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arxiv_dataset-76001608.03538 | Normalising graphs of groups
math.GR
We discuss a partial normalisation of a finite graph of finite groups
$(\Gamma(-), X)$ which leaves invariant the fundamental group. In conjunction
with an easy graph-theoretic result, this provides a flexible and rather useful
tool in the study of finitely generated virtually free groups. Applications
discussed here include (i) an important inequality for the number of edges in a
Stallings decomposition $\Gamma \cong \pi_1(\Gamma(-), X)$ of a finitely
generated virtually free group, (ii) the proof of equivalence of a number of
conditions for such a group to be `large', as well as (iii) the classification
up to isomorphism of virtually free groups of (free) rank $2$. We also discuss
some number-theoretic consequences of the last result.
| arxiv topic:math.GR |
arxiv_dataset-76011608.03638 | Downlink Performance of Pilot-Reused HetNet with Large-Scale Antenna
Arrays
cs.IT math.IT
Considering a heterogeneous network (HetNet) where both macro base station
(BS) and small cell (SC) nodes are equipped with massive antennas, this paper
studies the performance for multiple-input multiple-output (MIMO) downlinks
when the macro and small cells share the same spectrum and hence interfere with
each other. Suppose that the large-scale antenna arrays at both macro BS and SC
nodes employ maximum-ratio transmission (MRT) or zero-forcing transmission
(ZFT) precoding, and transmit data streams to the served users simultaneously.
A new pilot reuse pattern among SCs is proposed for channel estimation. Taking
into account imperfect channel state information (CSI), capacity lower bounds
for MRT and ZFT are derived, respectively, in closed-form expressions involving
only statistical CSI. Then asymptotic analyses for massive arrays are presented
under specific power scaling laws. Subsequently, two user scheduling
algorithms, greedy scheduling algorithm and asymptotical scheduling algorithm
(ASA), are proposed based on derived capacity lower bounds and asymptotic
analyses, respectively. ASA is demonstrated to be a near optimal in the
asymptotic regime and has low complexity. Finally, the derived closed-form
expressions are verified to be accurate predictors of the system performance by
Monte-Carlo simulations. Numerical results demonstrate the effectiveness of
asymptotic analysis and proposed user scheduling schemes.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-76021608.03738 | Holographic fermions at strong translational symmetry breaking: a
Bianchi-VII case study
hep-th cond-mat.str-el
It is presently unknown how strong lattice potentials influence the fermion
spectral function of the holographic strange metals predicted by the AdS/CFT
correspondence. This embodies a crucial test for the application of holography
to condensed matter experiments. We show that for one particular momentum
direction this spectrum can be computed for arbitrary strength of the effective
translational symmetry breaking potential of the so-called Bianchi-VII geometry
employing ordinary differential equations. Deep in the strange metal regime we
find rather small changes to the single-fermion response computed by the
emergent quantum critical IR, even when the potential becomes relevant in the
infra-red. However, in the regime where holographic quasi-particles occur,
defining a Fermi surface in the continuum, they acquire a finite lifetime at
any finite potential strength. At the transition from irrelevancy to relevancy
of the Bianchi potential in the deep infra-red the quasi-particle remnants
disappear completely and the fermion spectrum exhibits a purely relaxational
behaviour.
| arxiv topic:hep-th cond-mat.str-el |
arxiv_dataset-76031608.03838 | Exclusive J/psi and Upsilon photoproduction and the low x gluon
hep-ph
We discuss the potential to constrain the small-$x$ PDFs using the exclusive
production of heavy vector mesons. The calculation of $J/\psi$ and $\Upsilon$
photoproduction at NLO in collinear factorisation is described. The different
behaviour of the NLO corrections for $J/\psi$ and $\Upsilon$ is highlighted and
we outline what might be expected from the inclusion of these processes in a
PDF fit.
| arxiv topic:hep-ph |
arxiv_dataset-76041608.03938 | Determining Health Utilities through Data Mining of Social Media
cs.CL cs.AI cs.CY cs.SI
'Health utilities' measure patient preferences for perfect health compared to
specific unhealthy states, such as asthma, a fractured hip, or colon cancer.
When integrated over time, these estimations are called quality adjusted life
years (QALYs). Until now, characterizing health utilities (HUs) required
detailed patient interviews or written surveys. While reliable and specific,
this data remained costly due to efforts to locate, enlist and coordinate
participants. Thus the scope, context and temporality of diseases examined has
remained limited.
Now that more than a billion people use social media, we propose a novel
strategy: use natural language processing to analyze public online
conversations for signals of the severity of medical conditions and correlate
these to known HUs using machine learning. In this work, we filter a dataset
that originally contained 2 billion tweets for relevant content on 60 diseases.
Using this data, our algorithm successfully distinguished mild from severe
diseases, which had previously been categorized only by traditional techniques.
This represents progress towards two related applications: first, predicting
HUs where such information is nonexistent; and second, (where rich HU data
already exists) estimating temporal or geographic patterns of disease severity
through data mining.
| arxiv topic:cs.CL cs.AI cs.CY cs.SI |
arxiv_dataset-76051608.04038 | Prediction of the bed-load transport by gas-liquid stratified flows in
horizontal ducts
physics.flu-dyn
Solid particles can be transported as a mobile granular bed, known as
bed-load, by pressure-driven flows. A common case in industry is the presence
of bed-load in stratified gas-liquid flows in horizontal ducts. In this case,
an initially flat granular bed may be unstable, generating ripples and dunes.
This three-phase flow, although complex, can be modeled under some simplifying
assumptions. This paper presents a model for the estimation of some bed-load
characteristics. Based on parameters easily measurable in industry, the model
can predict the local bed-load flow rates and the celerity and the wavelength
of instabilities appearing on the granular bed.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-76061608.04138 | Sub-Nyquist SAR via Fourier Domain Range Doppler Processing
cs.IT math.IT
Conventional Synthetic Aperture Radar (SAR) systems are limited in their
ability to satisfy the increasing requirement for improved spatial resolution
and wider coverage. The demand for high resolution requires high sampling
rates, while coverage is limited by the pulse repetition frequency.
Consequently, sampling rate reduction is of high practical value in SAR
imaging. In this paper, we introduce a new algorithm, equivalent to the
well-known Range-Doppler method, to process SAR data using the Fourier series
coefficients of the raw signals. We then demonstrate how to exploit the
algorithm features to reduce sampling rate in both range and azimuth axes and
process the signals at sub-Nyquist rates, by using compressed sensing (CS)
tools. In particular, we demonstrate recovery of an image using only a portion
of the received signal's bandwidth and also while dropping a large percentage
of the transmitted pulses. The complementary pulses may be used to capture
other scenes within the same coherent processing interval. In addition, we
propose exploiting the ability to reconstruct the image from narrow bands in
order to dynamically adapt the transmitted waveform energy to vacant spectral
bands, paving the way to cognitive SAR. The proposed recovery algorithms form a
new CS-SAR imaging method that can be applied to high-resolution SAR data
acquired at sub-Nyquist rates in range and azimuth. The performance of our
method is assessed using simulated and real data sets. Finally, our approach is
implemented in hardware using a previously suggested Xampling radar prototype.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-76071608.04238 | A monolithic collapse origin for the thin/thick disc structure of ESO
243-49
astro-ph.GA
ESO 243-49 is a high-mass (circular velocity $v_{\rm c}\approx200\,{\rm
km\,s^{-1}}$) edge-on S0 galaxy in the Abell 2877 cluster at a distance of
$\sim95\,{\rm Mpc}$. To elucidate the origin of its thick disc, we use MUSE
science verification data to study its kinematics and stellar populations. The
thick disc emits $\sim80\%$ of the light at heights in excess of
$3.5^{\prime\prime}$ ($1.6\,{\rm kpc}$). The rotation velocities of its stars
lag by $30-40\,{\rm km\,s^{-1}}$ compared to those in the thin disc, which is
compatible with the asymmetric drift. The thick disc is found to be more
metal-poor than the thin disc, but both discs have old ages. We suggest an
internal origin for the thick disc stars in high-mass galaxies. We propose that
the thick disc formed either ${\rm a)}$ first in a turbulent phase with a high
star formation rate and that a thin disc formed shortly afterwards, or ${\rm
b)}$ because of the dynamical heating of a thin pre-existing component. Either
way, the star formation in ESO 243-49 was quenched just a few Gyrs after the
galaxy was born and the formation of a thin and a thick disc must have occurred
before the galaxy stopped forming stars. The formation of the discs was so fast
that it could be described as a monolithic collapse where several generations
of stars formed in a rapid succession.
| arxiv topic:astro-ph.GA |
arxiv_dataset-76081608.04338 | On generalizations of Fermat curves over finite fields and their
automorphisms
math.AG
Let $\mathcal{X}$ be an irreducible algebraic curve defined over a finite
field $\mathbb{F}_q$ of characteristic $p>2$. Assume that the
$\mathbb{F}_q$-automorphism group of $\mathcal{X}$ admits as an automorphism
group the direct product of two cyclic groups $C_m$ and $C_n$ of orders $m$ and
$n$ prime to $p$ such that both quotient curves $\mathcal{X}/C_n$ and
$\mathcal{X}/C_m$ are rational. In this paper, we provide a complete
classification of such curves, as well as a characterization of their full
automorphism groups.
| arxiv topic:math.AG |
arxiv_dataset-76091608.04438 | Chalcogenide glass planar MIR couplers for future chip based Bracewell
interferometers
astro-ph.IM astro-ph.EP physics.optics
Photonic integrated circuits are established as the technique of choice for a
number of astronomical processing functions due to their compactness, high
level of integration, low losses, and stability. Temperature control,
mechanical vibration and acoustic noise become controllable for such a device
enabling much more complex processing than can realistically be considered with
bulk optics. To date the benefits have mainly been at wavelengths around 1550
nm but in the important Mid-Infrared region, standard photonic chips absorb
light strongly. Chalcogenide glasses are well known for their transparency to
beyond 10000 nm, and the first results from coupler devices intended for use in
an interferometric nuller for exoplanetary observation in the Mid-Infrared L
band (3800-4200 nm) are presented here showing that suitable performance can be
obtained both theoretically and experimentally for the first fabricated devices
operating at 4000 nm.
| arxiv topic:astro-ph.IM astro-ph.EP physics.optics |
arxiv_dataset-76101608.04538 | Closed inverse subsemigroups of graph inverse semigroups
math.GR
As part of his study of representations of the polycylic monoids, M.V. Lawson
described all the closed inverse submonoids of a polycyclic monoid $P_n$ and
classified them up to conjugacy. We show that Lawson's description can be
extended to closed inverse subsemigroups of graph inverse semigroups. We then
apply B. Schein's theory of cosets in inverse semigroups to the closed inverse
subsemigroups of graph inverse semigroups: we give necessary and sufficient
conditions for a closed inverse subsemigroup of a graph inverse semigroup to
have finite index, and determine the value of the index when it is finite.
| arxiv topic:math.GR |
arxiv_dataset-76111608.04638 | Finite size effects for spacing distributions in random matrix theory:
circular ensembles and Riemann zeros
math-ph math.MP math.PR
According to Dyson's three fold way, from the viewpoint of global time
reversal symmetry there are three circular ensembles of unitary random matrices
relevant to the study of chaotic spectra in quantum mechanics. These are the
circular orthogonal, unitary and symplectic ensembles, denoted COE, CUE and CSE
respectively. For each of these three ensembles and their thinned versions,
whereby each eigenvalue is deleted independently with probability $1-\xi$, we
take up the problem of calculating the first two terms in the scaled large $N$
expansion of the spacing distributions. It is well known that the leading term
admits a characterisation in terms of both Fredholm determinants and Painlev\'e
transcendents. We show that modifications of these characterisations also
remain valid for the next to leading term, and that they provide schemes for
high precision numerical computations. In the case of the CUE there is an
application to the analysis of Odlyzko's data set for the Riemann zeros, and in
that case some further statistics are similarly analysed.
| arxiv topic:math-ph math.MP math.PR |
arxiv_dataset-76121608.04738 | An Efficient Character-Level Neural Machine Translation
cs.CL stat.ML
Neural machine translation aims at building a single large neural network
that can be trained to maximize translation performance. The encoder-decoder
architecture with an attention mechanism achieves a translation performance
comparable to the existing state-of-the-art phrase-based systems on the task of
English-to-French translation. However, the use of large vocabulary becomes the
bottleneck in both training and improving the performance. In this paper, we
propose an efficient architecture to train a deep character-level neural
machine translation by introducing a decimator and an interpolator. The
decimator is used to sample the source sequence before encoding while the
interpolator is used to resample after decoding. Such a deep model has two
major advantages. It avoids the large vocabulary issue radically; at the same
time, it is much faster and more memory-efficient in training than conventional
character-based models. More interestingly, our model is able to translate the
misspelled word like human beings.
| arxiv topic:cs.CL stat.ML |
arxiv_dataset-76131608.04838 | Almost perfect matchings in $k$-partite $k$-graphs
math.CO
The minimum co-degree threshold for a perfect matching in a $k$-graph with
$n$ vertices was determined by R\"odl, Ruci\'nski and Szemer\'edi for the case
when $n\equiv 0\pmod k$. Recently, Han resolved the remaining cases when $n
\not\equiv 0\pmod k$, establishing a conjecture of R\"odl, Ruci\'nski and
Szemer\'edi. In this paper, we determine the minimum co-degree threshold for
almost perfect matchings in $k$-partite $k$-graphs, answering a question of
R\"odl and Ruci\'nski.
| arxiv topic:math.CO |
arxiv_dataset-76141608.04938 | Doped carbon nanotubes as a model system of biased graphene
cond-mat.str-el cond-mat.mes-hall
Albeit difficult to access experimentally, the density of states (DOS) is a
key parameter in solid state systems which governs several important phenomena
including transport, magnetism, thermal, and thermoelectric properties. We
study DOS in an ensemble of potassium intercalated single-wall carbon nanotubes
(SWCNT) and show using electron spin resonance spectroscopy that a sizeable
number of electron states are present, which gives rise to a Fermi-liquid
behavior in this material. A comparison between theoretical and the
experimental DOS indicates that it does not display significant correlation
effects, even though the pristine nanotube material shows a Luttinger-liquid
behavior. We argue that the carbon nanotube ensemble essentially maps out the
whole Brillouin zone of graphene thus it acts as a model system of biased
graphene.
| arxiv topic:cond-mat.str-el cond-mat.mes-hall |
arxiv_dataset-76151608.05038 | Electoral Stability and Rigidity
q-fin.EC physics.soc-ph
Some argue that political stability is best served through a two-party
system. This study refutes this. The author mathematically defines the
stability and rigidity of electoral systems comprised of any quantity of
electors and parties. In fact, stability is a function of the quantity of
electors - i.e., the number of occupied seats at the table. As the number of
electors increases, the properties of an electorate are increasingly well
resolved, and well described by those of an electorate that is least excessive
-- that is to say an electorate that is closest to equilibrium. Further,
electoral rigidity is a function of the quantity of parties and their
probabilities of representation. An absolutely rigid system admits no
fluctuations -- whatever happens to one elector will happen to all electors. As
the quantity of parties increases so does the number of party lines, and with
it the quantity of alternatives with which to respond to an external stimulus.
Rigidity is significant in a social system that places high value on party
loyalty. In conclusion, (i) electoral stability is best served by increasing
the quantity of electors; (ii) electoral rigidity is best served by decreasing
the quantity of parties, and by increasing the representation of some parties
at the expense of others; and (iii) the less stable a branch of government, the
more concern is placed on those who would hold those offices for the people.
| arxiv topic:q-fin.EC physics.soc-ph |
arxiv_dataset-76161608.05138 | Hybrid CPU-GPU Framework for Network Motifs
cs.DC cs.SI stat.ML
Massively parallel architectures such as the GPU are becoming increasingly
important due to the recent proliferation of data. In this paper, we propose a
key class of hybrid parallel graphlet algorithms that leverages multiple CPUs
and GPUs simultaneously for computing k-vertex induced subgraph statistics
(called graphlets). In addition to the hybrid multi-core CPU-GPU framework, we
also investigate single GPU methods (using multiple cores) and multi-GPU
methods that leverage all available GPUs simultaneously for computing induced
subgraph statistics. Both methods leverage GPU devices only, whereas the hybrid
multi-core CPU-GPU framework leverages all available multi-core CPUs and
multiple GPUs for computing graphlets in large networks. Compared to recent
approaches, our methods are orders of magnitude faster, while also more cost
effective enjoying superior performance per capita and per watt. In particular,
the methods are up to 300 times faster than the recent state-of-the-art method.
To the best of our knowledge, this is the first work to leverage multiple CPUs
and GPUs simultaneously for computing induced subgraph statistics.
| arxiv topic:cs.DC cs.SI stat.ML |
arxiv_dataset-76171608.05238 | Quantitative photoacoustic tomography using forward and adjoint Monte
Carlo models of radiance
physics.med-ph
Forward and adjoint Monte Carlo (MC) models of radiance are proposed for use
in model-based quantitative photoacoustic tomography. A 2D radiance MC model
using a harmonic angular basis is introduced and validated against analytic
solutions for the radiance in heterogeneous media. A gradient-based
optimisation scheme is then used to recover 2D absorption and scattering
coefficients distributions from simulated photoacoustic measurements. It is
shown that the functional gradients, which are a challenge to compute
efficiently using MC models, can be calculated directly from the coefficients
of the harmonic angular basis used in the forward and adjoint models. This work
establishes a framework for transport-based quantitative photoacoustic
tomography that can fully exploit emerging highly parallel computing
architectures.
| arxiv topic:physics.med-ph |
arxiv_dataset-76181608.05338 | The multi-level Monte Carlo method for simulations of turbulent flows
stat.CO cs.CE math.NA
In this paper the application of the multi-level Monte Carlo (MLMC) method on
numerical simulations of turbulent flows with uncertain parameters is
investigated. Several strategies for setting up the MLMC method are presented,
and the advantages and disadvantages of each strategy are also discussed. A
numerical experiment is carried out using the Antarctic Circumpolar Current
(ACC) with uncertain, small-scale bottom topographic features. It is
demonstrated that, unlike the pointwise solutions, the averaged volume
transports are correlated across grid resolutions, and the MLMC method could
increase simulation efficiency without losing accuracy in uncertainty
assessment.
| arxiv topic:stat.CO cs.CE math.NA |
arxiv_dataset-76191608.05438 | A reaction network approach to the convergence to equilibrium of quantum
Boltzmann equations for Bose gases
math.AP math-ph math.CA math.DS math.MP
When the temperature of a trapped Bose gas is below the Bose-Einstein
transition temperature and above absolute zero, the gas is composed of two
distinct components: the Bose-Einstein condensate and the cloud of thermal
excitations. The dynamics of the excitations can be described by quantum
Boltzmann models. We establish a connection between quantum Boltzmann models
and chemical reaction networks. We prove that the discrete differential
equations for these quantum Boltzmann models converge to an equilibrium point.
Moreover, this point is unique for all initial conditions that satisfy the same
conservation laws. In the proof, we then employ a toric dynamical system
approach, similar to the one used to prove the global attractor conjecture, to
study the convergence to equilibrium of quantum kinetic equations, derived in
[49,50].
| arxiv topic:math.AP math-ph math.CA math.DS math.MP |
arxiv_dataset-76201608.05538 | A Survey on Routing in Anonymous Communication Protocols
cs.CR
The Internet has undergone dramatic changes in the past 15 years, and now
forms a global communication platform that billions of users rely on for their
daily activities. While this transformation has brought tremendous benefits to
society, it has also created new threats to online privacy, ranging from
profiling of users for monetizing personal information to nearly omnipotent
governmental surveillance. As a result, public interest in systems for
anonymous communication has drastically increased. Several such systems have
been proposed in the literature, each of which offers anonymity guarantees in
different scenarios and under different assumptions, reflecting the plurality
of approaches for how messages can be anonymously routed to their destination.
Understanding this space of competing approaches with their different
guarantees and assumptions is vital for users to understand the consequences of
different design options.
In this work, we survey previous research on designing, developing, and
deploying systems for anonymous communication. To this end, we provide a
taxonomy for clustering all prevalently considered approaches (including
Mixnets, DC-nets, onion routing, and DHT-based protocols) with respect to their
unique routing characteristics, deployability, and performance. This, in
particular, encompasses the topological structure of the underlying network;
the routing information that has to be made available to the initiator of the
conversation; the underlying communication model; and performance-related
indicators such as latency and communication layer. Our taxonomy and
comparative assessment provide important insights about the differences between
the existing classes of anonymous communication protocols, and it also helps to
clarify the relationship between the routing characteristics of these
protocols, and their performance and scalability.
| arxiv topic:cs.CR |
arxiv_dataset-76211608.05638 | Measurements and analysis of current-voltage characteristic of a pn
diode for an undergraduate physics laboratory
physics.ed-ph
We show that in a simple experiment at undergraduate level, suitable to be
performed in classes of science and engineering students, it is possible to
test accurately, on a popular 1N4148 p-n diode, the range of the junction
currents where the Shockley equation model can be considered satisfactory. The
experiment benefits from a system of temperature control and data collection
driven in a LabVIEW environment. With these tools a large quantity of data can
be recorded in the temporal frame of a lab session. Significant deviations of
the experimental I-V with respect to the ideal behaviour curve predicted by the
Shockley equation are observed, both at low and high current. A better
agreement over the entire range is obtained introducing, as is customary, a
four parameters model, including a parallel and a series resistance. A new
iterative fitting procedure is presented which treats the I-V data of different
regimes on the same level, and allows a simultaneous determination of the four
parameters for each temperature selected. Moreover, the knowledge of the
temperature dependence of saturation current is used to estimate the energy gap
of silicon. The connection of a macroscopic measure with a microscopic quantity
is another valuable feature of this experiment, from an educational point of
view.
| arxiv topic:physics.ed-ph |
arxiv_dataset-76221608.05738 | Embedding-Based Interpolation on the Special Orthogonal Group
math.NA
We study schemes for interpolating functions that take values in the special
orthogonal group $SO(n)$. Our focus is on interpolation schemes obtained by
embedding $SO(n)$ in a linear space, interpolating in the linear space, and
mapping the result onto $SO(n)$ via the closest point projection. The resulting
interpolants inherit both the order of accuracy and the regularity of the
underlying interpolants on the linear space. The values and derivatives of the
interpolants admit efficient evaluation via either explicit formulas or
iterative algorithms, which we detail for two choices of embeddings: the
embedding of $SO(n)$ in the space of $n \times n$ matrices and, when $n=3$, the
identification of $SO(3)$ with the set of unit quaternions. Along the way, we
point out a connection between these interpolation schemes and geodesic finite
elements. We illustrate the utility of these interpolation schemes by
numerically computing minimum acceleration curves on $SO(n)$, a task which is
handled naturally with $SO(n)$-valued finite elements having $C^1$-continuity.
| arxiv topic:math.NA |
arxiv_dataset-76231608.05838 | Proving chaotic behaviour of CBC mode of operation
cs.CR math.DS
The cipher block chaining (CBC) block cipher mode of operation was invented
by IBM (International Business Machine) in 1976. It presents a very popular way
of encrypting which is used in various applications. In this paper, we have
mathematically proven that, under some conditions, the CBC mode of operation
can admit a chaotic behaviour according to Devaney. Some cases will be properly
studied in order to put in evidence this idea.
| arxiv topic:cs.CR math.DS |
arxiv_dataset-76241608.05938 | On smoothing singularities of elliptic orbital integrals on GL(n) and
Beyond Endoscopy
math.NT math.RT
Recent work of Altu\u{g} continues the preliminary analysis of Langlands'
Beyond Endoscopy proposal for $GL(2)$ by removing the contribution of the
trivial representation to the trace formula using a Poisson summation formula.
We show that Altu\u{g}'s method of smoothing real elliptic orbital integrals by
an approximate functional equation extends to $GL(n)$. We also discuss the case
of an arbitrary reductive group, and remaining obstructions for applying
Poisson summation.
| arxiv topic:math.NT math.RT |
arxiv_dataset-76251608.06038 | Charged Particle Monitor on the AstroSat mission
astro-ph.IM physics.ins-det
Charged Particle Monitor (CPM) on-board the AstroSat satellite is an
instrument designed to detect the flux of charged particles at the satellite
location. A Cesium Iodide Thallium (CsI(Tl)) crystal is used with a Kapton
window to detect protons with energies greater than 1 MeV. The ground
calibration of CPM was done using gamma-rays from radioactive sources and
protons from particle accelerators. Based on the ground calibration results,
energy deposition above 1 MeV are accepted and particle counts are recorded. It
is found that CPM counts are steady and the signal for the onset and exit of
South Atlantic Anomaly (SAA) region are generated in a very reliable and stable
manner.
| arxiv topic:astro-ph.IM physics.ins-det |
arxiv_dataset-76261608.06138 | Stochastic resonance in a sinusoidal potential system: An analog
simulation experiment
nlin.CD cond-mat.stat-mech
Recently, stochastic resonance was obtained numerically in an underdamped
periodic potential system driven by a periodic force and a Gaussian white
noise. In that numerical work, the occurrence of stochastic resonance was
explained in terms of the existence of two dynamical states having different
amplitude and phase lag. At zero temperature these two initial condition
dependent dynamical states are stable. However, at elevated temperatures, these
two states make transitions from one to the other at a mean rate. In the
present work, we setup an analog simulation experiment to show the existence of
the two dynamical states in a sinusoidal potential system as well as to verify
the occurrence of stochastic resonance in the same system. The experimental
procedure includes setting the initial conditions for the experiment.
| arxiv topic:nlin.CD cond-mat.stat-mech |
arxiv_dataset-76271608.06238 | Single-shot Adaptive Measurement for Quantum-enhanced Metrology
quant-ph stat.ML
Quantum-enhanced metrology aims to estimate an unknown parameter such that
the precision scales better than the shot-noise bound. Single-shot adaptive
quantum-enhanced metrology (AQEM) is a promising approach that uses feedback to
tweak the quantum process according to previous measurement outcomes.
Techniques and formalism for the adaptive case are quite different from the
usual non-adaptive quantum metrology approach due to the causal relationship
between measurements and outcomes. We construct a formal framework for AQEM by
modeling the procedure as a decision-making process, and we derive the
imprecision and the Cram\'{e}r-Rao lower bound with explicit dependence on the
feedback policy. We also explain the reinforcement learning approach for
generating quantum control policies, which is adopted due to the optimal policy
being non-trivial to devise. Applying a learning algorithm based on
differential evolution enables us to attain imprecision for adaptive
interferometric phase estimation, which turns out to be SQL when non-entangled
particles are used in the scheme.
| arxiv topic:quant-ph stat.ML |
arxiv_dataset-76281608.06338 | Large-scale Continuous Gesture Recognition Using Convolutional Neural
Networks
cs.CV
This paper addresses the problem of continuous gesture recognition from
sequences of depth maps using convolutional neutral networks (ConvNets). The
proposed method first segments individual gestures from a depth sequence based
on quantity of movement (QOM). For each segmented gesture, an Improved Depth
Motion Map (IDMM), which converts the depth sequence into one image, is
constructed and fed to a ConvNet for recognition. The IDMM effectively encodes
both spatial and temporal information and allows the fine-tuning with existing
ConvNet models for classification without introducing millions of parameters to
learn. The proposed method is evaluated on the Large-scale Continuous Gesture
Recognition of the ChaLearn Looking at People (LAP) challenge 2016. It achieved
the performance of 0.2655 (Mean Jaccard Index) and ranked $3^{rd}$ place in
this challenge.
| arxiv topic:cs.CV |
arxiv_dataset-76291608.06438 | Hopf hypersurfaces in spaces of oriented geodesics
math.DG
A Hopf hypersurface in a (para-)Kaehler manifold is a real hypersurface for
which one of the principal directions of the second fundamental form is the
(para-)complex dual of the normal vector.
We consider particular Hopf hypersurfaces in the space of oriented geodesics
of a non-flat space form of dimension greater than 2. For spherical and
hyperbolic space forms, the oriented geodesic space admits a canonical
Kaehler-Einstein and para-Kaehler-Einstein structure, respectively, so that a
natural notion of a Hopf hypersurface exists.
The particular hypersurfaces considered are formed by the oriented geodesics
that are tangent to a given convex hypersurface in the underlying space form.
We prove that a tangent hypersurface is Hopf in the space of oriented geodesics
with respect to this canonical (para-)Kaehler structure iff the underlying
convex hypersurface is totally umbilic and non-flat.
In the case of 3 dimensional space forms, however, there exists a second
canonical complex structure which can also be used to define Hopf
hypersurfaces. We prove that in this dimension, the tangent hypersurface of a
convex hypersurface in the space form is always Hopf with respect to this
second complex structure.
| arxiv topic:math.DG |
arxiv_dataset-76301608.06538 | Dressed photon-orbital states in a quantum dot: Inter-valley spin
resonance
cond-mat.mes-hall
The valley degree of freedom is intrinsic to spin qubits in Si/SiGe quantum
dots. It has been viewed alternately as a hazard, especially when the lowest
valley-orbit splitting is small compared to the thermal energy, or as an asset,
most prominently in proposals to use the valley degree of freedom itself as a
qubit. Here we present experiments in which microwave electric field driving
induces transitions between both valley-orbit and spin states. We show that
this system is highly nonlinear and can be understood through the use of
dressed photon-orbital states, enabling a unified understanding of the six
microwave resonance lines we observe. Some of these resonances are inter-valley
spin transitions that arise from a non-adiabatic process in which both the
valley and the spin degree of freedom are excited simultaneously. For these
transitions, involving a change in valley-orbit state, we find a tenfold
increase in sensitivity to electric fields and electrical noise compared to
pure spin transitions, strongly reducing the phase coherence when changes in
valley-orbit index are incurred. In contrast to this non-adiabatic transition,
the pure spin transitions, whether arising from harmonic or subharmonic
generation, are shown to be adiabatic in the orbital sector. The non-linearity
of the system is most strikingly manifest in the observation of a dynamical
anti-crossing between a spin-flip, inter-valley transition and a three-photon
transition enabled by the strong nonlinearity we find in this seemly simple
system.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-76311608.06638 | RG Flows and Bifurcations
hep-th cond-mat.str-el hep-ph math.DS
Interpreting RG flows as dynamical systems in the space of couplings we
produce a variety of constraints, global (topological) as well as local. These
constraints, in turn, rule out some of the proposed RG flows and also predict
new phases and fixed points, surprisingly, even in familiar theories such as
O(N) model, QED-3, or QCD-4.
| arxiv topic:hep-th cond-mat.str-el hep-ph math.DS |
arxiv_dataset-76321608.06738 | The Cramer-Wold theorem on quadratic surfaces and Heisenberg uniqueness
pairs
math.CA math.AP math.CV math.FA math.PR
Two measurable sets $S, \Lambda \subseteq \mathcal{R}^d$ form a Heisenberg
uniqueness pair, if every bounded measure $\mu$ with support in S whose Fourier
transform vanishes on {\Lambda} must be zero. We show that a quadratic
hypersurface and the union of two hyperplanes in general position form a
Heisenberg uniqueness pair in $\mathcal{R}^d$. As a corollary we obtain a new,
surprising version of the classical Cram\'er-Wold theorem: a bounded measure
supported on a quadratic hypersurface is uniquely determined by its projections
onto two generic hyperplanes (whereas an arbitrary measure requires the
knowledge of a dense set of projections). We also give an application to the
unique continuation of eigenfunctions of second-order PDEs with constant
coefficients .
| arxiv topic:math.CA math.AP math.CV math.FA math.PR |
arxiv_dataset-76331608.06838 | Global well-posedness of the derivative nonlinear Schr\"odinger equation
with periodic boundary condition in $H^{\frac12}$
math.AP
We establish the global well-posedness of the derivative nonlinear
Schr\"odinger equation with periodic boundary condition in the Sobolev space
$H^{\frac12}$, provided that the mass of initial data is less than $4\pi$. This
result matches the one by Miao, Wu, and Xu and its recent mass threshold
improvement by Guo and Wu in the non-periodic setting. Below $H^{\frac12}$, we
show that the uniform continuity of the solution map on bounded subsets of
$H^s$ does not hold, for any gauge equivalent equation.
| arxiv topic:math.AP |
arxiv_dataset-76341608.06938 | The impact of baryonic physics on the subhalo mass function and
implications for gravitational lensing
astro-ph.GA astro-ph.CO
We investigate the impact of baryonic physics on the subhalo population by
analyzing the results of two recent hydrodynamical simulations (EAGLE and
Illustris), which have very similar configuration, but a different model of
baryonic physics. We concentrate on haloes with a mass between $10^{12.5}$ and
$10^{14}M_{\odot}h^{-1}$ and redshift between 0.2 and 0.5, comparing with
observational results and subhalo detections in early-type galaxy lenses. We
compare the number and the spatial distribution of subhaloes in the fully hydro
runs and in their dark matter only counterparts, focusing on the differences
between the two simulations. We find that the presence of baryons reduces the
number of subhaloes, especially at the low mass end ($\leq
10^{10}M_{\odot}h^{-1}$), by different amounts depending on the model. The
variations in the subhalo mass function are strongly dependent on those in the
halo mass function, which is shifted by the effect of stellar and AGN feedback.
Finally, we search for analogues of the observed lenses (SLACS) in the
simulations, selecting them in velocity dispersion and dynamical properties. We
use the selected galaxies to quantify detection expectations based on the
subhalo populations in the different simulations, calculating the detection
probability and the predicted values for the projected dark matter fraction in
subhaloes $f_{DM}$ and the slope of the mass function $\alpha$. We compare
these values with those derived from subhalo detections in observations and
conclude that the dark-matter-only and hydro EAGLE runs are both compatible
with observational results, while results from the hydro Illustris run do not
lie within the errors.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-76351608.07038 | The (minimum) rank of typical fooling set matrices
cs.DM
A fooling-set matrix has nonzero diagonal, but at least one in every pair of
diagonally opposite entries is 0. Dietzfelbinger et al. '96 proved that the
rank of such a matrix is at least $\sqrt n$. It is known that the bound is
tight (up to a multiplicative constant).
We ask for the "typical" minimum rank of a fooling-set matrix: For a
fooling-set zero-nonzero pattern chosen at random, is the minimum rank of a
matrix with that zero-nonzero pattern over a field $\mathbb F$ closer to its
lower bound $\sqrt{n}$ or to its upper bound $n$? We study random patterns with
a given density $p$, and prove an $\Omega(n)$ bound for the cases when: (a) $p$
tends to $0$ quickly enough, (b) $p$ tends to $0$ slowly, and $|\mathbb
F|=O(1)$, (c) $p\in(0,1]$ is a constant.
We have to leave open the case when $p\to 0$ slowly and $\mathbb F$ is a
large or infinite field (e.g., $\mathbb F=GF(2^n)$, $F=\mathbb{R}$).
| arxiv topic:cs.DM |
arxiv_dataset-76361608.07138 | Sympathy for the Details: Dense Trajectories and Hybrid Classification
Architectures for Action Recognition
cs.CV
Action recognition in videos is a challenging task due to the complexity of
the spatio-temporal patterns to model and the difficulty to acquire and learn
on large quantities of video data. Deep learning, although a breakthrough for
image classification and showing promise for videos, has still not clearly
superseded action recognition methods using hand-crafted features, even when
training on massive datasets. In this paper, we introduce hybrid video
classification architectures based on carefully designed unsupervised
representations of hand-crafted spatio-temporal features classified by
supervised deep networks. As we show in our experiments on five popular
benchmarks for action recognition, our hybrid model combines the best of both
worlds: it is data efficient (trained on 150 to 10000 short clips) and yet
improves significantly on the state of the art, including recent deep models
trained on millions of manually labelled images and videos.
| arxiv topic:cs.CV |
arxiv_dataset-76371608.07238 | Homotopy of Planar Lie Group Equivariant Presheaves
math.AT math.CT
We utilise the theory of crossed simplicial groups to introduce a collection
of local Quillen model structures on the category of simplicial presheaves with
a compact planar Lie group action on a small Grothendieck site. As an
application, we give a characterisation of equivariant cohomology theories on a
site as derived mapping spaces in these model categories.
| arxiv topic:math.AT math.CT |
arxiv_dataset-76381608.07338 | Fast Trajectory Simplification Algorithm for Natural User Interfaces in
Robot Programming by Demonstration
cs.CV
Trajectory simplification is a problem encountered in areas like Robot
programming by demonstration, CAD/CAM, computer vision, and in GPS-based
applications like traffic analysis. This problem entails reduction of the
points in a given trajectory while keeping the relevant points which preserve
important information. The benefits include storage reduction, computational
expense, while making data more manageable. Common techniques formulate a
minimization problem to be solved, where the solution is found iteratively
under some error metric, which causes the algorithms to work in super-linear
time. We present an algorithm called FastSTray, which selects the relevant
points in the trajectory in linear time by following an open loop heuristic
approach. While most current trajectory simplification algorithms are tailored
for GPS trajectories, our approach focuses on smooth trajectories for robot
programming by demonstration recorded using motion capture systems.Two
variations of the algorithm are presented: 1. aims to preserve shape and
temporal information; 2. preserves only shape information. Using the points in
the simplified trajectory we use cubic splines to interpolate between these
points and recreate the original trajectory. The presented algorithm was tested
on trajectories recorded from a hand-tracking system. It was able to eliminate
about 90% of the points in the original trajectories while maintaining errors
between 0.78-2cm which corresponds to 1%-2.4% relative error with respect to
the bounding box of the trajectories.
| arxiv topic:cs.CV |
arxiv_dataset-76391608.07438 | Location and Weyl formula for the eigenvalues of some non self-adjoint
operators
math.SP math-ph math.MP
We present a survey of some recent results concerning the location and the
Weyl formula for the complex eigenvalues of two non self-adjoint operators. We
study the eigenvalues of the generator $G$ of the contraction semigroup
$e^{tG}, \: t \geq 0,$ related to the wave equation in an unbounded domain
$\Omega$ with dissipative boundary conditions on $\partial \Omega$. Also one
examines the interior transmission eigenvalues (ITE) in a bounded domain $K$
obtaining a Weyl formula with remainder for the counting function $N(r)$ of
complex (ITE). The analysis is based on a semi-classical approach.
| arxiv topic:math.SP math-ph math.MP |
arxiv_dataset-76401608.07538 | Higgs Physics at the CLIC Electron-Positron Linear Collider
hep-ex hep-ph
The Compact Linear Collider (CLIC) is an option for a future e+e- collider
operating at centre-of-mass energies up to 3 TeV, providing sensitivity to a
wide range of new physics phenomena and precision physics measurements at the
energy frontier. This paper is the first comprehensive presentation of the
Higgs physics reach of CLIC operating at three energy stages: sqrt(s) = 350
GeV, 1.4 TeV and 3 TeV. The initial stage of operation allows the study of
Higgs boson production in Higgsstrahlung (e+e- -> ZH) and WW-fusion (e+e- ->
Hnunu), resulting in precise measurements of the production cross sections, the
Higgs total decay width Gamma_H, and model-independent determinations of the
Higgs couplings. Operation at sqrt(s) > 1 TeV provides high-statistics samples
of Higgs bosons produced through WW-fusion, enabling tight constraints on the
Higgs boson couplings. Studies of the rarer processes e+e- -> ttH and e+e- ->
HHnunu allow measurements of the top Yukawa coupling and the Higgs boson
self-coupling. This paper presents detailed studies of the precision achievable
with Higgs measurements at CLIC and describes the interpretation of these
measurements in a global fit.
| arxiv topic:hep-ex hep-ph |
arxiv_dataset-76411608.07638 | Reconstructing parton densities at large fractional momenta
hep-ph hep-ex nucl-ex nucl-th
Parton distribution functions (PDFs) are nonperturbative objects defined by
nonlocal light-cone correlations. They cannot be computed directly from Quantum
Chromodynamics (QCD). Using a standard lattice QCD approach, it is possible to
compute moments of PDFs, which are matrix elements of local operators.
Recently, an alternative approach has been proposed, based on the introduction
of quasi-parton distribution functions (quasi-PDFs), which are matrix elements
of equal-time spatial correlations and hence calculable on lattice. Quasi-PDFs
approach standard PDFs in the limit of very large longitudinal proton momenta
$P^z$. This limit is not attainable in lattice simulations, and quasi-PDFs fail
to reproduce PDFs at high fractional longitudinal momenta. In this paper, we
propose a method to improve the reconstruction of PDFs by combining information
from quasi-PDFs and from the Mellin moments of regular PDFs. We test our method
using the diquark spectator model for up and down valence distributions of both
unpolarized and helicity PDFs. In the future, the method can be used to produce
PDFs entirely based on lattice QCD results.
| arxiv topic:hep-ph hep-ex nucl-ex nucl-th |
arxiv_dataset-76421608.07738 | Testing APSyn against Vector Cosine on Similarity Estimation
cs.CL
In Distributional Semantic Models (DSMs), Vector Cosine is widely used to
estimate similarity between word vectors, although this measure was noticed to
suffer from several shortcomings. The recent literature has proposed other
methods which attempt to mitigate such biases. In this paper, we intend to
investigate APSyn, a measure that computes the extent of the intersection
between the most associated contexts of two target words, weighting it by
context relevance. We evaluated this metric in a similarity estimation task on
several popular test sets, and our results show that APSyn is in fact highly
competitive, even with respect to the results reported in the literature for
word embeddings. On top of it, APSyn addresses some of the weaknesses of Vector
Cosine, performing well also on genuine similarity estimation.
| arxiv topic:cs.CL |
arxiv_dataset-76431608.07838 | Can one see the shape of a network?
math.CO cs.DM
Traditionally, network analysis is based on local properties of vertices,
like their degree or clustering, and their statistical behavior across the
network in question. This paper develops an approach which is different in two
respects. We investigate edge-based properties, and we define global
characteristics of networks directly. The latter will provide our affirmative
answer to the question raised in the title. More concretely, we start with
Forman's notion of the Ricci curvature of a graph, or more generally, a
polyhedral complex. This will allow us to pass from a graph as representing a
network to a polyhedral complex for instance by filling in triangles into
connected triples of edges and to investigate the resulting effect on the
curvature. This is insightful for two reasons: First, we can define a curvature
flow in order to asymptotically simplify a network and reduce it to its
essentials. Second, using a construction of Bloch, which yields a discrete
Gauss-Bonnet theorem, we have the Euler characteristic of a network as a global
characteristic. These two aspects beautifully merge in the sense that the
asymptotic properties of the curvature flow are indicated by that Euler
characteristic.
| arxiv topic:math.CO cs.DM |
arxiv_dataset-76441608.07938 | Interacting Dynamics
math.DS math.CT math.GN
The "theory of open sub-functorial dynamics" is a new theory that defines
interacting generalized dynamical systems. The interactions between these
dynamics produce new dynamics which, of course, can then enter into other
interactions. A major part of this article can already be found in two
unpublished texts and it has been partially exposed in conferences. However, we
need to give a new, unified and therefore more convenient presentation of this
material, and we also need some examples to illustrate it. Moreover, we
introduce in this article the new concepts of "normal interaction" and
"concrete interaction", and replace the previously used rigid synchronizations
by much more general flexible ones.
| arxiv topic:math.DS math.CT math.GN |
arxiv_dataset-76451608.08038 | Numerical integration of dynamical systems with Lie series: Relativistic
acceleration and non-gravitational forces
astro-ph.EP
The integration of the equations of motion in gravitational dynamical systems
-- either in our Solar System or for extra-solar planetary system -- being non
integrable in the global case, is usually performed by means of numerical
integration. Among the different numerical techniques available for solving
ordinary differential equations, the numerical integration using Lie series has
shown some advantages. In its original form (Hanslmeier 1984), it was limited
to the N-body problem where only gravitational interactions are taken into
account. We present in this paper a generalisation of the method by deriving an
expression of the Lie-terms when other major forces are considered. As a matter
of fact, previous studies had been made but only for objects moving under
gravitational attraction. If other perturbations are added, the Lie integrator
has to be re-built. In the present work we consider two cases involving
position and position-velocity dependent perturbations: relativistic
acceleration in the framework of General Relativity and a simplified force for
the Yarkovsky effect. A general iteration procedure is applied to derive the
Lie series to any order and precision. We then give an application to the
integration of the equation of motions for typical Near-Earth objects and
planet Mercury.
| arxiv topic:astro-ph.EP |
arxiv_dataset-76461608.08138 | Dust polarization and ISM turbulence
astro-ph.CO astro-ph.GA
Perhaps the most intriguing result of Planck's dust-polarization measurements
is the observation that the power in the E-mode polarization is twice that in
the B mode, as opposed to pre-Planck expectations of roughly equal dust powers
in E and B modes. Here we show how the E- and B-mode powers depend on the
detailed properties of the fluctuations in the magnetized interstellar medium.
These fluctuations are classified into the slow, fast, and Alfv\'en
magnetohydrodynamic (MHD) waves, which are determined once the ratio of gas to
magnetic-field pressures is specified. We also parametrize models in terms of
the power amplitudes and power anisotropies for the three types of waves. We
find that the observed EE/BB ratio (and its scale invariance) and positive TE
correlation cannot be easily explained in terms of favored models for MHD
turbulence. The observed power-law index for temperature/polarization
fluctuations also disfavors MHD turbulence. We thus speculate that the 0.1--30
pc length scales probed by these dust-polarization measurements are not
described by MHD turbulence but, rather, probe the large-scale physics that
drives ISM turbulence. We develop a simple phenomenological model, based on
random displacements of the magnetized fluid, that produces EE/BB $\simeq2$ and
a positive TE cross-correlation. According to this model, the EE/BB and TE
signals are due to longitudinal, rather than transverse, modes in the
random-displacement field, providing, perhaps, some clue to the mechanism that
stirs the ISM. Future investigations involving the spatial dependence of the
EE/BB ratio, TE correlation, and local departures from statistical isotropy in
dust-polarization maps, as well as further tests of some of the assumptions in
this analysis, are outlined. This work may also aid in the improvement of
foreground-separation techniques for studies of CMB polarization.
| arxiv topic:astro-ph.CO astro-ph.GA |
arxiv_dataset-76471608.08238 | A discrete chemo-dynamical model of the giant elliptical galaxy NGC
5846: dark matter fraction, internal rotation and velocity anisotropy out to
six effective radii
astro-ph.GA
We construct a suite of discrete chemo-dynamical models of the giant
elliptical galaxy NGC 5846. These models are a powerful tool to constrain both
the mass distribution and internal dynamics of multiple tracer populations. We
use Jeans models to simultaneously fit stellar kinematics within the effective
radius $R_{\rm e}$, planetary nebula (PN) radial velocities out to $3\, R_{\rm
e}$, and globular cluster (GC) radial velocities and colours out to $6\,R_{\rm
e}$. The best-fitting model is a cored DM halo which contributes $\sim 10\%$ of
the total mass within $1\,R_{\rm e}$, and $67\% \pm 10\%$ within $6\,R_{\rm
e}$, although a cusped DM halo is also acceptable. The red GCs exhibit mild
rotation with $v_{\rm max}/\sigma_0 \sim 0.3$ in the region $R > \,R_{\rm e}$,
aligned with but counter-rotating to the stars in the inner parts, while the
blue GCs and PNe kinematics are consistent with no rotation. The red GCs are
tangentially anisotropic, the blue GCs are mildly radially anisotropic, and the
PNe vary from radially to tangentially anisotropic from the inner to the outer
region. This is confirmed by general made-to-measure models. The tangential
anisotropy of the red GCs in the inner regions could stem from the preferential
destruction of red GCs on more radial orbits, while their outer tangential
anisotropy -- similar to the PNe in this region -- has no good explanation. The
mild radial anisotropy of the blue GCs is consistent with an accretion
scenario.
| arxiv topic:astro-ph.GA |
arxiv_dataset-76481608.08338 | Doping-Induced Alterations in Electronic Structure of Copper Oxide
Superconductors and a New Horizon for Higher Tc materials
cond-mat.supr-con
By paying special attention to the fact that the doped holes induce
deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors,
we develop a non-rigid band theory treating doping-induced alterations of
energy-band structures in copper oxide superconductors. Thanks to this theory,
we obtain a complete picture of the doping-induced alteration in the electronic
structure of La2CuO4, from the spin-disordered insulating phase to the metallic
phase. We conclude that the Fermi surface structure of this cuprate in the
underdoped region consists of Fermi pockets in the antinodal region and Fermi
arcs in the nodal region, and thus that the origin of a so-called pseudogap is
closely related to the existence of Fermi pockets. Moreover, we show that the
carriers on the Fermi pockets contribute to the phonon mechanism in d-wave
superconductivity. Finally, we discuss how one will be able to find higher Tc
materials, based on the conclusions mentioned above.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-76491608.08438 | Revisiting virtual difference ideals
math.LO
The main idea of [4] was that structures built from periodic prime ideals
have better properties from the usual ones built from invariant ideals; but
unable to work with periodic ideals alone, we had to generalise further to a
somewhat ephemeral setting called virtual ideals. This text has two purposes.
It corrects an error in [4] discovered by Tom Scanlon's UCB seminar, recovering
all results for all virtual ideals. In addition, based on results in [3], we
describe a wide family of difference equations where virtual ideals reduce to
periodic ideals.
| arxiv topic:math.LO |
arxiv_dataset-76501608.08538 | Low Ply Drawings of Trees
cs.DS
We consider the recently introduced model of \emph{low ply graph drawing}, in
which the ply-disks of the vertices do not have many common overlaps, which
results in a good distribution of the vertices in the plane. The
\emph{ply-disk} of a vertex in a straight-line drawing is the disk centered at
it whose radius is half the length of its longest incident edge. The largest
number of ply-disks having a common overlap is called the \emph{ply-number} of
the drawing.
We focus on trees. We first consider drawings of trees with constant
ply-number, proving that they may require exponential area, even for stars, and
that they may not even exist for bounded-degree trees. Then, we turn our
attention to drawings with logarithmic ply-number and show that trees with
maximum degree $6$ always admit such drawings in polynomial area.
| arxiv topic:cs.DS |
arxiv_dataset-76511608.08638 | A detection of the integrated Sachs-Wolfe imprint of cosmic
superstructures using a matched-filter approach
astro-ph.CO
We present a new method for detection of the integrated Sachs-Wolfe (ISW)
imprints of cosmic superstructures on the cosmic microwave background, based on
a matched filtering approach. The expected signal-to-noise ratio for this
method is comparable to that obtained from the full cross-correlation, and
unlike other stacked filtering techniques it is not subject to an a posteriori
bias. We apply this method to Planck CMB data using voids and superclusters
identified in the CMASS galaxy data from the Sloan Digital Sky Survey Data
Release 12, and measure the ISW amplitude to be $A_\mathrm{ISW}=1.64\pm0.53$
relative to the $\Lambda$CDM expectation, corresponding to a $3.1\sigma$
detection. In contrast to some previous measurements of the ISW effect of
superstructures, our result is in agreement with the $\Lambda$CDM model.
| arxiv topic:astro-ph.CO |
arxiv_dataset-76521608.08738 | A Dictionary-based Approach to Racism Detection in Dutch Social Media
cs.CL
We present a dictionary-based approach to racism detection in Dutch social
media comments, which were retrieved from two public Belgian social media sites
likely to attract racist reactions. These comments were labeled as racist or
non-racist by multiple annotators. For our approach, three discourse
dictionaries were created: first, we created a dictionary by retrieving
possibly racist and more neutral terms from the training data, and then
augmenting these with more general words to remove some bias. A second
dictionary was created through automatic expansion using a \texttt{word2vec}
model trained on a large corpus of general Dutch text. Finally, a third
dictionary was created by manually filtering out incorrect expansions. We
trained multiple Support Vector Machines, using the distribution of words over
the different categories in the dictionaries as features. The best-performing
model used the manually cleaned dictionary and obtained an F-score of 0.46 for
the racist class on a test set consisting of unseen Dutch comments, retrieved
from the same sites used for the training set. The automated expansion of the
dictionary only slightly boosted the model's performance, and this increase in
performance was not statistically significant. The fact that the coverage of
the expanded dictionaries did increase indicates that the words that were
automatically added did occur in the corpus, but were not able to meaningfully
impact performance. The dictionaries, code, and the procedure for requesting
the corpus are available at: https://github.com/clips/hades
| arxiv topic:cs.CL |
arxiv_dataset-76531608.08838 | Gravitational relaxation of electroweak hierarchy problem
hep-ph gr-qc hep-th
In the present paper, we discuss gravitational relaxation models for the
electroweak hierarchy problem. We show that modified gravity can naturally
relax the electroweak hierarchy problem where conformal transformation provides
a crucial rule about what modified gravity theories are favored to relax the
electroweak hierarchy. The conformal transformation connects different
gravitational theories and rescaling the metric changes the dimensional
parameters like the Higgs mass or the cosmological constant in different frames
drastically. When the electroweak scale is naturally realized by dynamical and
running behavior of dilatonic scalar field or scaling parameter, the modified
gravity theories can relax the electroweak hierarchy problem. We discuss the
theoretical and phenomenological validity of the gravitational relaxation
models.
| arxiv topic:hep-ph gr-qc hep-th |
arxiv_dataset-76541608.08938 | Measuring out-of-time-order correlations and multiple quantum spectra in
a trapped ion quantum magnet
quant-ph cond-mat.quant-gas
Controllable arrays of ions and ultra-cold atoms can simulate complex
many-body phenomena and may provide insights into unsolved problems in modern
science. To this end, experimentally feasible protocols for quantifying the
buildup of quantum correlations and coherence are needed, as performing full
state tomography does not scale favorably with the number of particles. Here we
develop and experimentally demonstrate such a protocol, which uses time
reversal of the many-body dynamics to measure out-of-time-order correlation
functions (OTOCs) in a long-range Ising spin quantum simulator with more than
100 ions in a Penning trap. By measuring a family of OTOCs as a function of a
tunable parameter we obtain fine-grained information about the state of the
system encoded in the multiple quantum coherence spectrum, extract the quantum
state purity, and demonstrate the buildup of up to 8-body correlations. Future
applications of this protocol could enable studies of many-body localization,
quantum phase transitions, and tests of the holographic duality between quantum
and gravitational systems.
| arxiv topic:quant-ph cond-mat.quant-gas |
arxiv_dataset-76551609.00022 | Supernova Progenitors, Their Variability, and the Type IIP Supernova
ASASSN-16fq in M66
astro-ph.SR astro-ph.GA astro-ph.HE
We identify a pre-explosion counterpart to the nearby Type IIP supernova
ASASSN-16fq (SN 2016cok) in archival Hubble Space Telescope (HST) data. The
source appears to be a blend of several stars that prevents obtaining accurate
photometry. However, with reasonable assumptions about the stellar temperature
and extinction, the progenitor almost certainly had an initial mass M<17Msun,
and was most likely in the mass range 8-12Msun. Observations once ASASSN-16fq
has faded will have no difficulty accurately determining the properties of the
progenitor. In 8 years of Large Binocular Telescope (LBT) data, no significant
progenitor variability is detected to RMS limits of roughly 0.03 mag. Of the
six nearby SN with constraints on low level variability, SN 1987A, SN 1993J, SN
2008cn, SN 2011dh, SN 2013ej and ASASSN-16fq, only the slowly fading progenitor
of SN 2011dh showed clear evidence of variability. Excluding SN 1987A, the 90%
confidence limit implied by these sources on the number of outbursts over the
last decade before the SN that last longer than 0.1 years (FWHM) and are
brighter than M_R<-8 mag is approximately N<3. Our continuing LBT monitoring
program will steadily improve constraints on pre-SN progenitor variability at
amplitudes far lower than achievable by SN surveys.
| arxiv topic:astro-ph.SR astro-ph.GA astro-ph.HE |
arxiv_dataset-76561609.00122 | Convergence rates and $W^{1,p}$ estimates in homogenization theory of
Stokes systems in Lipschitz domains
math.AP
Concerned with the Stokes systems with rapidly oscillating periodic
coefficients, we mainly extend the recent works in \cite{SGZWS,G} to those in
term of Lipschitz domains.
The arguments employed here are quite different from theirs, and the basic
idea comes from \cite{QX2}, originally motivated by \cite{SZW2,SZW12,TS}. We
obtain an almost-sharp $O(\varepsilon\ln(r_0/\varepsilon))$ convergence rate in
$L^2$ space, and a sharp $O(\varepsilon)$ error estimate in
$L^{\frac{2d}{d-1}}$ space by a little stronger assumption.
Under the dimensional condition $d=2$, we also establish the optimal
$O(\varepsilon)$ convergence rate on pressure terms in $L^2$ space. Then
utilizing the convergence rates we can derive the $W^{1,p}$ estimates uniformly
down to microscopic scale $\varepsilon$ without any smoothness assumption on
the coefficients, where $|\frac{1}{p}-\frac{1}{2}|<\frac{1}{2d}+\epsilon$ and
$\epsilon$ is a positive constant independent of $\varepsilon$. Combining the
local estimates, based upon $\text{VMO}$ coefficients, consequently leads to
the uniform $W^{1,p}$ estimates. Here the proofs do not rely on the well known
compactness methods.
| arxiv topic:math.AP |
arxiv_dataset-76571609.00222 | Ternary Neural Networks for Resource-Efficient AI Applications
cs.LG cs.AI cs.NE
The computation and storage requirements for Deep Neural Networks (DNNs) are
usually high. This issue limits their deployability on ubiquitous computing
devices such as smart phones, wearables and autonomous drones. In this paper,
we propose ternary neural networks (TNNs) in order to make deep learning more
resource-efficient. We train these TNNs using a teacher-student approach based
on a novel, layer-wise greedy methodology. Thanks to our two-stage training
procedure, the teacher network is still able to use state-of-the-art methods
such as dropout and batch normalization to increase accuracy and reduce
training time. Using only ternary weights and activations, the student ternary
network learns to mimic the behavior of its teacher network without using any
multiplication. Unlike its -1,1 binary counterparts, a ternary neural network
inherently prunes the smaller weights by setting them to zero during training.
This makes them sparser and thus more energy-efficient. We design a
purpose-built hardware architecture for TNNs and implement it on FPGA and ASIC.
We evaluate TNNs on several benchmark datasets and demonstrate up to 3.1x
better energy efficiency with respect to the state of the art while also
improving accuracy.
| arxiv topic:cs.LG cs.AI cs.NE |
arxiv_dataset-76581609.00322 | Open Call-by-Value (Extended Version)
cs.LO
The elegant theory of the call-by-value lambda-calculus relies on weak
evaluation and closed terms, that are natural hypotheses in the study of
programming languages. To model proof assistants, however, strong evaluation
and open terms are required, and it is well known that the operational
semantics of call-by-value becomes problematic in this case. Here we study the
intermediate setting -- that we call Open Call-by-Value -- of weak evaluation
with open terms, on top of which Gr\'egoire and Leroy designed the abstract
machine of Coq. Various calculi for Open Call-by-Value already exist, each one
with its pros and cons. This paper presents a detailed comparative study of the
operational semantics of four of them, coming from different areas such as the
study of abstract machines, denotational semantics, linear logic proof nets,
and sequent calculus. We show that these calculi are all equivalent from a
termination point of view, justifying the slogan Open Call-by-Value.
| arxiv topic:cs.LO |
arxiv_dataset-76591609.00422 | Nuclear relaxation rates in the Herbertsmithite Kagome antiferromagnets
ZnCu3(OH)6Cl2
cond-mat.str-el
Local spectral functions and Nuclear Magnetic Relaxation (NMR) rates, 1/T1,
for the spin-half Heisenberg antiferromagnet on the Kagome Lattice are
calculated using Moriyas Gaussian approximation, as well as through an
extrapolation of multiple frequency moments. The temperature dependence of the
calculated rates is compared with the oxygen 1/T1 NMR data in Herbertsmithite.
We find that the Gaussian approximation for 1/T1 shows behavior qualitatively
similar to experiments with a sharp drop in rates at low temperatures,
consistent with a spin-gapped behavior. However, this approximation
significantly underestimates the magnitude of 1/T1 even at room temperature.
Rates obtained from extrapolation of multiple frequency moments give very good
agreement with the room temperature NMR data with J = 195 +/- 20 K and
hyperfine couplings determined independently from other measurements. The use
of multiple frequency moments also leads to additional low frequency weight in
the local structure factors. The convergence of our calculations with higher
frequency moments breaks down at low temperatures suggesting the existence of
longer range dynamic correlations in the system despite the very short-range
static correlations.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-76601609.00522 | Espaces de configuration g\'en\'eralis\'es. Espaces topologiques
$i$-acycliques. Suites spectrales "basiques"
math.AT math.GR math.RT
The generalized (ordered) configuration spaces associated to a topological
space $X$ are the spaces $\Delta_{\leq\ell}X^{m}:=\{(x_1,\ldots,x_{m})\in
X^{m}\mid\#\{x_1,\ldots,x_{m}\}\leq \ell\}$ and
$\Delta_{\ell}X^{m}:=\Delta_{\leq\ell}X^{m}\setminus \Delta_{\leq\ell-1}$. They
are equipped with the action of the symmetric group $S_m$ permuting
coordinates. When $X$ has no interior cohomology (i.e. is $i$-acyclic) we are
able to compute explicitly the character formula of $S_m$ acting on the
cohomology of these spaces, and if $X$ is furthermore a connected and oriented
pseudomanifold of dimension $\geq2$ we generalize Church's representation
stability theorem to the case of the families $\{\Delta_{\leq m-a}X^m\}_m$ and
$\{\Delta_{\ell-a}X^m\}_m$. We show that, for fixed $a,i\in\mathbb N$, the
families of representations $\{ S_m: H ^{i}(\Delta_{?m-a}X^{m})\}_{m}$ are
monotone and stationary for $m\geq4i+4a$, if $d_{X}=2$, and for $m\geq2i+4a$,
if $d_{X}\geq3$. The corresponding families of characters and Betti numbers are
(hence) polynomial and the families of integers $\{\mathop{\rm
Betti}_{i}({\Delta_{?m-a}X^{m} / S_m})\}_{m}$ are constant within the same
range of integers $m$. We further show that the family $\{\mathop{\rm
Betti}_{i}({\Delta_{m}X^{m}/ S_m})\}_{m}$ is constant for $m\geq 2i$, if
$d_{X}=2$, and for $m\geq i$, if $d_{X}\geq3$. In particular, complex algebraic
varieties whether they are smooth on not verify these generalizations of
Church's stability theorems.
| arxiv topic:math.AT math.GR math.RT |
arxiv_dataset-76611609.00622 | Dissipative entanglement of solid-state spins in diamond
quant-ph cond-mat.mes-hall
Generating robust entanglement among solid-state spins is key for
applications in quantum information processing and precision sensing. We show
here a dissipative approach to generate such entanglement among the hyperfine
coupled electron nuclear spins using the rapid optical decay of electronic
excited states. The combined dark state interference effects of the optical and
microwave driving fields in the presence of spontaneous emission from the
short-lived excited state leads to a dissipative formation of an entangled
steady state. We show that the dissipative entanglement is generated for any
initial state conditions of the spins and is resilient to external field
fluctuations. We analyze the scheme both for continuous and pulsed driving
fields in the presence of realistic noise sources.
| arxiv topic:quant-ph cond-mat.mes-hall |
arxiv_dataset-76621609.00722 | Quantum walks and gravitational waves
quant-ph gr-qc
A new family of discrete-time quantum walks (DTQWs) propagating on a regular
$(1+2)$D spacetime lattice is introduced. The continuous limit of these DTQWs
is shown to coincide with the dynamics of a Dirac fermion interacting with an
arbitrary relativistic gravitational field. This family is used to model the
influence of arbitrary linear gravitational waves (GWs) on DTQWs. Pure shear
GWs are studied in detail. On large spatial scales, pure shear GWs do not
modify the polarizations of the fermion eigen-modes, but rescale all energies
by a common factor. On smaller scales typically comparable to two or three
lattice steps, both polarizations and energies are modified in a non-trivial
way. This effect is particularly salient on interference patterns between the
fermion eigen-modes.
| arxiv topic:quant-ph gr-qc |
arxiv_dataset-76631609.00822 | Classical and Quantum Logics with Multiple and a Common Lattice Models
quant-ph math-ph math.LO math.MP
We consider a proper propositional quantum logic and show that it has
multiple disjoint lattice models, only one of which is an orthomodular lattice
(algebra) underlying Hilbert (quantum) space. We give an equivalent proof for
the classical logic which turns out to have disjoint distributive and
non-distributive ortholattices as its models. In particular, we prove that both
classical and quantum logics are sound and complete with respect to each of
these lattices. We also show that there is one common non-orthomodular lattice
that is a model of both quantum and classical logics. In technical terms, that
enables us to run the same classical logic on both a digital (standard, two
subset, 0-1 bit) computer and on a non-digital (say, a six subset) computer
(with appropriate chips and circuits). With quantum logic, the same six element
common lattice can serve us as a benchmark for an efficient evaluation of
equations of bigger lattice models or theorems of the logic.
| arxiv topic:quant-ph math-ph math.LO math.MP |
arxiv_dataset-76641609.00922 | Renormalized solutions of semilinear elliptic equations with general
measure data
math.AP
In the paper, we first propose a definition of renormalized solution of
semilinear elliptic equation involving operator corresponding to a general
(possibly nonlocal) symmetric regular Dirichlet form satisfying the so-called
absolute continuity condition and general (possibly nonsmooth) measure data.
Then we analyze the relationship between our definition and other concepts of
solutions considered in the literature (probabilistic solutions, solution
defined via the resolvent kernel of the underlying Dirichlet form,
Stampacchia's definition by duality). We show that under mild integrability
assumption on the data all these concepts coincide.
| arxiv topic:math.AP |
arxiv_dataset-76651609.01022 | Local Kernel Dimension Reduction in Approximate Bayesian Computation
stat.CO
Approximate Bayesian Computation (ABC) is a popular sampling method in
applications involving intractable likelihood functions. Without evaluating the
likelihood function, ABC approximates the posterior distribution by the set of
accepted samples which are simulated with parameters drawn from the prior
distribution, where acceptance is determined by the distance between the
summary statistics of the sample and the observation. The sufficiency and
dimensionality of the summary statistics play a central role in the application
of ABC. This paper proposes Local Gradient Kernel Dimension Reduction (LGKDR)
to construct low dimensional summary statistics for ABC. The proposed method
identifies a sufficient subspace of the original summary statistics by
implicitly considers all nonlinear transforms therein, and a weighting kernel
is used for the concentration of the projections. No strong assumptions are
made on the marginal distributions nor the regression model, permitting usage
in a wide range of applications. Experiments are done with both simple
rejection ABC and sequential Monte Carlo ABC methods. Results are reported as
competitive in the former and substantially better in the latter cases in which
Monte Carlo errors are compressed as much as possible.
| arxiv topic:stat.CO |
arxiv_dataset-76661609.01122 | H-alpha features with hot onsets III. Fibrils in Lyman-alpha and with
ALMA
astro-ph.SR
In H-alpha most of the solar surface is covered by dense canopies of long
opaque fibrils, but predictions for quiet-Sun observations with ALMA have
ignored this fact. Comparison with Ly-alpha suggests that the large opacity of
H-alpha fibrils is caused by hot precursor events. Application of a recipe that
assumes momentary Saha-Boltzmann extinction during their hot onset to
millimeter wavelengths suggests that ALMA will observe H-alpha-like fibril
canopies, not acoustic shocks underneath, and will yield data more interesting
than if these canopies were transparent.
| arxiv topic:astro-ph.SR |
arxiv_dataset-76671609.01222 | Stability of the rotation set of area-preserving toral homeomorphisms
math.DS
We show that if the rotation set of a homeomorphism of the torus is stable
under small perturbations of the dynamics, then it is a convex polygon with
rational vertices. We also show that such homeomorphisms are $C^0$-generic and
have bounded rotational deviations (even for pseudo-orbits). The results hold
both in the area-preserving setting and in the general setting. When the
rotation set is stable, we give explicit estimates on the type of rationals
that may appear as vertices of rotation sets in terms of the stability
constants.
| arxiv topic:math.DS |
arxiv_dataset-76681609.01322 | Mobile Relays for Smart Cities: Mathematical Proofs
cs.IT math.IT
The increasing number of connected vehicles in densely populated urban areas
provides an interesting opportunity to counteract the high wireless data
demands in high density and highly mobile scenarios. The idea is to support the
macro base station (BS) with a secondary communication tier composed of a set
of smart and connected vehicles that are in movement in the urban area.
As a first step towards a comprehensive cost-benefit analysis of this
architecture, this paper considers the case where these vehicles are equipped
with femto-mobile Access Points (fmAPs) and constitute a mobile out-of-band
relay infrastructure. In particular, three techniques to select an fmAP (if
more than one is available) are proposed and the maximal feasible gain in the
packet delivery rate and data rate as a function of the vehicle density,
average vehicle speeds, handoff overhead cost, as well as physical layer
parameters is characterized. The analytical and simulation results provide a
first benchmark characterizing this architecture and the definition of
guidelines for its future realistic study and implementation.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-76691609.01422 | Discovery of a Perseus-like cloud in the early Universe: HI-to-H2
transition, carbon monoxide and small dust grains at zabs=2.53 towards the
quasar J0000+0048
astro-ph.GA astro-ph.CO
We present the discovery of a molecular cloud at zabs=2.5255 along the line
of sight to the quasar J0000+0048. We perform a detailed analysis of the
absorption lines from ionic, neutral atomic and molecular species in different
excitation levels, as well as the broad-band dust extinction. We find that the
absorber classifies as a Damped Lyman-alpha system (DLA) with
logN(HI)(cm^-2)=20.8+/-0.1. The DLA has super-Solar metallicity with a
depletion pattern typical of cold gas and an overall molecular fraction ~50%.
This is the highest f-value observed to date in a high-z intervening system.
Most of the molecular hydrogen arises from a clearly identified narrow (b~0.7
km/s), cold component in which CO molecules are also found, with logN(CO)~15.
We study the chemical and physical conditions in the cold gas. We find that the
line of sight probes the gas deep after the HI-to-H2 transition in a ~4-5
pc-size cloud with volumic density nH~80 cm^-3 and temperature of only 50 K.
Our model suggests that the presence of small dust grains (down to about 0.001
{\mu}m) and high cosmic ray ionisation rate (zeta_H a few times 10^-15 s^-1)
are needed to explain the observed atomic and molecular abundances. The
presence of small grains is also in agreement with the observed steep
extinction curve that also features a 2175 A bump. The properties of this cloud
are very similar to what is seen in diffuse molecular regions of the nearby
Perseus complex. The high excitation temperature of CO rotational levels
towards J0000+0048 betrays however the higher temperature of the cosmic
microwave background. Using the derived physical conditions, we correct for a
small contribution (0.3 K) of collisional excitation and obtain TCMB(z =
2.53)~9.6 K, in perfect agreement with the predicted adiabatic cooling of the
Universe. [abridged]
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-76701609.01522 | Made-to-measure galaxy modelling utilising absorption line strength data
astro-ph.GA
We enhance the Syer & Tremaine made-to-measure (M2M) particle method of
stellar dynamical modelling to model simultaneously both kinematic data and
absorption line strength data thus creating a `chemo-M2M' modelling scheme. We
apply the enhanced method to four galaxies (NGC 1248, NGC 3838, NGC 4452, NGC
4551) observed using the SAURON integral-field spectrograph as part of the
ATLAS3D programme. We are able to reproduce successfully the 2D line strength
data achieving mean chi^2 per bin values of ~1 with >95\% of particles having
converged weights. Because M2M uses a 3D particle system, we are also able to
examine the underlying 3D line strength distributions. The extent to which
these distributions are plausible representations of real galaxies requires
further consideration. Overall we consider the modelling exercise to be a
promising first step in developing a `chemo-M2M' modelling system and in
understanding some of the issues to be addressed. Whilst the made-to-measure
techniques developed have been applied to absorption line strength data, they
are in fact general and may be of value in modelling other aspects of galaxies.
| arxiv topic:astro-ph.GA |
arxiv_dataset-76711609.01622 | A Cross-layer Contention Based Synchronous MAC Protocol for Transmission
Delay Reduction in Multi-Hop WSNs
cs.NI
Recently designed cross-layer contention based synchronous MAC protocols like
the PRMAC protocol, for wireless sensor networks (WSNs) enable a node to
schedule multi-hop transmission of multiple data packets in a cycle. However,
these systems accommodate both the request-to-send data process and the
confirmation-to-send data process in the same data transmission scheduling
window (i.e. data window). This reduces the length of the multi-hop flow setup
in the data window. In a multi-hop scenario, this degrades both the packet
delivery ratio (PDR) and the end-to-end transmission delay (E2ETD). In this
paper, we propose a cross-layer contention based synchronous MAC protocol,
which accommodates the request-to-send data process in the data window and the
confirmation-to-send data process in the sleep window for increased efficiency.
We evaluate our proposed protocol through ns-2.35 simulations and compare its
performance with the PRMAC protocol. Results suggest that in multi-hop
scenario, proposed protocol outperforms PRMAC both in terms of the E2ETD and
the packet delivery ratio (PDR).
| arxiv topic:cs.NI |
arxiv_dataset-76721609.01722 | Applying Relativistic Reconnection to Blazar Jets
astro-ph.HE physics.plasm-ph
Rapid and luminous flares of non-thermal radiation observed in blazars
require an efficient mechanism of energy dissipation and particle acceleration
in relativistic active galactic nuclei (AGN) jets. Particle acceleration in
relativistic magnetic reconnection is being actively studied by kinetic
numerical simulations. Relativistic reconnection produces hard power-law
electron energy distributions N(gamma) = N_0 gamma^(-p) exp(-gamma/gamma_max)
with index p -> 1 and exponential cut-off Lorentz factor gamma_max ~ sigma in
the limit of magnetization sigma = B^2/(4 pi w) >> 1 (where w is the
relativistic enthalpy density). Reconnection in electron-proton plasma can
additionally boost gamma_max by the mass ratio m_p/m_e. Hence, in order to
accelerate particles to gamma_max ~ 10^6 in the case of BL Lacs, reconnection
should proceed in plasma of very high magnetization sigma_max >~ 10^3. On the
other hand, moderate mean jet magnetization values are required for magnetic
bulk acceleration of relativistic jets, sigma_mean ~ Gamma_j <~ 20 (where
Gamma_j is the jet bulk Lorentz factor). I propose that the systematic
dependence of gamma_max on blazar luminosity class -- the blazar sequence --
may result from a systematic trend in sigma_max due to homogeneous loading of
leptons by pair creation regulated by the energy density of high-energy
external radiation fields. At the same time, relativistic AGN jets should be
highly inhomogeneous due to filamentary loading of protons, which should
determine the value of sigma_mean roughly independently of the blazar class.
| arxiv topic:astro-ph.HE physics.plasm-ph |
arxiv_dataset-76731609.01822 | Multi-Tenancy Issues with Service Delivery in Developing Economies:
Privacy, Trust and Availability Concerns
cs.CY
Cloud computing is a new paradigm and innovation in the technology service
delivery. It is utilized for IT-enabled value creation. The capex-free nature
of cloud service delivery renders it very attractive to many SMEs. But it is
saddled with multi-tenancy issues; prominent under this study are concerns of
privacy, trust and availability. How do end-users trust providers with their
sensitive data? How secured and confidential are their corporate assets? Amidst
the perennial power outages (a.k.a. Dumsor), what is the acceptable available
uptime? We sampled and interviewed cloud service providers (CSPs) as well as
end-users in Ghana, a developing economy. We also gleaned through some
secondary data to ascertain some operational concerns. The results indicate
that security and service level agreements (SLAs) are key concerns in respect
of privacy and trust issues. Similarly, perennial power outages and security
were key availability concerns. This was expected as end-users use cloud
services for mission critical information assets, and so requires high
availability. The implications are that the cyber-security concerns ought to be
addressed if SMEs in developing economies are to adopt and accept cloud
computing resources for IT-enabled competitive advantage.
| arxiv topic:cs.CY |
arxiv_dataset-76741609.01922 | Topological Triplon Modes and Bound States in a Shastry-Sutherland
Magnet
cond-mat.str-el
The twin discoveries of the quantum Hall effect, in the 1980's, and of
topological band insulators, in the 2000's, were landmarks in physics that
enriched our view of the electronic properties of solids. In a nutshell, these
discoveries have taught us that quantum mechanical wavefunctions in crystalline
solids may carry nontrivial topological invariants which have ramifications for
the observable physics. One of the side effects of the recent topological
insulator revolution has been that such physics is much more widespread than
was appreciated ten years ago. For example, while topological insulators were
originally studied in the context of electron wavefunctions, recent work has
led to proposals of topological insulators in bosonic systems: in photonic
crystals, in the vibrational modes of crystals, and in the excitations of
ordered magnets. Here we confirm the recent proposal that, in a weak magnetic
field, the dimerized quantum magnet SrCu$_{2}$(BO$_{3}$)$_2$ is a bosonic
topological insulator with nonzero Chern number in the triplon bands and
topologically protected chiral edge excitations.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-76751609.02022 | Decouplings for three-dimensional surfaces in $\mathbb{R}^{6}$
math.CA
We obtain the sharp $l^p$ decoupling for three-dimensional nondegenerate
surfaces in $\mathbb{R}^6$. This can be thought of as a generalization of
Bourgain and Demeter's result, which is the sharp $l^p$ decoupling for
two-dimensional nondegenerate surfaces in $\mathbb{R}^4$.
| arxiv topic:math.CA |
arxiv_dataset-76761609.02122 | Entropy, topological transitivity, and dimensional properties of unique
$q$-expansions
math.DS math.NT
Let $M$ be a positive integer and $q \in(1,M+1].$ We consider expansions of
real numbers in base $q$ over the alphabet $\{0,\ldots, M\}$. In particular, we
study the set $\mathcal{U}_{q}$ of real numbers with a unique $q$-expansion,
and the set $\mathbf{U}_q$ of corresponding sequences.
It was shown in (Komornik et al, 2017 Adv. Math.) that the function $H$,
which associates to each $q\in(1, M+1]$ the topological entropy of
$\mathcal{U}_q$, is a Devil's staircase. In this paper we explicitly determine
the plateaus of $H$, and characterize the bifurcation set $\mathcal E$ of $q$'s
where the function $H$ is not locally constant. Moreover, we show that
$\mathcal E$ is a Cantor set of full Hausdorff dimension. We also investigate
the topological transitivity of a naturally occurring subshift $(\mathbf{V}_q,
\sigma),$ which has a close connection with open dynamical systems. Finally, we
prove that the Hausdorff dimension and box dimension of $\mathcal{U}_q$
coincide for all $q\in(1,M+1]$.
| arxiv topic:math.DS math.NT |
arxiv_dataset-76771609.02222 | Stellar nuclei and inner polar disks in lenticular galaxies
astro-ph.GA
I analyze statistics of the stellar population properties for stellar nuclei
and bulges of nearby lenticular galaxies in different environments by using
panoramic spectral data of the integral-field spectrograph SAURON retrieved
from the open archive of Isaac Newton Group. I estimate also the fraction of
nearby lenticular galaxies having inner polar gaseous disks by exploring the
volume-limited sample of early-type galaxies of the ATLAS-3D survey. By
inspecting the two-dimensional velocity fields of the stellar and gaseous
components with running tilted-ring technique, I have found 7 new cases of the
inner polar disks. Together with those, the frequency of inner polar disks in
nearby S0 galaxies reaches 10% that is much higher than the frequency of
large-scale polar rings. Interestingly, the properties of the nuclear stellar
populations in the inner polar ring hosts are statistically the same as those
in the whole S0 sample implying similar histories of multiple gas accretion
events from various directions.
| arxiv topic:astro-ph.GA |
arxiv_dataset-76781609.02322 | Classical and Quantum Mechanics with Lie Brackets and Pseudocanonical
Transformations
quant-ph
We emphasize the usefulness of the Lie brackets in the context of classical
and quantum mechanics. By way of examples we show that many dynamical systems,
especially the ones with (gauge) constraints, can equally be treated in their
time development with non-canonical variables and Hamiltonians. After a short
presentation of the Lie bracket algebra and treating some easier standard
problems with the Lie bracket techniques, we concentrate mainly on charged
particles with gauge constraint in a constant external magnetic field. Since
most of our quantum field theories are meanwhile considered effective, we have
purposely treated our final problems with $c$-number instead of field -operator
Lagrangians. The van Vleck determinant, which is exact for our problems, is
employed to calculate the $c$-number Feynman-Schwinger propagation function.
There is no need for operators or renormalization. In particular, the
non-relativistic propagator in $2+1$ dimensions and the more complicated one in
$3+1$ dimensions are presented in all their glorious detail. On the more
editorial side: we have dispensed with numerating the various problems. They
are not so much disjoint that they needed an extra title. Also, the article is
written in a self-consistent way, meaning one should be able to read it without
time-consuming research in textbooks and journals - with a few exceptions, in
particular Schwinger's paper [J. Schwinger, Phys. Rev. 82, 664 (1951)], which
is the most-cited paper in modern quantum-field-theory physics. Most of the
prerequisites for reading the present article can be found in extenso in [W.
Dittrich and M. Reuter, Classical and quantum dynamics (Springer, Berlin,
Germany, 2016)].
| arxiv topic:quant-ph |
arxiv_dataset-76791609.02422 | What can (partition) logic contribute to information theory?
cs.IT math.IT
Logical probability theory was developed as a quantitative measure based on
Boole's logic of subsets. But information theory was developed into a mature
theory by Claude Shannon with no such connection to logic. A recent development
in logic changes this situation. In category theory, the notion of a subset is
dual to the notion of a quotient set or partition, and recently the logic of
partitions has been developed in a parallel relationship to the Boolean logic
of subsets (subset logic is usually mis-specified as the special case of
propositional logic). What then is the quantitative measure based on partition
logic in the same sense that logical probability theory is based on subset
logic? It is a measure of information that is named "logical entropy" in view
of that logical basis. This paper develops the notion of logical entropy and
the basic notions of the resulting logical information theory. Then an
extensive comparison is made with the corresponding notions based on Shannon
entropy.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-76801609.02522 | On the correspondence between classical geometric phase of gyro-motion
and quantum Berry phase
physics.plasm-ph quant-ph
We show that the geometric phase of the gyro-motion of a classical charged
particle in a uniform time-dependent magnetic field described by Newton's
equation can be derived from a coherent Berry phase for the coherent states of
the Schroedinger equation or the Dirac equation. This correspondence is
established by constructing coherent states for a particle using the energy
eigenstates on the Landau levels and proving that the coherent states can
maintain their status of coherent states during the slow varying of the
magnetic field. It is discovered that orbital Berry phases of the eigenstates
interfere coherently to produce an observable effect (which we termed "coherent
Berry phase"), which is exactly the geometric phase of the classical
gyro-motion. This technique works for particles with and without spin. For
particles with spin, on each of the eigenstates that makes up the coherent
states, the Berry phase consists of two parts that can be identified as those
due to the orbital and the spin motion. It is the orbital Berry phases that
interfere coherently to produce a coherent Berry phase corresponding to the
classical geometric phase of the gyro-motion. The spin Berry phases of the
eigenstates, on the other hand, remain to be quantum phase factors for the
coherent states and have no classical counterpart.
| arxiv topic:physics.plasm-ph quant-ph |
arxiv_dataset-76811609.02622 | Identifying Community Structures in Dynamic Networks
cs.SI physics.soc-ph
Most real-world social networks are inherently dynamic, composed of
communities that are constantly changing in membership. To track these evolving
communities, we need dynamic community detection techniques. This article
evaluates the performance of a set of game theoretic approaches for identifying
communities in dynamic networks. Our method, D-GT (Dynamic Game Theoretic
community detection), models each network node as a rational agent who
periodically plays a community membership game with its neighbors. During game
play, nodes seek to maximize their local utility by joining or leaving the
communities of network neighbors. The community structure emerges after the
game reaches a Nash equilibrium. Compared to the benchmark community detection
methods, D-GT more accurately predicts the number of communities and finds
community assignments with a higher normalized mutual information, while
retaining a good modularity.
| arxiv topic:cs.SI physics.soc-ph |
arxiv_dataset-76821609.02722 | Energy localization enhanced ground-state cooling of mechanical
resonator from room temperature in optomechanics using a gain cavity
quant-ph
When a gain system is coupled to a loss system, the energy usually flows from
the gain system to the loss one. We here present a counterintuitive theory for
the ground-state cooling of the mechanical resonator in optomechanical system
via a gain cavity. The energy flows first from the mechanical resonator into
the loss cavity, then into the gain cavity, and finally localizes there. The
energy localization in the gain cavity dramatically enhances the cooling rate
of the mechanical resonator. Moreover, we show that unconventional optical
spring effect, e.g., giant frequency shift and optically induced damping of the
mechanical resonator, can be realized. Those feature a pre-cooling free
ground-state cooling, i.e., the mechanical resonator in thermal excitation at
room temperature can directly be cooled to its ground state. This cooling
approach has the potential application for fundamental tests of quantum physics
without complicated cryogenic setups.
| arxiv topic:quant-ph |
arxiv_dataset-76831609.02822 | The GALAH Survey: Observational Overview and Gaia DR1 companion
astro-ph.IM astro-ph.GA astro-ph.SR
The Galactic Archaeology with HERMES (GALAH) Survey is a massive
observational project to trace the Milky Way's history of star formation,
chemical enrichment, stellar migration and minor mergers. Using high-resolution
(R$\simeq$28,000) spectra taken with the High Efficiency and Resolution
Multi-Element Spectrograph (HERMES) instrument at the Anglo-Australian
Telescope (AAT), GALAH will determine stellar parameters and abundances of up
to 29 elements for up to one million stars. Selecting targets from a
colour-unbiased catalogue built from 2MASS, APASS and UCAC4 data, we expect to
observe dwarfs at 0.3 to 3 kpc and giants at 1 to 10 kpc. This enables a
thorough local chemical inventory of the Galactic thin and thick disks, and
also captures smaller samples of the bulge and halo. In this paper we present
the plan, process and progress as of early 2016 for GALAH survey observations.
In our first two years of survey observing we have accumulated the largest
high-quality spectroscopic data set at this resolution, over 200,000 stars. We
also present the first public GALAH data catalogue: stellar parameters (Teff,
log(g), [Fe/H], [alpha/Fe]), radial velocity, distance modulus and reddening
for 10680 observations of 9860 Tycho-2 stars that may be included in the first
Gaia data release.
| arxiv topic:astro-ph.IM astro-ph.GA astro-ph.SR |
arxiv_dataset-76841609.02922 | Revisiting the Lick Observatory Supernova Search Volume-Limited Sample:
Updated Classifications and Revised Stripped-Envelope Supernova Fractions
astro-ph.HE
We re-examine the classifications of supernovae (SNe) presented in the Lick
Observatory Supernova Search (LOSS) volume-limited sample with a focus on the
stripped-envelope SNe. The LOSS volume-limited sample, presented by Leaman et
al. (2011) and Li et al. (2011b), was calibrated to provide meaningful
measurements of SN rates in the local universe; the results presented therein
continue to be used for comparisons to theoretical and modeling efforts. Many
of the objects from the LOSS sample were originally classified based upon only
a small subset of the data now available, however, and recent studies have both
updated some subtype distinctions and improved our ability to perform robust
classications, especially for stripped-envelope SNe. We re-examine the
spectroscopic classifications of all events in the LOSS volume-limited sample
(180 SNe and SN impostors) and update them if necessary. We discuss the
populations of rare objects in our sample including broad-lined Type Ic SNe,
Ca-rich SNe, SN 1987A-like events (we identify SN 2005io as SN 1987A-like here
for the first time), and peculiar subtypes. The relative fractions of Type Ia
SNe, Type II SNe, and stripped-envelope SNe in the local universe are not
affected, but those of some subtypes are. Most significantly, after discussing
the often unclear boundary between SNe Ib and Ic when only noisy spectra are
available, we find a higher SN Ib fraction and a lower SN Ic fraction than
calculated by Li et al. (2011b): spectroscopically normal SNe Ib occur in the
local universe $1.7 \pm 0.9$ times more often than do normal SNe Ic.
| arxiv topic:astro-ph.HE |
arxiv_dataset-76851609.03022 | Escape probability of the super-Penrose process
gr-qc astro-ph.HE hep-th
We consider a head-on collision of two massive particles that move in the
equatorial plane of an extremal Kerr black hole, which results in the
production of two massless particles. Focusing on a typical case, where both of
the colliding particles have zero angular momenta, we show that a massless
particle produced in such a collision can escape to infinity with arbitrarily
large energy in the near-horizon limit of the collision point. Furthermore, if
we assume that the emission of the produced massless particles is isotropic in
the center-of-mass frame but confined to the equatorial plane, the escape
probability of the produced massless particle approaches $5/12$ and almost all
escaping massless particles have arbitrarily large energy at infinity and an
impact parameter approaching $2GM/c^2$, where $M$ is the mass of the black
hole.
| arxiv topic:gr-qc astro-ph.HE hep-th |
arxiv_dataset-76861609.03122 | Color groups of colorings of $N$-planar modules
math.MG math.CO
A submodule of a $\mathbb{Z}$-module determines a coloring of the module
where each coset of the submodule is associated to a unique color. Given a
submodule coloring of a $\mathbb{Z}$-module, the group formed by the symmetries
of the module that induces a permutation of colors is referred to as the color
group of the coloring. In this contribution, a method to solve for the color
groups of colorings of $N$-planar modules where $N=4$ and $N=6$ are given.
Examples of colorings of rectangular lattices and of the vertices of the
Ammann-Beenker tiling are given to exhibit how these methods may be extended to
the general case.
| arxiv topic:math.MG math.CO |
arxiv_dataset-76871609.03222 | Reflection maps
math.AG
Given a reflection group $G$ acting on a complex vector space $V$, a
reflection map is the composition of an embedding $X \hookrightarrow V$ with
the orbit map $V\to\mathbb C^p$ that maps a $G$-orbit to a point. Reflection
maps can be very singular, but we give tools to study them easily. We find
obstructions to $\mathcal A$-stability of reflection maps and produce, in the
unobstructed cases, infinite families of $\mathcal A$-finite map-germs of any
corank. We also relate them to conjectures of L\^e, Mond and Ruas.
| arxiv topic:math.AG |
arxiv_dataset-76881609.03322 | SecComp: Towards Practically Defending Against Component Hijacking in
Android Applications
cs.CR
Cross-app collaboration via inter-component communication is a fundamental
mechanism on Android. Although it brings the benefits such as functionality
reuse and data sharing, a threat called component hijacking is also introduced.
By hijacking a vulnerable component in victim apps, an attack app can escalate
its privilege for originally prohibited operations. Many prior studies have
been performed to understand and mitigate this issue, but component hijacking
remains a serious open problem in the Android ecosystem due to no effective
defense deployed in the wild. In this paper, we present our vision on
practically defending against component hijacking in Android apps. First, we
argue that to fundamentally prevent component hijacking, we need to switch from
the previous mindset (i.e., performing system-level control or repackaging
vulnerable apps after they are already released) to a more proactive version
that aims to help security-inexperienced developers make secure components in
the first place. To this end, we propose to embed into apps a secure component
library (SecComp), which performs in-app mandatory access control on behalf of
app components. An important factor for SecComp to be effective is that we find
it is possible to devise a set of practical in-app policies to stop component
hijacking. Furthermore, we allow developers design custom policies, beyond our
by-default generic policies, to support more fine-grained access control. We
have overcome challenges to implement a preliminary SecComp prototype, which
stops component hijacking with very low performance overhead. We hope the
future research that fully implements our vision can eventually help real-world
apps get rid of component hijacking.
| arxiv topic:cs.CR |
arxiv_dataset-76891609.03422 | Orthorhombic boron oxide under pressure: in situ study by X-ray
diffraction and Raman scattering
cond-mat.mtrl-sci
High-pressure phase of boron oxide, orthorhombic \b{eta}-B2O3, has been
studied in situ by synchrotron X-ray diffraction to 22 GPa and Raman scattering
to 46 GPa at room temperature. The bulk modulus of \b{eta}-B2O3 has been found
to be 169(3) GPa that is in good agreement with our ab initio calculations.
Raman and IR spectra of \b{eta}-B2O3 have been measured at ambient pressure,
all experimentally observed bands have been attributed to the theoretically
calculated ones, and the mode assignment has been performed. Based on the data
on Raman shift as a function of pressure, combined with equation-of-state data,
the Gr\"uneisen parameters of all experimentally observed Raman bands have been
calculated. \b{eta}-B2O3 enriched by 10B isotope has been synthesized, and the
effect of boron isotopic substitution on Raman spectra has been studied.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-76901609.03522 | The location, clustering, and propagation of massive star formation in
giant molecular clouds
astro-ph.GA
Massive stars are key players in the evolution of galaxies, yet their
formation pathway remains unclear. In this work, we use data from several
galaxy-wide surveys to build an unbiased dataset of ~700 massive young stellar
objects (MYSOs), ~200 giant molecular clouds (GMCs), and ~100 young (<10 Myr)
optical stellar clusters (SCs) in the Large Magellanic Cloud. We employ this
data to quantitatively study the location and clustering of massive star
formation and its relation to the internal structure of GMCs. We reveal that
massive stars do not typically form at the highest column densities nor centers
of their parent GMCs at the ~6 pc resolution of our observations. Massive star
formation clusters over multiple generations and on size scales much smaller
than the size of the parent GMC. We find that massive star formation is
significantly boosted in clouds near SCs. Yet, whether a cloud is associated
with a SC does not depend on either the cloud's mass or global surface density.
These results reveal a connection between different generations of massive
stars on timescales up to 10 Myr. We compare our work with Galactic studies and
discuss our findings in terms of GMC collapse, triggered star formation, and a
potential dichotomy between low- and high-mass star formation.
| arxiv topic:astro-ph.GA |
arxiv_dataset-76911609.03622 | A Computational Analysis of the Function of Three Inhibitory Cell Types
in Contextual Visual Processing
q-bio.NC
Most cortical inhibitory cell types exclusively express one of three genes,
parvalbumin, somatostatin and 5HT3a. The visual responses of cortical neurons
are affected not only by local cues, but also by visual context. As the
inhibitory neuron types have distinctive synaptic sources and targets over
different spatial extents and from different areas, we conjecture that they
possess distinct roles in contextual processing. We use modeling to relate
structural information to function in primary visual cortex (V1) of the mouse,
and investigate their role in contextual visual processing. Our findings are
threefold. First, the inhibition mediated by parvalbumin positive (PV) cells
mediates local processing and could underlie their role in boundary detection.
Second, the inhibition mediated by somatostatin-positive (SST) cells
facilitates longer range spatial competition among receptive fields. Third,
non-specific top-down modulation to interneurons expressing vasoactive
intestinal polypeptide (VIP), a subclass of 5HT3a neurons, can selectively
enhance V1 responses.
| arxiv topic:q-bio.NC |
arxiv_dataset-76921609.03722 | On the local closure of clones on countable sets
math.LO math.RA
We consider clones on countable sets. If such a clone has quasigroup
operations, is locally closed and countable, then there is a function $f :
\mathbb{N} \to \mathbb{N}$ such that the $n$-ary part of $C$ is equal to the
$n$-ary part of $\mathrm{Pol}\,\mathrm{Inv}^{[f(n)]} C$, where
$\mathrm{Inv}^{[f(n)]} C$ denotes the set of $f(n)$-ary invariant relations of
$C$.
| arxiv topic:math.LO math.RA |
arxiv_dataset-76931609.03822 | Search reliability and search efficiency of combined L\'evy-Brownian
motion: long relocations mingled with thorough local exploration
cond-mat.stat-mech q-bio.PE q-bio.QM
A combined dynamics consisting of Brownian motion and L\'evy flights is
exhibited by a variety of biological systems performing search processes.
Assessing the search reliability of ever locating the target and the search
efficiency of doing so economically of such dynamics thus poses an important
problem. Here we model this dynamics by a one-dimensional fractional
Fokker-Planck equation combining unbiased Brownian motion and L\'evy flights.
By solving this equation both analytically and numerically we show that the
superposition of recurrent Brownian motion and L\'evy flights with stable
exponent $\alpha<1$, by itself implying zero probability of hitting a point on
a line, lead to transient motion with finite probability of hitting any point
on the line. We present results for the exact dependence of the values of both
the search reliability and the search efficiency on the distance between the
starting and target positions as well as the choice of the scaling exponent
$\alpha$ of the L\'evy flight component.
| arxiv topic:cond-mat.stat-mech q-bio.PE q-bio.QM |
arxiv_dataset-76941609.03922 | Hyperbolic periodic orbits in nongradient systems and
small-noise-induced metastable transitions
math.DS math.NA math.PR
Small noise can induce rare transitions between metastable states, which can
be characterized by Maximum Likelihood Paths (MLPs). Nongradient systems
contrast gradient systems in that MLP does not have to cross the separatrix at
a saddle point, but instead possibly at a point on a hyperbolic periodic orbit.
A numerical approach for identifying such unstable periodic orbits is proposed
based on String method. In a special class of nongradient systems
(`orthogonal-type'), there are provably local MLPs that cross such saddle point
or hyperbolic periodic orbit, and the separatrix crossing location determines
the associated local maximum of transition rate. In general cases, however, the
separatrix crossing may not determine a unique local maximum of the rate, as we
numerically observed a counter-example in a sheared 2D-space Allen-Cahn SPDE.
It is a reasonable conjecture that there are always local MLPs associated with
each attractor on the separatrix, such as saddle point or hyperbolic periodic
orbit; our numerical experiments did not disprove so.
| arxiv topic:math.DS math.NA math.PR |
arxiv_dataset-76951609.04022 | Cosmology with Peculiar Velocities: Observational Effects
astro-ph.CO
In this paper we investigate how observational effects could possibly bias
cosmological inferences from peculiar velocity measurements. Specifically, we
look at how bulk flow measurements are compared with theoretical predictions.
Usually bulk flow calculations try to approximate the flow that would occur in
a sphere around the observer. Using the Horizon Run 2 simulation we show that
the traditional methods for bulk flow estimation can overestimate the magnitude
of the bulk flow for two reasons: when the survey geometry is not spherical
(the data do not cover the whole sky), and when the observations undersample
the velocity distributions. Our results may explain why several bulk flow
measurements found bulk flow velocities that seem larger than those expected in
standard {\Lambda}CDM cosmologies. We recommend a different approach when
comparing bulk flows to cosmological models, in which the theoretical
prediction for each bulk flow measurement is calculated specifically for the
geometry and sampling rate of that survey. This means that bulk flow values
will not be comparable between surveys, but instead they are comparable with
cosmological models, which is the more important measure.
| arxiv topic:astro-ph.CO |
arxiv_dataset-76961609.04122 | Rashba-Edelstein Magnetoresistance in Metallic Heterostructure
cond-mat.mes-hall
We report the observation of magnetoresistance originating from Rashba
spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein
(RE) magnetoresistance. We show that the simultaneous action of the direct and
inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin
accumulation to the electric resistance. The electric resistance changes with
the magnetic-field angle, reminiscent of the spin Hall magnetoresistance,
despite the fact that bulk SOC is not responsible for the magnetoresistance. We
further found that, even when the magnetization is saturated, the resistance
increases with increasing the magnetic-field strength, which is attributed to
the Hanle magnetoresistance in this system.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-76971609.04222 | Grouped functional time series forecasting: An application to
age-specific mortality rates
stat.AP
Age-specific mortality rates are often disaggregated by different attributes,
such as sex, state and ethnicity. Forecasting age-specific mortality rates at
the national and sub-national levels plays an important role in developing
social policy. However, independent forecasts at the sub-national levels may
not add up to the forecasts at the national level. To address this issue, we
consider reconciling forecasts of age-specific mortality rates, extending the
methods of Hyndman et al. (2011) to functional time series, where age is
considered as a continuum. The grouped functional time series methods are used
to produce point forecasts of mortality rates that are aggregated appropriately
across different disaggregation factors. For evaluating forecast uncertainty,
we propose a bootstrap method for reconciling interval forecasts. Using the
regional age-specific mortality rates in Japan, obtained from the Japanese
Mortality Database, we investigate the one- to ten-step-ahead point and
interval forecast accuracies between the independent and grouped functional
time series forecasting methods. The proposed methods are shown to be useful
for reconciling forecasts of age-specific mortality rates at the national and
sub-national levels. They also enjoy improved forecast accuracy averaged over
different disaggregation factors. Supplemental materials for the article are
available online.
| arxiv topic:stat.AP |
arxiv_dataset-76981609.04322 | Compact maximal hypersurfaces in stably causal spacetimes
math.DG
Several uniqueness results on compact maximal hypersurfaces in a wide class
of sta- bly causal spacetimes are given. They are obtained from the study of a
distinguished function on the maximal hypersurface, under suitable natural
first order conditions of the spacetime. As a consequence several applications
to Geometric Analysis are given.
| arxiv topic:math.DG |
arxiv_dataset-76991609.04422 | Manifest Covariant Hamiltonian Theory of General Relativity
gr-qc
The problem of formulating a manifest covariant Hamiltonian theory of General
Relativity in the presence of source fields is addressed, by extending the
so-called "DeDonder-Weyl" formalism to the treatment of classical fields in
curved space-time. The theory is based on a synchronous variational principle
for the Einstein equation, formulated in terms of superabundant variables. The
technique permits one to determine the continuum covariant Hamiltonian
structure associated with the Einstein equation. The corresponding continuum
Poisson bracket representation is also determined. The theory relies on
first-principles, in the sense that the conclusions are reached in the
framework of a non-perturbative covariant approach, which allows one to
preserve both the 4-scalar nature of Lagrangian and Hamiltonian densities as
well as the gauge invariance property of the theory.
| arxiv topic:gr-qc |
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