Erich Fromm and the Critical Theory of Communication

Erich Fromm (1900-1980) was a Marxist psychoanalyst, philosopher and socialist humanist. This paper asks: How can Fromm’s critical theory of communication be used and updated to provide a critical perspective in the age of digital and communicative capitalism? In order to provide an answer, the article discusses elements from Fromm’s work that allow us to better understand the human communication process. The focus is on communication (section 2), ideology (section 3), and technology (section 4). Fromm’s approach can inform a critical theory of communication in multiple respects: His notion of the social character allows to underpin such a theory with foundations from critical psychology. Fromm’s distinction between the authoritarian and the humanistic character can be used for discerning among authoritarian and humanistic communication. Fromm’s work can also inform ideology critique: The ideology of having shapes life, thought, language and social action in capitalism. In capitalism, technology (including computing) is fetishized and the logic of quantification shapes social relations. Fromm’s quest for humanist technology and participatory computing can inform contemporary debates about digital capitalism and its alternatives

Spectral Evolution in Blazars : The Case of CTA 102

Active Galactic Nuclei (AGN) are among the most powerful objects in the universe. In their centre they host a supermassive black hole (BH) with up to 1010 solar masses and an accretion disk is formed around them feeding the system. A fraction of the in-falling mater is ejected perpendicularly to the accretion disk forming the so-called jets. These relativistic flows are highly collimated and propagate up to kiloparsec distances from their central engine. The observed emission of AGN jets shows strong variability throughout the electro-magnetic spectrum which reflects variations in source intrinsic parameters such as the magnetic field and the rest-mass density. The variation in the emission of AGN jets can be best studied in their most powerful representatives, the blazars (AGN jets seen under a small viewing angle). The blazar CTA 102 underwent a historic radio outburst in April 2006 which provides a perfect laboratory for studying the spectral evolution. CTA 102 has been a target of single-dish and VLBI observations for several years. In this work we use both kind of observations to study and model the spectral evolution during the flare. We use the dense sampling of the single-dish observations to trace the evolution of the flare in the turnover-frequency and turnover flux density plane and modelled the results with a modified shock-in-jet model, assuming a travelling shock recollimation shock interaction. To test this hypothesis, we combine archival VLBI observations from the MOJAVE program (15 GHz) and Boston University Blazar Monitoring program (43 GHz) with our multi-frequency VLBI observations during the 2006 flare. The VLBI kinematic provides a unique view on the parsec-scale structure of CTA 102 over the last 15 years and reveals several stationary features. Our hypothesis of a shock-shock interaction as possible mechanism behind the 2006 is confirmed by a detailed spectral analysis of the multi-frequency VLBI observations. We use 2D relativistic hydrodynamic simulations (RHD) to bridge the sparse time sampling of the observations and to further investigate the non-linear process of travelling shock recollimation shock interaction. From the simulations we compute the non-thermal emission taking adiabatic and radiative losses into account. The synthetic single dish spectra and radio maps can reproduce the observed structure in the VLBI maps and variation in the single dish spectra during the flare. In addition, we present observable predictions for the interaction between a travelling shock and a recollimation shock

Detecting the local transport properties and the dimensionality of transport of epitaxial graphene by a multi-point probe approach

The electronic transport properties of epitaxial monolayer graphene (MLG) and hydrogen-intercalated quasi free-standing bilayer graphene (QFBLG) on SiC(0001) are investigated by micro multi-point probes. Using a probe with 12 contacts, we perform four-point probe measurements with the possibility to effectively vary the contact spacing over more than one order of magnitude, allowing us to establish that the transport is purely two-dimensional. Combined with the carrier density obtained by angle-resolved photoemission spectroscopy, we find the room temperature mobility of MLG to be (870+-120)cm2/Vs. The transport in QFBLG is also found to be two-dimensional with a mobility of (1600+-160) cm2/Vs

The Accelerating Jet of 3C 279

Analysis of the proper motions of the sub-parsec scale jet of the quasar 3C 279 at 15 GHz with the VLBA shows significant accelerations in four of nine superluminal features. Analysis of these motions is combined with the analysis of flux density light curves to constrain values of Lorentz factor and viewing angle (and their derivatives) for each component. The data for each of these components is consistent with significant changes to the Lorentz factor, viewing angle and azimuthal angle, suggesting jet bending with changes in speed. We see that for these observed components Lorentz factors are in the range Γ = 10−41, viewing angles are in the range ϑ = 0.1◦ −5.0◦ , and intrinsic (source frame) flux density is in the range, Fν , int = 1.5×10−9−1.5×10−5 Jy. Considering individual components, the Lorentz factors vary from Γ = 11 − 16 for C1, Γ = 31 − 41 for C5, Γ = 29 − 41 for C6 and Γ = 9 − 12 for C8, indicating that there is no single underlying flow speed to the jet and likely we are seeing pattern speeds from shocks in the jet. The viewing angles vary in time from 0.6◦ to 1.5◦ in the case of C1 (the least extreme example), vary from 0.5◦ to 5.0◦ in the case of C8 and vary from 0.1◦ to 0.9◦ for C5 (the last two being the most extreme examples). The intrinsic flux density varies by factors from 1.4 for C8 and 430 for C5. Theoretical analysis of the accelerations also indicates potential jet bending. In addition, for one component, C5, polarization measurements also set limits to the trajectory of the jet

A sensitive study of the peculiar jet structure HST-1 in M87

To obtain a better understanding of the location and mechanisms for the production of the gamma-ray emission in jets of AGN we present a detailed study of the HST-1 structure, 0.8 arcsec downstream the jet of M87, previously identified as a possible candidate for TeV emission. HST-1 shows a very peculiar structure with superluminal as well as possible stationary sub-components, and appears to be located in the transition from a parabolic to a conical jet shape, presumably leading to the formation of a recollimation shock. This scenario is supported by our new RHD simulations in which the interaction of a moving component with a recollimation shock leads to the appearance of a new superluminal component. To discern whether HST-1 is produced by a recollimation shock or some other MHD instability, we present new polarimetric 2.2 and 5 GHz VLBA, as well as 15, 22 and 43 GHz JVLA observations obtained between November 2012 and March 2013.Comment: 6 page

The Current Ability to Test Theories of Gravity with Black Hole Shadows

Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (BH), as suggested by observations tracking individual orbiting stars. Upcoming sub-millimetre very-long-baseline-interferometry (VLBI) images of Sgr A* carried out by the Event-Horizon-Telescope Collaboration (EHTC) are expected to provide critical evidence for the existence of this supermassive BH. We assess our present ability to use EHTC images to determine if they correspond to a Kerr BH as predicted by Einstein's theory of general relativity (GR) or to a BH in alternative theories of gravity. To this end, we perform general-relativistic magnetohydrodynamical (GRMHD) simulations and use general-relativistic radiative transfer (GRRT) calculations to generate synthetic shadow images of a magnetised accretion flow onto a Kerr BH. In addition, and for the first time, we perform GRMHD simulations and GRRT calculations for a dilaton BH, which we take as a representative solution of an alternative theory of gravity. Adopting the VLBI configuration from the 2017 EHTC campaign, we find that it could be extremely difficult to distinguish between BHs from different theories of gravity, thus highlighting that great caution is needed when interpreting BH images as tests of GR.Comment: Published in Nature Astronomy on 16.04.18 (including supplementary information); simulations at https://blackholecam.org/telling_bhs_apart

How to tell an accreting boson star from a black hole

The capability of the Event Horizon Telescope (EHT) to image the nearest supermassive black hole candidates at horizon-scale resolutions offers a novel means to study gravity in its strongest regimes and to test different models for these objects. Here, we study the observational appearance at 230 GHz of a surfaceless black hole mimicker, namely a non-rotating boson star, in a scenario consistent with the properties of the accretion flow onto Sgr A*. To this end, we perform general relativistic magnetohydrodynamic simulations followed by general relativistic radiative transfer calculations in the boson star space-time. Synthetic reconstructed images considering realistic astronomical observing conditions show that, despite qualitative similarities, the differences in the appearance of a black hole -- either rotating or not -- and a boson star of the type considered here are large enough to be detectable. These differences arise from dynamical effects directly related to the absence of an event horizon, in particular, the accumulation of matter in the form of a small torus or a spheroidal cloud in the interior of the boson star, and the absence of an evacuated high-magnetization funnel in the polar regions. The mechanism behind these effects is general enough to apply to other horizonless and surfaceless black hole mimickers, strengthening confidence in the ability of the EHT to identify such objects via radio observations.Comment: 16 pages, 12 figures. Published in MNRAS. Adding more information in the form of appendices, and a new simulation of a different boson star model. The conclusions do not chang