4,265 research outputs found
Humblonium: Classical Atoms and the Earnshaw Plasma
It is shown that electrostatic and diamagnetic forces can combine to give
long lasting metastable bound dimers of macro and mesoscopically sized objects
for a physically attainable material regime. This can be a large enough effect
to support itself in a trap against Earth's gravity and they can stable at very
high temperatures. For a more restricted material parameter set, we investigate
the possibility of stable many particle collections that lose their identity as
bound pairs and create a kind of plasma. These would constitute a kind of
transitional state between fluids and granular materials but, unlike usual
approaches, the fluid is a gas rather than a liquid
Interfacial depinning transitions in disordered media: revisiting an old puzzle
Interfaces advancing through random media represent a number of different
problems in physics, biology and other disciplines. Here, we study the
pinning/depinning transition of the prototypical non-equilibrium interfacial
model, i.e. the Kardar-Parisi-Zhang equation, advancing in a disordered medium.
We analyze separately the cases of positive and negative non-linearity
coefficients, which are believed to exhibit qualitatively different behavior:
the positive case shows a continuous transition that can be related to
directed-percolation-depinning while in the negative case there is a
discontinuous transition and faceted interfaces appear. Some studies have
argued from different perspectives that both cases share the same universal
behavior. Here, by using a number of computational and scaling techniques we
shed light on this puzzling situation and conclude that the two cases are
intrinsically different.Comment: 13 pages, 9 figure
A Collection of Challenging Optimization Problems in Science, Engineering and Economics
Function optimization and finding simultaneous solutions of a system of
nonlinear equations (SNE) are two closely related and important optimization
problems. However, unlike in the case of function optimization in which one is
required to find the global minimum and sometimes local minima, a database of
challenging SNEs where one is required to find stationary points (extrama and
saddle points) is not readily available. In this article, we initiate building
such a database of important SNE (which also includes related function
optimization problems), arising from Science, Engineering and Economics. After
providing a short review of the most commonly used mathematical and
computational approaches to find solutions of such systems, we provide a
preliminary list of challenging problems by writing the Mathematical
formulation down, briefly explaning the origin and importance of the problem
and giving a short account on the currently known results, for each of the
problems. We anticipate that this database will not only help benchmarking
novel numerical methods for solving SNEs and function optimization problems but
also will help advancing the corresponding research areas.Comment: Accepted as an invited contribution to the special session on
Evolutionary Computation for Nonlinear Equation Systems at the 2015 IEEE
Congress on Evolutionary Computation (at Sendai International Center, Sendai,
Japan, from 25th to 28th May, 2015.
Security and Privacy Issues of Big Data
This chapter revises the most important aspects in how computing
infrastructures should be configured and intelligently managed to fulfill the
most notably security aspects required by Big Data applications. One of them is
privacy. It is a pertinent aspect to be addressed because users share more and
more personal data and content through their devices and computers to social
networks and public clouds. So, a secure framework to social networks is a very
hot topic research. This last topic is addressed in one of the two sections of
the current chapter with case studies. In addition, the traditional mechanisms
to support security such as firewalls and demilitarized zones are not suitable
to be applied in computing systems to support Big Data. SDN is an emergent
management solution that could become a convenient mechanism to implement
security in Big Data systems, as we show through a second case study at the end
of the chapter. This also discusses current relevant work and identifies open
issues.Comment: In book Handbook of Research on Trends and Future Directions in Big
Data and Web Intelligence, IGI Global, 201
Anomalously Weak Solar Convection
Convection in the solar interior is thought to comprise structures on a
spectrum of scales. This conclusion emerges from phenomenological studies and
numerical simulations, though neither covers the proper range of dynamical
parameters of solar convection. Here, we analyze observations of the wavefield
in the solar photosphere using techniques of time-distance helioseismology to
image flows in the solar interior. We downsample and synthesize 900 billion
wavefield observations to produce 3 billion cross-correlations, which we
average and fit, measuring 5 million wave travel times. Using these travel
times, we deduce the underlying flow systems and study their statistics to
bound convective velocity magnitudes in the solar interior, as a function of
depth and spherical-harmonic degree . Within the wavenumber band
, Convective velocities are 20-100 times weaker than current
theoretical estimates. This suggests the prevalence of a different paradigm of
turbulence from that predicted by existing models, prompting the question: what
mechanism transports the heat flux of a solar luminosity outwards? Advection is
dominated by Coriolis forces for wavenumbers , with Rossby numbers
smaller than at , suggesting that the Sun may be
a much faster rotator than previously thought, and that large-scale convection
may be quasi-geostrophic. The fact that iso-rotation contours in the Sun are
not co-aligned with the axis of rotation suggests the presence of a latitudinal
entropy gradient.Comment: PNAS; 5 figures, 5 page
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