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arxiv_dataset-70001601.07972 | Receding Horizon Consensus of General Linear Multi-agent Systems with
Input Constraints: An Inverse Optimality Approach
math.OC
It is desirable but challenging to fulfill system constraints and reach
optimal performance in consensus protocol design for practical multi-agent
systems (MASs). This paper investigates the optimal consensus problem for
general linear MASs subject to control input constraints. Two classes of MASs
including subsystems with semi-stable and unstable dynamics are considered. For
both classes of MASs without input constraints, the results on designing
optimal consensus protocols are first developed by inverse optimality approach.
Utilizing the optimal consensus protocols, the receding horizon control
(RHC)-based consensus strategies are designed for these two classes of MASs
with input constraints. The conditions for assigning the cost functions
distributively are derived, based on which the distributed RHC-based consensus
frameworks are formulated. Next, the feasibility and consensus properties of
the closed-loop systems are analyzed. It is shown that 1) the optimal
performance indices under the inverse optimal consensus protocols are coupled
with the network topologies and the system matrices of subsystems, but they are
different for MASs with semi-stable and unstable subsystems; 2) the unstable
modes of subsystems impose more stringent requirements for the parameter
design; 3) the designed RHC-based consensus strategies can make the control
input constraints fulfilled and ensure consensus for the closed-loop systems in
both cases. But for MASs with semi-stable subsystems, the {\em convergent
consensus} can be reached. Finally, two examples are provided to verify the
effectiveness of the proposed results.
| arxiv topic:math.OC |
arxiv_dataset-70011601.08072 | Analysis on the Intersection of Pseudoconvex Domains
math.CV
In this note, we discuss the preservation of certain analytic properties of
the $\overline{\partial}$-Neumann operator, Bergman projection and Hankel
operators on the intersection of pseudoconvex domains.
| arxiv topic:math.CV |
arxiv_dataset-70021601.08172 | Isometries of nilpotent metric groups
math.MG math.DG math.GR
We consider Lie groups equipped with arbitrary distances. We only assume that
the distance is left-invariant and induces the manifold topology. For brevity,
we call such object metric Lie groups. Apart from Riemannian Lie groups,
distinguished examples are sub-Riemannian Lie groups and, in particular, Carnot
groups equipped with Carnot-Carath\'eodory distances. We study the regularity
of isometries, i.e., distance-preserving homeomorphisms. Our first result is
the analyticity of such maps between metric Lie groups. The second result is
that if two metric Lie groups are connected and nilpotent then every isometry
between the groups is the composition of a left translation and an isomorphism.
There are counterexamples if one does not assume the groups to be either
connected or nilpotent. The first result is based on a solution of the Hilbert
5th problem by Montgomery and Zippin. The second result is proved, via the
first result, considering the Riemannian case, which for self-isometries was
solved by Wolf.
| arxiv topic:math.MG math.DG math.GR |
arxiv_dataset-70031602.00021 | Decomposable approximations revisited
math.OA
Nuclear C*-algebras enjoy a number of approximation properties, most famously
the completely positive approximation property. This was recently sharpened to
arrange for the incoming maps to be sums of order-zero maps. We show that, in
addition, the outgoing maps can be chosen to be asymptotically order-zero.
Further these maps can be chosen to be asymptotically multiplicative if and
only if the C*-algebra and all its traces are quasidiagonal.
| arxiv topic:math.OA |
arxiv_dataset-70041602.00121 | Relativistic structure formation models and gravitoelectromagnetism
gr-qc astro-ph.CO
In the framework of Lagrangian perturbation theory in general relativity we
discuss the possibility to split the Einstein equations, written in terms of
spatial Cartan coframes within a 3+1 foliation of spacetime, into
gravitoelectric and gravitomagnetic parts. While the former reproduces the full
hierarchy of the Newtonian perturbation solutions, the latter contains
non-Newtonian aspects like gravitational waves. This split can be understood
and made unique through the Hodge decomposition of Cartan coframe fields.
| arxiv topic:gr-qc astro-ph.CO |
arxiv_dataset-70051602.00221 | Principal Polynomial Analysis
stat.ML
This paper presents a new framework for manifold learning based on a sequence
of principal polynomials that capture the possibly nonlinear nature of the
data. The proposed Principal Polynomial Analysis (PPA) generalizes PCA by
modeling the directions of maximal variance by means of curves, instead of
straight lines. Contrarily to previous approaches, PPA reduces to performing
simple univariate regressions, which makes it computationally feasible and
robust. Moreover, PPA shows a number of interesting analytical properties.
First, PPA is a volume-preserving map, which in turn guarantees the existence
of the inverse. Second, such an inverse can be obtained in closed form.
Invertibility is an important advantage over other learning methods, because it
permits to understand the identified features in the input domain where the
data has physical meaning. Moreover, it allows to evaluate the performance of
dimensionality reduction in sensible (input-domain) units. Volume preservation
also allows an easy computation of information theoretic quantities, such as
the reduction in multi-information after the transform. Third, the analytical
nature of PPA leads to a clear geometrical interpretation of the manifold: it
allows the computation of Frenet-Serret frames (local features) and of
generalized curvatures at any point of the space. And fourth, the analytical
Jacobian allows the computation of the metric induced by the data, thus
generalizing the Mahalanobis distance. These properties are demonstrated
theoretically and illustrated experimentally. The performance of PPA is
evaluated in dimensionality and redundancy reduction, in both synthetic and
real datasets from the UCI repository.
| arxiv topic:stat.ML |
arxiv_dataset-70061602.00321 | BSDEs with nonlinear weak terminal condition
math.PR math.OC
In a recent paper, Bouchard, Elie and Reveillac \cite{BER} have studied a new
class of Backward Stochastic Differential Equations with weak terminal
condition, for which the $T$-terminal value $Y_T$ of the solution $(Y,Z)$ is
not fixed as a random variable, but only satisfies a constraint of the form
$E[\Psi(Y_T)] \geq m.$ The aim of this paper is to introduce a more general
class of BSDEs with {\em nonlinear weak terminal condition}. More precisely,
the constraint takes the form $\mathcal{E}^f_{0,T}[\Psi(Y_T)] \geq m,$ where
$\mathcal{E}^f$ represents the $f$-conditional expectation associated to a {\em
nonlinear driver} $f$.
We carry out a similar analysis as in \cite{BER} of the value function
corresponding to the minimal solution $Y$ of the BSDE with nonlinear weak
terminal condition: we study the regularity, establish the main properties, in
particular continuity and convexity with respect to the parameter $m$, and
finally provide a dual representation and the existence of an optimal control
in the case of concave constraints. From a financial point of view, our study
is closely related to the approximative hedging of an European option under
dynamic risk measures constraints. The nonlinearity $f$ raises subtle
difficulties, highlighted throughout the paper, which cannot be handled by the
arguments used in the case of classical expectations constraints studied in
\cite{BER}.
| arxiv topic:math.PR math.OC |
arxiv_dataset-70071602.00421 | On the associated primes of local cohomology
math.AC
Let $R$ be a commutative Noetherian ring of prime characteristic $p$. In this
paper we give a short proof using filter regular sequences that the set of
associated prime ideals of $H^t_I(R)$ is finite for any ideal $I$ and for any
$t \ge 0$ when $R$ has finite $F$-representation type or finite singular locus.
This extends a previous result by Takagi-Takahashi and gives affirmative
answers for a problem of Huneke in many new classes of rings in positive
characteristic. We also give a criterion about the singularities of $R$ (in any
characteristic) to guarantee that the set of associated primes of $H^2_I(R)$ is
always finite.
| arxiv topic:math.AC |
arxiv_dataset-70081602.00521 | The Real-rootedness of Generalized Narayana Polynomials
math.CO
In this paper, we prove the real-rootedness of two classes of generalized
Narayana polynomials: one arising as the $h$-polynomials of the generalized
associahedron associated to the finite Weyl groups, the other arising in the
study of the infinite log-concavity of the Boros-Moll polynomials. For the
former, Br\"{a}nd\'{e}n has already proved that these $h$-polynomials have only
real zeros. We establish certain recurrence relations for the two classes of
Narayana polynomials, from which we derive the real-rootedness. To prove the
real-rootedness, we use a sufficient condition, due to Liu and Wang, to
determine whether two polynomials have interlaced zeros. The recurrence
relations are verified with the help of the Mathematica package
\textit{HolonomicFunctions}.
| arxiv topic:math.CO |
arxiv_dataset-70091602.00621 | On pattern matching with k mismatches and few don't cares
cs.DS
We consider the problem of pattern matching with $k$ mismatches, where there
can be don't care or wild card characters in the pattern. Specifically, given a
pattern $P$ of length $m$ and a text $T$ of length $n$, we want to find all
occurrences of $P$ in $T$ that have no more than $k$ mismatches. The pattern
can have don't care characters, which match any character. Without don't cares,
the best known algorithm for pattern matching with $k$ mismatches has a runtime
of $O(n\sqrt{k \log k})$. With don't cares in the pattern, the best
deterministic algorithm has a runtime of $O(nk polylog m)$. Therefore, there is
an important gap between the versions with and without don't cares.
In this paper we give an algorithm whose runtime increases with the number of
don't cares. We define an {\em island} to be a maximal length substring of $P$
that does not contain don't cares. Let $q$ be the number of islands in $P$. We
present an algorithm that runs in $O(n\sqrt{k\log m}+n\min\{\sqrt[3]{qk\log^2
m},\sqrt{q\log m}\})$ time. If the number of islands $q$ is $O(k)$ this runtime
becomes $O(n\sqrt{k\log m})$, which essentially matches the best known runtime
for pattern matching with $k$ mismatches without don't cares. If the number of
islands $q$ is $O(k^2)$, this algorithm is asymptotically faster than the
previous best algorithm for pattern matching with $k$ mismatches with don't
cares in the pattern.
| arxiv topic:cs.DS |
arxiv_dataset-70101602.00721 | Concentration of measure without independence: a unified approach via
the martingale method
math.PR cs.IT math.IT
The concentration of measure phenomenon may be summarized as follows: a
function of many weakly dependent random variables that is not too sensitive to
any of its individual arguments will tend to take values very close to its
expectation. This phenomenon is most completely understood when the arguments
are mutually independent random variables, and there exist several powerful
complementary methods for proving concentration inequalities, such as the
martingale method, the entropy method, and the method of transportation
inequalities. The setting of dependent arguments is much less well understood.
This chapter focuses on the martingale method for deriving concentration
inequalities without independence assumptions. In particular, we use the
machinery of so-called Wasserstein matrices to show that the Azuma-Hoeffding
concentration inequality for martingales with almost surely bounded
differences, when applied in a sufficiently abstract setting, is powerful
enough to recover and sharpen several known concentration results for
nonproduct measures. Wasserstein matrices provide a natural formalism for
capturing the interplay between the metric and the probabilistic structures,
which is fundamental to the concentration phenomenon.
| arxiv topic:math.PR cs.IT math.IT |
arxiv_dataset-70111602.00821 | Multiferroic properties of uniaxially compressed orthorhombic HoMnO3
thin films
cond-mat.mtrl-sci cond-mat.str-el
Multiferroic properties of orthorhombic HoMnO3 (Pbnm space group) are
significantly modified by epitaxial compressive strain along the a-axis. We are
able to focus on the effect of strain solely along the a-axis by using an YAlO3
(010) substrate, which has only a small lattice mismatch with HoMnO3 along the
other in-plane direction (the c-axis). Multiferroic properties of strained and
relaxed HoMnO3 thin films are compared with those reported for bulk, and are
found to differ widely. A relaxed film exhibits bulk-like properties such as a
ferroelectric transition temperature of 25 K and an incommensurate
antiferromagnetic order below 39 K, with an ordering wave vector of (0 qb 0)
with qb ~ 0.41 at 10 K. A strained film becomes ferroelectric already at 37.5 K
and has an incommensurate magnetic order with qb ~ 0.49 at 10 K.
| arxiv topic:cond-mat.mtrl-sci cond-mat.str-el |
arxiv_dataset-70121602.00921 | Double q-Analytic q-Hermite Binomial Formula and q-Traveling Waves
math.QA math-ph math.MP
Motivated by derivation of the Dirac type delta-function for quantum states
in Fock-Bargmann representation, we find q-binomial expansion in terms of
q-Hermite polynomials, analytic in two complex arguments. Based on this
representation, we introduce a new class of complex functions of two complex
arguments, which we call the double q-analytic functions. The real version of
these functions describe the q-analogue of traveling waves, which is not
preserving the shape during evolution as the usual traveling wave. For
corresponding q-wave equation we solve IVP in the q-D'Alembert form.
| arxiv topic:math.QA math-ph math.MP |
arxiv_dataset-70131602.01021 | Universality of charge transport in weakly interacting fermionic systems
math-ph math.MP
We review two rigorous results on the transport properties of weakly
interacting fermionic systems on $2d$ lattices, in the linear response regime.
First, we discuss the universality of the longitudinal conductivity for
interacting graphene. Then, we focus on the transverse conductivity of general
weakly interacting gapped fermionic systems, and we establish its universality.
This last result proves the stability of the integer quantum Hall effect
against weak interactions. The proofs are based on combinations of fermionic
cluster expansion techniques, renormalization group and lattice Ward
identities.
| arxiv topic:math-ph math.MP |
arxiv_dataset-70141602.01121 | Solar and Stellar Photospheric Abundances
astro-ph.SR
The determination of photospheric abundances in late-type stars from
spectroscopic observations is a well-established field, built on solid
theoretical foundations. Improving those foundations to refine the accuracy of
the inferred abundances has proven challenging, but progress has been made. In
parallel, developments on instrumentation, chiefly regarding multi-object
spectroscopy, have been spectacular, and a number of projects are collecting
large numbers of observations for stars across the Milky Way and nearby
galaxies, promising important advances in our understanding of galaxy formation
and evolution. After providing a brief description of the basic physics and
input data involved in the analysis of stellar spectra, a review is made of the
analysis steps, and the available tools to cope with large observational
efforts. The paper closes with a quick overview of relevant ongoing and planned
spectroscopic surveys, and highlights of recent research on photospheric
abundances.
| arxiv topic:astro-ph.SR |
arxiv_dataset-70151602.01221 | Oscillatory power spectrum and strongly $k$-dependent $r$ in hybrid
inflation
gr-qc
For the original hybrid inflation model, we calculate the power spectrum of
curvature perturbations generated during the waterfall, taking into account the
contribution of entropic modes. We study the regime where the potential is very
flat, and in which inflation continues for more than about 60 e-folds. Results
show oscillations in the scalar power spectrum, qualitatively similar to that
of a single field axion monodromy potential; however no feature is displayed in
the tensor power spectrum. Directions to develop a template for this power
spectrum are also discussed.
| arxiv topic:gr-qc |
arxiv_dataset-70161602.01321 | A continuum among logarithmic, linear, and exponential functions, and
its potential to improve generalization in neural networks
cs.NE
We present the soft exponential activation function for artificial neural
networks that continuously interpolates between logarithmic, linear, and
exponential functions. This activation function is simple, differentiable, and
parameterized so that it can be trained as the rest of the network is trained.
We hypothesize that soft exponential has the potential to improve neural
network learning, as it can exactly calculate many natural operations that
typical neural networks can only approximate, including addition,
multiplication, inner product, distance, polynomials, and sinusoids.
| arxiv topic:cs.NE |
arxiv_dataset-70171602.01421 | An SSD-based eigensolver for spectral analysis on billion-node graphs
cs.DC cs.MS
Many eigensolvers such as ARPACK and Anasazi have been developed to compute
eigenvalues of a large sparse matrix. These eigensolvers are limited by the
capacity of RAM. They run in memory of a single machine for smaller eigenvalue
problems and require the distributed memory for larger problems.
In contrast, we develop an SSD-based eigensolver framework called FlashEigen,
which extends Anasazi eigensolvers to SSDs, to compute eigenvalues of a graph
with hundreds of millions or even billions of vertices in a single machine.
FlashEigen performs sparse matrix multiplication in a semi-external memory
fashion, i.e., we keep the sparse matrix on SSDs and the dense matrix in
memory. We store the entire vector subspace on SSDs and reduce I/O to improve
performance through caching the most recent dense matrix. Our result shows that
FlashEigen is able to achieve 40%-60% performance of its in-memory
implementation and has performance comparable to the Anasazi eigensolvers on a
machine with 48 CPU cores. Furthermore, it is capable of scaling to a graph
with 3.4 billion vertices and 129 billion edges. It takes about four hours to
compute eight eigenvalues of the billion-node graph using 120 GB memory.
| arxiv topic:cs.DC cs.MS |
arxiv_dataset-70181602.01521 | Banach spaces from a construction scheme
math.LO math.FA
We construct a Banach space $\mathcal X_\varepsilon$ with an uncountable
$\varepsilon$-biorthogonal system but no uncountable $\tau$-biorthogonal system
for $\tau<\varepsilon$. In particular the space have no uncountable
biorthogonal system. We also construct a Banach space $\mathcal X_K$ with an
uncountable $K$-basic sequence but no uncountable $K'$-basic sequence, for
$1\leq K'<K$. A common feature of these examples is that they are both
constructed by recursive amalgamations using a single construction scheme.
| arxiv topic:math.LO math.FA |
arxiv_dataset-70191602.01621 | Frequency dependent visco-elastic properties of a water nanomeniscus :
an AFM study in Force Feedback Mode
cond-mat.soft
Recently, using an Atomic Force Microscope and a single cantilever excited at
different frequencies it was shown that water nanomeniscus can exhibit a
transition in mechanical responses when submitted to stimuli above few tens of
kHz. The use of a single cantilever to explore phenomena at frequencies far
from the cantilever resonance frequency is not a common and well-established
strategy, and because water meniscus are ubiquitous in nature, we have also
studied the water meniscus mechanical response, the stiffness G' (N/m) and the
dissipation G"(kg/s), as a function of frequency by using cantilevers with
different resonance frequencies. These results, based on classic dynamical AFM
technics, confirm the anomalous mechanical response of water nanomeniscus when
stimulated at frequencies high enough.
| arxiv topic:cond-mat.soft |
arxiv_dataset-70201602.01721 | Spiral-driven accretion in protoplanetary discs - II Self-similar
solutions
astro-ph.GA
Accretion discs are ubiquitous in the universe and it is a crucial issue to
understand how angular momentum and mass are being radially transported in
these objects. Here, we study the role played by non-linear spiral patterns
within hydrodynamical and non self-gravitating accretion disc assuming that
external disturbances such as infall onto the disc may trigger them. To do so,
we computed self-similar solutions that describe discs in which a spiral wave
propagates. Such solutions present both shocks and critical sonic points that
we carefully analyze. For all allowed temperatures and for several spiral
shocks, we calculated the wave structure. In particular we inferred the angle
of the spiral patern, the stress it exerts on the disc as well as the
associated flux of mass and angular momentum as a function of temperature. We
quantified the rate of angular momentum transport by means of the dimensionless
$\alpha$ parameter. For the thickest disc we considered (corresponding to $h/r$
values of about 1/3), we found values of $\alpha$ as high as $0.1$, and scaling
with the temperature $T$ such that $\alpha \propto T^{3/2} \propto (h/r)^3$.
The spiral angle scales with the temperature as $\arctan(r/h)$. The existence
of these solutions suggests that perturbations occurring at disc outer
boundaries, such as for example perturbations due to infall motions, can
propagate deep inside the disc and therefore should not be ignored, even when
considering small radii.
| arxiv topic:astro-ph.GA |
arxiv_dataset-70211602.01821 | Sampling in de Branges Spaces and Naimark Dilation
math.CV
We consider the problem of sampling in de Branges spaces and develop some
necessary conditions and some sufficient conditions for sampling sequences,
which generalize some well-known sampling results in the Paley-Wiener space.
These conditions are obtained by identifying the main construction with Naimark
dilation of frames--embedding the de Branges space into a larger de Branges
space while embedding the kernel functions associated with a sampling sequence
into a Riesz basis for the larger space.
| arxiv topic:math.CV |
arxiv_dataset-70221602.01921 | Recognition of Visually Perceived Compositional Human Actions by
Multiple Spatio-Temporal Scales Recurrent Neural Networks
cs.CV cs.AI cs.LG
The current paper proposes a novel neural network model for recognizing
visually perceived human actions. The proposed multiple spatio-temporal scales
recurrent neural network (MSTRNN) model is derived by introducing multiple
timescale recurrent dynamics to the conventional convolutional neural network
model. One of the essential characteristics of the MSTRNN is that its
architecture imposes both spatial and temporal constraints simultaneously on
the neural activity which vary in multiple scales among different layers. As
suggested by the principle of the upward and downward causation, it is assumed
that the network can develop meaningful structures such as functional hierarchy
by taking advantage of such constraints during the course of learning. To
evaluate the characteristics of the model, the current study uses three types
of human action video dataset consisting of different types of primitive
actions and different levels of compositionality on them. The performance of
the MSTRNN in testing with these dataset is compared with the ones by other
representative deep learning models used in the field. The analysis of the
internal representation obtained through the learning with the dataset
clarifies what sorts of functional hierarchy can be developed by extracting the
essential compositionality underlying the dataset.
| arxiv topic:cs.CV cs.AI cs.LG |
arxiv_dataset-70231602.02021 | Holomorphic extensions associated with series expansions
math-ph cond-mat.stat-mech math.MP
We study the holomorphic extension associated with power series, i.e., the
analytic continuation from the unit disk to the cut-plane $\mathbb{C} \setminus
[1,+\infty)$. Analogous results are obtained also in the study of trigonometric
series: we establish conditions on the series coefficients which are sufficient
to guarantee the series to have a KMS analytic structure. In the case of power
series we show the connection between the unique (Carlsonian) interpolation of
the coefficients of the series and the Laplace transform of a probability
distribution. Finally, we outline a procedure which allows us to obtain a
numerical approximation of the jump function across the cut starting from a
finite number of power series coefficients. By using the same methodology, the
thermal Green functions at real time can be numerically approximated from the
knowledge of a finite number of noisy Fourier coefficients in the expansion of
the thermal Green functions along the imaginary axis of the complex time plane.
| arxiv topic:math-ph cond-mat.stat-mech math.MP |
arxiv_dataset-70241602.02121 | Accuracy requirements to test the applicability of the random cascade
model to supersonic turbulence
astro-ph.CO astro-ph.GA astro-ph.SR
A model, which is widely used for inertial rang statistics of supersonic
turbulence in the context of molecular clouds and star formation, expresses
(measurable) relative scaling exponents Z_p of two-point velocity statistics as
a function of two parameters, beta and Delta. The model relates them to the
dimension D of the most dissipative structures, D=3-Delta/(1-beta). While this
description has proved most successful for incompressible turbulence
(beta=Delta=2/3, and D=1), its applicability in the highly compressible regime
remains debated. For this regime, theoretical arguments suggest D=2 and
Delta=2/3, or Delta=1. Best estimates based on 3D periodic box simulations of
supersonic isothermal turbulence yield Delta=0.71 and D=1.9, with uncertainty
ranges of Delta in [0.67, 0.78] and D in [2.04,1.60]. With these 5-10\%
uncertainty ranges just marginally including the theoretical values of
Delta=2/3 and D=2, doubts remain whether the model indeed applies and, if it
applies, for what values of beta and Delta. We use a Monte Carlo approach to
mimic actual simulation data and examine what factors are most relevant for the
fit quality. We estimate that 0.1% (0.05%) accurate Z_p, with p=1...5, should
allow for 2% (1%) accurate estimates of beta and Delta in the highly
compressible regime, but not in the mildly compressible regime. We argue that
simulation-based Z_p with such accuracy are within reach of today's computer
resources. If this kind of data does not allow for the expected high quality
fit of beta and Delta, then this may indicate the inapplicability of the model
for the simulation data. In fact, other models than the one we examine here
have been suggested.
| arxiv topic:astro-ph.CO astro-ph.GA astro-ph.SR |
arxiv_dataset-70251602.02221 | Photon-phonon parametric oscillation induced by the quadratic coupling
in an optomechanical resonator
nlin.CD physics.optics quant-ph
A direct photon-phonon parametric effect of the quadratic coupling on the
mean-field dynamics of an optomechanical resonator in the large-scale-movement
regime is found and investigated. Under a weak pumping power, the mechanical
resonator damps to steady state with a nonlinear static response sensitively
modified by the quadratic coupling. When the driving powerincreases beyond the
static energy balance, the steady states lose their stabilities via Hopf
bifurcations and the resonator produces stable self-sustained
oscillation(limit-circle behavior) of discrete energies with step-like
amplitudes due to the parametric effect of the quadratic coupling, which can be
understood roughly by the power balance between gain and loss on the resonator.
A further increase of the pumping power can induce chaotic dynamic of the
resonator via a typical routine of period-doubling bifurcation but which can be
stabilized by the parametric effect through an inversion bifurcation process
back to limit-circle states. The bifurcation-to-inverse-bifurcation transitions
are numerically verified by the maximal Lyapunov exponents of the dynamics and
which indicate an efficient way to suppress the chaotic behavior of the
optomechanical resonator by the quadratic coupling. Furthermore, the parametric
effect of the quadratic coupling on the dynamic transitions of an
optomechanical resonator can be conveniently detected or traced by the output
power spectrum of the cavity field.
| arxiv topic:nlin.CD physics.optics quant-ph |
arxiv_dataset-70261602.02321 | Large-gap quantum spin Hall state in functionalized dumbbell stanene
cond-mat.mtrl-sci
Two-dimensional dumbbell (DB) stanene has been proposed as a promising
candidate material for realizing quantum spin Hall effect (QSHE) by Tang et al
[P. Tang, P. Chen, W. Cao, H. Huang, S. Cahangirov, L. Xian, Y. Xu, S. C.
Zhang, W. Duan, A. Rubio. Phys. Rev. B, 90, 121408 (2014)]. However, the small
bulk-gap limits its possible applications at room temperature. Based on
first-principles calculations, we predict that its band gap can be enhanced to
148 meV under methyl-functionalization, which can be further tuned by applying
lattice strain. The QSHE is confirmed by s-px,y band inversion, topological
invariant Z2 = 1, and helical gapless edge within bulk band gap. Notably, the
characteristic properties of edge states, such as the large Fermi velocity and
Dirac cone, can be modulated by edge modification. The effects of substrates on
topological properties are explored when it is grown on various substrates,
like SiC, h-BN, and Bi2Te3 sheets. These findings provide significant guidance
for future fabrication and realistic applications of QSHE based on stanene in
spintronics.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-70271602.02421 | Super-renormalizable or Finite Lee-Wick Quantum Gravity
hep-th gr-qc hep-ph
We propose a class of multidimensional higher derivative theories of gravity
without extra real degrees of freedom besides the graviton field. The
propagator shows up the usual real graviton pole and extra complex conjugates
poles that do not contribute to the absorptive part of the physical scattering
amplitudes. Indeed, they may consistently be excluded from the asymptotic
observable states of the theory making use of the Lee-Wick and Cutkoski,
Landshoff, Olive and Polkinghorne prescription for the construction of a
unitary S-matrix. Therefore, the spectrum consists on the graviton and short
lived elementary unstable particles that we named "anti-gravitons" because of
their repulsive contribution to the gravitational potential at short distance.
However, another interpretation of the complex conjugate pairs is proposed
based on the Calmet's suggestion, i.e. they could be understood as black hole
precursors long established in the classical theory. Since the theory is CPT
invariant, the complex conjugate of the micro black hole precursor has received
as a white hole precursor consistently with the t'Hooft complementary
principle. It is proved that the quantum theory is super-renormalizable in even
dimension, i.e. only a finite number of divergent diagrams survive, and finite
in odd dimension. Furthermore, turning on a local potential of the Riemann
tensor we can make the theory finite in any dimension. The singularity-free
Newtonian gravitational potential is explicitly computed for a range of higher
derivative theories. Finally, we propose a new super-reneromalizable or finite
Lee-Wick standard model of particle physics.
| arxiv topic:hep-th gr-qc hep-ph |
arxiv_dataset-70281602.02521 | On Boundary Damped Inhomogeneous Timoshenko Beams and Related Problems
math.AP
We consider the model equations for the Timoshenko beam as a first order
system in the framework of evolutionary equations. The focus is on boundary
damping, which is implemented as a dynamic boundary condition. A change of
material laws allows to include a large class of cases of boundary damping. By
choosing a particular material law, it is shown that the first order approach
to Sturm-Liouville problems with boundary damping is also covered.
| arxiv topic:math.AP |
arxiv_dataset-70291602.02621 | Tackling excess noise from bilinear and nonlinear couplings in
gravitational-wave interferometers
astro-ph.IM
We describe a tool we improved to detect excess noise in the gravitational
wave (GW) channel arising from its bilinear or nonlinear coupling with
fluctuations of various components of a GW interferometer and its environment.
We also describe a higher-order statistics tool we developed to characterize
these couplings, e.g., by unraveling the frequencies of the fluctuations
contributing to such noise, and demonstrate its utility by applying it to
understand nonlinear couplings in Advanced LIGO engineering data. Once such
noise is detected, it is highly desirable to remove it or correct for it. Such
action in the past has been shown to improve the sensitivity of the instrument
in searches of astrophysical signals. If this is not possible, then steps must
be taken to mitigate its influence, e.g., by characterizing its effect on
astrophysical searches. We illustrate this through a study of the effect of
transient sine-Gaussian noise artifacts on a compact binary coalescence
template bank.
| arxiv topic:astro-ph.IM |
arxiv_dataset-70301602.02721 | Ground-based Observations of the Solar Sources of Space Weather (Invited
Review)
astro-ph.SR
Monitoring of the Sun and its activity is a task of growing importance in the
frame of space weather research and awareness. Major space weather disturbances
at Earth have their origin in energetic outbursts from the Sun: solar flares,
coronal mass ejections and associated solar energetic particles. In this review
we discuss the importance and complementarity of ground-based and space-based
observations for space weather studies. The main focus is drawn on ground-based
observations in the visible range of the spectrum, in particular in the
diagnostically manifold H$\alpha$ spectral line, which enables us to detect and
study solar flares, filaments, filament eruptions, and Moreton waves. Existing
H$\alpha$ networks such as the GONG and the Global High-Resolution H$\alpha$
Network are discussed. As an example of solar observations from space weather
research to operations, we present the system of real-time detection of
H$\alpha$ flares and filaments established at Kanzelh\"ohe Observatory (KSO;
Austria) in the frame of the ESA Space Situational Awareness programme. During
the evaluation period 7/2013 - 11/2015, KSO provided 3020 hours of real-time
H$\alpha$ observations at the SWE portal. In total, 824 H$\alpha$ flares were
detected and classified by the real-time detection system, including 174 events
of H$\alpha$ importance class 1 and larger. For the total sample of events,
95\% of the automatically determined flare peak times lie within $\pm$5 min of
the values given in the official optical flares reports (by NOAA and KSO), and
76\% of the start times. The heliographic positions determined are better than
$\pm$5$^\circ$. The probability of detection of flares of importance 1 or
larger is 95\%, with a false alarm rate of 16\%. These numbers confirm the high
potential of automatic flare detection and alerting from ground-based
observatories.
| arxiv topic:astro-ph.SR |
arxiv_dataset-70311602.02821 | The Riesz transform of codimension smaller than one and the Wolff energy
math.AP math.CA
Fix $d\geq 2$, and $s\in (d-1,d)$. We characterize the non-negative locally
finite non-atomic Borel measures $\mu$ in $\mathbb{R}^d$ for which the
associated $s$-Riesz transform is bounded in $L^2(\mu)$ in terms of the Wolff
energy. This extends the range of $s$ in which the Mateu-Prat-Verdera
characterization of measures with bounded $s$-Riesz transform is known.
As an application, we give a metric characterization of the removable sets
for locally Lipschitz continuous solutions of the fractional Laplacian operator
$(-\Delta)^{\alpha/2}$, $\alpha\in (1,2)$, in terms of a well-known capacity
from non-linear potential theory. This result contrasts sharply with
removability results for Lipschitz harmonic functions.
| arxiv topic:math.AP math.CA |
arxiv_dataset-70321602.02921 | More on the initial singularity problem in gravity's rainbow cosmology
gr-qc hep-th
Using a one-dimensional minisuperspace model with a dimensionless ratio
$\frac{E}{E_{Pl}}$, we study the initial singularity problem at the quantum
level for the closed rainbow cosmology with a homogeneous, isotropic classical
space-time background. We derive the classical Hamiltonian within the framework
of Schutz's formalism for an ideal fluid with a cosmological constant. We
characterize the behavior of the system at the early stages of the universe
evolution through analyzing the relevant shapes for the potential sector of the
classical Hamiltonian for various matter sources, each separately modified by
two rainbow functions. We show that for both rainbow universe models presented
here, there is the possibility of eliminating the initial singularity by
forming a potential barrier and static universe for a non-zero value of the
scale factor. We investigate their quantum stability and show that for an
energy-dependent space-time geometry with energies comparable with the Planck
energy, the non-zero value of the scale factor may be stable. It is shown that
under certain constraints the rainbow universe model filled with an exotic
matter as a domain wall fluid plus a cosmological constant can result in a
non-singular harmonic universe. In addition, we demonstrate that the
harmonically oscillating universe with respect to the scale factor is sensitive
to $\frac{E}{E_{Pl}}$ and that at high energies it may become stable quantum
mechanically. Through a Schr\"{o}dinger-Wheeler-De Witt (SWD) equation obtained
from the quantization of the classical Hamiltonian, we also extract the wave
packet of the universe with a focus on the early stages of the evolution.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-70331602.03021 | L-mode filament characteristics on MAST as a function of plasma current
measured using visible imaging
physics.plasm-ph
Clear filamentary structures are observed at the edge of tokamak plasmas.
These filaments are ejected out radially and carry plasma in the far Scrape Off
Layer (SOL) region, where they are responsible for producing most of the
transport. A study has been performed of the characteristics of the filaments
observed in L-mode plasma on MAST, using visible imaging. A comparison has then
been made with the observed particle and power profiles obtained at the
divertor as a function of the plasma current. The radial velocity and to a
lesser extent the radial size of the filaments are found to decrease as the
plasma current is increased at constant density and input power. The results
obtained in this paper on the dependence of the average filament dynamics on
plasma current are consistent with the idea that the filaments are responsible
for determining the particle profiles at the divertor.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-70341602.03121 | Probing the sparse tails of redshift distributions with Voronoi
tessellations
astro-ph.CO
We introduce an algorithm to estimate the redshift distribution of a sample
of galaxies selected photometrically given a subsample with measured
spectroscopic redshifts. The approach uses a non-parametric Voronoi
tessellation density estimator to interpolate the galaxy distribution in the
redshift and photometric color space. We test the method on a mock dataset with
a known color-redshift distribution. We find that the Voronoi tessellation
estimator performs well at reconstructing the tails of the redshift
distribution of individual galaxies and gives unbiased estimates of the first
and second moments. The source code is publicly available at
http://bitbucket.org/bengranett/tailz.
| arxiv topic:astro-ph.CO |
arxiv_dataset-70351602.03221 | On Waring's problem for intermediate powers
math.NT
Let $G(k)$ denote the least number $s$ such that every sufficiently large
natural number is the sum of at most $s$ positive integral $k$th powers. We
show that $G(7)\le 31$, $G(8)\le 39$, $G(9)\le 47$, $G(10)\le 55$, $G(11)\le
63$, $G(12)\le 72$, $G(13)\le 81$, $G(14)\le 90$, $G(15)\le 99$, $G(16)\le
108$.
| arxiv topic:math.NT |
arxiv_dataset-70361602.03321 | Optomechanical interactions in non-Hermitian photonic molecules
physics.optics
We study optomechanical interactions in non-Hermitian photonic molecules that
support two photonic states and one acoustic mode. The nonlinear steady-state
solutions and their linear stability landscapes are investigated as a function
of the system's parameters and excitation power levels. We also examine the
temporal evolution of the system and uncover different regimes of nonlinear
dynamics. Our analysis reveals several important results: (1) Parity-time
($\mathcal{PT}$) symmetry is not necessarily the optimum choice for maximum
optomechanical interaction. (2) Stable steady-state solutions are not always
reached under continuous wave (CW) optical excitations. (3) Accounting for gain
saturation effects can regulate the behavior of the otherwise unbounded
oscillation amplitudes. Our study provides a deeper insight into the interplay
between optical non-Hermiticity and optomechanical coupling and can thus pave
the way for new device applications.
| arxiv topic:physics.optics |
arxiv_dataset-70371602.03421 | On the dislocation density tensor in the Cosserat theory of elastic
shells
math.AP
We consider the Cosserat continuum in its finite strain setting and discuss
the dislocation density tensor as a possible alternative curvature strain
measure in three-dimensional Cosserat models and in Cosserat shell models. We
establish a close relationship (one-to-one correspondence) between the new
shell dislocation density tensor and the bending-curvature tensor of
6-parameter shells.
| arxiv topic:math.AP |
arxiv_dataset-70381602.03521 | Tops as Building Blocks for G2 Manifolds
hep-th math.AG
A large number of examples of compact $G_2$ manifolds, relevant to
supersymmetric compactifications of M-Theory to four dimensions, can be
constructed by forming a twisted connected sum of two appropriate building
blocks times a circle. These building blocks, which are appropriate $K3$-fibred
threefolds, are shown to have a natural and elegant construction in terms of
tops, which parallels the construction of Calabi-Yau manifolds via reflexive
polytopes.
| arxiv topic:hep-th math.AG |
arxiv_dataset-70391602.03621 | Towards thermal noise free optomechanics
physics.optics quant-ph
Thermal noise generally greatly exceeds quantum noise in optomechanical
devices unless the mechanical frequency is very high or the thermodynamic
temperature is very low. This paper addresses the design concept for a novel
optomechanical device capable of ultrahigh quality factors in the audio
frequency band with negligible thermal noise. The proposed system consists of a
minimally supported millimeter scale pendulum mounted in a Double End-Mirror
Sloshing (DEMS) cavity that is topologically equivalent to a
Membrane-in-the-Middle (MIM) cavity. The radiation pressure inside the
high-finesse cavity allows for high optical stiffness, cancellation of terms
which lead to unwanted negative damping and suppression of quantum radiation
pressure noise. We solve for the optical spring dynamics of the system using
the Hamiltonian, find the noise spectral density and show that stable optical
trapping is possible. We also assess various loss mechanisms, one of the most
important being the acceleration loss due to the optical spring. We show that
practical devices, starting from a centre-of-mass pendulum frequency of 0.1 Hz,
could achieve a maximum quality factor of $10^{14}$ with optical spring
stiffened frequency 1-10 kHz. Small resonators of mass 1 $\mu$g or less could
achieve a Q-factor of $10^{11}$ at a frequency of 100 kHz. Applications for
such devices include white light cavities for improvement of gravitational wave
detectors, or sensors able to operate near the quantum limit.
| arxiv topic:physics.optics quant-ph |
arxiv_dataset-70401602.03721 | The $\Lambda_2$ limit of massive gravity
hep-th astro-ph.CO gr-qc
Lorentz-invariant massive gravity is usually associated with a strong
coupling scale $\Lambda_3$. By including non-trivial effects from the
Stueckelberg modes, we show that about these vacua, one can push the strong
coupling scale to higher values and evade the linear vDVZ-discontinuity. For
generic parameters of the theory and generic vacua for the Stueckelberg fields,
the $\Lambda_2$-decoupling limit of the theory is well-behaved and free of any
ghost or gradient-like instabilities. We also discuss the implications for
nonlinear sigma models with Lorentzian target spaces.
| arxiv topic:hep-th astro-ph.CO gr-qc |
arxiv_dataset-70411602.03821 | Analysis of Flows Inside Quiescent Prominences as Captured by
Hinode/Solar Optical Telescope
astro-ph.SR physics.flu-dyn physics.plasm-ph
Developing an understanding of how magnetic fields can become entangled in a
prominence is important for predicting a possible eruption. This work
investigates the kinetic energy and vorticity associated with plasma motion
residing inside quiescent prominences (QPs). These plasma flow characteristics
can be utilized to improve our understanding of how the prominence maintains a
stable magnetic field configuration. Three different contrast-enhanced solar
prominence observations from Hinode/Solar Optical Telescope were used to
construct velocity maps -- in the plane of the sky -- via a Fourier local
correlation tracking program. The resulting velocities were then used to
perform the first ever analysis of the two-dimensional kinetic energy and
enstrophy spectra of a prominence. Enstrophy is introduced here as a means of
quantifying the vorticity that has been observed in many QPs. The kinetic
energy power spectral density (PSD) produced indices ranging from -1.00 to
-1.60. There was a consistent anisotropy in the kinetic energy spectrum of all
three prominences examined. Examination of the intensity PSD reveals that a
different scaling relationship exists between the observed prominence structure
and velocity maps. All of the prominences exhibited an inertial range of at
least $0.8 \leq k\leq 2.0\; \textrm{rads} \: \textrm{Mm}^{-1}$. Quasi-periodic
oscillations were also detected in the centroid of the velocity distributions
for one prominence. Additionally, a lower limit was placed on the kinetic
energy density ($\epsilon \, \sim 0.22-7.04\: \mathrm{km}^{2}\textrm{s}^{-2}$)
and enstrophy density ($\omega \, \sim 1.43-13.69\: \times 10^{-16} \,
\textrm{s}^{-2}$) associated with each prominence.
| arxiv topic:astro-ph.SR physics.flu-dyn physics.plasm-ph |
arxiv_dataset-70421602.03921 | Energy density distribution of shaped waves inside scattering media
mapped onto a complete set of diffusion modes
physics.optics cond-mat.dis-nn
We show that the spatial distribution of the energy density of optimally
shaped waves inside a scattering medium can be described by considering only a
few of the lowest eigenfunctions of the diffusion equation. Taking into account
only the fundamental eigenfunction, the total internal energy inside the sample
is underestimated by only 2%. The spatial distribution of the shaped energy
density is very similar to the fundamental eigenfunction, up to a cosine
distance of about 0.01. We obtained the energy density inside a quasi-1D
disordered waveguide by numerical calculation of the joined scattering matrix.
Computing the transmission-averaged energy density over all transmission
channels yields the ensemble averaged energy density of shaped waves. From the
averaged energy density obtained, we reconstruct its spatial distribution using
the eigenfunctions of the diffusion equation. The results from our study have
exciting applications in controlled biomedical imaging, efficient light
harvesting in solar cells, enhanced energy conversion in solid-state lighting,
and low threshold random lasers.
| arxiv topic:physics.optics cond-mat.dis-nn |
arxiv_dataset-70431602.04021 | Scalar field conformally coupled to a charged BTZ black hole
gr-qc
We study the Klein-Gordon equation of a scalar field conformally coupled to a
charged BTZ black hole. The background metric is obtained by coupling a
non-linear and conformal invariant Maxwell field to (2+1) gravity. We show that
the radial part is generally solved by a Heun function and, in the pure gravity
limit, by a hypergeometric function.
| arxiv topic:gr-qc |
arxiv_dataset-70441602.04121 | Justification of the Coupled Mode Asymptotics for Localized Wavepackets
in the Periodic Nonlinear Schr\"odinger Equation
math.AP nlin.PS
We consider wavepackets composed of two modulated carrier Bloch waves with
opposite group velocities in the one dimensional periodic Nonlinear
Schroedinger/Gross-Pitaevskii equation. These can be approximated by first
order coupled mode equations (CMEs) for the two slowly varying envelopes. Under
a suitably selected periodic perturbation of the periodic structure the CMEs
possess a spectral gap of the corresponding spatial operator and allow families
of exponentially localized solitary waves parametrized by velocity. This leads
to a family of approximate solitary waves in the periodic nonlinear
Schroedinger equation. Besides a formal derivation of the CMEs a rigorous
justification of the approximation and an error estimate in the supremum norm
are provided. Several numerical tests corroborate the analysis.
| arxiv topic:math.AP nlin.PS |
arxiv_dataset-70451602.04221 | UV Completions for Non-Critical Strings
hep-th
Compactifications of the physical superstring to two dimensions provide a
general template for realizing 2D conformal field theories coupled to
worldsheet gravity, i.e. non-critical string theories. Motivated by this
observation, in this paper we determine the quasi-topological 8D theory which
governs the vacua of 2D N = (0,2) gauged linear sigma models (GLSMs) obtained
from compactifications of type I and heterotic strings on a Calabi-Yau
fourfold. We also determine the quasi-topological 6D theory governing the 2D
vacua of intersecting 7-branes in compactifications of F-theory on an
elliptically fibered Calabi-Yau fivefold, where matter fields and interaction
terms localize on lower-dimensional subspaces, i.e. defect operators. To cancel
anomalies / cancel tadpoles, these GLSMs must couple to additional chiral
sectors, which in some cases do not admit a known description in terms of a UV
GLSM. Additionally, we find that constructing an anomaly free spectrum can
sometimes break supersymmetry due to spacetime filling anti-branes. We also
study various canonical examples such as the standard embedding of heterotic
strings on a Calabi-Yau fourfold and F-theoretic "rigid clusters" with no local
deformation moduli of the elliptic fibration.
| arxiv topic:hep-th |
arxiv_dataset-70461602.04321 | Silting modules over commutative rings
math.RT math.AC
Tilting modules over commutative rings were recently classified in [12]: they
correspond bijectively to faithful Gabriel topologies of finite type. In this
note we extend this classification by dropping faithfulness. The counterpart of
an arbitrary Gabriel topology of finite type is obtained by replacing tilting
with the more general notion of a silting module.
| arxiv topic:math.RT math.AC |
arxiv_dataset-70471602.04421 | Randomized approximate nearest neighbor search with limited adaptivity
cs.DS
We study the fundamental problem of approximate nearest neighbor search in
$d$-dimensional Hamming space $\{0,1\}^d$. We study the complexity of the
problem in the famous cell-probe model, a classic model for data structures. We
consider algorithms in the cell-probe model with limited adaptivity, where the
algorithm makes $k$ rounds of parallel accesses to the data structure for a
given $k$. For any $k\ge 1$, we give a simple randomized algorithm solving the
approximate nearest neighbor search using $k$ rounds of parallel memory
accesses, with $O(k(\log d)^{1/k})$ accesses in total. We also give a more
sophisticated randomized algorithm using $O(k+(\frac{1}{k}\log d)^{O(1/k)})$
memory accesses in $k$ rounds for large enough $k$. Both algorithms use data
structures of size polynomial in $n$, the number of points in the database.
For the lower bound, we prove an $\Omega(\frac{1}{k}(\log d)^{1/k})$ lower
bound for the total number of memory accesses required by any randomized
algorithm solving the approximate nearest neighbor search within
$k\le\frac{\log\log d}{2\log\log\log d}$ rounds of parallel memory accesses on
any data structures of polynomial size. This lower bound shows that our first
algorithm is asymptotically optimal for any constant round $k$. And our second
algorithm approaches the asymptotically optimal tradeoff between rounds and
memory accesses, in a sense that the lower bound of memory accesses for any
$k_1$ rounds can be matched by the algorithm within $k_2=O(k_1)$ rounds. In the
extreme, for some large enough $k=\Theta\left(\frac{\log\log d}{\log\log\log
d}\right)$, our second algorithm matches the $\Theta\left(\frac{\log\log
d}{\log\log\log d}\right)$ tight bound for fully adaptive algorithms for
approximate nearest neighbor search due to Chakrabarti and Regev.
| arxiv topic:cs.DS |
arxiv_dataset-70481602.04521 | Quasi Linear Codes: Application to Point-to-Point and Multi-Terminal
Source Coding
cs.IT math.IT
A new ensemble of structured codes is introduced. These codes are called
Quasi Linear Codes (QLC). The QLC's are constructed by taking subsets of linear
codes. They have a looser structure compared to linear codes and are not closed
under addition. We argue that these codes provide gains in terms of achievable
Rate-Distortions (RD) in different multi-terminal source coding problems. We
derive the necessary covering bounds for analyzing the performance of QLC's. We
then consider the Multiple-Descriptions (MD) problem, and prove through an
example that the application of QLC's gives an improved achievable RD region
for this problem. Finally, we derive an inner bound to the achievable RD region
for the general MD problem which strictly contains all of the previous known
achievable regions.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-70491602.04621 | Deep Exploration via Bootstrapped DQN
cs.LG cs.AI cs.SY stat.ML
Efficient exploration in complex environments remains a major challenge for
reinforcement learning. We propose bootstrapped DQN, a simple algorithm that
explores in a computationally and statistically efficient manner through use of
randomized value functions. Unlike dithering strategies such as epsilon-greedy
exploration, bootstrapped DQN carries out temporally-extended (or deep)
exploration; this can lead to exponentially faster learning. We demonstrate
these benefits in complex stochastic MDPs and in the large-scale Arcade
Learning Environment. Bootstrapped DQN substantially improves learning times
and performance across most Atari games.
| arxiv topic:cs.LG cs.AI cs.SY stat.ML |
arxiv_dataset-70501602.04721 | Evaluating hospital infection control measures for
antimicrobial-resistant pathogens using stochastic transmission models:
application to Vancomycin-Resistant Enterococci in intensive care units
stat.AP q-bio.PE
Nosocomial pathogens such as Methicillin-Resistant {\em Staphylococcus
aureus} (MRSA) and Vancomycin-resistant {\em Enterococci} (VRE) are the cause
of significant morbidity and mortality among hospital patients. It is important
to be able to assess the efficacy of control measures using data on patient
outcomes. In this paper we describe methods for analysing such data using
patient-level stochastic models which seek to describe the underlying
unobserved process of transmission. The methods are applied to detailed
longitudinal patient-level data on VRE from a study in a US hospital with eight
intensive care units (ICUs). The data comprise admission and discharge dates,
dates and results of screening tests, and dates during which precautionary
measures were in place for each patient during the study period. Results
include estimates of the efficacy of the control measures, the proportion of
unobserved patients colonized with VRE and the proportion of patients colonized
on admission.
| arxiv topic:stat.AP q-bio.PE |
arxiv_dataset-70511602.04821 | Baryon number violation in supersymmetry: Neutron-antineutron
oscillations as a probe beyond the LHC
hep-ph hep-ex
We summarize the current status of baryon number violation in supersymmetry
and provide prospects for going beyond the present reach by means of a new
search for neutron-antineutron oscillations. The main motivation is the
recently proposed neutron-antineutron oscillation experiment at the European
Spallation Source in Lund, Sweden, which is projected to be able to improve the
current bound on the transition probability in the quasi-free regime by three
orders of magnitude. We consider various processes involving superpartners that
give rise to neutron-antineutron oscillations and extract the corresponding
simplified models, including only the most relevant superpartners and
couplings. In terms of these models we recast and determine the exclusion
limits from LHC searches as well as from searches for flavor transitions, CP
violation and di-nucleon decays. We find that, for certain regions of the
parameter space, the proposed neutron-antineutron experiment has a reach that
goes beyond all other experiments, as it can probe gluino and squark masses in
the multi-TeV range.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-70521602.04921 | A diffusion and clustering-based approach for finding coherent motions
and understanding crowd scenes
cs.CV cs.AI cs.MM
This paper addresses the problem of detecting coherent motions in crowd
scenes and presents its two applications in crowd scene understanding: semantic
region detection and recurrent activity mining. It processes input motion
fields (e.g., optical flow fields) and produces a coherent motion filed, named
as thermal energy field. The thermal energy field is able to capture both
motion correlation among particles and the motion trends of individual
particles which are helpful to discover coherency among them. We further
introduce a two-step clustering process to construct stable semantic regions
from the extracted time-varying coherent motions. These semantic regions can be
used to recognize pre-defined activities in crowd scenes. Finally, we introduce
a cluster-and-merge process which automatically discovers recurrent activities
in crowd scenes by clustering and merging the extracted coherent motions.
Experiments on various videos demonstrate the effectiveness of our approach.
| arxiv topic:cs.CV cs.AI cs.MM |
arxiv_dataset-70531602.05021 | Technology for the next gravitational wave detectors
astro-ph.IM physics.ins-det physics.optics
This paper reviews some of the key enabling technologies for advanced and
future laser interferometer gravitational wave detectors, which must combine
test masses with the lowest possible optical and acoustic losses, with high
stability lasers and various techniques for suppressing noise. Sect. 1 of this
paper presents a review of the acoustic properties of test masses. Sect. 2
reviews the technology of the amorphous dielectric coatings which are currently
universally used for the mirrors in advanced laser interferometers, but for
which lower acoustic loss would be very advantageous. In sect. 3 a new
generation of crystalline optical coatings that offer a substantial reduction
in thermal noise is reviewed. The optical properties of test masses are
reviewed in sect. 4, with special focus on the properties of silicon, an
important candidate material for future detectors. Sect. 5 of this paper
presents the very low noise, high stability laser technology that underpins all
advanced and next generation laser interferometers.
| arxiv topic:astro-ph.IM physics.ins-det physics.optics |
arxiv_dataset-70541602.05121 | Fragile singlet ground state magnetism in pyrochlore osmates R2Os2O7
(R=Y and Ho)
cond-mat.str-el cond-mat.mtrl-sci
The singlet ground state magnetism in pyrochlore osmates Y$_2$Os$_2$O$_7$ and
Ho$_2$Os$_2$O$_7$ is studied by DC and AC susceptibility, specific heat, and
neutron powder diffraction measurements. Despite the expected non-magnetic
singlet in the strong spin-orbit coupling (SOC) limit for Os$^{4+}$ ($5d^4$),
Y$_2$Os$_2$O$_7$ exhibits a spin-glass (SG) ground state below 4 K with weak
magnetism, suggesting possible proximity to a quantum phase transition between
the non-magnetic state in the strong SOC limit and the magnetic state in the
strong superexchange limit. Ho$_2$Os$_2$O$_7$ has the same structural
distortion as occurs in Y$_2$Os$_2$O$_7$. However, the Os sublattice in
Ho$_2$Os$_2$O$_7$ shows long-range magnetic ordering below 36\,K. The sharp
difference of the magnetic ground state between Y$_2$Os$_2$O$_7$ and
Ho$_2$Os$_2$O$_7$ signals the singlet ground state magnetism in
$R_2$Os$_2$O$_7$ is fragile and can be disturbed by the weak $4f-5d$
interactions.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-70551602.05221 | Patterns of Scalable Bayesian Inference
stat.ML
Datasets are growing not just in size but in complexity, creating a demand
for rich models and quantification of uncertainty. Bayesian methods are an
excellent fit for this demand, but scaling Bayesian inference is a challenge.
In response to this challenge, there has been considerable recent work based on
varying assumptions about model structure, underlying computational resources,
and the importance of asymptotic correctness. As a result, there is a zoo of
ideas with few clear overarching principles.
In this paper, we seek to identify unifying principles, patterns, and
intuitions for scaling Bayesian inference. We review existing work on utilizing
modern computing resources with both MCMC and variational approximation
techniques. From this taxonomy of ideas, we characterize the general principles
that have proven successful for designing scalable inference procedures and
comment on the path forward.
| arxiv topic:stat.ML |
arxiv_dataset-70561602.05321 | The G-JF Thermostat for Accurate Configurational Sampling in Soft-Matter
Simulations
physics.comp-ph cond-mat.soft cond-mat.stat-mech
We implement the statistically sound G-JF thermostat for Langevin Dynamics
simulations into the ESPREesSo molecular package for large-scale simulations of
soft matter systems. The implemented integration method is tested against the
integrator currently used by the molecular package in simulations of a fluid
bilayer membrane. While the latter exhibits deviations in the sampling
statistics that increase with the integration time step dt, the former
reproduces near-correct configurational statistics for all dt within the
stability range of the simulations. We conclude that, with very modest
revisions to existing codes, one can significantly improve the performance of
statistical sampling using Langevin thermostats.
| arxiv topic:physics.comp-ph cond-mat.soft cond-mat.stat-mech |
arxiv_dataset-70571602.05421 | $\mu$MECH Micromechanics Library
physics.comp-ph cond-mat.mtrl-sci
The paper presents the project of an open source C/C++ library of analytical
solutions to micromechanical fields within media with ellipsoidal
heterogeneities. The solutions are based on Eshelby's stress-free, in general
polynomial, eigenstrains and equivalent inclusion method. To some extent, the
interactions among inclusions in a non-dilute medium are taken into account by
means of the self-compatibility algorithm. Moreover, the library is furnished
with a powerful I/O interface and conventional homogenization tools. Advantages
and limitations of the implemented strategies are addressed through comparisons
with reference solutions by means of the Finite Element Method.
| arxiv topic:physics.comp-ph cond-mat.mtrl-sci |
arxiv_dataset-70581602.05521 | Joint Transmit and Receive Beamforming for Multi-Relay MIMO-OFDMA
Cellular Networks
cs.IT math.IT
A novel transmission protocol is conceived for a multi-user, multi-relay,
multiple-input--multiple-output orthogonal frequency-division multiple-access
(MIMO-OFDMA) cellular network based on joint transmit and receive beamforming.
More specifically, the network's MIMO channels are mathematically decomposed
into several effective multiple-input--single-output (MISO) channels, which are
spatially multiplexed for transmission. For the sake of improving the
attainable capacity, these MISO channels are grouped using a pair of novel
grouping algorithms, which are then evaluated in terms of their performance
versus complexity trade-off\footnote{This paper concisely focuses on the
transmission protocol proposed in our previous work [1]. For more details,
please refer to [1].}.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-70591602.05621 | Universal N\'eron models for curves with marked points
math.AG
We consider the problem of constructing universal N\'eron models for families
of curves with sections. By applying a construction of the author of universal
compactified Jacobians over the moduli stack of reduced curves with markings
and a result by J. Kass, we get a positive answer for smooth families of curves
with planar singularities over Dedekind schemes.
| arxiv topic:math.AG |
arxiv_dataset-70601602.05721 | Restricted deterministic Watson-Crick automata
cs.FL
In this paper, we introduce a new model of deterministic Watson-Crick
automaton namely restricted deterministic Watson- Crick automaton which is a
deterministic Watson-Crick automaton where the complementarity string in the
lower strand is restricted to a language L. We examine the computational power
of the restricted model with respect to L being in different language classes
such as regular, unary regular, finite, context free and context sensitive. We
also show that computational power of restricted deterministic Watson- Crick
automata with L in regular languages is same as that of deterministic
Watson-Crick automata and that the set of all languages accepted by restricted
deterministic Watson-Crick automata with L in unary regular languages is a
proper subset of context free languages.
| arxiv topic:cs.FL |
arxiv_dataset-70611602.05821 | A dichotomy of self-conformal subsets of the real line with overlaps
math.DS math.MG
We show that self-conformal subsets of $\mathbb{R}$ that do not satisfy the
weak separation condition have full Assouad dimension. Combining this with a
recent results by K\"aenm\"aki and Rossi we conclude that an interesting
dichotomy applies to self-conformal and not just self-similar sets: if
$F\subset\mathbb{R}$ is self-conformal with Hausdorff dimension strictly less
than $1$, either the Hausdorff dimension and Assouad dimension agree or the
Assouad dimension is $1$. We conclude that the weak separation property is in
this case equivalent to Assouad and Hausdorff dimension coinciding. (This
manuscript contains errors, see comment below.)
| arxiv topic:math.DS math.MG |
arxiv_dataset-70621602.05921 | Multiscale Modeling of the effect of Pressure on the Interfacial Tension
and other Cohesion Parameters in Binary Mixtures
physics.chem-ph cond-mat.soft
We study and predict the interfacial tension, solubility parameters and
Flory-Huggins parameters of binary mixtures as functions of pressure and
temperature, using multiscale numerical simulation. A mesoscopic approach is
proposed for simulating the pressure dependence of the interfacial tension for
binary mixtures, at different temperatures, using classical Dissipative
Particle Dynamics (DPD). The thermodynamic properties of real systems are
reproduced via the parametrization of the repulsive interaction parameters as
functions of pressure and temperature via Molecular Dynamics simulations. Using
this methodology, we calculate and analyze the cohesive density energy and the
solubility parameters of different species obtaining excellent agreement with
reported experimental behavior. The pressure- and temperature-dependent
Flory-Huggins and repulsive DPD interaction parameters for binary mixtures are
also obtained and validated against experimental data. This multiscale
methodology offers the benefit of being applicable for any species and under
difficult or non-feasible experimental conditions, at a relatively low
computational cost.
| arxiv topic:physics.chem-ph cond-mat.soft |
arxiv_dataset-70631602.06021 | The stability of 3 transmembrane and 4 transmembrane human vitamin K
epoxide reductase models
q-bio.BM
3 transmembrane and 4 transmembrane helices models are suggested for the
human vitamin K epoxide reductase (VKOR). In this study, we investigate the
stability of the human 3 transmembrane/4 transmembrane VKOR models employing a
coarse-grained normal mode analysis and molecular dynamics simulation. Based on
the analysis of the mobility of each transmembrane domain, we suggest that the
3 transmembrane human VKOR model is more stable than the 4 transmembrane human
VKOR model.
| arxiv topic:q-bio.BM |
arxiv_dataset-70641602.06121 | Asymptotic Analysis of a Viscous Fluid in a Curved Pipe with Elastic
Walls
math.AP
This communication is devoted to the presentation of our recent results
regarding the asymptotic analysis of a viscous flow in a tube with elastic
walls. This study can be applied, for example, to the blood flow in an artery.
With this aim, we consider the dynamic problem of the incompressible flow of a
viscous fluid through a curved pipe with a smooth central curve. Our analysis
leads to obtain an one dimensional model via singular perturbation of the
Navier-Stokes system as $\varepsilon$, a non dimensional parameter related to
the radius of cross-section of the tube, tends to zero. We allow the radius
depend on tangential direction and time, so a coupling with an elastic or
viscoelastic law on the wall of the pipe is possible.
To perform the asymptotic analysis, we do a change of variable to a reference
domain where we assume the existence of asymptotic expansions on $\varepsilon$
for both velocity and pressure which, upon substitution on Navier-Stokes
equations, leads to the characterization of various terms of the expansion.
This allows us to obtain an approximation of the solution of the Navier-Stokes
equations.
| arxiv topic:math.AP |
arxiv_dataset-70651602.06221 | Endofunctors modelling higher-order behaviours
cs.LO
In this paper we show how the abstract behaviours of higher-order systems can
be modelled as final coalgebras of suitable behavioural functors. These
functors have the challenging peculiarity to be circularly defined with their
own final coalgebra. Our main contribution is a general construction for
defining these functors, solving this circularity which is the essence of
higher-order behaviours. This characterisation is syntax agnostic. To achieve
this property, we shift from term passing to behaviour passing: in the former
higher-order is expressed by passing around syntactic objects (such as terms or
processes) as representations of behaviours whereas the former ditches the
syntactic encoding altogether and works directly with behaviours i.e. semantic
objects. From this perspective, the former can be seen as syntactic
higher-order whereas the later as semantic higher-order.
| arxiv topic:cs.LO |
arxiv_dataset-70661602.06321 | The First Detection of Photometric Variability in a Y Dwarf: WISE
J140518.39+553421.3
astro-ph.SR
We present the first detection of photometric variability of a
spectroscopically-confirmed Y dwarf. The Infrared Array Camera on board the
Spitzer Space Telescope was used to obtain times series photometry at 3.6 and
4.5 microns over a twenty four hour period at two different epochs separated by
149 days. Variability is evident at 4.5 um in the first epoch and at 3.6 and
4.5 um in the second epoch which suggests that the underlying cause or causes
of this variability change on the timescales of months. The second-epoch [3.6]
and [4.5] light curves are nearly sinusoidal in form, in phase, have periods of
roughly 8.5 hours, and have semi-amplitudes of 3.5%. We find that a simple
geometric spot model with a single bright spot reproduces these observations
well. We also compare our measured semi-amplitudes of the second epoch light
curves to predictions of the static, one-dimensional, partly cloudy and hot
spot models of Morley and collaborators and find that neither set of models can
reproduce the observed [3.6] and[4.5] semi-amplitudes simultaneously. More
advanced two- or three-dimensional models that include time-dependent phenomena
like vertical mixing, cloud formation, and thermal relaxation are therefore
sorely needed in order to properly interpret our observations.
| arxiv topic:astro-ph.SR |
arxiv_dataset-70671602.06421 | Localizations of inductively factored arrangements
math.CO
We show that the class of inductively factored arrangements is closed under
taking localizations. We illustrate the usefulness of this with an application.
| arxiv topic:math.CO |
arxiv_dataset-70681602.06521 | Light-Front Dynamics and the 3He Spectral Function
nucl-th
Two topics are presented. The first one is a novel approach for a Poincare'
covariant description of nuclear dynamics based on light-front Hamiltonian
dynamics. The key quantity is the light-front spectral function, where both
normalization and momentum sum rule can be satisfied at the same time.
Preliminary results are discussed for an initial analysis of the role of
relativity in the EMC effect in 3He. A second issue, very challenging, is
considered in a non-relativistic framework, namely a distorted spin-dependent
spectral function for 3He in order to take care of the final state interaction
between the observed pion and the remnant in semi-inclusive deep inelastic
electron scattering off polarized 3He. The generalization of the analysis
within the light-front dynamics is outlined.
| arxiv topic:nucl-th |
arxiv_dataset-70691602.06621 | Stochastic Matrix-Free Equilibration
math.OC
We present a novel method for approximately equilibrating a matrix $A \in
{\bf R}^{m \times n}$ using only multiplication by $A$ and $A^T$. Our method is
based on convex optimization and projected stochastic gradient descent, using
an unbiased estimate of a gradient obtained by a randomized method. Our method
provably converges in expectation with an $O(1/t)$ convergence rate and
empirically gets good results with a small number of iterations. We show how
the method can be applied as a preconditioner for matrix-free iterative
algorithms such as LSQR and Chambolle-Cremers-Pock, substantially reducing the
iterations required to reach a given level of precision. We also derive a novel
connection between equilibration and condition number, showing that
equilibration minimizes an upper bound on the condition number over all choices
of row and column scalings.
| arxiv topic:math.OC |
arxiv_dataset-70701602.06721 | Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure
cond-mat.mtrl-sci
The pressure evolution of the local structure of Fe2O3 hematite has been
determined for the first time by extended x-ray absorption fine structure up to
79 GPa. The comparison to the different high-pressure forms proposed in the
literature suggests that the orthorhombic structure with space group Aba2 is
the most probable. The crossover from Fe high-spin to low-spin states with
pressure increase has been monitored from the pre-edge region of the Fe K-edge
absorption spectra. The "simultaneous" comparison with the local structural
changes allows us to definitively conclude that it is the electronic transition
that drives the structural transition and not viceversa.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-70711602.06821 | Na\"ive Physics and Quantum Mechanics: The Cognitive Bias of Everett's
Many-Worlds Interpretation
quant-ph physics.hist-ph
We discuss the role that intuitive theories of physics play in the
interpretation of quantum mechanics. We compare and contrast na\"ive physics
with quantum mechanics and argue that quantum mechanics is not just hard to
understand but that it is difficult to believe, often appearing magical in
nature. Quantum mechanics is often discussed in the context of "quantum
weirdness" and quantum entanglement is known as "spooky action at a distance."
This spookiness is more than just because quantum mechanics doesn't match
everyday experience; it ruffles the feathers of our na\"ive physics cognitive
module. In Everett's many-worlds interpretation of quantum mechanics, we
preserve a form of deterministic thinking that can alleviate some of the
perceived weirdness inherent in other interpretations of quantum mechanics, at
the cost of having the universe split into parallel worlds at every quantum
measurement. By examining the role cognitive modules play in interpreting
quantum mechanics, we conclude that the many-worlds interpretation of quantum
mechanics involves a cognitive bias not seen in the Copenhagen interpretation.
| arxiv topic:quant-ph physics.hist-ph |
arxiv_dataset-70721602.06921 | Differential Borel equivariant cohomology via connections
math.AT math.DG
For a compact Lie group acting on a smooth manifold, we define the
differential cohomology of a certain quotient stack involving principal bundles
with connection. This produces differential equivariant cohomology groups that
map to the Cartan-Weil equivariant forms and to Borel's equivariant integral
cohomology. We show the Chern-Weil homomorphism for equivariant vector bundles
with connection naturally factors through differential equivariant cohomology.
| arxiv topic:math.AT math.DG |
arxiv_dataset-70731602.07021 | Computing Jacobi Forms
math.NT
We describe an implementation for computing holomorphic and skew-holomorphic
Jacobi forms of integral weight and scalar index on the full modular group.
This implementation is based on formulas derived by one of the authors which
express Jacobi forms in terms of modular symbols of elliptic modular forms.
Since this method allows to generate a Jacobi eigenform directly from a given
modular eigensymbol without reference to the whole ambient space of Jacobi
forms it makes it possible to compute Jacobi Hecke eigenforms of large index.
We illustrate our method with several examples.
| arxiv topic:math.NT |
arxiv_dataset-70741602.07121 | Abundances and kinematics for ten anticentre open clusters
astro-ph.GA
Open clusters are distributed all across the disk and are convenient tracers
of its properties. In particular, outer disk clusters bear a key role for the
investigation of the chemical evolution of the Galactic disk. The goal of this
study is to derive homogeneous elemental abundances for a sample of ten outer
disk OCs, and investigate possible links with disk structures such as the
Galactic Anticenter Stellar Structure. We analyse high-resolution spectra of
red giants, obtained from the HIRES@Keck and UVES@VLT archives. We derive
elemental abundances and stellar atmosphere parameters by means of the
classical equivalent width method. We also performed orbit integrations using
proper motions. The Fe abundances we derive trace a shallow negative radial
metallicity gradient of slope -0.027+/-0.007 dex.kpc-1 in the outer 12 kpc of
the disk. The [alpha/Fe] gradient appears flat, with a slope of 0.006+/-0.007
dex.kpc-1 . The two outermost clusters (Be 29 and Sau 1) appear to follow
elliptical orbits. Be 20 also exhibits a peculiar orbit with a large excursion
above the plane. The irregular orbits of the three most metal-poor clusters (of
which two are located at the edge of the Galactic disk), if confirmed by more
robust astrometric measurements such as those of the Gaia mission, are
compatible with an inside-out formation scenario for the Milky Way, in which
extragalactic material is accreted onto the outer disk. We cannot determine if
Be 20, Be 29,and Sau 1 are of extragalactic origin, as they may be old genuine
Galactic clusters whose orbits were perturbed by accretion events or minor
mergers in the past 5 Gyr, or they may be representants of the thick disk
population. The nature of these objects is intriguing and deserves further
investigations in the near future.
| arxiv topic:astro-ph.GA |
arxiv_dataset-70751602.07221 | Isomonodromic deformations and SU2-invariant instantons on S4
math-ph math.MP
Anti-self-dual (ASD) solutions to the Yang-Mills equation (or instantons)
over an anti-self-dual four manifold, which are invariant under an appropriate
action of a three dimensional Lie group, give rise, via twistor construction,
to isomonodromic deformations of connections on C P 1 having four simple
singularities. As is well known this kind of deformations is governed by the
sixth Painlev\'e equation P vi ({\alpha}, \b{eta}, {\gamma}, {\delta}) . We
work out the particular case of the SU 2 -action on S 4 , obtained from the
irreducible representation on R 5 . In particular, we express the pa- rameters
({\alpha}, \b{eta}, {\gamma}, {\delta}) in terms of the instanton number. The
present paper contains the proof of the result anounced in [16].
| arxiv topic:math-ph math.MP |
arxiv_dataset-70761602.07321 | Global well-posedness of the Euler-Korteweg system for small
irrotational data
math.AP
The Euler-Korteweg equations are a modification of the Euler equations that
takes into account capillary effects. In the general case they form a
quasi-linear system that can be recast as a degenerate Schr\"odinger type
equation. Local well-posedness (in subcritical Sobolev spaces) was obtained by
Benzoni-Danchin-Descombes in any space dimension, however, except in some
special case (semi-linear with particular pressure) no global well-posedness is
known. We prove here that under a natural stability condition on the pressure,
global well-posedness holds in dimension $d\geq 3$ for small irrotational
initial data. The proof is based on a modified energy estimate, standard
dispersive properties if $d\geq 5$, and a careful study of the nonlinear
structure of the quadratic terms in dimension $3$ and $4$ involving the theory
of space time resonance.
| arxiv topic:math.AP |
arxiv_dataset-70771602.07421 | Exchange stiffness in ultrathin perpendicularly-magnetized CoFeB layers
determined using spin wave spectroscopy
cond-mat.str-el cond-mat.mes-hall
We measure the frequencies of spin waves in nm-thick perpendicularly
magnetized FeCoB systems, and model the frequencies to deduce the exchange
stiffness of this material in the ultrathin limit. For this, we embody the
layers in magnetic tunnel junctions patterned into circular nanopillars of
diameters ranging from 100 to 300 nm and we use magneto-resistance to determine
which rf-current frequencies are efficient in populating the spin wave modes.
Micromagnetic calculations indicate that the ultrathin nature of the layer and
the large wave vectors used ensure that the spin wave frequencies are
predominantly determined by the exchange stiffness, such that the number of
modes in a given frequency window can be used to estimate the exchange. For 1
nm layers the experimental data are consistent with an exchange stiffness A= 20
pJ/m, which is slightly lower that its bulk counterpart. The thickness
dependence of the exchange stiffness has strong implications for the numerous
situations that involve ultrathin films hosting strong magnetization gradients,
and the micromagnetic description thereof.
| arxiv topic:cond-mat.str-el cond-mat.mes-hall |
arxiv_dataset-70781602.07521 | On the significance of asperity models predictions of rough contact with
respect to recent alternative theories
cond-mat.mtrl-sci
Recently, it has been shown that while asperity models show correctly
qualitative features of rough contact problems (linearity in area-load,
negative exponential dependence of load on separation which means also
linearity of stiffness with load), the exact value of the coefficients are not
precise for the idealized case of Gaussian distribution of heigths. This is due
to the intrinsic simplifications, neglecting asperity coalescence and
interaction effects. However, the issue of Gaussianity has not been proved or
experimentally verified in many cases, and here we show that, for example,
assuming a Weibull distribution of asperity heigths, the area-load linear
coefficient is not much affected, while the relationships load-separation and
therefore also stiffness-load do change largely, particularly when considering
bounded distributions of asperity heigths. It is suggested that Gaussianity of
surfaces should be further tested in experiments, before applying the most
sophisticated rough contact models based on the Gaussian assumption.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-70791602.07621 | Investigation of $B\bar B$ four-quark systems using lattice QCD
hep-lat hep-ex hep-ph
We investigate $B \bar B$ systems by computing potentials of two static
quarks in the presence of two quarks of finite mass using lattice QCD. By
solving the Schr\"odinger equation we check whether these potentials are
sufficiently attractive to host bound states. Particular focus is put on the
experimentally most promising bottomonium-like tetraquark candidate $Z_b^\pm$
with quantum numbers $I(J^P)=1(1^+)$.
| arxiv topic:hep-lat hep-ex hep-ph |
arxiv_dataset-70801602.07721 | Toward Game Level Generation from Gameplay Videos
cs.AI
Algorithms that generate computer game content require game design knowledge.
We present an approach to automatically learn game design knowledge for level
design from gameplay videos. We further demonstrate how the acquired design
knowledge can be used to generate sections of game levels. Our approach
involves parsing video of people playing a game to detect the appearance of
patterns of sprites and utilizing machine learning to build a probabilistic
model of sprite placement. We show how rich game design information can be
automatically parsed from gameplay videos and represented as a set of
generative probabilistic models. We use Super Mario Bros. as a proof of
concept. We evaluate our approach on a measure of playability and stylistic
similarity to the original levels as represented in the gameplay videos.
| arxiv topic:cs.AI |
arxiv_dataset-70811602.07821 | Radially excited axial mesons and the enigmatic $Z_c$ and $Z_b$ in a
coupled-channel model
hep-ph
The enigmatic charged states $Z_c(3900)$, $Z_c(4020)$, $Z_c(4050)$,
$Z_b(10610)$, and $Z_b(10650)$ are studied within a coupled-channel
Schr\"odinger model, where radially excited quark-antiquark pairs, with the
same angular momenta and isospin as the $a_1(1260)$ and $b_1(1235)$, are
strongly coupled to their Okubo-Zweig-Iizuka - allowed decay channels
$D\bar{D}^*+\bar{D}D^*$ and $D^*\bar{D}^*$, or $B\bar{B}^*+\bar{B}B^*$ and
$B^*\bar{B}^*$, in $S$ and $D$-wave. Poles, matching the experimental mass and
width of all the above states, are found by varying only two free parameters.
From the wave-function analysis of each resonance, the probability of each of
the components contributing to the coupled system is estimated, and predictions
can be made for the relative decay fractions among the coupled open-charm or
open-bottom decay channels.
| arxiv topic:hep-ph |
arxiv_dataset-70821602.07921 | Inhomogenous Multispecies TASEP on a ring with spectral parameters
math-ph math.MP
We study an inhomogenous multispecies version of the Totally Asymmetric
Simple Exclusion Process (TASEP) on a periodic oriented one dimensional
lattice, which depends on two sets of parameters $({\bf \tau},{\bf \nu})$,
attached to the particles. After discussing the Yang-Baxter integrability of
our model, we study its (unnormalized) stationary measure. Motivated by the
integrability of the model we introduce a further set of spectral parameters
${\bf z}$, attached to the sites of the lattice, and we uncover a remarkable
underlying algebraic structure. We provide exact formulas for the stationary
measure and prove the factorization of the stationary probability of certain
configurations in terms of double Schubert polynomials in $({\bf \tau},{\bf
\nu})$.
| arxiv topic:math-ph math.MP |
arxiv_dataset-70831602.08021 | Stochastic forward-backward and primal-dual approximation algorithms
with application to online image restoration
math.OC
Stochastic approximation techniques have been used in various contexts in
data science. We propose a stochastic version of the forward-backward algorithm
for minimizing the sum of two convex functions, one of which is not necessarily
smooth. Our framework can handle stochastic approximations of the gradient of
the smooth function and allows for stochastic errors in the evaluation of the
proximity operator of the nonsmooth function. The almost sure convergence of
the iterates generated by the algorithm to a minimizer is established under
relatively mild assumptions. We also propose a stochastic version of a popular
primal-dual proximal splitting algorithm, establish its convergence, and apply
it to an online image restoration problem.
| arxiv topic:math.OC |
arxiv_dataset-70841602.08121 | Dark matter component decaying after recombination: lensing constraints
with Planck data
astro-ph.CO hep-ph
It has been recently suggested~\cite{Berezhiani:2015yta} that emerging
tension between cosmological parameter values derived in high-redshift (CMB
anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can
be reconciled in a model which contains subdominant fraction of dark matter
decaying after recombination. We check the model against the CMB Planck data.
We find that lensing of the CMB anisotropies by the large-scale structure gives
strong extra constraints on this model, limiting the fraction as $F<8\%$ at
2\,$\sigma$ confidence level. However, investigating the combined data set of
CMB and conflicting low-$z$ measurements, we obtain that the model with
$F\approx2\!-\!5$\% exhibits better fit (by 1.5-3\,$\sigma$ depending on the
lensing priors) compared to that of the concordance $\Lambda$CDM cosmological
model.
| arxiv topic:astro-ph.CO hep-ph |
arxiv_dataset-70851602.08221 | Symplectic Parabolicity and L^2 Symplectic Harmonic Forms
math.SG
In this paper, we study the symplectic cohomologies and symplectic harmonic
forms which introduced by Tseng and Yau. Based on this, we get if
$(M^{2n},\omega)$ is a compact symplectic parabolic manifold which satisfies
the hard Lefschetz property, then its Euler number satisfies the inequality
$(-1)^n\chi(M)\geq 0$.
| arxiv topic:math.SG |
arxiv_dataset-70861602.08321 | The Virtues of Conflict: Analyzing Modern Concurrency
cs.SE
Modern shared memory multiprocessors permit reordering of memory operations
for performance reasons. These reorderings are often a source of subtle bugs in
programs written for such architectures. Traditional approaches to verify weak
memory programs often rely on interleaving semantics, which is prone to state
space explosion, and thus severely limits the scalability of the analysis. In
recent times, there has been a renewed interest in modelling dynamic executions
of weak memory programs using partial orders. However, such an approach
typically requires ad-hoc mechanisms to correctly capture the data and
control-flow choices/conflicts present in real-world programs. In this work, we
propose a novel, conflict-aware, composable, truly concurrent semantics for
programs written using C/C++ for modern weak memory architectures. We exploit
our symbolic semantics based on general event structures to build an efficient
decision procedure that detects assertion violations in bounded multi-threaded
programs. Using a large, representative set of benchmarks, we show that our
conflict-aware semantics outperforms the state-of-the-art partial-order based
approaches.
| arxiv topic:cs.SE |
arxiv_dataset-70871602.08421 | $\chi^{\vphantom\dagger}_{c0}(3915)$ As the Lightest $c\bar c s \bar s$
State
hep-ph nucl-th
The state $\chi^{\vphantom\dagger}_{c0}(3915)$ has recently been demoted by
the Particle Data Group from its previous status as the conventional $c\bar c$
$2 {}^3P_0$ state, largely due to the absence of expected $D\bar D$ decays. We
propose that $\chi^{\vphantom\dagger}_{c0}(3915)$ is actually the lightest
$c\bar c s \bar s$ state, and calculate the spectrum of such states using the
diquark model, identifying many of the observed charmoniumlike states that lack
open-charm decay modes as $c\bar c s \bar s$. Among other results, we argue
that $Y(4140)$ is a $J^{PC} = 1^{++}$ $c\bar c s \bar s$ state that has been
not been seen in two-photon fusion largely as a consequence of the Landau-Yang
theorem.
| arxiv topic:hep-ph nucl-th |
arxiv_dataset-70881602.08521 | Theoretical Properties and Practical Performance of Fully Robust
One-Sided Cross-Validation
stat.ME
Fully robust OSCV is a modification of the OSCV method that produces
consistent bandwidth in the cases of smooth and nonsmooth regression functions.
The current implementation of the method uses the kernel $H_I$ that is almost
indistinguishable from the Gaussian kernel on the interval $[-4,4]$, but has
negative tails. The theoretical properties and practical performances of the
$H_I$- and $\phi$-based OSCV versions are compared. The kernel $H_I$ tends to
produce too low bandwidths in the smooth case. The $H_I$-based OSCV curves are
shown to have wiggles appearing in the neighborhood of zero. The kernel $H_I$
uncovers sensitivity of the OSCV method to a tiny modification of the kernel
used for the cross-validation purposes. The recently found robust bimodal
kernels tend to produce OSCV curves with multiple local minima. The problem of
finding a robust unimodal nonnegative kernel remains open.
| arxiv topic:stat.ME |
arxiv_dataset-70891602.08621 | Self-referenced characterization of space-time couplings in near
single-cycle laser pulses
physics.optics
We report on the characterization of space-time couplings in high energy
sub-2-cycle 770nm laser pulses using a self-referencing single-shot method.
Using spatially-encoded arrangement filter-based spectral phase interferometry
for direct electric field reconstruction (SEA-F-SPIDER) we characterize
few-cycle pulses with a wave-front rotation of 2.8x?10^11 rev/sec (1.38 mrad
per half-cycle) and pulses with pulse front tilts ranging from to -0.33 fs/um
to -3.03 fs/um.
| arxiv topic:physics.optics |
arxiv_dataset-70901602.08721 | Flexible Caching in Trie Joins
cs.DB
Traditional algorithms for multiway join computation are based on rewriting
the order of joins and combining results of intermediate subqueries. Recently,
several approaches have been proposed for algorithms that are "worst-case
optimal" wherein all relations are scanned simultaneously. An example is
Veldhuizen's Leapfrog Trie Join (LFTJ). An important advantage of LFTJ is its
small memory footprint, due to the fact that intermediate results are full
tuples that can be dumped immediately. However, since the algorithm does not
store intermediate results, recurring joins must be reconstructed from the
source relations, resulting in excessive memory traffic. In this paper, we
address this problem by incorporating caches into LFTJ. We do so by adopting
recent developments on join optimization, tying variable ordering to tree
decomposition. While the traditional usage of tree decomposition computes the
result for each bag in advance, our proposed approach incorporates caching
directly into LFTJ and can dynamically adjust the size of the cache.
Consequently, our solution balances memory usage and repeated computation, as
confirmed by our experiments over SNAP datasets.
| arxiv topic:cs.DB |
arxiv_dataset-70911602.08821 | Lagrangian isotopy of tori in $S^2 \times S^2$ and $\mathbb{C}P^2$
math.SG
We show that, up to Lagrangian isotopy, there is a unique Lagrangian torus
inside each of the following uniruled symplectic four-manifolds: the symplectic
vector space $\mathbb{R}^4$, the projective plane $\mathbb{C}P^2$, and the
monotone $S^2 \times S^2$. The result is proven by studying pseudoholomorphic
foliations while performing the splitting construction from symplectic field
theory along the Lagrangian torus. A number of other related results are also
shown. Notably, the nearby Lagrangian conjecture is established for
$T^*\mathbb{T}^2$, i.e.~it is shown that every closed exact Lagrangian
submanifold in this cotangent bundle is Hamiltonian isotopic to the
zero-section.
| arxiv topic:math.SG |
arxiv_dataset-70921602.08921 | Effect of the electromagnetic environment on current fluctuations in
driven tunnel junctions
cond-mat.mes-hall
We examine current fluctuations in tunnel junctions driven by a superposition
of a constant and a sinusoidal voltage source. In standard setups the external
voltage is applied to the tunneling element via an impedance providing an
electromagnetic environment of the junction. The modes of this environment are
excited by the time-dependent voltage and are the source of Johnson-Nyquist
noise. We determine the autocorrelation function of the current flowing in the
leads of the junction in the weak tunneling limit up to terms of second order
in the tunneling Hamiltonian. The driven modes of the electromagnetic
environment are treated exactly by means of a unitary transformation introduced
recently. Particular emphasis is placed on the spectral function of the current
fluctuations. The spectrum is found to comprise three contributions: a term
arising from the Johnson-Nyquist noise of the environmental impedance, a part
due to the shot noise of the tunneling element and a third contribution which
comes from the cross-correlation between fluctuations caused by the
electromagnetic environment and fluctuations of the tunneling current. All
three parts of the spectral function occur already for devices under dc bias.
The spectral function of ac driven tunneling elements can be determined from
the result for a dc bias by means of a photo-assisted tunneling relation of the
Tien-Gordon type. Specific results are given for an Ohmic environment and for a
junction driven through a resonator.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-70931602.09021 | Asymptotic dynamics of three-dimensional gravity
hep-th
These are the lectures notes of the course given at the Eleventh Modave
Summer School in Mathematical Physics, 2015, aimed at PhD candidates and junior
researchers in theoretical physics. We review in details the result of
Coussaert-Henneaux-van Driel showing that the asymptotic dynamics of $(2+1)$-
dimensional gravity with negative cosmological constant is described at the
classical level by Liouville theory. Boundary conditions implement the
asymptotic reduction in two steps: the first set reduces the $SL(2,\mathbb
R)\times SL(2,\mathbb R)$ Chern-Simons action, equivalent to the Einstein
action, to a non-chiral $SL(2,\mathbb R)$ Wess-Zumino-Witten model, while the
second set imposes constraints on the WZW currents that reduce further the
action to Liouville theory. We discuss the issues of considering the latter as
an effective description of the dual conformal field theory describing AdS$_3$
gravity beyond the semi-classical regime.
| arxiv topic:hep-th |
arxiv_dataset-70941602.09121 | Exploring the faint source population at 15.7 GHz
astro-ph.GA astro-ph.CO
We discuss our current understanding of the nature of the faint,
high-frequency radio sky. The Tenth Cambridge (10C) survey at 15.7 GHz is the
deepest high-frequency radio survey to date, covering 12 square degrees to a
completeness limit of 0.5 mJy, making it the ideal starting point from which to
study this population. In this work we have matched the 10C survey to several
lower-frequency radio catalogues and a wide range of multi-wavelength data
(near- and far-infrared, optical and X-ray). We find a significant increase in
the proportion of flat-spectrum sources at flux densities below 1 mJy - the
median radio spectral index between 15.7 GHz and 610 MHz changes from 0.75 for
flux densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8
mJy. The multi-wavelength analysis shows that the vast majority (> 94 percent)
of the 10C sources are radio galaxies; it is therefore likely that these faint,
flat spectrum sources are a result of the cores of radio galaxies becoming
dominant at high frequencies. We have used new observations to extend this
study to even fainter flux densities, calculating the 15.7-GHz radio source
count down to 0.1 mJy, a factor of five deeper than previous studies. There is
no evidence for a new population of sources, showing that the high-frequency
sky continues to be dominated by radio galaxies down to at least 0.1 mJy.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-70951603.00079 | Mating, paper folding, and an endomorphism of PC^2
math.DS
We are studying topological properties of the Julia set of the map $F(z,
p)=((2z/(p+1)-1)^2, ((p-1)/(p+1))^2)$ of the complex projective plane $PC^2$ to
itself. We show a relation of this rational function with an uncountable family
of "paper folding" plane filling curves.
| arxiv topic:math.DS |
arxiv_dataset-70961603.00179 | Phase diagram of the two-fluid Lipkin model: a butterfly catastrophe
nucl-th
Background: In the last few decades quantum phase transitions have been of
great interest in Nuclear Physics. In this context, two-fluid algebraic models
are ideal systems to study how the concept of quantum phase transition evolves
when moving into more complex systems, but the number of publications along
this line has been scarce up to now.
Purpose: We intend to determine the phase diagram of a two-fluid Lipkin
model, that resembles the nuclear proton-neutron interacting boson model
Hamiltonian, using both numerical results and analytic tools, i.e., catastrophe
theory, and to compare the mean-field results with exact diagonalizations for
large systems. Method: The mean-field energy surface of a consistent-Q-like
two-fluid Lipkin Hamiltonian is studied and compared with exact results coming
from a direct diagonalization. The mean-field results are analyzed using the
framework of catastrophe theory.
Results: The phase diagram of the model is obtained and the order of the
different phase-transition lines and surfaces is determined using a catastrophe
theory analysis.
Conclusions: There are two first order surfaces in the phase diagram, one
separating the spherical and the deformed shapes, while the other separates two
different deformed phases. A second order line, where the later surfaces merge,
is found. This line finishes in a transition point with a divergence in the
second order derivative of the energy that corresponds to a tricritical point
in the language of the Ginzburg-Landau theory for phase transitions.
| arxiv topic:nucl-th |
arxiv_dataset-70971603.00279 | Fast iterative method with a second order implicit difference scheme for
time-space fractional convection-diffusion equations
math.NA
In this paper we want to propose practical numerical methods to solve a class
of initial-boundary problem of time-space fractional convection-diffusion
equations (TSFCDEs). To start with, an implicit difference method based on
two-sided weighted shifted Gr\"{u}nwald formulae is proposed with a discussion
of the stability and convergence. We construct an implicit difference scheme
(IDS) and show that it converges with second order accuracy in both time and
space. Then, we develop fast solution methods for handling the resulting system
of linear equation with the Toeplitz matrix. The fast Krylov subspace solvers
with suitable circulant preconditioners are designed to deal with the resulting
Toeplitz linear systems. Each time level of these methods reduces the memory
requirement of the proposed implicit difference scheme from $\mathcal{O}(N^2)$
to $\mathcal{O}(N)$ and the computational complexity from $O(N^3)$ to $O(N\log
N)$ in each iterative step, where $N$ is the number of grid nodes. Extensive
numerical example runs show the utility of these methods over the traditional
direct solvers of the implicit difference methods, in terms of computational
cost and memory requirements.
| arxiv topic:math.NA |
arxiv_dataset-70981603.00379 | Brendle's inequality on static manifolds
math.DG gr-qc
We generalize Brendle's geometric inequality considered in \cite{B} to static
manifolds. The inequality bounds the integral of inverse mean curvature of an
embedded mean-convex hypersurface by geometric data of the horizon. As a
consequence, we obtain a reverse Penrose inequality on static asymptotically
locally hyperbolic manifolds in the spirit of Chru\'{s}ciel and Simon
\cite{CS}.
| arxiv topic:math.DG gr-qc |
arxiv_dataset-70991603.00479 | Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys
cond-mat.mtrl-sci
Weyl fermions have recently been observed in several time-reversal-invariant
semimetals and photonics materials with broken inversion symmetry. These
systems are expected to have exotic transport properties such as the chiral
anomaly. However, most discovered Weyl materials possess a substantial number
of Weyl nodes close to the Fermi level that give rise to complicated transport
properties. Here we predict, for the first time, a new family of Weyl systems
defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler
materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions
in the centrosymmetric magnetic systems, we recall an easy and practical
inversion invariant, which has been calculated to be -1, guaranteeing the
existence of an odd number of pairs of Weyl fermions. These materials exhibit,
when alloyed, only two Weyl nodes at the Fermi level - the minimum number
possible in a condensed matter system. The Weyl nodes are protected by the
rotational symmetry along the magnetic axis and separated by a large distance
(of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been
calculated as well. This discovery provides a realistic and promising platform
for manipulating and studying the magnetic Weyl physics in experiments.
| arxiv topic:cond-mat.mtrl-sci |
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