708 research outputs found
Spectral boundary conditions and solitonic solutions in a classical Sellmeier dielectric
Electromagnetic field interactions in a dielectric medium represent a
longstanding field of investigation, both at the classical level and at the
quantum one. We propose a 1+1 dimensional toy-model which consists of an
half-line filling dielectric medium, with the aim to set up a simplified
situation where technicalities related to gauge invariance and, as a
consequence, physics of constrained systems are avoided, and still interesting
features appear. In particular, we simulate the electromagnetic field and the
polarization field by means of two coupled scalar fields ,
respectively, in a Hopfield-like model. We find that, in order to obtain a
physically meaningful behaviour for the model, one has to introduce spectral
boundary conditions depending on the particle spectrum one is dealing with.
This is the first interesting achievement of our analysis. The second relevant
achievement is that, by introducing a nonlinear contribution in the
polarization field , with the aim of mimicking a third order nonlinearity
in a nonlinear dielectric, we obtain solitonic solutions in the Hopfield model
framework, whose classical behaviour is analyzed too.Comment: 12 pages, 1 figur
Time-stamped claim logic
The main objective of this paper is to define a logic for reasoning about distributed time-stamped claims. Such a logic is interesting for theoretical reasons, i.e., as a logic per se, but also because it has a number of practical applications, in particular when one needs to reason about a huge amount of pieces of evidence collected from different sources, where some of the pieces of evidence may be contradictory and some sources are considered to be more trustworthy than others. We introduce the Time-Stamped Claim Logic including a sound and complete sequent calculus. In order to show how Time-Stamped Claim Logic can be used in practice, we consider a concrete cyber-attribution case study
Pushing context-awareness down to the core: moreflexibility for the PerLa language
Information technology is increasingly pervading our envi-
ronment, making real Mark Weiserâs vision of a âdisappear-
ing technologyâ. The work described in this paper focuses
on using context to enable pervasive system personaliza-
tion, allowing context-aware sensor-data tailoring. Since
sensor networks, besides data collection, are also able to pro-
duce active behaviours, the tailoring capabilities are also ex-
tended to these, thus applying context-awareness to generic
system operations. Moreover, because the number of pos-
sible context can grow rapidly with the complexity of the
application, the design phase is also supported by the possi-
bility to speed-up and modularize the definition of the data
and operations associated with each specific context, pro-
ducing a support tool that eases the job of the designers of
modern context-aware pervasive systems
Towards autonomic pervasive systems: the PerLa context language
The property of context-awareness, inherent to a Pervasive
System, requires a clear definition of context and of how the
context parameter values must be extracted from the real
world. Since often the same variables are common to the
operational system and to the context it operates into, the
usage of the same language to manage both the application
and the context can lead to substantial savings in application
development time and costs. In this paper we propose a
context-management extension to the PerLa language and
middleware that allows for declarative gathering of context
data from the environment, feeding this data to the internal
context model and, once a context is active, acting on the
relevant resources of the pervasive system, according to the
chosen contextual policy
Non-collaborative Attackers and How and Where to Defend Flawed Security Protocols (Extended Version)
Security protocols are often found to be flawed after their deployment. We
present an approach that aims at the neutralization or mitigation of the
attacks to flawed protocols: it avoids the complete dismissal of the interested
protocol and allows honest agents to continue to use it until a corrected
version is released. Our approach is based on the knowledge of the network
topology, which we model as a graph, and on the consequent possibility of
creating an interference to an ongoing attack of a Dolev-Yao attacker, by means
of non-collaboration actuated by ad-hoc benign attackers that play the role of
network guardians. Such guardians, positioned in strategical points of the
network, have the task of monitoring the messages in transit and discovering at
runtime, through particular types of inference, whether an attack is ongoing,
interrupting the run of the protocol in the positive case. We study not only
how but also where we can attempt to defend flawed security protocols: we
investigate the different network topologies that make security protocol
defense feasible and illustrate our approach by means of concrete examples.Comment: 29 page
From Display to Labelled Proofs for Tense Logics
We introduce an effective translation from proofs in the display calculus to proofs in the labelled calculus in the context of tense logics. We identify the labelled calculus proofs in the image of this translation as those built from labelled sequents whose underlying directed graph possesses certain properties. For the basic normal tense logic Kt, the image is shown to be the set of all proofs in the labelled calculus G3Kt
Automating Agential Reasoning: Proof-Calculi and Syntactic Decidability for STIT Logics
This work provides proof-search algorithms and automated counter-model extraction for a class of STIT logics. With this, we answer an open problem concerning syntactic decision procedures and cut-free calculi for STIT logics. A new class of cut-free complete labelled sequent calculi G3LdmL^m_n, for multi-agent STIT with at most n-many choices, is introduced. We refine the calculi G3LdmL^m_n through the use of propagation rules and demonstrate the admissibility of their structural rules, resulting in auxiliary calculi Ldm^m_nL. In the single-agent case, we show that the refined calculi Ldm^m_nL derive theorems within a restricted class of (forestlike) sequents, allowing us to provide proof-search algorithms that decide single-agent STIT logics. We prove that the proof-search algorithms are correct and terminate
Searching for small-scale diffuse emission around SGR 1806-20
Diffuse radio emission was detected around the soft gamma-ray repeater SGR
1806-20, after its 2004 powerful giant flare. We study the possible extended
X-ray emission at small scales around SGR 1806-20, in two observations by the
High Resolution Camera Spectrometer (HRC-S) on board of the Chandra X-ray
Observatory: in 2005, 115 days after the giant flare, and in 2013, during
quiescence. We compare the radial profiles extracted from data images and PSF
simulations, carefully considering various issues related with the uncertain
calibration of the HRC PSF at sub-arcsecond scales. We do not see statistically
significant excesses pointing to an extended emission on scales of arcseconds.
As a consequence, SGR 1806-20 is compatible with being point-like in X-rays,
months after the giant flare, as well as in quiescence.Comment: Accepted for publication in Journal of High-Energy Astrophysics. 13
pages, 4 figures, 2 table
On Deriving Nested Calculi for Intuitionistic Logics from Semantic Systems
This paper shows how to derive nested calculi from labelled calculi for propositional intuitionistic logic and first-order intuitionistic logic with constant domains, thus connecting the general results for labelled calculi with the more refined formalism of nested sequents. The extraction of nested calculi from labelled calculi obtains via considerations pertaining to the elimination of structural rules in labelled derivations. Each aspect of the extraction process is motivated and detailed, showing that each nested calculus inherits favorable proof-theoretic properties from its associated labelled calculus
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