Preprint arXiv: 2106.05030 Submitted on 9 Jun 2021

Non-Hermitian Hamiltonians, which effectively describe dissipative systems, and analogue gravity models, which simulate properties of gravitational objects, comprise seemingly different areas of current research. Here, we investigate the interplay between the two by relating parity-time-symmetric dissipative Weyl-type Hamiltonians to analogue Schwarzschild black holes emitting Hawking radiation. We show that the exceptional points of these Hamiltonians form tilted cones mimicking the behavior of the light cone of a radially infalling observer approaching a black hole horizon. We further investigate the presence of tunneling processes, reminiscent of those happening in black holes, in a concrete example model. We interpret the non-trivial result as the purely thermal contribution to analogue Hawking radiation in a Schwarzschild black hole. Assuming that our particular Hamiltonian models a photonic crystal of experimental relevance, we argue that the loss from the latter in the form of thermal radiation can be interpreted as the blackbody contribution to analogue black hole radiation when measuring at the exceptional cone. As such, these systems are promising candidates for black hole analogue models

Globalizacion, centro y fronteras simbólicas en la teoría sobre la sociedad contemporánea

This paper focuses on specific implications of the process of globalisation taking place in Western societies and the efforts to build a theory of modem societies by several classic and contemporary sociologists. It argües that the scope of the changes generated by this macro process requires an in depth revisión of the theory of modem society. For that purpose, it also focuses on the breakdown of the monolithic image of the latter and the functionalist model of the unity of knowledge at the University, which are interrelated. It reviews the influence of the idea that there is symbolic centre of society which provides the basis for the evaluation of knowledge and which regulates the boundaries between the economy, politics and culture in information societies.Este trabajo analiza algunas implicaciones del proceso de globalización de las sociedades occidentales desde una perspectiva constructivista y sostiene que la magnitud de los cambios generados por ese proceso requiere una revisión en profundidad de la teoría sobre la sociedad moderna. Para ello, se presta especial atención a la crisis de la imagen monolítica de la sociedad y de la teoría funcionalista sobre la unidad del saber en la Universidad. El trabajo examina la influencia que ha tenido la idea según la cual existe un lugar central institucional que genera los criterios para la evaluación de los conocimientos y regula las relaciones entre el orden tecnoeconómico, la política y la cultura en las sociedades de la información

PT symmetry-protected exceptional cones and analogue Hawking radiation

We show that the exceptional surfaces of linear three-dimensional non-Hermitian parity-time-symmetric two-band models attain the form of topologically stable tilted exceptional cones. By relating the exceptional cones to energy cones of two-dimensional Hermitian parity-time-symmetric two-band models, we find a connection between the exceptional cone and the light cone of an observer in the vicinity of a Schwarzschild black hole. When the cone overtilts, light-like particle-antiparticle pairs are created resembling Hawking radiation. We also investigate dissipative features of the non-Hermitian Hamiltonian related to the latter and comment on potential realizations in laboratory setups

ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations

From Indymedia to Anonymous: rethinking action and identity in digital cultures

The period following the social mobilizations of 2011 has seen a renewed focus on the place of communication in collective action, linked to the increasing importance of digital communications. Framed in terms of personalized ‘connective action’ or the social morphology of networks, these analyses have criticized previously dominant models of ‘collective identity’, arguing that collective action needs to be understood as ‘digital networking’. These influential approaches have been significantly constructed as a response to models of communication and action evident in the rise of Independent Media Centres in the period following 1999. After considering the rise of the ‘digital networking’ paradigm linked to analyses of Indymedia, this article considers the emergence of the internet-based collaboration known as Anonymous, focusing on its origins on the 4chan manga site and its 2008 campaign against Scientology, and also considers the ‘I am the 99%’ microblog that emerged as part of the Occupy movement. The emergence of Anonymous highlights dimensions of digital culture such as the ephemeral, the importance of memes, an ethic of lulz, the mask and the grotesque. These forms of communication are discussed in the light of dominant attempts to shape digital space in terms of radical transparency, the knowable and the calculable. It is argued that these contrasting approaches may amount to opposing social models of an emerging information society, and that the analysis of contemporary conflicts and mobilizations needs to be alert to novel forms of communicative practice at work in digital cultures today

ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction - Part I - Influence of the RANS Simulation

A benchmark of Reynolds-Averaged Navier-Stokes (RANS)-informed analytical methods, which are attractive for predicting fan broadband noise, was conducted within the framework of the European project TurboNoiseBB. This paper discusses the first part of the benchmark, which investigates the influence of the RANS inputs. Its companion paper focuses on the influence of the applied acoustic models on predicted fan broadband noise levels. While similar benchmarking activities were conducted in the past, this benchmark is unique due to its large and diverse data set involving members from more than ten institutions. In this work, the authors analyze RANS solutions performed at approach conditions for the ACAT1 fan. The RANS solutions were obtained using different CFD codes, mesh resolutions, and computational settings. The flow, turbulence, and resulting fan broadband noise predictions are analyzed to pinpoint critical influencing parameters related to the RANS inputs. Experimental data are used for comparison. It is shown that when turbomachinery experts perform RANS simulations using the same geometry and the same operating conditions, the most crucial choices in terms of predicted fan broadband noise are the type of turbulence model and applied turbulence model extensions. Chosen mesh resolutions, CFD solvers, and other computational settings are less critical

The crisis of party democracy, cognitive mobilization, and the case for making parties more deliberative

The much-discussed crisis of political parties poses a challenge to democratic theorists as institutional designers: how can the capacity of parties to mediate between society and state be resuscitated? In this paper, we suggest that parties need to become more internally deliberative, allowing partisans to debate policy and more general visions for the polity. We outline a prescriptive model of deliberative intra-party democracy, drawing on the empirical literature on the changing structure of civic and political engagement. We argue that deliberative reforms are the most appropriate response to the demands of an increasingly more cognitively mobilized citizenry which seeks self-expression and non-hierarchical forms of political engagement. We highlight the model’s distinctive strengths and defend it against several objections

Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of $\sqrt s =1.96$ TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is $A_{\mathrm{FB}}^{t\bar{t}} = 0.128 \pm 0.025$. The combined inclusive and differential asymmetries are consistent with recent standard model predictions