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arxiv_dataset-85001705.06459 | Solar off-limb emission of the OI 7772 \AA\ line
astro-ph.SR
The aim of this paper is to understand the formation of the OI line at 7772
\AA\ in the solar chromosphere. We used SST/CRISP observations to observe OI
7772 \AA\ in several places around the solar limb. We compared the observations
with synthetic spectra calculated with the RH code in the one-dimension
spherical geometry mode. New accurate hydrogen collisional rates were included
for the RH calculations. The observations reveal a dark gap in the lower
chromosphere, which is caused by variations in the line opacity as shown by our
models. The lower level of the 7772 \AA\ transition is populated by a downward
cascade from the continuum. We study the effect of Lyman-$\beta$ pumping and
hydrogen collisions between the triplet and quintet system in OI. Both have a
small but non-negligible influence on the line intensity.
| arxiv topic:astro-ph.SR |
arxiv_dataset-85011705.06559 | Exemplar or Matching: Modeling DCJ Problems with Unequal Content Genome
Data
cs.DS cs.CE q-bio.GN
The edit distance under the DCJ model can be computed in linear time for
genomes with equal content or with Indels. But it becomes NP-Hard in the
presence of duplications, a problem largely unsolved especially when Indels are
considered. In this paper, we compare two mainstream methods to deal with
duplications and associate them with Indels: one by deletion, namely
DCJ-Indel-Exemplar distance; versus the other by gene matching, namely
DCJ-Indel-Matching distance. We design branch-and-bound algorithms with set of
optimization methods to compute exact distances for both. Furthermore, median
problems are discussed in alignment with both of these distance methods, which
are to find a median genome that minimizes distances between itself and three
given genomes. Lin-Kernighan (LK) heuristic is leveraged and powered up by
sub-graph decomposition and search space reduction technologies to handle
median computation. A wide range of experiments are conducted on synthetic data
sets and real data sets to show pros and cons of these two distance metrics per
se, as well as putting them in the median computation scenario.
| arxiv topic:cs.DS cs.CE q-bio.GN |
arxiv_dataset-85021705.06659 | Anomaly Detection in Business Process Runtime Behavior -- Challenges and
Limitations
cs.CR
Anomaly detection is generally acknowledged as an important problem that has
already drawn attention to various domains and research areas, such as, network
security. For such "classic" application domains a wide range of surveys and
literature reviews exist already - which is not the case for the process
domain. Hence, this systematic literature review strives to provide an
organized holistic view on research related to business process runtime
behavior anomaly detection. For this the unique challenges of the process
domain are outlined along with the nature of the analyzed data and data
sources. Moreover, existing work is identified and categorized based on the
underlying fundamental technology applied by each work. Furthermore, this work
describes advantages and disadvantages of each identified approach. Based on
these information limitations and gaps in existing research are identified and
recommendations are proposed to tackle them. This work aims to foster the
understanding and development of the process anomaly detection domain.
| arxiv topic:cs.CR |
arxiv_dataset-85031705.06759 | Stellar Parameters in an Instant with Machine Learning: Application to
Kepler LEGACY Targets
astro-ph.SR
With the advent of dedicated photometric space missions, the ability to
rapidly process huge catalogues of stars has become paramount. Bellinger and
Angelou et al. (2016) recently introduced a new method based on machine
learning for inferring the stellar parameters of main-sequence stars exhibiting
solar-like oscillations. The method makes precise predictions that are
consistent with other methods, but with the advantages of being able to explore
many more parameters while costing practically no time. Here we apply the
method to 52 so-called "LEGACY" main-sequence stars observed by the Kepler
space mission. For each star, we present estimates and uncertainties of mass,
age, radius, luminosity, core hydrogen abundance, surface helium abundance,
surface gravity, initial helium abundance, and initial metallicity as well as
estimates of their evolutionary model parameters of mixing length, overshooting
coefficient, and diffusion multiplication factor. We obtain median
uncertainties in stellar age, mass, and radius of 14.8%, 3.6%, and 1.7%,
respectively.
The source code for all analyses and for all figures appearing in this
manuscript can be found electronically at:
https://github.com/earlbellinger/asteroseismology
| arxiv topic:astro-ph.SR |
arxiv_dataset-85041705.06859 | Massive and supermassive black holes in the contemporary and early
universe and the new problems of cosmology and astrophysics
astro-ph.CO hep-th
This is the translation into English of the introduction, conclusion, and the
list of references of the review on massive primordial black holes, which is
submitted in Russian to Uspekhi Fizicheskikh Nauk (Physics-Uspekhi). If
accepted, this review is translated into English by the Journal and published
in Russian and a little later in English.
The review concerns the recent astronomical data which show that massive
primordial black holes play much more significant role in the universe than it
was previously believed. This is true both for the the contemporary and the
early universe at the red-shifts about 10. The mechanism, proposed in 1993, of
primordial creation of heavy and superheavy black holes in the very early
universe is discussed. This mechanism predicts the log-normal mass spectrum of
the primordial black holes, which became very popular during the last couple of
years. The proposed mechanism presents a natural explanation of a large amount
of the recent observational data, which do not fit the standard cosmology and
astrophysics.
| arxiv topic:astro-ph.CO hep-th |
arxiv_dataset-85051705.06959 | Beam Design and User Scheduling for Non-Orthogonal Multiple Access with
Multiple Antennas Based on Pareto-Optimality
cs.IT math.IT
In this paper, an efficient transmit beam design and user scheduling method
is proposed for multi-user (MU) multiple-input single-output (MISO)
non-orthogonal multiple access (NOMA) downlink, based on Pareto-optimality. The
proposed beam design and user scheduling method groups simultaneously-served
users into multiple clusters with practical two users in each cluster, and then
applies spatical zeroforcing (ZF) across clusters to control inter-cluster
interference (ICI) and Pareto-optimal beam design with successive interference
cancellation (SIC) to two users in each cluster to remove interference to
strong users and leverage signal-to-interference-plus-noise ratios (SINRs) of
interference-experiencing weak users. The proposed method has flexibility to
control the rates of strong and weak users and numerical results show that the
proposed method yields good performance.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-85061705.07059 | Pressure-tuning of bond-directional exchange interactions and magnetic
frustration in hyperhoneycomb iridate $\beta$-$\mathrm{Li_2IrO_3}$
cond-mat.str-el
We explore the response of Ir $5d$ orbitals to pressure in
$\beta$-$\mathrm{Li_2IrO_3}$, a hyperhoneycomb iridate in proximity to a Kitaev
quantum spin liquid (QSL) ground state. X-ray absorption spectroscopy reveals a
reconstruction of the electronic ground state below 2 GPa, the same pressure
range where x-ray magnetic circular dichroism shows an apparent collapse of
magnetic order. The electronic reconstruction, which manifests a reduction in
the effective spin-orbit (SO) interaction in $5d$ orbitals, pushes
$\beta$-$\mathrm{Li_2IrO_3}$ further away from the pure $J_{\rm eff}=1/2$
limit. Although lattice symmetry is preserved across the electronic transition,
x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb
lattice which affects the balance of bond-directional Ir-Ir exchange
interactions driven by spin-orbit coupling at Ir sites. An enhancement of
symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions
seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond
compression provides one possible route to realization of a QSL state in this
hyperhoneycomb iridate at high pressures.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-85071705.07159 | Multiphoton Effects Enhanced Due to Ultrafast Photon-Number Fluctuations
quant-ph
Multi-photon processes are the essence of nonlinear optics. Optical harmonics
generation and multi-photon absorption, ionization, polymerization or
spectroscopy are widely used in practical applications. Generally, the rate of
an n-photon effect scales as the n-th order autocorrelation function of the
incident light, which is high for light with strong photon-number fluctuations.
Therefore `noisy' light sources are much more efficient for multi-photon
effects than coherent sources with the same mean power, pulse duration and
repetition rate. Here we generate optical harmonics of order 2-4 from bright
squeezed vacuum (BSV), a state of light consisting of only quantum noise with
no coherent component. We observe up to two orders of magnitude enhancement in
the generation of optical harmonics due to ultrafast photon-number
fluctuations. This feature is especially important for the nonlinear optics of
fragile structures where the use of a `noisy' pump can considerably increase
the effect without overcoming the damage threshold.
| arxiv topic:quant-ph |
arxiv_dataset-85081705.07259 | Generalized multiple summing multilinear operators on Banach spaces
math.FA
In this paper we provide an abstract aproach to the study of classes of
multiple summing multilinear operators between Banach spaces. The main purpose
is unify the study of several known classes and results, for example multiple
$(p, q_1,\dots, q_n)$-summing operators, multiple mixing $(s, q, p)$-summing
operators and multiple strong $(s, q, p)$-mixing summing operators. We also
define new class of multiple summing multilinear operator that are particular
cases of our construction and, therefore, satisfy the results proved in the
paper.
| arxiv topic:math.FA |
arxiv_dataset-85091705.07359 | Field Testing of Software Applications
cs.SE
When interacting with their software systems, users may have to deal with
problems like crashes, failures, and program instability. Faulty software
running in the field is not only the consequence of ineffective in-house
verification and validation techniques, but it is also due to the complexity
and diversity of the interactions between an application and its environment.
Many of these interactions can be hardly predicted at testing time, and even
when they could be predicted, often there are so many cases to be tested that
they cannot be all feasibly addressed before the software is released.
This Ph.D. thesis investigates the idea of addressing the faults that cannot
be effectively addressed in house directly in the field, exploiting the field
itself as testbed for running the test cases. An enormous number of diverse
environments would then be available for testing, giving the possibility to run
many test cases in many different situations, timely revealing the many
failures that would be hard to detect otherwise.
| arxiv topic:cs.SE |
arxiv_dataset-85101705.07459 | Extracting the orbital axis from gravitational waves of precessing
binary systems
gr-qc
We present a new method for extracting the instantaneous orbital axis only
from gravitational wave strains of precessing binary systems observed from a
particular observer direction. This method enables us to reconstruct the
co-precessing frame waveforms only from observed quantities for the ideal case
that the signal-to-noise ratio is high enough to analyze the waveforms
directly. Specifically, we do not assume knowledge of the time evolution of the
instantaneous orbital axis and the co-precessing waveforms before analyzing the
data in our method. We test and measure the accuracy of our method using the
numerical relativity simulation data of precessing binary black holes taken
from the SXS Catalog. We show that the direction of the orbital axis is
extracted within $\approx0.02~{\rm rad}$ error from gravitational waves emitted
during the inspiral phase. The co-precessing waveforms are also reconstructed
with high accuracy; the mismatch (assuming white noise) between them and the
original co-precessing waveforms is typically a few times $10^{-3}$ including
the merger-ringdown phase, and can be improved by an order of magnitude
focusing only on the inspiral waveform. In this method, the co-precessing frame
waveforms are not only the purely technical tools for understanding the complex
nature of precessing waveforms but also direct observables.
| arxiv topic:gr-qc |
arxiv_dataset-85111705.07559 | L-groups and the Langlands program for covering groups: a historical
introduction
math.RT math.HO math.NT
In this joint introduction to an Asterisque volume, we give a short
discussion of the historical developments in the study of nonlinear covering
groups, touching on their structure theory, representation theory and the
theory of automorphic forms. This serves as a historical motivation and sets
the scene for the papers in the volume. Our discussion is necessarily
subjective and will undoubtedly leave out the contributions of many authors, to
whom we apologize in earnest.
| arxiv topic:math.RT math.HO math.NT |
arxiv_dataset-85121705.07659 | HI content in the galactic discs: the role of gravitational instability
astro-ph.GA
We examine the dependence between hydrogen total mass $M_{HI}$ and rotation
speed $V_{rot}$, optical size $D_{25}$ or disc radial scale $R_0$ for two
samples of late-type galaxies: a) isolated galaxy (AMIGA sample), and b) the
edge-on galaxies (flat galaxies of Karachentsev et al. 1999). Estimates of
$M_{HI}$, given in the HYPERLEDA database for flat galaxies appear to be on
average higher at $\sim $0.2 dex, than for isolated galaxies with similar
$V_{rot}$ or $D_{25}$ values, most probably, due to the overvaluation of
self-absorption in the HI line. We confirm that the hydrogen mass for both
samples closely correlates with galactic disc integral specific angular
momentum $J$, which is proportional to $V_{rot}D_{25}$ or $V_{rot}R_0$, with
low surface brightness galaxies lie along a common $V_{rot}R_0$ sequence. This
relationship can be explained, assuming that gas mass in the disc is regulated
by marginal gravitational stability condition of gas layer. A comparison of the
observed and theoretically expected dependences leads to a conclusion that
either gravitational stability corresponds to higher values of Toomre parameter
than is usually assumed, or the threshold stability condition for most galaxies
took place only in the past, when gas mass in discs was 2-4 times higher than
at present (with the exception of galaxies with abnormally high $HI$ content).
The last condition requires that the gas accretion was not compensated by gas
consumption during the evolution of most of galaxies.
| arxiv topic:astro-ph.GA |
arxiv_dataset-85131705.07759 | Scale of non-locality for a system of $n$ particles
hep-th
Higher derivative theories of gravity are associated with a mass scale to
insure the correct dimensionality of the covariant derivatives. This mass scale
is known as the scale of non-locality. In this paper, by considering a higher
derivative toy model, we show that for a system of $n$ particles the effective
mass scale is inversely proportional to the square root of the number of
particles. We demonstrate that as the number of particles increases the
corresponding effective mass scale associated with the scattering amplitude
decreases.
| arxiv topic:hep-th |
arxiv_dataset-85141705.07859 | First results from the use of the relativistic and slim disc model
SLIMULX in XSPEC
astro-ph.HE
Ultra-Luminous X-ray sources (ULXs) are accreting black holes for which their
X-ray properties have been seen to be different to the case of stellar-mass
black hole binaries. For most of the cases their intrinsic energy spectra are
well described by a cold accretion disc (thermal) plus a curved high-energy
emission components. The mass of the black hole (BH) derived from the thermal
disc component is usually in the range of 100-1000 solar masses, which have led
to the idea that this might represent strong evidence of the Intermediate Mass
Black Holes (IMBH), proposed to exist by theoretical studies but with no firm
detection (as a class) so far. Recent theoretical and observational
developments are leading towards the idea that these sources are instead
stellar-mass BHs accreting at an unusual super-Eddington regime. In this paper
we briefly describe the model SLIMULX that can be used in XSPEC for the fit of
thermal spectra of slim discs around stellar mass black holes in the
super-Eddington regime. This model consistently takes all relativistic effects
into account. We present the obtained results from the fit of the X-ray spectra
from NGC 5408 X-1.
| arxiv topic:astro-ph.HE |
arxiv_dataset-85151705.07959 | Comparison of statistical sampling methods with ScannerBit, the GAMBIT
scanning module
hep-ph astro-ph.CO astro-ph.IM physics.data-an stat.CO
We introduce ScannerBit, the statistics and sampling module of the public,
open-source global fitting framework GAMBIT. ScannerBit provides a standardised
interface to different sampling algorithms, enabling the use and comparison of
multiple computational methods for inferring profile likelihoods, Bayesian
posteriors, and other statistical quantities. The current version offers
random, grid, raster, nested sampling, differential evolution, Markov Chain
Monte Carlo (MCMC) and ensemble Monte Carlo samplers. We also announce the
release of a new standalone differential evolution sampler, Diver, and describe
its design, usage and interface to ScannerBit. We subject Diver and three other
samplers (the nested sampler MultiNest, the MCMC GreAT, and the native
ScannerBit implementation of the ensemble Monte Carlo algorithm T-Walk) to a
battery of statistical tests. For this we use a realistic physical likelihood
function, based on the scalar singlet model of dark matter. We examine the
performance of each sampler as a function of its adjustable settings, and the
dimensionality of the sampling problem. We evaluate performance on four
metrics: optimality of the best fit found, completeness in exploring the
best-fit region, number of likelihood evaluations, and total runtime. For
Bayesian posterior estimation at high resolution, T-Walk provides the most
accurate and timely mapping of the full parameter space. For profile likelihood
analysis in less than about ten dimensions, we find that Diver and MultiNest
score similarly in terms of best fit and speed, outperforming GreAT and T-Walk;
in ten or more dimensions, Diver substantially outperforms the other three
samplers on all metrics.
| arxiv topic:hep-ph astro-ph.CO astro-ph.IM physics.data-an stat.CO |
arxiv_dataset-85161705.08059 | Baseline Metal Enrichment from Population III Star Formation in
Cosmological Volume Simulations
astro-ph.GA astro-ph.CO
We utilize the hydrodynamic and N-body code {\small GIZMO} coupled with our
newly developed sub-grid Population~III (Pop~III) Legacy model, designed
specifically for cosmological volume simulations, to study the baseline metal
enrichment from Pop~III star formation at $z>7$. In this idealized numerical
experiment, we only consider Pop~III star formation. We find that our model
Pop~III star formation rate density (SFRD), which peaks at $\sim 10^{-3}\ {\rm
M_\odot yr^{-1} Mpc^{-1}}$ near $z\sim10$, agrees well with previous numerical
studies and is consistent with the observed estimates for Pop~II SFRDs. The
mean Pop~III metallicity rises smoothly from $z=25-7$, but does not reach the
critical metallicity value, $Z_{\rm crit}=10^{-4}\ Z_\odot$, required for the
Pop~III to Pop~II transition in star formation mode until $z\simeq7$. This
suggests that, while individual halos can suppress in-situ Pop~III star
formation, the external enrichment is insufficient to globally terminate
Pop~III star formation. The maximum enrichment from Pop~III star formation in
star forming dark matter halos is $Z\sim10^{-2}\ Z_\odot$, whereas the minimum
found in externally enriched haloes is $Z\gtrsim10^{-7}\ Z_\odot$. Finally,
mock observations of our simulated IGM enriched with Pop~III metals produce
equivalent widths similar to observations of an extremely metal poor damped
Lyman alpha (DLA) system at $z=7.04$, which is thought to be enriched by
Pop~III star formation only.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-85171705.08159 | Diagonal forms of higher degree over function fields of $p$-adic curves
math.NT math.AG
We investigate diagonal forms of degree $d$ over the function field $F$ of a
smooth projective $p$-adic curve: if a form is isotropic over the completion of
$F$ with respect to each discrete valuation of $F$, then it is isotropic over
certain fields $F_U$, $F_P$ and $F_p$. These fields appear naturally when
applying the methodology of patching; $F$ is the inverse limit of the finite
inverse system of fields $\{F_U,F_P,F_p\}$. Our observations complement some
known bounds on the higher $u$-invariant of diagonal forms of degree $d$. We
only consider diagonal forms of degree $d$ over fields of characteristic not
dividing $d!$.
| arxiv topic:math.NT math.AG |
arxiv_dataset-85181705.08259 | Generalized orthogonal matching pursuit for multiple measurements - A
structural approach
math.NA
Sparse data approximation has become a popular research topic in signal
processing. However, in most cases only a single measurement vector (SMV) is
considered. In applications, the multiple measurement vector (MMV) case is more
usual, i.e., the sparse approximation problem has to be solved for several data
vectors coming from closely related measurements. Thus, there is an unknown
inter-vector correlation between the data vectors. Using SMV methods typically
does not return the best approximation result as the correlation is ignored. In
the past few years several algorithms for the MMV case have been designed to
overcome this problem. Most of these techniques focus on the approximation
quality while quite strong assumptions to the type of inter-vector correlation
are made. While we still want to find a sparse approximation, our focus lies on
preserving (possibly complex) structures in the data. Structural knowledge is
of interest in many applications. It can give information about e.g., type,
form, number or size of objects of interest. This may even be more useful than
information given by the non-zero amplitudes itself. Moreover, it allows
efficient post processing of the data. We numerically compare our new approach
with other techniques and demonstrate its benefits in two applications.
| arxiv topic:math.NA |
arxiv_dataset-85191705.08359 | Discovery of the first quadruple gravitationally lensed quasar candidate
with Pan-STARRS
astro-ph.GA astro-ph.CO
We report the serendipitous discovery of the first gravitationally lensed
quasar candidate from Pan-STARRS. The grizy images reveal four point-like
images with magnitudes between 14.9 mag and 18.1 mag. The colors of the point
sources are similar, and they are more consistent with quasars than with stars
or galaxies. The lensing galaxy is detected in the izy bands, with an inferred
photometric redshift of ~0.6, lower than that of the point sources. We
successfully model the system with a singular isothermal ellipsoid with shear,
using the relative positions of the five objects as constraints. While the
brightness ranking of the point sources is consistent with that of the model,
we find discrepancies between the model-predicted and observed fluxes, likely
due to microlensing by stars and millilensing due to the dark matter
substructure. In order to fully confirm the gravitational lens nature of this
system and add it to the small but growing number of the powerful probes of
cosmology and astrophysics represented by quadruply lensed quasars, we require
further spectroscopy and high-resolution imaging.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-85201705.08459 | A complete characterisation of All-versus-Nothing arguments for
stabiliser states
quant-ph cs.LO
An important class of contextuality arguments in quantum foundations are the
All-versus-Nothing (AvN) proofs, generalising a construction originally due to
Mermin. We present a general formulation of All-versus-Nothing arguments, and a
complete characterisation of all such arguments which arise from stabiliser
states. We show that every AvN argument for an n-qubit stabiliser state can be
reduced to an AvN proof for a three-qubit state which is local
Clifford-equivalent to the tripartite GHZ state. This is achieved through a
combinatorial characterisation of AvN arguments, the AvN triple Theorem, whose
proof makes use of the theory of graph states. This result enables the
development of a computational method to generate all the AvN arguments in
$\mathbb{Z}_2$ on n-qubit stabiliser states. We also present new insights into
the stabiliser formalism and its connections with logic.
| arxiv topic:quant-ph cs.LO |
arxiv_dataset-85211705.08559 | Random ordering formula for sofic and Rokhlin entropy of Gibbs measures
math.DS math.PR
We prove the explicit formula for sofic and Rokhlin entropy of actions
arising from some class of Gibbs measures. It provides a new set of examples
with sofic entropy independent of sofic approximations. It is particularilly
interresting, since in non-amenable case Rokhlin entropy was computed only in
case of Bernoulli actions and for some examples with zero Rokhlin entropy. As
an example we show that our formula holds for the supercritical Ising model. We
also establish a criterion for uniqueness of Gibbs measure by means of
f-invariant.
| arxiv topic:math.DS math.PR |
arxiv_dataset-85221705.08659 | Josephson Current in Ballistic Graphene Corbino Disk
cond-mat.mes-hall
We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation in a
superconductor-normal graphene superconductor (SGS) junction with Corbino disk
structure to investigate the Josephson current through this junction. We find
that the critical current $I_c$ has a nonzero value at Dirac point in which the
concentration of the carriers is zero. We show this nonzero critical current
depends on the system geometry and it decreases monotonically to zero by
increasing the ratio of the outer to inner radii of the Corbino disk
($R_2/R_1$), while in the limit of $R_2/R_1 \rightarrow 1$ it scales like a
diffusive Corbino disk. The product of the critical current and the
normal-state resistance $I_cR_N$ attains the same value for the planar
structure at zero doping. These results reveals the pseudodiffusive behavior of
the graphene Corbino Josephson junction similar to the planar structure.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-85231705.08759 | Bidirectional Beam Search: Forward-Backward Inference in Neural Sequence
Models for Fill-in-the-Blank Image Captioning
cs.CV
We develop the first approximate inference algorithm for 1-Best (and M-Best)
decoding in bidirectional neural sequence models by extending Beam Search (BS)
to reason about both forward and backward time dependencies. Beam Search (BS)
is a widely used approximate inference algorithm for decoding sequences from
unidirectional neural sequence models. Interestingly, approximate inference in
bidirectional models remains an open problem, despite their significant
advantage in modeling information from both the past and future. To enable the
use of bidirectional models, we present Bidirectional Beam Search (BiBS), an
efficient algorithm for approximate bidirectional inference.To evaluate our
method and as an interesting problem in its own right, we introduce a novel
Fill-in-the-Blank Image Captioning task which requires reasoning about both
past and future sentence structure to reconstruct sensible image descriptions.
We use this task as well as the Visual Madlibs dataset to demonstrate the
effectiveness of our approach, consistently outperforming all baseline methods.
| arxiv topic:cs.CV |
arxiv_dataset-85241705.08859 | More Circulant Graphs exhibiting Pretty Good State Transfer
math.CO
The transition matrix of a graph $G$ corresponding to the adjacency matrix
$A$ is defined by $H(t):=\exp{\left(-itA\right)},$ where $t\in\mathbb{R}$. The
graph is said to exhibit pretty good state transfer between a pair of vertices
$u$ and $v$ if there exists a sequence $\left\lbrace t_k\right\rbrace$ of real
numbers such that $\lim\limits_{k\rightarrow\infty} H(t_k) {\bf e}_u=\gamma
{\bf e}_v$, where $\gamma$ is a complex number of unit modulus. We classify
some circulant graphs exhibiting or not exhibiting pretty good state transfer.
This generalize several pre-existing results on circulant graphs admitting
pretty good state transfer.
| arxiv topic:math.CO |
arxiv_dataset-85251705.08959 | Gravity from Quantum Spacetime by Twisted Deformation of the Quantum
Poincar\'e Group
math-ph gr-qc hep-th math.MP
We investigate a quantum geometric space in the context of what could be
considered an emerging effective theory from Quantum Gravity. Specifically we
consider a two-parameter class of twisted Poincar\'e algebras, from which
Lie-algebraic noncommutativities of the translations are derived as well as
associative star-products, deformed Riemannian geometries, Lie-algebraic
twisted Minkowski spaces and quantum effects that arise as noncommutativities.
Starting from a universal differential algebra of forms based on the above
mentioned Lie-algebraic noncommutativities of the translations, we construct
the noncommutative differential forms and Inner and Outer derivations, which
are the noncommutative equivalents of the vector fields in the case of
commutative differential geometry. Having established the essentials of this
formalism we construct a bimodule, required to be central under the action of
the Inner derivations in order to have well defined contractions and from where
the algebraic dependence of its coefficients is derived. This again then
defines the noncommutative equivalent of the geometrical line-element in
commutative differential geometry. We stress, however, that even though the
components of the twisted metric are by construction symmetric in their algebra
valuation, this is not so for their inverse and thus to construct it we made
use of Gel'fand's theory of quasi-determinants, which is conceptually
straightforward but computationally becoming quite complicate beyond an algebra
of 3 generators. The consequences of the noncommutativity of the Lie-algebra
twisted geometry are further discussed.
| arxiv topic:math-ph gr-qc hep-th math.MP |
arxiv_dataset-85261705.09059 | Vector Transport-Free SVRG with General Retraction for Riemannian
Optimization: Complexity Analysis and Practical Implementation
math.OC
In this paper, we propose a vector transport-free stochastic variance reduced
gradient (SVRG) method with general retraction for empirical risk minimization
over Riemannian manifold. Existing SVRG methods on manifold usually consider a
specific retraction operation, and involve additional computational costs such
as parallel transport or vector transport. The vector transport-free SVRG with
general retraction we propose in this paper handles general retraction
operations, and do not need additional computational costs mentioned above. As
a result, we name our algorithm S-SVRG, where the first "S" means simple. We
analyze the iteration complexity of S-SVRG for obtaining an
$\epsilon$-stationary point and its local linear convergence by assuming the \L
ojasiewicz inequality, which naturally holds for PCA and holds with high
probability for matrix completion problem. We also incorporate the
Barzilai-Borwein step size and design a very practical S-SVRG-BB method.
Numerical results on PCA and matrix completion problems are reported to
demonstrate the efficiency of our methods.
| arxiv topic:math.OC |
arxiv_dataset-85271705.09159 | Approximating sums by integrals only: multiple sums and sums over
lattice polytopes
math.CA math.CO
The Euler--Maclaurin (EM) summation formula is used in many theoretical
studies and numerical calculations. It approximates the sum $\sum_{k=0}^{n-1}
f(k)$ of values of a function $f$ by a linear combination of a corresponding
integral of $f$ and values of its higher-order derivatives $f^{(j)}$. An
alternative (Alt) summation formula was recently presented by the author, which
approximates the sum by a linear combination of integrals only, without using
high-order derivatives of $f$. It was shown that the Alt formula will in most
cases outperform, or greatly outperform, the EM formula in terms of the
execution time and memory use. In the present paper, a
multiple-sum/multi-index-sum extension of the Alt formula is given, with
applications to summing possibly divergent multi-index series and to sums over
the integral points of integral lattice polytopes.
| arxiv topic:math.CA math.CO |
arxiv_dataset-85281705.09259 | Experimental demonstration of fault-tolerant state preparation with
superconducting qubits
quant-ph
Robust quantum computation requires encoding delicate quantum information
into degrees of freedom that are hard for the environment to change. Quantum
encodings have been demonstrated in many physical systems by observing and
correcting storage errors, but applications require not just storing
information; we must accurately compute even with faulty operations. The theory
of fault-tolerant quantum computing illuminates a way forward by providing a
foundation and collection of techniques for limiting the spread of errors. Here
we implement one of the smallest quantum codes in a five-qubit superconducting
transmon device and demonstrate fault-tolerant state preparation. We
characterize the resulting codewords through quantum process tomography and
study the free evolution of the logical observables. Our results are consistent
with fault-tolerant state preparation in a protected qubit subspace.
| arxiv topic:quant-ph |
arxiv_dataset-85291705.09359 | Generating Time-Based Label Refinements to Discover More Precise Process
Models
cs.LG cs.AI cs.DB
Process mining is a research field focused on the analysis of event data with
the aim of extracting insights related to dynamic behavior. Applying process
mining techniques on data from smart home environments has the potential to
provide valuable insights in (un)healthy habits and to contribute to ambient
assisted living solutions. Finding the right event labels to enable the
application of process mining techniques is however far from trivial, as simply
using the triggering sensor as the label for sensor events results in
uninformative models that allow for too much behavior (overgeneralizing).
Refinements of sensor level event labels suggested by domain experts have been
shown to enable discovery of more precise and insightful process models.
However, there exists no automated approach to generate refinements of event
labels in the context of process mining. In this paper we propose a framework
for the automated generation of label refinements based on the time attribute
of events, allowing us to distinguish behaviourally different instances of the
same event type based on their time attribute. We show on a case study with
real life smart home event data that using automatically generated refined
labels in process discovery, we can find more specific, and therefore more
insightful, process models. We observe that one label refinement could have an
effect on the usefulness of other label refinements when used together.
Therefore, we explore four strategies to generate useful combinations of
multiple label refinements and evaluate those on three real life smart home
event logs.
| arxiv topic:cs.LG cs.AI cs.DB |
arxiv_dataset-85301705.09459 | On the higher derivates of arctan
math.CA
WWe give a rational closed form expression for the higher derivatives of the
inverse tangent function and discuss its relation to Chebyshev polynomials,
trigonometric expansions and Appell sequences of polynomials.
| arxiv topic:math.CA |
arxiv_dataset-85311705.09559 | Factors Determining the Carrier Distribution in InGaN/GaN
Multiple-Quantum-Well Light-Emitting Diodes
physics.app-ph
Factors determining the carrier distribution in InGaN/GaN
multiple-quantum-well (MQW) light-emitting diodes (LEDs) are studied via
photoluminescence and temperature-dependent electroluminescence spectra.
Employing a dichromatic LED device, we demonstrate that the carrier
recombination rate should be considered playing an important role in
determining the carrier distribution in the MQW active region, not just the
simple hole characteristics such as low mobility and large effective mass.
| arxiv topic:physics.app-ph |
arxiv_dataset-85321705.09659 | Role of the spin-orbit coupling in the Kugel-Khomskii model on the
honeycomb lattice
cond-mat.str-el
We study the effective spin-orbital model for honeycomb-layered transition
metal compounds, applying the second-order perturbation theory to the
three-orbital Hubbard model with the anisotropic hoppings. This model is
reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining
the cluster mean-field approximations with the exact diagonalization, we treat
the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an
equal footing to discuss ground-state properties. We find that a zigzag ordered
state is realized in the model within nearest-neighbor interactions. We clarify
how the ordered state competes with the nonmagnetic state, which is
adiabatically connected to the quantum spin liquid state realized in a strong
spin-orbit coupling limit. Thermodynamic properties are also addressed. The
present work should provide another route to account for the Kitaev-based
magnetic properties in candidate materials.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-85331705.09759 | CASENet: Deep Category-Aware Semantic Edge Detection
cs.CV
Boundary and edge cues are highly beneficial in improving a wide variety of
vision tasks such as semantic segmentation, object recognition, stereo, and
object proposal generation. Recently, the problem of edge detection has been
revisited and significant progress has been made with deep learning. While
classical edge detection is a challenging binary problem in itself, the
category-aware semantic edge detection by nature is an even more challenging
multi-label problem. We model the problem such that each edge pixel can be
associated with more than one class as they appear in contours or junctions
belonging to two or more semantic classes. To this end, we propose a novel
end-to-end deep semantic edge learning architecture based on ResNet and a new
skip-layer architecture where category-wise edge activations at the top
convolution layer share and are fused with the same set of bottom layer
features. We then propose a multi-label loss function to supervise the fused
activations. We show that our proposed architecture benefits this problem with
better performance, and we outperform the current state-of-the-art semantic
edge detection methods by a large margin on standard data sets such as SBD and
Cityscapes.
| arxiv topic:cs.CV |
arxiv_dataset-85341705.09859 | On shortened and punctured cyclic codes
cs.IT math.IT
The problem of identifying whether the family of cyclic codes is
asymptotically good or not is a long-standing open problem in the field of
coding theory. It is known in the literature that some families of cyclic codes
such as BCH codes and Reed-Solomon codes are asymptotically bad, however in
general the answer to this question is not known. A recent result by Nelson and
Van Zwam shows that, all linear codes can be obtained by a sequence of
puncturing and/or shortening of a collection of asymptotically good
codes~\cite{Nelson_2015}. In this paper, we prove that any linear code can be
obtained by a sequence of puncturing and/or shortening of some cyclic code.
Therefore the result that all codes can be obtained by shortening and/or
puncturing cyclic codes leaves the possibility open that cyclic codes are
asymptotically good.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-85351705.09959 | Mechanisms of localization in isotope-substituted dynamical Jahn-Teller
systems
physics.chem-ph
The mechanisms of localization of Jahn-Teller deformations and vibronic
wavefunctions in isotope substituted dynamical Jahn-Teller systems are
elucidated. It is found that the localization in the trough is of potential
type in the case of strong vibronic coupling, while it becomes of kinetic type
in the case of intermediate and weak coupling. It is shown that the vibronic
levels in the linear $E\otimes e$-problem remain double degenerate upon
arbitrary isotope substitution on the reasons similar to time reversal symmetry
in which the role of spin is played by orbital pseudospin.
| arxiv topic:physics.chem-ph |
arxiv_dataset-85361705.10059 | Origin of threshold current density for asymmetric magnetoresistance in
Pt/Py bilayers
cond-mat.mtrl-sci
An asymmetric magnetoresistance (MR) is investigated in Py/Pt bilayers. The
asymmetric MR linearly increases with current density up to a threshold, and
increases more rapidly above the threshold. To reveal the origin of threshold
behavior, we investigate the magnetic field dependence of the asymmetric MR. It
is found that the magnetic field strongly suppresses the asymmetric MR only
above the threshold current density. Micromagnetic simulation reveals that the
reduction of magnetization due to the spin-torque oscillation can be the origin
of the threshold behavior of asymmetric MR.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-85371705.10159 | Anisotropic electronic transport of the two-dimensional electron system
in Al2O3/SrTiO3 heterostructures
cond-mat.str-el
Transport measurements on the two dimensional electron system in Al2O3 SrTiO3
heterostructures indicate significant noncrystalline anisotropic behavior below
T = 30 K. Lattice dislocations in SrTiO3 and interfacial steps are suggested to
be the main sources for electronic anisotropy. Anisotropic defect scattering
likewise alters magnetoresistance at low temperature remarkably and influences
spin-orbit coupling significantly by the Elliot Yafet mechanism of spin
relaxation resulting in anisotropic weak localization. Applying a magnetic
field parallel to the interface results in an additional field induced
anisotropy of the conductance, which can be attributed to Rashba spin orbit
interaction. Compared to LaAlO3 SrTiO3, Rashba coupling seems to be reduced
indicating a weaker polarity in Al2O3 SrTiO3 heterostructures.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-85381705.10259 | Distributed Communication-aware Motion Planning for Multi-agent Systems
from STL and SpaTeL Specifications
cs.MA cs.LO cs.RO cs.SY
In future intelligent transportation systems, networked vehicles coordinate
with each other to achieve safe operations based on an assumption that
communications among vehicles and infrastructure are reliable. Traditional
methods usually deal with the design of control systems and communication
networks in a separated manner. However, control and communication systems are
tightly coupled as the motions of vehicles will affect the overall
communication quality. Hence, we are motivated to study the co-design of both
control and communication systems. In particular, we propose a control
theoretical framework for distributed motion planning for multi-agent systems
which satisfies complex and high-level spatial and temporal specifications
while accounting for communication quality at the same time. Towards this end,
desired motion specifications and communication performances are formulated as
signal temporal logic (STL) and spatial-temporal logic (SpaTeL) formulas,
respectively. The specifications are encoded as constraints on system and
environment state variables of mixed integer linear programs (MILP), and upon
which control strategies satisfying both STL and SpaTeL specifications are
generated for each agent by employing a distributed model predictive control
(MPC) framework. Effectiveness of the proposed framework is validated by a
simulation of distributed communication-aware motion planning for multi-agent
systems.
| arxiv topic:cs.MA cs.LO cs.RO cs.SY |
arxiv_dataset-85391705.10359 | Neural Embeddings of Graphs in Hyperbolic Space
stat.ML cs.LG
Neural embeddings have been used with great success in Natural Language
Processing (NLP). They provide compact representations that encapsulate word
similarity and attain state-of-the-art performance in a range of linguistic
tasks. The success of neural embeddings has prompted significant amounts of
research into applications in domains other than language. One such domain is
graph-structured data, where embeddings of vertices can be learned that
encapsulate vertex similarity and improve performance on tasks including edge
prediction and vertex labelling. For both NLP and graph based tasks, embeddings
have been learned in high-dimensional Euclidean spaces. However, recent work
has shown that the appropriate isometric space for embedding complex networks
is not the flat Euclidean space, but negatively curved, hyperbolic space. We
present a new concept that exploits these recent insights and propose learning
neural embeddings of graphs in hyperbolic space. We provide experimental
evidence that embedding graphs in their natural geometry significantly improves
performance on downstream tasks for several real-world public datasets.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-85401705.10459 | Deep-LMS for gigabit transmission over unshielded twisted pair cables
cs.IT math.IT
In this paper we propose a rapidly converging LMS algorithm for crosstalk
cancellation. The architecture is similar to deep neural networks, where
multiple layers are adapted sequentially. The application motivating this
approach is gigabit rate transmission over unshielded twisted pairs using a
vectored system. The crosstalk cancellation algorithm uses an adaptive
non-diagonal preprocessing matrix prior to a conventional LMS crosstalk
canceler. The update of the preprocessing matrix is inspired by deep neural
networks. However, since most the operations in the Deep-LMS algorithm are
linear, we are capable of providing an exact convergence speed analysis. The
role of the preprocessing matrix is to speed up the convergence of the
conventional LMS crosstalk canceler and hence the convergence of the overall
system. The Deep-LMS is important for crosstalk cancellation in the novel
G.fast standard, where traditional LMS converges very slowly due to the
ill-conditioned covariance matrix of the received signal at the extended
bandwidth. Simulation results support our analysis and show significant
reduction in convergence time compared to existing LMS variants.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-85411705.10559 | Generalized linearization techniques in electrical impedance tomography
math.NA
Electrical impedance tomography aims at reconstructing the interior
electrical conductivity from surface measurements of currents and voltages. As
the current-voltage pairs depend nonlinearly on the conductivity, impedance
tomography leads to a nonlinear inverse problem. Often, the forward problem is
linearized with respect to the conductivity and the resulting linear inverse
problem is regarded as a subproblem in an iterative algorithm or as a simple
reconstruction method as such. In this paper, we compare this basic
linearization approach to linearizations with respect to the resistivity or the
logarithm of the conductivity. It is numerically demonstrated that the
conductivity linearization often results in compromised accuracy in both
forward and inverse computations. Inspired by these observations, we present
and analyze a new linearization technique which is based on the logarithm of
the Neumann-to-Dirichlet operator. The method is directly applicable to
discrete settings, including the complete electrode model. We also consider
Fr\'echet derivatives of the logarithmic operators. Numerical examples indicate
that the proposed method is an accurate way of linearizing the problem of
electrical impedance tomography.
| arxiv topic:math.NA |
arxiv_dataset-85421705.10659 | Discovering Visual Concept Structure with Sparse and Incomplete Tags
cs.CV
Discovering automatically the semantic structure of tagged visual data (e.g.
web videos and images) is important for visual data analysis and
interpretation, enabling the machine intelligence for effectively processing
the fast-growing amount of multi-media data. However, this is non-trivial due
to the need for jointly learning underlying correlations between heterogeneous
visual and tag data. The task is made more challenging by inherently sparse and
incomplete tags. In this work, we develop a method for modelling the inherent
visual data concept structures based on a novel Hierarchical-Multi-Label Random
Forest model capable of correlating structured visual and tag information so as
to more accurately interpret the visual semantics, e.g. disclosing meaningful
visual groups with similar high-level concepts, and recovering missing tags for
individual visual data samples. Specifically, our model exploits hierarchically
structured tags of different semantic abstractness and multiple tag statistical
correlations in addition to modelling visual and tag interactions. As a result,
our model is able to discover more accurate semantic correlation between
textual tags and visual features, and finally providing favourable visual
semantics interpretation even with highly sparse and incomplete tags. We
demonstrate the advantages of our proposed approach in two fundamental
applications, visual data clustering and missing tag completion, on
benchmarking video (i.e. TRECVID MED 2011) and image (i.e. NUS-WIDE) datasets.
| arxiv topic:cs.CV |
arxiv_dataset-85431705.10759 | Drop pattern resulting from the breakup of a bidimensional grid of
liquid filaments
physics.flu-dyn
A rectangular grid formed by liquid filaments on a partially wetting
substrate evolves in a series of breakups leading to arrays of drops with
different shapes distributed in a rather regular bidimensional pattern. Our
study is focused on the configuration produced when two long parallel filaments
of silicone oil, which are placed upon a glass substrate previously coated with
a fluorinated solution, are crossed perpendicularly by another pair of long
parallel filaments. A remarkable feature of this kind of grids is that there
are two qualitatively different types of drops. While one set is formed at the
crossing points, the rest are consequence of the breakup of shorter filaments
formed between the crossings. Here, we analyze the main geometric features of
all types of drops, such as shape of the footprint and contact angle
distribution along the drop periphery. The formation of a series of short
filaments with similar geometric and physical properties allows us to have
simultaneously quasi identical experiments to study the subsequent breakups. We
develop a simple hydrodynamic model to predict the number of drops that results
from a filament of given initial length and width. This model is able to yield
the length intervals corresponding to a small number of drops and its
predictions are successfully compared with the experimental data as well as
with numerical simulations of the full Navier--Stokes equation that provide a
detailed time evolution of the dewetting motion of the filament till the
breakup into drops. Finally, the prediction for finite filaments is contrasted
with the existing theories for infinite ones.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-85441705.10859 | Corrections for a constant radial magnetic field in the g-2 and
electric-dipole-moment experiments with muons in storage rings
physics.acc-ph hep-ex
We calculate the corrections for constant radial magnetic field in muon g--2
and electric-dipole-moment experiments in storage rings. While the correction
is negligible for the current generation of g--2 experiments, it affects the
upcoming muon electric-dipole-moment experiment at Fermilab.
| arxiv topic:physics.acc-ph hep-ex |
arxiv_dataset-85451705.10959 | Double $J$-function of stable quasimap invariants for complete
intersection in Grassmannian
math.AG
Using localization methods on the moduli space of stable quasimaps to
Grassmannian, we give explicit formulas of $J$-function and double $J$-function
of stable quasimaps for complete intersection in Grassmannian.
| arxiv topic:math.AG |
arxiv_dataset-85461705.11059 | The Chaotic Saddle in the Lozi map, autonomous and non-autonomous
versions
math.DS
In this paper we prove the existence of a chaotic saddle for a piecewise
linear map of the plane, referred to as the Lozi map. We study the Lozi map in
its orientation and area preserving version. First, we consider the autonomous
version of the Lozi map to which we apply the Conley-Moser conditions to obtain
the proof of a chaotic saddle. Then we generalize the Lozi map on a
non-autonomous version and we prove that the first and the third Conley-Moser
conditions are satisfied, which imply the existence of a chaotic saddle.
Finally, we numerically demonstrate how the structure of this nonautonomous
chaotic saddle varies as parameters are varied.
| arxiv topic:math.DS |
arxiv_dataset-85471705.11159 | Reinforcement Learning for Learning Rate Control
cs.LG
Stochastic gradient descent (SGD), which updates the model parameters by
adding a local gradient times a learning rate at each step, is widely used in
model training of machine learning algorithms such as neural networks. It is
observed that the models trained by SGD are sensitive to learning rates and
good learning rates are problem specific. We propose an algorithm to
automatically learn learning rates using neural network based actor-critic
methods from deep reinforcement learning (RL).In particular, we train a policy
network called actor to decide the learning rate at each step during training,
and a value network called critic to give feedback about quality of the
decision (e.g., the goodness of the learning rate outputted by the actor) that
the actor made. The introduction of auxiliary actor and critic networks helps
the main network achieve better performance. Experiments on different datasets
and network architectures show that our approach leads to better convergence of
SGD than human-designed competitors.
| arxiv topic:cs.LG |
arxiv_dataset-85481706.00065 | Torsion-free Aluffi Algebras
math.AC
A pair of ideals $J\subseteq I\subseteq R$ has been called Aluffi
torsion-free if the Aluffi algebra of $I/J$ is isomorphic with the
corresponding Rees algebra. We give necessary and sufficient conditions for the
Aluffi torsion-free property in terms of the first syzygy module of the form
ideal $J^*$ in the associated graded ring of $I$. For two pairs of ideals
$J_1,J_2\subseteq I$ such that $J_1-J_2\in I^2$, we prove that if one pair is
Aluffi torsion-free the other one is so if and only if the first syzygy modules
of $J_1$ and $J_2$ have the same form ideals. We introduce the notion of
strongly Aluffi torsion-free ideals and present some results on these ideals.
| arxiv topic:math.AC |
arxiv_dataset-85491706.00165 | Woon's tree and sums over compositions
math.CO
This article studies sums over all compositions of an integer. We derive a
generating function for this quantity, and apply it to several special
functions, including various generalized Bernoulli numbers. We connect
composition sums with a recursive tree introduced by S.G. Woon and extended by
P. Fuchs under the name "general PI tree", in which an output sequence
$\{x_n\}$ is associated to the input sequence $\{g_n\}$ by summing over each
row of the tree built from $\{g_n\}$. Our link with the notion of compositions
allows to introduce a modification of Fuchs' tree that takes into account
nonlinear transforms of the generating function of the input sequence. We also
introduce the notion of \textit{generalized sums over compositions}, where we
look at composition sums over each part of a composition.
| arxiv topic:math.CO |
arxiv_dataset-85501706.00265 | A complete non-perturbative renormalization prescription for quasi-PDFs
hep-lat hep-ex hep-ph hep-th nucl-th
In this work we present, for the first time, the non-perturbative
renormalization for the unpolarized, helicity and transversity quasi-PDFs, in
an RI' scheme. The proposed prescription addresses simultaneously all aspects
of renormalization: logarithmic divergences, finite renormalization as well as
the linear divergence which is present in the matrix elements of fermion
operators with Wilson lines. Furthermore, for the case of the unpolarized
quasi-PDFs, we describe how to eliminate the unwanted mixing with the twist-3
scalar operator. We utilize perturbation theory for the one-loop conversion
factor that brings the renormalization functions to the MS-scheme at a scale of
2 GeV. We also explain how to improve the estimates on the renormalization
functions by eliminating lattice artifacts. The latter can be computed in
one-loop perturbation theory and to all orders in the lattice spacing. We apply
the methodology for the renormalization to an ensemble of twisted mass fermions
with Nf=2+1+1 dynamical light quarks, and a pion mass of around 375 MeV.
| arxiv topic:hep-lat hep-ex hep-ph hep-th nucl-th |
arxiv_dataset-85511706.00365 | Energy Input Flux in the Global Quiet-Sun Corona
astro-ph.SR
We present first results of a novel technique that provides, for the first
time, constraints on the energy input flux at the coronal base
($r\sim\,1.025\,{\rm R}_\odot$) of the quiet-Sun at a global scale. By
combining differential emission measure tomography (DEMT) of EUV images, with
global models of the coronal magnetic field, we estimate the energy input flux
at the coronal base that is required to maintain thermodynamically stable
structures. The technique is described in detail and first applied to data
provided by the Extreme Ultraviolet Imager (EUVI) instrument, on board the
Solar TErrestrial RElations Observatory (STEREO) mission, and the Atmospheric
Imaging Assembly (AIA) instrument, on board the Solar Dynamics Observatory
(SDO) mission, for two solar rotations with different levels of activity. Our
analysis indicates that the typical energy input flux at the coronal base of
magnetic loops in the quiet-Sun is in the range $\sim\,0.5-2.0\times 10^5\,{\rm
(erg\,sec^{-1}\,{\rm cm}^{-2})}$, depending on the structure size and level of
activity. A large fraction of this energy input, or even its totality, could be
accounted for by Alfv\'en waves, as shown by recent independent observational
estimates derived from determinations of the non-thermal broadening of spectral
lines in the coronal base of quiet-Sun regions. This new tomography product
will be useful for validation of coronal heating models in magnetohydrodinamic
simulations of the global corona.
| arxiv topic:astro-ph.SR |
arxiv_dataset-85521706.00465 | Machine Assisted Analysis of Vowel Length Contrasts in Wolof
cs.CL
Growing digital archives and improving algorithms for automatic analysis of
text and speech create new research opportunities for fundamental research in
phonetics. Such empirical approaches allow statistical evaluation of a much
larger set of hypothesis about phonetic variation and its conditioning factors
(among them geographical / dialectal variants). This paper illustrates this
vision and proposes to challenge automatic methods for the analysis of a not
easily observable phenomenon: vowel length contrast. We focus on Wolof, an
under-resourced language from Sub-Saharan Africa. In particular, we propose
multiple features to make a fine evaluation of the degree of length contrast
under different factors such as: read vs semi spontaneous speech ; standard vs
dialectal Wolof. Our measures made fully automatically on more than 20k vowel
tokens show that our proposed features can highlight different degrees of
contrast for each vowel considered. We notably show that contrast is weaker in
semi-spontaneous speech and in a non standard semi-spontaneous dialect.
| arxiv topic:cs.CL |
arxiv_dataset-85531706.00565 | A Ramsey Algebraic Study of Matrices
math.LO
The notion of a topological Ramsey space was introduced by Carlson some 30
years ago. Studying the topological Ramsey space of variable words, Carlson was
able to derive many classical combinatorial results in a unifying manner. For
the class of spaces generated by algebras, Carlson had suggested that one
should attempt a purely combinatorial approach to the study. This approach was
later formulated and named Ramsey algebra. In this paper, we continue to look
at heterogeneous Ramsey algebras, mainly characterizing various Ramsey algebras
involving matrices.
| arxiv topic:math.LO |
arxiv_dataset-85541706.00665 | Bubble size statistics during reionization from 21-cm tomography
astro-ph.CO
The upcoming SKA1-Low radio interferometer will be sensitive enough to
produce tomographic imaging data of the redshifted 21-cm signal from the Epoch
of Reionization. Due to the non-Gaussian distribution of the signal, a power
spectrum analysis alone will not provide a complete description of its
properties. Here, we consider an additional metric which could be derived from
tomographic imaging data, namely the bubble size distribution of ionized
regions. We study three methods that have previously been used to characterize
bubble size distributions in simulation data for the hydrogen ionization
fraction - the spherical-average, mean-free-path and friends-of-friends methods
- and apply them to simulated 21-cm data cubes. Our simulated data cubes have
the (sensitivity-dictated) resolution expected for the SKA1-Low reionization
experiment and we study the impact of both the light-cone and redshift space
distortion effects. To identify ionized regions in the 21-cm data we introduce
a new, self-adjusting thresholding approach based on the K-Means algorithm. We
find that the fraction of ionized cells identified in this way consistently
falls below the mean volume-averaged ionized fraction. From a comparison of the
three bubble size methods, we conclude that all three methods are useful, but
that the mean-free-path method performs best in terms of tracking the progress
of reionization and separating different reionization scenarios. The light-cone
effect is found to affect data spanning more than about 10~MHz in frequency
($\Delta z\sim0.5$). We find that redshift space distortions only marginally
affect the bubble size distributions.
| arxiv topic:astro-ph.CO |
arxiv_dataset-85551706.00765 | Temporal Logic Task Planning and Intermittent Connectivity Control of
Mobile Robot Networks
cs.RO cs.MA
In this paper, we develop a distributed intermittent communication and task
planning framework for mobile robot teams. The goal of the robots is to
accomplish complex tasks, captured by local Linear Temporal Logic formulas, and
share the collected information with all other robots and possibly also with a
user. Specifically, we consider situations where the robot communication
capabilities are not sufficient to form reliable and connected networks while
the robots move to accomplish their tasks. In this case, intermittent
communication protocols are necessary that allow the robots to temporarily
disconnect from the network in order to accomplish their tasks free of
communication constraints. We assume that the robots can only communicate with
each other when they meet at common locations in space. Our distributed control
framework jointly determines local plans that allow all robots fulfill their
assigned temporal tasks, sequences of communication events that guarantee
information exchange infinitely often, and optimal communication locations that
minimize a desired distance metric. Simulation results verify the efficacy of
the proposed controllers.
| arxiv topic:cs.RO cs.MA |
arxiv_dataset-85561706.00865 | Inference for penalized spline regression: Improving confidence
intervals by reducing the penalty
stat.ME
Penalized spline regression is a popular method for scatterplot smoothing,
but there has long been a debate on how to construct confidence intervals for
penalized spline fits. Due to the penalty, the fitted smooth curve is a biased
estimate of the target function. Many methods, including Bayesian intervals and
the simple-shift bias-reduction, have been proposed to upgrade the coverage of
the confidence intervals, but these methods usually fail to adequately improve
the situation at predictor values where the function is sharply curved. In this
paper, we develop a novel approach to improving the confidence intervals by
using a smaller smoothing strength than that of the spline fits. With a
carefully selected amount of reduction in smoothing strength, the confidence
intervals achieve nearly nominal coverage without being excessively wide or
wiggly. The coverage performance of the proposed method is investigated via
simulation experiments in comparison with the bias-correction techniques
proposed by Hodges (2013) and Kuusela and Panaretos (2015).
| arxiv topic:stat.ME |
arxiv_dataset-85571706.00965 | Einstein's Equations from Varying Complexity
hep-th
A recent proposal equates the circuit complexity of a quantum gravity state
with the gravitational action of a certain patch of spacetime. Since Einstein's
equations follow from varying the action, it should be possible to derive them
by varying complexity. I present such a derivation for vacuum solutions of pure
Einstein gravity in three-dimensional asymptotically anti-de Sitter space. The
argument relies on known facts about holography and on properties of Tensor
Network Renormalization, an algorithm for coarse-graining (and optimizing)
tensor networks.
| arxiv topic:hep-th |
arxiv_dataset-85581706.01065 | Pinning and hysteresis in the field dependent diameter evolution of
skyrmions in Pt/Co/Ir superlattice stacks
cond-mat.mes-hall
We have imaged N\'eel skyrmion bubbles in perpendicularly magnetised
polycrystalline multilayers patterned into 1 \mu m diameter dots, using
scanning transmission x-ray microscopy. The skyrmion bubbles can be nucleated
by the application of an external magnetic field and are stable at zero field
with a diameter of 260 nm. Applying an out of plane field that opposes the
magnetisation of the skyrmion bubble core moment applies pressure to the bubble
and gradually compresses it to a diameter of approximately 100 nm. On removing
the field the skyrmion bubble returns to its original diameter via a hysteretic
pathway where most of the expansion occurs in a single abrupt step. This
contradicts analytical models of homogeneous materials in which the skyrmion
compression and expansion are reversible. Micromagnetic simulations
incorporating disorder can explain this behaviour using an effective thickness
modulation between 10 nm grains.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-85591706.01165 | Incorporating Current Research into Formal Higher Education Settings
using Astrobites
physics.ed-ph astro-ph.IM
A primary goal of many undergraduate- and graduate-level courses in the
physical sciences is to prepare students to engage in scientific research, or
to prepare students for careers that leverage skillsets similar to those used
by research scientists. Even for students who may not intend to pursue a career
with these characteristics, exposure to the context of applications in modern
research can be a valuable tool for teaching and learning. However, a
persistent barrier to student participation in research is familiarity with the
technical language, format, and context that academic researchers use to
communicate research methods and findings with each other: the literature of
the field. Astrobites, an online web resource authored by graduate students,
has published brief and accessible summaries of more than 1,300 articles from
the astrophysical literature since its founding in 2010. This article presents
three methods for introducing students at all levels within the formal higher
education setting to approaches and results from modern research. For each
method, we provide a sample lesson plan that integrates content and principles
from Astrobites, including step-by-step instructions for instructors,
suggestions for adapting the lesson to different class levels across the
undergraduate and graduate spectrum, sample student handouts, and a grading
rubric.
| arxiv topic:physics.ed-ph astro-ph.IM |
arxiv_dataset-85601706.01265 | Quadratic Frobenius probable prime tests costing two selfridges
math.NT
By an elementary observation about the computation of the difference of
squares for large in- tegers, deterministic quadratic Frobenius probable prime
tests are given with running times of approximately 2 selfridges.
| arxiv topic:math.NT |
arxiv_dataset-85611706.01365 | Synchronization and separation in the Johnson schemes
math.GR
Recently Peter Keevash solved asymptotically the existence question for
Steiner systems by showing that $S(t,k,n)$ exists whenever the necessary
divisibility conditions on the parameters are satisfied and $n$ is sufficiently
large in terms of $k$ and $t$. The purpose of this paper is to make a
conjecture which if true would be a significant extension of Keevash's theorem,
and to give some theoretical and computational evidence for the conjecture.
We phrase the conjecture in terms of the notions (which we define here) of
synchronization and separation for association schemes. These definitions are
based on those for permutation groups which grow out of the theory of
synchronization in finite automata. In this theory, two classes of permutation
groups (called \emph{synchronizing} and \emph{separating}) lying between
primitive and $2$-homogeneous are defined. A big open question is how the
permutation group induced by $S_n$ on $k$-subsets of $\{1,\ldots,n\}$ fits in
this hierarchy; our conjecture would give a solution to this problem for $n$
large in terms of $k$. We prove the conjecture in the case $k=4$: our result
asserts that $S_n$ acting on $4$-sets is separating for $n\ge10$ (it fails to
be synchronizing for $n=9$).
| arxiv topic:math.GR |
arxiv_dataset-85621706.01465 | Extracting the sigma-term from low-energy pion-nucleon scattering
hep-ph hep-lat nucl-ex nucl-th
We present an extraction of the pion-nucleon ($\pi N$) scattering lengths
from low-energy $\pi N$ scattering, by fitting a representation based on
Roy-Steiner equations to the low-energy data base. We show that the resulting
values confirm the scattering-length determination from pionic atoms, and
discuss the stability of the fit results regarding electromagnetic corrections
and experimental normalization uncertainties in detail. Our results provide
further evidence for a large $\pi N$ $\sigma$-term, $\sigma_{\pi N}=58(5)$ MeV,
in agreement with, albeit less precise than, the determination from pionic
atoms.
| arxiv topic:hep-ph hep-lat nucl-ex nucl-th |
arxiv_dataset-85631706.01565 | Two-color phase-of-the-phase spectroscopy in the multiphoton regime
physics.atom-ph physics.optics quant-ph
Momentum-resolved photoelectron emission from xenon in colinearly polarized
two-color laser fields at above-threshold ionization conditions is studied both
experimentally and theoretically. We utilize phase-of-the-phase spectroscopy as
recently introduced by Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015)
to analyze the dependence of the yields on the relative phase $\varphi$ between
the fundamental and second harmonic laser fields. The resulting phase-of-phase
spectra feature a characteristic checkerboard pattern, which can analytically
be described within the strong-field approximation.
| arxiv topic:physics.atom-ph physics.optics quant-ph |
arxiv_dataset-85641706.01665 | Stochastic Multi-objective Optimization on a Budget: Application to
multi-pass wire drawing with quantified uncertainties
math.OC math.PR
Design optimization of engineering systems with multiple competing objectives
is a painstakingly tedious process especially when the objective functions are
expensive-to-evaluate computer codes with parametric uncertainties. The
effectiveness of the state-of-the-art techniques is greatly diminished because
they require a large number of objective evaluations, which makes them
impractical for problems of the above kind. Bayesian global optimization (BGO),
has managed to deal with these challenges in solving single-objective
optimization problems and has recently been extended to multi-objective
optimization (MOO). BGO models the objectives via probabilistic surrogates and
uses the epistemic uncertainty to define an information acquisition function
(IAF) that quantifies the merit of evaluating the objective at new designs.
This iterative data acquisition process continues until a stopping criterion is
met. The most commonly used IAF for MOO is the expected improvement over the
dominated hypervolume (EIHV) which in its original form is unable to deal with
parametric uncertainties or measurement noise. In this work, we provide a
systematic reformulation of EIHV to deal with stochastic MOO problems. The
primary contribution of this paper lies in being able to filter out the noise
and reformulate the EIHV without having to observe or estimate the stochastic
parameters. An addendum of the probabilistic nature of our methodology is that
it enables us to characterize our confidence about the predicted Pareto front.
We verify and validate the proposed methodology by applying it to synthetic
test problems with known solutions. We demonstrate our approach on an
industrial problem of die pass design for a steel wire drawing process.
| arxiv topic:math.OC math.PR |
arxiv_dataset-85651706.01765 | Accessing the gluon Wigner distribution in ultraperipheral $pA$
collisions
hep-ph
We propose to constrain the gluon Wigner distribution in the nucleon by
studying the exclusive diffractive dijet production process in ultraperipheral
proton-nucleus collisions (UPCs) at RHIC and the LHC. Compared to the previous
proposal in Ref. [Y. Hatta, B. W. Xiao, and F. Yuan, Phys. Rev. Lett. 116,
202301 (2016).] to study the same observable in lepton-nucleon scattering, the
use of UPCs has a few advantages: not only is the cross section larger, but the
extraction of the Wigner distribution from the data also becomes simpler,
including its elliptic angular dependence. We compute the corresponding cross
section and evaluate the coefficients using models which include the gluon
saturation effects. A potential for the measurements of the Wigner distribution
at current and future experimental facilities is also discussed.
| arxiv topic:hep-ph |
arxiv_dataset-85661706.01865 | Estimating Shape Parameters of Piecewise Linear-Quadratic Problems
stat.ML
Piecewise Linear-Quadratic (PLQ) penalties are widely used to develop models
in statistical inference, signal processing, and machine learning. Common
examples of PLQ penalties include least squares, Huber, Vapnik, 1-norm, and
their asymmetric generalizations. Properties of these estimators depend on the
choice of penalty and its shape parameters, such as degree of asymmetry for the
quantile loss, and transition point between linear and quadratic pieces for the
Huber function. In this paper, we develop a statistical framework that can help
the modeler to automatically tune shape parameters once the shape of the
penalty has been chosen. The choice of the parameter is informed by the basic
notion that each QS penalty should correspond to a true statistical density.
The normalization constant inherent in this requirement helps to inform the
optimization over shape parameters, giving a joint optimization problem over
these as well as primary parameters of interest. A second contribution is to
consider optimization methods for these joint problems. We show that basic
first-order methods can be immediately brought to bear, and design specialized
extensions of interior point (IP) methods for PLQ problems that can quickly and
efficiently solve the joint problem. Synthetic problems and larger-scale
practical examples illustrate the potential of the approach.
| arxiv topic:stat.ML |
arxiv_dataset-85671706.01965 | Positive solutions to a fractional equation with singular nonlinearity
math.AP
In this paper, we study the positive solutions to the following singular and
non local elliptic problem posed in a bounded and smooth domain $\Omega\subset
\R^N$, $N> 2s$: % \begin{eqnarray*} (P_\lambda)\left\{\begin{array}{lll}
&(-\Delta)^s u=\lambda(K(x)u^{-\delta}+f(u))\mbox{ in }\Omega &u>0 \mbox{ in
}\Omega & u\equiv\, 0\mbox{ in }\R^N\backslash\Omega. \end{array}\right.
\end{eqnarray*} % Here $0<s<1$, $\delta>0$, $\lambda>0$ and $f\,:\,
\R^+\to\R^+$ is a positive $C^2$ function. $K\,:\, \Omega\to \R^+$ is a
H\"older continuous function in $\Omega$ which behave as ${\rm
dist}(x,\partial\Omega)^{-\beta}$ near the boundary with $0\leq \beta<2s$.
First, for any $\delta>0$ and for $\lambda>$ small enough, we prove the
existence of solutions to $(P_\lambda)$. Next, for a suitable range of values
of $\delta$, we show the existence of an unbounded connected branch of
solutions to $(P_\lambda)$ emanating from the trivial solution at $\lambda=0$.
For a certain class of nonlinearities $f$, we derive a global multiplicity
result that extends results proved in \cite{peral-al}. To establish the
results, we prove new properties which are of independent interest and deal
with the behavior and H\"older regularity of solutions to $(P_\lambda)$.
| arxiv topic:math.AP |
arxiv_dataset-85681706.02065 | General description of spin motion in storage rings in presence of
oscillating horizontal fields
physics.acc-ph
The general theoretical description of the influence of oscillating
horizontal magnetic and quasimagnetic fields on the spin evolution in storage
rings is presented. Previous results are generalized to the case when both of
the horizontal components of the oscillating field are nonzero and the vector
of this field circumscribes an ellipse. General equations describing a behavior
of all components of the polarization vector are derived and the case of an
arbitrary initial polarization is considered. The derivation is fulfilled in
the case when the oscillation frequency is nonresonant. The general spin
evolution in storage rings conditioned by vertical betatron oscillations is
calculated as an example.
| arxiv topic:physics.acc-ph |
arxiv_dataset-85691706.02165 | Angular Momentum of Early and Late Type Galaxies: Nature or Nurture?
astro-ph.GA
We investigate the origin, the shape, the scatter, and the cosmic evolution
in the observed relationship between specific angular momentum $j_\star$ and
the stellar mass $M_\star$ in early-type (ETGs) and late-type galaxies (LTGs).
Specifically, we exploit the observed star-formation efficiency and chemical
abundance to infer the fraction $f_{\rm inf}$ of baryons that infall toward the
central regions of galaxies where star formation can occur. We find $f_{\rm
inf}\approx 1$ for LTGs and $\approx 0.4$ for ETGs with an uncertainty of about
$0.25$ dex, consistent with a biased collapse. By comparing with the locally
observed $j_\star$ vs. $M_\star$ relations for LTGs and ETGs we estimate the
fraction $f_j$ of the initial specific angular momentum associated to the
infalling gas that is retained in the stellar component: for LTGs we find
$f_j\approx 1.11^{+0.75}_{-0.44}$, in line with the classic disc formation
picture; for ETGs we infer $f_j\approx 0.64^{+0.20}_{-0.16}$, that can be
traced back to a $z<1$ evolution via dry mergers. We also show that the
observed scatter in the $j_{\star}$ vs. $M_{\star}$ relation for both galaxy
types is mainly contributed by the intrinsic dispersion in the spin parameters
of the host dark matter halo. The biased collapse plus mergers scenario implies
that the specific angular momentum in the stellar components of ETG progenitors
at $z\sim 2$ is already close to the local values, in pleasing agreement with
observations. All in all, we argue such a behavior to be imprinted by nature
and not nurtured substantially by the environment.
| arxiv topic:astro-ph.GA |
arxiv_dataset-85701706.02265 | Level bounds for exceptional quantum subgroups in rank two
math.QA
There is a long-standing belief that the modular tensor categories
$\mathcal{C}(\mathfrak{g},k)$, for $k\in\mathbb{Z}_{\geq1}$ and
finite-dimensional simple complex Lie algebras $\mathfrak{g}$, contain
exceptional connected \'etale algebras at only finitely many levels $k$. This
premise has known implications for the study of relations in the Witt group of
nondegenerate braided fusion categories, modular invariants of conformal field
theories, and the classification of subfactors in the theory of von Neumann
algebras. Here we confirm this conjecture when $\mathfrak{g}$ has rank 2,
contributing proofs and explicit bounds when $\mathfrak{g}$ is of type $B_2$ or
$G_2$, adding to the previously known positive results for types $A_1$ and
$A_2$.
| arxiv topic:math.QA |
arxiv_dataset-85711706.02365 | Gravitational waves from non-Abelian gauge fields at a tachyonic
transition
hep-ph hep-lat
We compute the gravitational wave spectrum from a tachyonic preheating
transition of a Standard Model-like SU(2)-Higgs system. Tachyonic preheating
involves exponentially growing IR modes, at scales as large as the horizon.
Such a transition at the electroweak scale could be detectable by LISA, if
these non-perturbatively large modes translate into non-linear dynamics
sourcing gravitational waves. Through large-scale numerical simulations, we
find that the spectrum of gravitational waves does not exhibit such IR
features. Instead, we find two peaks corresponding to the Higgs and gauge field
mass, respectively. We find that the gravitational wave production is reduced
when adding non-Abelian gauge fields to a scalar-only theory, but increases
when adding Abelian gauge fields. In particular, gauge fields suppress the
gravitational wave spectrum in the IR. A tachyonic transition in the early
Universe will therefore not be detectable by LISA, even if it involves
non-Abelian gauge fields.
| arxiv topic:hep-ph hep-lat |
arxiv_dataset-85721706.02465 | Observations of Cyanopolyynes toward Four High-Mass Star-Forming Regions
Containing Hot Cores
astro-ph.GA astro-ph.SR
We carried out line survey observations at the 26-30 GHz band toward the four
high-mass star-forming regions containing hot cores, G10.30-0.15, G12.89+0.49,
G16.86-2.16, and G28.28-0.36, with the Robert C. Byrd Green Bank Telescope. We
have detected HC5N from all of the sources, and HC7N from the three sources,
except for G10.30-0.15. We further conducted observations of HC5N at the 42-46
GHz and 82-103 GHz bands toward the three sources, G12.89+0.49, G16.86-2.16,
and G28.28-0.36, with the Nobeyama 45 m radio telescope. The rotational lines
of HC5N with the high excitation energies (Eu/k=63-100 K), which are hardly
excited in the cold dark clouds, have been detected from the three sources. The
rotational temperatures of HC5N are found to be 13-20 K in the three sources.
The detection of the lines with the high excitation energies and the derived
rotational temperatures indicate that HC5N exists in the warm gas within
0.07-0.1 pc radii around massive young stellar objects. The column densities of
HC5N in the three sources are derived to be (2.0+-2.8)*10^(13) cm-2 . We
compare the ratios between N(HC5N) the column density of HC5N and W(CH3OH) the
integrated intensity of the thermal CH3OH emission line among the three
high-mass star-forming regions. We found a possibility of the chemical
differentiation in the three high-mass star-forming regions; G28.28-0.36 shows
the largest N (HC5N)/W (CH3OH) ratio of > 8.0*10^(14) in units of (K km s-1 )-1
cm-2 , while G12.89+0.49 and G16.86-2.16 show the smaller values (~2*10^(13) ).
| arxiv topic:astro-ph.GA astro-ph.SR |
arxiv_dataset-85731706.02565 | CFD simulations of turbulent flow in the human upper airways
physics.med-ph physics.flu-dyn
In this paper, investigations are conducted using Reynolds-averaged
Navier-Stokes (RANS) turbulence models to investigate the importance of
turbulence modelling for nasal inspiration at a constant flow rate of 250 ml/s.
Four different, standard turbulence models are tested in a model geometry based
on pre-operative CT images of a selected obstructive sleep-apnea syndrome
(OSAS) patient. The results show only minor differences between them.
Furthermore, the turbulence models do not give significantly different results
than a laminar flow model. Thus, the main conclusion is that effects of
turbulence are insignificant in CFD modelling of the airflow in the
pre-operative model of the upper airways of the chosen patient.
| arxiv topic:physics.med-ph physics.flu-dyn |
arxiv_dataset-85741706.02665 | Charge and Magnetic Properties of Three-Nucleon Systems in Pionless
Effective Field Theory
nucl-th
A method to calculate the form factor for an external current with
non-derivative coupling for the three-body system in an effective field theory
(EFT) of short-range interactions is shown. Using this method the point charge
radius of ${}^3\mathrm{He}$ is calculated to next-to-next-to-leading order
(NNLO) in pionless EFT ($\mathrm{EFT}(\not{\!\pi})$), and the magnetic moment
and magnetic radius of ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ are calculated to
next-to-leading order (NLO). For the ${}^3\mathrm{He}$ charge and magnetic form
factors Coulomb interactions are ignored. The ${}^3\mathrm{He}$ point charge
radius is given by 1.74(4) fm at NNLO. This agrees well with the experimental
${}^3\mathrm{He}$ point charge radius of 1.7753(54) fm [Angeli and Marinova,
At. Data Nucl. Data Tables 99, 69 (2013)]. The ${}^3\mathrm{H}$
(${}^3\mathrm{He}$) magnetic moment in units of nuclear magnetons is found to
be 2.92(35) (-2.08(25)) at NLO in agreement with the experimental value of
2.979 (-2.127). For ${}^3\mathrm{H}$ (${}^3\mathrm{He}$) the NLO magnetic
radius is 1.78(11) fm (1.85(11) fm) which agrees with the experimental value of
1.840(182) fm (1.965(154) fm) [I. Sick, Prog. Part. Nucl. Phys. 47, 245
(2001)]. The fitting of the low-energy constant $L_{1}$ of the isovector
two-body magnetic current and the consequences of Wigner-SU(4) symmetry for the
three-nucleon magnetic moments are also discussed.
| arxiv topic:nucl-th |
arxiv_dataset-85751706.02765 | Perfect Anomalous Reflection with an Aggressively Discretized Huygens'
Metasurface
physics.app-ph
This paper investigates the discretization of a periodic metasurface and
demonstrates how such a surface can achieve perfect anomalous reflection.
Whilst most contemporary theoretical works on metasurfaces deal with continuous
current or impedance distributions, we examine how discretization affects a
metasurface, and show that in some cases one can discretize a metasurface
aggressively --- to the extent of having only two cells per spatial period.
Such aggressive discretization can lead to great simplifications in metasurface
design, and perhaps more surprisingly, a possible performance improvement from
continuous metasurfaces. Using this aggressive discretization technique, we
report the design of a binary Huygens' metasurface which reflects an incident
plane wave at 50$^\circ$ into a reflected direction of -22.5$^\circ$. Full-wave
electromagnetic simulation shows the achievement of anomalous reflection with a
power efficiency of 99.1%, which dramatically surpasses the performance of a
corresponding passive continuous metasurface, for which the power efficiency is
fundamentally limited to 69.6%.
| arxiv topic:physics.app-ph |
arxiv_dataset-85761706.02865 | Covariant Jacobi Brackets for Test Particles
math-ph math.MP
We show that the space of observables of test particles carries a natural
Jacobi structure which is manifestly invariant under the action of the
Poincar\'{e} group. Poisson algebras may be obtained by imposing further
requirements. A generalization of Peierls procedure is used to extend this
Jacobi bracket on the space of time-like geodesics on Minkowski space-time.
| arxiv topic:math-ph math.MP |
arxiv_dataset-85771706.02965 | Comparative Autoignition Trends in the Butanol Isomers at Elevated
Pressure
physics.chem-ph
Autoignition experiments of stoichiometric mixtures of s-, t-, and i-butanol
in air have been performed using a heated rapid compression machine (RCM). At
compressed pressures of 15 and 30 bar and for compressed temperatures in the
range of 715-910 K, no evidence of a negative temperature coefficient region in
terms of ignition delay response is found. The present experimental results are
also compared with previously reported RCM data of n-butanol in air. The order
of reactivity of the butanols is
n-butanol>s-butanol$\approx$i-butanol>t-butanol at the lower pressure, but
changes to n-butanol>t-butanol>s-butanol>i-butanol at higher pressure. In
addition, t-butanol shows pre-ignition heat release behavior, which is
especially evident at higher pressures. To help identify the controlling
chemistry leading to this pre-ignition heat release, off-stoichiometric
experiments are further performed at 30 bar compressed pressure, for t-butanol
at $\phi$ = 0.5 and $\phi$ = 2.0 in air. For these experiments, higher fuel
loading (i.e. $\phi$ = 2.0) causes greater pre-ignition heat release (as
indicated by greater pressure rise) than the stoichiometric or $\phi$ = 0.5
cases. Comparison of the experimental ignition delays with the simulated
results using two literature kinetic mechanisms shows generally good agreement,
and one mechanism is further used to explore and compare the fuel decomposition
pathways of the butanol isomers. Using this mechanism, the importance of peroxy
chemistry in the autoignition of the butanol isomers is highlighted and
discussed.
| arxiv topic:physics.chem-ph |
arxiv_dataset-85781706.03065 | Towards balanced clustering - part 1 (preliminaries)
cs.DS cs.AI
The article contains a preliminary glance at balanced clustering problems.
Basic balanced structures and combinatorial balanced problems are briefly
described. A special attention is targeted to various balance/unbalance indices
(including some new versions of the indices): by cluster cardinality, by
cluster weights, by inter-cluster edge/arc weights, by cluster element
structure (for element multi-type clustering). Further, versions of
optimization clustering problems are suggested (including multicriteria problem
formulations). Illustrative numerical examples describe calculation of balance
indices and element multi-type balance clustering problems (including example
for design of student teams).
| arxiv topic:cs.DS cs.AI |
arxiv_dataset-85791706.03165 | Manipulating the direction of Einstein-Podolsky-Rosen steering
quant-ph
Einstein-Podolsky-Rosen (EPR) steering exhibits an inherent asymmetric
feature that differs from both entanglement and Bell nonlocality, which leads
to one-way EPR steering. Although this one-way EPR steering phenomenon has been
experimentally observed, the schemes to manipulate the direction of EPR
steering have not been investigated thoroughly. In this paper, we propose and
experimentally demonstrate three schemes to manipulate the direction of EPR
steering, either by varying the noise on one party of a two-mode squeezed state
(TMSS) or transmitting the TMSS in a noisy channel. The dependence of the
direction of EPR steering on the noise and transmission efficiency in the
quantum channel is analyzed. The experimental results show that the direction
of EPR steering of the TMSS can be changed in the presented schemes. Our work
is helpful in understanding the fundamental asymmetry of quantum nonlocality
and has potential applications in future asymmetric quantum information
processing.
| arxiv topic:quant-ph |
arxiv_dataset-85801706.03265 | Stepwise regression for unsupervised learning
cs.LG stat.ML
I consider unsupervised extensions of the fast stepwise linear regression
algorithm \cite{efroymson1960multiple}. These extensions allow one to
efficiently identify highly-representative feature variable subsets within a
given set of jointly distributed variables. This in turn allows for the
efficient dimensional reduction of large data sets via the removal of redundant
features. Fast search is effected here through the avoidance of repeat
computations across trial fits, allowing for a full representative-importance
ranking of a set of feature variables to be carried out in $O(n^2 m)$ time,
where $n$ is the number of variables and $m$ is the number of data samples
available. This runtime complexity matches that needed to carry out a single
regression and is $O(n^2)$ faster than that of naive implementations. I present
pseudocode suitable for efficient forward, reverse, and forward-reverse
unsupervised feature selection. To illustrate the algorithm's application, I
apply it to the problem of identifying representative stocks within a given
financial market index -- a challenge relevant to the design of Exchange Traded
Funds (ETFs). I also characterize the growth of numerical error with iteration
step in these algorithms, and finally demonstrate and rationalize the
observation that the forward and reverse algorithms return exactly inverted
feature orderings in the weakly-correlated feature set regime.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-85811706.03365 | Geometric Low-Energy Effective Action in a Doubled Spacetime
hep-th
The ten-dimensional supergravity theory is a geometric low-energy effective
theory and the equations of motion for its fields can be obtained from string
theory by computing $\beta$ functions. With $d$ compact dimensions, we can add
to it an $O(d, d;\mathbb{Z})$ geometric structure and construct the
supergravity theory inspired by double field theory through the use of a
suitable commutative star product. The latter implements the weak constraint of
the double field theory on its fields and gauge parameters in order to have a
closed gauge symmetry algebra. The consistency of the action here proposed is
based on the orthogonality of the momenta associated with fields in their
triple star products in the cubic terms defined for $d\ge1$. This orthogonality
holds also for an arbitrary number of star products of fields for $d=1$.
Finally, we extend our analysis to the double sigma model, non-commutative
geometry and open string theory.
| arxiv topic:hep-th |
arxiv_dataset-85821706.03465 | Nilpotent elements of operator ideals as single commutators
math.OA
For an arbitrary operator ideal I, every nilpotent element of I is a single
commutator of operators from I^t, for an exponent t that depends on the degree
of nilpotency.
| arxiv topic:math.OA |
arxiv_dataset-85831706.03565 | Prevalent Intrinsic Emission from Nonaromatic Amino Acids and Poly(Amino
Acids)
physics.chem-ph
Nonaromatic amino acids are generally believed to be nonemissive, owing to
their lack of apparently remarkable conjugation within individual molecules.
Here we report the intrinsic visible emission of nonaromatic amino acids and
poly(amino acids) in concentrated solutions and solid powders. This unique and
widespread luminescent characteristic can be well rationalized by the
clustering-triggered emission (CTE) mechanism, namely the clustering of
nonconventional chromophores (i.e. amino, carbonyl, and hydroxyl) and
subsequent electron cloud overlap with simultaneously conformation
rigidification. Such CTE mechanism is further supported by the single crystal
structure analysis. Besides prompt fluorescence, room temperature
phosphorescence (RTP) are also detected from the solids. Moreover, persistent
RTP is observed in the powders of exampled poly(amino acid) of
{\epsilon}-poly-L-lysine ({\epsilon}-PLL) after ceasing UV irradiation. These
results not only illustrate the feasibility of employing the building blocks of
nonaromatic amino acids in the exploration of new luminescent biomolecules, but
also provide significant implications for the RTP of peptides and proteins at
aggregated or crystalline states.
| arxiv topic:physics.chem-ph |
arxiv_dataset-85841706.03665 | Statistical properties of sketching algorithms
stat.ME stat.CO
Sketching is a probabilistic data compression technique that has been largely
developed in the computer science community. Numerical operations on big
datasets can be intolerably slow; sketching algorithms address this issue by
generating a smaller surrogate dataset. Typically, inference proceeds on the
compressed dataset. Sketching algorithms generally use random projections to
compress the original dataset and this stochastic generation process makes them
amenable to statistical analysis. We argue that the sketched data can be
modelled as a random sample, thus placing this family of data compression
methods firmly within an inferential framework. In particular, we focus on the
Gaussian, Hadamard and Clarkson-Woodruff sketches, and their use in single pass
sketching algorithms for linear regression with huge $n$. We explore the
statistical properties of sketched regression algorithms and derive new
distributional results for a large class of sketched estimators. A key result
is a conditional central limit theorem for data oblivious sketches. An
important finding is that the best choice of sketching algorithm in terms of
mean square error is related to the signal to noise ratio in the source
dataset. Finally, we demonstrate the theory and the limits of its applicability
on two real datasets.
| arxiv topic:stat.ME stat.CO |
arxiv_dataset-85851706.03765 | Axion Gauge Field Inflation and Gravitational Leptogenesis: A Lower
Bound on B Modes from the Matter-Antimatter Asymmetry of the Universe
astro-ph.CO
We present a toy model of an axion gauge field inflation scenario that yields
viable density and gravitational wave spectra. The scenario consists of an
axionic inflaton in a steep potential that is effectively flattened by a
coupling to a collection of non-Abelian gauge fields. The model predicts a
blue-tilted gravitational wave spectrum that is dominated by one circular
polarization, resulting in unique observational targets for cosmic microwave
background and gravitational wave experiments. The handedness of the
gravitational wave spectrum is incorporated in a model of leptogenesis through
the axial-gravitational anomaly; assuming electroweak sphaeleron processes
convert the lepton asymmetry into baryons, we predict an approximate lower
bound on the tensor-to-scalar ratio r ~ 3-4e-2 for models that also explain the
matter-antimatter asymmetry of the Universe.
| arxiv topic:astro-ph.CO |
arxiv_dataset-85861706.03865 | Correcting for the solar wind in pulsar timing observations: the role of
simultaneous a nd l ow-frequency observations
astro-ph.IM astro-ph.CO astro-ph.GA astro-ph.HE astro-ph.SR
The primary goal of the pulsar timing array projects is to detect
ultra-low-frequency gravitational waves. The pulsar data sets are affected by
numerous noise processes including varying dispersive delays in the
interstellar medium and from the solar wind. The solar wind can lead to rapidly
changing variations that, with existing telescopes, can be hard to measure and
then remove. In this paper we study the possibility of using a low frequency
telescope to aid in such correction for the Parkes Pulsar Timing Array (PPTA)
and also discuss whether the ultra-wide-bandwidth receiver for the FAST
telescope is sufficient to model the solar wind variations. Our key result is
that a single wide-bandwidth receiver can be used to model and remove the
effect of the solar wind. However, for pulsars that pass close to the Sun such
as PSR J1022+1022, the solar wind is so variable that observations at two
telescopes separated by a day are insufficient to correct the solar wind
effect.
| arxiv topic:astro-ph.IM astro-ph.CO astro-ph.GA astro-ph.HE astro-ph.SR |
arxiv_dataset-85871706.03965 | Structural and bonding character of potassium-doped p-terphenyl
superconductors
cond-mat.supr-con
Recently, there is a series of reports by Wang et al. on the
superconductivity in K-doped p-terphenyl (KxC18H14) with the transition
temperatures range from 7 to 123 Kelvin. Identifying the structural and bonding
character is the key to understand the superconducting phases and the related
properties. Therefore we carried out an extensive study on the crystal
structures with different doping levels and investigate the thermodynamic
stability, structural, electronic, and magnetic properties by the
first-principles calculations. Our calculated structures capture most features
of the experimentally observed X-ray diffraction patterns. The K doping
concentration is constrained to within the range of 2 and 3. The obtained
formation energy indicates that the system at x = 2.5 is more stable. The
strong ionic bonding interaction is found in between K atoms and organic
molecules. The charge transfer accounts for the metallic feature of the doped
materials. For a small amount of charge transferred, the tilting force between
the two successive benzenes drives the system to stabilize at the
antiferromagnetic ground state, while the system exhibits non-magnetic behavior
with increasing charge transfer. The multiformity of band structures near the
Fermi level indicates that the driving force for superconductivity is
complicated.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-85881706.04065 | Deleting vertices to graphs of bounded genus
cs.DS
We show that a problem of deleting a minimum number of vertices from a graph
to obtain a graph embeddable on a surface of a given Euler genus is solvable in
time $2^{C_g \cdot k^2 \log k} n^{O(1)}$, where $k$ is the size of the deletion
set, $C_g$ is a constant depending on the Euler genus $g$ of the target
surface, and $n$ is the size of the input graph. On the way to this result, we
develop an algorithm solving the problem in question in time $2^{O((t+g) \log
(t+g))} n$, given a tree decomposition of the input graph of width $t$. The
results generalize previous algorithms for the surface being a sphere by Marx
and Schlotter [Algorithmica 2012], Kawarabayashi [FOCS 2009], and Jansen,
Lokshtanov, and Saurabh [SODA 2014].
| arxiv topic:cs.DS |
arxiv_dataset-85891706.04165 | An accurate scheme to calculate the interatomic Dzyaloshinskii-Moriya
interaction parameters
cond-mat.mtrl-sci
An new and accurate scheme to calculate the interatomic Dzyaloshinskii-Moriya
interaction (DMI) parameters is presented, which is based on the fully
relativistic Korringa-Kohn-Rostoker Green function (KKR-GF) technique.
Corresponding numerical results are compared with those obtained using other
schemes reported in the literature.
The differences found can be attributed primarily to the different reference
states used in the various approaches. In addition an expression for the DMI
parameters formulated for a micromagnetic model Hamiltonian is presented that
provides a connection to the DMI parameters calculated for atomistic
Hamiltonians. This formulation also allows the discussion of the DMI in terms
of specific features of the electronic band structure.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-85901706.04265 | Transfer entropy-based feedback improves performance in artificial
neural networks
cs.LG cs.IT cs.NE math.IT
The structure of the majority of modern deep neural networks is characterized
by uni- directional feed-forward connectivity across a very large number of
layers. By contrast, the architecture of the cortex of vertebrates contains
fewer hierarchical levels but many recurrent and feedback connections. Here we
show that a small, few-layer artificial neural network that employs feedback
will reach top level performance on a standard benchmark task, otherwise only
obtained by large feed-forward structures. To achieve this we use feed-forward
transfer entropy between neurons to structure feedback connectivity. Transfer
entropy can here intuitively be understood as a measure for the relevance of
certain pathways in the network, which are then amplified by feedback. Feedback
may therefore be key for high network performance in small brain-like
architectures.
| arxiv topic:cs.LG cs.IT cs.NE math.IT |
arxiv_dataset-85911706.04365 | Landau-Ginzburg-Wilson approach to critical phenomena in the presence of
gauge symmetries
hep-lat cond-mat.stat-mech
We critically reconsider the Landau-Ginzburg-Wilson (LGW) approach to
critical phenomena in the presence of gauge symmetries. In the LGW framework,
to obtain the universal features of a continuous transition, one identifies the
order parameter Phi and considers the corresponding most general Phi4 field
theory that has the same symmetries as the original model. In the presence of
gauge symmetries, one usually considers a gauge-invariant order parameter and a
LGW field theory that is invariant under the global symmetries of the original
model. We show that this approach, in which the gauge dynamics is effectively
integrated out, may sometimes lead to erroneous conclusions on the nature of
the critical behavior. As an explicit example, we show that the above-described
LGW approach generally fails for the three-dimensional ferromagnetic and
antiferromagnetic CP(N-1) models, which are invariant under global U(N) and
local U(1) transformations. We point out possible implications for the
finite-temperature chiral transition of nuclear matter.
| arxiv topic:hep-lat cond-mat.stat-mech |
arxiv_dataset-85921706.04465 | Stress intrepretation of graphene E-2g and A-1g vibrational modes:
theoretical analysis
cond-mat.mtrl-sci
We here focus on only one graphene ring and examine to which stress tensor
components the E2g and the A1g vibration mode of graphene correspond. These
modes are typically related with the G-peak and the D-peak, respectively, and
are strongly related to the stress distribution along the specimen. We adopt
the theoretical framework of Admal and Tadmor ([1]) for the macroscopic
definition of the Cauchy stress tensor and we introduce into this framework the
E2g and the A1g as appropriate perturbations. We use these perturbations to the
stress tensor expression and evaluate which stress tensor components are
related to each vibrational mode. This approach, though qualitative in nature,
incorporates all the main physics and reveals that E2g and A1g vibration modes
should be related to shear as well as axial stress components when graphene is
at rest (i.e. no external applied loading). To bring our framework closer to
more concrete results, we evaluate the instantaneous Hardy stress tensor for a
pair potential which correspond to the E2g and A1g modes at rest. Our analysis
expands to take into account an applied external tensile field. Taking the
armchair direction to be along the x-axis, when tension applies along the
armchair direction, it is the axial $\sigma$11 stress component which dominates
over $\sigma$12, $\sigma$22, which are of smaller order. When tension is along
the zig-zag direction, it is the axial $\sigma$22 stress component that
dominates over $\sigma$12, $\sigma$11. When tension is at an arbitrary
direction between the armchair and the zig-zag direction, all stress components
are of the same order and should all be taken into account even at small
strains.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-85931706.04565 | A Generalization of the Gauss-Kuzmin-Wirsing constant
math.DS math.NT
We generalize the result of Wirsing on Gauss transformation to the
generalized tranformation $T_p(x)=\{\cfrac{p}{x}\}$ for any positive integer
$p$. We give an estimate for the generalized Gauss-Kuzmin-Wirsing constant.
| arxiv topic:math.DS math.NT |
arxiv_dataset-85941706.04665 | A fundamental theorem for submanifolds in semi-Riemannian warped
products
math.DG
In this paper we find necessary and sufficient conditions for a nondegenerate
arbitrary signature manifold $M^n$ to be realized as a submanifold in the large
class of warped product manifolds $\varepsilon
I\times_a\mathbb{M}^{N}_{\lambda}(c)$, where $\varepsilon=\pm 1,\
a:I\subset\mathbb{R}\to\mathbb{R}^+$ is the scale factor and
$\mathbb{M}^{N}_{\lambda}(c)$ is the $N$-dimensional semi-Riemannian space form
of index $\lambda$ and constant curvature $c\in\{-1,1\}.$ We prove that if
$M^n$ satisfies Gauss, Codazzi and Ricci equations for a submanifold in
$\varepsilon I\times_a\mathbb{M}^{N}_{\lambda}(c)$, along with some additional
conditions, then $M^n$ can be isometrically immersed into $\varepsilon
I\times_a\mathbb{M}^{N}_{\lambda}(c)$. This comprises the case of hypersurfaces
immersed in semi-Riemannian warped products proved by M.A. Lawn and M. Ortega
(see [6]), which is an extension of the isometric immersion result obtained by
J. Roth in the Lorentzian products $\mathbb{S}^n\times\mathbb{R}_1$ and
$\mathbb{H}^n\times\mathbb{R}_1$ (see [12]), where $\mathbb{S}^n$ and
$\mathbb{H}^n$ stand for the sphere and hyperbolic space of dimension $n$,
respectively. This last result, in turn, is an expansion to pseudo-Riemannian
manifolds of the isometric immersion result proved by B. Daniel in
$\mathbb{S}^n\times\mathbb{R}$ and $\mathbb{H}^n\times\mathbb{R}$ (see [2]),
one of the first generalizations of the classical theorem for submanifolds in
space forms (see [13]). Although additional conditions to Gauss, Codazzi and
Ricci equations are not necessary in the classical theorem for submanifolds in
space forms, they appear in all other cases cited above.
| arxiv topic:math.DG |
arxiv_dataset-85951706.04765 | Hidden-charm Pentaquark Production at $e^+e^-$ Colliders
hep-ph
We study one possible production mechanism for hidden charm pentaquark in
e+e- collision, where it is produced via a color-octet c \bar c pair
fragmentation. The pentaquark production at B factory energy is dominated by
e+e- to c \bar c g to Pc + X. At Z^0 pole, for the pentaquark production, there
are several partonic processes playing significant role. Our results show that
it is possible to search for the direct pentaquark production signal at e+e-
colliders, which is important to understand the properties of pentaquark.
| arxiv topic:hep-ph |
arxiv_dataset-85961706.04865 | Approximation of maps into spheres by regulous maps
math.AG
Let $X$ be a compact real algebraic set of dimension $n$. We prove that every
Euclidean continuous map from $X$ into the unit $n$-sphere can be approximated
by regulous map. This strengthens and generalizes previously known results.
| arxiv topic:math.AG |
arxiv_dataset-85971706.04965 | Particle-flow reconstruction and global event description with the CMS
detector
physics.ins-det hep-ex
The CMS apparatus was identified, a few years before the start of the LHC
operation at CERN, to feature properties well suited to particle-flow (PF)
reconstruction: a highly-segmented tracker, a fine-grained electromagnetic
calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an
excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned
to the CMS detector was therefore developed and has been consistently used in
physics analyses for the first time at a hadron collider. For each collision,
the comprehensive list of final-state particles identified and reconstructed by
the algorithm provides a global event description that leads to unprecedented
CMS performance for jet and hadronic tau decay reconstruction, missing
transverse momentum determination, and electron and muon identification. This
approach also allows particles from pileup interactions to be identified and
enables efficient pileup mitigation methods. The data collected by CMS at a
centre-of-mass energy of 8 TeV show excellent agreement with the simulation and
confirm the superior PF performance at least up to an average of 20 pileup
interactions.
| arxiv topic:physics.ins-det hep-ex |
arxiv_dataset-85981706.05065 | Orientation of topological defects in 2D nematic liquid crystals
cond-mat.soft
Topological defects are an essential part of the structure and dynamics of
all liquid crystals, and they are particularly important in experiments and
simulations on active liquid crystals. In a recent paper, Vromans and Giomi
[Soft Matter, 2016, 12, 6490] pointed out that topological defects are not
point-like objects but actually have orientational properties, which strongly
affect the energetics and motion of the defects. That paper developed a
mathematical formalism which describes the orientational properties as vectors.
Here, we agree with the basic concept of defect orientation, but we suggest an
alternative mathematical formalism. We represent the defect orientation by a
tensor, with a rank that depends on the topological charge: rank 1 for a charge
of +1/2, rank 3 for a charge of -1/2. Using this tensor formalism, we calculate
the orientation-dependent interaction between defects, and we present numerical
simulations of defect motion.
| arxiv topic:cond-mat.soft |
arxiv_dataset-85991706.05165 | Observation of Effective Pseudospin Scattering in ZrSiS
cond-mat.mtrl-sci
3D Dirac semimetals are an emerging class of materials that possess
topological electronic states with a Dirac dispersion in their bulk. In
nodal-line Dirac semimetals, the conductance and valence bands connect along a
closed path in momentum space, leading to the prediction of pseudospin vortex
rings and pseudospin skyrmions. Here, we use Fourier transform scanning
tunneling spectroscopy (FT-STS) at 4.5 K to resolve quasiparticle interference
(QPI) patterns at single defect centers on the surface of the line nodal
semimetal zirconium silicon sulfide (ZrSiS). Our QPI measurements show
pseudospin conservation at energies close to the line node. In addition, we
determine the Fermi velocity to be $\hbar v_F = 2.65 \pm 0.10$ eV {\AA} in the
{\Gamma}-M direction ~300 meV above the Fermi energy $E_F$, and the line node
to be ~140 meV above $E_F$. More importantly, we find that certain scatterers
can introduce energy-dependent non-preservation of pseudospins, giving rise to
effective scattering between states with opposite valley pseudospin deep inside
valence and conduction bands. Further investigations of quasiparticle
interference at the atomic level will aid defect engineering at the synthesis
level, needed for the development of lower-power electronics via
dissipationless electronic transport in the future.
| arxiv topic:cond-mat.mtrl-sci |
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