Search results for "Causa"
showing 10 items of 661 documents
Spectral incoherent solitons: a localized soliton behavior in the frequency domain
2008
We show both theoretically and experimentally in an optical fiber system that a noninstantaneous nonlinear environment supports the existence of spectral incoherent solitons. Contrary to conventional solitons, spectral incoherent solitons do not exhibit a confinement in the spatiotemporal domain, but exclusively in the frequency domain. The theory reveals that the causality condition inherent to the nonlinear response function is the key property underlying the existence of spectral incoherent solitons. These solitons constitute nonequilibrium stable states of the incoherent field and are shown to be robust with respect to binary collisions.
Asymptotic Safety in Quantum Einstein Gravity: Nonperturbative Renormalizability and Fractal Spacetime Structure
2007
The asymptotic safety scenario of Quantum Einstein Gravity, the quantum field theory of the spacetime metric, is reviewed and it is argued that the theory is likely to be nonperturbatively renormalizable. It is also shown that asymptotic safety implies that spacetime is a fractal in general, with a fractal dimension of 2 on sub-Planckian length scales.
Non-locality and causal evolution in QFT
2006
Non locality appearing in QFT during the free evolution of localized field states and in the Feynman propagator function is analyzed. It is shown to be connected to the initial non local properties present at the level of quantum states and then it does not imply a violation of Einstein's causality. Then it is investigated a simple QFT system with interaction, consisting of a classical source coupled linearly to a quantum scalar field, that is exactly solved. The expression for the time evolution of the state describing the system is given. The expectation value of any arbitrary ``good'' local observable, expressed as a function of the field operator and its space and time derivatives, is o…
Nonlocal field correlations and dynamical Casimir-Polder forces between one excited- and two ground-state atoms
2006
The problem of nonlocality in the dynamical three-body Casimir-Polder interaction between an initially excited and two ground-state atoms is considered. It is shown that the nonlocal spatial correlations of the field emitted by the excited atom during the initial part of its spontaneous decay may become manifest in the three-body interaction. The observability of this new phenomenon is discussed.
Specialization and herding behavior of trading firms in a financial market
2008
Agent-based models of financial markets usually make assumptions about agent’s preferred stylized strategies. Empirical validations of these assumptions have not been performed so far on a full-market scale. Here we present a comprehensive study of the resulting strategies followed by the firms which are members of the Spanish Stock Exchange. We are able to show that they can be characterized by a resulting strategy and classified in three well- defined groups of firms. Firms of the first group have a change of inventory of the traded stock which is positively correlated with the synchronous stock return whereas firms of the second group show a negative correlation. Firms of the third group…
Newtonian and relativistic location systems
2008
The theory of location systems involves the geometric and physical description of the protocols allowing the realization of coordinate systems. In this communication, the incidence of the space-time causal structure (Newtonian or relativistic) on the construction of location systems is remarked. Specifically, we focus our attention: (i) on the construction of Newtonian emission coordinates that are contrasted with those associated with relativistic positioning systems, and (ii) on the role played by non-absolute synchronizations (like the one provided by the local Solar time) in the comprehension of Newtonian and relativistic location systems.
Ancient Theories of Reasoning
2013
In this section, the central question is whether we can find ancient discussions concerning what happens in the mind when a conclusion is drawn. Did ancient authors suppose that there is a psychological force that compels us to accept the conclusion when the premises are accepted and the inference is valid? Or, if the inference is not deductively valid but adds to the credibility of the conclusion in another way, e.g., by being inductive, what happens in the mind when such an inference is drawn? In general, psychology of reasoning was not a vital topic in antiquity. Reasoning was typically considered from a logical, not from a psychological point of view. For example, in Stoic sources the n…
The Impact of Population Ageing and Social Stratification: The Case of Latvia
2019
Population ageing and social stratification is widely assumed to have detrimental effects on the economy yet there is little empirical evidence about the magnitude of its effects. The aim of this article is to investigate the relationships between population ageing and social stratification and the state of economy of a small and post-transition economy. We are looking for these relationships and their strength of influence; at what time after shocking these variables reach their original levels. We apply standard Granger (non-) causality tests, VAR (Vector Auto-Regressive), IRF (Impulse Response Function) and the prediction error variance analysis by using quarterly data from 2000 to 2018.…
Exploring the concept of causal power in a critical realist tradition
2007
This article analyses and evaluates the uses of the concept of causal power in the critical realist tradition, which is based on Roy Bhaskar's philosophy of science. The concept of causal power that appears in the early works of Rom Harre and his associates is compared to Bhaskar's account of this concept and its uses in the critical realist social ontology. It is argued that the concept of emergence should be incorporated to any adequate notion of causal power. The concept of emergence used in Bhaskar and other critical realists' works is shown to be ambiguous. It is also pointed out that the concept of causal power should be analysed in an anti-essentialist way. Ontological and methodolog…
Generating students' information seeking questions in the scholar lab: what benefits can we expect from inquiry teaching approaches?
2013
ABSTARCT: Physics teachers use experimental devices to show students how scientific concepts, principles, and laws are applied to understand the real world. This paper studies question generation of secondary and under-graduate university students when they are confronted with experimental devices in different but usual teaching situations: reading about devices while studying still images or diagrams, watching an experimental demonstration, and handling the devices in the laboratory. The influence of the prior scientific knowledge on the questions asked is also analysed. Inquiry learning environments, involving lab projects, seemed to stimulate more inferences addressed to causality when s…