1,827 research outputs found
Event-by-event Simulation of Quantum Cryptography Protocols
We present a new approach to simulate quantum cryptography protocols using
event-based processes. The method is validated by simulating the BB84 protocol
and the Ekert protocol, both without and with the presence of an eavesdropper
The influences of surface temperature on upwellings in planetary convection with phase transitions
The importance of surface temperature for mantle convection appears with the presence of adiabatic heating and cooling
and the release and consumption of latent heat in the presence of phase transitions. For some planetary bodies these effects
cannot be neglected. The dimensionless surface temperature T0, which is the ratio between the temperature at the top of
the convective region and the temperature drop across the mantle, is close to one for Mars and Venus. For the Earth,
T0 lies between 0.2 and 0.5. The dynamical influence of T0 is especially poignant for internally heated convection with
temperature-dependent viscosity. There is a tight coupling between the magnitude of the temperature field and the viscosity
itself. We have studied temperature-dependent viscosity convection for both low-T0 (0.2) and high-T0 (1.2) situations and
with internal heating in mantle convection with two upper-mantle phase transitions. Our results show that within this range
of T0 there exist two regimes for the evolution of upwellings in the mantle. In transient situations plumeplume collisions
lead to the formation of megaplumes for high-T0 regimes but are less likely to do so for low T0. In the long-term regime,
plumes with low T0 are prone to develop from the transition zone with a supply of hot material coming from the shallow
lower mantle. In systems with high T0, however, long-lived plumes tend to have deeper mantle origins. In quasi-layered
situations high T0 may act as a positive feed-back mechanism in inducing powerful hot upwellings into the upper mantle.
Ă“ 1998 Elsevier Science B.V. All rights reserved
Phase field modelling of grain boundary premelting using obstacle potentials
We investigate the multi-order parameter phase field model of Steinbach and
Pezzolla [I. Steinbach, F. Pezzolla, A generalized field method for multiphase
transformations using interface fields, Physica D 134 (1999) 385-393]
concerning its ability to describe grain boundary premelting. For a single
order parameter situation solid-melt interfaces are always attractive, which
allows to have (unstable) equilibrium solid-melt-solid coexistence above the
bulk melting point. The temperature dependent melt layer thickness and the
disjoining potential, which describe the interface interaction, are affected by
the choice of the thermal coupling function and the measure to define the
amount of the liquid phase. Due to the strictly finite interface thickness also
the interaction range is finite. For a multi-order parameter model we find
either purely attractive or purely repulsive finite-ranged interactions. The
premelting transition is then directly linked to the ratio of the grain
boundary and solid-melt interfacial energy.Comment: 12 page
Electron shot noise beyond the second moment
The form of electron counting statistics of the tunneling current noise in a
generic many-body interacting electron system is obtained. The third correlator
of current fluctuations (the skewness of the charge counting distribution) has
a universal relation with the current I and the quasiparticle charge q. This
relation C_3 = q^2 I holds in a wide bias voltage range, both at large and
small eV/kT, thereby representing an advantage compared to the Schottky
formula. We consider the possibility of using the counting statistics for
detecting quasiparticle charge at high temperature.Comment: 4 pages, 2 figure
Rf-induced transport of Cooper pairs in superconducting single electron transistors in a dissipative environment
We investigate low-temperature and low-voltage-bias charge transport in a
superconducting Al single electron transistor in a dissipating environment,
realized as on-chip high-ohmic Cr microstrips. In our samples with relatively
large charging energy values Ec > EJ, where EJ is the energy of the Josephson
coupling, two transport mechanisms were found to be dominating, both based on
discrete tunneling of individual Cooper pairs: Depending on the gate voltage
Vg, either sequential tunneling of pairs via the transistor island (in the open
state of the transistor around the points Qg = CgVg = e mod(2e), where Cg is
the gate capacitance) or their cotunneling through the transistor (for Qg away
of these points) was found to prevail in the net current. As the open states of
our transistors had been found to be unstable with respect to quasiparticle
poisoning, high-frequency gate cycling (at f ~ 1 MHz) was applied to study the
sequential tunneling mechanism. A simple model based on the master equation was
found to be in a good agreement with the experimental data.Comment: 8 pages, 6 figure
Exciton-LO-phonon dynamics in InAs/GaAs quantum dots: Effects of zone-edge phonon damping
The dynamics of an exciton-LO-phonon system after an ultrafast optical
excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of
anharmonic phonon damping and its interplay with the phonon dispersion is
analyzed. The signatures of the zone-edge decay process in the absorption
spectrum and time evolution are highlighted, providing a possible way of
experimental investigation on phonon anharmonicity effects.Comment: 10 pages, 2 figure
p-Adic Models of Ultrametric Diffusion Constrained by Hierarchical Energy Landscapes
We demonstrate that p-adic analysis is a natural basis for the construction
of a wide variety of the ultrametric diffusion models constrained by
hierarchical energy landscapes. A general analytical description in terms of
p-adic analysis is given for a class of models. Two exactly solvable examples,
i.e. the ultrametric diffusion constraned by the linear energy landscape and
the ultrametric diffusion with reaction sink, are considered. We show that such
models can be applied to both the relaxation in complex systems and the rate
processes coupled to rearrangenment of the complex surrounding.Comment: 14 pages, 6 eps figures, LaTeX 2.0
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