22,137 research outputs found
Demonstrating Universal Scaling in Quench Dynamics of a Yukawa One-Component Plasma
The Yukawa one-component plasma (OCP) is a paradigm model for describing
plasmas that contain one component of interest and one or more other components
that can be treated as a neutralizing, screening background. In appropriately
scaled units, interactions are characterized entirely by a screening parameter,
. As a result, systems of similar show the same dynamics,
regardless of the underlying parameters (e.g., density and temperature). We
demonstrate this behavior using ultracold neutral plasmas (UNP) created by
photoionizing a cold ( mK) gas. The ions in UNP systems are well
described by the Yukawa model, with the electrons providing the screening.
Creation of the plasma through photoionization can be thought of as a rapid
quench from to a final value set by the electron
density and temperature. We demonstrate experimentally that the post-quench
dynamics are universal in over a factor of 30 in density and an order
of magnitude in temperature. Results are compared with molecular dynamics
simulations. We also demonstrate that features of the post-quench kinetic
energy evolution, such as disorder-induced heating and kinetic-energy
oscillations, can be used to determine the plasma density and the electron
temperature.Comment: 10 pages, 12 figures, to be submitted to Physical Review
On the treatment of -changing proton-hydrogen Rydberg atom collisions
Energy-conserving, angular momentum-changing collisions between protons and
highly excited Rydberg hydrogen atoms are important for precise understanding
of atomic recombination at the photon decoupling era, and the elemental
abundance after primordial nucleosynthesis. Early approaches to -changing
collisions used perturbation theory for only dipole-allowed () transitions. An exact non-perturbative quantum mechanical treatment is
possible, but it comes at computational cost for highly excited Rydberg states.
In this note we show how to obtain a semi-classical limit that is accurate and
simple, and develop further physical insights afforded by the non-perturbative
quantum mechanical treatment
Theory and simulation of spectral line broadening by exoplanetary atmospheric haze
Atmospheric haze is the leading candidate for the flattening of expolanetary
spectra, as it's also an important source of opacity in the atmospheres of
solar system planets, satellites, and comets. Exoplanetary transmission
spectra, which carry information about how the planetary atmospheres become
opaque to stellar light in transit, show broad featureless absorption in the
region of wavelengths corresponding to spectral lines of sodium, potassium and
water. We develop a detailed atomistic model, describing interactions of atomic
or molecular radiators with dust and atmospheric haze particulates. This model
incorporates a realistic structure of haze particulates from small nano-size
seed particles up to sub-micron irregularly shaped aggregates, accounting for
both pairwise collisions between the radiator and haze perturbers, and
quasi-static mean field shift of levels in haze environments. This formalism
can explain large flattening of absorption and emission spectra in haze
atmospheres and shows how the radiator - haze particle interaction affects the
absorption spectral shape in the wings of spectral lines and near their
centers. The theory can account for nearly all realistic structure, size and
chemical composition of haze particulates and predict their influence on
absorption and emission spectra in hazy environments. We illustrate the utility
of the method by computing shift and broadening of the emission spectra of the
sodium D line in an argon haze. The simplicity, elegance and generality of the
proposed model should make it amenable to a broad community of users in
astrophysics and chemistry.Comment: 16 pages, 4 figures, submitted to MNRA
A Deep Spatio-Temporal Fuzzy Neural Network for Passenger Demand Prediction
In spite of its importance, passenger demand prediction is a highly
challenging problem, because the demand is simultaneously influenced by the
complex interactions among many spatial and temporal factors and other external
factors such as weather. To address this problem, we propose a Spatio-TEmporal
Fuzzy neural Network (STEF-Net) to accurately predict passenger demands
incorporating the complex interactions of all known important factors. We
design an end-to-end learning framework with different neural networks modeling
different factors. Specifically, we propose to capture spatio-temporal feature
interactions via a convolutional long short-term memory network and model
external factors via a fuzzy neural network that handles data uncertainty
significantly better than deterministic methods. To keep the temporal relations
when fusing two networks and emphasize discriminative spatio-temporal feature
interactions, we employ a novel feature fusion method with a convolution
operation and an attention layer. As far as we know, our work is the first to
fuse a deep recurrent neural network and a fuzzy neural network to model
complex spatial-temporal feature interactions with additional uncertain input
features for predictive learning. Experiments on a large-scale real-world
dataset show that our model achieves more than 10% improvement over the
state-of-the-art approaches.Comment: https://epubs.siam.org/doi/abs/10.1137/1.9781611975673.1
A Grand Old Church Rose in the East: The Church of God in Christ (COGIC) in East Texas
This essay traces the history of the Church of God in Christ and its early beginnings in East Texas
Extreme value laws for fractal intensity functions in dynamical systems: Minkowski analysis
Typically, in the dynamical theory of extremal events, the function that
gauges the intensity of a phenomenon is assumed to be convex and maximal, or
singular, at a single, or at most a finite collection of points in
phase--space. In this paper we generalize this situation to fractal landscapes,
i.e. intensity functions characterized by an uncountable set of singularities,
located on a Cantor set. This reveals the dynamical r\^ole of classical
quantities like the Minkowski dimension and content, whose definition we extend
to account for singular continuous invariant measures. We also introduce the
concept of extremely rare event, quantified by non--standard Minkowski
constants and we study its consequences to extreme value statistics. Limit laws
are derived from formal calculations and are verified by numerical experiments.Comment: 20 pages, 13 figure
Probing dynamical symmetry breaking using quantum-entangled photons
We present an input/output analysis of photon-correlation experiments whereby
a quantum mechanically entangled bi-photon state interacts with a material
sample placed in one arm of a Hong-Ou-Mandel (HOM) apparatus. We show that the
output signal contains detailed information about subsequent entanglement with
the microscopic quantum states in the sample. In particular, we apply the
method to an ensemble of emitters interacting with a common photon mode within
the open-system Dicke Model. Our results indicate considerable dynamical
information concerning spontaneous symmetry breaking can be revealed with such
an experimental system
Discrete structure of the brain rhythms
Neuronal activity in the brain generates synchronous oscillations of the
Local Field Potential (LFP). The traditional analyses of the LFPs are based on
decomposing the signal into simpler components, such as sinusoidal harmonics.
However, a common drawback of such methods is that the decomposition primitives
are usually presumed from the onset, which may bias our understanding of the
signal's structure. Here, we introduce an alternative approach that allows an
impartial, high resolution, hands-off decomposition of the brain waves into a
small number of discrete, frequency-modulated oscillatory processes, which we
call oscillons. In particular, we demonstrate that mouse hippocampal LFP
contain a single oscillon that occupies the -frequency band and a
couple of -oscillons that correspond, respectively, to slow and fast
-waves. Since the oscillons were identified empirically, they may
represent the actual, physical structure of synchronous oscillations in
neuronal ensembles, whereas Fourier-defined "brain waves" are nothing but
poorly resolved oscillons.Comment: 17 pages, 9 figure
Matrix methods for Pad\'e approximation: numerical calculation of poles, zeros and residues
A representation of the Pad\'e approximation of the -transform of a signal
as a resolvent of a tridiagonal matrix is given. Several formulas for the
poles, zeros and residues of the Pad\'e approximation in terms of the matrix
are proposed. Their numerical stability is tested and compared. Methods for
computing forward and backward errors are presented
- …