45 research outputs found
Frontiers of open quantum system dynamics
We briefly examine recent developments in the field of open quantum system
theory, devoted to the introduction of a satisfactory notion of memory for a
quantum dynamics. In particular, we will consider a possible formalization of
the notion of non-Markovian dynamics, as well as the construction of quantum
evolution equations featuring a memory kernel. Connections will be drawn to the
corresponding notions in the framework of classical stochastic processes, thus
pointing to the key differences between a quantum and classical formalization
of the notion of memory effects.Comment: 15 pages, contribution to "Quantum Physics and Geometry", Lecture
Notes of the Unione Matematica Italiana 25,E. Ballico et al. (eds.
Nonlinear solar cycle forecasting: theory and perspectives
In this paper we develop a modern approach to solar cycle forecasting, based
on the mathematical theory of nonlinear dynamics. We start from the design
of a static curve fitting model for the experimental yearly sunspot number
series, over a time scale of 306 years, starting from year 1700 and we
establish a least-squares optimal pulse shape of a solar cycle. The
cycle-to-cycle evolution of the parameters of the cycle shape displays
different patterns, such as a Gleissberg cycle and a strong anomaly in the
cycle evolution during the Dalton minimum. In a second step, we extract a
chaotic mapping for the successive values of one of the key model parameters
– the rate of the exponential growth-decrease of the solar activity during
the n-th cycle. We examine piece-wise linear techniques for the approximation
of the derived mapping and we provide its probabilistic analysis:
calculation of the invariant distribution and autocorrelation function. We
find analytical relationships for the sunspot maxima and minima, as well as
their occurrence times, as functions of chaotic values of the above
parameter. Based on a Lyapunov spectrum analysis of the embedded
mapping, we finally establish a horizon of predictability for the method,
which allows us to give the most probable forecasting of the upcoming solar
cycle 24, with an expected peak height of 93±21 occurring in 2011/2012
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DEPOSITION OF NIOBIUM AND OTHER SUPERCONDUCTING MATERIALS WITH HIGH POWER IMPULSE MAGNETRON SPUTTERING: CONCEPT AND FIRST RESULTS
Niobium coatings on copper cavities have been considered as a cost-efficient replacement of bulk niobium RF cavities, however, coatings made by magnetron sputtering have not quite lived up to high expectations due to Q-slope and other issues. High power impulse magnetron sputtering (HIPIMS) is a promising emerging coatings technology which combines magnetron sputtering with a pulsed power approach. The magnetron is turned into a metal plasma source by using very high peak power density of ~ 1 kW/cm{sup 2}. In this contribution, the cavity coatings concept with HIPIMS is explained. A system with two cylindrical, movable magnetrons was set up with custom magnetrons small enough to be inserted into 1.3 GHz cavities. Preliminary data on niobium HIPIMS plasma and the resulting coatings are presented. The HIPIMS approach has the potential to be extended to film systems beyond niobium, including other superconducting materials and/or multilayer systems