14,390 research outputs found
A graph theoretical analysis of the energy landscape of model polymers
In systems characterized by a rough potential energy landscape, local
energetic minima and saddles define a network of metastable states whose
topology strongly influences the dynamics. Changes in temperature, causing the
merging and splitting of metastable states, have non trivial effects on such
networks and must be taken into account. We do this by means of a recently
proposed renormalization procedure. This method is applied to analyze the
topology of the network of metastable states for different polypeptidic
sequences in a minimalistic polymer model. A smaller spectral dimension emerges
as a hallmark of stability of the global energy minimum and highlights a
non-obvious link between dynamic and thermodynamic properties.Comment: 15 pages, 15 figure
Optimization by Quantum Annealing: Lessons from Simple Cases
This paper investigates the basic behavior and performance of simulated
quantum annealing (QA) in comparison with classical annealing (CA). Three
simple one dimensional case study systems are considered, namely a parabolic
well, a double well, and a curved washboard. The time dependent Schr\"odinger
evolution in either real or imaginary time describing QA is contrasted with the
Fokker Planck evolution of CA. The asymptotic decrease of excess energy with
annealing time is studied in each case, and the reasons for differences are
examined and discussed. The Huse-Fisher classical power law of double well CA
is replaced with a different power law in QA. The multi-well washboard problem
studied in CA by Shinomoto and Kabashima and leading classically to a
logarithmic annealing even in the absence of disorder, turns to a power law
behavior when annealed with QA. The crucial role of disorder and localization
is briefly discussed.Comment: 16 pages, 9 figure
On the Four-Dimensional Diluted Ising Model
In this letter we show strong numerical evidence that the four dimensional
Diluted Ising Model for a large dilution is not described by the Mean Field
exponents. These results suggest the existence of a new fixed point with
non-gaussian exponents.Comment: 9 pages. compressed ps-file (uufiles
A new approach to the chap LQ regulator exploiting the geometric properties of the Hamiltonian system
The cheap LQ regulator is reinterpreted as an output nulling problem which is a basic problem of the geometric control theory. In fact, solving the LQ regulator problem is equivalent to keep the output of the related Hamiltonian system identically zero. The solution lies on a controlled invariant subspace whose dimension is characterized in terms of the minimal conditioned invariant of the original system, and the optimal feedback gain is computed as the friend matrix of the resolving subspace. This study yields a new computational framework for the cheap LQ regulator, relying only on the very basic and simple tools of the geometric approach, namely the algorithms for controlled and conditioned invariant subspaces and invariant zeros
3_D modeling using TLS and GPR techniques to characterize above and below-ground wood distribution in pyroclastic deposits along the Blanco River (Chilean Patagonia)
To date, the study of in-stream wood in rivers has been focused mainly on quantifying wood pieces deposited above
the ground. However, in some particular river systems, the presence of buried dead wood can also represent an
important component of wood recruitment and budgeting dynamics. This is the case of the Blanco River (Southern
Chile) severely affected by the eruption of Chait\ue9n Volcano occurred between 2008 and 2009. The high pyroclastic
sediment deposition and transport affected the channel and the adjacent forest, burying wood logs and standing
trees. The aim of this contribution is to assess the presence and distribution of wood in two study areas (483 m2 and
1989 m2, respectively) located along the lower streambank of the Blanco River, and covered by thick pyroclastic
deposition up to 5 m. The study areas were surveyed using two different devices, a Terrestrial Laser Scanner (TLS)
and a Ground Penetrating Radar (GPR). The first was used to scan the above surface achieving a high point cloud
density ( 48 2000 points m-2) which allowed us to identify and measure the wood volume. The second, was used
to characterize the internal morphology of the volcanic deposits and to detect the presence and spatial distribution
of buried wood up to a depth of 4 m. Preliminary results have demonstrated differences in the numerousness and
volume of above wood between the two study areas. In the first one, there were 43 wood elements, 33 standing
trees and 10 logs, with a total volume of 2.96 m3 (109.47 m3 km-1), whereas the second one was characterized
by the presence of just 7 standing trees and 11 wood pieces, for a total amount of 0.77 m3 (7.73 m3 km-1). The
dimensions of the wood elements vary greatly according to the typology, standing trees show the higher median
values in diameter and length (0.15 m and 2.91 m, respectively), whereas the wood logs were smaller (0.06 m and
1.12 m, respectively). The low dimensions of deposited wood can be probably connected to their origin, suggesting
that these elements were generated by toppling and breaking of surrounding dead trees. Results obtained with the
GPR confirm the ability of this instrument to localize the presence and distribution of buried wood. From the 3-
D analysis it was possible to assess the spatial distribution and to estimate, as first approach, the volume of the
buried wood which represents approximately 0.04% of the entire volcanic deposit. Further analysis will focus on
additional GPR calibration with different wood sizes for a more accurate estimation of the volume. The knowledge
of the overall wood amount stored in a fluvial system that can be remobilized over time, represent an essential
factor to ensure better forest and river management actions
Quorum of observables for universal quantum estimation
Any method for estimating the ensemble average of arbitrary operator
(observables or not, including the density matrix) relates the quantity of
interest to a complete set of observables, i.e. a quorum}. This corresponds to
an expansion on an irreducible set of operators in the Liouville space. We give
two general characterizations of these sets. All the known unbiased
reconstruction techniques, i.e. ``quantum tomographies'', can be described in
this framework. New operatorial resolutions are given that can be used to
implement novel reconstruction schemes.Comment: Latex, no figure
An alternative derivation of the gravitomagnetic clock effect
The possibility of detecting the gravitomagnetic clock effect using
artificial Earth satellites provides the incentive to develop a more intuitive
approach to its derivation. We first consider two test electric charges moving
on the same circular orbit but in opposite directions in orthogonal electric
and magnetic fields and show that the particles take different times in
describing a full orbit. The expression for the time difference is completely
analogous to that of the general relativistic gravitomagnetic clock effect in
the weak-field and slow-motion approximation. The latter is obtained by
considering the gravitomagnetic force as a small classical non-central
perturbation of the main central Newtonian monopole force. A general expression
for the clock effect is given for a spherical orbit with an arbitrary
inclination angle. This formula differs from the result of the general
relativistic calculations by terms of order c^{-4}.Comment: LaTex2e, 11 pages, 1 figure, IOP macros. Submitted to Classical and
Quantum Gravit
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