5,445 research outputs found
Tests for Establishing Security Properties
Ensuring strong security properties in some cases requires participants to carry out tests during the execution of a protocol. A classical example is electronic voting: participants are required to verify the presence of their ballots on a bulletin board, and to verify the computation of the election outcome. The notion of certificate transparency is another example, in which participants in the protocol are required to perform tests to verify the integrity of a certificate log.
We present a framework for modelling systems with such `testable properties', using the applied pi calculus. We model the tests that are made by participants in order to obtain the security properties. Underlying our work is an attacker model called ``malicious but cautious'', which lies in between the Dolev-Yao model and the ``honest but curious'' model. The malicious-but-cautious model is appropriate for cloud computing providers that are potentially malicious but are assumed to be cautious about launching attacks that might cause user tests to fail
Palatini approach to 1/R gravity and its implications to the late Universe
By applying the Palatini approach to the 1/R-gravity model it is possible to
explain the present accelerated expansion of the Universe. Investigation of the
late Universe limiting case shows that: (i) due to the curvature effects the
energy-momentum tensor of the matter field is not covariantly conserved; (ii)
however, it is possible to reinterpret the curvature corrections as sources of
the gravitational field, by defining a modified energy-momentum tensor; (iii)
with the adoption of this modified energy-momentum tensor the Einstein's field
equations are recovered with two main modifications: the first one is the
weakening of the gravitational effects of matter whereas the second is the
emergence of an effective varying "cosmological constant"; (iv) there is a
transition in the evolution of the cosmic scale factor from a power-law scaling
to an asymptotically exponential scaling ; (v) the energy density of the matter field scales as ; (vi) the present age of the Universe and the
decelerated-accelerated transition redshift are smaller than the corresponding
ones in the CDM model.Comment: 5 pages and 2 figures. Accepted in PR
Analysis of the Reaction Rate Coefficients for Slow Bimolecular Chemical Reactions
Simple bimolecular reactions are analyzed
within the framework of the Boltzmann equation in the initial stage of a
chemical reaction with the system far from chemical equilibrium. The
Chapman-Enskog methodology is applied to determine the coefficients of the
expansion of the distribution functions in terms of Sonine polynomials for
peculiar molecular velocities. The results are applied to the reaction
, and the influence of the non-Maxwellian
distribution and of the activation-energy dependent reactive cross sections
upon the forward and reverse reaction rate coefficients are discussed.Comment: 11 pages, 5 figures, to appear in vol.42 of the Brazilian Journal of
Physic
Irreversible Processes in a Universe modelled as a mixture of a Chaplygin gas and radiation
The evolution of a Universe modelled as a mixture of a Chaplygin gas and
radiation is determined by taking into account irreversible processes. This
mixture could interpolate periods of a radiation dominated, a matter dominated
and a cosmological constant dominated Universe. The results of a Universe
modelled by this mixture are compared with the results of a mixture whose
constituents are radiation and quintessence. Among other results it is shown
that: (a) for both models there exists a period of a past deceleration with a
present acceleration; (b) the slope of the acceleration of the Universe
modelled as a mixture of a Chaplygin gas with radiation is more pronounced than
that modelled as a mixture of quintessence and radiation; (c) the energy
density of the Chaplygin gas tends to a constant value at earlier times than
the energy density of quintessence does; (d) the energy density of radiation
for both mixtures coincide and decay more rapidly than the energy densities of
the Chaplygin gas and of quintessence.Comment: 8 pages, 1 figure, to be published in GR
Strong Attraction between Charged Spheres due to Metastable Ionized States
We report a mechanism which can lead to long range attractions between
like-charged spherical macroions, stemming from the existence of metastable
ionized states. We show that the ground state of a single highly charged
colloid plus a few excess counterions is overcharged. For the case of two
highly charged macroions in their neutralizing divalent counterion solution we
demonstrate that, in the regime of strong Coulomb coupling, the counterion
clouds are very likely to be unevenly distributed, leading to one overcharged
and one undercharged macroion. This long-living metastable configuration in
turn leads to a long range Coulomb attraction.Comment: REVTEX-published versio
Combined antiapoptotic and antioxidant approach to acute neuroprotection for stroke in hypertensive rats
We hypothesized that targeting key points in the ischemic cascade with combined neuroglobin (Ngb) overexpression and c-jun N-terminal kinase (JNK) inhibition (SP600125) would offer greater neuroprotection than single treatment after in vitro hypoxia/reoxygenation and in a randomized, blinded in vivo experimental stroke study using a clinically relevant rat strain. Male spontaneously hypertensive stroke-prone rats underwent transient middle cerebral artery occlusion (tMCAO) and were divided into the following groups: tMCAO; tMCAO+control GFP-expressing canine adenovirus-2, CAVGFP; tMCAO+Ngb-expressing CAV-2, CAVNgb; tMCAO+SP600125; tMCAO+CAVNgb+SP600125; or sham procedure. Rats were assessed till day 14 for neurologic outcome before infarct determination. In vitro, combined lentivirus-mediated Ngb overexpression+SP600125 significantly reduced oxidative stress and apoptosis compared with single treatment(s) after hypoxia/reoxygenation in B50 cells. In vivo, infarct volume was significantly reduced by CAVNgb, SP600125, and further by CAVNgb+SP600125. The number of Ngb-positive cells in the peri-infarct cortex and striatum was significantly increased 14 days after tMCAO in animals receiving CAVNgb. Neurologic outcome, measured using a 32-point neurologic score, significantly improved with CAVNgb+SP600125 compared with single treatments at 14 days after tMCAO. Combined Ngb overexpression with JNK inhibition reduced hypoxia/reoxygenation-induced oxidative stress and apoptosis in cultured neurons and reduced infarct and improved neurologic outcome more than single therapy after in vivo experimental stroke in hypertensive rats
Emergence of active topological glass through directed chain dynamics and nonequilibrium phase segregation
Active matter states defy many notions that have been established for systems in thermodynamic equilibrium. Nevertheless, the lack of detailed balance might be utilized to design nonequilibrium materials with unique properties. Recently we have shown, employing a model of ring polymers containing segments with a larger mobility than given by equilibrium thermal fluctuations, that making polymers with intrinsic topology active can result in states that relax extremely slowly, the so-called active topological glass. In this paper, we focus on the role of nonequilibrium phase separation in the vitrification process. In particular, we detail the polymer dynamics and show that such activity-driven glassy states arise from heterogeneity of segmental dynamics that emerges on all scales. Provided that the activity quench is strong enough, the rings feature an oriented reptationlike motion, with the active segment serving as an effective chain's end, resulting into a dramatic increase of inter-ring treading that vitrifies the system. The scaling properties of the ensuing steady-state ring conformations, which are significantly elongated and usually possess a doubly folded structure, are discussed and compared to equilibrium counterparts. We further examine the connection between the glass formation and the nonequilibrium phase separation and we find that both appear to be initiated by the contrasting dynamics of ring segments. Finally, we consider the effect of nonequilibrium phase separation in other active copolymer architectures
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