Search for short-period acoustic waves with high resolution 2D-spectra

The data for this contributionw ere takeninAugust 2000 with the “G¨ottingen” two-dimensional spectrometer in the VTT on Tenerife. Our spectrometer is based on two scanning Fabry-Perot Interferometers (FPIs). The non-magnetic Fe I 5434˚A line was observed in the quiet Sun at disk center. Time sequences of 41 min duration and with 25 s cadence were taken. Strictly simultaneously with the narrow-band FPI images (32m˚A FWHM), broad-band images were recorded. The latter were reconstructed with speckle methods. With the known “true” broad-band object we are able to restore the narrow-band images as well. Our aim is to find propagating acoustic waves at short periods and small scales. The results obtained so far are presented and the prospects are discussed

With a rebel yell: Video gamers’ responses to mass shooting moral panics

When a moral panic happens, society believes that a group of people and/or their behaviour is responsible for a threat to society – without any evidentiary basis. How does the target group respond? In the video game context, gamers may fear that their pastime will be blamed for mass shootings leading to social stigma. Group members so threatened are hypothesized to react to protect their group identity. This leads to increased engagement in the activity under threat. In contrast, disasters that do not threaten the group would not affect the amount of video game play. We test these hypotheses by relating the amount of game play to incidents of mass shootings and non-shooting disasters for a large sample of individuals (N = 170,000). Incidents of mass shootings that threaten the gamer community lead to increases in game playing while incidents of other disasters unrelated to gaming divert time away from gaming

Time-dependent hydrogen ionisation in the solar chromosphere. I: Methods and first results

An approximate method for solving the rate equations for the hydrogen populations was extended and implemented in the three-dimensional radiation (magneto-)hydrodynamics code CO5BOLD. The method is based on a model atom with six energy levels and fixed radiative rates. It has been tested extensively in one-dimensional simulations. The extended method has been used to create a three-dimensional model that extends from the upper convection zone to the chromosphere. The ionisation degree of hydrogen in our time-dependent simulation is comparable to the corresponding equilibrium value up to 500 km above optical depth unity. Above this height, the non-equilibrium ionisation degree is fairly constant over time and space, and tends to be at a value set by hot propagating shock waves. The hydrogen level populations and electron density are much more constant than the corresponding values for statistical equilibrium, too. In contrast, the equilibrium ionisation degree varies by more than 20 orders of magnitude between hot, shocked regions and cool, non-shocked regions. The simulation shows for the first time in 3D that the chromospheric hydrogen ionisation degree and electron density cannot be calculated in equilibrium. Our simulation can provide realistic values of those quantities for detailed radiative transfer computations.Comment: 8 pages, 7 figure

Channeling 5-min photospheric oscillations into the solar outer atmosphere through small-scale vertical magnetic flux tubes

We report two-dimensional MHD simulations which demonstrate that photospheric 5-min oscillations can leak into the chromosphere inside small-scale vertical magnetic flux tubes. The results of our numerical experiments are compatible with those inferred from simultaneous spectropolarimetric observations of the photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter (TIP) at 10830 A. We conclude that the efficiency of energy exchange by radiation in the solar photosphere can lead to a significant reduction of the cut-off frequency and may allow for the propagation of the 5 minutes waves vertically into the chromosphere.Comment: accepted by ApJ

Urban Influencers: An Analysis of Urban Identity in YouTube Content of Local Social Media Influencers in a Super-Diverse City

Influencers belong to the daily media diet of many adolescents. As role models, they have the potential to play a crucial role in the identity construction of their viewers. In the age of social media, such role models may now be found more locally – in the same city – and perhaps with more diverse backgrounds. This may be particularly valuable to adolescents growing up in super-diverse cities, as they are surrounded by a multitude of groups and identities during a life phase in which they have to make sense of who they are and where they belong. Despite the heterogeneity of these identities, there is one thing all have in common: the city they live in. With the city as a common framework, local influencers may be important role models for these adolescents, particularly in negotiating their urban identity. This paper aims toward mapping the ways in which social media can play a role in the negotiation of urban identity among youngsters by investigating how YouTube influencers from a super-diverse city are related to each other online, and how their content relates to the (super-diverse) city of Rotterdam. Findings show that in their videos and on their channel pages, influencers mainly affiliate themselves with the city through having the city as the background and context of the videos, through their involvement with cultural trends (e.g., soccer, hip-hop) that link to the city, and through their affiliation with other local influencers. We argue that influencers may therefore provide their viewers with

Magnetic properties of photospheric regions having very low magnetic flux

The magnetic properties of the quiet Sun are investigated using a novel inversion code, FATIMA, based on the Principal Component Analysis of the observed Stokes profiles. The stability and relatively low noise sensitivity of this inversion procedure allows for the systematic inversion of large data sets with very weak polarization signal. Its application to quiet Sun observations of network and internetwork regions reveals that a significant fraction of the quiet Sun contains kilogauss fields (usually with very small filling factors) and confirms that the pixels with weak polarization account for most of the magnetic flux. Mixed polarities in the resolution element are also found to occur more likely as the polarization weakens.Comment: To apapear in ApJ. 39 pages, 12 figures (2 of them are color figures

Dissipative Dynamics of an Open Bose Einstein Condensate

As an atomic Bose Einstein condensate (BEC) is coupled to a source of uncondensed atoms at the same temperature and to a sink (extraction towards an atom laser) the idealized description in terms of a Gross-Pitaevsky equation (GP) no longer holds. Under suitable physical assumptions we show that the dissipative BEC obeys a Complex Ginzburg Landau equation (CGL) and for some parameter range it undergoes a space time patterning. As a consequence, the density of BEC atoms within the trap displays non trivial space time correlations, which can be detected by monitoring the density profile of the outgoing atom laser. The patterning condition requires a negative scattering length, as e.g. in $^7$Li. In such a case we expect a many domain collapsed regime, rather than a single one as reported for a closed BEC.Comment: 13 pages, 5 figures, submitt. to Optics Comm., 18th Aug. 99 (special issue Scully Festschrift

Radiative transfer in moving media II. Solution of the radiative transfer equation in axial symmetry

A new method for the formal solution of the 2D radiative transfer equation in axial symmetry in the presence of arbitrary velocity fields is presented. The combination of long and short characteristics methods is used to solve the radiative transfer equation. We include the velocity field in detail using the Local Lorentz Transformation. This allows us to obtain a significantly better description of the photospheric region, where the gradient of the global velocity is too small for the Sobolev approximation to be valid. Sample test calculations for the case of a stellar wind and a rotating atmosphere are presented.Comment: 11 pages, 19 figures. accepted by Astronomy and Astrophysic