14,564 research outputs found
Value Creation in a QoE Environment
User behavior of multimedia services currently undergoes strong changes. This is reflected in several recent trends, e.g. the increase of rich media content consumption, preferences for more individual and personalized services and the higher sensitivity of end users for quality issues. These changes will eventually lead to strong changes in network traffic characteristics: rising congestion in peak times and less availability of bandwidth for the individual user. As a result, the quality as perceived by the end-user will decrease if network operators and service providers do not anticipate the required changes for the network. Measurable network requirements such as available video and speech quality, security and reliability are addressed by technologies that are commonly summed up in the Quality of Service (QoS) concept. However, the end-users' perception of quality is only reflected in the wider concept of Quality of Experience (QoE). This takes the measurable network requirements into account as well as customer needs, wants and preferences. For the implementation of QoE technologies several network components need to be added or changed resulting in high capital expenditures. Yet, it is not clear if these costs can be compensated with efficiency increases. Thus, new revenue streams for the network operator are necessary to incentivize investments in QoE technologies. In this paper we address four new value creation models that can serve as basis for more elaborated business models for network operators and other actors. We show how interest in QoE of the user, the content provider, the service provider and the advertiser induces new revenue streams. These models are embedded in five possible future QoE scenarios that reveal regulation, end user quality sensibility and end-to-end support as major issues for the future. --Business Models,Quality of Experience (QoE),Quality of Service (QoS),Value Creation
A physical-space version of the stretched-vortex subgrid-stress model for large-eddy simulation
A physical-space version of the stretched-vortex subgrid-stress model is presented and applied to large-eddy simulations of incompressible flows. This version estimates the subgrid-kinetic energy required for evaluation of the subgrid-stress tensor using local second-order structure-function information of the resolved velocity field at separations of order the local cell size. A relation between the structure function and the energy spectrum is derived using the kinematic assumptions of the stretched-vortex model for locally homogeneous anisotropic turbulence. Results of large-eddy simulations using this model are compared to experimental and direct numerical simulation data. Comparisons are shown for the decay of kinetic energy and energy spectra of decaying isotropic turbulence and for mean velocities, root-mean-square velocity fluctuations and turbulence-kinetic energy balances of channel flow at three different Reynolds numbers
On the existence of quantum representations for two dichotomic measurements
Under which conditions do outcome probabilities of measurements possess a
quantum-mechanical model? This kind of problem is solved here for the case of
two dichotomic von Neumann measurements which can be applied repeatedly to a
quantum system with trivial dynamics. The solution uses methods from the theory
of operator algebras and the theory of moment problems. The ensuing conditions
reveal surprisingly simple relations between certain quantum-mechanical
probabilities. It also shown that generally, none of these relations holds in
general probabilistic models. This result might facilitate further experimental
discrimination between quantum mechanics and other general probabilistic
theories.Comment: 16+7 pages, presentation improved and minor errors correcte
Two-dimensional arrays of low capacitance tunnel junctions: general properties, phase transitions and Hall effect
We describe transport properties of two-dimensional arrays of low capacitance
tunnel junctions, such as the current voltage characteristic and its dependence
on external magnetic field and temperature. We discuss several experiments in
which the small capacitance of the junctions plays an important role. In arrays
where the junctions have a relatively large charging energy, (i.e. when they
have a low capacitance) and a high normal state resistance, the low bias
resistance increases with decreasing temperature and eventually at very low
temperature the array becomes insulating even though the electrodes in the
array are superconducting. This transition to the insulating state can be
described by thermal activation. In an intermediate region where the junction
resistance is of the order of the quantum resistance and the charging energy is
of the order of the Josephson coupling energy, the arrays can be tuned between
a superconducting and an insulating state with a magnetic field. We describe
measurements of this magnetic-field-tuned superconductor insulator transition,
and we show that the resistance data can be scaled over several orders of
magnitude. Four arrays follow the same universal function. At the transition
the transverse (Hall) resistance is found to be very small in comparison with
the longitudinal resistance. However, for magnetic field values larger than the
critical value.we observe a substantial Hall resistance. The Hall resistance of
these arrays oscillates with the applied magnetic field. features in the
magnetic field dependence of the Hall resistance can qualitatively be
correlated to features in the derivative of the longitudinal resistance,
similar to what is found in the quantum Hall effect.Comment: 29 pages, 16 eps figures, uses aipproc.sty and epsfig.sty,
contribution to Euroschool on "Superconductivity in Networks and Mesoscopic
Systems", held in Siena, Italy (8-20 september 1997
Microscopic theory of the Andreev gap
We present a microscopic theory of the Andreev gap, i.e. the phenomenon that
the density of states (DoS) of normal chaotic cavities attached to
superconductors displays a hard gap centered around the Fermi energy. Our
approach is based on a solution of the quantum Eilenberger equation in the
regime , where and are the classical dwell time and
Ehrenfest-time, respectively. We show how quantum fluctuations eradicate the
DoS at low energies and compute the profile of the gap to leading order in the
parameter .Comment: 4 pages, 3 figures; revised version, more details, extra figure, new
titl
Breaking Kelvin: Circulation conservation and vortex breakup in MHD at low Magnetic Prandtl Number
In this paper we examine the role of weak magnetic fields in breaking
Kelvin's circulation theorem and in vortex breakup in two-dimensional
magnetohydrodynamics for the physically important case of a low magnetic
Prandtl number (low ) fluid. We consider three canonical inviscid solutions
for the purely hydrodynamical problem, namely a Gaussian vortex, a circular
vortex patch and an elliptical vortex patch. We examine how magnetic fields
lead to an initial loss of circulation and attempt to derive scaling
laws for the loss of circulation as a function of field strength and diffusion
as measured by two non-dimensional parameters. We show that for all cases the
loss of circulation depends on the integrated effects of the Lorentz force,
with the patch cases leading to significantly greater circulation loss. For the
case of the elliptical vortex the loss of circulation depends on the total area
swept out by the rotating vortex and so this leads to more efficient
circulation loss than for a circular vortex.Comment: 21 pages, 12 figure
Heralded qubit amplifiers for practical device-independent quantum key distribution
Device-independent quantum key distribution does not need a precise quantum
mechanical model of employed devices to guarantee security. Despite of its
beauty, it is still a very challenging experimental task. We compare a recent
proposal by Gisin et al. [Phys. Rev. Lett. 105, 070501 (2010)] to close the
detection loophole problem with that of a simpler quantum relay based on
entanglement swapping with linear optics. Our full-mode analysis for both
schemes confirms that, in contrast to recent beliefs, the second scheme can
indeed provide a positive key rate which is even considerably higher than that
of the first alternative. The resulting key rates and required detection
efficiencies of approx. 95% for both schemes, however, strongly depend on the
underlying security proof.Comment: 5 pages, 3 figure
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