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In this work we study the thermodynamics of a cosmological unimodular gravity model at late times by considering two different energy diffusion functions that emerges in these scenarios, and that encodes the current for the non-conservation of the energy-momentum tensor, usually termed as $Q(t)$. Specifically, we discuss the barotropic and the continuous spontaneous localization models as energy diffusion functions. The consistency conditions demanded for the entropy of the system in terms of the cosmological parameters of the model: positive production ($dS/dt>0$) and convexity condition ($d^{2}S/dt^{2} <0$), are investigated. We show that these conditions strongly constraint the viavility of these models. Additionally, we comment about our results and compare with those obtained in recent works where the restriction of the parameters for these two diffusion models was implemented with the use of cosmological data., Comment: 8 pages, no figures

We investigate a generalized Chaplygin-like gas with an anisotropic equation of state, characterizing a dark fluid within which a static spherically symmetric black hole is assumed. By solving the Einstein equations for this black hole spacetime, we explicitly derive the metric function. The spacetime is parametrized by two critical parameters, $\mathcal{B}$ and $\alpha$, which measure the deviation from the Schwarzschild black hole and the extent of the dark fluid's anisotropy, respectively. We explore the behavior of light rays in the vicinity of the black hole by calculating its shadow and comparing our results with the Event Horizon Telescope observations. This comparison constrains the parameters to $0 \leq \mathcal{B} < 0.03$ and $0 < \alpha < 0.1$. Additionally, we calculate the deflection angles to determine the extent to which light is bent by the black hole. These calculations are further utilized to formulate possible Einstein rings, estimating the angular radius of the rings to be approximately $37.6\,\mathrm{\mu as}$. Throughout this work, we present analytical solutions wherever feasible, and employ reliable approximations where necessary to provide comprehensive insights into the spacetime characteristics and their observable effects., Comment: 24 pages, 10 figures, 2 tables

In the context of an homogeneous and isotropic universe, we consider the degeneracy condition at background level between two scenarios in which processes out of equilibrium are possible to explore their cosmological implications; this consideration allows us to deviate from the perfect fluid description and in this case bulk viscosity represents a viable candidate to describe entirely such effects. The cosmological model describing an unstable dark matter sector is mapped into a slight modification of the $\Lambda$CDM model characterized by a viscous dark matter sector; under this consideration our description does not depend on a specific formulation of viscous effects and these can be fully reconstructed and characterized by the parameter that determines the decay ratio of dark matter. However, in this new scenario the cosmic expansion is influenced by the viscous pressure and the dark energy sector given by the cosmological constant is translated into a dynamical one. As consequence of our formulation, the test against observations of the model indicates consistency with quintessence dark energy but the crossing of the phantom divide can be accessible., Comment: 11 pages, 6 figures

In this work we establish only at background dynamics level, the equivalence between the Created Cold Dark Matter (CCDM) model and diverse dark energy (DE) models. We find that for a barotropic or linear equation of state (EoS) for the DE, $p=w \rho$, and standard matter sector the corresponding CCDM model is described by the same functional structure of the ratio of particle production, $\Gamma$. For a different EoS the functional form of the $\Gamma$ term is not longer maintained, however, in the case of a polytropic EoS given by the Chaplygin gas the resulting $\Gamma$ term can be written as the one obtained in the barotropic case under certain considerations., Comment: 7 pages, no figures. Published version in Physics of the Dark Universe

In the framework of Einstein's gravity, we study the thermodynamic equation state, $P=P(V,T)$, associated with a flat Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. In this scenario, we consider the components of the dark sector as non-interacting fluids that dominate the universe's energy content at late times. Under these circumstances, the functional structure of the cosmological coincidence parameter plays a relevant role in admitting first-order $P-V$ phase transitions; specifically, the dark energy density and the coincidence parameter must be given in terms of the radius of the apparent horizon., Comment: 20 pages, 4 figures. Accepted for publication in Physics of the Dark Universe

Wind tunnels are a key source of data collection, but their cost and size can be a significant obstacle to their acquisition and usage, especially for applications such as instrument calibration, instruction, or in-class demonstrations. Here we propose a design for a cost-effective, desktop wind tunnel. This design takes advantage of readily available, inexpensive materials. Special consideration was taken to allow the wind tunnel to be serviceable, as well as giving the operator the ability to change key features without a complete redesign. There are three main sections, the first being a fan enclosure, which holds seven ducted fans in a hexagonal array. The second section holds honeycomb flow straighteners, and provides an enclosed volume suitable for larger, lower-speed experiments. The third section is a contraction, terminating in a 2in x 2in, higher-speed square section. The wind tunnel has a footprint of approximately 13.5in x 5.5in, making it small enough to be portable and to fit on a desk. An off-the-shelf masked stereolithography apparatus (MSLA) 3D printer was used to prepare the parts. This allows the wind tunnel to be built for under \$500; even including the cost of a 3D printer, the overall cost remains under \$1,000. This design is able to produce flow at up to 44.1 m/s, enabling a variety of aerodynamic demonstrations.

In this work, a generalized force-field methodology for the relaxation of large moir\'e heterostructures is proposed. The force-field parameters are optimized to accurately reproduce the structural degrees of freedom of some computationally manageable cells relaxed using density functional theory. The parameters can then be used to handle large moir\'e systems. We specialize to the case of 2H-phased twisted transition-metal dichalcogenide homo- and heterobilayers using a combination of the Stillinger-Weber intralayer- and the Kolmogorov-Crespi interlayer-potential. Force-field parameters are developed for all combinations of MX$_2$ for $\text{M}\in\{\text{Mo},\text{W}\}$ and $\text{X}\in\{\text{S},\text{Se},\text{Te}\}$. The results show agreement within 20 meV in terms of band structure between density functional theory and force-field relaxation. Using the relaxed structures, a simplified and systematic scheme for the extraction of the interlayer moir\'e potential is presented for both R- and H-stacked systems. We show that in-plane and out-of-plane relaxation effects on the moir\'e potential, which is made both deeper and wider after relaxation, are essential. An interpolation based methodology for the calculation of the interlayer binding energy is also proposed. Finally, we show that atomic reconstruction, which is captured by the force-field method, becomes especially prominent for angles below 4-5$^\circ$, when there is no mismatch in lattice constant between layers., Comment: 11 pages, 12 figures. Accepted by and to be published in Physical Review B

This work is devoted to the thermodynamics description of a phantom scenario proposed previously by the authors. The presence of negative chemical potential is unavoidable if we allege for a well defined thermodynamics framework since the cosmological model passages from phantom stage at present time to a future de Sitter evolution. As noted earlier in other works, we find that the negativity of the chemical potential is necessary to save phantom dark energy from thermodynamics inconsistencies., Comment: 7 pages, 1 figure. Published version in Physics of the Dark Universe

This work is focused on the exploration of the thermodynamics foundations of the matter creation scenario when a generalized form of the second law of thermodynamics for this scheme is implemented. In this scenario we consider an expanding cosmology in which the created matter is trapped by the apparent horizon. The scheme leads to phantom evolution but at first glance it lacks of physical consistency. However, the inclusion of chemical potential into the description solves the thermodynamics issues of the model and determines the behavior of the cosmic fluid, in other words, the cosmic fluid now can behave as phantom dark energy or as quintessence one., Comment: 7 pages, no figures. Accepted for publication in EPJ Plus

We review a dynamical dark energy model scarcely studied in the literature and we introduce two possible generalizations. We discuss separately the behavior of the original model and a minimal extension of it by exploring some early and late times limits, we find that the cosmic components are related by their parameters state. In order to have access to the phantom regime we present two dark energy densities inspired from the holographic approach and from the emergent entropic forces model in the early universe. For the first case we obtain a Type III singularity and in the second proposal we have a transition from decelerated to accelerated cosmic expansion that starts as phantom type. However, the final stage of the universe is a de Sitter state., Comment: 16 pages, 1 figure. Accepted for publication in PRD

The consideration of the holographic dark energy approach and matter creation effects in a single cosmological model is carried out in this work accordingly, we discuss some cases of interest. We test this cosmological proposal against recent observations. Considering the best fit values obtained for the free cosmological parameters, the model exhibits a transition from a decelerated cosmic expansion to an accelerated one. The deceleration-acceleration transition can not be determined consistently from the coincidence parameter for this kind of model. At effective level the parameter state associated to the whole energy density contribution describes a quintessence scenario in the fluid analogy at present time., Comment: 9 pages, 7 figures. Accepted for publication in Physics of the Dark Universe

We explore the dynamical properties of a cosmological model that includes viscous effects in the dark matter sector of the fluid equations in a flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. The bulk viscous effects are described by a non linear extension of the full Israel-Stewart model. We allow the interchange of energy in the dark sector by means of the interaction term, namely $Q$. We establish the dynamical system corresponding to Friedmann and fluid set of equations associated to the model and study the linear stability of its critical points. From the dynamical system, we show the appearance of a critical point characterizing a de Sitter universe within the non interacting and interacting dark sector. We focus our study to analyse the stability of this fixed point in a large region of parameter space and derive linearized solutions around it. These approximate and analytical solutions are potentially able to describe the expansion of the universe since they are close to a de Sitter stationary solution. Within this regime with $Q \neq 0$, we realize the existence of regions in the space of parameters where this critical point is stable and describes the behavior of dark energy as quintessence, cosmological constant and phantom like fluids. We perform a comparison between numerical and linearized solutions nearby the critical points within the full non linear regimes and also contrast them against $\Lambda$CDM model. We find that fully non linear regime is favored by observations and closer to the concordance model due to the non-zero value of the parameter $j$, which controls the non linear effects. In fact, at low redshift values, the expansion rate associated to the full non linear regime is practically indistinguishable from $\Lambda$CDM. The deceleration parameter obtained in this regime exhibits a transition from decelerated to accelerated cosmic expansion., Comment: Improved version, 18 pages, 3 figures, references added

In this work, we test the capability of an exact solution found in the framework of a nonlinear extension of the Israel-Stewart theory to fit the supernovae Ia, gravitational lensing, and black hole shadow data. This exact solution is a generalization of one previously found for a dissipative unified dark matter model in the context of the near-equilibrium description of dissipative processes, where we do not have the full regime of the nonlinear picture. This generalized solution is restricted to the case where a positive entropy production is guaranteed and is tested under the condition that ensures its causality, local existence, and uniqueness. From the observational constraints, we found that this generalized solution is a good candidate in the description of the observational late-time data used in this work, with best-fit values $H_{0}=73.2_{-0.9}^{+0.8}\,\frac{km/s}{Mpc}$, $q_{0}=-0.41_{-0.03}^{+0.03}$, $\hat{\xi}_{0}=0.88_{-0.17}^{+0.09}$, $\epsilon=0.34_{-0.04}^{+0.03}$, and $k=0.27_{-0.20}^{+0.37}$. Therefore, we show that the nonlinear regime of the Israel-Stewart theory consistently describes the recent accelerated expansion of the universe without the inclusion of some kind of dark energy component and also provides a more realistic description of the fluids that make up the late Universe., Comment: 13 pages, 4 figures. Improved version, updated data analysis in the "Observational Constraints" section

In this work we explore the scope of two holographic dark energy models within the interacting scenario for the dark sector and spatial curvature. For one holographic model we consider the usual formula for the dark energy density with the Hubble scale and the second model is given in terms of a function instead of a constant parameter as in the usual holographic formula. In this description both holographic models admit a future singularity. The use of recent cosmological data is considered only to support the physical results of our proposal. The interaction term for each holographic model, $Q$, keeps positive along the cosmic evolution and are not given a priori, they are reconstructed from the dynamics of the model. The temperatures for the components of the dark sector are computed and exhibit a growing behavior in both scenarios. The cosmic evolution in this context it is not adiabatic and the second law it is fulfilled only under certain well-established conditions for the temperatures of the cosmic components and positive $Q$-terms., Comment: 26 pages, 7 figures

The Transformer architecture has been successful across many domains, including natural language processing, computer vision and speech recognition. In keyword spotting, self-attention has primarily been used on top of convolutional or recurrent encoders. We investigate a range of ways to adapt the Transformer architecture to keyword spotting and introduce the Keyword Transformer (KWT), a fully self-attentional architecture that exceeds state-of-the-art performance across multiple tasks without any pre-training or additional data. Surprisingly, this simple architecture outperforms more complex models that mix convolutional, recurrent and attentive layers. KWT can be used as a drop-in replacement for these models, setting two new benchmark records on the Google Speech Commands dataset with 98.6% and 97.7% accuracy on the 12 and 35-command tasks respectively., Comment: Proceedings of INTERSPEECH