121 research outputs found
New light on electromagnetic corrections to the scattering parameters obtained from experiments on pionium
We calculate the electromagnetic corrections needed to obtain isospin
invariant hadronic pion-pion s-wave scattering lengths a^0, a^2 from the
elements a_cc, a_0c of the s-wave scattering matrix for the (\pi^+ \pi^-, \pi^0
\pi^0) system at the \pi^+ \pi^- threshold. These elements can be extracted
from experiments on pionium. Our calculation uses energy independent hadronic
pion-pion potentials that satisfactorily reproduce the low-energy phase shifts
given by two-loop chiral pertur- bation theory. We also take into account an
important relativistic effect whose inclusion influences the corrections
considerably.Comment: 14 pages including 3 figures. Uses elsart.cls. Some numbers have been
updated and a few typos have been correcte
The effect of vacuum polarisation on muon-proton scattering at small energies and angles
We give a compact expression for the unpolarised differential cross section
for muon-proton scattering in the one photon exchange approximation. The effect
of adding the vacuum polarisation amplitude to the no-spin-flip amplitude for
one photon exchange is calculated at small energies and scattering angles and
is found to be negligible for present experiments.Comment: 6 pages, one figur
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Reliability modeling of a 1-out-of-2 system: Research with diverse Off-the-shelf SQL database servers
Fault tolerance via design diversity is often the only viable way of achieving sufficient dependability levels when using off-the-shelf components. We have reported previously on studies with bug reports of four open-source and commercial off-the-shelf database servers and later release of two of them. The results were very promising for designers of fault-tolerant solutions that wish to employ diverse servers: very few bugs caused failures in more than one server and none caused failure in more than two. In this paper we offer details of two approaches we have studied to construct reliability growth models for a 1-out-of-2 fault-tolerant server which utilize the bug reports. The models presented are of practical significance to system designers wishing to employ diversity with off-the-shelf components since often the bug reports are the only direct dependability evidence available to them
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Diversity for Security: a Study with Off-The-Shelf AntiVirus Engines
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Diverse protection systems for improving security: a study with AntiVirus engines
Diverse âbarriersâ or âprotection systemsâ are very common in many industries, especially in safety-critical ones where the designers must use âdefense in depthâ techniques to prevent safety failures. Similar techniques are also commonly prescribed for security systems: using multiple, diverse detection systems to prevent security breaches. However empirical evidence of the effectiveness of diversity is rare. We present results of an empirical study which uses a large-scale dataset to assess the benefits of diversity with an important category of security systems: AntiVirus products. The analysis was based on 1599 malware samples collected from a distributed honeypot deployment over a period of 178 days. The malware samples were sent to the signature engines of 32 different AntiVirus products hosted by the VirusTotal service. We also present an exploratory model which shows that the number of diverse protection layers that are needed to achieve âperfectâ detection with our dataset follows an exponential power-law distribution. If this distribution is shown to be generic with other datasets, it would be a cost-effective means for predicting the probability of perfect detection for systems that use a large number of barriers based on measurements made with systems that are composed of fewer (say 2, 3) barriers
Hadronic Effects in the Pionium Ion
The hadronic properties of the pionium ion (Coulomb bound system of three
charged pions) are estimated using the results for the positronium ion
. It turns out that the hadronic shift of the ground state energy and
the lifetime of the pionium ion are approximately the same as for pionium.Comment: RevTex, 5 page
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