Hemeroteca de la sección ‘Ciencia y tecnología’

Resilience Dynamics of Urban Water Security in Archetype Cities

Por • 18 abr, 2019 • Category: Ciencia y tecnología

Cities are the drivers of socio-economic innovation, and are also forced to address the accelerating risk of failure in providing essential services such as water supply today and in the future. In this contribution, we investigate the resilience of urban water supply security, which is defined in terms of the services that citizens receive. The resilience of services is determined by the availability and robustness of critical system elements, or ‘capitals’ (water resources, infrastructure, finances, management efficacy and community adaptation). We translate quantitative information about this portfolio of capitals from seven contrasting cities on four continents into parameters of a coupled systems dynamics model. Water services in each city are disrupted by recurring stochastic shocks, and we simulate the dynamics of impact and recovery cycles.

Formalisation in Constructive Type Theory of Barendregt’s Variable Convention for Generic Structures with Binders

Por • 11 abr, 2019 • Category: Ciencia y tecnología

We introduce a universe of regular datatypes with variable binding information, for which we define generic formation and elimination (i.e. induction /recursion) operators. We then define a generic alpha-equivalence relation over the types of the universe based on name-swapping, and derive iteration and induction principles which work modulo alpha-conversion capturing Barendregt’s Variable Convention. We instantiate the resulting framework so as to obtain the Lambda Calculus and System F, for which we derive substitution operations and substitution lemmas for alpha-conversion and substitution composition.

A review on the complementarity of renewable energy sources: concept, metrics, application and future research directions

Por • 5 abr, 2019 • Category: Ciencia y tecnología

It is expected, and regionally observed, that energy demand will soon be covered by a widespread deployment of renewable energy sources. However, the weather and climate driven energy sources are characterized by a significant spatial and temporal variability. One of the commonly mentioned solutions to overcome the mismatch between demand and supply provided by renewable generation is a hybridization of two or more energy sources in a single power station (like wind-solar, solar-hydro or solar-wind-hydro). The operation of hybrid energy sources is based on the complementary nature of renewable sources.

Black Hole Entropy is Thermodynamic Entropy

Por • 23 mar, 2019 • Category: Ciencia y tecnología

The comparison of geometrical properties of black holes with classical thermodynamic variables reveals surprising parallels between the laws of black hole mechanics and the laws of thermodynamics. Since Hawking’s discovery that black holes when coupled to quantum matter fields emit radiation at a temperature proportional to their surface gravity, the idea that black holes are genuine thermodynamic objects with a well-defined thermodynamic entropy has become more and more popular. Surprisingly, arguments that justify this assumption are both sparse and rarely convincing. Most of them rely on an information-theoretic interpretation of entropy, which in itself is a highly debated topic in the philosophy of physics.

Closing in on the Cosmos: Cosmology’s Rebirth and the Rise of the Dark Matter Problem

Por • 15 mar, 2019 • Category: Ciencia y tecnología

Influenced by the renaissance of general relativity that came to pass in the 1950s, the character of cosmology fundamentally changed in the 1960s as it became a well-established empirical science. Although observations went to dominate its practice, extra-theoretical beliefs and principles reminiscent of methodological debates in the 1950s kept playing an important tacit role in cosmological considerations. Specifically, belief in cosmologies that modeled a “closed universe” based on Machian insights remained influential. The rise of the dark matter problem in the early 1970s serves to illustrate this hybrid methodological character of cosmological science.

Magnetic Shielding for Interplanetary Travel

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

A proposed design for radiation shielding in interplanetary travel is presented with primary shielding created by a superconducting split toroid magnetic field and unconfined magnetic fields created by two deployable superconducting loops. The split toroid’s shielding effectiveness is analyzed with calculations of mass, field, particle path, and synchrotron radiation provided. The creation of plasma regions is also taken into consideration. The design has a wire mass of 8.08×10^4 kg, which creates a 0.47 T shielding field, and a field less than 2.17×10^-4 T in the crew area. Calculations show the shielding field deflects concerning particles of solar wind, solar flares, and high energy high atomic number particles found in galactic cosmic radiation. This design might also be used to generate power and thrust from the radiation to create a potentially self-sufficient mobile station.

Newton’s Bucket Experiment from Kantian Perspective

Por • 9 mar, 2019 • Category: Ciencia y tecnología

Newton’s absolute pace-time view is the basis of his classical mechanics, and his description of relative motion is based on absolute space. However, the existence of this absolute space has been questioned by the academic circles. In order to defend its theoretical foundation, Newton established a famous bucket experiment to prove the existence of absolute space. But his experiment was also questioned, and the experiment is also divided into different opinions. This paper hopes to find the answer to the question from Kantian perspective.

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion and Steady States

Por • 1 mar, 2019 • Category: Ciencia y tecnología

We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We explore the problem in a way that avoids assumptions about the intent and motivation of any exo-civilization seeking to settle other planetary systems. We first consider the speed of an advancing settlement via probes of finite velocity and range to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. The results of these models demonstrate that the Milky Way can be readily ‘filled-in’ with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates.

Quantum gravity from general relativity

Por • 22 feb, 2019 • Category: Ciencia y tecnología

Although general relativity is a predictively successful theory, it treats matter as classical rather than as quantum. For this reason, it will have to be replaced by a more fundamental quantum theory of gravity. Attempts to formulate a quantum theory of gravity suggest that such a theory may have radical consequences for the nature, and indeed the fate, of spacetime. The present article articulates what this problem of spacetime is and traces it through three approaches to quantum gravity taking general relativity as their vantage point: semi-classical gravity, causal set theory, and loop quantum gravity.

Electromagnetism as Quantum Physics

Por • 16 feb, 2019 • Category: Ciencia y tecnología

One can interpret the Dirac equation either as giving the dynamics for a classical field or a quantum wave function. Here I examine whether Maxwell’s equations, which are standardly interpreted as giving the dynamics for the classical electromagnetic field, can alternatively be interpreted as giving the dynamics for the photon’s quantum wave function. I explain why this quantum interpretation would only be viable if the electromagnetic field were sufficiently weak, then motivate a particular approach to introducing a wave function for the photon (following Good, 1957). This wave function ultimately turns out to be unsatisfactory because the probabilities derived from it do not always transform properly under Lorentz transformations. The fact that such a quantum interpretation of Maxwell’s equations is unsatisfactory suggests that the electromagnetic and Dirac fields are more fundamental than the photon or electron.