Network Selection and Resource Allocation Games for Wireless Access Networks

Wireless access networks are often characterized by the interaction of different end users, communication technologies, and network operators. This paper analyzes the dynamics among these "actors" by focusing on the processes of wireless network selection, where end users may choose among multiple available access networks to get connectivity, and resource allocation, where network operators may set their radio resources to provide connectivity. The interaction among end users is modeled as a non-cooperative congestion game where players (end users) selfishly select the access network that minimizes their perceived selection cost. A method based on mathematical programming is proposed to find Nash equilibria and characterize their optimality under three cost functions, which are representative of different technological scenarios. System level simulations are then used to evaluate the actual throughput and fairness of the equilibrium points. The interaction among end users and network operators is then assessed through a two-stage multi-leader/multi-follower game, where network operators (leaders) play in the first stage by properly setting the radio resources to maximize their users, and end users (followers) play in the second stage the aforementioned network selection game. The existence of exact and approximated subgame perfect Nash equilibria of the two-stage game is thoroughly assessed and numerical results are provided on the "quality" of such equilibria

Critical Field of MGB2 : Crossover from Clean to Dirty Regimes

We have studied the upper critical field, Bc2, in poly-crystalline MgB2 samples in which disorder was varied in a controlled way to carry selectively p and s bands from clean to dirty limit. We have found that the clean regime survives when p bands are dirty and s bands are midway between clean and dirty. In this framework we can explain the anomalous behaviour of Al doped samples, in which Bc2 decreases as doping increases.Comment: 11 pages, 2 figure

Quantum memory for images - a quantum hologram

Matter-light quantum interface and quantum memory for light are important ingredients of quantum information protocols, such as quantum networks, distributed quantum computation, etc. In this Letter we present a spatially multimode scheme for quantum memory for light, which we call a quantum hologram. Our approach uses a multi-atom ensemble which has been shown to be efficient for a single spatial mode quantum memory. Due to the multi-atom nature of the ensemble it is capable of storing many spatial modes, a feature critical for the present proposal. A quantum hologram has a higher storage capacity compared to a classical hologram, and is capable of storing quantum features of an image, such as multimode superposition and entangled quantum states, something that a standard hologram is unable to achieve. Due to optical parallelism, the information capacity of the quantum hologram will obviously exceed that of a single-mode scheme.Comment: 5 pages, 3 figure

Quantum teleportation of optical images with frequency conversion

We describe a new version of continuous variables quantum holographic teleportation of optical images. Unlike the previously proposed scheme, it is based on the continuous variables quantum entanglement between the light fields of different frequencies and allows for the wavelength conversion between the original and the teleported images. The frequency tunable holographic teleportation protocol can be used as a part of light-matter interface in parallel quantum information processing and parallel quantum memoryComment: 4 pages, 3 Postscript figures, RevTeX

Neutron Irradiation of Mg11B2 : From the Enhancement to the Suppression of Superconducting Properties

In this letter we present the effect of neutron irradiation up to fluences of 3.9 1019 n/cm2 on the superconducting properties of MgB2. In order to obtain a disorder structure homogeneously distributed, the experiment was carried out on bulk samples prepared with the 11B isotope. Up to fluences of 1018 n/cm2 the critical temperature is slightly diminished (36 K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K. For larger neutron fluences the critical temperature is suppressed down to 12 K and the superconducting properties come out strongly degraded.Comment: 13 pages, 4 figures. Submitted to Appl.Phys.Let

Quantum Imaging

We provide a brief overview of the newly born field of quantum imaging, and discuss some concepts that lie at the root of this field.Comment: 8 pages, 19 figure

Multimode Squeezing Properties of a Confocal Opo: Beyond the Thin Crystal Approximation

Up to now, transverse quantum effects (usually labelled as "quantum imaging" effects) which are generated by nonlinear devices inserted in resonant optical cavities have been calculated using the "thin crystal approximation", i.e. taking into account the effect of diffraction only inside the empty part of the cavity, and neglecting its effect in the nonlinear propagation inside the nonlinear crystal. We introduce in the present paper a theoretical method which is not restricted by this approximation. It allows us in particular to treat configurations closer to the actual experimental ones, where the crystal length is comparable to the Rayleigh length of the cavity mode. We use this method in the case of the confocal OPO, where the thin crystal approximation predicts perfect squeezing on any area of the transverse plane, whatever its size and shape. We find that there exists in this case a "coherence length" which gives the minimum size of a detector on which perfect squeezing can be observed, and which gives therefore a limit to the improvement of optical resolution that can be obtained using such devices.Comment: soumis le 04.03.2005 a PR

Spatial correlations in hexagons generated via a Kerr nonlinearity

We consider the hexagonal pattern forming in the cross-section of an optical beam produced by a Kerr cavity, and we study the quantum correlations characterizing this structure. By using arguments related to the symmetry broken by the pattern formation, we identify a complete scenario of six-mode entanglement. Five independent phase quadratures combinations, connecting the hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of a non-linear quantum calculation technique, quantum correlations among the mode photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure

Teachers’ stress experiences during COVID-19-related emergency remote teaching: Results from an exploratory study

The study provides a portrait of teachers’ stress experience in the face of the needed introduction of information systems (IS) during COVID-19-related emergency remote teaching. Researchers contacted the headmasters at several Italian schools, who choose teacher’s representatives. The latters shared the online questionnaire among colleagues; the teachers voluntarily decided to participate. The cross-sectional study involved 237 Italian teachers (81.5% female; Mage = 50.20; SDage = 8.87). This survey wanted to detect information systems-related distress and eustress on the job, and technostress creators and inhibitors. Descriptive statistics, correlational analyses, and a multiple regression model using structural equation modeling were run. As according to the model, IS-related distress and eustress on the job were the dependent variables, technostress creators and inhibitors the independent ones, and respondents’ gender and age the control ones. Both technostress creators and inhibitors showed significant relationships with IS-related distress and eustress. Technostress creators showed a positive relationship with IS-related distress and a negative one with IS-related eustress; conversely, technostress inhibitors showed an opposite pattern of relationships. Only technostress creators significantly associate to both age and gender in the model, suggesting that older, female teachers tended to experience more technostress creators. Due to the increases in remote work, the awareness of IS-related stress experiences represents a key factor to evaluate work-related risks and prevent stress-related problems. The results from this study suggest that using technologies can represent both a threat to one’s well-being, highlighting the need to provide adequate trainings and support, but also a resource for personal enrichment