7,493 research outputs found
Information geometric complexity of a trivariate Gaussian statistical model
We evaluate the information geometric complexity of entropic motion on
low-dimensional Gaussian statistical manifolds in order to quantify how
difficult is making macroscopic predictions about a systems in the presence of
limited information. Specifically, we observe that the complexity of such
entropic inferences not only depends on the amount of available pieces of
information but also on the manner in which such pieces are correlated.
Finally, we uncover that for certain correlational structures, the
impossibility of reaching the most favorable configuration from an entropic
inference viewpoint, seems to lead to an information geometric analog of the
well-known frustration effect that occurs in statistical physics.Comment: 16 pages, 1 figur
Information geometric methods for complexity
Research on the use of information geometry (IG) in modern physics has
witnessed significant advances recently. In this review article, we report on
the utilization of IG methods to define measures of complexity in both
classical and, whenever available, quantum physical settings. A paradigmatic
example of a dramatic change in complexity is given by phase transitions (PTs).
Hence we review both global and local aspects of PTs described in terms of the
scalar curvature of the parameter manifold and the components of the metric
tensor, respectively. We also report on the behavior of geodesic paths on the
parameter manifold used to gain insight into the dynamics of PTs. Going
further, we survey measures of complexity arising in the geometric framework.
In particular, we quantify complexity of networks in terms of the Riemannian
volume of the parameter space of a statistical manifold associated with a given
network. We are also concerned with complexity measures that account for the
interactions of a given number of parts of a system that cannot be described in
terms of a smaller number of parts of the system. Finally, we investigate
complexity measures of entropic motion on curved statistical manifolds that
arise from a probabilistic description of physical systems in the presence of
limited information. The Kullback-Leibler divergence, the distance to an
exponential family and volumes of curved parameter manifolds, are examples of
essential IG notions exploited in our discussion of complexity. We conclude by
discussing strengths, limits, and possible future applications of IG methods to
the physics of complexity.Comment: review article, 60 pages, no figure
Rotary mechanism for wind tunnel stall/spin studies
The critical problem of stall-spin characteristics of high performance aircraft and the need for experimental data in this area are reviewed. A rotary mechanism for obtaining this aerodynamic data in a conventional wind tunnel is presented. The intricacies of the drive systems and the articulation available through such a mechanism are described
Motional Squashed States
We show that by using a feedback loop it is possible to reduce the
fluctuations in one quadrature of the vibrational degree of freedom of a
trapped ion below the quantum limit. The stationary state is not a proper
squeezed state, but rather a ``squashed'' state, since the uncertainty in the
orthogonal quadrature, which is larger than the standard quantum limit, is
unaffected by the feedback action.Comment: 8 pages, 2 figures, to appear in the special Issue "Quantum
Correlations and Fluctuations" of J. Opt.
Quantum State Reconstruction of a Bose-Einstein Condensate
We propose a tomographic scheme to reconstruct the quantum state of a
Bose-Einstein condensate, exploiting the radiation field as a probe and
considering the atomic internal degrees of freedom. The density matrix in the
number state basis can be directly retrieved from the atom counting
probabilities.Comment: 11 pages, LaTeX file, no figures, to appear in Europhysics Letter
Overcoming the false-minima problem in direct methods: Structure determination of the packaging enzyme P4 from bacteriophage φ13
The problems encountered during the phasing and structure determination of the packaging enzyme P4 from bacteriophage φ13 using the anomalous signal from selenium in a single-wavelength anomalous dispersion experiment (SAD) are described. The oligomeric state of P4 in the virus is a hexamer (with sixfold rotational symmetry) and it crystallizes in space group C2, with four hexamers in the crystallographic asymmetric unit. Current state-of-the-art ab initio phasing software yielded solutions consisting of 96 atoms arranged as sixfold symmetric clusters of Se atoms. However, although these solutions showed high correlation coefficients indicative that the substructure had been solved, the resulting phases produced uninterpretable electron-density maps. Only after further analysis were correct solutions found (also of 96 atoms), leading to the eventual identification of the positions of 120 Se atoms. Here, it is demonstrated how the difficulties in finding a correct phase solution arise from an intricate false-minima problem. © 2005 International Union of Crystallography - all rights reserved
Ground state of the Kondo model
Journal ArticleThe single-impurity Kondo problem is investigated with the use of the nonperturbative Lanczos (tridiagonalization) method. We are able to obtain an explicit expression for the ground-state energy in terms of the Kondo coupling constant J. The method places no restrictions on the range of J
Application of tridiagonalization to the many-body problem. II. Finite T
Journal ArticleIn a previous paper of the same title, we obtained the ground-state energy of a magnetic (Wolff-model) impurity in a nonmagnetic metal. In the present Brief Report, we calculate the impurity's contribution to the density of states and heat capacity of the metal at low temperatures. Here, the Lanczös reduction ("tridiagonalization") converges less rapidly, so that our results are of qualitative merit only. Nevertheless, we confirm the validity of perturbation theory in the weak-coupling regime, and find, at strong coupling, that the interaction introduces an extra fraction 2/N of states at the Fermi level
Kepler-447b: a hot-Jupiter with an extremely grazing transit
We present the radial velocity confirmation of the extrasolar planet
Kepler-447b, initially detected as a candidate by the Kepler mission. In this
work, we analyze its transit signal and the radial velocity data obtained with
the Calar Alto Fiber-fed Echelle spectrograph (CAFE). By simultaneously
modeling both datasets, we obtain the orbital and physical properties of the
system. According to our results, Kepler-447b is a Jupiter-mass planet
(), with an estimated radius of
(uncertainties provided in this work are
unless specified). This translates into a sub-Jupiter density. The
planet revolves every days in a slightly eccentric orbit
() around a G8V star with detected activity in the
Kepler light curve. Kepler-447b transits its host with a large impact parameter
(), being one of the few planetary grazing transits
confirmed so far and the first in the Kepler large crop of exoplanets. We
estimate that only around 20% of the projected planet disk occults the stellar
disk. The relatively large uncertainties in the planet radius are due to the
large impact parameter and short duration of the transit. Planets with such an
extremely large impact parameter can be used to detect and analyze interesting
configurations such as additional perturbing bodies, stellar pulsations,
rotation of a non-spherical planet, or polar spot-crossing events. All these
scenarios would periodically modify the transit properties (depth, duration,
and time of mid-transit), what could be detectable with sufficient accurate
photometry. Short-cadence photometric data (at the 1 minute level) would help
in the search for these exotic configurations in grazing planetary transits
like that of Kepler-447b.Comment: Accepted for publication in A&A. 13 pages, 8 figures, 4 tables. This
version replaces an earlier version of the pape
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