cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
The effect of heavy ions on the dispersion properties of kinetic Alfvén waves in astrophysical plasmas
Creators: name: Villarroel-Sepúlveda, Nicolás
name: López, Rodrigo A.
name: Moya, Pablo S.
Publisher: name: arXiv
Year: 2023
Subjects: subject: Plasma Physics (physics.plasm-ph)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: Context. Spacecraft measurements have shown Kinetic Alfvén Waves propagating in the terrestrial magnetosphere at lower wavenormal angles than predicted by linear Vlasov theory of electron-proton plasmas. To explain these observations, it has been suggested that the abundant heavy ion populations in this region may have strong, non-trivial effects that allow Alfvénic waves to acquire right-handed polarization at lower angles with respect to the background magnetic field, as in the case of typical electron-proton plasma. Aims. We study the dispersion properties of Alfvénic waves in plasmas with stationary phase-space distribution functions with different heavy ion populations. Our extensive numerical analysis has allowed us to quantify the role of the heavy ion components on the transition from the left-hand polarized electromagnetic ion-cyclotron (EMIC) mode to the right-hand polarized kinetic Alfvén wave (KAW) mode. Methods. We used linear Vlasov-Maxwell theory to obtain the dispersion relation for oblique electromagnetic waves. The dispersion relation of Alfvén waves was obtained numerically by considering four different oxygen ion concentrations ranging between 0.0 and 0.2 for all propagation angles, as a function of both the wavenumber and the plasma beta parameter. Results. The inclusion of the heavy O+ ions is found to considerably reduce the transition angle from EMIC to KAW both as a function of the wave number and plasma beta. With increasing O+ concentrations, waves become more damped in specific wavenumber regions. However, the inclusion of oxygen ions may allow weakly damped KAW to effectively propagate at smaller wave-normal angles than in the electron-proton case, as suggested by observations.
description: 11 pages, 8 figures
Noncommutative Dirac quantization condition using the Seiberg-Witten map
Creators: name: Maceda, Marco
name: Martínez-Carbajal, Daniel
Publisher: name: arXiv
Year: 2016
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: We investigate the validity of the Dirac quantization condition (DQC) for magnetic monopoles in noncommutative space-time. We use an approach based on an extension of the method introduced by Wu and Yang; the effects of noncommutativity are analyzed using the Seiberg-Witten map and the corresponding deformed Maxwell's equations are discussed. By means of a perturbation expansion in the noncommutativity parameter $θ$, we show first that the DQC remains unmodified up to the first and second order. This result is then generalized to all orders in the expansion parameter for a class of noncommutative electric currents induced by the Seiberg-Witten map; these currents reduce to the Dirac delta function in the commutative limit.
description: 12 pages
Electron-Scale Current Sheets and Energy Dissipation in 3D Kinetic-Scale Plasma Turbulence with Low Electron Beta
Creators: name: Vega, Cristian
name: Roytershteyn, Vadim
name: Delzanno, Gian Luca
name: Boldyrev, Stanislav
Publisher: name: arXiv
Year: 2023
Subjects: subject: Plasma Physics (physics.plasm-ph)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: 3D kinetic-scale turbulence is studied numerically in the regime where electrons are strongly magnetized (the ratio of plasma species pressure to magnetic pressure is $β_e=0.1$ for electrons and $β_i=1$ for ions). Such a regime is relevant in the vicinity of the solar corona, the Earth's magnetosheath, and other astrophysical systems. The simulations, performed using the fluid-kinetic spectral plasma solver (SPS) code, demonstrate that the turbulent cascade in such regimes can reach scales smaller than the electron inertial scale, and results in the formation of electron-scale current sheets (ESCS). Statistical analysis of the geometrical properties of the detected ESCS is performed using an algorithm based on the medial axis transform. A typical half-thickness of the current sheets is found to be on the order of electron inertial length or below, while their half-length falls between the electron and ion inertial length. The pressure-strain interaction, used as a measure of energy dissipation, exhibits high intermittency, with the majority of the total energy exchange occurring in current structures occupying approximately 20\% of the total volume. Some of the current sheets corresponding to the largest pressure-strain interaction are found to be associated with Alfvénic electron jets and magnetic configurations typical of reconnection. These reconnection candidates represent about $1$\% of all the current sheets identified.
description: 9 pages, 6 figures. Submitted for publication to MNRAS. Fixed missing references
A Hybrid Model for Estimating Software Project Effort from Use Case Points
Creators: name: Azzeh, Mohammad
name: Nassif, Ali Bou
Publisher: name: arXiv
Year: 2016
Subjects: subject: Software Engineering (cs.SE)
subject: FOS: Computer and information sciences

description: Early software effort estimation is a hallmark of successful software project management. Building a reliable effort estimation model usually requires historical data. Unfortunately, since the information available at early stages of software development is scarce, it is recommended to use software size metrics as key cost factor of effort estimation. Use Case Points (UCP) is a prominent size measure designed mainly for object-oriented projects. Nevertheless, there are no established models that can translate UCP into its corresponding effort, therefore, most models use productivity as a second cost driver. The productivity in those models is usually guessed by experts and does not depend on historical data, which makes it subject to uncertainty. Thus, these models were not well examined using a large number of historical data. In this paper, we designed a hybrid model that consists of classification and prediction stages using a support vector machine and radial basis neural networks. The proposed model was constructed over a large number of observations collected from industrial and student projects. The proposed model was compared against previous UCP prediction models. The validation and empirical results demonstrated that the proposed model significantly surpasses these models on all datasets. The main conclusion is that the environmental factors of UCP can be used to classify and estimate productivity.
Clifford group is not a semidirect product in dimensions $N$ divisible by four
Creators: name: Korbelář, Miroslav
name: Tolar, Jiří
Publisher: name: arXiv
Year: 2023
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: The paper is devoted to projective Clifford groups of quantum $N$-dimensional systems. Clearly, Clifford gates allow only the simplest quantum computations which can be simulated on a classical computer (Gottesmann-Knill theorem). However, it may serve as a cornerstone of full quantum computation. As to its group structure it is well-known that -- in $N$-dimensional quantum mechanics -- the Clifford group is a natural semidirect product provided the dimension $N$ is an odd number. For even $N$ special results on the Clifford groups are scattered in the mathematical literature, but they don't concern the semidirect structure. Using appropriate group presentation of $SL(2,Z_N)$ it is proved that for even $N$ projective Clifford groups are not natural semidirect products if and only if $N$ is divisible by four.
description: 28 pages
The prediction of using LHAASO's cosmic-ray electron measurements to constrain decaying heavy dark matter
Creators: name: Zhu, Ben-Yang
name: Liang, Yun-Feng
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: LHAASO is an instrument designed for detecting cosmic rays (CRs) and gamma rays at TeV to PeV energies. The decays of heavy dark matter particles in the Galactic halo may produce high-energy electrons that can be detected by LHAASO. The main background for the LHAASO's CR electron measurements is the hadron residuals due to mis-identification of the particle species. In this paper, we estimate the LHAASO's electron background using the known all-particle CR spectrum and the hadron rejection efficiency of LHAASO. With the estimated background, we predict the capability of LHAASO to constrain DM decay lifetime at 95% confidence level for various channels. We find that, if neglecting systematic uncertainties, the CR electron measurement by LHAASO can improve the current best results by up to on order of magnitude for DM masses between 100 - 1000TeV. However, indirect measurements of CR electrons by ground-based experiments suffer from uncertainties included in the calculation, the projected constraints will be largely weakened. So for using the CR electron observation of LHAASO to constrain the DM parameters, the key point is whether the systematic error can be effectively reduced.
description: 11 pages, 8 figures, accepted for publication in PRD
Supplementary Tables
Creators: name: Byeon, Woo Jin
name: Lee, Sung Jae
name: Khil, Tae Gyu
name: Jeoung, Ah Young
name: Han, Byoung Duck
name: Sohn, Min Sung
name: Choi, Jae Wook
name: Yang-Hyun Kim
Publisher: name: Zenodo
Year: 2023

description: Supplementary Files for the publication "Association between a marine healing program and metabolic syndrome components and mental health indicators"
HST imaging of the dusty filaments and nucleus swirl in NGC4696 at the centre of the Centaurus Cluster
Creators: name: Fabian, A. C.
name: Walker, S. A.
name: Russell, H. R.
name: Pinto, C.
name: Canning, R. E. A.
name: Salome, P.
name: Sanders, J. S.
name: Taylor, G. B.
name: Zweibel, E. G.
name: Conselice, C. J.
name: Combes, F.
name: Crawford, C. S.
name: Ferland, G. J.
name: Gallagher, J. S.
name: Hatch, N. A.
name: Johnstone, R. M.
name: Reynolds, C. S.
Publisher: name: arXiv
Year: 2016
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: Narrow-band HST imaging has resolved the detailed internal structure of the 10 kpc diameter H alpha+[NII] emission line nebulosity in NGC4696, the central galaxy in the nearby Centaurus cluster, showing that the dusty, molecular, filaments have a width of about 60pc. Optical morphology and velocity measurements indicate that the filaments are dragged out by the bubbling action of the radio source as part of the AGN feedback cycle. Using the drag force we find that the magnetic field in the filaments is in approximate pressure equipartition with the hot gas. The filamentary nature of the cold gas continues inward, swirling around and within the Bondi accretion radius of the central black hole, revealing the magnetic nature of the gas flows in massive elliptical galaxies. HST imaging resolves the magnetic, dusty, molecular filaments at the centre of the Centaurus cluster to a swirl around and within the Bondi radius.
description: 7 pages, 10 figures, MNRAS in press
$f(\bar{R}, L(X))$-gravity in the context of dark energy with power law expansion and energy conditions
Creators: name: Manna, Goutam
name: Panda, Arijit
name: Karmakar, Aninda
name: Ray, Saibal
name: Islam, Md. Rabiul
Publisher: name: arXiv
Year: 2020
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: The motto of this work is to generate a general formalism of $f(\bar{R}, L(X))-$gravity in the context of dark energy under the framework of the {\bf K-}essence emergent geometry with the Dirac-Born-Infeld (DBI) variety of action, where $\bar{R}$ is the familiar Ricci scalar, $L(X)$ is the DBI type non-canonical Lagrangian with $X={1\over 2}g^{μν}\nabla_μϕ\nabla_νϕ$ and $ϕ$ is the {\bf K-}essence scalar field. The emergent gravity metric $\bar{G}_{μν}$ and the well known gravitational metric $g_{μν}$ are not conformally equivalent. We have constructed a modified field equation using the metric formalism in $f(\bar{R}, L(X))$-gravity incorporating the corresponding Friedmann equations in the framework of the background gravitational metric which is of Friedmann-Lema{î}tre-Robertson-Walker (FLRW) type. The solution of modified Friedmann equations have been deduced for the specific choice of $f(\bar{R}, L(X))$, which is of Starobinsky-type, using power law expansion method. The consistency of the model with the accelerating phase of the Universe has been shown, when we restrict ourselves to consider the value of the dark energy density, as $\dotϕ^{2}=\frac{8}{9}=0.888 <1$, which indicates that the present Universe is dark energy dominated. Graphical plots for the energy density ($ρ$), pressure ($p$) and equation of state parameter ($ω$) w.r.t. time ($t$) based on parametric values are interestingly consistent with the dark energy domination and hence accelerating features. We also put some light on the corresponding energy conditions and constraints of the $f(\bar{R}, L(X))$ theory with one basic example.
description: 21 pages, 4 figures, 1 Table
Investigating the impact of vertically extended coronae on X-ray reverberation mapping
Creators: name: Lucchini, Matteo
name: Mastroserio, Guglielmo
name: Wang, Jingyi
name: Kara, Erin
name: Ingram, Adam
name: Garcia, Javier
name: Dauser, Thomas
name: van der Klis, Michiel
name: Konig, Ole
name: Lewin, Collin
name: Nathan, Edward
name: Panagiotou, Christos
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: Accreting black holes commonly exhibit hard X-ray emission, originating from a region of hot plasma near the central engine referred to as the corona. The origin and geometry of the corona are poorly understood, and models invoking either inflowing or outflowing material (or both) can successfully explain only parts of the observed phenomenology. In particular, recent works indicate that the time-averaged and variability property might originate in different regions of the corona. In this paper we present a model designed to move beyond the lamp post paradigm, with the goal of accounting for the vertical extent of the corona. In particular, we highlight the impact of including self consistently a second lamp post, mimicking for example an extended jet base. We fully include the effect that the second source has on the time-dependent disk ionization, reflection spectrum, and reverberation lags. We also present an application of this new model to NICER observations of the X-ray binary MAXI J1820+070 near its hard-to-soft state transition. We demonstrate that in these observations, a vertically extended corona can capture both spectral and timing properties, while a single lamp post model can not. In this scenario, the illumination responsible for the time-averaged spectrum originates close to the black hole, while the variability is likely associated with the ballistic jet.
description: 17 pages, 12 figures, accepted for publication on ApJ
A New, Low Braking Index For the LMC Pulsar B0540-69
Creators: name: Marshall, F. E.
name: Guillemot, L.
name: Harding, A. K.
name: Martin, P.
name: Smith, D. A.
Publisher: name: arXiv
Year: 2016
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: We report the results of a 16-month monitoring campaign using the Swift satellite of PSR B0540-69, a young pulsar in the Large Magellanic Cloud. Phase connection was maintained throughout the campaign so that a reliable ephemeris could be determined, and the length of the campaign is adequate to accurately determine the spin frequency and its first and second derivatives. The braking index is 0.031 +/- 0.013 (90% confidence), a value much lower than previously reported for B0540-69 and almost all other young pulsars. We use data from the extensive monitoring campaign with RXTE to show that timing noise is unlikely to significantly affect the measurement. This is the first measurement of the braking index in the pulsar's recently discovered high spin-down state. We discuss possible mechanisms for producing the low braking index.
description: 6 pages, 1 figure accepted for publication in ApJ Letters
Relationships between the number of inputs and other complexity measures of Boolean functions
Creators: name: Wellens, Jake
Publisher: name: arXiv
Year: 2020
Subjects: subject: Combinatorics (math.CO)
subject: Discrete Mathematics (cs.DM)
subject: FOS: Mathematics
subject: FOS: Computer and information sciences

description: We generalize and extend the ideas in a recent paper of Chiarelli, Hatami and Saks to prove new bounds on the number of relevant variables for boolean functions in terms of a variety of complexity measures. Our approach unifies and refines all previously known bounds of this type. We also improve Nisan and Szegedy's well-known block sensitivity vs. degree inequality by a constant factor, thereby improving Huang's recent proof of the sensitivity conjecture by the same constant.
The Absolute Age of M92
Creators: name: Jiaqi
name: Ying
name: Chaboyer, Brian
name: Boudreaux, Emily M.
name: Slaughter, Catherine
name: Boylan-Kolchin, Michael
name: Weisz, Daniel
Publisher: name: arXiv
Year: 2023
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: The \textit{absolute age} of a simple stellar population is of fundamental interest for a wide range of applications but is difficult to measure in practice, as it requires an understanding of the uncertainties in a variety of stellar evolution processes as well as the uncertainty in the distance, reddening and composition. As a result, most studies focus only on the \textit{relative age} by assuming that stellar evolution calculations are accurate and using age determinations techniques that are relatively independent of distance and reddening. Here, we construct $20,000$ sets of theoretical isochrones through Monte Carlo simulation using the Dartmouth Stellar Evolution Program to measure the absolute age of the globular cluster M92. For each model, we vary a range of input physics used in the stellar evolution models, including opacities, nuclear reaction rates, diffusion coefficients, atmospheric boundary conditions, helium abundance, and treatment of convection. We also explore variations in the distance and reddening as well as its overall metallicity and $α$ enhancement. We generate simulated Hess diagrams around the main-sequence turn-off region from each set of isochrones and use a Voronoi binning method to fit the diagrams to HST ACS data. We find the age of M92 to be $13.80 \pm 0.75$ Gyr. The $5.4\%$ error in the absolute age is dominated by the uncertainty in the distance to M92 ($\sim 80\%$ of the error budget); of the remaining parameters, only the total metallicity, $α$ element abundance, and treatment of helium diffusion contribute significantly to the total error.
description: 15 Pages, 14 Figures, 2 Tables; Accepted for Publication AJ
Multiplication of distributions in a linear gain and loss system
Creators: name: Bagarello, Fabio
Publisher: name: arXiv
Year: 2023
Subjects: subject: Mathematical Physics (math-ph)
subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We consider a model of coupled oscillators which can be seen as a gain and loss system. In the attempt to quantize the system we propose a new definition of multiplication between distributions, and we check that this definition can be adopted when checking the biorthonormality of the eigenstates of the Hamiltonian $H$ of the system, and of its adjoint $H^\dagger$. In the analysis carried out here, the role of {\em weak pseudo-bosonic} ladder operators is relevant.
description: in press in ZAMP
Improved estimates of the pion-photon transition form factor in the $(\mathbf{1\leq Q^2\leq5})$~GeV$^\mathbf{2}$ range and their theoretical uncertainties
Creators: name: Mikhailov, S. V.
name: Pimikov, A. V.
name: Stefanis, N. G.
Publisher: name: arXiv
Year: 2016
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: We consider the pion-photon transition form factor at low to intermediate spacelike momenta within the theoretical framework of light-cone sum rules. We derive predictions which take into account all currently known contributions stemming from QCD perturbation theory up to the next-to-next-to-leading order (NNLO) and by including all twist terms up to order six. In order to enable a more detailed comparison with forthcoming high-precision data, we also estimate the main systematic theoretical uncertainties, stemming from various sources, and discuss their influence on the calculations --- in particular the dominant one related to the still uncalculated part of the NNLO contribution. The analysis addresses, in broad terms, also the role of the twist-two pion distribution amplitude derived with different approaches.
description: 10 pages, 3 figures, Based on the talk given at the XIIth International Conference "Quark Confinement and the Hadronic Spectrum" (Thessaloniki, Greece, 28 August - 4 September 2016)
Second order local minimal-time Mean Field Games
Creators: name: Ducasse, Romain
name: Mazanti, Guilherme
name: Santambrogio, Filippo
Publisher: name: arXiv
Year: 2020
Subjects: subject: Analysis of PDEs (math.AP)
subject: FOS: Mathematics
subject: 35Q89, 35K40, 35B40, 35A01, 35D30

description: The paper considers a forward-backward system of parabolic PDEs arising in a Mean Field Game (MFG) model where every agent controls the drift of a trajectory subject to Brownian diffusion, trying to escape a given bounded domain $Ω$ in minimal expected time. Agents are constrained by a bound on the drift depending on the density of other agents at their location. Existence for a finite time horizon $T$ is proven via a fixed point argument, but the natural setting for this problem is in infinite time horizon. Estimates are needed to treat the limit $T\to\infty$, and the asymptotic behavior of the solution obtained in this way is also studied. This passes through classical parabolic arguments and specific computations for MFGs. Both the Fokker--Planck equation on the density of agents and the Hamilton--Jacobi--Bellman equation on the value function display Dirichlet boundary conditions as a consequence of the fact that agents stop as soon as they reach $\partialΩ$. The initial datum for the density is given, and the long-time limit of the value function is characterized as the solution of a stationary problem.
Interior-Boundary Conditions for the Dirac Equation at Point Sources in 3 Dimensions
Creators: name: Henheik, Joscha
name: Tumulka, Roderich
Publisher: name: arXiv
Year: 2020
Subjects: subject: Mathematical Physics (math-ph)
subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: A recently proposed approach for avoiding the ultraviolet divergence of Hamiltonians with particle creation is based on interior-boundary conditions (IBCs). The approach works well in the non-relativistic case, that is, for the Laplacian operator. Here, we study how the approach can be applied to Dirac operators. While this has been done successfully already in 1 space dimension, and more generally for codimension-1 boundaries, the situation of point sources in 3 dimensions corresponds to a codimension-3 boundary. One would expect that, for such a boundary, Dirac operators do not allow for boundary conditions because they are known not to allow for point interactions in 3d, which also correspond to a boundary condition. And indeed, we confirm this expectation here by proving that there is no self-adjoint operator on (a truncated) Fock space that would correspond to a Dirac operator with an IBC at configurations with a particle at the origin. However, we also present a positive result showing that there are self-adjoint operators with IBC (on the boundary consisting of configurations with a particle at the origin) that are, away from those configurations, given by a Dirac operator plus a sufficiently strong Coulomb potential.
description: 22 pages LaTeX, no figures
Reduced Memory Region Based Deep Convolutional Neural Network Detection
Creators: name: Tome', Denis
name: Bondi, Luca
name: Plebani, Emanuele
name: Baroffio, Luca
name: Pau, Danilo
name: Tubaro, Stefano
Publisher: name: arXiv
Year: 2016
Subjects: subject: Computer Vision and Pattern Recognition (cs.CV)
subject: FOS: Computer and information sciences

description: Accurate pedestrian detection has a primary role in automotive safety: for example, by issuing warnings to the driver or acting actively on car's brakes, it helps decreasing the probability of injuries and human fatalities. In order to achieve very high accuracy, recent pedestrian detectors have been based on Convolutional Neural Networks (CNN). Unfortunately, such approaches require vast amounts of computational power and memory, preventing efficient implementations on embedded systems. This work proposes a CNN-based detector, adapting a general-purpose convolutional network to the task at hand. By thoroughly analyzing and optimizing each step of the detection pipeline, we develop an architecture that outperforms methods based on traditional image features and achieves an accuracy close to the state-of-the-art while having low computational complexity. Furthermore, the model is compressed in order to fit the tight constrains of low power devices with a limited amount of embedded memory available. This paper makes two main contributions: (1) it proves that a region based deep neural network can be finely tuned to achieve adequate accuracy for pedestrian detection (2) it achieves a very low memory usage without reducing detection accuracy on the Caltech Pedestrian dataset.
description: IEEE 2016 ICCE-Berlin
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Creators: name: ads
Publisher: name: Zenodo
Year: 2019

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Riemannian Low-Rank Model Compression for Federated Learning with Over-the-Air Aggregation
Creators: name: Xue, Ye
name: Lau, Vincent
Publisher: name: arXiv
Year: 2023
Subjects: subject: Signal Processing (eess.SP)
subject: Machine Learning (cs.LG)
subject: FOS: Electrical engineering, electronic engineering, information engineering
subject: FOS: Computer and information sciences

description: Low-rank model compression is a widely used technique for reducing the computational load when training machine learning models. However, existing methods often rely on relaxing the low-rank constraint of the model weights using a regularized nuclear norm penalty, which requires an appropriate hyperparameter that can be difficult to determine in practice. Furthermore, existing compression techniques are not directly applicable to efficient over-the-air (OTA) aggregation in federated learning (FL) systems for distributed Internet-of-Things (IoT) scenarios. In this paper, we propose a novel manifold optimization formulation for low-rank model compression in FL that does not relax the low-rank constraint. Our optimization is conducted directly over the low-rank manifold, guaranteeing that the model is exactly low-rank. We also introduce a consensus penalty in the optimization formulation to support OTA aggregation. Based on our optimization formulation, we propose an alternating Riemannian optimization algorithm with a precoder that enables efficient OTA aggregation of low-rank local models without sacrificing training performance. Additionally, we provide convergence analysis in terms of key system parameters and conduct extensive experiments with real-world datasets to demonstrate the effectiveness of our proposed Riemannian low-rank model compression scheme compared to various state-of-the-art baselines.
description: This paper has been accepted for publication as a REGULAR paper in the IEEE Transactions on Signal Processing
Transport and localization of waves in ladder-shaped lattices with locally $\mathcal{PT}$-symmetric potentials
Creators: name: Nguyen, Ba Phi
name: Kim, Kihong
Publisher: name: arXiv
Year: 2016
Subjects: subject: Disordered Systems and Neural Networks (cond-mat.dis-nn)
subject: Optics (physics.optics)
subject: FOS: Physical sciences

description: We study numerically the transport and localization properties of waves in ordered and disordered ladder-shaped lattices with local $\mathcal{PT}$ symmetry. Using a transfer matrix method, we calculate the transmittance and the reflectance for the individual channels and the Lyapunov exponent for the whole system. In the absence of disorder, we find that when the gain/loss parameter $ρ$ is smaller than the interchain coupling parameter $t_{v}$, the transmittance and the reflectance are periodic functions of the system size, whereas when $ρ$ is larger than $t_{v}$, the transmittance is found to be an exponentially-decaying function while the reflectance attains a saturation value in the thermodynamic limit. For a fixed system size, there appear perfect transmission resonances in each individual channel at several values of the gain/loss strength smaller than $t_{v}$. A singular behavior of the transmittance is also found to appear at various values of $ρ$ for a given system size. When disorder is inserted into the on-site potentials, these behaviors are changed substantially due to the interplay between disorder and the gain/loss effect. When $ρ$ is smaller than $t_{v}$, we find that the presence of locally $\mathcal{PT}$-symmetric potentials suppresses Anderson localization, as compared to the localization in the corresponding Hermitian system. When $ρ$ is larger than $t_{v}$, we find that localization becomes more pronounced at higher gain/loss strengths. We also find that the phenomenon of anomalous localization occurs in disordered locally $\mathcal{PT}$-symmetric systems precisely at the spectral positions $E=0$ and $E=\pm\sqrt{t_{v}^2-ρ^2}$. The anomaly at the band center manifests as a sharp peak contrary to the conventional cases, whereas the anomalies at $E=\pm\sqrt{t_{v}^2-ρ^2}$ manifest as sharp dips.
description: 10 pages, 11 figures
Energy storage properties of ferroelectric nanocomposites
Creators: name: Jiang, Zhijun
name: Zhang, Zhenlong
name: Prokhorenko, Sergei
name: Nahas, Yousra
name: Prosandeev, Sergey
name: Bellaiche, Laurent
Publisher: name: arXiv
Year: 2023
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: An atomistic effective Hamiltonian technique is used to investigate the finite-temperature energy storage properties of a ferroelectric nanocomposite consisting of an array of BaTiO$_{3}$ nanowires embedded in a SrTiO$_{3}$ matrix, for electric field applied along the long axis of the nanowires. We find that the energy density \textit{versus} temperature curve adopts a nonlinear, mostly temperature-independent response when the system exhibits phases possessing an out-of-plane polarization and vortices while the energy density more linearly increases with temperature when the nanocomposite either only possesses vortices (and thus no spontaneous polarization) or is in a paraelectric and paratoroidic phase for its equilibrium state. Ultrahigh energy density up to $\simeq$140 J/cm$^{3}$ and an ideal 100% efficiency are also predicted in this nanocomposite. A phenomenological model, involving a coupling between polarization and toroidal moment, is further proposed to interpret these energy density results.
description: 7 pages, 5 figures
Analysis of NASA's DSN Venus Express radio occultation data for year 2014
Creators: name: Gramigna, Edoardo
name: Parisi, Marzia
name: Buccino, Dustin
name: Casajus, Luis Gomez
name: Zannoni, Marco
name: Bourgoin, Adrien
name: Tortora, Paolo
name: Oudrhiri, Kamal
Publisher: name: arXiv
Year: 2021
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: The Venus Express Radio Science Experiment (VeRa) was part of the scientific payload of the Venus Express (VEX) spacecraft and was targeted at the investigation of Venus' atmosphere, surface, and gravity field as well as the interplanetary medium. This paper describes the methods and the required calibrations applied to VEX-VeRa raw radio occultation data used to retrieve vertical profiles of Venus' ionosphere and neutral atmosphere. In this work we perform an independent analysis of a set of 25 VEX, single-frequency (X-band), occultations carried out in 2014, recorded in open-loop at the NASA Deep Space Network. Our temperature, pressure and electron density vertical profiles are in agreement with previous studies available in the literature. Furthermore, our analysis shows that Venus' ionosphere is more influenced by the day/night condition than the latitude variations, while the neutral atmosphere experiences the opposite. Our scientific interpretation of these results is based on two major responsible effects: Venus' high thermal inertia and the zonal winds. Their presence within Venus' neutral atmosphere determine why in these regions a latitude dependence is predominant on the day/night condition. On the contrary, at higher altitudes the two aforementioned effects are less important or null, and Venus' ionosphere shows higher electron density peaks in the probed day-time occultations, regardless of the latitude.
Hunting for gamma-ray emission from Fast Radio Bursts
Creators: name: Principe, G.
name: Di Venere, L.
name: Negro, M.
name: Di Lalla, N.
name: Omodei, N.
name: Di Tria, R.
name: Mazziotta, M. N.
name: Longo, F.
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: Fast radio bursts (FRBs) are a recently discovered class of GHz-band, ms-duration, Jy-level-flux astrophysical transients, which origin is still a mystery. Exploring their gamma-ray counterpart is crucial for constraining their origin and emission mechanism. Thanks to more than 13 years of gamma-ray data collected by the Fermi-Large Area Telescope, and to more than 1000 FRB events, one of the largest sample created as of today, we perform the largest and deepest search for gamma-ray emission from FRB sources to date. In addition to the study of individual FRB events on different time-scales (from few seconds up to several years), we performed, for the first time, a stacking analysis on the full sample of FRB events as well as a search for triplet photons in coincidence with the radio event. We do not detect significant emission, reporting the most stringent constraints, on short time scales, for the FRB-like emission from SGR 1935+2154 with $E<10^{41}$ erg, corresponding to a factor $<10^7$ with respect to the emitted radio energy. For the stacked signal of steady emission from all repeaters, the obtained upper limit (UL) on the FRBs luminosity ($L<1.6\times10^{43}$ erg s$^{-1}$) is more than two orders of magnitudes lower than those derived from the individual sources. Finally, no individual or triplet photons have been significantly associated with FRB events. We derived the LAT ms energy sensitivity to be $E<10^{47}$ (D$_L$/150 Mpc)$^2$ erg, ruling out a gamma-ray-to-radio energy ratio greater than $10^9$ on ms timescales. The results reported here represent the most stringent UL reported so far on the high-energy emission from FRBs on short and long time scales, as well as on cumulative emission and individual photon searches. While the origin of FRBs is still unclear, our work provides important constraints for FRB modeling, which might shed light on their emission mechanism.
description: 18 pages, 15 figures, Accepted for publication on Astronomy & Astrophysics
On the size of superconducting islands on the density-wave background in organic metals
Creators: name: Kochev, Vladislav D.
name: Seidov, Seidali S.
name: Grigoriev, Pavel D.
Publisher: name: arXiv
Year: 2023
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: FOS: Physical sciences

description: Most high-$T_c$ superconductors are spatially inhomogeneous. Usually, this heterogeneity originates from the interplay of various types of electronic ordering. It affects various superconducting properties, such as the transition temperature, the magnetic upper critical field, the critical current, etc. In this paper, we analyze the parameters of spatial phase segregation during the first-order transition between superconductivity (SC) and a charge- or spin-density wave state in quasi-one-dimensional metals with imperfect nesting, typical of organic superconductors. An external pressure or another driving parameter increases the transfer integrals in electron dispersion, which only slightly affects SC but violates the Fermi surface nesting and suppresses the density wave (DW). At a critical pressure $P_{c}$, the transition from a DW to SC occurs. We estimate the characteristic size of superconducting islands during this phase transition in organic metals in two ways. Using the Ginzburg-Landau expansion, we analytically obtain a lower bound for the size of SC domains. To estimate a more specific interval of the possible size of the superconducting islands in (TMTSF)$_2$PF$_6$ samples, we perform numerical calculations of the percolation probability via SC domains and compare the results with experimental resistivity data. This helps to develop a consistent microscopic description of SC spatial heterogeneity in various organic superconductors.
description: 11 pages, 3 figures
First Detection of A Linear Structure in the Midplane of the Young HH 211 Protostellar Disk: A Spiral Arm?
Creators: name: Lee, Chin-Fei
name: Jhan, Kai-Syun
name: Moraghan, Anthony
Publisher: name: arXiv
Year: 2023
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: Spiral structures have been detected in evolved protostellar disks, driving the disk accretion towards the central protostars to facilitate star formation. However, it is still unclear if these structures can form earlier in young protostellar disks. With the Atacama Large Millimeter/submillimeter Array (ALMA), we have detected and spatially resolved a very young and nearly edge-on dusty disk with a radius of only ~ 20 au in the HH 211 protostellar system at submillimeter wavelength. It is geometrically thick, indicating that the submillimeter light-emitting dust grains have yet to settle to the midplane for planet formation. Intriguingly, it shows 3 bright linear structures parallel to the equatorial plane, resembling a 3-layer pancake that has not been seen before. The top and bottom ones arise from the warm disk surfaces, unveiling the flared structure of the disk. More importantly, the middle one is in the dense midplane of the disk and can be modeled as a trailing spiral arm excited by disk gravity, as seen in evolved protostellar disks, supporting the presence of spiral structures in the very early phase for disk accretion.
description: 19 pages, 4 figures
Minimal codewords arising from the incidence of points and hyperplanes in projective spaces
Creators: name: Bartoli, Daniele
name: Denaux, Lins
Publisher: name: arXiv
Year: 2021
Subjects: subject: Combinatorics (math.CO)
subject: FOS: Mathematics
subject: 94A62, 05B25, 94B05

description: Over the past few years, the codes $\mathcal{C}_{n-1}(n,q)$ arising from the incidence of points and hyperplanes in the projective space $\text{PG}(n,q)$ attracted a lot of attention. In particular, small weight codewords of $\mathcal{C}_{n-1}(n,q)$ are a topic of investigation. The main result of this work states that, if $q$ is large enough and not prime, a codeword having weight smaller than roughly $\frac{1}{2^{n-2}}q^{n-1}\sqrt{q}$ can be written as a linear combination of a few hyperplanes. Consequently, we use this result to provide a graph-theoretical sufficient condition for these codewords of small weight to be minimal.
description: [v1] 18 pages [v2] 19 pages, 2 figures: added some clarifications and practical examples to the second part of the paper
High Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides
Creators: name: Di Castro, D.
name: Cantoni, C.
name: Ridolfi, F.
name: Aruta, C.
name: Tebano, A.
name: Yang, N.
name: Balestrino, G.
Publisher: name: arXiv
Year: 2016
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: FOS: Physical sciences

description: At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case extra oxygen ions can be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. A detailed hole doping spatial profile has been obtained by STEM/EELS at the O K-edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explain the dependence of Tc on the number of CuO2 planes in these systems.
description: 14 pages, 4 figures
Deep and Statistical Learning in Biomedical Imaging: State of the Art in 3D MRI Brain Tumor Segmentation
Creators: name: Fernando, K. Ruwani M.
name: Tsokos, Chris P.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Image and Video Processing (eess.IV)
subject: Computer Vision and Pattern Recognition (cs.CV)
subject: FOS: Electrical engineering, electronic engineering, information engineering
subject: FOS: Computer and information sciences

description: Clinical diagnostic and treatment decisions rely upon the integration of patient-specific data with clinical reasoning. Cancer presents a unique context that influence treatment decisions, given its diverse forms of disease evolution. Biomedical imaging allows noninvasive assessment of disease based on visual evaluations leading to better clinical outcome prediction and therapeutic planning. Early methods of brain cancer characterization predominantly relied upon statistical modeling of neuroimaging data. Driven by the breakthroughs in computer vision, deep learning became the de facto standard in the domain of medical imaging. Integrated statistical and deep learning methods have recently emerged as a new direction in the automation of the medical practice unifying multi-disciplinary knowledge in medicine, statistics, and artificial intelligence. In this study, we critically review major statistical and deep learning models and their applications in brain imaging research with a focus on MRI-based brain tumor segmentation. The results do highlight that model-driven classical statistics and data-driven deep learning is a potent combination for developing automated systems in clinical oncology.
description: 21 pages, 7 figures
A modified combined active-set Newton method for solving phase-field fracture into the monolithic limit
Creators: name: Kolditz, Leon Maximilian
name: Mang, Katrin
name: Wick, Thomas
Publisher: name: arXiv
Year: 2023
Subjects: subject: Numerical Analysis (math.NA)
subject: FOS: Mathematics
subject: 65M22, 65M60, 65K15, 74R10

description: In this work, we examine a numerical phase-field fracture framework in which the crack irreversibility constraint is treated with a primal-dual active set method and a linearization is used in the degradation function to enhance the numerical stability. The first goal is to carefully derive from a complementarity system our primal-dual active set formulation, which has been used in the literature in numerous studies, but for phase-field fracture without its detailed mathematical derivation yet. Based on the latter, we formulate a modified combined active-set Newton approach that significantly reduces the computational cost in comparison to comparable prior algorithms for quasi-monolithic settings. For many practical problems, Newton converges fast, but active set needs many iterations, for which three different efficiency improvements are suggested in this paper. Afterwards, we design an iteration on the linearization in order to iterate the problem to the monolithic limit. Our new algorithms are implemented in the programming framework pfm-cracks [T. Heister, T. Wick; pfm-cracks: A parallel-adaptive framework for phase-field fracture propagation, Software Impacts, Vol. 6 (2020), 100045]. In the numerical examples, we conduct performance studies and investigate efficiency enhancements. The main emphasis is on the cost complexity by keeping the accuracy of numerical solutions and goal functionals. Our algorithmic suggestions are substantiated with the help of several benchmarks in two and three spatial dimensions. Therein, predictor-corrector adaptivity and parallel performance studies are explored as well.
description: 49 pages, 45 figures, 9 tables
A search for inter-cluster filaments with LOFAR and eROSITA
Creators: name: Hoang, D. N.
name: Brüggen, M.
name: Shimwell, T. W.
name: Botteon, A.
name: O'Sullivan, S. P.
name: Pasini, T.
name: Zhang, X.
name: Bonafede, A.
name: Liu, A.
name: Liu, T.
name: Brunetti, G.
name: Bulbul, E.
name: Di Gennaro, G.
name: Röttgering, H. J. A.
name: Vernstrom, T.
name: van Weeren, R. J.
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: Cosmological simulations predict the presence of warm hot thermal gas in the cosmic filaments that connect galaxy clusters. This gas is thought to constitute an important part of the missing baryons in the Universe. In addition to the thermal gas, cosmic filaments could contain a population of relativistic particles and magnetic fields. A detection of magnetic fields in filaments can constrain early magnetogenesis in the cosmos. So far, the resulting diffuse synchrotron emission has only been indirectly detected. We present our search for thermal and non-thermal diffuse emission from inter-cluster regions of 106 paired galaxy clusters by stacking the $0.6-2.3$~keV X-ray and 144~MHz radio data obtained with the eROSITA telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory and LOw Frequency ARray (LOFAR), respectively. The stacked data do not show the presence of X-ray and radio diffuse emission in the inter-cluster regions. This could be due to the sensitivity of the data sets and/or the limited number of cluster pairs used in this study. Assuming a constant radio emissivity in the filaments, we find that the mean radio emissivity is not higher than $1.2\times10^{-44}\,{\rm erg \, s^{-1} \, cm^{-3} \, Hz^{-1}}$. Under equipartition conditions, our upper limit on the mean emissivity translates to an upper limit of $\sim75\,{\rm nG}$ for the mean magnetic field strength in the filaments, depending on the spectral index and the minimum energy cutoff. We discuss the constraint for the magnetic field strength in the context of the models for the formation of magnetic fields in cosmic filaments.
description: Accepted for publication on MNRAS on June 5, 2023