Invertible Gaussian Reparameterization: Revisiting the Gumbel-Softmax

The Gumbel-Softmax is a continuous distribution over the simplex that is often used as a relaxation of discrete distributions. Because it can be readily interpreted and easily reparameterized, it enjoys widespread use. We propose a conceptually simpler and more flexible alternative family of reparameterizable distributions where Gaussian noise is transformed into a one-hot approximation through an invertible function. This invertible function is composed of a modified softmax and can incorporate diverse transformations that serve different specific purposes. For example, the stick-breaking procedure allows us to extend the reparameterization trick to distributions with countably infinite support, or normalizing flows let us increase the flexibility of the distribution. Our construction enjoys theoretical advantages over the Gumbel-Softmax, such as closed form KL, and significantly outperforms it in a variety of experiments

A one way coupled thermo-mechanical model to determine residual stresses and deformations in butt welding of two ASTM A36 steel plates

To simulate the gas metal arc welding (GMAW) process in two ASTM A36 steel plates a finite element numerical model was developed, to obtain the corresponding residual stresses and deformations. The welding process was simulated as a one way coupled thermo-structural problem, considering that the structural field has very little influence in the thermal field, which is widely accepted in the specialized literature. To solve the thermal field, a nonlinear transient problem was created using finite second order elements that have temperature as the only degree of freedom in their nodes. The thermal properties of material were defined as a function of temperature and a combined convection-radiation coefficient was used as boundary condition. The double ellipsoidal model presented by Goldak was used to simulate the heat source and its dimensions were determined from the expressions developed by Christensen. To solve the structural field another nonlinear transient problem was created, considering the same mesh and the same time step of the thermal problem, using finite second order elements that have three displacements as degrees of freedom in their nodes. The mechanical properties of material were defined as a function of temperature, a thermo-elasto-plastic material model was used and the necessary displacement constraints were applied as boundary conditions. The temperature distribution obtained by solving the thermal field at each time step was transferred as a load to the structural problem. In both problems the “birth and death” technique was used to simulate the material deposition, which is implemented in the ANSYS software used in the present study. The activation of “dead” elements of the weld bead in the thermal analysis was performed simultaneously with the passage of the heat source, while in the structural analysis “dead” elements were activated as a function of their temperature. Different activation temperatures of “dead” elements were tested in the structural analysis, obtaining the best results when this temperature takes a value of 80% of material solidification temperature. The model used in this study was validated experimentally, taking as reference the residual displacements in several points of the welded plates. It was verified that there is a good correspondence between numerical and experimental results, with an error of less than 10%

High-dimensional quantum cryptography with twisted light

Quantum key distributions (QKD) systems often rely on polarization of light for encoding, thus limiting the amount of information that can be sent per photon and placing tight bounds on the error that such a system can tolerate. Here we describe a proof-of-principle experiment that indicates the feasibility of high-dimensional QKD based on the transverse structure of the light field, allowing for the transfer of more than 1 bit per photon. Our implementation uses the orbital angular momentum (OAM) of photons and the corresponding mutually unbiased basis of angular position (ANG). Our experiment uses a digital micro-mirror device for the rapid generation of OAM and ANG modes at 4 kHz, and a mode sorter capable of sorting single photons based on their OAM and ANG content with a separation efficiency of 93\%. Through the use of a 7-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel capacity of 2.05 bits per sifted photon. Our experiment shows that, in addition to having an increased information capacity, QKD systems based on spatial-mode encoding will be more tolerant to errors and thus more robust against eavesdropping attacks

INFORMATION AND COMMUNICATION TECHNOLOGIES IN THE NATIONAL UNIVERSITY OF EDUCATION OF ECUADOR

El presente estudio es un avance parcial de una investigación en curso que tiene por objeto principal la creación, contribución y el análisis de indicadores culturales en el contexto universitario ecuatoriano. Este trabajo se enfoca específicamente en proveer una serie de indicadores sobre el equipamiento, uso y consumo de las TIC de los estudiantes de la Universidad Nacional de Educación de Ecuador (UNAE). La metodología usada es de orden cuantitativo/descriptiva, a partir de los datos recolectados en una encuesta aplicada a una muestra compuesta de 438 estudiantes del total del universo entre las diferentes carreras y ciclos ofertados por la UNAE. La muestra tiene un nivel de confianza del 95% y un 5% de margen de error. Los resultados obtenidos muestran un alto nivel de equipamiento, uso y consumo de diferentes dispositivos tecnológicos. También, esta población universitaria usa su tiempo en actividades académicas y de ocio con su celular, televisión, videos e internet.This study is a partial advance of ongoing research whose main objective is the creation, contribution, and analysis of cultural indicators in the Ecuadorian university context. This work focuses specifically on providing a series of indicators on the equipment, use, and consumption of the TIC of students of the National University of Education of Ecuador (UNAE). The methodology used is the quantitative of descriptive-analytical order, based on the data collected in a survey applied on a population sample, made up of 438 students of the total universe between the different careers and cycles offered by the UNAE. The sample has a margin of 95% reliability and an error of 5%. The obtained results showed a high level of equipment, use, and consumption of the different technological devices. Also, this university population spends daily hours in academic and free time activities in cellphones, television, videos, and internet