1,705 research outputs found
Advancing Shannon entropy for measuring diversity in systems
From economic inequality and species diversity to power laws and the analysis of multiple trends and trajectories, diversity within systems is a major issue for science. Part of the challenge is measuring it. Shannon entropy H has been used to re-think diversity within probability distributions, based on the notion of information. However, there are two major limitations to Shannon's approach. First, it cannot be used to compare diversity distributions that have different levels of scale. Second, it cannot be used to compare parts of diversity distributions to the whole. To address these limitations, we introduce a re-normalization of probability distributions based on the notion of case-based entropy Cc as a function of the cumulative probability c. Given a probability density p(x), Cc measures the diversity of the distribution up to a cumulative probability of c, by computing the length or support of an equivalent uniform distribution that has the same Shannon information as the conditional distribution of ^pc(x) up to cumulative probability c. We illustrate the utility of our approach by re-normalizing and comparing three well-known energy distributions in physics, namely, the Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac distributions for energy of sub-atomic particles. The comparison shows that Cc is a vast improvement over H as it provides a scale-free comparison of these diversity distributions and also allows for a comparison between parts of these diversity distributions
Seismic Earth Pressure Development in Sheet Pile Retaining Walls: A Numerical Study
The design of retaining walls requires the complete knowledge of the earth
pressure distribution behind the wall. Due to the complex soil-structure
effect, the estimation of earth pressure is not an easy task; even in the
static case. The problem becomes even more complex for the dynamic (i.e.,
seismic) analysis and design of retaining walls. Several earth pressure models
have been developed over the years to integrate the dynamic earth pressure with
the static earth pressure and to improve the design of retaining wall in
seismic regions. Among all the models, MononobeOkabe (M-O) method is commonly
used to estimate the magnitude of seismic earth pressures in retaining walls
and is adopted in design practices around the world (e.g., EuroCode and
Australian Standards). However, the M-O method has several drawbacks and does
not provide reliable estimate of the earth pressure in many instances. This
study investigates the accuracy of the M-O method to predict the dynamic earth
pressure in sheet pile wall. A 2D plane strain finite element model of the
wall-soil system was developed in DIANA. The backfill soil was modelled with
Mohr-Coulomb failure criterion while the wall was assumed behave elastically.
The numerically predicted dynamic earth pressure was compared with the M-O
model prediction. Further, the point of application of total dynamic force was
determined and compared with the static case. Finally, the applicability of M-O
methods to compute the seismic earth pressure was discussed
Exactly solvable -symmetric models in two dimensions
Non-hermitian, -symmetric Hamiltonians, experimentally realized
in optical systems, accurately model the properties of open, bosonic systems
with balanced, spatially separated gain and loss. We present a family of
exactly solvable, two-dimensional, potentials for a
non-relativistic particle confined in a circular geometry. We show that the
symmetry threshold can be tuned by introducing a second
gain-loss potential or its hermitian counterpart. Our results explicitly
demonstrate that breaking in two dimensions has a rich phase
diagram, with multiple re-entrant symmetric phases.Comment: 6 pages, 6 figure
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