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arxiv_dataset-95001802.1046 | Characteristics of type III radio bursts and solar S bursts
astro-ph.SR
The Sun is an active source of radio emission which is often associated with
the acceleration of electrons arising from processes such as solar flares and
coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous
solar S bursts (where S stands for short) and storms of Type III radio bursts
have been observed, that are not directly relates to flares and CMEs. Here, we
expand our understanding on the spectral characteristic of these two different
types of radio bursts based on observations from the Low Frequency Array
(LOFAR). On 9 July 2013, over 3000 solar S bursts accompanied by over 800 Type
III radio bursts were observed over a time period of ~8 hours. The
characteristics of Type III radio bursts are consistent to previous studies,
while S bursts show narrow bandwidths, durations and drift rates of about 1/2
the drift rate of Type III bursts. Type III bursts and solar S bursts occur in
a region in the corona where plasma emission is the dominant emission mechanism
as determined by data constrained density and magnetic field models.
| arxiv topic:astro-ph.SR |
arxiv_dataset-95011802.1056 | Novelty Detection with GAN
cs.CV
The ability of a classifier to recognize unknown inputs is important for many
classification-based systems. We discuss the problem of simultaneous
classification and novelty detection, i.e. determining whether an input is from
the known set of classes and from which specific class, or from an unknown
domain and does not belong to any of the known classes. We propose a method
based on the Generative Adversarial Networks (GAN) framework. We show that a
multi-class discriminator trained with a generator that generates samples from
a mixture of nominal and novel data distributions is the optimal novelty
detector. We approximate that generator with a mixture generator trained with
the Feature Matching loss and empirically show that the proposed method
outperforms conventional methods for novelty detection. Our findings
demonstrate a simple, yet powerful new application of the GAN framework for the
task of novelty detection.
| arxiv topic:cs.CV |
arxiv_dataset-95021803.00067 | Constrained Classification and Ranking via Quantiles
cs.LG stat.ML
In most machine learning applications, classification accuracy is not the
primary metric of interest. Binary classifiers which face class imbalance are
often evaluated by the $F_\beta$ score, area under the precision-recall curve,
Precision at K, and more. The maximization of many of these metrics can be
expressed as a constrained optimization problem, where the constraint is a
function of the classifier's predictions.
In this paper we propose a novel framework for learning with constraints that
can be expressed as a predicted positive rate (or negative rate) on a subset of
the training data. We explicitly model the threshold at which a classifier must
operate to satisfy the constraint, yielding a surrogate loss function which
avoids the complexity of constrained optimization. The method is model-agnostic
and only marginally more expensive than minimization of the unconstrained loss.
Experiments on a variety of benchmarks show competitive performance relative to
existing baselines.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-95031803.00167 | From Octopus to Dendrite - Semiflexible Polyelectrolyte Brush
Condensates in Trivalent Counterion Solution
cond-mat.soft physics.bio-ph
Interplay between counterion-mediated interaction and stiffness inherent to
polymer chain can bring substantial complexity to the morphology and dynamics
of polyelectrolyte brush condensates. Trivalent counterions induce collapse of
flexible polyelectrolyte brushes, over a certain range of grafting density,
into octopus-like surface micelles; however, if individual chains are rigid
enough, the ion-mediated local nematic ordering assembles the brush chains into
fractal-like dendritic condensates whose relaxation dynamics is significantly
slower than that in the surface micelles. Notably, the trivalent ions condensed
in the dendritic condensates are highly mobile displaying quasi-one-dimensional
diffusion in parallel along the dendritic branches. Our findings in this study
are potentially of great significance to understanding the response of cellular
organization such as chromosomes and charged polysaccharides on membranes to
the change in ionic environment.
| arxiv topic:cond-mat.soft physics.bio-ph |
arxiv_dataset-95041803.00267 | A fresh look at the Semiparametric Cram\'{e}r-Rao Bound
eess.SP
This paper aims at providing a fresh look at semiparametric estimation theory
and, in particular, at the Semiparametric Cram\'{e}r-Rao Bound (SCRB).
Semiparametric models are characterized by a finite-dimensional parameter
vector of interest and by an infinite-dimensional nuisance function that is
often related to an unspecified functional form of the density of the noise
underlying the observations. We summarize the main motivations and the
intuitive concepts about semiparametric models. Then we provide a new look at
the classical estimation theory based on a geometrical Hilbert space-based
approach. Finally, the semiparametric version of the Cram\'{e}r-Rao Bound for
the estimation of the finite-dimensional vector of the parameters of interest
is provided.
| arxiv topic:eess.SP |
arxiv_dataset-95051803.00367 | A Benchmark Problem in Transportation Networks
cs.SY
In this note, we propose a case study of freeway traffic flow modeled as a
hybrid system. We describe two general classes of networks that model flow
along a freeway with merging onramps. The admission rate of traffic flow from
each onramp is metered via a control input. Both classes of networks are easily
scaled to accommodate arbitrary state dimension. The model is discrete-time and
possesses piecewise-affine dynamics. Moreover, we present several control
objectives that are especially relevant for traffic flow management. The
proposed model is flexible and extensible and offers a benchmark for evaluating
tools and techniques developed for hybrid systems.
| arxiv topic:cs.SY |
arxiv_dataset-95061803.00467 | Negacyclic codes over the local ring $\mathbb{Z}_4[v]/\langle
v^2+2v\rangle$ of oddly even length and their Gray images
cs.IT math.IT
Let $R=\mathbb{Z}_{4}[v]/\langle
v^2+2v\rangle=\mathbb{Z}_{4}+v\mathbb{Z}_{4}$ ($v^2=2v$) and $n$ be an odd
positive integer. Then $R$ is a local non-principal ideal ring of $16$ elements
and there is a $\mathbb{Z}_{4}$-linear Gray map from $R$ onto
$\mathbb{Z}_{4}^2$ which preserves Lee distance and orthogonality. First, a
canonical form decomposition and the structure for any negacyclic code over $R$
of length $2n$ are presented. From this decomposition, a complete
classification of all these codes is obtained. Then the cardinality and the
dual code for each of these codes are given, and self-dual negacyclic codes
over $R$ of length $2n$ are presented. Moreover, all $23\cdot(4^p+5\cdot
2^p+9)^{\frac{2^{p}-2}{p}}$ negacyclic codes over $R$ of length $2M_p$ and all
$3\cdot(4^p+5\cdot 2^p+9)^{\frac{2^{p-1}-1}{p}}$ self-dual codes among them are
presented precisely, where $M_p=2^p-1$ is a Mersenne prime. Finally, $36$ new
and good self-dual $2$-quasi-twisted linear codes over $\mathbb{Z}_4$ with
basic parameters $(28,2^{28}, d_L=8,d_E=12)$ and of type $2^{14}4^7$ and basic
parameters $(28,2^{28}, d_L=6,d_E=12)$ and of type $2^{16}4^6$ which are Gray
images of self-dual negacyclic codes over $R$ of length $14$ are listed.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-95071803.00567 | Computational Optimal Transport
stat.ML
Optimal transport (OT) theory can be informally described using the words of
the French mathematician Gaspard Monge (1746-1818): A worker with a shovel in
hand has to move a large pile of sand lying on a construction site. The goal of
the worker is to erect with all that sand a target pile with a prescribed shape
(for example, that of a giant sand castle). Naturally, the worker wishes to
minimize her total effort, quantified for instance as the total distance or
time spent carrying shovelfuls of sand. Mathematicians interested in OT cast
that problem as that of comparing two probability distributions, two different
piles of sand of the same volume. They consider all of the many possible ways
to morph, transport or reshape the first pile into the second, and associate a
"global" cost to every such transport, using the "local" consideration of how
much it costs to move a grain of sand from one place to another. Recent years
have witnessed the spread of OT in several fields, thanks to the emergence of
approximate solvers that can scale to sizes and dimensions that are relevant to
data sciences. Thanks to this newfound scalability, OT is being increasingly
used to unlock various problems in imaging sciences (such as color or texture
processing), computer vision and graphics (for shape manipulation) or machine
learning (for regression, classification and density fitting). This short book
reviews OT with a bias toward numerical methods and their applications in data
sciences, and sheds lights on the theoretical properties of OT that make it
particularly useful for some of these applications.
| arxiv topic:stat.ML |
arxiv_dataset-95081803.00667 | Can cut generating functions be good and efficient?
math.OC
Making cut generating functions (CGFs) computationally viable is a central
question in modern integer programming research. One would like to find CGFs
that are simultaneously good, i.e., there are good guarantees for the cutting
planes they generate, and efficient, meaning that the values of the CGFs can be
computed cheaply (with procedures that have some hope of being implemented in
current solvers). We investigate in this paper to what extent this balance can
be struck. We propose a family of CGFs which, in a sense, achieves this harmony
between good and efficient. In particular, we provide a parameterized family of
$b+\Z^n$ free sets to derive CGFs from and show that our proposed CGFs give a
good approximation of the closure given by CGFs obtained from all maximal
$b+\Z^n$ free sets and their so-called trivial liftings, and simultaneously,
show that these CGFs can be computed with explicit, efficient procedures. We
provide a constructive framework to identify these sets as well as computing
their trivial lifting. We follow it up with computational experiments to
demonstrate this and to evaluate their practical use. Our proposed family of
cuts seem to give some tangible improvement on randomly generated instances
compared to GMI cuts; however, in MIPLIB 3.0 instances, and vertex cover and
stable problems on random graph instances, their performance is poor.
| arxiv topic:math.OC |
arxiv_dataset-95091803.00767 | Black Hole Space-time In Dark Matter Halo
gr-qc astro-ph.CO astro-ph.HE
For the first time, we obtain the analytical form of black hole space-time
metric in dark matter halo for the stationary situation. Using the relation
between the rotation velocity (in the equatorial plane) and the spherical
symmetric space-time metric coefficient, we obtain the space-time metric for
pure dark matter. By considering the dark matter halo in spherical symmetric
space-time as part of the energy-momentum tensors in the Einstein field
equation, we then obtain the spherical symmetric black hole solutions in dark
matter halo. Utilizing Newman-Jains method, we further generalize spherical
symmetric black holes to rotational black holes. As examples, we obtain the
space-time metric of black holes surrounded by Cold Dark Matter and Scalar
Field Dark Matter halos, respectively. Our main results regarding the
interaction between black hole and dark matter halo are as follows: (i) For
both dark matter models, the density profile always produces "cusp" phenomenon
in small scale in the relativity situation; (ii) Dark matter halo makes the
black hole horizon to increase but the ergosphere to decrease, while the
magnitude is small; (iii) Dark matter does not change the singularity of black
holes. These results are useful to study the interaction of black hole and dark
matter halo in stationary situation. Particularly, the "cusp" produced in the
$0\sim 1$ kpc scale would be observable in the Milky Way. Perspectives on
future work regarding the applications of our results in astrophysics are also
briefly discussed.
| arxiv topic:gr-qc astro-ph.CO astro-ph.HE |
arxiv_dataset-95101803.00867 | Probing vorticity structure in heavy-ion collisions by local $\Lambda$
polarization
nucl-th hep-ph
We study the local structure of the vorticity field and the $\Lambda$
polarization in Au+Au collisions in the energy range
$\sqrt{s_{\mathrm{NN}}}=7.7$--$200$ GeV and Pb+Pb collisions at
$\sqrt{s_{\mathrm{NN}}}=2760$ GeV using A Multi-Phase Transport (AMPT) model.
We focus on the vorticity field arising from the non-uniform expansion of the
fireball, which gives the circular structure of the transverse vorticity
$\boldsymbol{\omega}_{\perp}=(\omega_{x},\omega_{y})$ around the $z$ direction
as well as the quadrupole pattern of the longitudinal vorticity $\omega_{z}$ in
the transverse plane. As a consequence, the three components of the
polarization vector $\mathbf{P}=(P_{x},P_{y},P_{z})$ for $\Lambda$ hyperons
show harmonic behaviors as $\mathrm{sgn}(Y)\sin\phi_{p}$,
$-\mathrm{sgn}(Y)\cos\phi_{p}$, and $-\sin(2\phi_{p})$, where $\phi_{p}$ and
$Y$ are the azimuthal angle and rapidity in momentum space. These patterns of
the local $\Lambda$ polarization are expected to be tested in future
experiments.
| arxiv topic:nucl-th hep-ph |
arxiv_dataset-95111803.00967 | Active model learning and diverse action sampling for task and motion
planning
cs.RO cs.AI cs.LG stat.AP stat.ML
The objective of this work is to augment the basic abilities of a robot by
learning to use new sensorimotor primitives to enable the solution of complex
long-horizon problems. Solving long-horizon problems in complex domains
requires flexible generative planning that can combine primitive abilities in
novel combinations to solve problems as they arise in the world. In order to
plan to combine primitive actions, we must have models of the preconditions and
effects of those actions: under what circumstances will executing this
primitive achieve some particular effect in the world?
We use, and develop novel improvements on, state-of-the-art methods for
active learning and sampling. We use Gaussian process methods for learning the
conditions of operator effectiveness from small numbers of expensive training
examples collected by experimentation on a robot. We develop adaptive sampling
methods for generating diverse elements of continuous sets (such as robot
configurations and object poses) during planning for solving a new task, so
that planning is as efficient as possible. We demonstrate these methods in an
integrated system, combining newly learned models with an efficient
continuous-space robot task and motion planner to learn to solve long horizon
problems more efficiently than was previously possible.
| arxiv topic:cs.RO cs.AI cs.LG stat.AP stat.ML |
arxiv_dataset-95121803.01067 | Improved Charge Transfer Multiplet Method to Simulate M- and L-Edge
X-ray Absorption Spectra of Metal-Centered Excited States
physics.chem-ph cond-mat.mtrl-sci
Charge transfer multiplet (CTM) theory is a computationally undemanding and
highly mature method for simulating the soft X-ray spectra of first-row
transition metal complexes. However, CTM theory has seldom been applied to the
simulation of excited state spectra. In this article, we extend the CTM4XAS
software package to simulate M2,3- and L2,3-edge spectra of excited states of
first-row transition metals and to interpret CTM eigenfunctions in terms of
Russell-Saunders term symbols. We use these new programs to reinterpret the
recently reported excited state M2,3-edge difference spectra of photogenerated
ferrocenium cations and propose alternative assignments for the electronic
state of the photogenerated ferrocenium cations supported by CTM theory
simulations. We also use these new programs to model the L2,3-edge spectra of
FeII compounds during nuclear relaxation following photoinduced spin crossover,
and propose spectroscopic signatures for their vibrationally hot states
| arxiv topic:physics.chem-ph cond-mat.mtrl-sci |
arxiv_dataset-95131803.01167 | Dissipative dynamics of an interacting spin system with collective
damping
quant-ph cond-mat.stat-mech
The competition between Hamiltonian and Lindblad dynamics in quantum systems
give rise to non-equillibrium phenomena with no counter part in conventional
condensed matter physics. In this paper, we investigate this interplay of
dynamics in infinite range Heisenberg model coupled to a non-Markovian bath and
subjected to Lindblad dynamics due to spin flipping at a given site. The spin
model is bosonized via Holstein-Primakoff transformations and is shown to be
valid for narrow range of parameters in the thermodynamic limit. Using
Schwinger-Keldysh technique, we derive mean field solution of the model and
observe that the system breaks $\mathcal{Z}_2$-symmetry at the transition
point. We calculate effective temperature that has linear dependence on the
effective system-bath coupling, and is independent of the dissipation rate and
cutoff frequency of the bath spectral density. Furthermore, we study the
fluctuations over mean field and show that the dissipative spectrum is modified
by ${\rm O}(\frac{1}{N})$ correction term which results change in various
physically measurable quantities.
| arxiv topic:quant-ph cond-mat.stat-mech |
arxiv_dataset-95141803.01267 | Laplacians on spheres
math.RT
Spheres can be written as homogeneous spaces $G/H$ for compact Lie groups in
a small number of ways. In each case, the decomposition of $L^2(G/H)$ into
irreducible representations of $G$ contains interesting information. We recall
these decompositions, and see what they can reveal about the analogous problem
for noncompact real forms of $G$ and $H$.
| arxiv topic:math.RT |
arxiv_dataset-95151803.01367 | Wafer-scale fabrication and room-temperature experiments on
graphene-based gates for quantum computation
cond-mat.mes-hall quant-ph
We have fabricated at wafer scale graphene-based configurations suitable for
implementing at room temperature one-qubit quantum gates and a modified
Deutsch-Jozsa algorithm. Our measurements confirmed the (quasi-)ballistic
nature of charge carrier propagation through both types of devices, which have
dimensions smaller than the room-temperature mean-free-path in graphene. As
such, both graphene-based configurations were found to be suitable for quantum
computation. These results are encouraging for demonstrating a miniaturized,
room-temperature quantum computer based on graphene.
| arxiv topic:cond-mat.mes-hall quant-ph |
arxiv_dataset-95161803.01467 | The Sequent Calculus Trainer with Automated Reasoning - Helping Students
to Find Proofs
cs.LO cs.CY
The sequent calculus is a formalism for proving validity of statements
formulated in First-Order Logic. It is routinely used in computer science
modules on mathematical logic. Formal proofs in the sequent calculus are finite
trees obtained by successively applying proof rules to formulas, thus
simplifying them step-by-step.
Students often struggle with the mathematical formalities and the level of
abstraction that topics like formal logic and formal proofs involve. The
difficulties can be categorised as syntactic or semantic. On the syntactic
level, students need to understand what a correctly formed proof is, how rules
can be applied (on paper for instance) without leaving the mathematical
framework of the sequent calculus, and so on. Beyond this, on the semantic
level, students need to acquire strategies that let them find the right proof.
The Sequent Calculus Trainer is a tool that is designed to aid students in
learning the techniques of proving given statements formally. In this paper we
describe the didactical motivation behind the tool and the techniques used to
address issues on the syntactic as well as on the semantic level.
| arxiv topic:cs.LO cs.CY |
arxiv_dataset-95171803.01567 | Controlled Film Flow in Granulation of Metals for the Development of
Amorphous Superhard and Functionally Unique New Materials
physics.app-ph
The problem of granulation is very bright by the granulated materials, as
well as by their application. In the paper, some history of the granulation
problem during over century and modern applications of the metallic granulates
and amorphous materials are given at the beginning. Then the specific own
granulation problem is presented, which has concern to the controlled liquid
metal jet and film flows for a production of the uniform by size and form
particles (granules) cooled with a high rate, to be amorphous or close to the
amorphous materials. Such granules of the given size and form are needed for
the new material science. The basics of developed theory of the controlled jet
and film flow disintegration with further rapid cooling of the drops obtained
after flow disintegration are presented together with the new patented
granulation devices. The developed methods and devices can be used for
production of the amorphous or close to amorphous granules in a wide range of
the given sizes, with very narrow (plus-minus 50% deviation of size from the
average one).
| arxiv topic:physics.app-ph |
arxiv_dataset-95181803.01667 | The high voltage system for the novel MPGD-based photon detectors of
COMPASS RICH-1
physics.ins-det hep-ex nucl-ex
The architecture of the novel MPGD-based photon detectors of COMPASS RICH-1
consists in a large-size hybrid MPGD multilayer layout combining two layers of
Thick-GEMs and a bulk resistive MICROMEGAS. Concerning biasing voltage, the
Thick-GEMs are segmented in order to reduce the energy released in case of
occasional discharges, while the MICROMEGAS anode is segmented in pads
individually biased at positive voltage, while the micromesh is grounded. In
total, there are ten different electrode types and more than 20000 electrodes
supplied by more than 100 HV channels. Commercial power supply units are used.
The original elements of the power supply system are the architecture of the
voltage distribution net, the compensation, by voltage adjustment, of the
effects of pressure and temperature variation affecting the detector gain and a
sophisticated control software, which allows to protect the detectors against
errors by the operator, to monitor and log voltages and current at 1 Hz rate
and to automatically react to detector misbehaviors. The HV system and its
performance are described in detail as well as the electrical stability of the
detector during the operation at COMPASS.
| arxiv topic:physics.ins-det hep-ex nucl-ex |
arxiv_dataset-95191803.01767 | Mutation and selection in bacteria: modelling and calibration
q-bio.PE math.PR q-bio.QM
Temporal evolution of a clonal bacterial population is modelled taking into
account reversible mutation and selection mechanisms. For the mutation model,
an efficient algorithm is proposed to verify whether experimental data can be
explained by this model. The selection-mutation model has unobservable fitness
parameters and, to estimate them, we use an Approximate Bayesian Computation
(ABC) algorithm. The algorithms are illustrated using in vitro data for phase
variable genes of Campylobacter jejuni.
| arxiv topic:q-bio.PE math.PR q-bio.QM |
arxiv_dataset-95201803.01867 | Relativistic Quantum Optics: On the relativistic invariance of the
light-matter interaction models
quant-ph gr-qc hep-th
In this note we discuss the invariance under general changes of reference
frame of all the physical predictions of particle detector models in quantum
field theory in general and, in particular, of those used in quantum optics to
model atoms interacting with light. We find explicitly how the light-matter
interaction Hamiltonians change under general coordinate transformations, and
analyze the subtleties of the Hamiltonians commonly used to describe the
light-matter interaction when relativistic motion is taken into account.
| arxiv topic:quant-ph gr-qc hep-th |
arxiv_dataset-95211803.01967 | Learning Scene Gist with Convolutional Neural Networks to Improve Object
Recognition
cs.CV
Advancements in convolutional neural networks (CNNs) have made significant
strides toward achieving high performance levels on multiple object recognition
tasks. While some approaches utilize information from the entire scene to
propose regions of interest, the task of interpreting a particular region or
object is still performed independently of other objects and features in the
image. Here we demonstrate that a scene's 'gist' can significantly contribute
to how well humans can recognize objects. These findings are consistent with
the notion that humans foveate on an object and incorporate information from
the periphery to aid in recognition. We use a biologically inspired two-part
convolutional neural network ('GistNet') that models the fovea and periphery to
provide a proof-of-principle demonstration that computational object
recognition can significantly benefit from the gist of the scene as contextual
information. Our model yields accuracy improvements of up to 50% in certain
object categories when incorporating contextual gist, while only increasing the
original model size by 5%. This proposed model mirrors our intuition about how
the human visual system recognizes objects, suggesting specific biologically
plausible constraints to improve machine vision and building initial steps
towards the challenge of scene understanding.
| arxiv topic:cs.CV |
arxiv_dataset-95221803.02067 | On cycles of pairing-friendly elliptic curves
math.NT math.AG
A cycle of elliptic curves is a list of elliptic curves over finite fields
such that the number of points on one curve is equal to the size of the field
of definition of the next, in a cyclic way. We study cycles of elliptic curves
in which every curve is pairing-friendly. These have recently found notable
applications in pairing-based cryptography, for instance in improving the
scalability of distributed ledger technologies. We construct a new cycle of
length 4 consisting of MNT curves, and characterize all the possibilities for
cycles consisting of MNT curves. We rule out cycles of length 2 for particular
choices of small embedding degrees. We show that long cycles cannot be
constructed from families of curves with the same complex multiplication
discriminant, and that cycles of composite order elliptic curves cannot exist.
We show that there are no cycles consisting of curves from only the Freeman or
Barreto--Naehrig families.
| arxiv topic:math.NT math.AG |
arxiv_dataset-95231803.02167 | Dissipation induced $W$ state in a Rydberg-atom-cavity system
quant-ph
A dissipative scheme is proposed to prepare tripartite $W$ state in a
Rydberg-atom-cavity system. It is an organic combination of quantum Zeno
dynamics, Rydberg antiblockade and atomic spontaneous emission to turn the
tripartite $W$ state into the unique steady state of the whole system. The
robustness against the loss of cavity and the feasibility of the scheme are
demonstrated thoroughly by the current experimental parameters, which leads to
a high fidelity above $98\%$.
| arxiv topic:quant-ph |
arxiv_dataset-95241803.02267 | An overview of $\Lambda_c$ decays
hep-ph hep-ex
The decays of the ground-state charmed baryon $\Lambda_c$ are now close to
being completely mapped out. In this paper we discuss some remaining open
questions, whose answers can help shed light on weak processes contributing to
those decays, on calculations of such quantities as transition form factors in
lattice QCD, and on missing decay modes such as $\Lambda_c \to \Lambda^* \ell^+
\nu_\ell$, where $\Lambda^*$ is an excited resonance. The discussion is in part
a counterpart to a previous analysis of inclusive $D_s$ decays.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-95251803.02367 | Evidence for a Variable Ultrafast Outflow in the Newly Discovered
Ultraluminous Pulsar NGC 300 ULX-1
astro-ph.HE
Ultraluminous pulsars are a definite proof that persistent super-Eddington
accretion occurs in nature. They support the scenario according to which most
Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar
mass rather than sub-Eddington intermediate mass black holes. An important
prediction of theories of supercritical accretion is the existence of powerful
outflows of moderately ionized gas at mildly relativistic speeds. In practice,
the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is
required to resolve their observational signatures in ULXs. Using RGS, outflows
have been discovered in the spectra of 3 ULXs (none of which are currently
known to be pulsars). Most recently, the fourth ultraluminous pulsar was
discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO)
in the X-ray spectrum of the object, with a significance of more than
3{\sigma}, during one of the two simultaneous observations of the source by
XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of
65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This
is the first direct evidence for a UFO in a neutron star ULX and also the first
time that this its evidence in a ULX spectrum is seen in both soft and hard
X-ray data simultaneously. We find no evidence of the UFO during the other
observation of the object, which could be explained by either clumpy nature of
the absorber or a slight change in our viewing angle of the accretion flow.
| arxiv topic:astro-ph.HE |
arxiv_dataset-95261803.02467 | A $q$-analogue for Euler's evaluations of the Riemann zeta function
math.NT
We provide a $q$-analogue of Euler's formula for $\zeta(2k)$ for
$k\in\mathbb{Z}^+$. Our main results are stated in Theorems 3.1 and 3.2 below.
The result generalizes a recent result of Z.W. Sun who obtained $q$-analogues
of $\zeta(2)=\pi^2/6$ and $\zeta(4)=\pi^4/90$.
| arxiv topic:math.NT |
arxiv_dataset-95271803.02567 | On two-spectra inverse problems
math.SP math-ph math.CA math.FA math.MP
We consider a two-spectra inverse problem for the one-dimensional
Schr\"{o}dinger equation with boundary conditions containing rational
Herglotz--Nevanlinna functions of the eigenvalue parameter and provide a
complete solution of this problem.
| arxiv topic:math.SP math-ph math.CA math.FA math.MP |
arxiv_dataset-95281803.02667 | A limit theorem for the six-length of random functional graphs with a
fixed degree sequence
math.CO
We obtain results on the limiting distribution of the six-length of a random
functional graph, also called a functional digraph or random mapping, with
given in-degree sequence. The six-length of a vertex $v\in V$ is defined from
the associated mapping, $f:V\to V$, to be the maximum $i\in V$ such that the
elements $v, f(v), \ldots, f^{i-1}(v)$ are all distinct. This has relevance to
the study of algorithms for integer factorisation.
| arxiv topic:math.CO |
arxiv_dataset-95291803.02767 | Babenko's equation for periodic gravity waves on water of finite depth:
derivation and numerical solution
math.AP math-ph math.MP
The nonlinear two-dimensional problem, describing periodic steady waves on
water of finite depth is considered in the absence of surface tension. It is
reduced to a single pseudo-differential operator equation (Babenko's equation),
which is investigated analytically and numerically. This equation has the same
form as the equation for waves on infinitely deep water; the latter had been
proposed by Babenko and studied in detail by Buffoni, Dancer and Toland.
Instead of the $2 \pi$-periodic Hilbert transform $\mathcal{C}$ used in the
equation for deep water, the equation obtained here contains a certain operator
$\mathcal{B}_r$, which is the sum of $\mathcal{C}$ and a compact operator whose
dependence on the parameter involves on the depth of water. Numerical
computations are based on an equivalent form of Babenko's equation derived by
virtue of the spectral decomposition of the operator $\mathcal{B}_r \D / \D t$.
Bifurcation curves and wave profiles of the extreme form are obtained
numerically.
| arxiv topic:math.AP math-ph math.MP |
arxiv_dataset-95301803.02867 | Phase transitions for a model with uncountable spin space on the Cayley
tree: the general case
math.PR
In this paper we complete the analysis of a statistical mechanics model on
Cayley trees of any degree, started in
[EsHaRo12,EsRo10,BoEsRo13,JaKuBo14,Bo17]. The potential is of nearest-neighbor
type and the local state space is compact but uncountable. Based on the system
parameters we prove existence of a critical value $\theta_{\rm c}$ such that
for $\theta\le \theta_{\rm c}$ there is a unique translation-invariant
splitting Gibbs measure. For $\theta_{\rm c}<\theta$ there is a phase
transition with exactly three translation-invariant splitting Gibbs measures.
The proof rests on an analysis of fixed points of an associated non-linear
Hammerstein integral operator for the boundary laws.
| arxiv topic:math.PR |
arxiv_dataset-95311803.02967 | Decomposition of Nonlinear Dynamical Networks via Comparison Systems
math.DS math.OC
In analysis and control of large-scale nonlinear dynamical systems, a
distributed approach is often an attractive option due to its computational
tractability and usually low communication requirements. Success of the
distributed control design relies on the separability of the network into
weakly interacting subsystems such that minimal information exchange between
subsystems is sufficient to achieve satisfactory control performance. While
distributed analysis and control design for dynamical network have been well
studied, decomposition of nonlinear networks into weakly interacting subsystems
has not received as much attention. In this article we propose a vector
Lyapunov functions based approach to quantify the energy-flow in a dynamical
network via a model of a comparison system. Introducing a notion of power and
energy flow in a dynamical network, we use sum-of-squares programming tools to
partition polynomial networks into weakly interacting subsystems. Examples are
provided to illustrate the proposed method of decomposition.
| arxiv topic:math.DS math.OC |
arxiv_dataset-95321803.03067 | Compositional Attention Networks for Machine Reasoning
cs.AI
We present the MAC network, a novel fully differentiable neural network
architecture, designed to facilitate explicit and expressive reasoning. MAC
moves away from monolithic black-box neural architectures towards a design that
encourages both transparency and versatility. The model approaches problems by
decomposing them into a series of attention-based reasoning steps, each
performed by a novel recurrent Memory, Attention, and Composition (MAC) cell
that maintains a separation between control and memory. By stringing the cells
together and imposing structural constraints that regulate their interaction,
MAC effectively learns to perform iterative reasoning processes that are
directly inferred from the data in an end-to-end approach. We demonstrate the
model's strength, robustness and interpretability on the challenging CLEVR
dataset for visual reasoning, achieving a new state-of-the-art 98.9% accuracy,
halving the error rate of the previous best model. More importantly, we show
that the model is computationally-efficient and data-efficient, in particular
requiring 5x less data than existing models to achieve strong results.
| arxiv topic:cs.AI |
arxiv_dataset-95331803.03167 | Physical explanation of the universal "inverse-3rd-power-of-separation"
law found numerically for the electrostatic interaction between two
protruding nanostructures
cond-mat.mes-hall
Two conducting nanostructures on a conducting base-plate, and with a common
applied electrostatic field, interact because their electrons are a common
electron-thermodynamic system. Except at small separations, the interaction
reduces the apex field enhancement factor (FEF) of each nanostructure, by means
of "charge blunting". A parameter of interest is the fractional reduction (-d)
of the apex FEF, as compared with the apex FEF for the same emitter when
standing alone on the base-plate. For systems of two or a few identical
post-like emitters, or regular arrays of such emitters, details have been
investigated by methods based on numerical solution of Laplace's equation, and
by using line-charge models. For post separations c comparable with post height
h, several authors have shown that the variation of (-d) with c is well
described by formulae having exponential or quasi-exponential form. By
contrast, explorations of the two-emitter situation using the
"floating-sphere-at-emitter-plane potential" (FSEPP) model have predicted that,
for large c-values, (-d) falls off as 1/c*c*c. Numerical Laplace-type
simulations carried out by de Assis and Dall'Agnol (arXiv:1711.00601v2) have
confirmed this limiting dependence for six different situations involving pairs
of protruding nanostructures; hence they suggest it as an universal law. By
using the FSEPP model for the central structure, and by adopting a "first
moments" representation for the distant structure, this letter shows that a
clear physical reason can be given for this numerically discovered general
limiting (1/c*c*c) dependence. An implication is that the quasi-exponential
formula found useful for c comparable with h is simply a good fitting formula.
A second implication is that the FSEPP model, which currently is used mainly in
nanoscience, may have much wider applicability to electrostatic phenomena.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-95341803.03267 | Resonating valence bonds and spinon pairing in the Dicke model
quant-ph cond-mat.supr-con
Resonating valence bond (RVB) states are a class of entangled quantum many
body wavefunctions with great significance in condensed matter physics. We
propose a scheme to synthesize a family of RVB states using a cavity QED setup
with two-level atoms (with states $\vert 0 \rangle$ and $\vert 1 \rangle$)
coupled to a common photon mode. In the lossy cavity limit, starting with an
initial state of $M$ atoms excited and $N$ atoms in the ground state, we show
that this setup can be configured as a Stern Gerlach experiment. A measurement
of photon emission collapses the wavefunction of atoms onto an RVB state
composed of resonating long-ranged singlets of the form
$\frac{1}{\sqrt{2}}[\vert 0 1 \rangle - \vert 1 0 \rangle]$. Each emitted
photon reduces the number of singlets by unity, replacing it with a pair of
lone spins or `spinons'. As spinons are formed coherently in pairs, they are
analogous to Cooper pairs in a superconductor. To simulate pair fluctuations,
we propose a protocol in which photons are allowed to escape the cavity
undetected. This leads to a mixed quantum state with a fluctuating number of
spinon pairs -- an inchoate superconductor. Remarkably, in the limit of large
system sizes, this protocol reveals an underlying quantum phase transition.
Upon tuning the initial spin polarization ($M-N$), the emission exhibits a
continuous transition from a dark state to a bright state. This is reflected in
the spinon pair number distribution which can be tuned from sub-poissonian to
super-poissonian regimes. This opens an exciting route to simulate RVB states
and superconductivity.
| arxiv topic:quant-ph cond-mat.supr-con |
arxiv_dataset-95351803.03367 | NeuroStorm: Accelerating Brain Science Discovery in the Cloud
q-bio.OT
Neuroscientists are now able to acquire data at staggering rates across
spatiotemporal scales. However, our ability to capitalize on existing datasets,
tools, and intellectual capacities is hampered by technical challenges. The key
barriers to accelerating scientific discovery correspond to the FAIR data
principles: findability, global access to data, software interoperability, and
reproducibility/re-usability. We conducted a hackathon dedicated to making
strides in those steps. This manuscript is a technical report summarizing these
achievements, and we hope serves as an example of the effectiveness of focused,
deliberate hackathons towards the advancement of our quickly-evolving field.
| arxiv topic:q-bio.OT |
arxiv_dataset-95361803.03467 | RippleNet: Propagating User Preferences on the Knowledge Graph for
Recommender Systems
cs.IR cs.LG stat.ML
To address the sparsity and cold start problem of collaborative filtering,
researchers usually make use of side information, such as social networks or
item attributes, to improve recommendation performance. This paper considers
the knowledge graph as the source of side information. To address the
limitations of existing embedding-based and path-based methods for
knowledge-graph-aware recommendation, we propose Ripple Network, an end-to-end
framework that naturally incorporates the knowledge graph into recommender
systems. Similar to actual ripples propagating on the surface of water, Ripple
Network stimulates the propagation of user preferences over the set of
knowledge entities by automatically and iteratively extending a user's
potential interests along links in the knowledge graph. The multiple "ripples"
activated by a user's historically clicked items are thus superposed to form
the preference distribution of the user with respect to a candidate item, which
could be used for predicting the final clicking probability. Through extensive
experiments on real-world datasets, we demonstrate that Ripple Network achieves
substantial gains in a variety of scenarios, including movie, book and news
recommendation, over several state-of-the-art baselines.
| arxiv topic:cs.IR cs.LG stat.ML |
arxiv_dataset-95371803.03567 | Review of Blockchain Technology and its Expectations: Case of the Energy
Sector
cs.CY
This article suggests that the worldwide relevance of blockchain technology
is motivated by the changes that it is expected to cause in: (i) the way that
business is organised and (ii) regulated, as well as (iii) by the way that it
changes the role of individuals within a society. The article presents an
overview of the features of blockchain technology. It then takes a closer look
into the developments within the energy sector across the world to gain a
preliminary indication of whether the stated expectations are coming to
reality. As a result of this review, we remain cautiously optimistic that
blockchain technology could deliver the expected impact.
| arxiv topic:cs.CY |
arxiv_dataset-95381803.03667 | Co-occurrence of the Benford-like and Zipf Laws Arising from the Texts
Representing Human and Artificial Languages
cs.CL physics.soc-ph stat.OT
We demonstrate that large texts, representing human (English, Russian,
Ukrainian) and artificial (C++, Java) languages, display quantitative patterns
characterized by the Benford-like and Zipf laws. The frequency of a word
following the Zipf law is inversely proportional to its rank, whereas the total
numbers of a certain word appearing in the text generate the uneven
Benford-like distribution of leading numbers. Excluding the most popular words
essentially improves the correlation of actual textual data with the Zipfian
distribution, whereas the Benford distribution of leading numbers (arising from
the overall amount of a certain word) is insensitive to the same elimination
procedure. The calculated values of the moduli of slopes of double
logarithmical plots for artificial languages (C++, Java) are markedly larger
than those for human ones.
| arxiv topic:cs.CL physics.soc-ph stat.OT |
arxiv_dataset-95391803.03767 | Multi-Agent Submodular Optimization
cs.DS
Recent years have seen many algorithmic advances in the area of submodular
optimization: (SO) $\min/\max~f(S): S \in \mathcal{F}$, where $\mathcal{F}$ is
a given family of feasible sets over a ground set $V$ and $f:2^V \rightarrow
\mathbb{R}$ is submodular. This progress has been coupled with a wealth of new
applications for these models. Our focus is on a more general class of
\emph{multi-agent submodular optimization} (MASO) which was introduced by Goel
et al. in the minimization setting: $\min \sum_i f_i(S_i): S_1 \uplus S_2
\uplus \cdots \uplus S_k \in \mathcal{F}$. Here we use $\uplus$ to denote
disjoint union and hence this model is attractive where resources are being
allocated across $k$ agents, each with its own submodular cost function
$f_i()$. In this paper we explore the extent to which the approximability of
the multi-agent problems are linked to their single-agent {\em primitives},
referred to informally as the {\em multi-agent gap}.
We present different reductions that transform a multi-agent problem into a
single-agent one. For maximization we show that (MASO) admits an
$O(\alpha)$-approximation whenever (SO) admits an $\alpha$-approximation over
the multilinear formulation, and thus substantially expanding the family of
tractable models. We also discuss several family classes (such as spanning
trees, matroids, and $p$-systems) that have a provable multi-agent gap of 1. In
the minimization setting we show that (MASO) has an $O(\alpha \cdot \min \{k,
\log^2 (n)\})$-approximation whenever (SO) admits an $\alpha$-approximation
over the convex formulation. In addition, we discuss the class of "bounded
blocker" families where there is a provably tight O$(\log n)$ gap between
(MASO) and (SO).
| arxiv topic:cs.DS |
arxiv_dataset-95401803.03867 | Attosecond electronic recollision as field detector
physics.optics
We demonstrate the complete reconstruction of the electric field of
visible-infrared pulses with energy as low as a few tens of nanojoules. The
technique allows for the reconstruction of the instantaneous electric field
vector direction and magnitude, thus giving access to the characterisation of
pulses with an arbitrary time-dependent polarisation state. The technique
combines extreme ultraviolet interferometry with the generation of isolated
attosecond pulses.
| arxiv topic:physics.optics |
arxiv_dataset-95411803.03967 | A multi-wavelength study of the evolution of Early-Type Galaxies in
Groups: the ultraviolet view
astro-ph.GA
ABRIDGED- The UV-optical color magnitude diagram (CMD) of rich galaxy groups
is characterised by a well developed Red Sequence (RS), a Blue Cloud (BC) and
the so-called Green Valley (GV). Loose, less evolved groups of galaxies likely
not virialized yet may lack a well defined RS. This is actually explained in
the framework of galaxy evolution. We are focussing on understanding galaxy
migration towards the RS, checking for signatures of such a transition in their
photometric and morphological properties. We report on the UV properties of a
sample of ETGs galaxies inhabiting the RS. The analysis of their structures, as
derived by fitting a Sersic law to their UV luminosity profiles, suggests the
presence of an underlying disk. This is the hallmark of dissipation processes
that still must have a role in the evolution of this class of galaxies. SPH
simulations with chemo-photometric implementations able to match the global
properties of our targets are used to derive their evolutionary paths through
UV-optical CDM, providing some fundamental information such as the crossing
time through the GV, which depends on their luminosity. The transition from the
BC to the RS takes several Gyrs, being about 3-5 Gyr for the the brightest
galaxies and more long for fainter ones, if it occurs. The photometric study of
nearby galaxy structures in UV is seriously hampered by either the limited FoV
of the cameras (e.g in HST) or by the low spatial resolution of the images (e.g
in the GALEX). Current missions equipped with telescopes and cameras sensitive
to UV wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively
large FoV and better resolution than the GALEX. More powerful UV instruments
(size, resolution and FoV) are obviously bound to yield fundamental advances in
the accuracy and depth of the surface photometry and in the characterisation of
the galaxy environment.
| arxiv topic:astro-ph.GA |
arxiv_dataset-95421803.04067 | Valley-selective exciton bistability in a suspended monolayer
semiconductor
cond-mat.mes-hall
We demonstrate robust power- and wavelength-dependent optical bistability in
fully suspended monolayers of WSe2 near the exciton resonance. Bistability has
been achieved under continuous-wave optical excitation at an intensity level of
10^3 W/cm^2. The observed bistability is originated from a photo-thermal
mechanism, which provides both optical nonlinearity and passive feedback, two
essential elements for optical bistability. Under a finite magnetic field, the
exciton bistability becomes helicity dependent, which enables repeatable
switching of light purely by its polarization.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-95431803.04167 | Methods for Classically Simulating Noisy Networked Quantum Architectures
quant-ph
As research on building scalable quantum computers advances, it is important
to be able to certify their correctness. Due to the exponential hardness of
classically simulating quantum computation, straight-forward verification
through classical simulation fails. However, we can classically simulate small
scale quantum computations and hence we are able to test that devices behave as
expected in this domain. This constitutes the first step towards obtaining
confidence in the anticipated quantum-advantage when we extend to scales which
can no longer be simulated.
Realistic devices have restrictions due to their architecture and limitations
due to physical imperfections and noise. Here we extend the usual ideal
simulations by considering those effects. We provide a general methodology for
constructing realistic simulations emulating the physical system which will
both provide a benchmark for realistic devices, and guide experimental research
in the quest for quantum-advantage.
We exemplify our methodology by simulating a networked architecture and
corresponding noise-model; in particular that of the device developed in the
Networked Quantum Information Technologies Hub (NQIT). For our simulations we
use, with suitable modification, the classical simulator of of Bravyi and
Gosset. The specific problems considered belong to the class of Instantaneous
Quantum Polynomial-time (IQP) problems, a class believed to be hard for
classical computing devices, and to be a promising candidate for the first
demonstration of quantum-advantage. We first consider a subclass of IQP,
defined by Bermejo-Vega et al, involving two-dimensional dynamical quantum
simulators, before moving to more general instances of IQP, but which are still
restricted to the architecture of NQIT.
| arxiv topic:quant-ph |
arxiv_dataset-95441803.04267 | Gravitational collapse and structure formation in an expanding universe
with dark energy
physics.pop-ph astro-ph.CO gr-qc
Observations show that the expansion of the Universe is accelerating. This
requires that the dominant constituent of matter in the Universe has some
unusual properties like negative pressure. This exotic component has been given
the name dark energy. We work with the simplest model of dark energy, the
cosmological constant introduced by Einstein. We study the evolution of
spherical over-densities in such a model and show that there is a minimum
over-density required for collapse: perturbations with a smaller amplitude do
not collapse. This threshold is interesting as even perturbations with a
positive over-density and negative energy do not collapse in finite time.
Further, we show that perturbations with an amplitude larger than, but
comparable to the threshold value, take a very long time to collapse. We
compare the solutions with the case when dark energy is absent.
| arxiv topic:physics.pop-ph astro-ph.CO gr-qc |
arxiv_dataset-95451803.04367 | Graded Holonomic D-modules on Monomial Curves
math.RT math.RA
In this paper, we study the holonomic $D$-modules when $D$ is the ring of
$k$-linear differential operators on $A = k[\Gamma]$, the coordinate ring of an
affine monomial curve over the complex numbers $k = \mathbb C$. In particular,
we consider the graded case, and classify the simple graded $D$-modules and
compute their extensions. The classification over the first Weyl algebra $D =
A_1(k)$ is obtained as a special case.
| arxiv topic:math.RT math.RA |
arxiv_dataset-95461803.04467 | Witnessing Planetary Systems in the Making with the Next Generation Very
Large Array
astro-ph.EP
The discovery of thousands of exoplanets over the last couple of decades has
shown that the birth of planets is a very efficient process in nature. Theories
invoke a multitude of mechanisms to describe the assembly of planets in the
disks around pre-main-sequence stars, but observational constraints have been
sparse on account of insufficient sensitivity and resolution. Understanding how
planets form and interact with their parental disk is crucial also to
illuminate the main characteristics of a large portion of the full population
of planets that is inaccessible to current and near-future observations. This
White Paper describes some of the main issues for our current understanding of
the formation and evolution of planets, and the critical contribution expected
in this field by the Next Generation Very Large Array.
| arxiv topic:astro-ph.EP |
arxiv_dataset-95471803.04567 | Convolutional Neural Networks and Language Embeddings for End-to-End
Dialect Recognition
cs.SD eess.AS
Dialect identification (DID) is a special case of general language
identification (LID), but a more challenging problem due to the linguistic
similarity between dialects. In this paper, we propose an end-to-end DID system
and a Siamese neural network to extract language embeddings. We use both
acoustic and linguistic features for the DID task on the Arabic dialectal
speech dataset: Multi-Genre Broadcast 3 (MGB-3). The end-to-end DID system was
trained using three kinds of acoustic features: Mel-Frequency Cepstral
Coefficients (MFCCs), log Mel-scale Filter Bank energies (FBANK) and
spectrogram energies. We also investigated a dataset augmentation approach to
achieve robust performance with limited data resources. Our linguistic feature
research focused on learning similarities and dissimilarities between dialects
using the Siamese network, so that we can reduce feature dimensionality as well
as improve DID performance. The best system using a single feature set achieves
73% accuracy, while a fusion system using multiple features yields 78% on the
MGB-3 dialect test set consisting of 5 dialects. The experimental results
indicate that FBANK features achieve slightly better results than MFCCs.
Dataset augmentation via speed perturbation appears to add significant
robustness to the system. Although the Siamese network with language embeddings
did not achieve as good a result as the end-to-end DID system, the two
approaches had good synergy when combined together in a fused system.
| arxiv topic:cs.SD eess.AS |
arxiv_dataset-95481803.04667 | Dynamic Vision Sensors for Human Activity Recognition
cs.CV
Unlike conventional cameras which capture video at a fixed frame rate,
Dynamic Vision Sensors (DVS) record only changes in pixel intensity values. The
output of DVS is simply a stream of discrete ON/OFF events based on the
polarity of change in its pixel values. DVS has many attractive features such
as low power consumption, high temporal resolution, high dynamic range and
fewer storage requirements. All these make DVS a very promising camera for
potential applications in wearable platforms where power consumption is a major
concern.
In this paper, we explore the feasibility of using DVS for Human Activity
Recognition (HAR). We propose to use the various slices (such as $x-y$, $x-t$,
and $y-t$) of the DVS video as a feature map for HAR and denote them as Motion
Maps. We show that fusing motion maps with Motion Boundary Histogram (MBH) give
good performance on the benchmark DVS dataset as well as on a real DVS gesture
dataset collected by us. Interestingly, the performance of DVS is comparable to
that of conventional videos although DVS captures only sparse motion
information.
| arxiv topic:cs.CV |
arxiv_dataset-95491803.04767 | SU(3) Quantum Spin Ladders as a Regularization of the CP(2) Model at
Non-Zero Density: From Classical to Quantum Simulation
hep-lat cond-mat.str-el quant-ph
Quantum simulations would be highly desirable in order to investigate the
finite density physics of QCD. $(1+1)$-d $\mathbb{C}P(N-1)$ quantum field
theories are toy models that share many important features of QCD: they are
asymptotically free, have a non-perturbatively generated massgap, as well as
$\theta$-vacua. $SU(N)$ quantum spin ladders provide an unconventional
regularization of $\mathbb{C}P(N-1)$ models that is well-suited for quantum
simulation with ultracold alkaline-earth atoms in an optical lattice. In order
to validate future quantum simulation experiments of $\mathbb{C}P(2)$ models at
finite density, here we use quantum Monte Carlo simulations on classical
computers to investigate $SU(3)$ quantum spin ladders at non-zero chemical
potential. This reveals a rich phase structure, with single- or double-species
Bose-Einstein "condensates", with or without ferromagnetic order.
| arxiv topic:hep-lat cond-mat.str-el quant-ph |
arxiv_dataset-95501803.04867 | Extreme field-sensitivity of the magnetic tunneling in Fe-doped Li$_3$N
cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.str-el
The magnetic properties of dilute Li$_2$(Li$_{1-x}$Fe$_x$)N with $x \sim
0.001$ are dominated by the spin of single, isolated Fe atoms. Below $T = 10$ K
the spin-relaxation times become temperature-independent indicating a crossover
from thermal excitations to the quantum tunneling regime. We report on a strong
increase of the spin-flip probability in $\textit{transverse}$ magnetic fields
that proves the resonant character of this tunneling process.
$\textit{Longitudinal}$ fields, on the other hand, lift the ground-state
degeneracy and destroy the tunneling condition. An increase of the relaxation
time by four orders of magnitude in applied fields of only a few milliTesla
reveals exceptionally sharp tunneling resonances. Li$_2$(Li$_{1-x}$Fe$_x$)N
represents a comparatively simple and clean model system that opens the
possibility to study quantum tunneling of the magnetization at liquid helium
temperatures.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.str-el |
arxiv_dataset-95511803.04967 | Recurrent Neural Network Attention Mechanisms for Interpretable System
Log Anomaly Detection
cs.LG cs.NE stat.ML
Deep learning has recently demonstrated state-of-the art performance on key
tasks related to the maintenance of computer systems, such as intrusion
detection, denial of service attack detection, hardware and software system
failures, and malware detection. In these contexts, model interpretability is
vital for administrator and analyst to trust and act on the automated analysis
of machine learning models. Deep learning methods have been criticized as black
box oracles which allow limited insight into decision factors. In this work we
seek to "bridge the gap" between the impressive performance of deep learning
models and the need for interpretable model introspection. To this end we
present recurrent neural network (RNN) language models augmented with attention
for anomaly detection in system logs. Our methods are generally applicable to
any computer system and logging source.
By incorporating attention variants into our RNN language models we create
opportunities for model introspection and analysis without sacrificing
state-of-the art performance.
We demonstrate model performance and illustrate model interpretability on an
intrusion detection task using the Los Alamos National Laboratory (LANL) cyber
security dataset, reporting upward of 0.99 area under the receiver operator
characteristic curve despite being trained only on a single day's worth of
data.
| arxiv topic:cs.LG cs.NE stat.ML |
arxiv_dataset-95521803.05067 | Applications of Psychological Science for Actionable Analytics
cs.SE
Actionable analytics are those that humans can understand, and
operationalize. What kind of data mining models generate such actionable
analytics? According to psychological scientists, humans understand models that
most match their own internal models, which they characterize as lists of
"heuristic" (i.e., lists of very succinct rules). One such heuristic rule
generator is the Fast-and-Frugal Trees (FFT) preferred by psychological
scientists. Despite their successful use in many applied domains, FFTs have not
been applied in software analytics. Accordingly, this paper assesses FFTs for
software analytics.
We find that FFTs are remarkably effective. Their models are very succinct (5
lines or less describing a binary decision tree). These succinct models
outperform state-of-the-art defect prediction algorithms defined by Ghortra et
al. at ICSE'15. Also, when we restrict training data to operational attributes
(i.e., those attributes that are frequently changed by developers), FFTs
perform much better than standard learners.
Our conclusions are two-fold. Firstly, there is much that software analytics
community could learn from psychological science. Secondly, proponents of
complex methods should always baseline those methods against simpler
alternatives. For example, FFTs could be used as a standard baseline learner
against which other software analytics tools are compared.
| arxiv topic:cs.SE |
arxiv_dataset-95531803.05167 | A generalization of the steepest-edge rule and its number of simplex
iterations for a nondegenerate LP
math.OC
In this paper, we propose a $p$-norm rule, which is a generalization of the
steepest-edge rule, as a pivoting rule for the simplex method. For a
nondegenerate linear programming problem, we show upper bounds for the number
of iterations of the simplex method with the steepest-edge and $p$-norm rules.
One of the upper bounds is given by a function of the number of variables, that
of constraints, and the minimum and maximum positive elements in all basic
feasible solutions.
| arxiv topic:math.OC |
arxiv_dataset-95541803.05267 | $P_{c}$-like pentaquarks in hidden strange sector
hep-ph nucl-th
Analogous to the work of hidden charm molecular pentaquarks, we study
possible hidden strange molecular pentaquarks composed of $\Sigma$ (or
$\Sigma^{*}$) and $K$ (or $K^{*}$) in the framework of quark delocalization
color screening model. Our results suggest that the $\Sigma K$, $\Sigma K^{*}$
and $\Sigma^{*} K^{*}$ with $IJ^{P}=\frac{1}{2}\frac{1}{2}^{-}$ and $\Sigma
K^{*}$, $\Sigma^{*} K$ and $\Sigma^{*} K^{*}$ with
$IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$ are all resonance states by coupling the
open channels. The molecular pentaquark $\Sigma^{*} K$ with quantum numbers
$IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$ can be seen as a strange partner of the
LHCb $P_{c}(4380)$ state, and it can be identified as the nucleon resonance
$N^{*}(1875)$ listed in PDG. The $\Sigma K^{*}$ with quantum numbers
$IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$ can be identified as the $N^{*}(2100)$,
which was experimentally observed in the $\phi$ photo-production.
| arxiv topic:hep-ph nucl-th |
arxiv_dataset-95551803.05367 | Integrating UML with Service Refinement for Requirements Modeling and
Analysis
cs.SE
Unified Modeling Language (UML) is the de facto standard for requirements
modeling and system design. UML as a visual language can tremendously help
customers, project managers, and developers to specify the requirements of a
target system. However, UML lacks the ability to specify the requirements
precisely such as the contracts of the system operation, and verify the
consistency and refinement of the requirements. These disadvantages result in
that the potential faults of software are hard to be discovered in the early
stage of software development process, and then requiring more efforts in
software testing to find the bugs. Service refinement is a formal method, which
could be a supplement to enhance the UML. In this paper, we show how to
integrate UML with service refinement to specify requirements, and verify the
consistency and refinements of the requirements through a case study of online
shopping system. Particularly, requirements are modeled through UML diagrams,
which includes a) use case diagram, b) system sequence diagrams and c)
conceptual class diagram. Service refinement enhances the requirements model by
introducing the contracts. Furthermore, the consistency and refinements of
requirement model can be verified through service refinement. Our approach
demonstrates integrating UML with service refinement can require fewer efforts
to achieve the consistency requirements than only using UML for requirement
modeling.
| arxiv topic:cs.SE |
arxiv_dataset-95561803.05467 | The phase-separation mechanism of a binary mixture in a ring trimer
cond-mat.quant-gas
We show that, depending on the ratio between the inter- and the intra-species
interactions, a binary mixture trapped in a three-well potential with periodic
boundary conditions exhibits three macroscopic ground-state configurations
which differ in the degree of mixing. Accordingly, the corresponding quantum
states feature either delocalization or a Schr\"odinger cat-like structure. The
two-step phase separation occurring in the system, which is smoothed by the
activation of tunnelling processes, is confirmed by the analysis of the energy
spectrum that collapses and rearranges at the two critical points. In such
points, we show that also Entanglement Entropy, a quantity borrowed from
quantum-information theory, features singularities, thus demonstrating its
ability to witness the double mixining-demixing phase transition. The developed
analysis, which is of interest to both the experimental and theoretical
communities, opens the door to the study of the demixing mechanism in complex
lattice geometries.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-95571803.05567 | Achieving Human Parity on Automatic Chinese to English News Translation
cs.CL
Machine translation has made rapid advances in recent years. Millions of
people are using it today in online translation systems and mobile applications
in order to communicate across language barriers. The question naturally arises
whether such systems can approach or achieve parity with human translations. In
this paper, we first address the problem of how to define and accurately
measure human parity in translation. We then describe Microsoft's machine
translation system and measure the quality of its translations on the widely
used WMT 2017 news translation task from Chinese to English. We find that our
latest neural machine translation system has reached a new state-of-the-art,
and that the translation quality is at human parity when compared to
professional human translations. We also find that it significantly exceeds the
quality of crowd-sourced non-professional translations.
| arxiv topic:cs.CL |
arxiv_dataset-95581803.05667 | A Study of Recent Contributions on Information Extraction
cs.IR cs.CL
This paper reports on modern approaches in Information Extraction (IE) and
its two main sub-tasks of Named Entity Recognition (NER) and Relation
Extraction (RE). Basic concepts and the most recent approaches in this area are
reviewed, which mainly include Machine Learning (ML) based approaches and the
more recent trend to Deep Learning (DL) based methods.
| arxiv topic:cs.IR cs.CL |
arxiv_dataset-95591803.05767 | Multiplicity Dependence of Charged Particle, $\phi$ Meson and
Multi-strange Particle Productions in p+p Collisions at $\sqrt{\rm s}$ = 200
GeV with PYTHIA Simulation
hep-ph nucl-th
We report the multiplicity dependence of charged particle productions for
$\pi^{\pm}$, $K^{\pm}$, $p$, $\overline{p}$ and $\phi$ meson at $|y| < 1.0$ in
p+p collisions at $\sqrt{\rm s}$ = 200 GeV with $\rm PYTHIA$ simulation. The
impact of parton multiple interactions and gluon contributions is studied and
found to be possible sources of the particle yields splitting as a function of
$p_T$ with respect to multiplicity. No obvious particle species dependence for
the splitting is observed. The multiplicity dependence on ratios of
$K^-/\pi^-$, $K^+/\pi^+$, $\overline{p}/\pi^-$, $p/\pi^+$ and
$\Lambda/K^{0}_{s}$ in mid-rapidity in p+p collisions is found following the
similar tendency as that in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from
RHIC, which heralds the similar underlying initial production mechanisms
despite the differences in the initial colliding systems.
| arxiv topic:hep-ph nucl-th |
arxiv_dataset-95601803.05867 | Capturing Structure Implicitly from Time-Series having Limited Data
stat.ML cs.LG
Scientific fields such as insider-threat detection and highway-safety
planning often lack sufficient amounts of time-series data to estimate
statistical models for the purpose of scientific discovery. Moreover, the
available limited data are quite noisy. This presents a major challenge when
estimating time-series models that are robust to overfitting and have
well-calibrated uncertainty estimates. Most of the current literature in these
fields involve visualizing the time-series for noticeable structure and hard
coding them into pre-specified parametric functions. This approach is
associated with two limitations. First, given that such trends may not be
easily noticeable in small data, it is difficult to explicitly incorporate
expressive structure into the models during formulation. Second, it is
difficult to know $\textit{a priori}$ the most appropriate functional form to
use. To address these limitations, a nonparametric Bayesian approach was
proposed to implicitly capture hidden structure from time series having limited
data. The proposed model, a Gaussian process with a spectral mixture kernel,
precludes the need to pre-specify a functional form and hard code trends, is
robust to overfitting and has well-calibrated uncertainty estimates.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-95611803.05967 | Earth: Atmospheric Evolution of a Habitable Planet
astro-ph.EP
Our present-day atmosphere is often used as an analog for potentially
habitable exoplanets, but Earth's atmosphere has changed dramatically
throughout its 4.5 billion year history. For example, molecular oxygen is
abundant in the atmosphere today but was absent on the early Earth. Meanwhile,
the physical and chemical evolution of Earth's atmosphere has also resulted in
major swings in surface temperature, at times resulting in extreme glaciation
or warm greenhouse climates. Despite this dynamic and occasionally dramatic
history, the Earth has been persistently habitable--and, in fact,
inhabited--for roughly 4 billion years. Understanding Earth's momentous changes
and its enduring habitability is essential as a guide to the diversity of
habitable planetary environments that may exist beyond our solar system and for
ultimately recognizing spectroscopic fingerprints of life elsewhere in the
Universe. Here, we review long-term trends in the composition of Earth's
atmosphere as it relates to both planetary habitability and inhabitation. We
focus on gases that may serve as habitability markers (CO2, N2) or
biosignatures (CH4, O2), especially as related to the redox evolution of the
atmosphere and the coupled evolution of Earth's climate system. We emphasize
that in the search for Earth-like planets we must be mindful that the example
provided by the modern atmosphere merely represents a single snapshot of
Earth's long-term evolution. In exploring the many former states of our own
planet, we emphasize Earth's atmospheric evolution during the Archean,
Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of
potential atmospheric trajectories into the distant future, many millions to
billions of years from now. All of these 'Alternative Earth' scenarios provide
insight to the potential diversity of Earth-like, habitable, and inhabited
worlds.
| arxiv topic:astro-ph.EP |
arxiv_dataset-95621803.06067 | Dynamic-structured Semantic Propagation Network
cs.CV
Semantic concept hierarchy is still under-explored for semantic segmentation
due to the inefficiency and complicated optimization of incorporating
structural inference into dense prediction. This lack of modeling semantic
correlations also makes prior works must tune highly-specified models for each
task due to the label discrepancy across datasets. It severely limits the
generalization capability of segmentation models for open set concept
vocabulary and annotation utilization. In this paper, we propose a
Dynamic-Structured Semantic Propagation Network (DSSPN) that builds a semantic
neuron graph by explicitly incorporating the semantic concept hierarchy into
network construction. Each neuron represents the instantiated module for
recognizing a specific type of entity such as a super-class (e.g. food) or a
specific concept (e.g. pizza). During training, DSSPN performs the
dynamic-structured neuron computation graph by only activating a sub-graph of
neurons for each image in a principled way. A dense semantic-enhanced neural
block is proposed to propagate the learned knowledge of all ancestor neurons
into each fine-grained child neuron for feature evolving. Another merit of such
semantic explainable structure is the ability of learning a unified model
concurrently on diverse datasets by selectively activating different neuron
sub-graphs for each annotation at each step. Extensive experiments on four
public semantic segmentation datasets (i.e. ADE20K, COCO-Stuff, Cityscape and
Mapillary) demonstrate the superiority of our DSSPN over state-of-the-art
segmentation models. Moreoever, we demonstrate a universal segmentation model
that is jointly trained on diverse datasets can surpass the performance of the
common fine-tuning scheme for exploiting multiple domain knowledge.
| arxiv topic:cs.CV |
arxiv_dataset-95631803.06167 | Semantic Segmentation of Pathological Lung Tissue with Dilated Fully
Convolutional Networks
cs.CV
Early and accurate diagnosis of interstitial lung diseases (ILDs) is crucial
for making treatment decisions, but can be challenging even for experienced
radiologists. The diagnostic procedure is based on the detection and
recognition of the different ILD pathologies in thoracic CT scans, yet their
manifestation often appears similar. In this study, we propose the use of a
deep purely convolutional neural network for the semantic segmentation of ILD
patterns, as the basic component of a computer aided diagnosis (CAD) system for
ILDs. The proposed CNN, which consists of convolutional layers with dilated
filters, takes as input a lung CT image of arbitrary size and outputs the
corresponding label map. We trained and tested the network on a dataset of 172
sparsely annotated CT scans, within a cross-validation scheme. The training was
performed in an end-to-end and semi-supervised fashion, utilizing both labeled
and non-labeled image regions. The experimental results show significant
performance improvement with respect to the state of the art.
| arxiv topic:cs.CV |
arxiv_dataset-95641803.06267 | Consistent sets of lines with no colorful incidence
cs.CG cs.CV math.CO
We consider incidences among colored sets of lines in $\mathbb{R}^d$ and
examine whether the existence of certain concurrences between lines of $k$
colors force the existence of at least one concurrence between lines of $k+1$
colors. This question is relevant for problems in 3D reconstruction in computer
vision.
| arxiv topic:cs.CG cs.CV math.CO |
arxiv_dataset-95651803.06367 | The supernova remnant population in the very-high-energy sky: prospects
for CTA
astro-ph.HE
The detection of very-high-energy gamma rays from supernova remnant shells
testifies of the acceleration of particles at strong shocks. Many aspects of
the particle acceleration remain however unclear. The study of individual
objects is very helpful, but the study of the entire population of SNRs
detected in this range and its characteristics can also bring valuable science.
Using Monte-Carlo simulations, the population of shells bright in the TeV and
multi-TeV range can be simulated. The results of these simulations aim at being
compared with observations of in struments operating in these ranges, such as
the Cherenkov Telescope Array (CTA). Our results suggest that CTA should be
able to effectively constrain the slope of particles accelerated at SNRs and
the electron-to-proton ratio.
| arxiv topic:astro-ph.HE |
arxiv_dataset-95661803.06467 | Optimizing Information Freshness in Wireless Networks under General
Interference Constraints
cs.IT cs.NI math.IT
Age of information (AoI) is a recently proposed metric for measuring
information freshness. AoI measures the time that elapsed since the last
received update was generated. We consider the problem of minimizing average
and peak AoI in a wireless networks, consisting of a set of source-destination
links, under general interference constraints. When fresh information is always
available for transmission, we show that a stationary scheduling policy is peak
age optimal. We also prove that this policy achieves average age that is within
a factor of two of the optimal average age. In the case where fresh information
is not always available, and packet/information generation rate has to be
controlled along with scheduling links for transmission, we prove an important
separation principle: the optimal scheduling policy can be designed assuming
fresh information, and independently, the packet generation rate control can be
done by ignoring interference. Peak and average AoI for discrete time G/Ber/1
queue is analyzed for the first time, which may be of independent interest.
| arxiv topic:cs.IT cs.NI math.IT |
arxiv_dataset-95671803.06567 | A Dual Approach to Scalable Verification of Deep Networks
cs.LG stat.ML
This paper addresses the problem of formally verifying desirable properties
of neural networks, i.e., obtaining provable guarantees that neural networks
satisfy specifications relating their inputs and outputs (robustness to bounded
norm adversarial perturbations, for example). Most previous work on this topic
was limited in its applicability by the size of the network, network
architecture and the complexity of properties to be verified. In contrast, our
framework applies to a general class of activation functions and specifications
on neural network inputs and outputs. We formulate verification as an
optimization problem (seeking to find the largest violation of the
specification) and solve a Lagrangian relaxation of the optimization problem to
obtain an upper bound on the worst case violation of the specification being
verified. Our approach is anytime i.e. it can be stopped at any time and a
valid bound on the maximum violation can be obtained. We develop specialized
verification algorithms with provable tightness guarantees under special
assumptions and demonstrate the practical significance of our general
verification approach on a variety of verification tasks.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-95681803.06667 | Subleading-power corrections to the radiative leptonic $B \to \gamma
\ell \nu$ decay in QCD
hep-ph hep-ex hep-lat
Applying the method of light-cone sum rules with photon distribution
amplitudes, we compute the subleading-power correction to the radiative
leptonic $B \to \gamma \ell \nu$ decay, at next-to-leading order in QCD for the
twist-two contribution and at leading order in $\alpha_s$ for the higher-twist
contributions, induced by the hadronic component of the collinear photon. The
leading-twist hadronic photon effect turns out to preserve the symmetry
relation between the two $B \to \gamma$ form factors due to the helicity
conservation, however, the higher-twist hadronic photon corrections can yield
symmetry-breaking effect already at tree level in QCD. Using the conformal
expansion of photon distribution amplitudes with the non-perturbative
parameters estimated from QCD sum rules, the twist-two hadronic photon
contribution can give rise to approximately 30\% correction to the
leading-power "direct photon" effect computed from the perturbative QCD
factorization approach. In contrast, the subleading-power corrections from the
higher-twist two-particle and three-particle photon distribution amplitudes are
estimated to be of ${\cal O} (3 \sim 5\%)$ with the light-cone sum rule
approach. We further predict the partial branching fractions of $B \to \gamma
\ell \nu $ with a photon-energy cut $E_{\gamma} \geq E_{\rm cut}$, which are of
interest for determining the inverse moment of the leading-twist $B$-meson
distribution amplitude thanks to the forthcoming high-luminosity Belle II
experiment at KEK.
| arxiv topic:hep-ph hep-ex hep-lat |
arxiv_dataset-95691803.06767 | Generation and detection of non-Gaussian phonon-added coherent states in
optomechanical systems
quant-ph cond-mat.mes-hall physics.optics
Adding excitations on a coherent state provides an effective way to observe
nonclassical properties of radiation fields. Here we describe and analyse how
to apply this concept to the motional state of a mechanical oscillator and
present a full scheme to prepare non-Gaussian {\it phonon}-added coherent
states of the mechanical motion in cavity optomechanics. We first generate a
mechanical coherent state using electromagnetically induced transparency. We
then add a single phonon onto the coherent state via optomechanical parametric
down-conversion combined with single photon detection. We validate this
single-phonon-added coherent state by using a red-detuned beam and reading out
the state of the optical output field. This approach allows us to verify
nonclassical properties of the phonon state, such as sub-Poissonian character
and quadrature squeezing. We further show that our scheme can be directly
implemented using existing devices, and is generic in nature and hence
applicable to a variety of systems in opto- and electromechanics.
| arxiv topic:quant-ph cond-mat.mes-hall physics.optics |
arxiv_dataset-95701803.06867 | Cloud Infrastructure Provenance Collection and Management to Reproduce
Scientific Workflow Execution
cs.DC
The emergence of Cloud computing provides a new computing paradigm for
scientific workflow execution. It provides dynamic, on-demand and scalable
resources that enable the processing of complex workflow-based experiments.
With the ever growing size of the experimental data and increasingly complex
processing workflows, the need for reproducibility has also become essential.
Provenance has been thought of a mechanism to verify a workflow and to provide
workflow reproducibility. One of the obstacles in reproducing an experiment
execution is the lack of information about the execution infrastructure in the
collected provenance. This information becomes critical in the context of Cloud
in which resources are provisioned on-demand and by specifying resource
configurations. Therefore, a mechanism is required that enables capturing of
infrastructure information along with the provenance of workflows executing on
the Cloud to facilitate the re-creation of execution environment on the Cloud.
This paper presents a framework, ReCAP, along with the proposed mapping
approaches that aid in capturing the Cloud-aware provenance information and
help in re-provisioning the execution resource on the Cloud with similar
configurations. Experimental evaluation has shown the impact of different
resource configurations on the workflow execution performance, therefore
justifies the need for collecting such provenance information in the context of
Cloud. The evaluation has also demonstrated that the proposed mapping
approaches can capture Cloud information in various Cloud usage scenarios
without causing performance overhead and can also enable the re-provisioning of
resources on Cloud. Experiments were conducted using workflows from different
scientific domains such as astronomy and neuroscience to demonstrate the
applicability of this research for different workflows.
| arxiv topic:cs.DC |
arxiv_dataset-95711803.06967 | Phenomenology of coupled non linear oscillators
nlin.CD
A recently introduced model of coupled non linear oscillators in a ring is
revisited in terms of its information processing capabilities. The use of
Lempel-Ziv based entropic measures allows to study thoroughly the complex
patterns appearing in the system for different values of the control
parameters. Such behaviors, resembling cellular automata, have been
characterized both spatially and temporally. Information distance is used to
study the stability of the system to perturbations in the initial conditions
and in the control parameters. The latter is not an issue in cellular automata
theory, where the rules form a numerable set, contrary to the continuous nature
of the parameter space in the system studied in this contribution. The
variation in the density of the digits, as a function of time is also studied.
Local transitions in the control parameter space are also discussed.
| arxiv topic:nlin.CD |
arxiv_dataset-95721803.07067 | Setting up a Reinforcement Learning Task with a Real-World Robot
cs.LG cs.AI cs.RO stat.ML
Reinforcement learning is a promising approach to developing hard-to-engineer
adaptive solutions for complex and diverse robotic tasks. However, learning
with real-world robots is often unreliable and difficult, which resulted in
their low adoption in reinforcement learning research. This difficulty is
worsened by the lack of guidelines for setting up learning tasks with robots.
In this work, we develop a learning task with a UR5 robotic arm to bring to
light some key elements of a task setup and study their contributions to the
challenges with robots. We find that learning performance can be highly
sensitive to the setup, and thus oversights and omissions in setup details can
make effective learning, reproducibility, and fair comparison hard. Our study
suggests some mitigating steps to help future experimenters avoid difficulties
and pitfalls. We show that highly reliable and repeatable experiments can be
performed in our setup, indicating the possibility of reinforcement learning
research extensively based on real-world robots.
| arxiv topic:cs.LG cs.AI cs.RO stat.ML |
arxiv_dataset-95731803.07167 | Soft Pomerons and the Forward LHC Data
hep-ph hep-ex
Recent data from LHC13 by the TOTEM Collaboration on $\sigma_{tot}$ and
$\rho$ have indicated disagreement with all the Pomeron model predictions by
the COMPETE Collaboration (2002). On the other hand, as recently demonstrated
by Martynov and Nicolescu (MN), the new $\sigma_{tot}$ datum and the unexpected
decrease in the $\rho$ value are well described by the maximal Odderon
dominance at the highest energies. Here, we discuss the applicability of
Pomeron dominance through fits to the \textit{most complete set} of forward
data from $pp$ and $\bar{p}p$ scattering. We consider an analytic
parametrization for $\sigma_{tot}(s)$ consisting of non-degenerated Regge
trajectories for even and odd amplitudes (as in the MN analysis) and two
Pomeron components associated with double and triple poles in the complex
angular momentum plane. The $\rho$ parameter is analytically determined by
means of dispersion relations. We carry out fits to $pp$ and $\bar{p}p$ data on
$\sigma_{tot}$ and $\rho$ in the interval 5 GeV - 13 TeV (as in the MN
analysis). Two novel aspects of our analysis are: (1) the dataset comprises all
the accelerator data below 7 TeV and we consider \textit{three independent
ensembles} by adding: either only the TOTEM data (as in the MN analysis), or
only the ATLAS data, or both sets; (2) in the data reductions to each ensemble,
uncertainty regions are evaluated through error propagation from the fit
parameters, with 90 \% CL. We argument that, within the uncertainties, this
analytic model corresponding to soft Pomeron dominance, does not seem to be
excluded by the \textit{complete} set of experimental data presently available.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-95741803.07267 | Does the chiral magnetic effect change the dynamic universality class in
QCD?
hep-ph cond-mat.mes-hall cond-mat.stat-mech nucl-th
In QCD matter under an external magnetic field, the chiral magnetic effect
(CME) leads to the collective gapless mode called the chiral magnetic wave
(CMW). Since dynamic universality class generally depends on low-energy gapless
modes, it is nontrivial whether the CME and the resulting CMW change that of
the second-order chiral phase transition in QCD. To address this question, we
study the critical dynamics near the chiral phase transition in massless
two-flavor QCD under an external magnetic field. By performing the dynamic
renormalization-group analysis within the epsilon expansion, we find that the
presence of the CME changes the dynamic universality class to that of model A.
We also show that the transport coefficient of the CME is not renormalized by
the critical fluctuations of the order parameter.
| arxiv topic:hep-ph cond-mat.mes-hall cond-mat.stat-mech nucl-th |
arxiv_dataset-95751803.07367 | Muon anomalies and the $SU(5)$ Yukawa relations
hep-ph
We show that, within the framework of $SU(5)$ Grand Unified Theories (GUTs),
multiple vector-like families at the GUT scale which transform under a gauged
$U(1)'$ (under which the three chiral families are neutral) can result in a
single vector-like family at low energies which can induce non-universal and
flavourful $Z'$ couplings, which can account for the B physics anomalies in
$R_{K^{(*)}}$. In such theories, we show that the same muon couplings which
explain $R_{K^{(*)}}$ also correct the Yukawa relation $Y_e=Y_d^T$ in the muon
sector without the need for higher Higgs representations. To illustrate the
mechanism, we construct a concrete a model based on $SU(5)\times A_4 \times
Z_3\times Z_7$ with two vector-like families at the GUT scale, and two
right-handed neutrinos, leading to a successful fit to quark and lepton
(including neutrino) masses, mixing angles and CP phases, where the constraints
from lepton flavour violation require $Y_e$ to be diagonal.
| arxiv topic:hep-ph |
arxiv_dataset-95761803.07467 | Laser Cooling at Resonance
cond-mat.quant-gas physics.atom-ph
We show experimentally that 3-D laser cooling of lithium atoms is achieved
when the laser light is tuned exactly to resonance with the atomic transition.
For a theoretical description of this surprising phenomenon we resolve to a
full model which takes into account both the entire atomic structure and the
laser light polarization. Here we build such a model for $^7$Li atoms cooled on
the $D_{2}$-line in a $\sigma^+-\sigma^-$ laser configuration. We take all 24
Zeeman sub-levels into account and obtain good agreement with the experimental
data. Moreover, by means of Monte-Carlo simulations we show that coherent
processes play an important role in showing consistency between the theory and
the experimental results.
| arxiv topic:cond-mat.quant-gas physics.atom-ph |
arxiv_dataset-95771803.07567 | Umbral Moonshine and String Duality
hep-th
By studying 2d string compactifications with half-maximal supersymmetry in a
variety of duality frames, we find a natural physical setting for understanding
Umbral moonshine. Near points in moduli space with enhanced gauge symmetry, we
find that the Umbral symmetry groups arise as symmetries of the theory. In one
duality frame -- a flux compactification on $T^4/Z_2\times T^4$ -- the
24-dimensional permutation representations of the Umbral groups act on
D1-branes strung between a set of NS5-branes. The presence of these NS5-branes
is used to explain the Umbral moonshine decompositions of the K3 twining
genera, and in particular of the K3 elliptic genus. The fundamental string in
this frame is dual to the type IIA string on K3$\times T^4$ and to a
compactified heterotic little string theory. The latter provides an interesting
example of a little string theory, as the string-scale geometry transverse to
the 5-brane plays an important role in its construction.
| arxiv topic:hep-th |
arxiv_dataset-95781803.07667 | Edgeworth expansions for weakly dependent random variables
math.PR math.DS
We discuss sufficient conditions that guarantee the existence of asymptotic
expansions for the Central Limit Theorem for weakly dependent random variables
including observations arising from sufficiently chaotic dynamical systems like
piece-wise expanding maps, and strongly ergodic Markov chains. We primarily use
spectral techniques to obtain the results.
| arxiv topic:math.PR math.DS |
arxiv_dataset-95791803.07767 | Composite fermion Hall conductivity and the half-filled Landau level
cond-mat.str-el
We consider the Hall conductivity of composite fermions in the theory of
Halperin, Lee, and Read (HLR). We present a fully quantum mechanical numerical
calculation that shows, under suitable conditions, the HLR theory exhibits a
particle-hole symmetric dc electrical Hall response in the presence of quenched
disorder. Remarkably, this response of the HLR theory remains robust even when
the disorder range is of the order of the Fermi wavelength. We find that
deviations from particle-hole symmetric response can appear in the ac Hall
conductivity at frequencies sufficiently large compared to the inverse system
size. Our results agree with a recent semi-classical analysis by Wang et al.,
Phys. Rev. X 7, 031029 (2017) and complement the arguments based on the fully
quantum-mechanical model by Kumar et al., Phys. Rev. B 98, 11505 (2018). These
results provide further evidence that the HLR theory is compatible with an
emergent particle-hole symmetry.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-95801803.07867 | Transit Photometry as an Exoplanet Discovery Method
astro-ph.EP
Photometry with the transit method has arguably been the most successful
exoplanet discovery method to date. A short overview about the rise of that
method to its present status is given. The method's strength is the rich set of
parameters that can be obtained from transiting planets, in particular in
combination with radial velocity observations; the basic principles of these
parameters are given, with explicit formulations for the transit detection
probability and the times of transit epochs in comparison to radial velocity
epochs. The transit method has however also drawbacks, which are the low
probability of properly aligned planet systems and the presence of
astrophysical phenomena that may mimic transits and give rise to false
detection positives. In the second part, we outline the main factors that
determine the design of transit surveys, such as the size of the survey sample,
the temporal coverage, the photometric precision, the sample brightness and the
methods to extract transit events from observed light curves. Lastly, an
overview over past, current, and future transit surveys is given. For these
surveys we indicate their basic instrument configuration and their planet
catch, including the ranges of planet sizes and stellar magnitudes that were
encountered. Current and future transit detection experiments concentrate
primarily on bright or special targets, and we expect that the transit method
remains a principal driver of exoplanet science, through new discoveries to be
made and through the development of new generations of instruments.
| arxiv topic:astro-ph.EP |
arxiv_dataset-95811803.07967 | Long-wavelength phonons in the crystalline and pasta phases of
neutron-star crusts
nucl-th astro-ph.HE
We study the long-wavelength excitations of the inner crust of neutron stars,
considering three phases: cubic crystal at low densities, rods and plates near
the core-crust transition. To describe the phonons, we write an effective
Lagrangian density in terms of the coarse-grained phase of the neutron
superfluid gap and of the average displacement field of the clusters. The
kinetic energy, including the entrainment of the neutron gas by the clusters,
is obtained within a superfluid hydrodynamics approach. The potential energy is
determined from a model where clusters and neutron gas are considered in phase
coexistence, augmented by the elasticity of the lattice due to Coulomb and
surface effects. All three phases show strong anisotropy, i.e., angle
dependence of the phonon velocities. Consequences for the specific heat at low
temperature are discussed.
| arxiv topic:nucl-th astro-ph.HE |
arxiv_dataset-95821803.08067 | A Review of Situation Awareness Assessment Approaches in Aviation
Environments
cs.HC
Situation awareness (SA) is an important constituent in human information
processing and essential in pilots' decision-making processes. Acquiring and
maintaining appropriate levels of SA is critical in aviation environments as it
affects all decisions and actions taking place in flights and air traffic
control. This paper provides an overview of recent measurement models and
approaches to establishing and enhancing SA in aviation environments. Many
aspects of SA are examined including the classification of SA techniques into
six categories, and different theoretical SA models from individual, to shared
or team, and to distributed or system levels. Quantitative and qualitative
perspectives pertaining to SA methods and issues of SA for unmanned vehicles
are also addressed. Furthermore, future research directions regarding SA
assessment approaches are raised to deal with shortcomings of the existing
state-of-the-art methods in the literature.
| arxiv topic:cs.HC |
arxiv_dataset-95831803.08167 | A Staggered Explicit-Implicit Finite Element Formulation for
Electroactive Polymers
physics.comp-ph
Electroactive polymers such as dielectric elastomers (DEs) have attracted
significant attention in recent years. Computational techniques to solve the
coupled electromechanical system of equations for this class of materials have
universally centered around fully coupled monolithic formulations, which while
generating good accuracy requires significant computational expense. However,
this has significantly hindered the ability to solve large scale, fully
three-dimensional problems involving complex deformations and electromechanical
instabilities of DEs. In this work, we provide theoretical basis for the
effectiveness and accuracy of staggered explicit-implicit finite element
formulations for this class of electromechanically coupled materials, and
elicit the simplicity of the resulting staggered formulation. We demonstrate
the stability and accuracy of the staggered approach by solving complex
electromechanically coupled problems involving electroactive polymers, where we
focus on problems involving electromechanical instabilities such as creasing,
wrinkling, and bursting drops. In all examples, essentially identical results
to the fully monolithic solution are obtained, showing the accuracy of the
staggered approach at a significantly reduced computational cost.
| arxiv topic:physics.comp-ph |
arxiv_dataset-95841803.08267 | Cross-infrastructure holistic experiment design for cyber-physical
energy system validation
cs.SY
Strong digitalization and shifting from unidirectional to bidirectional
topology have transformed the electrical grid into a cyber-physical energy
system, i.e. smart grid, with strong interdependency among various domains. It
is mandatory to develop a comprehensive and holistic validation approach for
such large scale system. However, a single research infrastructure may not have
sufficient expertise and equipment for such test, without huge or eventually
unfeasible investment. In this paper, we propose another adequate approach:
connecting existing and established infrastructures with complementary
specialization and facilities into a cross-infrastructure holistic experiment.
The proposition enables testing of CPES assessment research in near real-world
scenario without significant investment while efficiently exploiting the
existing infrastructures. Hybrid cloud based architecture is considered as the
support for such setup and the design of cross-infrastructure experiment is
also covered.
| arxiv topic:cs.SY |
arxiv_dataset-95851803.08367 | Gradient Descent Quantizes ReLU Network Features
stat.ML cs.LG
Deep neural networks are often trained in the over-parametrized regime (i.e.
with far more parameters than training examples), and understanding why the
training converges to solutions that generalize remains an open problem.
Several studies have highlighted the fact that the training procedure, i.e.
mini-batch Stochastic Gradient Descent (SGD) leads to solutions that have
specific properties in the loss landscape. However, even with plain Gradient
Descent (GD) the solutions found in the over-parametrized regime are pretty
good and this phenomenon is poorly understood.
We propose an analysis of this behavior for feedforward networks with a ReLU
activation function under the assumption of small initialization and learning
rate and uncover a quantization effect: The weight vectors tend to concentrate
at a small number of directions determined by the input data. As a consequence,
we show that for given input data there are only finitely many, "simple"
functions that can be obtained, independent of the network size. This puts
these functions in analogy to linear interpolations (for given input data there
are finitely many triangulations, which each determine a function by linear
interpolation). We ask whether this analogy extends to the generalization
properties - while the usual distribution-independent generalization property
does not hold, it could be that for e.g. smooth functions with bounded second
derivative an approximation property holds which could "explain" generalization
of networks (of unbounded size) to unseen inputs.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-95861803.08467 | BSD-GAN: Branched Generative Adversarial Network for Scale-Disentangled
Representation Learning and Image Synthesis
cs.CV
We introduce BSD-GAN, a novel multi-branch and scale-disentangled training
method which enables unconditional Generative Adversarial Networks (GANs) to
learn image representations at multiple scales, benefiting a wide range of
generation and editing tasks. The key feature of BSD-GAN is that it is trained
in multiple branches, progressively covering both the breadth and depth of the
network, as resolutions of the training images increase to reveal finer-scale
features. Specifically, each noise vector, as input to the generator network of
BSD-GAN, is deliberately split into several sub-vectors, each corresponding to,
and is trained to learn, image representations at a particular scale. During
training, we progressively "de-freeze" the sub-vectors, one at a time, as a new
set of higher-resolution images is employed for training and more network
layers are added. A consequence of such an explicit sub-vector designation is
that we can directly manipulate and even combine latent (sub-vector) codes
which model different feature scales.Extensive experiments demonstrate the
effectiveness of our training method in scale-disentangled learning of image
representations and synthesis of novel image contents, without any extra labels
and without compromising quality of the synthesized high-resolution images. We
further demonstrate several image generation and manipulation applications
enabled or improved by BSD-GAN. Source codes are available at
https://github.com/duxingren14/BSD-GAN.
| arxiv topic:cs.CV |
arxiv_dataset-95871803.08567 | Property FW, differentiable structures, and smoothability of singular
actions
math.DS math.GR math.GT
We provide a smoothening criterion for group actions on manifolds by singular
diffeomorphisms. We prove that if a countable group $\Gamma$ has the fixed
point property FW for walls (e.g. if it has property (T)), every aperiodic
action of $\Gamma$ by diffeomorphisms that are of class $C^r$ with countably
many singularities is conjugate to an action by true diffeomorphisms of class
$C^r$ on a homeomorphic (possibly non-diffeomorphic) manifold. As applications,
we show that Navas's result for actions of Kazhdan groups on the circle, as
well as the recent solutions to Zimmer's conjecture, generalise to aperiodic
actions by diffeomorphisms with countably many singularities.
| arxiv topic:math.DS math.GR math.GT |
arxiv_dataset-95881803.08667 | On efficient global optimization via universal Kriging surrogate models
stat.ML
In this paper, we investigate the capability of the universal Kriging (UK)
model for single-objective global optimization applied within an efficient
global optimization (EGO) framework. We implemented this combined UK-EGO
framework and studied four variants of the UK methods, that is, a UK with a
first-order polynomial, a UK with a second-order polynomial, a blind Kriging
(BK) implementation from the ooDACE toolbox, and a polynomial-chaos Kriging
(PCK) implementation. The UK-EGO framework with automatic trend function
selection derived from the BK and PCK models works by building a UK surrogate
model and then performing optimizations via expected improvement criteria on
the Kriging model with the lowest leave-one-out cross-validation error. Next,
we studied and compared the UK-EGO variants and standard EGO using five
synthetic test functions and one aerodynamic problem. Our results show that the
proper choice for the trend function through automatic feature selection can
improve the optimization performance of UK-EGO relative to EGO. From our
results, we found that PCK-EGO was the best variant, as it had more robust
performance as compared to the rest of the UK-EGO schemes; however, total-order
expansion should be used to generate the candidate trend function set for
high-dimensional problems. Note that, for some test functions, the UK with
predetermined polynomial trend functions performed better than that of BK and
PCK, indicating that the use of automatic trend function selection does not
always lead to the best quality solutions. We also found that although some
variants of UK are not as globally accurate as the ordinary Kriging (OK), they
can still identify better-optimized solutions due to the addition of the trend
function, which helps the optimizer locate the global optimum.
| arxiv topic:stat.ML |
arxiv_dataset-95891803.08767 | A conservation law with spatially localized sublinear damping
math.AP math.OC
We consider a general conservation law on the circle, in the presence of a
sublinear damping. If the damping acts on the whole circle, then the solution
becomes identically zero in finite time, following the same mechanism as the
corresponding ordinary differential equation. When the damping acts only
locally in space, we show a dichotomy: if the flux function is not zero at the
origin, then the transport mechanism causes the extinction of the solution in
finite time, as in the first case. On the other hand, if zero is a
non-degenerate critical point of the flux function, then the solution becomes
extinct in finite time only inside the damping zone, decays algebraically
uniformly in space, and we exhibit a boundary layer, shrinking with time,
around the damping zone. Numerical illustrations show how similar phenomena may
be expected for other equations.
| arxiv topic:math.AP math.OC |
arxiv_dataset-95901803.08867 | Testing demand responsive shared transport services via agent-based
simulations
cs.MA physics.soc-ph
Demand Responsive Shared Transport DRST services take advantage of
Information and Communication Technologies ICT, to provide on demand transport
services booking in real time a ride on a shared vehicle. In this paper, an
agent-based model ABM is presented to test different the feasibility of
different service configurations in a real context. First results show the
impact of route choice strategy on the system performance.
| arxiv topic:cs.MA physics.soc-ph |
arxiv_dataset-95911803.08967 | Automatic phase calibration for RF cavities using beam-loading signals
physics.acc-ph
Precise calibration of the cavity phase signals is necessary for the
operation of any particle accelerator. For many systems this requires human in
the loop adjustments based on measurements of the beam parameters downstream.
Some recent work has developed a scheme for the calibration of the cavity phase
using beam measurements and beam-loading however this scheme is still a
multi-step process that requires heavy automation or human in the loop. In this
paper we analyze a new scheme that uses only RF signals reacting to
beam-loading to calculate the phase of the beam relative to the cavity. This
technique could be used in slow control loops to provide real-time adjustment
of the cavity phase calibration without human intervention thereby increasing
the stability and reliability of the accelerator.
| arxiv topic:physics.acc-ph |
arxiv_dataset-95921803.09067 | Gravity model explained by the radiation model on a population landscape
physics.soc-ph
Understanding the mechanisms behind human mobility patterns is crucial to
improve our ability to optimize and predict traffic flows. Two representative
mobility models, i.e., radiation and gravity models, have been extensively
compared to each other against various empirical data sets, while their
fundamental relation is far from being fully understood. In order to study such
a relation, we first model the heterogeneous population landscape by generating
a fractal geometry of sites and then by assigning to each site a population
independently drawn from a power-law distribution. Then the radiation model on
this population landscape, which we call the radiation-on-landscape (RoL)
model, is compared to the gravity model to derive the distance exponent in the
gravity model in terms of the properties of the population landscape, which is
confirmed by the numerical simulations. Consequently, we provide a possible
explanation for the origin of the distance exponent in terms of the properties
of the heterogeneous population landscape, enabling us to better understand
mobility patterns constrained by the travel distance.
| arxiv topic:physics.soc-ph |
arxiv_dataset-95931803.09167 | 3D Reconstruction & Assessment Framework based on affordable 2D Lidar
cs.RO
Lidar is extensively used in the industry and mass-market. Due to its
measurement accuracy and insensitivity to illumination compared to cameras, It
is applied onto a broad range of applications, like geodetic engineering, self
driving cars or virtual reality. But the 3D Lidar with multi-beam is very
expensive, and the massive measurements data can not be fully leveraged on some
constrained platforms. The purpose of this paper is to explore the possibility
of using cheap 2D Lidar off-the-shelf, to preform complex 3D Reconstruction,
moreover, the generated 3D map quality is evaluated by our proposed metrics at
the end. The 3D map is constructed in two ways, one way in which the scan is
performed at known positions with an external rotary axis at another plane. The
other way, in which the 2D Lidar for mapping and another 2D Lidar for
localization are placed on a trolley, the trolley is pushed on the ground
arbitrarily. The generated maps by different approaches are converted to
octomaps uniformly before the evaluation. The similarity and difference between
two maps will be evaluated by the proposed metrics thoroughly. The whole
mapping system is composed of several modular components. A 3D bracket was made
for assembling of the Lidar with a long range, the driver and the motor
together. A cover platform made for the IMU and 2D Lidar with a shorter range
but high accuracy. The software is stacked up in different ROS packages.
| arxiv topic:cs.RO |
arxiv_dataset-95941803.09267 | Frobenius Degenerations of Preprojective Algebras
math.RA math.RT math.SG
In this paper, we study a preprojective algebra for quivers decorated with
$k$-algebras and bimodules, which generalizes work of Gabriel for ordinary
quivers, work of Dlab and Ringel for $k$-species, and recent work of de
Thanhoffer de V\"olcsey and Presotto, which has recently appeared from a
different perspective in work of K\"ulshammer. As for undecorated quivers, we
show that its moduli space of representations recovers the Hamiltonian
reduction of the cotangent bundle over the space of representations of the
decorated quiver. These algebras yield degenerations of ordinary preprojective
algebras, by folding the quiver and then degenerating the decorations. We prove
that these degenerations are flat in the Dynkin case, and conjecture, based on
computer results, that this extends to arbitrary decorated quivers.
| arxiv topic:math.RA math.RT math.SG |
arxiv_dataset-95951803.09367 | Opposition diagrams for automorphisms of small spherical buildings
math.CO
An automorphism $\theta$ of a spherical building $\Delta$ is called
\textit{capped} if it satisfies the following property: if there exist both
type $J_1$ and $J_2$ simplices of $\Delta$ mapped onto opposite simplices by
$\theta$ then there exists a type $J_1\cup J_2$ simplex of $\Delta$ mapped onto
an opposite simplex by $\theta$. In previous work we showed that if $\Delta$ is
a thick irreducible spherical building of rank at least $3$ with no Fano plane
residues then every automorphism of $\Delta$ is capped. In the present work we
consider the spherical buildings with Fano plane residues (the \textit{small
buildings}). We show that uncapped automorphisms exist in these buildings and
develop an enhanced notion of "opposition diagrams" to capture the structure of
these automorphisms. Moreover we provide applications to the theory of
"domesticity" in spherical buildings, including the complete classification of
domestic automorphisms of small buildings of types $\mathsf{F}_4$ and
$\mathsf{E}_6$.
| arxiv topic:math.CO |
arxiv_dataset-95961803.09467 | A Switch to the Concern of User: Importance Coefficient in Utility
Distribution and Message Importance Measure
cs.IT math.IT math.PR math.ST stat.TH
This paper mainly focuses on the utilization frequency in receiving end of
communication systems, which shows the inclination of the user about different
symbols. When the average number of use is limited, a specific utility
distribution is proposed on the best effort in term of fairness, which is also
the closest one to occurring probability in the relative entropy. Similar to a
switch, its parameter can be selected to make it satisfy different users'
requirements: negative parameter means the user focus on high-probability
events and positive parameter means the user is interested in small-probability
events. In fact, the utility distribution is a measure of message importance in
essence. It illustrates the meaning of message importance measure (MIM), and
extend it to the general case by selecting the parameter. Numerical results
show that this utility distribution characterizes the message importance like
MIM and its parameter determines the concern of users.
| arxiv topic:cs.IT math.IT math.PR math.ST stat.TH |
arxiv_dataset-95971803.09567 | The Arches cluster revisited: I. Data presentation and stellar census
astro-ph.SR astro-ph.GA
Located within the central region of the Galaxy, the Arches cluster appears
to be one of the youngest, densest and most massive stellar aggregates within
the Milky Way. As such it has the potential to be a uniquely instructive
laboratory for the study of star formation in extreme environments and the
physics of very massive stars. In order to determine the fundamental physical
properties of both cluster and constituent stars, we provide and analyse new
HST+VLT near-IR datasets. Stacking multiple epochs of spectroscopy results in
the deepest view of the cluster ever obtained, allowing us to to identify
candidate giant and main sequence stars for the first time. All cluster members
are found to be WNLh or O stars, with the smooth and continuous progression in
spectral morphologies from O super-/hypergiants through to the WNLh cohort
implying a direct evolutionary connection. Importantly no H-free Wolf-Rayets
are found, while no products of binary interaction/mass-transfer may be
unambiguously identified, despite the presence of massive binaries within the
Arches. We infer a main sequence turn-off around O4-5V, corresponding to
~30-38Msun, while the eclipsing binary F2 implies current masses of ~80Msun and
~60Msun for the WNLh and O hypergiant cohorts, respectively. A cluster age of
~2-3Myr is suggested by the location of the main-sequence turn-off. While the
absence of H-free Wolf-Rayets argues against the prior occurrence of SNe, such
an age does accommodate such events for exceptionally massive stars. Future
progress requires quantitative analysis of cluster members combined with
additional spectroscopic observations to better constrain the binary
population; nevertheless it is already abundantly clear that the Arches offers
an unprecedented insight into the formation, evolution and death of the most
massive stars Nature allows to form in the local universe (Abridged).
| arxiv topic:astro-ph.SR astro-ph.GA |
arxiv_dataset-95981803.09667 | Spin subdiffusion in disordered Hubbard chain
cond-mat.str-el cond-mat.quant-gas
We derive and study the effective spin model that explains the anomalous spin
dynamics in the one-dimensional Hubbard model with strong potential disorder.
Assuming that charges are localized, we show that spins are delocalized and
their subdiffusive transport originates from a singular random distribution of
spin exchange interactions. The exponent relevant for the subdiffusion is
determined by the Anderson localization length and the density of electrons.
While the analytical derivations are valid for low particle density, numerical
results for the full model reveal a qualitative agreement up to half-filling.
| arxiv topic:cond-mat.str-el cond-mat.quant-gas |
arxiv_dataset-95991803.09767 | Unifying Dark Matter and Dark Energy with non-Canonical Scalars
gr-qc astro-ph.CO hep-ph hep-th
Non-canonical scalar fields with the Lagrangian ${\cal L} = X^\alpha -
V(\phi)$, possess the attractive property that the speed of sound, $c_s^{2} =
(2\,\alpha - 1)^{-1}$, can be exceedingly small for large values of $\alpha$.
This allows a non-canonical field to cluster and behave like warm/cold dark
matter on small scales. We demonstrate that simple potentials including $V =
V_0\coth^2{\phi}$ and a Starobinsky-type potential can unify dark matter and
dark energy. Cascading dark energy, in which the potential cascades to lower
values in a series of discrete steps, can also work as a unified model. In all
of these models the kinetic term $X^\alpha$ plays the role of dark matter,
while the potential term $V(\phi)$ plays the role of dark energy.
| arxiv topic:gr-qc astro-ph.CO hep-ph hep-th |
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