Hemeroteca de la sección ‘Ciencia y tecnología’

Elements of Scheduling

Por • 20 ene, 2020 • Category: Ciencia y tecnología

In the winter of 1976, Alexander Rinnooy Kan and Jan Karel Lenstra defended their PhD theses at the University of Amsterdam. Gene Lawler was on their committees. It was a natural idea to turn the theses into a textbook on scheduling. They set out to compile a survey with Ron Graham (1979), but progress on the book was hampered by the many research opportunities offered by the field. After David Shmoys joined the team in the mid 1980’s, several chapters were drafted, and the survey was rewritten (1993). Gene passed away in 1994. Colleagues were asked to contribute chapters or to complete existing drafts. However, by the turn of the century the project was losing its momentum, and finite convergence to completion fell beyond our reach. Over the years, several chapters have been used in the classroom.

Two-section reactor model for autothermal reforming of methane to synthesis gas

Por • 11 ene, 2020 • Category: Ciencia y tecnología

A one-dimensional and stationary reactor model is presented to describe the catalytic conversion of a gaseous hydrocarbon fuel with air and steam to synthesis gas by autothermal reforming (ATR) and catalytic partial oxidation (CPO). The model defines two subsequent sections in the reactor, namely an upstream oxidation section, and a downstream reforming section.

ELSI — An Open Infrastructure for Electronic Structure Solvers

Por • 5 ene, 2020 • Category: Ciencia y tecnología

Routine applications of electronic structure theory to molecules and periodic systems need to compute the electron density from given Hamiltonian and, in case of non-orthogonal basis sets, overlap matrices. System sizes can range from few to thousands or, in some examples, millions of atoms. Different discretization schemes (basis sets) and different system geometries (finite non-periodic vs. infinite periodic boundary conditions) yield matrices with different structures. The ELectronic Structure Infrastructure (ELSI) project provides an open-source software interface to facilitate the implementation and optimal use of high-performance solver libraries covering cubic scaling eigensolvers, linear scaling density-matrix-based algorithms, and other reduced scaling methods in between. In this paper, we present recent improvements and developments inside ELSI, mainly covering (1) new solvers connected to the interface, (2) matrix layout and communication adapted for parallel calculations of periodic and/or spin-polarized systems, (3) routines for density matrix extrapolation in geometry optimization and molecular dynamics calculations, and (4) general utilities such as parallel matrix I/O and JSON output.

Interfacial Atomic Number Contrast in Thick TEM Samples

Por • 1 ene, 2020 • Category: Ciencia y tecnología

The atomic number contrast imaging technique reveals an increase in intensity at interfaces of a high and low-density material in case of relatively thick samples. Elastic scattering factors and absorption coefficients are incorporated in a probabilistic model to study atomic contrast occurring at the interface of two materials when the High-Angle Annular Dark-Field (HAADF) detector is used in the Scanning TEM (STEM) mode. Simulations of thick samples reveal that electrons traverse from a higher density material to a lower density material near the interface which increases the HAADF-STEM signal.

Tecnología misilística y sus usos duales: aproximaciones políticas entre la ciencia y las Relaciones Internacionales en el caso del V2 alemán y el Cóndor II argentino

Por • 28 dic, 2019 • Category: Ciencia y tecnología

El presente trabajo explorará los orígenes de la política de investigación y desarrollo de los misiles V2 y Cóndor II. El punto de comparación radica en que su surgimiento, investigación y desarrollo se produjo en contextos políticos autoritarios, ambos programas misilísticos fueron combatidos por potencias extranjeras, y los dos fueron intentos para canalizar la transferencia tecnológica hacia los países opositores a su desarrollo, aunque ésta se logró con éxito sólo en el caso del V2. Se estudiará la trama política para el surgimiento del primer misil balístico fabricado por la autoritaria Alemania Nazi en el contexto prebélico de la Segunda Guerra Mundial, y aquella relacionada al desarrollo del Cóndor II argentino, contextuado en la dictadura militar autodenominada Proceso de Reorganización Nacional.

Born’s rule and measurement

Por • 27 dic, 2019 • Category: Ciencia y tecnología

Arnold Neumaier Born’s rule in its conventional textbook form applies to the small class of projective measurements only. It is well-known that a generalization of Born’s rule to realistic experiments must be phrased in terms of positive operator valued measures (POVMs). This generalization accounts for things like losses, imperfect measurements, limited detection accuracy, dark detector […]

Everett’s Multiverse and the World as Wavefunction

Por • 20 dic, 2019 • Category: Ciencia y tecnología

Everett suggested that there is no such thing as wavefunction collapse. He hypothesized that for an idealized spin measurement the apparatus evolves into a superposition on the pointer basis of two apparatuses, each displaying one of the two outcomes which are standardly thought of as alternatives. And as a result the observer splits into two observers, each perceiving a different outcome.There have been problems. Why the pointer basis? Decoherence is generally accepted by Everettian theorists to be the key to the right answer there. And in what sense is probability involved when all possible outcomes occur? Everett’s response to that problem was inadequate. A first attempt to find a different route to probability was introduce by Neil Graham in 1973 and the path from there has led to two distinct models of branching.

Cold numbers: Superconducting supercomputers and presumptive anomaly

Por • 17 dic, 2019 • Category: Ciencia y tecnología

In February 2014 Time magazine announced to the world that the first quantum computer had been put in use. One key component of this computer is the Josephson-junction, a superconducting device, based on completely different scientific and technological principles with respect to semiconductors. The origin of superconductors dates back to the 1960s, to a large-scale 20-year long IBM project aimed at building ultrafast computers. We present a detailed study of the relationship between Science and Technology making use of the theoretical tools of presumptive anomaly and technological paradigms: superconductors were developed whilst the semiconductors revolution was in full swing.

Antimatter gravity and the Universe

Por • 13 dic, 2019 • Category: Ciencia y tecnología

The aim of this brief review is twofold. First, we give an overview of the unprecedented experimental efforts to measure the gravitational acceleration of antimatter; with antihydrogen in three competing experiments at CERN (AEGIS, ALPHA and GBAR, and with muonium and positronium in other laboratories in the world. Second, we present the 21st Century’s attempts to develop a new model of the Universe with the assumed gravitational repulsion between matter and antimatter; so far, three radically different and incompatible theoretical paradigms have been proposed.

El hombre más peligroso del mundo

Por • 10 dic, 2019 • Category: Ciencia y tecnología

Los ocupantes de la lancha real eran portadores de una invitación del mismo Tolomeo II, para que Arquímedes de Siracusa asistiese a la comida mensual donde daría a conocer al nuevo escolar a los filólogos y científicos del Museum. Por supuesto que dispondría de una de las más de cien habitaciones del centro de estudios, aunque una rígida ordenanza limitaba el número de alumnos internos, para que sólo una élite de investigadores mantuviese el prestigio y la excelencia de la escuela palatina. El delegado del rey tuvo buen cuidado en recordar al recién llegado que todas esas atenciones no eran gracia sino obligación, en vista de las inmejorables relaciones presentes y futuras de las cortes de Egipto y Sicilia.