Quasi-normal mode analysis in BEC acoustic black holes

We perform a quasi-normal mode analysis of black hole configurations in Bose-Einstein condensates (BEC). In this analysis we use the full Bogoliubov dispersion relation, not just the hydrodynamic or geometric approximation. We restrict our attention to one-dimensional flows in BEC with step-like discontinuities. For this case we show that in the hydrodynamic approximation quasi-normal modes do not exist. The full dispersion relation, however, allows the existence of quasi-normal modes. Remarkably, the spectrum of these modes is not discrete but continuous.Comment: 7 pages, 3 figure

Three-dimensional turbulence vorticity: Numerical and experimental modeling

We show in this paper how a system of equations of motion, diffusion and continuity that present the effects of vorticity through a vorticity transfer length scale may be used to model 2D-3D vorticity behaviour. The local turbulent vorticity is separated from the large-scale flow following the Reynolds decomposition (Reynolds 1894, Taylor 1931)—∇×v +∇×v—similar to the technique used for velocity. The system of equations extended through the terms ∇× v and ∇× v is solved numerically using a purely statistical local method that details the role of vorticity transport in the turbulence behaviour of the flow. Moreover, this numerical model that shows the temporal evolution of both fields, 3D velocity and 3D vorticity is used to investigate the propagation of turbulent perturbations that arise from the development of a vortex placed in the centre of the numerical domain. Even with a small mesh (60 × 60 × 120), the results show the propagation of vorticity-related waves both in the plane and in the vertical. The numerical results are compared with experiments performed in a stratified flow, where velocity and vorticity are measured with PIV as turbulence behind a grid decay, these experiments have been performed both in a rotating frame of reference and with no rotation and show features also detected in the numerical simulations when the assumption of a quasi–two-dimensional flow is used

Improving School-Community Relationships

This School Improvement Plan responds to the challenge that schools alone cannot address the many obstacles students face. Research has shown that when schools develop positive and supportive partnerships with parents and the community, the overall benefits for students are overwhelming. Rather than three separate entities guiding students, the combination of the school, parental, and community support systems satisfy the critical role of positive school and community relationships in nurturing students\u27 development and meeting diverse learning needs. As revealed by the 2021 Conditions for Learning Family Survey in the Clayton Ridge School District, the school-community relationship has been damaged by unknown factors. This School Improvement Plan aims to provide insights and guidance on developing a positive school-community partnership, contributing to the overall goal of enhancing students\u27 well-being through improved relationships between all stakeholders

Effect of debris size on the tribological performance of thermally sprayed coatings

This research aims to assess the effect of the debris particle size on the tribological performance and lubrication regime parameters of a Ni-based alloy coating. This is a key industrial problem, and its resolution can contribute to better machine endurance and proper maintenance. The debris particles are simulated by hard Al2O3 particles of size ranging from nanometers to 45 μm and dispersed in an oil lubricant. The coating studied is NiCrBSi deposited by flame spraying technique followed by the Surface Flame Melting (SFM) process. The counterpart disk sample was fabricated from quenched and tempered F-5220 steel (in line with A681(O1) ASTM). This pair was tested under linear sliding contact. Our results show that the addition of alumina particles contributes to a significant increase in wear, particularly for the largest particles (micrometric size). In the case of micrometric particles, it is possible to observe the formation of higher surface roughness, numerous microgrooves, and plastic flow of NiCrBSi coating perpendicular to the sliding direction, resulting in higher loss of volume. It was found that the actual surface roughness (obtained as a function of the debris particle size) allows better identification and prediction of the lubrication regime for wear processes instead of the traditional approach that uses the initial surface roughness as a parameter

Social and Cultural Dimensions of Digital Inclusions

The state of Internet Adoption Curve in 2011 for the developed countries reveals an apparently optimistic picture: the majority of European and North American populations have adopted main online tools and resources. However, as access of the majority of these populations doesn’t mean universal access, we review some of the main proposals about Digital Divide and the use of EU Digital inclusion perspective in order to focus on the main obstacles for universal access to Internet

Quantum critical behavior of electrons at the edge of charge order

We consider quantum critical points (QCP) in which quantum fluctuations associated with charge rather than magnetic order induce unconventional metallic properties. Based on finite-T calculations on a two-dimensional extended Hubbard model we show how the coherence scale T* characteristic of Fermi liquid behavior of the homogeneous metal vanishes at the onset of charge order. A strong effective mass enhancement reminiscent of heavy fermion behavior indicates the possible destruction of quasiparticles at the QCP. Experimental probes on quarter-filled layered organic materials are proposed for unveiling the behavior of electrons across the quantum critical region.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Thorpe method applied to planetary boundary layer data

Turbulence affects the dynamics of atmospheric processes by enhancing the transport of mass, heat, humidity and pollutants. The global objective of our work is to analyze some direct turbulent descriptors which reflect the mixing processes in the atmospheric boundary layer (ABL). In this paper we present results related to the Thorpe displacements dT , the maximum Thorpe displacement (dT )max and the Thorpe scale LT , the Ozmidov scale and their time evolution in the ABL during a day cycle. A tethered balloon was used to obtain vertical profiles of the atmospheric physical magnitudes up to 1000m. We discuss the vertical and horizontal variability and how different descriptors are related to atmospheric mixing

Filtered deterministic waves and analysis of the fractal dimension of the components of the wind velocity

The difficulty in developing models for waves in turbulent flows is a key problem in the analysis of the complexity of turbulence. We present a method to find and filter perturbations that are generated by the flow of deterministic waves from the power spectrum in the atmospheric boundary layer (ABL). The perturbation model proposed assumes that the amplitude and frequency of such waves decay with time exponentially. For illustrative purposes, we apply the technique to three time series of wind velocities obtained with a sonic anemometer. This analytical procedure allows us to filter waves of the proposed structure with a 99% significance level in the power spectrum. We have applied the same method to 540 such wind series, all painting similar results. We then compare the fractal dimension of the original series to those from which the waves have been removed. We find that the fractal dimension of the filtered waves is slightly less than that of the original series. Finally, we consider the fractal dimension of the studied series as a function of the length-scales and dissipation rate of kinetic energy per unit mass. Our results suggest an increase of fractal dimension with both length-scale and dissipation rate of kinetic energy