2,404 research outputs found
Defining an approximation to formally verify cryptographic protocols
No full textElectronic forms of communication are abundant in todays world, and much emphasis is placed on these methods of communication in every day life. In order to guarantee the secrecy and authenticity of information exchanged, it is vital to formally verify the cryptographic protocols used in these forms of communications. This verification does, however, present many challenges. The systems to verify are infinite, with an infinite number of sessions and of p articipants. As if this was not enough, there is also a reactive element to deal with: th e intruder. The intruder will attack the protocol to achieve his goal: usurping identity, stealing confidential information, etc. His behavior is unpredictable!
This thesis describes a method of verification based 011 the verification of systems by approximation. Starting from an initial configuration of the network, an overapproximation of the set of messages exchanged is automatically computed. Secrecy and authentication properties can then be checked on the approximated system. Starting from an existing semi-automatic proof method developed by Genet and Klay, an automatic solution is developed.
Starting from an existing semi-automatic proof method developed by Genet and Klay, an automatic solution is developed. This thesis defines a particular approximation function that can be generated automatically and that guarantees that the computation of the approximated system terminates.
Th e verification by approximation only tells if properties are verified. When the verification fails no conclusion can be drawn on the property. Thus, this thesis also shows how the approximation technique can easily be combined with another verification technique to combine the strengths of both approaches.
Finally, the tool developed to validate these developments and the results of cryptographic protocol verifications carried out in the course of this research are included
Journal of Public Procurement
No full textVolume 15, Number 4, Winter 2015Public Infrastructure Procurement: A Review 0f Adversarial andNon-Adversarial Contracting Methods ....................................................... 405M. Regan, P. E.D. Love and J. SmithM. V. KidalovThe Enlightenment Underpinnings of the Public Procurement Profession.................................................................................................. 439W. E. Klay Public Procurement Reforms in Greece: The Impact of ImprovedTransparency on Government Expenditures ........................................... 458I. Giotopoulos, G. Pavlou, S. Danchev, and A. Tsakanikas The Role Of Accountability In Federal Acquisition: A Search for Context .................................................................................................... 514131 hlm,; 15 x 23 c
Coherent J/psi and psi ' photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=5.02 TeV
No full textThe coherent photoproduction of J / ψ and ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J / ψ is reconstructed using the dilepton (l+l-) and proton–antiproton decay channels, while for the ψ ′ the dilepton and the l+l-π+π- decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb - 1. The results are compared with theoretical models for coherent J / ψ and ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6 × 10 - 4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J / ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ ′ to J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons
Coherent J / ψ and {\uppsi '} ψ ′ photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at s NN = 5.02 TeV
No full textAbstract The coherent photoproduction of J / ψ and {\uppsi '} ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy s NN = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J / ψ is reconstructed using the dilepton ( l + l - ) and proton–antiproton decay channels, while for the {\uppsi '} ψ ′ the dilepton and the l + l - π + π - decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μ b - 1 . The results are compared with theoretical models for coherent J / ψ and {\uppsi '} ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6 × 10 - 4 , such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J / ψ cross section including ALICE measurements at forward rapidity. The ratio of {\uppsi '} ψ ′ to J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons
S-process nucleosynthesis in advanced burning phases of massive stars
No full textWe present a detailed study of s-process nucleosynthesis in massive stars of solar-like initial composition and masses 15, 20, 25, and 30 M ⊙. We update our previous results of s-process nucleosynthesis during the core He burning of these stars and then focus on an analysis of the 5-process under the physical conditions encountered during the shell carbon burning. We show that the recent compilation of the 22Ne(α, n)25Mg rate leads to a remarkable reduction of the efficiency of the s-process during core He burning. In particular, this rate leads to the lowest overproduction factor of 80Kr found to date during core He burning in massive stars. The s-process yields resulting from shell carbon burning turn out to be very sensitive to the structural evolution of the carbon shell. This structure is influenced by the mass fraction of 12C attained at the end of core helium burning, which in turn is mainly determined by the 12C(α, λ)16O reaction. The still-present uncertainty in the rate for this reaction implies that the s-process in massive stars is also subject to this uncertainty. We identify some isotopes like 70Zn and 87Rb as the signatures of the s-process during shell carbon burning in massive stars. In determining the relative contribution of our s-only stellar yields to the solar abundances, we find it is important to take into account the neutron exposure of shell carbon burning. When we analyze our yields with a Salpeter initial mass function, we find that massive stars contribute at least 40percent to s-only nuclei with mass A ≤ 87. For s-only nuclei with mass A andgt; 90, massive stars contribute on average ∼7percent, except for 152Gd, 187Os, and 198Hg, which contribute ∼14percent, ∼13percent, and ∼11percent, respectively. © 2007. The American Astronomical Society. 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J/ψ production at midrapidity in p-Pb collisions at √sNN = 8.16 TeV
No full textThe production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 μb −1. The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the p T-differential J/ψ production cross sections. The p T-differential nuclear modification factors R pPb of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing. [Figure not available: see fulltext.
Inclusive, prompt and non-prompt J/ψ production at midrapidity in p-Pb collisions at √sNN = 5.02 TeV
No full textA measurement of inclusive, prompt, and non-prompt J/ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy sNN = 5.02 TeV is presented. The inclusive J/ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum pT = 0. The inclusive J/ψ nuclear modification factor RpPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ψ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/ψ on a statistical basis for pT larger than 1.0 GeV/c. These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity Lint = 292 ± 11 μb−1, which is six times larger than the previous publications. The total uncertainty on the pT-integrated inclusive J/ψ and non-prompt J/ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and RpPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ψ production cross section, the b b ̄ production cross section at midrapidity, d σbb ̄/dy, and the total cross section extrapolated over full phase space, σbb ̄, are derived. [Figure not available: see fulltext.
Inclusive, prompt and non-prompt J/psi production at midrapidity in p-Pb collisions at root s(NN)=5.02 TeV
No full textA measurement of inclusive, prompt, and non-prompt J/psi production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy root s(NN) = 5.02 TeV is presented. The inclusive J/psi mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum p(T) = 0. The inclusive J/psi nuclear modification factor R-pPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/psi mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/psi on a statistical basis for p(T) larger than 1.0 GeV/c. These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity L-int = 292 +/- 11 mu b(-1), which is six times larger than the previous publications. The total uncertainty on the P-T-integrated inclusive J/psi and non-prompt J/psi cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and R-pPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/psi production cross section, the b (b) over bar production cross section at midrapidity, d sigma(b (b) over bar)/dy, and the total cross section extrapolated over full phase space sigma(b (b) over bar) are derived
First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production
No full textThe first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V
Prompt and non-prompt J/ψ production at midrapidity in Pb-Pb collisions at √sNN=5.02 TeV
No full textThe transverse momentum (pT) and centrality dependence of the nuclear modification factor RAA of prompt and non-prompt J/ψ, the latter originating from the weak decays of beauty hadrons, have been measured by the ALICE collaboration in Pb–Pb collisions at sNN = 5.02 TeV. The measurements are carried out through the e+e− decay channel at midrapidity (|y| < 0.9) in the transverse momentum region 1.5 < pT < 10 GeV/c. Both prompt and non-prompt J/ψ measurements indicate a significant suppression for pT > 5 GeV/c, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping pT intervals, and cover the kinematic region down to pT = 1.5 GeV/c at midrapidity, not accessible by other LHC experiments. The suppression of prompt J/ψ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J/ψ production from recombination of c and c ̄ quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J/ψ. For non-prompt J/ψ, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark-gluon plasma is consistent with measurements within uncertainties
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