The Work of Art in the Age of Digital Fragility

Impermanence and fragility have become the defining conditions of the digital age. Technologies that were ubiquitous barely a decade ago, like floppy disks, now look like archaeological relics. It takes only a few years, if not months, before software environments are replaced by newer versions, often with limited backward compatibility. At the same time, digital technologies rely on hardware that has short life expectancy. The radical obsolescence of this new digital register raises a number of important questions. How are we going to prevent the fragile memories of contemporary digital cultures from receding into oblivion? This essay answers this question by looking at one of the institutions in which the problems associated with digital fragility are most especially felt, the Museum of Modern Art (MoMA), and by exploring the ontological displacements that digital objects are operating at the heart of the museum

hh-AlN-Mg(OH)2_{2} vdW Bilayer Heterostructure: Tuning the excitonic characteristics

Motivated by recent studies that reported the successful synthesis of monolayer Mg(OH)$_{2}$ [Suslu \textit{et al.}, Sci. Rep. \textbf{6}, 20525 (2016)] and hexagonal (\textit{h}-)AlN [Tsipas \textit{et al}., Appl. Phys. Lett. \textbf{103}, 251605 (2013)], we investigate structural, electronic, and optical properties of vertically stacked $h$-AlN and Mg(OH)$_{2}$, through \textit{ab initio} density-functional theory (DFT), many-body quasi-particle calculations within the GW approximation, and the Bethe-Salpeter equation (BSE). It is obtained that the bilayer heterostructure prefers the $AB^{\prime}$ stacking having direct band gap at the $\Gamma$ with Type-II band alignment in which the valance band maximum and conduction band minimum originate from different layer. Regarding the optical properties, the imaginary part of the dielectric function of the individual layers and hetero-bilayer are investigated. The hetero-bilayer possesses excitonic peaks which appear only after the construction of the hetero-bilayer. The lowest three exciton peaks are detailedly analyzed by means of band decomposed charge density and the oscillator strength. Furthermore, the wave function calculation shows that the first peak of the hetero-bilayer originates from spatially indirect exciton where the electron and hole localized at $h$-AlN and Mg(OH)$_{2}$, respectively, which is important for the light harvesting applications.Comment: Accepted by Physical Review

Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region

We analyze data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. In time series of magnetograms a diverging bipolar configuration is observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing elementary flux emergence in the solar atmosphere, i.e small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising loops (once they reached chromospheric heights) with pre-existing magnetic fields as well as to reconnection/cancellation events in U-loop segments of emerging serpentine fields. We study the temporal evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet sun regions and serpentine flux emergence signatures in active regions. Incorporating the novel features of granular-scale flux emergence presented in this study we advance the scenario for serpentine flux emergence.Comment: 24 pages, 9 figures. Accepted for publication in Solar Physic

Exciton Control in a Room-Temperature Bulk Semiconductor with Coherent Strain Pulses

The coherent manipulation of excitons in bulk semiconductors via the lattice degrees of freedom is key to the development of acousto-optic and acousto-excitonic devices. Wide-bandgap transition metal oxides exhibit strongly bound excitons that are interesting for applications in the deep-ultraviolet, but their properties have remained elusive due to the lack of efficient generation and detection schemes in this spectral range. Here, we perform ultrafast broadband deep-ultraviolet spectroscopy on anatase TiO$_2$ single crystals at room temperature, and reveal a dramatic modulation of the exciton peak amplitude due to coherent acoustic phonons. This modulation is comparable to those of nanostructures where exciton-phonon coupling is enhanced by quantum confinement, and is accompanied by a giant exciton shift of 30-50 meV. We model these results by many-body perturbation theory and show that the deformation potential coupling within the nonlinear regime is the main mechanism for the generation and detection of the coherent acoustic phonons. Our findings pave the way to the design of exciton control schemes in the deep-ultraviolet with propagating strain pulses

Determination of aspartame in soft drinks using HPLC

The aim of this project is to determine the levels of aspartame in various cola products using High Pressure Liquid Chromatography (HPLC). Four different cola brands are examined, Coca-Cola Zero, Coca-Cola Light, Pepsi Max and Harboe Cola Minus. There is written a section of theory about aspartame, the environment and legislation for the substance. Additionally, there is made a theoretical section on HPLC and statistics. In the laboratory, a method for the examination of the aspartame in the coke product is created. This method is used to collect data for the various fabricates which are examined using various statistical parameters. In method development, it is found that aspartame can be separated completely from the other ingredients of the cola products. Aspartame content is verified by means of a certified standard substance. In the laboratory an Agilent HPLC is used with a C-18 column, 150 mm long and a particle diameter of 5 micrometers. The method uses a gradient program of acetonitrile and 22 mM phosphate buffer pH 2.5. The method is confirmed by statistical calculations that show that the data for the same cola is both repeatable and reproducible. Through tests of newer colas of the same brands, it is shown that the concentration of aspartame in the same brand vary significantly from bottle to bottle. The recovery of the method is close to 100 %, which is extremely essential for the validation of the method

Las publicaciones periódicas libertarias argentinas en el acervo del CeDInCI: “una hemerografía local esmerada”

Este artículo describe y ordena en una hemerografía las publicaciones anarquistas argentinas disponibles en el Centro de Documentación e  Investigación de la Cultura de Izquierda (CeDInCI). Según el caso, cada entrada incluye: título y subtítulo de cada publicación periódica, las fechas límite entre las que apareció, las épocas que tuvo, sus responsables y sus colaboradores, y otros datos relevantes dependiendo del periódico en cuestión. Su objetivo es constituir una herramienta útil para las futuras investigaciones sobre esta temática en tanto brinda información sobre publicaciones que hasta hace pocos años sólo estaban disponibles en el International Institute of Social History (IISH) de Amsterdam

Seismic structural performance of concrete blocks with steel and aluminum alloy fiber aggregates for building construction

[EN] Concrete is a highly versatile construction material thanks to its behavior and mechanical properties. However, little is known about improving its properties through including additives in its manufacture. Concrete also has drawbacks, such as brittleness, low ductility and poor flexural strength. This material is used in many parts of the structures and may be manufactured on site or prefabricated, e.g. in the form of blocks. Including steel and aluminum alloy fibers in concrete would improve the ductility and flexural strength. This study analyzed and compared the mechanical behavior of normal concrete blocks with others made with aggregates of steel and aluminum alloy fibers. Mechanical lab tests were carried out on blocks with five, four and three layers of fibers, taking into account the requirements of the Chilean RegulationsDominguez-Santos, D.; Pallarés Rubio, FJ.; Llanos, P. (2022). Seismic structural performance of concrete blocks with steel and aluminum alloy fiber aggregates for building construction. Mechanics of Advanced Materials and Structures. 29(27):6907-6918. https://doi.org/10.1080/15376494.2021.198819069076918292

Giant exciton Mott density in anatase TiO2

Elucidating the carrier density at which strongly bound excitons dissociate into a plasma of uncorrelated electron-hole pairs is a central topic in the many-body physics of semiconductors. However, there is a lack of information on the high-density response of excitons absorbing in the near-to-mid ultraviolet, due to the absence of suitable experimental probes in this elusive spectral range. Here, we present a unique combination of many-body perturbation theory and state-of-the-art ultrafast broadband ultraviolet spectroscopy to unveil the interplay between the ultraviolet-absorbing two-dimensional excitons of anatase TiO$_2$ and a sea of electron-hole pairs. We discover that the critical density for the exciton Mott transition in this material is the highest ever reported in semiconductors. These results deepen our knowledge of the exciton Mott transition and pave the route toward the investigation of the exciton phase diagram in a variety of wide-gap insulators