14,749 research outputs found
Branes are Waves and Monopoles
In a recent paper it was shown that fundamental strings are null waves in
Double Field Theory. Similarly, membranes are waves in exceptional extended
geometry. Here the story is continued by showing how various branes are
Kaluza-Klein monopoles of these higher dimensional theories. Examining the
specific case of the E7 exceptional extended geometry, we see that all branes
are both waves and monopoles. Along the way we discuss the O(d; d)
transformation of localized brane solutions not associated to an isometry and
how true T-duality emerges in Double Field Theory when the background possesses
isometries.Comment: 32 pages, Latex, v2, typos correcte
Quasilinear spin voltage profiles in spin thermoelectrics
Recent experiments show that spin thermoelectrics is a promising approach to
generate spin voltages. While spin chemical potentials are often limited to a
surface layer of the order of the spin diffusion length, we show that
thermoelectrically induced spin chemical potentials can extend much further in
itinerant ferromagnets with paramagnetic impurities. In some cases,
conservation laws, e.g., for a combination of spin and heat currents, give rise
to a linear spin voltage profile. More generally, we find quasilinear profiles
involving a spin thermoelectric length scale which far exceeds the spin
diffusion length.Comment: 4+ page
Structure and dynamics of binary liquid mixtures near their continuous demixing transitions
The dynamic and static critical behavior of five binary Lennard-Jones liquid
mixtures, close to their continuous demixing points (belonging to the so-called
model H' dynamic universality class), are studied computationally by combining
semi-grand canonical Monte Carlo simulations and large-scale molecular dynamics
(MD) simulations, accelerated by graphic processing units (GPU). The symmetric
binary liquid mixtures considered cover a variety of densities, a wide range of
compressibilities, and various interactions between the unlike particles. The
static quantities studied here encompass the bulk phase diagram (including both
the binodal and the -line), the correlation length, the concentration
susceptibility, the compressibility of the finite-sized systems at the bulk
critical temperature , and the pressure. Concerning the collective
transport properties, we focus on the Onsager coefficient and the shear
viscosity. The critical power-law singularities of these quantities are
analyzed in the mixed phase (above ) and non-universal critical amplitudes
are extracted. Two universal amplitude ratios are calculated. The first one
involves static amplitudes only and agrees well with the expectations for the
three-dimensional Ising universality class. The second ratio includes also
dynamic critical amplitudes and is related to the Einstein--Kawasaki relation
for the interdiffusion constant. Precise estimates of this amplitude ratio are
difficult to obtain from MD simulations, but within the error bars our results
are compatible with theoretical predictions and experimental values for model
H'. Evidence is reported for an inverse proportionality of the pressure and the
isothermal compressibility at the demixing transition, upon varying either the
number density or the repulsion strength between unlike particles.Comment: 15 pages, 12 figure
Graded Lie algebras with finite polydepth
If A is a graded connected algebra then we define a new invariant, polydepth
A, which is finite if for some A-module M of at most
polynomial growth. Theorem 1: If f : X \to Y is a continuous map of finite
category, and if the orbits of H_*(\Omega Y) acting in the homology of the
homotopy fibre grow at most polynomially, then H_*(\Omega Y) has finite
polydepth. Theorem 2: If L is a graded Lie algebra and polydepth UL is finite
then either L is solvable and UL grows at most polynomially or else for some
integer d and all r, , some
Sparsity-Sensitive Finite Abstraction
Abstraction of a continuous-space model into a finite state and input
dynamical model is a key step in formal controller synthesis tools. To date,
these software tools have been limited to systems of modest size (typically
6 dimensions) because the abstraction procedure suffers from an
exponential runtime with respect to the sum of state and input dimensions. We
present a simple modification to the abstraction algorithm that dramatically
reduces the computation time for systems exhibiting a sparse interconnection
structure. This modified procedure recovers the same abstraction as the one
computed by a brute force algorithm that disregards the sparsity. Examples
highlight speed-ups from existing benchmarks in the literature, synthesis of a
safety supervisory controller for a 12-dimensional and abstraction of a
51-dimensional vehicular traffic network
The perception of emotion in artificial agents
Given recent technological developments in robotics, artificial intelligence and virtual reality, it is perhaps unsurprising that the arrival of emotionally expressive and reactive artificial agents is imminent. However, if such agents are to become integrated into our social milieu, it is imperative to establish an understanding of whether and how humans perceive emotion in artificial agents. In this review, we incorporate recent findings from social robotics, virtual reality, psychology, and neuroscience to examine how people recognize and respond to emotions displayed by artificial agents. First, we review how people perceive emotions expressed by an artificial agent, such as facial and bodily expressions and vocal tone. Second, we evaluate the similarities and differences in the consequences of perceived emotions in artificial compared to human agents. Besides accurately recognizing the emotional state of an artificial agent, it is critical to understand how humans respond to those emotions. Does interacting with an angry robot induce the same responses in people as interacting with an angry person? Similarly, does watching a robot rejoice when it wins a game elicit similar feelings of elation in the human observer? Here we provide an overview of the current state of emotion expression and perception in social robotics, as well as a clear articulation of the challenges and guiding principles to be addressed as we move ever closer to truly emotional artificial agents
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