Τμήμα Φυσικής (Δημοσ. Π.Π. σε περιοδικά)
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- ItemOpen AccessDrunk person identification using thermal infrared images(Inderscience Enterprises Ltd Publishers, )Drunk person identification is carried out using thermal infrared images. Two different approaches are proposed for distinguishing a drunk person by means of radiometric values on its face. The features used in the first approach are simply the pixel values of specific points on the face of the person. It is proved that the cluster of a specific person moves in the feature space as the person consumes alcohol. Fisher linear discriminant approach is used for space dimensionality reduction. The feature space is found to be of very low dimensionality. The majority of the clusters moves towards the same direction and the feature space can easily be separated into the ‘sober’ and ‘drunk’ regions. Thus the ‘drunk’ feature space is introduced. In the second approach thermal differences between various locations on the face are evaluated and their value is monitored. It was found that specific areas in the face of a drunk person present an increased thermal illumination. These areas are the best candidates for identifying a drunk person. The concept behind this second proposed approach relies on a physiology-based face identification procedure.
- ItemOpen AccessThe role of the Science and Technology Museum in the development of Patras University cultural landscape(International Committee for University Museums and Collections (UMAC), International Council of Museums (ICOM), )This paper describes a study case of the Science and Technology Museum (STM) of Patras University, Greece. It highlights its role in the development of the University's cultural landscape and in its extension. STM succeeded to influence it by offering high quality non-formal education services to society. It was socially endorsed by the university and society. The key lies in sustainability which STM achieved to easily manage change and has endorsed strong and cost effective rules for functioning. New channels for distribution of scientific culture were developed. They have changed how people consume scientific and technological culture and created strong university-community partnerships.
- ItemOpen AccessSearch for vector mediator of dark matter production in invisible decay modeA search is performed for a new sub-GeV vector boson (A0) mediated production of dark matter (χ) in the fixed-target experiment, NA64, at the CERN SPS. The A0, called dark photon, can be generated in the reaction e−Z → e−ZA0 of 100 GeV electrons dumped against an active target followed by its prompt invisible decay A0 → χ ¯χ. The experimental signature of this process would be an event with an isolated electron and large missing energy in the detector. From the analysis of the data sample collected in 2016 corresponding to 4.3 × 1010 electrons on target no evidence of such a process has been found. New stringent constraints on the A0 mixing strength with photons, 10−5 ≲ ϵ ≲ 10−2, for the A0 mass range mA0 ≲ 1 GeV are derived. For models considering scalar and fermionic thermal dark matter interacting with the visible sector through the vector portal the 90% C.L. limits 10−11 ≲ y ≲ 10−6 on the dark-matter parameter y ¼ ϵ2αDðmχ mA0 Þ4 are obtained for the dark coupling constant αD ¼ 0.5 and dark-matter masses 0.001 ≲ mχ ≲ 0.5 GeV. The lower limits αD ≳ 10−3 for pseudo-Dirac dark matter in the mass region mχ ≲ 0.05 GeV are more stringent than the corresponding bounds from beam dump experiments. The results are obtained by using exact tree level calculations of the A0 production cross sections, which turn out to be significantly smaller compared to the one obtained in theWeizsäcker-Williams approximation for the mass region mA0 ≳ 0.1 GeV.
- ItemOpen AccessR-parity violating chargino decays at the LHCSupersymmetric models with R-parity violation (RPV) have become more popular following the lack of any excess of missing energy events at the 8 TeV LHC. To identify such models, the suggested searches generally rely on the decay products of the (effectively) lightest supersymmetric particle (LSP), with signals that depend on the identity of the LSP and the relevant RPV operators. Here we look at the prospects for detecting RPV chargino decays at the LHC and find substantial patches of parameter space in the Minimal Supersymmetric Standard Model with possibly spectacular signatures, such as three charged-lepton resonances.
- ItemOpen AccessThe thermodynamics of a black hole in equilibrium implies the breakdown of Einstein equations on a macroscopic near-horizon shellWe study a black hole of mass M, enclosed within a spherical box, in equilibrium with its Hawking radiation. We show that the spacetime geometry inside the box is described by the Oppenheimer-Volkoff equations for radiation, except for a {\em thin shell} around the horizon. We use the maximum entropy principle to show that the invariant width of the shell is of order M−−√, its entropy is of order M and its temperature of order 1/M−−√ (in Planck units). Thus, the width of the shell is {\em much larger} than the Planck length. Our approach is to insist on thermodynamic consistency when classical general relativity coexists with the Hawking temperature in the description of a gravitating system. No assumptions about an underlying theory are made and no restrictions are placed on the origins of the new physics near the horizon. We only employ classical general relativity and the principles of thermodynamics. Our result is strengthened by an analysis of the trace anomaly associated to the geometry inside the box, i.e., the regime where quantum field effects become significant corresponds to the shells of maximum entropy around the horizon.