3,108 research outputs found
Optimal control of many-body quantum dynamics: chaos and complexity
Achieving full control of the time-evolution of a many-body quantum system is
currently a major goal in physics. In this work we investigate the different
ways in which the controllability of a quantum system can be influenced by its
complexity, or even its chaotic properties. By using optimal control theory, we
are able to derive the control fields necessary to drive various physical
processes in a spin chain. Then, we study the spectral properties of such
fields and how they relate to different aspects of the system complexity. We
find that the spectral bandwidth of the fields is, quite generally, independent
of the system dimension. Conversely, the spectral complexity of such fields
does increase with the number of particles. Nevertheless, we find that the
regular o chaotic nature of the system does not affect signficantly its
controllability.Comment: 9 pages, 5 figure
Time-optimal control fields for quantum systems with multiple avoided crossings
We study time-optimal protocols for controlling quantum systems which show
several avoided level crossings in their energy spectrum. The structure of the
spectrum allows us to generate a robust guess which is time-optimal at each
crossing. We correct the field applying optimal control techniques in order to
find the minimal evolution or quantum speed limit (QSL) time. We investigate
its dependence as a function of the system parameters and show that it gets
proportionally smaller to the well-known two-level case as the dimension of the
system increases. Working at the QSL, we study the control fields derived from
the optimization procedure, and show that they present a very simple shape,
which can be described by a few parameters. Based on this result, we propose a
simple expression for the control field, and show that the full time-evolution
of the control problem can be analytically solved.Comment: 11 pages, 7 figure
A synthetic method for assessing small dams flood wave
River hydrodynamicsUnsteady open channel flow and dam brea
Time-Frequency-Wavenumber Analysis of Surface Waves Using the Continuous Wavelet Transform
A modified approach to surface wave dispersion analysis using active sources is proposed. The method is based on continuous recordings, and uses the continuous wavelet transform to analyze the phase velocity dispersion of surface waves. This gives the possibility to accurately localize the phase information in time, and to isolate the most significant contribution of the surface waves. To extract the dispersion information, then, a hybrid technique is applied to the narrowband filtered seismic recordings. The technique combines the flexibility of the slant stack method in identifying waves that propagate in space and time, with the resolution of f-k approaches. This is particularly beneficial for higher mode identification in cases of high noise levels. To process the continuous wavelet transform, a new mother wavelet is presented and compared to the classical and widely used Morlet type. The proposed wavelet is obtained from a raised-cosine envelope function (Hanning type). The proposed approach is particularly suitable when using continuous recordings (e.g., from seismological-like equipment) since it does not require any hardware-based source triggering. This can be subsequently done with the proposed method. Estimation of the surface wave phase delay is performed in the frequency domain by means of a covariance matrix averaging procedure over successive wave field excitations. Thus, no record stacking is necessary in the time domain and a large number of consecutive shots can be used. This leads to a certain simplification of the field procedures. To demonstrate the effectiveness of the method, we tested it on synthetics as well on real field data. For the real case we also combine dispersion curves from ambient vibrations and active measurement
A synthetic method for assessing small dams flood wave
River hydrodynamicsUnsteady open channel flow and dam brea
Characterizing dynamics with covariant Lyapunov vectors
A general method to determine covariant Lyapunov vectors in both discrete-
and continuous-time dynamical systems is introduced. This allows to address
fundamental questions such as the degree of hyperbolicity, which can be
quantified in terms of the transversality of these intrinsic vectors. For
spatially extended systems, the covariant Lyapunov vectors have localization
properties and spatial Fourier spectra qualitatively different from those
composing the orthonormalized basis obtained in the standard procedure used to
calculate the Lyapunov exponents.Comment: 4 pages, 3 figures, submitted to Physical Review letter
An innovative model for the sustainability of investments in the wind energy sector: the use of green sukuk in an Italian case study
In this paper we present the technical-energy-economic feasibility of wind power systems. An Italian 1 megawatt case study was considered to evaluate the importance of incentives in order to achieve the grid parity. Due to the severe reduction of incentives in the last years, in the present work we propose the use of Sukuk, a Shari’ah-compliant instrument used in the Islamic finance, as an alternative financial instrument used to limit the extent of leverage associated with financing. The building cost thresholds necessary to achieve the grid parity and a profitable and bankable project are presented with a sensitivity analysis. In the framework of the efforts against climate change and the emission of greenhouse gas, our results evidenced the importance of incentives and the applicability of the use of Shari’ah-compliant sukuk instruments in order to provide a feasible and sustainable investment in the wind energy sector
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