12,554 research outputs found
Vergleichende QualitÀtsforschung - Neue AnsÀtze und Impulse tÀten gut
Eine am FiBL durchgefĂŒhrte Auswertung neuer Studien im Bereich der vergleichenden QualitĂ€tsforschung brachte die BestĂ€tigung bekannter Befunde und Tendenzen, zeigte aber keine grundsĂ€tzlich neuen AnsĂ€tze.
FĂŒr den biologischen Landbau bleibt die QualitĂ€tsforschung von zentraler Bedeutung
Dynamics of a three-dimensional inextensible chain
In the first part of this work the classical and statistical aspects of the
dynamics of an inextensible chain in three dimensions are investigated. In the
second part the special case of a chain admitting only fixed angles with
respect to the axis is studied using a path integral approach. It is shown
that it is possible to reduce this problem to a two-dimensional case, in a way
which is similar to the reduction of the statistical mechanics of a directed
polymer to the random walk of a two-dimensional particle.Comment: 15 pages, 3 figures, LaTeX, version accepted for publicatio
Unifying approach to the quantification of bipartite correlations by Bures distance
The notion of distance defined on the set of states of a composite quantum
system can be used to quantify total, quantum and classical correlations in a
unifying way. We provide new closed formulae for classical and total
correlations of two-qubit Bell-diagonal states by considering the Bures
distance. Complementing the known corresponding expressions for entanglement
and more general quantum correlations, we thus complete the quantitative
hierarchy of Bures correlations for Bell-diagonal states. We then explicitly
calculate Bures correlations for two relevant families of states: Werner states
and rank-2 Bell-diagonal states, highlighting the subadditivity which holds for
total correlations with respect to the sum of classical and quantum ones when
using Bures distance. Finally, we analyse a dynamical model of two independent
qubits locally exposed to non-dissipative decoherence channels, where both
quantum and classical correlations measured by Bures distance exhibit freezing
phenomena, in analogy with other known quantifiers of correlations.Comment: 18 pages, 4 figures; published versio
Optimal stochastic modelling with unitary quantum dynamics
Identifying and extracting the past information relevant to the future
behaviour of stochastic processes is a central task in the quantitative
sciences. Quantum models offer a promising approach to this, allowing for
accurate simulation of future trajectories whilst using less past information
than any classical counterpart. Here we introduce a class of phase-enhanced
quantum models, representing the most general means of causal simulation with a
unitary quantum circuit. We show that the resulting constructions can display
advantages over previous state-of-art methods - both in the amount of
information they need to store about the past, and in the minimal memory
dimension they require to store this information. Moreover, we find that these
two features are generally competing factors in optimisation - leading to an
ambiguity in what constitutes the optimal model - a phenomenon that does not
manifest classically. Our results thus simultaneously offer new quantum
advantages for stochastic simulation, and illustrate further qualitative
differences in behaviour between classical and quantum notions of complexity.Comment: 9 pages, 5 figure
Width of the charge-transfer peak in the SU(N) impurity Anderson model and its relevance to nonequilibrium transport
We calculate the width 2ÎCT and intensity of the charge-transfer peak (the one lying at the on-site energy Ed) in the impurity spectral density of states as a function of Ed in the SU(N) impurity Anderson model (IAM). We use the dynamical density-matrix renormalization group (DDMRG) and the noncrossing approximation (NCA) for N=4 and a 1/N variational approximation in the general case. In particular, while for Ed Î, where Î is the resonant level half-width, ÎCT=Î as expected in the noninteracting case, for Ed NÎ one has ÎCT=NÎ. In the N=2 case, some effects of the variation of ÎCT with Ed were observed in the conductance through a quantum dot connected asymmetrically to conducting leads at finite bias [J. Könemann, Phys. Rev. B 73, 033313 (2006)PRBMDO1098-012110.1103/PhysRevB.73.033313]. More dramatic effects are expected in similar experiments that can be carried out in systems of two quantum dots, carbon nanotubes or other, realizing the SU(4) IAM.Fil: FernĂĄndez, JoaquĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Patagonia Norte; Argentina. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Ărea de EnergĂa Nuclear. Instituto Balseiro; ArgentinaFil: Lisandrini, Franco Thomas. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; ArgentinaFil: Roura Bas, Pablo Gines. ComisiĂłn Nacional de EnergĂa AtĂłmica. Centro AtĂłmico Constituyentes; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Gazza, Claudio Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; ArgentinaFil: Aligia, Armando Ăngel. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Ărea de EnergĂa Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Patagonia Norte; Argentin
Quantifying Volume Changing Perturbations in a Wave Chaotic System
A sensor was developed to quantitatively measure perturbations which change
the volume of a wave chaotic cavity while leaving its shape intact. The sensors
work in the time domain by using either scattering fidelity of the transmitted
signals or time reversal mirrors. The sensors were tested experimentally by
inducing volume changing perturbations to a one cubic meter mixed chaotic and
regular billiard system. Perturbations which caused a volume change that is as
small as 54 parts in a million were quantitatively measured. These results were
obtained by using electromagnetic waves with a wavelength of about 5cm,
therefore, the sensor is sensitive to extreme sub-wavelength changes of the
boundaries of a cavity. The experimental results were compared with Finite
Difference Time Domain (FDTD) simulation results, and good agreement was found.
Furthermore, the sensor was tested using a frequency domain approach on a
numerical model of the star graph, which is a representative wave chaotic
system. These results open up interesting applications such as: monitoring the
spatial uniformity of the temperature of a homogeneous cavity during heating up
/ cooling down procedures, verifying the uniform displacement of a fluid inside
a wave chaotic cavity by another fluid, etc.Comment: 13 pages, 13 figure
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