1,557 research outputs found
T-Duality in Sigma Models with Kaluza-Klein Metric as Electric-Magnetic Duality
It is shown that the T-duality in \sigma-model with Kaluza-Klein metric,
without or with a torsion term, can be interpreted as electric-magnetic duality
for some of their solitonic solutions. Actually Buscher's duality
transformation interchanges the topological and Noether charges.Comment: 12 Pages, Late
Mechanisms of Self-Organization and Finite Size Effects in a Minimal Agent Based Model
We present a detailed analysis of the self-organization phenomenon in which
the stylized facts originate from finite size effects with respect to the
number of agents considered and disappear in the limit of an infinite
population. By introducing the possibility that agents can enter or leave the
market depending on the behavior of the price, it is possible to show that the
system self-organizes in a regime with a finite number of agents which
corresponds to the stylized facts. The mechanism to enter or leave the market
is based on the idea that a too stable market is unappealing for traders while
the presence of price movements attracts agents to enter and speculate on the
market. We show that this mechanism is also compatible with the idea that
agents are scared by a noisy and risky market at shorter time scales. We also
show that the mechanism for self-organization is robust with respect to
variations of the exit/entry rules and that the attempt to trigger the system
to self-organize in a region without stylized facts leads to an unrealistic
dynamics. We study the self-organization in a specific agent based model but we
believe that the basic ideas should be of general validity.Comment: 14 pages, 7 figure
Nonclassical Light in Interferometric Measurements
It is shown that the even and odd coherent light and other nonclassical
states of light like superposition of coherent states with different phases may
replace the squeezed light in interferometric gravitational wave detector to
increase its sensitivity. (Contribution to the Second Workshop on Harmonic
Oscillator, Cocoyoc, Mexico, March 1994)Comment: 8 pages,LATEX,preprint of Naples University,
INFN-NA-IV-94/30,DSF-T-94/3
Critical Overview of Agent-Based Models for Economics
We present an overview of some representative Agent-Based Models in
Economics. We discuss why and how agent-based models represent an important
step in order to explain the dynamics and the statistical properties of
financial markets beyond the Classical Theory of Economics. We perform a
schematic analysis of several models with respect to some specific key
categories such as agents' strategies, price evolution, number of agents, etc.
In the conclusive part of this review we address some open questions and future
perspectives and highlight the conceptual importance of some usually neglected
topics, such as non-stationarity and the self-organization of financial
markets.Comment: 51 pages, 9 figures, Proceedings of the School of Physics "E. Fermi",
course CLXXVI, 2010, Varenn
Gas turbine size optimization in a hybrid system considering SOFC degradation
The coupling of a pressurized solid oxide fuel cell (SOFC) and a gas turbine has been proven to result in extremely high efficiency and reduced emissions. The presence of the gas turbine can improve system durability compared to a standalone SOFC, because the turbomachinery can supply additional power as the fuel cell degrades to meet the power request. Since performance degradation is an obstacles to SOFC systems commercialization, the optimization of the hybrid system to mitigate SOFC degradation effects is of great interest. In this work, an optimization approach was used to innovatively study the effect of gas turbine size on system durability for a 400 kW fuel cell stack. A larger turbine allowed a bigger reduction in SOFC power before replacing the stack, but increased the initial capital investment and decreased the initial turbine efficiency. Thus, the power ratio between SOFC and gas turbine significantly influenced system economic results
Meta-validation of bipartite network projections
Monopartite projections of bipartite networks are useful tools for modeling indirect interactions in complex systems. The standard approach to identify significant links is statistical validation using a suitable null network model, such as the popular configuration model (CM) that constrains node degrees and randomizes everything else. However different CM formulations exist, depending on how the constraints are imposed and for which sets of nodes. Here we systematically investigate the application of these formulations in validating the same network, showing that they lead to different results even when the same significance threshold is used. Instead a much better agreement is obtained for the same density of validated links. We thus propose a meta-validation approach that allows to identify model-specific significance thresholds for which the signal is strongest, and at the same time to obtain results independent of the way in which the null hypothesis is formulated. We illustrate this procedure using data on scientific production of world countries.The configuration model, in its various formulations, is a widely used null model for statistical validation of bipartite network projections. Here, the authors show that different formulations might bring to very different results, and propose a meta-validation approach that allows to identify model-specific significance thresholds while remaining null-model independent
Impact of structural defects on the performance of graphene plasmon-based molecular sensors
Graphene-based plasmonic devices are regarded to be suitable for a plethora
of applications, ranging from mid-infrared to terahertz frequencies. In this
regard, among the peculiarities associated with graphene, it is well known that
plasmons are tunable and tend to show stronger confinement as well as a longer
lifetime than in the noble-metal counterpart. However, due to the
two-dimensional specificity of graphene, the presence of defects might induce
stronger effects than in bulky noble metals. Here, we theoretically investigate
the impact of structural defects hosted by graphene on selected figures of
merit associated to localized plasmons, which are of key technological
importance for plasmon-based molecular sensing. By considering an optimized
graphene nanostructure, we provide a comparative analysis intended to shed
light on the impact of the type of defect on graphene localized plasmons, that
regards distinct types of defects commonly arising from fabrication procedures
or exposure to radiation. This understanding will help industry and academia in
better identifying the most suitable applications for graphene-based molecular
sensing.Comment: 8 pages, 5 figure
Stacked optical antennas for plasmon propagation in a 5 nm-confined cavity
The sub-wavelength concentration and propagation of electromagnetic energy are two complementary aspects of plasmonics that are not necessarily co-present in a single nanosystem. Here we exploit the strong nanofocusing properties of stacked optical antennas in order to highly concentrate the electromagnetic energy into a 5 nm metal-insulator-metal (MIM) cavity and convert free radiation into guided modes. The proposed nano-architecture combines the concentration properties of optical nanoantennas with the propagation capability of MIM systems, paving the way to highly miniaturized on-chip plasmonic waveguiding
Minimal Agent Based Model for Financial Markets II: Statistical Properties of the Linear and Multiplicative Dynamics
We present a detailed study of the statistical properties of an Agent Based
Model and of its generalization to the multiplicative dynamics. The aim of the
model is to consider the minimal elements for the understanding of the origin
of the Stylized Facts and their Self-Organization. The key elements are
fundamentalist agents, chartist agents, herding dynamics and price behavior.
The first two elements correspond to the competition between stability and
instability tendencies in the market. The herding behavior governs the
possibility of the agents to change strategy and it is a crucial element of
this class of models. The linear approximation permits a simple interpretation
of the model dynamics and, for many properties, it is possible to derive
analytical results. The generalized non linear dynamics results to be extremely
more sensible to the parameter space and much more difficult to analyze and
control. The main results for the nature and Self-Organization of the Stylized
Facts are, however, very similar in the two cases. The main peculiarity of the
non linear dynamics is an enhancement of the fluctuations and a more marked
evidence of the Stylized Facts. We will also discuss some modifications of the
model to introduce more realistic elements with respect to the real markets
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