title
string | abstract
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string | arxiv_id
string | date
string | category
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21 cm line signal from magnetic modes
|
The Lorentz term raises the linear matter power on small scale which leads to
interesting signatures in the 21 cm signal. Numerical simulations of the
resuting nonlinear density field, the distribution of ionized hydrogen and the
21 cm signal at different values of redshift are presented for magnetic fields
with field strength B=5 nG, and spectral indices $n_B=-2.9, -2.2$ and -1.5
together with the adiabatic mode for the best fit data of Planck13+WP.
Comparing the averaged global 21 cm signal with the projected SKA1-LOW
sensitivities of the Square Kilometre Array (SKA) it might be possible to
constrain the magnetic field parameters.
|
http://arxiv.org/abs/1805.10943v1
|
1805.10943
|
2018-05-28
|
natural-language-processing
|
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal
|
We introduce 21CMMC: a parallelized, Monte Carlo Markov Chain analysis tool,
incorporating the epoch of reionization (EoR) seminumerical simulation
21CMFAST. 21CMMC estimates astrophysical parameter constraints from 21 cm EoR
experiments, accommodating a variety of EoR models, as well as priors on model
parameters and the reionization history. To illustrate its utility, we consider
two different EoR scenarios, one with a single population of galaxies (with a
mass-independent ionizing efficiency) and a second, more general model with two
different, feedback-regulated populations (each with mass-dependent ionizing
efficiencies). As an example, combining three observations (z=8, 9 and 10) of
the 21 cm power spectrum with a conservative noise estimate and uniform model
priors, we find that interferometers with specifications like the Low Frequency
Array/Hydrogen Epoch of Reionization Array (HERA)/Square Kilometre Array 1
(SKA1) can constrain common reionization parameters: the ionizing efficiency
(or similarly the escape fraction), the mean free path of ionizing photons and
the log of the minimum virial temperature of star-forming haloes to within
45.3/22.0/16.7, 33.5/18.4/17.8 and 6.3/3.3/2.4 per cent, ~$1\sigma$ fractional
uncertainty, respectively. Instead, if we optimistically assume that we can
perfectly characterize the EoR modelling uncertainties, we can improve on these
constraints by up to a factor of ~few. Similarly, the fractional uncertainty on
the average neutral fraction can be constrained to within $\lesssim10$ per cent
for HERA and SKA1. By studying the resulting impact on astrophysical
constraints, 21CMMC can be used to optimize (i) interferometer designs; (ii)
foreground cleaning algorithms; (iii) observing strategies; (iv) alternative
statistics characterizing the 21 cm signal; and (v) synergies with other
observational programs.
|
http://arxiv.org/abs/1501.06576v2
|
1501.06576
|
2015-01-26
|
natural-language-processing
|
21CMMC with a 3D light-cone: the impact of the co-evolution approximation on the astrophysics of reionisation and cosmic dawn
|
We extend 21CMMC, a Monte Carlo Markov Chain sampler of 3D reionisation
simulations, to perform parameter estimation directly on 3D light-cones of the
cosmic 21cm signal. This brings theoretical analysis closer to the tomographic
21-cm observations achievable with next generation interferometers like HERA
and the SKA. Parameter recovery can therefore account for modes which evolve
with redshift/frequency. Additionally, simulated data can be more easily
corrupted to resemble real data. Using the light-cone version of 21CMMC, we
quantify the biases in the recovered astrophysical parameters if we use the
21cm power spectrum from the co-evolution approximation to fit a 3D light-cone
mock observation. While ignoring the light-cone effect under most assumptions
will not significantly bias the recovered astrophysical parameters, it can lead
to an underestimation of the associated uncertainty. However significant biases
($\sim$few -- 10 $\sigma$) can occur if the 21cm signal evolves rapidly (i.e.
the epochs of reionisation and heating overlap significantly) and: (i)
foreground removal is very efficient, allowing large physical scales
($k\lesssim0.1$~Mpc$^{-1}$) to be used in the analysis or (ii) theoretical
modelling is accurate to within $\sim10$ per cent in the power spectrum
amplitude.
|
http://arxiv.org/abs/1801.01592v1
|
1801.01592
|
2018-01-05
|
natural-language-processing
|
21-cm observations and warm dark matter models
|
Observations of the redshifted 21-cm signal (in absorption or emission) allow
us to peek into the epoch of "dark ages" and the onset of reionization. These
data can provide a novel way to learn about the nature of dark matter, in
particular about the formation of small size dark matter halos. However, the
connection between the formation of structures and 21-cm signal requires
knowledge of stellar to total mass relation, escape fraction of UV photons, and
other parameters that describe star formation and radiation at early times.
This baryonic physics depends on the properties of dark matter and in
particular in warm-dark-matter (WDM) models, star formation may follow a
completely different scenario, as compared to the cold-dark-matter case. We use
the recent measurements by the EDGES [J. D. Bowman, A. E. E. Rogers, R. A.
Monsalve, T. J. Mozdzen, and N. Mahesh, An absorption profile centred at 78
megahertz in thesky-averaged spectrum,Nature (London) 555, 67 (2018).] to
demonstrate that when taking the above considerations into account, the robust
WDM bounds are in fact weaker than those given by the Lyman-$\alpha$ forest
method and other structure formation bounds. In particular, we show that
resonantly produced 7 keV sterile neutrino dark matter model is consistent with
these data. However, a holistic approach to modelling of the WDM universe holds
great potential and may in the future make 21-cm data our main tool to learn
about dark matter clustering properties.
|
http://arxiv.org/abs/1904.03097v2
|
1904.03097
|
2019-12-10
|
natural-language-processing
|
21 cm observations: calibration, strategies, observables
|
This chapter aims to provide a review of the basics of 21 cm interferometric
observations and its methodologies. A summary of the main concepts of radio
interferometry and their connection with the 21 cm observables - power spectra
and images - is presented. I then provide a review of interferometric
calibration and its interplay with foreground separation, including the current
open challenges in calibration of 21 cm observations. Finally, a review of 21
cm instrument designs in the light of calibration choices and observing
strategies follows.
|
http://arxiv.org/abs/1909.11938v1
|
1909.11938
|
2019-09-26
|
natural-language-processing
|
21-cm power spectrum and ionization bias as a probe of long-mode modulated non Gaussian sky
|
The observed hemispherical power asymmetry in cosmic microwave background
radiation can be explained by long wavelength mode (long-mode) modulation. In
this work we study the prospect of the detection of this effect in the angular
power spectrum of 21-cm brightness temperature. For this task, we study the
effect of the neutral Hydrogen distribution on the angular power spectrum. This
is done by formulating the bias parameter of ionized fraction to the underlying
matter distribution. We also discuss the possibility that the long mode
modulation is companied with a primordial non-Gaussianity of local type. In
this case, we obtain the angular power spectrum with two effects of primordial
non-Gaussianity and long mode modulation. Finally, we show that the primordial
non-Gaussianity enhances the long mode modulated power of 21-cm signal via the
non-Gaussian scale-dependent bias up to four orders of magnitude. {Accordingly,
the observation of 21-cm signal with upcoming surveys such as the Square
Kilometer Array (SKA) is probably capable of detecting hemispherical power
asymmetry in the context of the long mode modulation.
|
http://arxiv.org/abs/1812.11150v3
|
1812.11150
|
2019-08-15
|
natural-language-processing
|
21 cm Power Spectrum for Bimetric Gravity and its Detectability with SKA1-Mid Telescope
|
We consider a modified gravity theory through a special kind of ghost-free bimetric gravity, where one massive spin-2 field interacts with a massless spin-2 field. In this bimetric gravity, the late time cosmic acceleration is achievable. Alongside the background expansion of the Universe, we also study the first-order cosmological perturbations and probe the signature of the bimetric gravity on large cosmological scales. One possible probe is to study the observational signatures of the bimetric gravity through the 21 cm power spectrum. We consider upcoming SKA1-mid antenna telescope specifications to show the prospects of the detectability of the ghost-free bimetric gravity through the 21 cm power spectrum. Depending on the values of the model parameter, there is a possibility to distinguish the ghost-free bimetric gravity from the standard $\Lambda$CDM model with the upcoming SKA1-mid telescope specifications.
|
https://arxiv.org/abs/2306.03875v1
|
2306.03875
|
2023-06-06
|
natural-language-processing
|
21 cm power spectrum in interacting cubic Galileon model
|
We show the detectability of interacting and non-interacting cubic Galileon models from the $\Lambda$CDM model through the 21 cm power spectrum. We show that the interferometric observations like the upcoming SKA1-mid can detect both the interacting and the non-interacting cubic Galileon model from the $\Lambda$CDM model depending on the parameter values.
|
https://arxiv.org/abs/2208.11560v1
|
2208.11560
|
2022-08-24
|
natural-language-processing
|
21cmSense v2: A modular, open-source 21cm sensitivity calculator
|
The 21cm line of neutral hydrogen is a powerful probe of the high-redshift universe (Cosmic Dawn and the Epoch of Reionization), with an unprecedented potential to inform us about key processes of early galaxy formation, the first stars and even cosmology and structure formation, via intensity mapping. It is the subject of a number of current and upcoming low-frequency radio experiments. This paper presents 21cmSense v2.0, which is a Python package that provides a modular framework for calculating the sensitivity of these experiments, in order to enhance the process of their design and forecasting their power for parameter inference. Version 2.0 of 21cmSense has been re-written from the ground up to be more modular and extensible than its venerable predecessor (Pober et al., 2013, 2014), and to provide a more user-friendly interface. The package is freely available both to use and contribute towards at https://github.com/rasg-affiliates/21cmSense.
|
https://arxiv.org/abs/2406.02415v1
|
2406.02415
|
2024-06-04
|
natural-language-processing
|
21-cm signal from cosmic dawn - II: Imprints of the light-cone effects
|
Details of various unknown physical processes during the cosmic dawn and the
epoch of reionization can be extracted from observations of the redshifted
21-cm signal. These observations, however, will be affected by the evolution of
the signal along the line-of-sight which is known as the "light-cone effect".
We model this effect by post-processing a dark matter $N-$body simulation with
an 1-D radiative transfer code. We find that the effect is much stronger and
dramatic in presence of inhomogeneous heating and Ly$\alpha$ coupling compared
to the case where these processes are not accounted for. One finds increase
(decrease) in the spherically averaged power spectrum up to a factor of 3 (0.6)
at large scales ($k \sim 0.05\, \rm Mpc^{-1}$) when the light-cone effect is
included, though these numbers are highly dependent on the source model. The
effect is particularly significant near the peak and dip-like features seen in
the power spectrum. The peaks and dips are suppressed and thus the power
spectrum can be smoothed out to a large extent if the width of the frequency
band used in the experiment is large. We argue that it is important to account
for the light-cone effect for any 21-cm signal prediction during cosmic dawn.
|
http://arxiv.org/abs/1504.05601v2
|
1504.05601
|
2015-08-12
|
natural-language-processing
|
21cm signal from Dark Ages collapsing halos with detailed molecular cooling treatment
|
Context. In order to understand the formation of the first stars, which set the transition between the Dark Ages and Cosmic Dawn epochs, it is necessary to provide a detailed description of the physics at work within the first clouds of gas which, during their gravitational collapse, will set the conditions for stars to be form through the mechanism of thermal instability. Aims. Our objective is to study in detail the molecular cooling of gas in the halos preceding the formation of the first stars. We are furthermore assessing the sensitivity of the 21cm hydrogen line to this cooling channel. Results. We present the CHEMFAST code, that we developed to compute the cosmological 21cm neutral hydrogen line inside collapsing matter overdensity. We precisely track evolution in the abundances of ions, atoms and molecules through a network of chemical reactions. Computing the molecular thermal function due to the excitation of the rotational levels of the H2 molecule, we find it strongly affects the gas temperature inside collapsing clouds of $10^8$ M$_\odot$. The gas temperature falls at the end of the collapse, when the molecular cooling takes over the heating due to gravitation. Conclusions. We find that the 21cm brightness temperature inside the collapsing cloud presents an emission feature, different from the one predicted in expansion scenario. It moreover follows the same behavior as the gas temperature, as it is also strongly affected by the molecular cooling. This makes it a promising probe in order to map the collapsing halos and thermal processes at work inside them.
|
https://arxiv.org/abs/2404.08479v1
|
2404.08479
|
2024-04-12
|
natural-language-processing
|
21-cm Signal from the Epoch of Reionization: A Machine Learning upgrade to Foreground Removal with Gaussian Process Regression
|
In recent years, a Gaussian Process Regression (GPR) based framework has been developed for foreground mitigation from data collected by the LOw-Frequency ARray (LOFAR), to measure the 21-cm signal power spectrum from the Epoch of Reionization (EoR) and Cosmic Dawn. However, it has been noted that through this method there can be a significant amount of signal loss if the EoR signal covariance is misestimated. To obtain better covariance models, we propose to use a kernel trained on the {\tt GRIZZLY} simulations using a Variational Auto-Encoder (VAE) based algorithm. In this work, we explore the abilities of this Machine Learning based kernel (VAE kernel) used with GPR, by testing it on mock signals from a variety of simulations, exploring noise levels corresponding to $\approx$10 nights ($\approx$141 hours) and $\approx$100 nights ($\approx$1410 hours) of observations with LOFAR. Our work suggests the possibility of successful extraction of the 21-cm signal within 2$\sigma$ uncertainty in most cases using the VAE kernel, with better recovery of both shape and power than with previously used covariance models. We also explore the role of the excess noise component identified in past applications of GPR and additionally analyse the possibility of redshift dependence on the performance of the VAE kernel. The latter allows us to prepare for future LOFAR observations at a range of redshifts, as well as compare with results from other telescopes.
|
https://arxiv.org/abs/2311.16633v2
|
2311.16633
|
2023-11-28
|
natural-language-processing
|
21cm signal predictions at Cosmic Dawn and Reionization with coupled radiative-hydrodynamics
|
The process of heating and reionization of the Universe at high redshift links small scale structures/galaxy formation and large scale inter-galactic medium properties. Even if the first one is difficult to observe, an observation window is opening on the second one, with the promising development of current and future radio telescopes. They will permit to observe the 21cm brightness temperature global signal and fluctuations. The need of large scale simulations is therefore strong to understand the properties of the IGM that will be observed. But at the same time the urge to resolve the structures responsible of those process is important. We introduce in this study, a coupled hydro-radiative transfer simulations of the Cosmic Dawn and Reionization with a simple sub-grid star formation process developed and calibrated on the state of the art simulation CoDaII. This scheme permits to follow consistently dark matter, hydrodynamics and radiative transfer evolution's on large scales, while the sub-grid models bridges to the galaxy formation scale. We process the simulation to produce 21cm signal as close as possible to the observations.
|
https://arxiv.org/abs/2103.03061v1
|
2103.03061
|
2021-03-04
|
natural-language-processing
|
21cm Signal Recovery via the Robust Principle Component Analysis
|
The redshifted 21~cm signal from neutral hydrogen (HI) is potentially a very
powerful probe for cosmology, but a difficulty in its observation is that it is
much weaker than foreground radiation from the Milky Way as well as
extragalactic radio sources. The foreground radiation at different frequencies
are however coherent along one line of sight, and various methods of foreground
subtraction based on this property have been proposed. In this paper, we
present a new method based on the Robust Principal Component Analysis (RPCA) to
subtract foreground and extract 21~cm signal, which explicitly uses both the
low-rank property of the frequency covariance matrix (i.e. frequency coherence)
of the foreground and the sparsity of the frequency covariance matrix of the
21~cm signal. The low-rank property of the foregrounds frequency covariance has
been exploited in many previous works on foreground subtraction, but to our
knowledge the sparsity of the frequency covariance of the 21~cm signal is first
explored here. By exploiting both properties in the RPCA method, in principle,
the foreground and signal may be separated without the signal loss problem. Our
method is applicable to both small patch of sky with the flat-sky
approximation, and to large area of sky where the sphericity has to be
considered. It is also easy to be extended to deal with more complex conditions
such as sky map with defects.
|
http://arxiv.org/abs/1801.04082v1
|
1801.04082
|
2018-01-12
|
natural-language-processing
|
21cm signal sensitivity to dark matter decay
|
The redshifted 21cm signal from the Cosmic Dawn is expected to provide unprecedented insights into early Universe astrophysics and cosmology. Here we explore how dark matter can heat the intergalactic medium before the first galaxies, leaving a distinctive imprint in the 21cm power spectrum. We provide the first dedicated Fisher matrix forecasts on the sensitivity of the Hydrogen Epoch of Reionization Array (HERA) telescope to dark matter decays. We show that with 1000 hours of observation, HERA has the potential to improve current cosmological constraints on the dark matter decay lifetime by up to three orders of magnitude. Even in extreme scenarios with strong X-ray emission from early-forming, metal-free galaxies, the bounds on the decay lifetime would be improved by up to two orders of magnitude. Overall, HERA shall improve on existing limits for dark matter masses below $2$ GeV$/c^2$ for decays into $e^+e^-$ and below few MeV$/c^2$ for decays into photons.
|
https://arxiv.org/abs/2308.16656v2
|
2308.16656
|
2023-08-31
|
natural-language-processing
|
21-cm signature of the first sources in the Universe: Prospects of detection with SKA
|
Currently several low-frequency experiments are being planned to study the
nature of the first stars using the redshifted 21-cm signal from the cosmic
dawn and epoch of reionization. Using a one-dimensional radiative transfer
code, we model the 21-cm signal pattern around the early sources for different
source models, i.e., the metal-free Population III (PopIII) stars, primordial
galaxies consisting of Population II (PopII) stars, mini-QSOs and high-mass
X-ray binaries (HMXBs). We investigate the detectability of these sources by
comparing the 21-cm visibility signal with the system noise appropriate for a
telescope like the SKA1-low. Upon integrating the visibility around a typical
source over all baselines and over a frequency interval of 16 MHz, we find that
it will be possible to make a $\sim 9-\sigma$ detection of the isolated sources
like PopII galaxies, mini-QSOs and HMXBs at $z \sim 15$ with the SKA1-low in
1000 hours. The exact value of the signal to noise ratio (SNR) will depend on
the source properties, in particular on the mass and age of the source and the
escape fraction of ionizing photons. The predicted SNR decreases with
increasing redshift. We provide simple scaling laws to estimate the SNR for
different values of the parameters which characterize the source and the
surrounding medium. We also argue that it will be possible to achieve a SNR
$\sim 9$ even in the presence of the astrophysical foregrounds by subtracting
out the frequency-independent component of the observed signal. These
calculations will be useful in planning 21-cm observations to detect the first
sources.
|
http://arxiv.org/abs/1511.07448v2
|
1511.07448
|
2016-05-12
|
natural-language-processing
|
21-cm signatures of residual HI inside cosmic HII regions during reionization
|
We investigate the impact of sinks of ionizing radiation on the
reionization-era 21-cm signal, focusing on 1-point statistics. We consider
sinks in both the intergalactic medium and inside galaxies. At a fixed filling
factor of HII regions, sinks will have two main effects on the 21-cm
morphology: (i) as inhomogeneous absorbers of ionizing photons they result in
smaller and more widespread cosmic HII patches; and (ii) as reservoirs of
neutral gas they contribute a non-zero 21-cm signal in otherwise ionized
regions. Both effects damp the contrast between neutral and ionized patches
during reionization, making detection of the epoch of reionization with 21-cm
interferometry more challenging. Here we systematically investigate these
effects using the latest semi-numerical simulations. We find that sinks
dramatically suppress the peak in the redshift evolution of the variance,
corresponding to the midpoint of reionization. As previously predicted,
skewness changes sign at midpoint, but the fluctuations in the residual HI
suppress a late-time rise. Furthermore, large levels of residual HI
dramatically alter the evolution of the variance, skewness and power spectrum
from that seen at lower levels. In general, the evolution of the large-scale
modes provides a better, cleaner, higher signal-to-noise probe of reionization.
|
http://arxiv.org/abs/1501.01970v2
|
1501.01970
|
2015-05-27
|
natural-language-processing
|
21cmVAE: A Very Accurate Emulator of the 21-cm Global Signal
|
Considerable observational efforts are being dedicated to measuring the sky-averaged (global) 21-cm signal of neutral hydrogen from Cosmic Dawn and the Epoch of Reionization. Deriving observational constraints on the astrophysics of this era requires modeling tools that can quickly and accurately generate theoretical signals across the wide astrophysical parameter space. For this purpose artificial neural networks were used to create the only two existing global signal emulators, 21cmGEM and globalemu. In this paper we introduce 21cmVAE, a neural network-based global signal emulator, trained on the same dataset of ~30,000 global signals as the other two emulators, but with a more direct prediction algorithm that prioritizes accuracy and simplicity. Using neural networks, we compute derivatives of the signals with respect to the astrophysical parameters and establish the most important astrophysical processes that drive the global 21-cm signal at different epochs. 21cmVAE has a relative rms error of only 0.34 - equivalently 0.54 mK - on average, which is a significant improvement compared to the existing emulators, and a run time of 0.04 seconds per parameter set. The emulator, the code, and the processed datasets are publicly available at https://github.com/christianhbye/21cmVAE and through https://zenodo.org/record/5904939.
|
https://arxiv.org/abs/2107.05581v4
|
2107.05581
|
2021-07-12
|
natural-language-processing
|
21-Component Compositionally Complex Ceramics: Discovery of Ultrahigh-Entropy Weberite and Fergusonite Phases and a Pyrochlore-Weberite Transition
|
Two new high-entropy ceramics (HECs) in the weberite and fergusonite structures, along with unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition, are discovered in a 21-component oxide system. While the Gibbs phase rule allows 21 equilibrium phases, nine out of the 13 compositions examined possess single HEC phases (with ultrahigh ideal configurational entropies: ~2.7kB per cation or higher on one sublattice in most cases). Notably, (15RE1/15)(Nb1/2Ta1/2)O4 possess a single monoclinic fergusonite (C2/c) phase and (15RE1/15)3(Nb1/2Ta1/2)1O7 form a single orthorhombic (C2221) weberite phase, where 15RE1/15 represents Sc1/15Y1/15La1/15Pr1/15Nd1/15Sm1/15Eu1/15Gd1/15Tb1/15Dy1/15Ho1/15Er1/15Tm1/15Yb1/15Lu1/15. Moreover, a series of eight (15RE1/15)2+x(Ti1/4Zr1/4Ce1/4Hf1/4)2-2x(Nb1/2Ta1/2)xO7 specimens all exhibit single phases, where a pyrochlore-weberite transition occurs within 0.75 < x < 0.8125. This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably, as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides. These discoveries expand the diversity and complexity of HECs, towards many-component compositionally complex ceramics (CCCs) and ultrahigh-entropy ceramics.
|
https://arxiv.org/abs/2112.15381v2
|
2112.15381
|
2021-12-31
|
natural-language-processing
|
2+1d Compact Lifshitz Theory, Tensor Gauge Theory, and Fractons
|
The 2+1d continuum Lifshitz theory of a free compact scalar field plays a prominent role in a variety of quantum systems in condensed matter physics and high energy physics. It is known that in compact space, it has an infinite ground state degeneracy. In order to understand this theory better, we consider two candidate lattice regularizations of it using the modified Villain formalism. We show that these two lattice theories have significantly different global symmetries (including a dipole global symmetry), anomalies, ground state degeneracies, and dualities. In particular, one of them is self-dual. Given these theories and their global symmetries, we can couple them to corresponding gauge theories. These are two different $U(1)$ tensor gauge theories. The resulting models have excitations with restricted mobility, i.e., fractons. Finally, we give an exact lattice realization of the fracton/lineon-elasticity dualities for the Lifshitz theory, scalar and vector charge gauge theories.
|
https://arxiv.org/abs/2209.10030v2
|
2209.10030
|
2022-09-20
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natural-language-processing
|
2+1 d Georgi Glashow Model Near Critical Temperature
|
We study correlations functions of magnetic vortices $V$ and Polyakov loop
$P$ operators in the 2+1 dimensional Georgi-Glashow model in the vicinity of
the deconfining phase transition. In this regime the (dimensionally reduced)
model is mapped onto a free theory of two massive Majorana fermions. We utilize
this fermionic representation to explicitly calculate the expectation values of
$V$ and $P$ as well as their correlators. In particular we show that the $VV$
correlator is large, and thus the anomalous breaking of the magnetic $U(1)$
symmetry is order one effect in the near critical region. We also calculate the
contribution of magnetic vortices to the entropy and the free energy of the
system.
|
http://arxiv.org/abs/1612.07267v2
|
1612.07267
|
2017-04-11
|
natural-language-processing
|
$(2+1)$-dimensional AKNS($-N$) Systems: $ N=3,4$
|
In this work we continue to study negative AKNS($N$) that is AKNS($-N$)
system for $N=3,4$. We obtain all possible local and nonlocal reductions of
these equations. We construct the Hirota bilinear forms of these equations and
find one-soliton solutions. From the reduction formulas we obtain also
one-soliton solutions of all reduced equations.
|
http://arxiv.org/abs/1910.11298v1
|
1910.11298
|
2019-10-24
|
natural-language-processing
|
$(2+1)$-Dimensional Black Holes in $f(R,φ)$ Gravity
|
We consider a $f(R)$ gravity theory in $(2+1)$-dimensions with a self-interacting scalar field non-minimally coupled to gravity. Without specifying the form of the $f(R)$ function, solving the field equations we find that the Ricci scalar receives a non-linear correction term which breaks the conformal invariance and leads to a massless black hole solution. When the non-linear term decouples, we get a well known hairy black hole solution with the scalar field conformally coupled to gravity. We also find that the entropy of our black hole may be higher than the corresponding conformal black hole which indicates that our solution may be thermodynamically preferred.
|
https://arxiv.org/abs/2201.00035v2
|
2201.00035
|
2021-12-31
|
natural-language-processing
|
(2+1)-dimensional Chern-Simons bi-gravity with AdS Lie bialgebra as an interacting theory of two massless spin-2 fields
|
We introduce a new Lie bialgebra structure for the anti de Sitter (AdS) Lie
algebra in (2+1)-dimensional spacetime. By gauging the resulting \textit{AdS
Lie bialgebra}, we write a Chern-Simons gauge theory of bi-gravity involving
two dreibeins rather than two metrics, which describes two interacting massless
spin-2 fields. Our ghost-free bi-gravity model which has no any local degrees
of freedom, has also a suitable free field limit. By solving its equations of
motion, we obtain a \textit{new black hole} solution which has two curvature
singularities and two horizons. We also study cosmological implications of this
massless bi-gravity model.
|
http://arxiv.org/abs/1706.02129v3
|
1706.02129
|
2018-08-27
|
natural-language-processing
|
(2+1) dimensional cosmological models in f(R; T) gravity with $Λ$(R; T)
|
We intend to study a new class of cosmological models in $f(R, T)$ modified theories of gravity, hence define the cosmological constant $\Lambda$ as a function of the trace of the stress energy-momentum-tensor $T$ and the Ricci scalar $R$, and name such a model "$\Lambda(R, T)$ gravity" where we have specified a certain form of $\Lambda(R, T)$. $\Lambda(R, T)$ is also defined in the perfect fluid and dust case. Some physical and geometric properties of the model are also discussed. The pressure, density and energy conditions are studied both when $\Lambda$ is a positive constant and when $\Lambda=\Lambda(t)$, i.e a function of cosmological time, t. We study the behaviour of some cosmological quantities such as Hubble and deceleration parameters. The model is innovative in the sense that it has been described in terms of both $R$ and $T$ and display a better understanding of the cosmological observations.
|
https://arxiv.org/abs/2003.11355v1
|
2003.11355
|
2020-03-19
|
natural-language-processing
|
(2 +1)-dimensional Duffin-Kemmer-Petiau oscillator under a magnetic field in the presence of a minimal length in the noncommutative space
|
Using the momentum space representation, we study the (2 +1)-dimensional
Duffin-Kemmer-Petiau oscillator for spin 0 particle under a magnetic field in
the presence of a minimal length in the noncommutative space. The explicit form
of energy eigenvalues are found, the wave functions and the corresponding
probability density are reported in terms of the Jacobi polynomials.
Additionally, we also discuss the special cases and depict the corresponding
numerical results.
|
http://arxiv.org/abs/1706.04298v1
|
1706.04298
|
2017-06-14
|
natural-language-processing
|
2+1 dimensional Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir-Polder force
|
We have calculated the Casimir-Polder interaction (CPI) of a micro-particle
with a sheet on the basis of the Klimchitskaya-Mostepanenko theory. We find the
result that for non-trivial susceptibility values of the sheet and
micro-particle, there is crossover between attractive and repulsive behavior.
The transition depends only on the impedance, involving permeability and
permittivity, apart from the ratio of the film thickness and the micro-particle
separation (D/d) and temperature. The approach to calculate CPI of a
micro-particle with a silicene sheet involves replacing the dielectric constant
of the sample by the static dielectric function obtained using the expressions
for the polarization function. The silicene is described by the low-energy
Liu-Yao-Feng-Ezawa (LYFE)Model Hamiltonian involving the Dirac matrices in the
chiral representation obeying the Clifford algebra.We find that the collective
charge excitations at zero doping, i.e., intrinsic plasmons, in this system,
are absent in the Dirac limit. The valley-spin-split intrinsic plasmons,
however, come into being in the case of the massive Dirac particles with
characteristic frequency close to 10 THz.Furthermore, there is a longitudinal
electric field induced topological insulator(TI) to spin-valley polarized metal
(SVPM) transition in silicene, which is also referred to as the topological
phase transition (TPT). The low-energy SVP carriers at TPT possess gap-less
(mass-less) and gapped (massive) energy spectra close to the two nodal points
in the Brillouin zone with maximum spin-polarization. We find that the
magnitude of the Casimir-Polder force at a given ratio of the film thickness
and the separation between the micro-particle and the film is greater at TPT
than at the topological insulator and trivial insulator phases.
|
http://arxiv.org/abs/1505.07036v3
|
1505.07036
|
2016-07-10
|
natural-language-processing
|
$2+1$ dimensional Floquet systems and lattice fermions: Exact bulk spectral equivalence
|
A connection has recently been proposed between periodically driven systems known as Floquet insulators in continuous time and static fermion theories in discrete time. This connection has been established in a $(1+1)$-dimensional free theory, where an explicit mapping between the spectra of a Floquet insulator and a discrete-time Dirac fermion theory has been formulated. Here we investigate the potential of static discrete-time theories to capture Floquet physics in higher dimensions, where so-called anomalous Floquet topological insulators can emerge that feature chiral edge states despite having bulk bands with zero Chern number. Starting from a particular model of an anomalous Floquet system, we provide an example of a static discrete-time theory whose bulk spectrum is an exact analytic match for the Floquet spectrum. The spectra with open boundary conditions in a particular strip geometry also match up to finite-size corrections. However, the models differ in several important respects. The discrete-time theory is spatially anisotropic, so that the spectra do not agree for all lattice terminations, e.g. other strip geometries or on half spaces. This difference can be attributed to the fact that the static discrete-time model is quasi-one-dimensional in nature and therefore has a different bulk-boundary correspondence than the Floquet model.
|
https://arxiv.org/abs/2410.18226v2
|
2410.18226
|
2024-10-23
|
natural-language-processing
|
(2+1)-dimensional f(R) gravity solutions via Hojman symmetry
|
In this paper, we use the Hojman symmetry approach to find new $(2+1)$-dimensional $f(R)$ gravity solutions, in comparison to Noether symmetry approach. In the special case of Hojman symmetry vector $X=R$, we recover $(2+1)$-dimensional BTZ black hole and generalized $(2+1)$-dimensional BTZ black hole solutions, obtained by Noether symmetry approach, and the interesting point is that the cosmological constant is appeared as the direct manifestation of Hojman symmetry.
|
https://arxiv.org/abs/2010.08424v3
|
2010.08424
|
2020-10-16
|
natural-language-processing
|
2+1 dimensional gravity
|
It gives me great pleasure to review some of the joint work by Tullio Regge
and myself. We worked intensely on 2+1-dimensional gravity from 1989 for about
five years, and published 16 articles. I will present and review two of our
early articles, highlighting what I believe are the most important results,
some of them really surprising, and discuss later developments.
|
http://arxiv.org/abs/1804.08456v2
|
1804.08456
|
2018-04-24
|
natural-language-processing
|
2+1-dimensional gravity coupled to a dust shell: quantization in terms of global phase space variables
|
We perform canonical analysis of a model in which gravity is coupled to a
spherically symmetric dust shell in 2+1 spacetime dimensions. The result is a
reduced action depending on a finite number of degrees of freedom. The emphasis
is made on finding canonical variables providing the global chart for the
entire phase space of the model. It turns out that all the distinct pieces of
momentum space could be assembled into a single manifold which has
ADS^{2}-geometry, and the global chart for it is provided by the Euler angles.
This results in both non-commutativity and discreteness in coordinate space,
which allows to resolve the central singularity. We also find the map between
ADS^{2} momentum space obtained here and momentum space in Kuchar variables,
which could be helpful in extending the present results to 3+1 dimensions.
|
http://arxiv.org/abs/1812.11425v1
|
1812.11425
|
2018-12-29
|
natural-language-processing
|
(2+1)-Dimensional Gravity in Weyl Integrable Spacetime
|
We investigate (2+1)-dimensional gravity in a Weyl integrable spacetime
(WIST). We show that, unlike general relativity, this scalar-tensor theory has
a Newtonian limit for any dimension and that in three dimensions the congruence
of world lines of particles of a pressureless fluid has a non-vanishing
geodesic deviation. We present and discuss a class of static vacuum solutions
generated by a circularly symmetric matter distribution that for certain values
of the parameter w corresponds to a space-time with a naked singularity at the
center of the matter distribution. We interpret all these results as being a
direct consequence of the space-time geometry.
|
http://arxiv.org/abs/1503.04186v1
|
1503.04186
|
2015-03-13
|
natural-language-processing
|
(2+1)-dimensional interacting model of two massless spin-2 fields as a bi-gravity model
|
We propose a new group-theoretical (Chern-Simons) formulation for the
bi-metric theory of gravity in (2+1)-dimensional spacetime which describe two
interacting massless spin-2 fields. Our model has been formulated in terms of
two dreibeins rather than two metrics. We obtain our Chern-Simons gravity model
by gauging {\it mixed AdS-AdS Lie algebra} and show that it has a two
dimensional conformal field theory (CFT) at the boundary of the anti de Sitter
(AdS) solution. We show that the central charge of the dual CFT is proportional
to the mass of the AdS solution. We also study cosmological implications of our
massless bi-gravity model.
|
http://arxiv.org/abs/1705.11042v4
|
1705.11042
|
2018-04-24
|
natural-language-processing
|
(2+1)-dimensional interface dynamics: mixing time, hydrodynamic limit and Anisotropic KPZ growth
|
Stochastic interface dynamics serve as mathematical models for diverse
time-dependent physical phenomena: the evolution of boundaries between
thermodynamic phases, crystal growth, random deposition... Interesting limits
arise at large space-time scales: after suitable rescaling, the randomly
evolving interface converges to the solution of a deterministic PDE
(hydrodynamic limit) and the fluctuation process to a (in general non-Gaussian)
limit process. In contrast with the case of $(1+1)$-dimensional models, there
are very few mathematical results in dimension $(d+1), d\ge2$. As far as growth
models are concerned, the $(2+1)$-dimensional case is particularly interesting:
D. Wolf conjectured the existence of two different universality classes (called
KPZ and Anisotropic KPZ), with different scaling exponents. Here, we review
recent mathematical results on (both reversible and irreversible) dynamics of
some $(2+1)$-dimensional discrete interfaces, mostly defined through a mapping
to two-dimensional dimer models. In particular, in the irreversible case, we
discuss mathematical support and remaining open problems concerning Wolf's
conjecture on the relation between the Hessian of the growth velocity on one
side, and the universality class of the model on the other.
|
http://arxiv.org/abs/1711.05571v1
|
1711.05571
|
2017-11-15
|
natural-language-processing
|
(2+1)-dimensional KdV, fifth-order KdV, and Gardner equations derived from the ideal fluid model. Soliton, cnoidal and superposition solutions
|
We study the problem of gravity surface waves for an ideal fluid model in the (2+1)-dimensional case. We apply a systematic procedure to derive the Boussinesq equations for a given relation between the orders of four expansion parameters, the amplitude parameter $\alpha$, the long-wavelength parameter $\beta$, the transverse wavelength parameter $\gamma$, and the bottom variation parameter $\delta$. We derived the only possible (2+1)-dimensional extensions of the Korteweg-de Vries equation, the fifth-order KdV equation, and the Gardner equation in three special cases of the relationship between these parameters. All these equations are non-local. When the bottom is flat, the (2+1)-dimensional KdV equation can be transformed to the Kadomtsev-Petviashvili equation in a fixed reference frame and next to the classical KP equation in a moving frame. We have found soliton, cnoidal, and superposition solutions (essentially one-dimensional) to the (2+1)-dimensional Korteweg-de Vries equation and the Kadomtsev-Petviashvili equation.
|
https://arxiv.org/abs/2206.08964v3
|
2206.08964
|
2022-06-17
|
natural-language-processing
|
2+1 dimensional loop quantum cosmology of Bianchi I models
|
We study the anisotropic Bianchi I loop quantum cosmology in 2+1 dimensions.
Both the $\mubar$ and $\mubar'$ schemes are considered in the present paper and
the following expected results are established: (i) the massless scalar field
again play the role of emergent time variables and serves as an internal clock;
(ii) By imposing the fundamental discreteness of length operator, the total
Hamiltonian constraint is obtained and gives rise the evolution as a difference
equation; and (iii) the exact solutions of Friedmann equation are constructed
rigorously for both classical and effective level. The investigation extends
the domain of validity of loop quantum cosmology to beyond the four dimensions.
|
http://arxiv.org/abs/1602.07478v1
|
1602.07478
|
2016-02-24
|
natural-language-processing
|
$(2+1)$-dimensional regular black holes with nonlinear electrodynamics sources
|
On the basis of two requirements: the avoidance of the curvature singularity
and the Maxwell theory as the weak field limit of the nonlinear
electrodynamics, we find two restricted conditions on the metric function of
$(2+1)$-dimensional regular black hole in general relativity coupled with
nonlinear electrodynamics sources. By the use of the two conditions, we obtain
a general approach to construct $(2+1)$-dimensional regular black holes. In
this manner, we construct four $(2+1)$-dimensional regular black holes as
examples. We also study the thermodynamic properties of the regular black holes
and verify the first law of black hole thermodynamics.
|
http://arxiv.org/abs/1709.09473v1
|
1709.09473
|
2017-09-27
|
natural-language-processing
|
(2+1)$-dimensional sonic black hole from spin-orbit coupled Bose-Einstein condensate and its analogue Hawking radiation
|
We study the properties of a $2+1$ dimensional Sonic black hole (SBH) that
can be realised, in a quasi-two-dimensional two-component spin-orbit coupled
Bose-Einstein condensate (BEC). The corresponding equation for phase
fluctuations in the total density mode that describes phonon field in the
hydrodynamic approximation is described by a scalar field equation in $2+1$
dimension whose space-time metric is significantly different from that of the
SBH realised from a single component BEC that was studied experimentally, and,
theoretically meticulously in literature. Given the breakdown of the
irrotationality constraint of the velocity field in such spin-orbit coupled
BEC, we study in detail how the time evolution of such condensate impacts the
various properties of the resulting SBH. By time evolving the condensate in a
suitably created laser-induced potential, we show that such a sonic black hole
is formed, in an annular region bounded by inner and outer event horizon as
well as elliptical ergo-surfaces. We observe amplifying density modulation due
to the formation of such sonic horizons and show how they change the nature of
analogue Hawking radiation emitted from such sonic black hole by evaluating the
density-density correlation at different times, using the truncated Wigner
approximation (TWA) for different values of spin-orbit coupling parameters. We
finally investigate the thermal nature of such analogue Hawking radiation.
|
http://arxiv.org/abs/1810.04860v3
|
1810.04860
|
2020-07-29
|
natural-language-processing
|
(2+1)-dimensional Static Cyclic Symmetric Traversable Wormhole: Quasinormal Modes and Causality
|
In this paper we study a static cyclic symmetric traversable wormhole in
$(2+1)-$dimensional gravity coupled to nonlinear electrodynamics in anti-de
Sitter spacetime. The solution is characterized by three parameters: mass $M$,
cosmological constant $\Lambda$ and one electromagnetic parameter,
$q_{\alpha}$. The causality of this spacetime is studied, determining its
maximal extension and constructing then the corresponding Kruskal-Szekeres and
Penrose diagrams. The quasinormal modes (QNMs) that result from considering a
massive scalar test field in the wormhole background are determined by solving
in exact form the Klein-Gordon equation; the effective potential resembles the
one of a harmonic oscillator shifted from its equilibrium position and,
consequently, the QNMs have a pure point spectrum.
|
http://arxiv.org/abs/1906.04360v2
|
1906.04360
|
2019-10-26
|
natural-language-processing
|
2+1-dimensional traversable wormholes supported by positive energy
|
We revisit the shapes of the throats of wormholes, including thin-shell
wormholes (TSWs) in $2+1-$dimensions. In particular, in the case of TSWs this
is done in a flat $2+1-$dimensional bulk spacetime by using the standard method
of cut-and-paste. Upon departing from a pure time-dependent circular shape
i.e., $r=a\left( t\right) $ for the throat, we employ a $% \theta -$dependent
closed loop of the form $r=R\left( t,\theta \right) ,$ and in terms of $R\left(
t,\theta \right) $ we find the surface energy density $\sigma $ on the throat.
For the specific convex shapes we find that the total energy which supports the
wormhole is positive and finite. In addition to that we analyze the general
wormhole's throat. By considering a specific equation of $r=R\left( \theta
\right) $ instead of $r=r_{0}=const.,$ and upon certain choices of functions
for $R\left( \theta \right) $ we find the total energy of the wormhole to be
positive.
|
http://arxiv.org/abs/1409.2686v2
|
1409.2686
|
2015-02-17
|
natural-language-processing
|
2+1-dimensional wormhole from a doublet of scalar fields
|
We present a class of exact solutions in the framework of $2+1-$dimensional
Einstein gravity coupled minimally to a doublet of scalar fields. Our solution
can be interpreted upon tuning of parameters as an asymptotically flat wormhole
as well as a particle model in $2+1-$dimensions.
|
http://arxiv.org/abs/1507.07257v1
|
1507.07257
|
2015-07-26
|
natural-language-processing
|
2+1D symmetry-topological-order from local symmetric operators in 1+1D
|
A generalized symmetry (defined by the algebra of local symmetric operators) can go beyond group or higher group description. A theory of generalized symmetry (up to holo-equivalence) was developed in terms of symmetry-TO -- a bosonic topological order (TO) with gappable boundary in one higher dimension. We propose a general method to compute the 2+1D symmetry-TO from the local symmetric operators in 1+1D systems. Our theory is based on the commutant patch operators, which are extended operators constructed as products and sums of local symmetric operators. A commutant patch operator commutes with all local symmetric operators away from its boundary. We argue that topological invariants associated with anyon diagrams in 2+1D can be computed as contracted products of commutant patch operators in 1+1D. In particular, we give concrete formulae for several topological invariants in terms of commutant patch operators. Topological invariants computed from patch operators include those beyond modular data, such as the link invariants associated with the Borromean rings and the Whitehead link. These results suggest that the algebra of commutant patch operators is described by 2+1D symmetry-TO. Based on our analysis, we also argue briefly that the commutant patch operators would serve as order parameters for gapped phases with finite symmetries.
|
https://arxiv.org/abs/2310.05790v1
|
2310.05790
|
2023-10-09
|
natural-language-processing
|
(2+1)D topological phases with RT symmetry: many-body invariant, classification, and higher order edge modes
|
It is common in condensed matter systems for reflection ($R$) and time-reversal ($T$) symmetry to both be broken while the combination $RT$ is preserved. In this paper we study invariants that arise due to $RT$ symmetry. We consider many-body systems of interacting fermions with fermionic symmetry groups $G_f = \mathbb{Z}_2^f \times \mathbb{Z}_2^{RT}$, $U(1)^f \rtimes \mathbb{Z}_2^{RT}$, and $U(1)^f \times \mathbb{Z}_2^{RT}$. We show that (2+1)D invertible fermionic topological phases with these symmetries have a $\mathbb{Z} \times \mathbb{Z}_8$, $\mathbb{Z}^2 \times \mathbb{Z}_2$, and $\mathbb{Z}^2 \times \mathbb{Z}_4$ classification, respectively, which we compute using the framework of $G$-crossed braided tensor categories. We provide a many-body $RT$ invariant in terms of a tripartite entanglement measure, and which we show can be understood using an edge conformal field theory computation in terms of vertex states. For $G_f = U(1)^f \rtimes \mathbb{Z}_2^{RT}$, which applies to charged fermions in a magnetic field, the non-trivial value of the $\mathbb{Z}_2$ invariant requires strong interactions. For symmetry-preserving boundaries, the phases are distinguished by zero modes at the intersection of the reflection axis and the boundary. Additional invariants arise in the presence of translation or rotation symmetry.
|
https://arxiv.org/abs/2403.18887v1
|
2403.18887
|
2024-03-27
|
natural-language-processing
|
$2+1$ Einstein-Klein-Gordon black holes by gravitational decoupling
|
In this work we study the 2+1 Einstein-Klein-Gordon system in the framework of Gravitational Decoupling. We associate the generic matter decoupling sector with a real scalar field so we can obtain a constraint which allows to close the system of differential equations. The constraint corresponds to a differential equation involving the decoupling functions and the metric of the seed sector and will be independent of the scalar field itself. We show that when the equation admits analytical solutions, the scalar field and the self-interacting potential can be obtained straightforwardly. We found that, in the cases under consideration, it is possible to express the potential as an explicit function of the scalar field only for certain particular cases corresponding to limiting values of the parameters involved.
|
https://arxiv.org/abs/2203.00661v2
|
2203.00661
|
2022-03-01
|
natural-language-processing
|
2+1 Flavor Domain Wall Fermion QCD Lattices: Ensemble Production and (some) Properties
|
The RBC and UKQCD Collaborations continue to produce 2+1 flavor domain wall
fermion ensembles, currently focusing on an ensemble with a $96^3 \times 192$
volume on SUMMIT at ORNL with $1/a \approx 2.8$ GeV, and smaller ensembles at
stronger couplings. The $1/a \approx 2.8$ GeV ensemble uses the Exact One
Flavor Algorithm for the strange quark, along with the Multisplitting
Preconditioned Conjugate Gradient for solving the Dirac equation. We report on
our progress and experience to date with the evolution of this ensemble.
|
http://arxiv.org/abs/1912.13150v1
|
1912.13150
|
2019-12-31
|
natural-language-processing
|
2+1 flavor fine lattice simulation at finite temperature with domain-wall fermions
|
Simulations for the thermodynamics of the 2+1 flavor QCD are performed employing chiral fermions. The use of M\"obius domain-wall fermions with stout-link smearing is more effective on the finer lattices where all the relevant chiral symmetries are realized more accurately. We report on the initial simulations near the (pseudo) critical point using the line of constant physics with an average $ud$ quark mass slightly heavier than physical at $a\lesssim 0.1$ fm.
|
https://arxiv.org/abs/2112.11771v1
|
2112.11771
|
2021-12-22
|
natural-language-processing
|
2+1 flavor QCD simulation on a $96^4$ lattice
|
We generate $2+1$ flavor QCD configurations near the physical point on a
$96^4$ lattice employing the 6-APE stout smeared Wilson clover action with a
nonperturbative $c_{\rm SW}$ and the Iwasaki gauge action at $\beta=1.82$. The
physical point is estimated based on the chiral perturbation theory using
several data points generated by the reweighting technique from the simulation
point, wherer $m_\pi$,$m_K$ and $m_\Omega$ are used as physical inputs. The
physics results include the quark masses, the hadron spectrum, the pseudoscalar
meson decay constants and nucleon sigma terms, using the nonperturbative
renormalization factors evaluated with the Schrodinger functional method.
|
http://arxiv.org/abs/1511.09222v1
|
1511.09222
|
2015-11-30
|
natural-language-processing
|
(2+1)-flavor QCD Thermodynamics from the Gradient Flow
|
Recently, we proposed a novel method to define and calculate the
energy-momentum tensor (EMT) in lattice gauge theory on the basis of the
Yang-Mills gradient flow [1]. In this proceedings, we summarize the basic idea
and technical steps to obtain the bulk thermodynamic quantities in lattice
gauge theory using this method for the quenched and $(2+1)$-flavor QCD. The
revised results of integration measure (trace anomaly) and entropy density of
the quenched QCD with corrected coefficients are shown. Furthermore, we also
show the flow time dependence of the parts of EMT including the dynamical
fermions. This work is based on a joint-collaboration between FlowQCD and WHOT
QCD.
|
http://arxiv.org/abs/1511.03009v1
|
1511.03009
|
2015-11-10
|
natural-language-processing
|
2+1 flavors QCD equation of state at zero temperature within Dyson-Schwinger equations
|
Within the framework of Dyson-Schwinger equations (DSEs), we discuss the
equation of state (EOS) and quark number densities of 2+1 flavors, that is to
say, $u$, $d$, and $s$ quarks. The chemical equilibrium and electric charge
neutrality conditions are used to constrain the chemical potential of different
quarks. The EOS in the cases of 2 flavors and 2+1 flavors are discussed, and
the quark number densities, the pressure, and energy density per baryon are
also studied. The results show that there is a critical chemical potential for
each flavor of quark, at which the quark number density turns to nonzero from
0; and furthermore, the system with 2+1 flavors of quarks is more stable than
that with 2 flavors in the system. These discussion may provide some useful
information to some research fields, such as the studies related to the QCD
phase transitions or compact stars.
|
http://arxiv.org/abs/1506.06846v1
|
1506.06846
|
2015-06-23
|
natural-language-processing
|
(2+1) Lorentzian quantum cosmology from spin-foams: opportunities and obstacles for semi-classicality
|
We construct an effective cosmological spin-foam model for a (2+1) dimensional spatially flat universe, discretized on a hypercubical lattice, containing both space- and time-like regions. Our starting point is the recently proposed coherent state spin-foam model for (2+1) Lorentzian quantum gravity. The full amplitude is assumed to factorize into single vertex amplitudes with boundary data corresponding to Lorentzian 3-frusta. A stationary phase approximation is performed at each vertex individually, where the inverse square root of the Hessian determinant serves as a measure for the effective path integral. Additionally, a massive scalar field is coupled to the geometry, and we show that its mass renders the partition function convergent. For a single 3-frustum with time-like struts, we compute the expectation value of the bulk strut length and show that it generically agrees with the classical solutions and that it is a discontinuous function of the scalar field mass. Allowing the struts to be space-like introduces causality violations, which drive the expectation values away from the classical solutions due to the lack of an exponential suppression of these configurations. This is a direct consequence of the semi-classical amplitude only containing the real part of deficit angles, in contrast with the Lorentzian Regge action used in effective spin-foams. We give an outlook on how to evaluate the partition function on an extended discretization including a bulk spatial slice. This serves as a foundation for future investigations of physically interesting scenarios such as a quantum bounce or the viability of massive scalar field clocks. Our results demonstrate that the effective path integral in the causally regular sector serves as a viable quantum cosmology model, but that the agreement of expectation values with classical solutions is tightly bound to the path integral measure.
|
https://arxiv.org/abs/2411.08109v3
|
2411.08109
|
2024-11-12
|
natural-language-processing
|
21 Million Opportunities: A 19 Facility Investigation of Factors Affecting Hand Hygiene Compliance via Linear Predictive Models
|
This large-scale study, consisting of 21.3 million hand hygiene opportunities
from 19 distinct facilities in 10 different states, uses linear predictive
models to expose factors that may affect hand hygiene compliance. We examine
the use of features such as temperature, relative humidity, influenza severity,
day/night shift, federal holidays and the presence of new medical residents in
predicting daily hand hygiene compliance; the investigation is undertaken using
both a "global" model to glean general trends, and facility-specific models to
elicit facility-specific insights. The results suggest that colder temperatures
and federal holidays have an adverse effect on hand hygiene compliance rates,
and that individual cultures and attitudes regarding hand hygiene exist among
facilities.
|
http://arxiv.org/abs/1801.09546v1
|
1801.09546
|
2018-01-26
|
natural-language-processing
|
21 new long-term variables in the GX 339-4 field: two years of MeerKAT monitoring
|
We present 21 new long-term variable radio sources found commensally in two years of weekly MeerKAT monitoring of the low-mass X-ray binary GX 339-4. The new sources vary on time scales of weeks to months and have a variety of light curve shapes and spectral index properties. Three of the new variable sources are coincident with multi-wavelength counterparts; and one of these is coincident with an optical source in deep MeerLICHT images. For most sources, we cannot eliminate refractive scintillation of active galactic nuclei as the cause of the variability. These new variable sources represent $2.2\pm0.5$ per cent of the unresolved sources in the field, which is consistent with the 1-2 per cent variability found in past radio variability surveys. However, we expect to find short-term variable sources in the field as well as these 21 new long-term variable sources. We present the radio light curves and spectral index variability of the new variable sources, as well as the absolute astrometry and matches to coincident sources at other wavelengths.
|
https://arxiv.org/abs/2203.09806v1
|
2203.09806
|
2022-03-18
|
natural-language-processing
|
(2+1) Regge Calculus: Discrete Curvatures, Bianchi Identity, and Gauss-Codazzi Equation
|
The first results presented in our article are the clear definitions of both
intrinsic and extrinsic discrete curvatures in terms of holonomy and
plane-angle representation, a clear relation with their deficit angles, and
their clear geometrical interpretations in the first order discrete geometry.
The second results are the discrete version of Bianchi identity and
Gauss-Codazzi equation, together with their geometrical interpretations. It
turns out that the discrete Bianchi identity and Gauss-Codazzi equation, at
least in 3-dimension, could be derived from the dihedral angle formula of a
tetrahedron, while the dihedral angle relation itself is the spherical law of
cosine in disguise. Furthermore, the continuous infinitesimal curvature 2-form,
the standard Bianchi identity, and Gauss-Codazzi equation could be recovered in
the continuum limit.
|
http://arxiv.org/abs/1709.08373v1
|
1709.08373
|
2017-09-25
|
natural-language-processing
|
21st century change in ocean response to climate forcing
|
Modeling globally averaged information on climate forcing from the land
surface temperature data, the sea surface temperatures (SST) and the
empirically determined relationship between the changes in SST and the
turbulent diffusion of heat into the upper ocean demonstrates a consistent
link. The modeling is accurate throughout the 20th century despite the
different phases of the Interdecadal Pacific Oscillation (IPO) or the strong
divergence between land and ocean surface warming. It only fails during the
last 15 years when SST drops well below the trend. The finding reinforces the
view that slower global warming over the previous 15 years is not a caused by a
negative phase of the IPO or by the variations in the upper ocean (top 700 m)
warming but results from a change in the ocean behavior leading to increased
heat transfer into the deeper ocean.
|
http://arxiv.org/abs/1507.04809v1
|
1507.04809
|
2015-07-17
|
natural-language-processing
|
21st Century Computer Architecture
|
Because most technology and computer architecture innovations were
(intentionally) invisible to higher layers, application and other software
developers could reap the benefits of this progress without engaging in it.
Higher performance has both made more computationally demanding applications
feasible (e.g., virtual assistants, computer vision) and made less demanding
applications easier to develop by enabling higher-level programming
abstractions (e.g., scripting languages and reusable components). Improvements
in computer system cost-effectiveness enabled value creation that could never
have been imagined by the field's founders (e.g., distributed web search
sufficiently inexpensive so as to be covered by advertising links).
The wide benefits of computer performance growth are clear. Recently,
Danowitz et al. apportioned computer performance growth roughly equally between
technology and architecture, with architecture credited with ~80x improvement
since 1985. As semiconductor technology approaches its "end-of-the-road" (see
below), computer architecture will need to play an increasing role in enabling
future ICT innovation. But instead of asking, "How can I make my chip run
faster?," architects must now ask, "How can I enable the 21st century
infrastructure, from sensors to clouds, adding value from performance to
privacy, but without the benefit of near-perfect technology scaling?". The
challenges are many, but with appropriate investment, opportunities abound.
Underlying these opportunities is a common theme that future architecture
innovations will require the engagement of and investments from innovators in
other ICT layers.
|
http://arxiv.org/abs/1609.06756v1
|
1609.06756
|
2016-09-21
|
natural-language-processing
|
21st Century Global and Regional Surface Temperature Projections
|
Many regions across the globe broke their surface temperature records in recent years, further sparking concerns about the impending arrival of "tipping points" later in the 21st century. This study analyzes observed global surface temperature trends in three target latitudinal regions: the Arctic Circle, the Tropics, and the Antarctic Circle. We show that global warming is accelerating unevenly across the planet, with the Arctic warming at approximately three times the average rate of our world. We further analyzed the reliability of latitude-dependent surface temperature simulations from a suite of Coupled Model Intercomparison Project Phase 6 models and their multi-model mean. We found that GISS-E2-1-G and FGOALS-g3 were the best-performing models based on their statistical abilities to reproduce observational, latitude-dependent data. Surface temperatures were projected from ensemble simulations of the Shared Socioeconomic Pathway 2-4.5 (SSP2-4.5). We estimate when the climate will warm by 1.5, 2.0, and 2.5 degrees C relative to the preindustrial period, globally and regionally. GISS-E2-1-G projects that global surface temperature anomalies would reach 1.5, 2.0, and 2.5 degrees C in 2024 (+/-1.34), 2039 (+/-2.83), and 2057 (+/-5.03) respectively, while FGOALS-g3 predicts these "tipping points" would arrive in 2024 (+/-2.50), 2054 (+/-7.90), and 2087 (+/-10.55) respectively. Our results reaffirm a dramatic, upward trend in projected climate warming acceleration, with upward concavity in 21st century projections of the Arctic, which could lead to catastrophic consequences across the Earth. Further studies are necessary to determine the most efficient solutions to reduce global warming acceleration and maintain a low SSP, both globally and regionally.
|
https://arxiv.org/abs/2210.03245v2
|
2210.03245
|
2022-10-06
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natural-language-processing
|
21st Century Planar Field Emission Theory and its Role in Vacuum Breakdown Science
|
For explaining electrical breakdown, field electron emission (FE) is a mechanism of interest. In the period 2006 to 2010 there were significant developments in basic FE theory, but these have not yet fully entered general thinking in technological FE areas, which are often still based on 1960s thinking or (in some contexts) 1920s thinking about FE theory. This paper outlines the history of FE theory and provides an overview of modern developments and of some related topics, in so far as these affect the interpretation of experiments and the explanation of physical phenomena. The paper concentrates on principles, with references given where details can be found. Some suggestions are made about moving to the use of "21st-Century" FE theory. In addition, an error in Feynman's treatment of the electrostatics of pointed conductors is displayed, and it is found that Zener tunneling is implausible as a primary cause of vacuum breakdown from a CuO overlayer.
|
https://arxiv.org/abs/2107.08801v2
|
2107.08801
|
2021-07-19
|
natural-language-processing
|
21st Century Statistical and Computational Challenges in Astrophysics
|
Modern astronomy has been rapidly increasing our ability to see deeper into
the universe, acquiring enormous samples of cosmic populations. Gaining
astrophysical insights from these datasets requires a wide range of
sophisticated statistical and machine learning methods. Long-standing problems
in cosmology include characterization of galaxy clustering and estimation of
galaxy distances from photometric colors. Bayesian inference, central to
linking astronomical data to nonlinear astrophysical models, addresses problems
in solar physics, properties of star clusters, and exoplanet systems.
Likelihood-free methods are growing in importance. Detection of faint signals
in complicated noise is needed to find periodic behaviors in stars and detect
explosive gravitational wave events. Open issues concern treatment of
heteroscedastic measurement errors and understanding probability distributions
characterizing astrophysical systems. The field of astrostatistics needs
increased collaboration with statisticians in the design and analysis stages of
research projects, and to jointly develop new statistical methodologies.
Together, they will draw more astrophysical insights into astronomical
populations and the cosmos itself.
|
http://arxiv.org/abs/2005.13025v1
|
2005.13025
|
2020-05-26
|
natural-language-processing
|
$21^{st}$ Century Statistical Disclosure Limitation: Motivations and Challenges
|
This chapter examines the motivations and imperatives for modernizing how statistical agencies approach statistical disclosure limitation for official data product releases. It discusses the implications for agencies' broader data governance and decision-making, and it identifies challenges that agencies will likely face along the way. In conclusion, the chapter proposes some principles and best practices that we believe can help guide agencies in navigating the transformation of their confidentiality programs.
|
https://arxiv.org/abs/2303.00845v1
|
2303.00845
|
2023-03-01
|
natural-language-processing
|
21 years of Astronomy at Warwick: celebrating the legacy of Prof. Tom Marsh
|
Between the 4th and 6th of September 2024, the Astronomy & Astrophysics group at the University of Warwick held a meeting to celebrate 21 years of astronomy at Warwick and the scientific legacy of the late Prof. Tom Marsh, the group founder. More than a hundred people attended the meeting, with about half of the attendees being external delegates and coming from as far afield as the USA and South Africa. Tom Marsh moved to the University of Warwick from Southampton in 2003, after the Department of Physics decided to expand the scope of its research. From its humble beginnings with only two staff members, Tom himself and Boris G\"ansicke, one postdoc and a couple of PhD students, the group has now grown to more than 95 members, including 25 staff. Tom pioneered the development of Doppler tomography, led key discoveries in the field of double-degenerate binary systems and made extensive contributions to instrumentation, primarily to developing the high-speed imaging photometers ULTRACAM, ULTRASPEC and HiPERCAM. This article provides a summary of Tom's legacy and Warwick's history as presented in the 21 years of Astronomy at Warwick meeting.
|
https://arxiv.org/abs/2504.20954v1
|
2504.20954
|
2025-04-29
|
natural-language-processing
|
21-year timing of the black-widow pulsar J2051-0827
|
Timing results for the black-widow pulsar J2051-0827 are presented, using a
21-year dataset from four European Pulsar Timing Array telescopes and the
Parkes radio telescope. This dataset, which is the longest published to date
for a black-widow system, allows for an improved analysis that addresses
previously unknown biases. While secular variations, as identified in previous
analyses, are recovered, short-term variations are detected for the first time.
Concurrently, a significant decrease of approx. 2.5x10-3 cm-3 pc in the
dispersion measure associated with PSR J2051-0827 is measured for the first
time and improvements are also made to estimates of the proper motion. Finally,
PSR J2051-0827 is shown to have entered a relatively stable state suggesting
the possibility of its eventual inclusion in pulsar timing arrays.
|
http://arxiv.org/abs/1607.04167v1
|
1607.04167
|
2016-07-14
|
natural-language-processing
|
220 GHz RIS-Aided Multi-user Terahertz Communication System: Prototype Design and Over-the-Air Experimental Trials
|
Terahertz (THz) communication technology is regarded as a promising enabler for achieving ultra-high data rate transmission in next-generation communication systems. To mitigate the high path loss in THz systems, the transmitting beams are typically narrow and highly directional, which makes it difficult for a single beam to serve multiple users simultaneously. To address this challenge, reconfigurable intelligent surfaces (RIS), which can dynamically manipulate the wireless propagation environment, have been integrated into THz communication systems to extend coverage. Existing works mostly remain theoretical analysis and simulation, while prototype validation of RIS-assisted THz communication systems is scarce. In this paper, we designed a liquid crystal-based RIS operating at 220 GHz supporting both single-user and multi-user communication scenarios, followed by a RIS-aided THz communication system prototype. To enhance the system performance, we developed a beamforming method including a real-time power feedback control, which is compatible with both single-beam and multibeam modes. To support simultaneous multi-user transmission, we designed an OFDM-based resource allocation scheme. In our experiments, the received power gain with RIS is no less than 10 dB in the single-beam mode, and no less than 5 dB in the multi-beam mode. With the assistance of RIS, the achievable rate of the system could reach 2.341 Gbps with 3 users sharing 400 MHz bandwidth and the bit error rate (BER) of the system decreased sharply. Finally, an image transmission experiment was conducted to vividly show that the receiver could recover the transmitted information correctly with the help of RIS. The experimental results also demonstrated that the received signal quality was enhanced through power feedback adjustments.
|
https://arxiv.org/abs/2502.16970v1
|
2502.16970
|
2025-02-24
|
natural-language-processing
|
220 GHz Urban Microcell Channel Measurement and Characterization on a University Campus
|
Owning abundant bandwidth resources, the Terahertz (THz) band (0.1-10~THz) is envisioned as a key technology to realize ultra-high-speed communications in 6G and beyond wireless networks. To realize reliable THz communications in urban microcell (UMi) environments, propagation analysis and channel characterization are still insufficient. In this paper, channel measurement campaigns are conducted in a UMi scenario at 220~GHz, using a correlation-based time domain channel sounder. 24 positions are measured along a road on the university campus, with distances ranging from 34~m to 410~m. Based on the measurement results, the spatial consistency and interaction of THz waves to the surrounding environments are analyzed. Moreover, the additional loss due to foliage blockage is calculated and an average value of 16.7~dB is observed. Furthermore, a full portrait of channel characteristics, including path loss, shadow fading, K-factor, delay and angular spreads, as well as cluster parameters, is calculated and analyzed. Specifically, an average K-factor value of 17.5 dB is measured in the line-of-sight (LoS) case, which is nearly two times larger than the extrapolated values from the 3GPP standard, revealing weak multipath effects in the THz band. Additionally, 2.5 clusters on average are observed in the LoS case, around one fifth of what is defined in the 3GPP model, which uncovers the strong sparsity in THz UMi. The results and analysis in this work can offer guidance for system design for future THz UMi networks.
|
https://arxiv.org/abs/2408.15772v1
|
2408.15772
|
2024-08-28
|
natural-language-processing
|
$^{222}$Rn contamination mechanisms on acrylic surfaces
|
In this work, the $^{222}$Rn contamination mechanisms on acrylic surfaces
have been investigated. $^{222}$Rn can represent a significant background
source for low-background experiments, and acrylic is a suitable material for
detector design thanks to its purity and transparency. Four acrylic samples
have been exposed to a $^{222}$Rn rich environment for different time periods,
being contaminated by $^{222}$Rn and its progenies. Subsequently, the time
evolution of radiocontaminants activity on the samples has been evaluated with
$\alpha$ and $\gamma$ measurements, highlighting the role of different decay
modes in the contamination process. A detailed analysis of the alpha spectra
allowed to quantify the implantation depth of the contaminants. Moreover, a
study of both $\alpha$ and $\gamma$ measurements pointed out the $^{222}$Rn
diffusion inside the samples.
|
http://arxiv.org/abs/1911.04836v1
|
1911.04836
|
2019-11-12
|
natural-language-processing
|
$^{222}$Rn content variations at ground and underground conditions
|
The activity of $^{222}$Rn and its daughter isotopes was measured in the air of several underground laboratories of the Baksan Neutrino Observatory at various distances from the entrance. The measurements were carried out with the help of the cylindrical ionionization air chamber. We found that the radon content in the ventilated airflow within the measurement accuracy does not depend on the distance travelled along the adit. In addition, we observed that the radon content increases abruptly in those locations where underground gases and water are released. As a result, we review various mechanisms of air enrichment with radon. We also outline our research methodology and present the results of our measurements of radon release from the rocky walls of the underground laboratory. Finally, we present the results of the measurements of the radon content of various ground and underground water sources.
|
https://arxiv.org/abs/2110.15289v2
|
2110.15289
|
2021-10-28
|
natural-language-processing
|
$^{222}$Rn emanation measurements for the XENON1T experiment
|
The selection of low-radioactive construction materials is of utmost
importance for the success of low-energy rare event search experiments. Besides
radioactive contaminants in the bulk, the emanation of radioactive radon atoms
from material surfaces attains increasing relevance in the effort to further
reduce the background of such experiments. In this work, we present the
$^{222}$Rn emanation measurements performed for the XENON1T dark matter
experiment. Together with the bulk impurity screening campaign, the results
enabled us to select the radio-purest construction materials, targeting a
$^{222}$Rn activity concentration of 10 $\mu$Bq/kg in 3.2 t of xenon. The
knowledge of the distribution of the $^{222}$Rn sources allowed us to
selectively eliminate critical components in the course of the experiment. The
predictions from the emanation measurements were compared to data of the
$^{222}$Rn activity concentration in XENON1T. The final $^{222}$Rn activity
concentration of (4.5 $\pm$ 0.1) $\mu$Bq/kg in the target of XENON1T is the
lowest ever achieved in a xenon dark matter experiment.
|
http://arxiv.org/abs/2009.13981v2
|
2009.13981
|
2020-09-30
|
natural-language-processing
|
$^{229}\mathrm{ThF}_4$ thin films for solid-state nuclear clocks
|
After nearly fifty years of searching, the vacuum ultraviolet $^{229}$Th nuclear isomeric transition has recently been directly laser excited [1,2] and measured with high spectroscopic precision [3]. Nuclear clocks based on this transition are expected to be more robust [4,5] than and may outperform [6,7] current optical atomic clocks. They also promise sensitive tests for new physics beyond the standard model [5,8,9]. In light of these important advances and applications, a dramatic increase in the need for $^{229}$Th spectroscopy targets in a variety of platforms is anticipated. However, the growth and handling of high-concentration $^{229}$Th-doped crystals [5] used in previous measurements [1-3,10] are challenging due to the scarcity and radioactivity of the $^{229}$Th material. Here, we demonstrate a potentially scalable solution to these problems by demonstrating laser excitation of the nuclear transition in $^{229}$ThF$_4$ thin films grown with a physical vapor deposition process, consuming only micrograms of $^{229}$Th material. The $^{229}$ThF$_4$ thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical \thor-doped crystals [1-3,10]. The high nuclear emitter density in $^{229}$ThF$_4$ also potentially enables quantum optics studies in a new regime. Finally, we describe the operation and present the estimation of the performance of a nuclear clock based on a defect-free ThF$_4$ crystal.
|
https://arxiv.org/abs/2410.01753v1
|
2410.01753
|
2024-10-02
|
natural-language-processing
|
229 nm UV LEDs using p-type silicon for increased hole injection
|
Ultraviolet (UV) light emission at 229 nm wavelength from diode structures
based on AlN/Al0.77Ga0.23N quantum wells and using p-type Si to significantly
increase hole injection was reported. Both electrical and optical
characteristics were measured. Owing to the large concentration of holes from
p-Si and efficient hole injection, no efficiency droop was observed up to a
current density of 76 A/cm2 under continuous wave operation and without
external thermal management. An optical output power of 160 uW was obtained
with corresponding external quantum efficiency of 0.027%. This study
demonstrates that by adopting p-type Si nanomembrane contacts as hole injector,
practical levels of hole injection can be realized in UV light-emitting diodes
with very high Al composition AlGaN quantum wells, enabling emission
wavelengths and power levels that were previously inaccessible using
traditional p-i-n structures with poor hole injection efficiency.
|
http://arxiv.org/abs/1708.03973v1
|
1708.03973
|
2017-08-13
|
natural-language-processing
|
229Th-doped nonlinear optical crystals for compact solid-state clocks
|
The recent laser excitation of the 229Th isomeric transition in a solid-state host opens the door for a portable solid-state nuclear optical clock. However, at present the vacuum-ultraviolet laser systems required for clock operation are not conducive to a fieldable form factor. Here, we propose a possible solution to this problem by using 229Th-doped nonlinear optical crystals, which would allow clock operation without a vacuum-ultraviolet laser system and without the need of maintaining the crystal under vacuum.
|
https://arxiv.org/abs/2410.23364v1
|
2410.23364
|
2024-10-30
|
natural-language-processing
|
(2,2) and (0,4) Supersymmetric Boundary Conditions in 3d N = 4 Theories and Type IIB Branes
|
The half-BPS boundary conditions preserving $\mathcal{N}=(2,2)$ and
$\mathcal{N}=(0,4)$ supersymmetry in 3d $\mathcal{N}=4$ supersymmetric gauge
theories are examined. The BPS equations admit decomposition of the bulk
supermultiplets into specific boundary supermultiplets of preserved
supersymmetry. Nahm-like equations arise in the vector multiplet BPS boundary
condition preserving $\mathcal{N}=(0,4)$ supersymmetry and Robin-type boundary
conditions appear for the hypermultiplet coupled to vector multiplet when
$\mathcal{N}=(2,2)$ supersymmetry is preserved. The half-BPS boundary
conditions are realized in the brane configurations of Type IIB string theory.
|
http://arxiv.org/abs/1608.05363v4
|
1608.05363
|
2017-11-30
|
natural-language-processing
|
2+2D Texture for Full Positive Parallax Effect
|
The representation of parallax on virtual environment is still a problem to be studied. Common algorithms, such as Bump Mapping, Parallax Mapping and Displacement Mapping, treats this problem for small disparity between a real object and a simplified model. This work will introduce a new texture structure and one possible render algorithm able to display parallax for large disparities, it is an approach based on the four-dimensional representation of the Light Field and was thought to positive parallax and to display the surfaces on the inside of our simplified model. These conditions are imposed to allow the free movement of an observer, if its movement is restrict, these conditions may be loosen. It is a high storage low process approach possible to be used in real time systems. As an example we will develop a scene with several objects and simplified them by a unique sphere that encloses them all, our system was able to run this scene with about 180fps.
|
https://arxiv.org/abs/2402.16815v1
|
2402.16815
|
2024-02-26
|
natural-language-processing
|
22 Examples of Solution Compression via Derandomization
|
We provide bounds on the compression size of the solutions to 22 problems in computer science. For each problem, we show that solutions exist with high probability, for some simple probability measure. Once this is proven, derandomization can be used to prove the existence of a simple solution.
|
https://arxiv.org/abs/2208.11562v4
|
2208.11562
|
2022-08-24
|
natural-language-processing
|
(2,2) Geometry from Gauge Theory
|
Using gauge theory, we describe how to construct generalized Kahler
geometries with (2,2) two-dimensional supersymmetry, which are analogues of
familiar examples like projective spaces and Calabi-Yau manifolds. For special
cases, T-dual descriptions can be found which are squashed Kahler spaces. We
explore the vacuum structure of these gauge theories by studying the Coulomb
branch, which usually encodes the quantum cohomology ring. Some models without
Kahler dual descriptions possess unusual Coulomb branches. Specifically, there
appear to be an infinite number of supersymmetric vacua.
|
http://arxiv.org/abs/1810.01388v2
|
1810.01388
|
2018-10-16
|
natural-language-processing
|
2-2-holes simplified
|
Quadratic gravity illustrates how a replacement for black holes can emerge from a UV completion of gravity. 2-2-holes are extremely compact horizonless objects with an entropy $S_{22}$ due to trapped normal matter, and in this way they are conceptually easy to understand. But the field equations are cumbersome and the numerical analysis has so far been restricted to relatively small size solutions. Here we show how the properties of arbitrarily large 2-2-holes can be found, including the time delay for gravitational wave echoes and the result $T_\infty S_{22}=M/2$. The starting point is to formulate the metric in terms of the tortoise coordinate, and to have one of the two metric functions be a conformal factor. A large conformally-related volume becomes associated with the interior of a 2-2-hole. We also discuss implications for the weak gravity conjecture.
|
https://arxiv.org/abs/2202.08442v2
|
2202.08442
|
2022-02-17
|
natural-language-processing
|
$^{22}$Na Activation Level Measurements of Fused Silica Rods in the LHC Target Absorber for Neutrals (TAN) Compared to FLUKA Simulations
|
The Target Absorbers for Neutrals (TANs) are located in a high-intensity radiation environment inside the tunnel of the Large Hadron Collider (LHC). TANs are positioned about $140$ m downstream from the beam interaction points. Seven $40$ cm long fused silica rods with different dopant specifications were irradiated in the TAN by the Beam RAte of Neutrals (BRAN) detector group during $p$+$p$ data taking from 2016 to 2018 at the LHC. The peak dose delivered to the fused silica rods was $18$ MGy. We report measurements of the $^{22}$Na activation of the fused silica rods carried out at the University of Illinois at Urbana-Champaign and Argonne National Laboratory. At the end of the irradiation campaign, the maximum $^{22}$Na activity observed was $A=21$ kBq$/{\rm cm^3}$ corresponding to a density, $\rho= 2.5\times 10^{12} /{\rm cm^3}$, of $^{22}$Na nuclei. FLUKA Monte Carlo simulations have been performed by the CERN FLUKA team to estimate $^{22}$Na activities for the irradiated BRAN rod samples. The simulations reproduce the $^{22}$Na activity profile measured along the rods, with a 35% underestimation of the experimental measurement results.
|
https://arxiv.org/abs/2204.01937v2
|
2204.01937
|
2022-04-05
|
natural-language-processing
|
$^{22}$Ne and $^{23}$Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for $^{22}$Ne(p,$\gamma$)$^{23}$Na
|
We investigate the impact of the new LUNA rate for the nuclear reaction
$^{22}$Ne$(p,\gamma)^{23}$Na on the chemical ejecta of intermediate-mass stars,
with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB)
stars that experience hot-bottom burning. To this aim we use the PARSEC and
COLIBRI codes to compute the complete evolution, from the pre-main sequence up
to the termination of the TP-AGB phase, of a set of stellar models with initial
masses in the range $3.0\,M_{\odot} - 6.0\,M_{\odot}$, and metallicities
$Z_{\rm i}=0.0005$, $Z_{\rm i}=0.006$, and $Z_{\rm i} = 0.014$. We find that
the new LUNA measures have much reduced the nuclear uncertainties of the
$^{22}$Ne and $^{23}$Na AGB ejecta, which drop from factors of $\simeq 10$ to
only a factor of few for the lowest metallicity models. Relying on the most
recent estimations for the destruction rate of $^{23}$Na, the uncertainties
that still affect the $^{22}$Ne and $^{23}$Na AGB ejecta are mainly dominated
by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection).
Finally, we discuss how the LUNA results impact on the hypothesis that invokes
massive AGB stars as the main agents of the observed O-Na anti-correlation in
Galactic globular clusters. We derive quantitative indications on the
efficiencies of key physical processes (mass loss, third dredge-up, sodium
destruction) in order to simultaneously reproduce both the Na-rich, O-poor
extreme of the anti-correlation, and the observational constraints on the CNO
abundance. Results for the corresponding chemical ejecta are made publicly
available.
|
http://arxiv.org/abs/1611.07742v1
|
1611.07742
|
2016-11-23
|
natural-language-processing
|
$^{22}$Ne Phase Separation As A Solution To The Ultramassive White Dwarf Cooling Anomaly
|
The precise astrometric measurements of the Gaia Data Release 2 have opened the door to detailed tests of the predictions of white dwarf cooling models. Significant discrepancies between theory and observations have been identified, the most striking affecting ultramassive white dwarfs. Cheng et al. (2019) found that a small fraction of white dwarfs on the so-called Q branch must experience an extra cooling delay of $\sim 8\,$Gyr not predicted by current models. $^{22}$Ne phase separation in a crystallizing C/O white dwarf can lead to a distillation process that efficiently transports $^{22}$Ne toward its center, thereby releasing a considerable amount of gravitational energy. Using state-of-the-art Monte Carlo simulations, we show that this mechanism can largely resolve the ultramassive cooling anomaly if the delayed population consists of white dwarfs with moderately above-average $^{22}$Ne abundances. We also argue that $^{22}$Ne phase separation can account for the smaller cooling delay currently missing for models of white dwarfs with more standard compositions.
|
https://arxiv.org/abs/2103.12892v1
|
2103.12892
|
2021-03-23
|
natural-language-processing
|
$(2,2p+1)$ minimal string and intersection theory I
|
In view of recent progress in studying matrix model-2D gravity duality, we reexamine some features of $(2,2p+1)$ minimal string. After reviewing both sides of the proposed correspondence in this case, a previously unnoted identification between correlation numbers of tachyon operators in certain domain of parameter space and "$p$-deformed volumes", which are certain integral transforms of topological recursion data, is described and clarified. This identification allows us to efficiently study correlation numbers at finite matter central charge. In particular, we obtain an intersection-theoretic formula and the simplest recurrent equations for them, analogous to the ones recently derived for Virasoro minimal string. These formulas might be useful in establishing a more thorough connection between worldsheet and matrix model approaches.
|
https://arxiv.org/abs/2403.02305v4
|
2403.02305
|
2024-03-04
|
natural-language-processing
|
$(2,2)$ Scattering and the Celestial Torus
|
Analytic continuation from Minkowski space to $(2,2)$ split signature spacetime has proven to be a powerful tool for the study of scattering amplitudes. Here we show that, under this continuation, null infinity becomes the product of a null interval with a celestial torus (replacing the celestial sphere) and has only one connected component. Spacelike and timelike infinity are time-periodic quotients of AdS$_3$. These three components of infinity combine to an $S^3$ represented as a toric fibration over the interval. Privileged scattering states of scalars organize into $SL(2,\mathbb{R})_L \times SL(2,\mathbb{R})_R$ conformal primary wave functions and their descendants with real integral or half-integral conformal weights, giving the normally continuous scattering problem a discrete character.
|
https://arxiv.org/abs/2101.09591v1
|
2101.09591
|
2021-01-23
|
natural-language-processing
|
(2,2) Superconformal Bootstrap in Two Dimensions
|
We find a simple relation between two-dimensional BPS N=2 superconformal
blocks and bosonic Virasoro conformal blocks, which allows us to analyze the
crossing equations for BPS 4-point functions in unitary (2,2) superconformal
theories numerically with semidefinite programming. We constrain gaps in the
non-BPS spectrum through the operator product expansion of BPS operators, in
ways that depend on the moduli of exactly marginal deformations through chiral
ring coefficients. In some cases, our bounds on the spectral gaps are observed
to be saturated by free theories, by N=2 Liouville theory, and by certain
Landau-Ginzburg models.
|
http://arxiv.org/abs/1610.05371v1
|
1610.05371
|
2016-10-17
|
natural-language-processing
|
22 Year Solar Magnetic Cycle and its relation to Convection Zone Dynamics
|
Using continuous observations for 22 years from ground-based network GONG and
space-borne instruments MDI onboard {\it SoHO} and HMI onboard {\it SDO}, we
report both global and local properties of the convection zone and their
variations with time.
|
http://arxiv.org/abs/1805.05371v1
|
1805.05371
|
2018-05-14
|
natural-language-processing
|
230,439 Test Failures Later: An Empirical Evaluation of Flaky Failure Classifiers
|
Flaky tests are tests that can non-deterministically pass or fail, even in the absence of code changes.Despite being a source of false alarms, flaky tests often remain in test suites once they are detected, as they also may be relied upon to detect true failures. Hence, a key open problem in flaky test research is: How to quickly determine if a test failed due to flakiness, or if it detected a bug? The state-of-the-practice is for developers to re-run failing tests: if a test fails and then passes, it is flaky by definition; if the test persistently fails, it is likely a true failure. However, this approach can be both ineffective and inefficient. An alternate approach that developers may already use for triaging test failures is failure de-duplication, which matches newly discovered test failures to previously witnessed flaky and true failures. However, because flaky test failure symptoms might resemble those of true failures, there is a risk of missclassifying a true test failure as a flaky failure to be ignored. Using a dataset of 498 flaky tests from 22 open-source Java projects, we collect a large dataset of 230,439 failure messages (both flaky and not), allowing us to empirically investigate the efficacy of failure de-duplication. We find that for some projects, this approach is extremely effective (with 100\% specificity), while for other projects, the approach is entirely ineffective. By analyzing the characteristics of these flaky and non-flaky failures, we provide useful guidance on how developers should rely on this approach.
|
https://arxiv.org/abs/2401.15788v1
|
2401.15788
|
2024-01-28
|
natural-language-processing
|
230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy $\rm \gamma$-ray state in 2012
|
We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon
Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and
Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI
interferometric phase information on M87 through measurement of closure phase
on the triangle of long baselines. Most of the measured closure phases are
consistent with 0$^{\circ}$ as expected by physically-motivated models for 230
GHz structure such as jet models and accretion disk models. The brightness
temperature of the event-horizon-scale structure is $\sim 1 \times 10^{10}$ K
derived from the compact flux density of $\sim 1$ Jy and the angular size of
$\sim 40 $ $\rm \mu$as $\sim$ 5.5 $R_{{\rm s}}$, which is broadly consistent
with the peak brightness of the radio cores at 1-86 GHz located within $\sim
10^2$ $R_{{\rm s}}$. Our observations occurred in the middle of an enhancement
in very-high-energy (VHE) $\rm \gamma$-ray flux, presumably originating in the
vicinity of the central black hole. Our measurements, combined with results of
multi-wavelength observations, favor a scenario in which the VHE region has an
extended size of $\sim$20-60 $R_{{\rm s}}$.
|
http://arxiv.org/abs/1505.03545v3
|
1505.03545
|
2015-06-19
|
natural-language-processing
|
23, 381, 6242, 103268, 1743183, ...: Hilbert series for CP-violating operators in SMEFT
|
We introduce a systematic method to classify the Standard Model Effective Field Theory (SMEFT) operators based on their CP properties with the Hilbert series techniques. Our method makes it possible to enumerate operators violating CP symmetry in a few seconds. We present the complete classification of dimension eight operators under CP transformation, and the number of CP-odd or CP-violating operators are listed up to dimension 14. We also provide a companion code in FORM that allows anybody to reproduce our results.
|
https://arxiv.org/abs/2212.02413v3
|
2212.02413
|
2022-12-05
|
natural-language-processing
|
23.8-GHz Acoustic Filter in Periodically Poled Piezoelectric Film Lithium Niobate With 1.52-dB IL and 19.4% FBW
|
This paper reports the first piezoelectric acoustic filter in periodically poled piezoelectric film (P3F) lithium niobate (LiNbO3) at 23.8 GHz with low insertion loss (IL) of 1.52 dB and 3-dB fractional bandwidth (FBW) of 19.4%. The filter features a compact footprint of 0.64 mm2. The third-order ladder filter is implemented with electrically coupled resonators in 150 nm bi-layer P3F 128 rotated Y-cut LiNbO3 thin film, operating in second-order symmetric (S2) Lamb mode. The record-breaking performance is enabled by the P3F LiNbO3 platform, where piezoelectric thin films of alternating orientations are transferred subsequently, facilitating efficient higher-order Lamb mode operation with simultaneously high quality factor (Q) and coupling coefficient (k2) at millimeter-wave (mmWave). Also, the multi-layer P3F stack promises smaller footprints and better nonlinearity than single-layer counterparts, thanks to the higher capacitance density and lower thermal resistance. Upon further development, the reported P3F LiNbO3 platform is promising for compact filters at mmWave.
|
https://arxiv.org/abs/2402.12194v2
|
2402.12194
|
2024-02-19
|
natural-language-processing
|
${}^{239}$Pu nuclear magnetic resonance in the candidate topological insulator PuB$_4$
|
We present a detailed nuclear magnetic resonance (NMR) study of ${}^{239}$Pu
in bulk and powdered single-crystal plutonium tetraboride (PuB$_4$), which has
recently been investigated as a potential correlated topological insulator.
This study constitutes the second-ever observation of the ${}^{239}$Pu NMR
signal, and provides unique on-site sensitivity to the rich $f$-electron
physics and insight into the bulk gap-like behavior in PuB$_4$. The
${}^{239}$Pu NMR spectra are consistent with axial symmetry of the shift tensor
showing for the first time that ${}^{239}$Pu NMR can be observed in an
anisotropic environment and up to room temperature. The temperature dependence
of the ${}^{239}$Pu shift, combined with a relatively long spin-lattice
relaxation time ($T_1$), indicate that PuB$_4$ adopts a non-magnetic state with
gap-like behavior consistent with our density functional theory (DFT)
calculations. The temperature dependencies of the NMR Knight shift and
$T_1^{-1}$--microscopic quantities sensitive only to bulk states--imply bulk
gap-like behavior confirming that PuB$_4$ is a good candidate topological
insulator. The large contrast between the ${}^{239}$Pu orbital shifts in the
ionic insulator PuO$_2$ ($\sim$~+24.7~\%) and PuB$_4$ ($\sim$~-0.5~\%) provides
a new tool to investigate the nature of chemical bonding in plutonium
materials.
|
http://arxiv.org/abs/1812.09202v1
|
1812.09202
|
2018-12-21
|
natural-language-processing
|
2-, 3- and 4-Body Decays in the Constructive Standard Model
|
We further develop the massive constructive theory of the Standard Model and
use it to calculate the amplitude and squared amplitude for all two-body
decays, a collection of weak three-body decays, as well as Higgs decay to four
neutrinos. We compare our results with those from Feynman diagrams and find
complete agreement. We show that in all the cases considered here, the
amplitudes of massive constructive theories are significantly simpler than
those resulting from Feynman diagrams. In fact, a naive counting of the number
of calculations required for a matrix-element generator to compute a
phase-space point is orders-of-magnitude smaller for the result coming from the
constructive method suggesting that these generators might benefit from this
method in the future, even in the case of massive weak amplitudes. We also
anticipate that our simpler expressions will produce numerically more stable
expressions.
|
http://arxiv.org/abs/1909.09164v2
|
1909.09164
|
2020-03-30
|
natural-language-processing
|
"23andMe confirms: I'm super white" -- Analyzing Twitter Discourse On Genetic Testing
|
Recent progress in genomics is bringing genetic testing to the masses.
Participatory public initiatives are underway to sequence the genome of
millions of volunteers, and a new market is booming with a number of companies
like 23andMe and AncestryDNA offering affordable tests directly to consumers.
Consequently, news, experiences, and views on genetic testing are increasingly
shared and discussed online and on social networks like Twitter. In this paper,
we present a large-scale analysis of Twitter discourse on genetic testing. We
collect 302K tweets from 113K users, posted over 2.5 years, by using thirteen
keywords related to genetic testing companies and public initiatives as search
keywords. We study both the tweets and the users posting them along several
axes, aiming to understand who tweets about genetic testing, what they talk
about, and how they use Twitter for that. Among other things, we find that
tweets about genetic testing originate from accounts that overall appear to be
interested in digital health and technology. Also, marketing efforts as well as
announcements, such as the FDA's suspension of 23andMe's health reports,
influence the type and the nature of user engagement.Finally, we report on
users who share screenshots of their results, and raise a few ethical and
societal questions as we find evidence of groups associating genetic testing to
racist ideologies.
|
http://arxiv.org/abs/1801.09946v2
|
1801.09946
|
2018-04-20
|
natural-language-processing
|
23-bit Metaknowledge Template Towards Big Data Knowledge Discovery and Management
|
The global influence of Big Data is not only growing but seemingly endless.
The trend is leaning towards knowledge that is attained easily and quickly from
massive pools of Big Data. Today we are living in the technological world that
Dr. Usama Fayyad and his distinguished research fellows discussed in the
introductory explanations of Knowledge Discovery in Databases (KDD) predicted
nearly two decades ago. Indeed, they were precise in their outlook on Big Data
analytics. In fact, the continued improvement of the interoperability of
machine learning, statistics, database building and querying fused to create
this increasingly popular science- Data Mining and Knowledge Discovery. The
next generation computational theories are geared towards helping to extract
insightful knowledge from even larger volumes of data at higher rates of speed.
As the trend increases in popularity, the need for a highly adaptive solution
for knowledge discovery will be necessary. In this research paper, we are
introducing the investigation and development of 23 bit-questions for a
Metaknowledge template for Big Data Processing and clustering purposes. This
research aims to demonstrate the construction of this methodology and proves
the validity and the beneficial utilization that brings Knowledge Discovery
from Big Data.
|
http://arxiv.org/abs/1503.00244v1
|
1503.00244
|
2015-03-01
|
natural-language-processing
|
(2,3)-Cordial Oriented Hypercubes
|
In this article we investigate the existence of (2,3)-cordial labelings of oriented hypercubes. In this investigation, we determine that there exists a (2,3)-cordial oriented hypercube for any dimension divisible by 3. Next, we provide examples of (2,3)-cordial oriented hypercubes of dimension not divisible by 3 and state a conjecture on existence for dimension 3k + 1. We close by presenting the only 3D oriented hypercubes up to isomorphism that are not (2,3)-cordial.
|
https://arxiv.org/abs/2012.11091v3
|
2012.11091
|
2020-12-21
|
natural-language-processing
|
(2,3) Cordial Trees and Paths
|
Recently L. B. Beasley introduced $(2,3)$-cordial labelings of directed graphs in [1]. He made two conjectures which we resolve in this article. He conjectured that every orientation of a path of length at least five is $(2,3)$ cordial, and that every tree of max degree $n =3$ has a cordial orientation. We show these two conjectures to be false. We also discuss the $(2,3)$ cordiality of orientations of the Petersen graph, and establish an upper bound for the number of edges a graph can have and still be $(2,3)$ cordial. An application of $(2,3)$ cordial labelings is also presented.
|
https://arxiv.org/abs/2012.10591v2
|
2012.10591
|
2020-12-19
|
natural-language-processing
|
23 DoF Grasping Policies from a Raw Point Cloud
|
Coordinating the motion of robots with high degrees of freedom (DoF) to grasp objects gives rise to many challenges. In this paper, we propose a novel imitation learning approach to learn a policy that directly predicts 23 DoF grasp trajectories from a partial point cloud provided by a single, fixed camera. At the core of the approach is a second-order geometric-based model of behavioral dynamics. This Neural Geometric Fabric (NGF) policy predicts accelerations directly in joint space. We show that our policy is capable of generalizing to novel objects, and combine our policy with a geometric fabric motion planner in a loop to generate stable grasping trajectories. We evaluate our approach on a set of three different objects, compare different policy structures, and run ablation studies to understand the importance of different object encodings for policy learning.
|
https://arxiv.org/abs/2411.14400v1
|
2411.14400
|
2024-11-21
|
natural-language-processing
|
23Na and 1H NMR Relaxometry of Shale at High Magnetic Field
|
Formation evaluation of unconventional reservoirs is challenging due to the
coexistence of different phases such as kerogen, bitumen, movable and bound
light hydrocarbon and water. Current low-frequency (0.05 T) nuclear magnetic
resonance (NMR) laboratory and logging methods are incapable of quantitatively
separating the different phases. We demonstrate the utility of high-field (9 T)
NMR 2D T1-T2 measurements for separating hydrocarbon and the clay-interacting
aqueous phases in shale based on the difference in the frequency dependence of
the spin-lattice relaxation time. Furthermore, we demonstrate 23Na NMR as a
promising complementary technique to conventional 1H NMR for shale fluid
typing, taking advantage of the fact that sodium ions are only present in the
aqueous phase. We validate high-field (9 T) 23Na-1H NMR relaxometry for
assessing brine-filled porosity and brine salinity in various porous materials,
including porous glass, conventional rocks, clays, and shale, and apply it for
differentiating hydrocarbon versus aqueous components and also the
clay-associated versus free water in Eagle Ford shale cores. This work lays the
groundwork for developing future downhole 23Na-1H NMR logging techniques.
|
http://arxiv.org/abs/1604.07731v1
|
1604.07731
|
2016-04-26
|
natural-language-processing
|
{23}Na nuclear spin-lattice relaxation studies of Na2Ni2TeO6
|
We report on {23}Na NMR studies of a honeycomb lattice antiferromagnet
Na2Ni2TeO6 by {23}Na nuclear spin-echo techniques. The {23}Na nuclear
spin-lattice relaxation rate 1/{23}T_1 exhibits critical divergence near a Neel
temperature T_N = 26 K, a narrow critical region, and a critical exponent w =
0.34 in 1/{23}T_1 = a (T/T_N - 1)^{-w} for Na2Ni2TeO6, and T_N = 18 K for
Na2(Ni{0.5}Cu{0.5})2TeO6. Although the uniform magnetic susceptibility of
Na2Ni2TeO6 exhibits a broad maximum at 35 K characteristic of low dimensional
spin systems, the NMR results indicate three dimensional critical phenomenon
around the Neel temperature.
|
http://arxiv.org/abs/1504.03003v1
|
1504.03003
|
2015-04-12
|
natural-language-processing
|
$^{23}$Ne Production at SARAF-I
|
In this article, we present a measurement of flow rate, yield and effusion
time of a $^{23}$Ne production and transport system. We used an
accelerator-driven Li(d,n) neutron source to produce neutrons up to 20 MeV. The
radioactive atoms were produced by a $^{23}$Na(n,p) reaction at a NaCl target.
Later, the atoms were diffused out from the NaCl crystals and effused from the
production chamber via a 10 m hose to a measurement cell and their decay
products were detected using high purity germanium (HPGe) and plastic
scintillator detectors. The resulting flow rate was $6.9\pm0.5\cdot
10^4\sfrac{atoms}{sec}$ and the total yield was
$3.2\pm0.4\cdot10^{-9}\sfrac{atoms}{deuteron}$. We summarize our methods and
estimates of efficiencies, rates of production and effusion.
|
http://arxiv.org/abs/2006.00478v1
|
2006.00478
|
2020-05-31
|
natural-language-processing
|
2413-balloon permutations and the growth of the M\"obius function
|
We show that the growth of the principal M\"obius function on the permutation
poset is exponential. This improves on previous work, which has shown that the
growth is at least polynomial. We define a method of constructing a permutation
from a smaller permutation which we call "ballooning". We show that if $\beta$
is a 2413-balloon, and $\pi$ is the 2413-balloon of $\beta$, then $\mu[1, \pi]
= 2 \mu[1, \beta]$. This allows us to construct a sequence of permutations
$\pi_1, \pi_2, \pi_3\ldots$ with lengths $n, n+4, n+8, \ldots$ such that $\mu
[1, \pi_{i+1}] = 2 \mu [1, \pi_{i}]$, and this gives us exponential growth.
Further, our construction method gives permutations that lie within a
hereditary class with finitely many simple permutations. We also find an
expression for the value of $\mu[1, \pi]$, where $\pi$ is a 2413-balloon, with
no restriction on the permutation being ballooned.
|
http://arxiv.org/abs/1812.05064v3
|
1812.05064
|
2019-12-12
|
natural-language-processing
|
$^{242m}$Am isomer yield in $^{243}$Am$(n, 2n)$ reaction
|
The reaction 243 Am (n, 2n) populates the T of 16 hours ground state 242 g Am with J of 1 or the 242 m Am isomer state J of 5 with T of 141 years. The former state 242 g Am mostly beta decays to 242 Cm, or transmutes to 242 Pu via electron capture. The absolute yield of 242 g Am is compatible with the measured data, estimated by the alpha activity of 242 Cm by Norris in 1983. The branching ratio defined by the ratio of the populations of the lowest intrinsic states of 242 Am. Calculated yields of ground 242 g Am and isomer 242 m Am states of the residual nucleus 242 Am are used to predict the relative yield of isomer. These populations defined by the gamma decay of the excited states, described by the standard kinetic equation. The ordering of the low and high spin states is different in case of 236 Np and 242 Am nuclei, that explains different shapes of relative yields near the (n, 2n) reaction threshold, though the excitation energy dependences are similar. Data of 243 Am (n, F) at 5 MeV and 15 MeV by Drapchinsky in 2004, support calculated 243Am (n,xnf) prefission neutron contribution to prompt fission neutron spectra and calculated exclusive neutron spectra of 243 Am (n, 2n) feeding the 242 g Am and isomer 242 m Am states.
|
https://arxiv.org/abs/2406.15445v1
|
2406.15445
|
2024-05-30
|
natural-language-processing
|
24/7 Place Recognition by View Synthesis
|
We address the problem of large-scale visual place recognition for situations where the scene undergoes a major change in appearance, for example, due to illumination (day/night), change of seasons, aging, or structural modifications over time such as buildings built or destroyed. Such situations represent a major challenge for current large-scale place recognition methods. This work has the following three principal contributions. First, we demonstrate that matching across large changes in the scene appearance becomes much easier when both the query image and the database image depict the scene from approximately the same viewpoint. Second, based on this observation, we develop a new place recognition approach that combines (i) an efficient synthesis of novel views with (ii) a compact indexable image representation. Third, we introduce a new challenging dataset of 1,125 camera-phone query images of Tokyo that contain major changes in illumination (day, sunset, night) as well as structural changes in the scene. We demonstrate that the proposed approach significantly outperforms other large-scale place recognition techniques on this challenging data.
|
http://openaccess.thecvf.com/content_cvpr_2015/html/Torii_247_Place_Recognition_2015_CVPR_paper.html
| null |
2015-06-01
|
natural-language-processing
|
$(2,4)$-Colorability of Planar Graphs Excluding $3$-, $4$-, and $6$-Cycles
|
A defective $k$-coloring is a coloring on the vertices of a graph using colors $1,2, \dots, k$ such that adjacent vertices may share the same color. A $(d_1,d_2)$-\emph{coloring} of a graph $G$ is a defective $2$-coloring of $G$ such that any vertex colored by color $i$ has at most $d_i$ adjacent vertices of the same color, where $i\in\{1,2\}$. A graph $G$ is said to be $(d_1,d_2)$-\emph{colorable} if it admits a $(d_1,d_2)$-coloring. Defective $2$-coloring in planar graphs without $3$-cycles, $4$-cycles, and $6$-cycles has been investigated by Dross and Ochem, as well as Sittitrai and Pimpasalee. They showed that such graphs are $(0,6)$-colorable and $(3,3)$-colorable, respectively. In this paper, we proved that these graphs are also $(2,4)$-colorable.
|
https://arxiv.org/abs/2501.07129v1
|
2501.07129
|
2025-01-13
|
natural-language-processing
|
24 days-stable CNOT-gate on fluxonium qubits with over 99.9% fidelity
|
Fluxonium qubit is a promising building block for quantum information processing due to its long coherence time and strong anharmonicity. In this paper, we realize a 60 ns direct CNOT-gate on two inductively-coupled fluxonium qubits using selective darkening approach, resulting in a gate fidelity as high as 99.94%. The fidelity remains above 99.9% for 24 days without any recalibration between randomized benchmarking measurements. Compared with the 99.96% fidelity of a 60 ns identity gate, our data brings the investigation of the non-decoherence-related errors during gate operations down to $2 \times 10^{-4}$. The present result adds a simple and robust two-qubit gate into the still relatively small family of "the beyond three nines" demonstrations on superconducting qubits.
|
https://arxiv.org/abs/2407.15783v2
|
2407.15783
|
2024-07-22
|
natural-language-processing
|
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