicas y Ciencias e Ingeniería de la UNAN – Managua; en el período del 15 de Julio al 15 de Noviembre del año 2015. Es de tipo Descriptivo, prospectivo y transversal, constituyéndose por una población de 160 trabajadores administrativo, y una muestra calculada mediante el método aleatorio simple, finito con un total de 114 trabajadores administrativos, de los cuales, 56 fueron participes por cumplir con los rangos de edad establecidos por el tipo de estudio. El grupo etario que resulto con mayor afectación fue entre los 34-37 años, siendo predominante en sexo Femenino, con un 54℅ en relación al sexo Masculino con un 46%. Por otra parte el estudio reveló, que hay altos porcentajes de problemas refractivos no corregidos, siendo predominante la hipermetropía simple y Astigmatismo hipermetrópico con más del 59%; las anomalías Acomodativas en un 51.8%, y las disfunciones binoculares en un 59%. Todas estas disfunciones y anomalías visuales tienden a entorpecer la visión cercana, demostrando que más del 37 % de la población a estudio tiene falsa presbicia, causada por una de estas disfunciones visuales

Differential in vitro and in vivo effect of barley cysteine and serine protease inhibitors on phytopathogenic microorganisms

Protease inhibitors from plants have been involved in defence mechanisms against pests and pathogens. Phytocystatins and trypsin/α-amylase inhibitors are two of the best characterized protease inhibitor families in plants. In barley, thirteen cystatins (HvCPI-1 to 13) and the BTI-CMe trypsin inhibitor have been previously studied. Their capacity to inhibit pest digestive proteases, and the negative in vivo effect caused by plants expressing these inhibitors on pests support the defence function of these proteins. Barley cystatins are also able to inhibit in vitro fungal growth. However, the antifungal effect of these inhibitors in vivo had not been previously tested. Moreover, their in vitro and in vivo effect on plant pathogenous bacteria is still unknown. In order to obtain new insights on this feature, in vitro assays were made against different bacterial and fungal pathogens of plants using the trypsin inhibitor BTI-CMe and the thirteen barley cystatins. Most barley cystatins and the BTI-CMe inhibitor were able to inhibit mycelial growth but no bacterial growth. Transgenic Arabidopsis plants independently expressing the BTI-CMe inhibitor and the cystatin HvCPI-6 were tested against the same bacterial and fungal pathogens. Neither the HvCPI-6 expressing transgenic plants nor the BTI-CMe ones were more resistant to plant pathogen fungi and bacteria than control Arabidopsis plants. The differences observed between the in vitro and in planta assays against phytopathogenic fungi are discusse

On the nomenclatural types of two taxa of Rhamnus (Rhamnaceae) from the Valencian flora (E of Spain)

Se designan los tipos nomenclaturales de dos taxones del género Rhamnus descritos de las comarcas valencianas. Por un lado, se lectotipifica el nombre Rh. lycioides var. pubescens Rouy −sinónimo de Rh. lycioides subsp. borgiae Rivas Mart. & J.M. Pizarro−, a partir del material original recolectado en las montañas de Játiva (Valencia). Por otro, se considera que el neótipo recientemente designado para el nombre Rh. valentina Willd. −sinónimo de Rh. pumila L.−, debería aceptarse realmente como un lectótipo.Nomenclatural types are designated for two taxa of the genus Rhamnus described from the Valencia Region (E of Spain). On the one hand, the name Rh. lycioides var. pubescens Rouy −a synonym of Rh. lycioides subsp. borgiae Rivas Mart. & J.M. Pizarro−, is lectotypified on the basis of the original material collected in the mountains near Játiva (Valencia province). On the other hand, the neotype recently selected for Rh. valentina Willd. −a synonym of Rh. pumila L.−, should be regarded a true lectotype