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The formation of massive black holes and their coevolution with host galaxies are pivotal areas of modern astrophysics. Spherical accretion onto a central point mass serves as a foundational framework in cosmological simulations, semianalytical models, and observational studies. This work extends the classical spherical accretion model by incorporating the gravitational potential of host galaxies, including contributions from stellar components and dark matter halos. Numerical solutions spanning parsec-scale to event-horizon-scale regimes reveal that the flow structure is highly sensitive to the mass and size of the dark matter halo. Adding low angular momentum to the accreting gas demonstrates that such flows resemble spherical Bondi accretion, with mass accretion rates converging towards the Bondi rate. We find that the low angular momentum flow resembles the spherical Bondi flow and its mass accretion rate approaches the Bondi accretion rate. Due to the presence of dark matter, the mass accretion rate is increased by a factor of more than ~ %100 in comparison to analogous hydrodynamic solutions. These findings underscore the critical role of stellar and dark matter gravitational potentials in shaping the dynamics and accretion rates of quasi-spherical flows, providing new insights into astrophysical accretion processes., Comment: 12 pages, 8 figures

In this paper, we classify helix (spacelike, timelike and null) curves, directed by the geodesic flow vector field, on the (3-dimensional) unit tangent bundle of a pseudo-Riemannian surface of constant Gaussian curvature endowed with a pseudo-Riemannian $g$-natural metric of Kaluza-Klein type. We find, in particular, that every such helix curve is, in fact, a circular helix in the senses that its curvature and torsion are constant., Comment: 36 pages, 2 figures

This study investigates the thermal stability of thin accretion disks in high-energy astrophysical systems, incorporating the effects of magnetic fields, winds, and coronae. We analyze how these factors influence disk stability, focusing on conditions under which magnetic fields enhance stability and on scenarios where winds and coronae can either stabilize or destabilize the disk. Our results reveal that increasing corona parameters raises disk thickness and reduces temperature, thereby affecting gas, radiation, and magnetic pressures. These interactions underscore the complex dependencies that shape accretion disk dynamics, offering insights into their structural and thermal behavior under varying physical conditions. The findings contribute to advancing theoretical models and numerical simulations of accretion processes in environments such as active galactic nuclei (AGN) and X-ray binaries, where disk stability plays a critical role in observed emissions and variability patterns., Comment: Accepted for publication in Journal if High Energy Astrophysics

In this paper, we introduce a broad class of metrics on the slit tangent bundle of Finsler manifolds, termed \emph{$F$-natural metrics}. These metrics parallel the well-established $g$-natural metrics on the tangent bundles of Riemannian manifolds and are constructed using six real functions defined over the domain of positive real numbers. We provide an in-depth characterization of conformal, homothetic, and Killing vector fields derived from specific lifts of vector fields and tensor sections on the slit tangent bundle, which is equipped with a general pseudo-Riemannian $F$-natural metric., Comment: 40 pages

Semiconductor quantum dots are an attractive platform for the realisation of quantum processors. To achieve long-range coupling between them, quantum dots have been integrated into microwave cavities. However, it has been shown that their coherence is then reduced compared to their cavity-free implementations. Here, we manipulate the quantum states of a suspended carbon nanotube double quantum dot with ferromagnetic contacts embedded in a microwave cavity. By performing quantum manipulations via the cavity photons, we demonstrate coherence times of the order of $1.3\mu s$, two orders of magnitude larger than those measured so far in any carbon quantum circuit and one order of magnitude larger than silicon-based quantum dots in comparable environment. This holds promise for carbon as a host material for spin qubits in circuit quantum electrodynamics., Comment: main text (7 pages, 4 figures); supplementary material (11 pages, 15 figures)

In this paper we consider an inflating universe with long straight cosmic string along z-axis. We show that the effect of cosmic string can be taken as a perturbation on the background of FRW metric. Then by doing cosmological perturbations on this inflating cosmic string background, we find linearized Einstein field equations. We show that at leading order (ignoring the mixing terms of cosmic string perturbations with gravitational tensor perturbations), the cosmic string appears as an inhomogeneous term on the right hand side of wave equation of tensor perturbations . Then by finding analytical solution of the wave equation for slow-roll inflation, we show how it effects on the spectrum of primordial gravitational waves., Comment: 10 pages, 1 fig

The industry increasingly relies on deep learning (DL) technology for manufacturing inspections, which are challenging to automate with rule-based machine vision algorithms. DL-powered inspection systems derive defect patterns from labeled images, combining human-like agility with the consistency of a computerized system. However, finite labeled datasets often fail to encompass all natural variations necessitating Continuous Training (CT) to regularly adjust their models with recent data. Effective CT requires fresh labeled samples from the original distribution; otherwise, selfgenerated labels can lead to silent performance degradation. To mitigate this risk, we develop a robust CT-based maintenance approach that updates DL models using reliable data selections through a two-stage filtering process. The initial stage filters out low-confidence predictions, as the model inherently discredits them. The second stage uses variational auto-encoders and histograms to generate image embeddings that capture latent and pixel characteristics, then rejects the inputs of substantially shifted embeddings as drifted data with erroneous overconfidence. Then, a fine-tuning of the original DL model is executed on the filtered inputs while validating on a mixture of recent production and original datasets. This strategy mitigates catastrophic forgetting and ensures the model adapts effectively to new operational conditions. Evaluations on industrial inspection systems for popsicle stick prints and glass bottles using critical real-world datasets showed less than 9% of erroneous self-labeled data are retained after filtering and used for fine-tuning, improving model performance on production data by up to 14% without compromising its results on original validation data.

Modeling of the collimator-detector response (CDR) in SPECT reconstruction enables improved resolution and accuracy, and is thus important for quantitative imaging applications such as dosimetry. The implementation of CDR modeling, however, can become a computational bottleneck when there are substantial components of septal penetration and scatter in the acquired data, since a direct convolution-based approach requires large 2D kernels. This work proposes a 1D convolution and rotation-based CDR model that reduces reconstruction times but maintains consistency with models that employ 2D convolutions. To enable open-source development and use of these models in image reconstruction, we release a SPECTPSFToolbox repository for the PyTomography project on GitHub.

This study investigates the detectability of intermediate-mass black holes (IMBHs) within the mass range $10^2-10^5$ solar masses in the globular star clusters of NGC 1399 at a frequency of 300.00 MHz. Employing the theoretical Bondi accretion model and the empirical fundamental plane of black hole accretion, we estimate IMBH masses based on bolometric luminosity and X-ray/radio luminosities, respectively. By simulating a 3-hour observation of 77 globular cluster candidates using the Square Kilometer Array, we identify radio detection benchmarks indicative of accretion onto IMBHs. Our results show that IMBHs inside the globular star clusters located in NGC 1399 are indeed detectable, with the Bondi accretion model providing IMBH mass estimates ranging from $2.93 \times 10^{3.0\pm 0.39}$ to $7.43 \times 10^{4.0 \pm 0.39}$ solar masses, and the empirical fundamental-plane relation suggesting IMBH mass estimation with $3.41\times 10^{5.0 \pm 0.96}$ solar masses. These findings highlight the presence and detectability of IMBHs in globular clusters, offering insights into their role as precursors to supermassive black holes and enriching our understanding of black hole formation and evolution in astrophysical environments., Comment: AAS journals, in press; 9 pages, 5 figures

In this paper, the redshift evolution of the galactic bar properties, like the bar length, pattern speed, and bar fraction, has been investigated for simulated galaxies at stellar masses $M_*>10^{10}\, M_{\odot}$ in the cosmological magnetohydrodynamical simulation TNG50. We focus on the redshift evolution of the bar pattern speeds and \textit{the fast bar tension}. We show that the median value of the pattern speed of the bars increases as the redshift grows. On the other hand, although the median value of the bar length increases over time, the ratio between the corotation radius and the bar radius, namely the $\mathcal{R}=R_{\text{CR}}/R_{\text{bar}}$ parameter, increases as well. In other words, the corotation radius increases with a higher rate compared to the bar length. This directly means that galactic bars slow down with time, or equivalently as the redshift declines. We discuss the possible mechanisms that reduce the pattern speeds in TNG50. We demonstrate that while mergers can have a significant impact on a galaxy's pattern speed, they do not play a crucial role in the overall evolution of mean pattern speed within the redshift range $z\leq 1.0$. Furthermore, we show that the $\mathcal{R}$ parameter does not correlate with the gas fraction. Consequently, the existence of gas in TNG50 does not alleviate the fast bar tension. We show that the mean value of the pattern speed, computed for all the galaxies irrespective of their mass, at $z=1.0$ is $\Omega_p=70.98\pm 2.34$ km s$^{-1}$ kpc$^{-1}$ and reduces to $\Omega_p=33.65 \pm 1.07$ km s$^{-1}$ kpc$^{-1}$ at $z=0.0$. This is a direct prediction by TNG50 that bars at $z=1.0$ rotate faster by a factor of $\sim 2$ compared to bars at $z=0.0$., Comment: 13 pages, Accepted for publication in A&A

Capsule networks are a type of neural network that identify image parts and form the instantiation parameters of a whole hierarchically. The goal behind the network is to perform an inverse computer graphics task, and the network parameters are the mapping weights that transform parts into a whole. The trainability of capsule networks in complex data with high intra-class or intra-part variation is challenging. This paper presents a multi-prototype architecture for guiding capsule networks to represent the variations in the image parts. To this end, instead of considering a single capsule for each class and part, the proposed method employs several capsules (co-group capsules), capturing multiple prototypes of an object. In the final layer, co-group capsules compete, and their soft output is considered the target for a competitive cross-entropy loss. Moreover, in the middle layers, the most active capsules map to the next layer with a shared weight among the co-groups. Consequently, due to the reduction in parameters, implicit weight-sharing makes it possible to have more deep capsule network layers. The experimental results on MNIST, SVHN, C-Cube, CEDAR, MCYT, and UTSig datasets reveal that the proposed model outperforms others regarding image classification accuracy.

We investigate the recoil heating phenomenon experienced by a dielectric spherical particle when it interacts with a linearly polarized plane wave within the Rayleigh regime. We derive the fluctuating force acted upon the particle arising from the fluctuations of the electromagnetic fields. Our derivations reveal that the spectral density of the fluctuating force along the propagation direction is $7\hbar \omega_0 P_{\mathrm{scat}}/5c^2$. Meanwhile, along the direction of the electric and magnetic fields, it is $\hbar \omega_0 P_{\mathrm{scat}}/5c^2$ and $2\hbar \omega_0 P_{\mathrm{scat}}/5c^2$, respectively. Here, $P_{\mathrm{scat}}$ denotes the power scattered by the particle, $\hbar\omega_0$ represents the energy of a photon, and $c$ is the speed of light. Recoil heating imposes fundamental limitations in levitated optomechanics, constraining the minimum temperatures achievable in cooling processes, the coherence time of the system, and the sensitivity of force measurements.

We investigate the radiation damping experienced by a dielectric spherical particle when it is illuminated by an electromagnetic plane wave within the Rayleigh regime. We derive the equivalent electric dipole of the moving particle and subsequently calculate the electromagnetic force acting on it from two different approaches. In the first approach, we calculate the force from the integration of stress tensor and field momentum. In the second one, we calculate the force directly from the integration of the force density. Our derivations reveal that the damping coefficient is equal to $6P_{scat}/mc^2$ along the propagation direction, whereas it is $P_{scat}/mc^2$ along perpendicular directions. Here, $P_{scat}$ denotes the power scattered by the particle, and $mc^2$ represents the particle's mass energy. The radiation damping derived in this study sets upper limits on the quality factor of optically levitated objects and ensures the existence of a steady-state solution of the particle's dynamics.

We present the structure of a low angular momentum accretion flows around rotating compact objects incorporating relativistic corrections up to the leading post-Newtonian order. To begin with, we formulate the governing post-Newtonian hydrodynamic equations for the mass and energy-momentum flux without imposing any symmetries. However, for the sake of simplicity, we consider the flow to be stationary, axisymmetric, and inviscid. Toward this, we adapt the polytropic equation of state (EoS) and analyze the vertically integrated accretion flow confined to the equatorial plane. It is shown that the spin-orbit effects manifest themselves in the accretion dynamics. In the present analysis, we focus on global transonic accretion solutions, where a subsonic flow enters far away from the compact object and gradually gains radial velocity as it moves inwards. Thus, the flow becomes supersonic after reaching a certain radius, known as the critical point. To better understand the transonic solutions and examine the effect of post-Newtonian corrections, we classify the post-Newtonian equations into semi-relativistic (SR), semi-Newtonian (SN), and non-relativistic (NR) limits and compare the accretion solutions and their corresponding flow variables. With these, we find that SR and SN flow are in good agreement all throughout, although they deviate largely from the NR ones. Interestingly, the density profile seems to follow the profile $\rho \propto r^{-3/2}$ in the post-Newtonian regime. The present study has the potential to connect Newtonian and GR descriptions of accretion dynamics., Comment: 42 pages, 9 figures, and 5 appendices, Accepted for publication in JCAP

Deep reinforcement learning (DRL), leveraging Deep Learning (DL) in reinforcement learning, has shown significant potential in achieving human-level autonomy in a wide range of domains, including robotics, computer vision, and computer games. This potential justifies the enthusiasm and growing interest in DRL in both academia and industry. However, the community currently focuses mostly on the development phase of DRL systems, with little attention devoted to DRL deployment. In this paper, we propose an empirical study on Stack Overflow (SO), the most popular Q&A forum for developers, to uncover and understand the challenges practitioners faced when deploying DRL systems. Specifically, we categorized relevant SO posts by deployment platforms: server/cloud, mobile/embedded system, browser, and game engine. After filtering and manual analysis, we examined 357 SO posts about DRL deployment, investigated the current state, and identified the challenges related to deploying DRL systems. Then, we investigate the prevalence and difficulty of these challenges. Results show that the general interest in DRL deployment is growing, confirming the study's relevance and importance. Results also show that DRL deployment is more difficult than other DRL issues. Additionally, we built a taxonomy of 31 unique challenges in deploying DRL to different platforms. On all platforms, RL environment-related challenges are the most popular, and communication-related challenges are the most difficult among practitioners. We hope our study inspires future research and helps the community overcome the most common and difficult challenges practitioners face when deploying DRL systems., Comment: Accepted for publication in The International Conference on Software Maintenance and Evolution (ICSME 2023)

This paper is devoted to the investigation of harmonic and biharmonic functions on vector bundles equipped with spherically symmetric metrics. We will study the biharmonicity of vertical lifts of functions as well as $r$-radial functions on vector bundle manifolds and, as a consequence, we will construct an infinite two-parameter family of proper biharmonic functions., Comment: 20 pages

We investigate the role of r-modes in the spin-down of pulsars, focusing on their implications for pulsar timing and gravitational wave emissions. Our study employs a non-linear differential equation incorporating the contribution of r-modes to derive time-dependent rotational frequency and period functions. This model is validated against observational data from the Crab pulsar, demonstrating a high degree of accuracy. By fitting the braking indices and spin-down coefficients, we establish direct and analytical relationships between observable pulsar properties and weak gravitational wave signals. We also derive analytical expressions for neutron star compactness and tidal deformability using Lambert W solutions, independent of the equation of state (EoS). These solutions provide new insights into the mathematical relationships between physical quantities, constraining the parameter space for r-mode gravitational wave frequency searches. Our results show that incorporating r-modes significantly enhances our ability to measure the neutron star EoS and predict pulsar age, rotational velocity, and gravitational wave frequencies. The seventh-order approximation used in our model is essential for accurately capturing the contributions of r-modes to the spin-down process. This framework can be applied to model pulsar timing residuals, account for glitches, and improve the detection and analysis of continuous gravitational waves from pulsars. With the advent of next-generation gravitational wave detectors, our findings offer promising prospects for disentangling individual events from the stochastic gravitational wave background, advancing our understanding of neutron star interiors and their dynamic processes., Comment: Prepared for submission to JCAP

Apart from the assumption that the inflation started at an infinite time in the past, the more realistic initial state of the quantum fluctuations is described by a mixed quantum state imposed at a finite value of the initial time. One of the most important non-trivial vacua is the $\alpha$-vacuum, which is specified by a momentum cutoff $\Lambda$ \cite{Danielsson:2002kx}. As a consequence, the initial condition is imposed at different initial times for the different $k$-modes. This modifies the amplitude of the quantum fluctuations, and thus the corresponding power spectra. In this paper, we consider the imprint of the $\alpha$-vacuum state on the power spectrum of scalar perturbations in a generic $f(R)$ gravity by assuming an ultraviolet cutoff $\Lambda$. As a specific model, we consider the Starobinsky model and find the trans-Planckian power spectrum. We find that the leading order corrections to the scalar power spectra in $f(R)$ gravity have an oscillatory behavior as in general relativity \cite{Lim}, and furthermore, the results are in sufficient agreement with the $\Lambda$CDM model., Comment: 21 pages, 5 figures, 1 table

Observational evidence and many numerical simulations show the existence of wind (i.e., uncollimated outflow) in accretion systems of the elliptical galaxy center. One of the primary aims of this study is to investigate the solutions of slowly rotating accretion flows around the supermassive black hole with outflow. This paper presents two distinct physical regions: supersonic and subsonic, that extend from the outer boundary to the black hole. In our numerical solution, the outer boundary is chosen beyond the Bondi radius. Due to strong gravity, we ignore outflow (i.e., $s = 0$) in the inner region (within $\sim 10 r_s$). The radial velocity of the flow at the outer region is significantly increased due to the presence of the outflow. Compared to previous works, the one accretion mode - namely, slowly rotating case, which corresponds to low accretion rates that have general wind output is carefully described, and the effect of galaxy potential and the feedback effects by the wind in this mode are taken into account. Since the power-law form of the mass accretion rate is mathematically compatible with our equations, we consider a radius-dependent mass accretion rate ($\dot{M}_{in} \propto r^s$), where $s$ is a free parameter and shows the intensity of outflow. There is an unknown mechanism for removing the mass, angular momentum, and energy by outflows in this study. The effects of the outflow appear well on the outer edge of the flow., Comment: Accepted for publication in Astrophysical Journal

We examine the effect of thermal conduction on the low-angular momentum hot accretion flow (HAF) around non-rotating black holes accreting mass at very low rate. While doing so, we adopt the conductive heat flux in the saturated form, and solve the set of dynamical equations corresponding to a steady, axisymmetric, viscous, advective accretion flow using numerical methods. We study the dynamical and thermodynamical properties of accreting matter in terms of the input parameters, namely energy ($\varepsilon_0$), angular momentum ($\ell_0$), viscosity parameter ($\alpha$), and saturation constant ($\Phi_{\rm s}$) regulating the effect of thermal conduction. We find that $\Phi_{\rm s}$ plays a pivotal role in deciding the transonic properties of the global accretion solutions. In general, when $\Phi_{\rm s}$ is increased, the critical point ($r_{\rm c}$) is receded away from the black hole, and flow variables are altered particularly in the outer part of the disc. To quantify the physically acceptable range of $\Phi_{\rm s}$, we compare the global transonic solutions with the self-similar solutions, and observe that the maximum saturation constant ($\Phi^{\rm max}_{\rm s}$) estimated from the global solutions exceeds the saturated thermal conduction limit ($\Phi_{\rm sc}$) derived from the self-similar formalism. Moreover, we calculate the correlation between $\alpha$ and $\Phi^{\rm max}_{\rm s}$ and find ample disagreement between global solutions and self-similar solutions. Further, using the global flow variables, we compute the Bernoulli parameter ($Be$) which remains positive all throughout the disc, although flow becomes loosely unbound for higher $\Phi_{\rm s}$. Finally, we indicate the relevance of this work in the astrophysical context in explaining the possibility of massloss/outflows from the unbound disc., Comment: 12 pages, 8 figures; accepted for publication in MNRAS

Orthogonal Time Frequency Space (OTFS) systems face significant challenges in channel estimation due to high pilot overhead and peak-to-average power ratio (PAPR). To address these issues, we propose a two-step channel estimation method for Zero-Pad OTFS (ZP-OTFS), a modified OTFS system characterized by multiple zero rows along the delay axis. This method strategically inserts pilot sequences into the zero bins of the ZP-OTFS system, effectively mitigating overhead and PAPR. Comprehensive simulation results validate the effectiveness of our proposed method, demonstrating its superior performance over traditional embedded pilot estimation in high Signal-to-Noise Ratio (SNR) scenarios. Specifically, our method achieves a lower normalized mean square error (NMSE) and better bit error rates (BER) at high SNRs.

In the present paper, the electronic, structural, thermodynamic, and elastic properties of cubic $PbGeO_{3}$ perovskite oxide are presented and computed using the WIEN2K code. The structural properties have been evaluated and they are in good agreement with the theoretical and experimental data. A phonon dispersion is made and it reveals that the cubic $PbGeO_{3}$ perovskite is dynamically stable. In addition, the electronic properties of $PbGeO_{3}$ shows an opening gap energy, meaning a semiconductor behavior with an indirect band gap equal to $1.67 eV$. Moreover, the obtained elastic constants of cubic $PbGeO_{3}$ satisfy Born's mechanical stability criteria, and this indicates that our compound behaves as a stable ductile material. The temperature-pressure effects on thermodynamic parameters are investigated using the Gibbs$2$ package. Finally, based on the obtained results about the cubic $PbGeO_{3}$ perovskite properties, we assume that this compound will have potential applications., Comment: 17 pages, 9 figures