Dark Energy vs. Modified Gravity

Understanding the reason for the observed accelerated expansion of the Universe represents one of the fundamental open questions in physics. In cosmology, a classification has emerged among physical models for the acceleration, distinguishing between Dark Energy and Modified Gravity. In this review, we give a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology. We also introduce a rigorous distinction between Dark Energy and Modified Gravity based on the strong and weak equivalence principles.Comment: 29 pages, 4 figures; invited review submitted to Annual Reviews of Nuclear and Particle Science; v2: some pertinent references added; v3: table with constraints added, reflects published version; v4 [trivial]: fixed missing references in arxiv versio

In All Likelihood, Deep Belief Is Not Enough

Statistical models of natural stimuli provide an important tool for researchers in the fields of machine learning and computational neuroscience. A canonical way to quantitatively assess and compare the performance of statistical models is given by the likelihood. One class of statistical models which has recently gained increasing popularity and has been applied to a variety of complex data are deep belief networks. Analyses of these models, however, have been typically limited to qualitative analyses based on samples due to the computationally intractable nature of the model likelihood. Motivated by these circumstances, the present article provides a consistent estimator for the likelihood that is both computationally tractable and simple to apply in practice. Using this estimator, a deep belief network which has been suggested for the modeling of natural image patches is quantitatively investigated and compared to other models of natural image patches. Contrary to earlier claims based on qualitative results, the results presented in this article provide evidence that the model under investigation is not a particularly good model for natural image

Theoretical investigation of n-butane isomerization in metal-substituted aluminosilicates

Der stetige Anstieg an Treibhausgasen in unserer Atmosphäre, welche der Grund für den konstanten Anstieg der Temperatur der Erde sind, beruht zu einem großen Teil auf der Emission dieser Gase, z.B. von Kohlenstoffdioxid (CO$_2$), durch industrielle Prozesse. Speziell in der petrochemischen Industrie wird eine große Menge an CO$_2$ durch Flaring von ungewollten leichten Kohlenwasserstoffen, wie z.B. Butan, produziert. Um das Problem des Klimawandels, welches auf dem erhöhten Ausstoß von Treibhausgasen beruht, zu bekämpfen, is es von hoher Wichtigkeit, diese Nebenprodukte effizient zu nutzen. Im Fall von Butan ist eine katalytische Isomerisierung zu Isobutan möglich. Isobutan ist ein sehr viel wertvolleres Molekül aufgrund der diversen Verwendungsmöglichkeiten in der Industrie, z.B. zur Verbesserung der Oktanzahl von Benzin oder in der Synthese von Methyl-tert-butyl-ether (MTBE) via Isobutylen. Jedoch enthalten gegenwärtig für diese Reaktion verwendete Katalysatoren toxische Komponenten, wodurch deren Verwendung gefährlich und umweltschädlich ist. Daher ist eine gründliche und breite Forschung notwendig, um effizientere, billigere und umweltfreundlichere Katalysatoren für die Isomerisierung von n-Butan zu Isobutan zu entdecken. In dieser Arbeit wird dieses Problem rechnerisch mithilfe von sehr genauen Dichtefunktionaltheorie (DFT) Rechnungen angegangen. Die zugrundeliegenden Mechanismen der n-Butan Isomerisierung werden mithilfe eines Modell-Katalysators, H-SSZ-13 (CHA), untersucht, welcher kostengünstig und einfach zu berechnen ist. Die zwei in der Literatur ausgiebig diskutierten Reaktionspfade für die Isomerisierung von 2-Buten, nämlich der monomolekulare und der bimolekulare Mechanismus, werden in dem Zeoliten H-SSZ-13 optimiert und miteinander verglichen. Zusätzlich wurden zwei weitere Reaktionsmechanismen vorgestellt, der (intermolekulare) Wasserstoff-Transfer-Mechanismus und der Methyl-Transfer-Mechanismus. Ersterer zeigt eine Möglichkeit auf, wie Olefine, welche während der Reaktion gebildet werden, die Reaktion selbst katalysieren können, während letzterer einen zweiten Reaktionspfad beschreibt, durch welchen die Bildung von ungewünschten Nebenprodukten der Reaktion erklärt werden können. Die Reaktionsbarrieren wurden für alle Mechanismen mithilfe sehr genauer Methoden berechnet. Diese Barrieren zeigen, dass für den Zeolit H-SSZ-13 mit einer Barriere von 152 kJ/mol bei einer Temperatur von 400 °C der monomolekulare Mechanismus gegenüber dem bimolekularen Mechanismus bevorzugt wird. Der Wasserstoff-Transfer-Mechanismus hat eine eher hohe freie Barriere der freien Energie von 203 kJ/mol, während die Barriere für den Methyl-Transfer-Mechanismus mit 227 kJ/mol sehr hoch und daher bei den betracheten Reaktionsbedingungen nicht plausibel ist. Diese Reaktionsmechanismen werden anschließend in einer Reihe von verschiedenen Zeoliten und Zeotypen von CHA, AFI und MOR neu optimiert. Für den monomolekularen Mechanismus werden abhängig von dem konkreten Zeoliten unterschiedliche Reaktionspfade als optimal berechnet. Für Zeolite, welche eine höhere Azidität aufweisen, wie es für AFI der Fall ist, wird der bimolekulare Mechanismus als konkurrierend oder sogar als dominant gegenüber den monomolekularen Mechanismus berechnet. Die Barrieren des Wasserstoff-Transfer-Mechanismus reichen von 181 kJ/mol bis 236 kJ/mol, was bedeutet, dass diese im Fall von stark aziden Zeoliten berücksichtigt werden müssen, während der Methyl-Transfer-Mechanismus nur Barrieren von $\geq$217 kJ/mol aufzeigt. Alle Resultate werden schlussendlich mittels linearer Skalierungsbeziehungen zusammengefasst, welche sich auf die Adsorptionsenergie von Ammoniak als Deskriptor beziehen. Es ist bekannt, dass diese Skalierungsbeziehungen Tendenzen in der Reaktivität von Zeolit-Katalysatoren voraussagen können, und dies gilt auch hier für die in dieser Arbeit untersuchten Reaktionsmechanismen

Analysis and Quality Assessment of LEO GPS Data for Geophysical and Ionospheric Applications

During the last few years, an ever-increasing fleet of Low Earth Orbiting (LEO) satellites for scientific purposes became operative. Most of these satellites carry dual-frequency Global Positioning System (GPS) receivers. The highly accurate dual-frequency observations allow mitigating the ionospheric signal contribution to estimate precise orbits and eventually the earth's gravity field. However, when comparing the obtained GPS only gravity fields derived from Swarm to gravity field solutions obtained by the dedicated gravity field mission GRACE, systematic band-shaped differences are visible in the vicinity of the geomagnetic equator. In this work, an empirical approach for the appropriate weighting of GPS observations is derived to mitigate these ionospheric artifacts. The cause of the artifacts is further analyzed by investigating the loop filter implementation. A tracking loop-specific transfer function is derived and used to invert the loop filter response to derive corrections for the GPS phase observations. Both methods are evaluated to achieve the best possible Swarm GPS only gravity field. Vice versa, the collected GPS observations from the LEO precise orbit determination antenna can also be used to gain insight into the topside ionosphere and plasmasphere. A three-dimensional model approach is developed using a fleet of LEO satellites to estimate a model of the electron density distribution between LEO and GPS satellites. Both aspects represent possibilities of using GPS/GNSS on-board of LEO satellites for geophysical applications

El precio justo

El precio justoFil: Schinder, Alejandro Fabian. Fundación Instituto Leloir; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; ArgentinaFil: Mongiat, Lucas Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación En Biodiversidad y Medioambiente; Argentin

CHALLENGES IN THE DEPLOYMENT AND OPERATION OF MACHINE LEARNING IN PRACTICE

Machine learning has recently emerged as a powerful technique to increase operational efficiency or to develop new value propositions. However, the translation of a prediction algorithm into an operationally usable machine learning model is a time-consuming and in various ways challenging task. In this work, we target to systematically elicit the challenges in deployment and operation to enable broader practical dissemination of machine learning applications. To this end, we first identify relevant challenges with a structured literature analysis. Subsequently, we conduct an interview study with machine learning practitioners across various industries, perform a qualitative content analysis, and identify challenges organized along three distinct categories as well as six overarching clusters. Eventually, results from both literature and interviews are evaluated with a comparative analysis. Key issues identified include automated strategies for data drift detection and handling, standardization of machine learning infrastructure, and appropriate communication and expectation management

Digital media artefacts: hybrid praxis

The special issue on Digital Media Artefacts, “Hybrid Praxis”, is a post-congress collective reflection about technology, science, and art. The invited authors participated in ARTeFACTo 2020 or ARTECH 2021; two key congresses were exploring state-of-the-art digital media arts. These encounters gather experiences from the academic world, practitioner world, and hybrid praxis, with art practice-based research as the common thread. If we reflect on contemporary technology, science, and art, we can see that technology is pushing more profound changes in sciences and arts than the other way around. Just take your eyes off the screen, look around you, and compare your daily life to what it was twenty or even ten years ago. Digital technology has profoundly changed your everyday life, relationships, possibilities, and how you express, explore, research, share, and do. We could therefore look exclusively into the digital domain to frame the relationship between the elements of this triad as it now stands.info:eu-repo/semantics/publishedVersio

Enhancement of cruzipain activity by quinoxaline derivatives: an attempt to explain it by molecular dynamics studies

The design of cruzipain (CZP) inhibitors, a key protease in the life cycle of the Trypanosoma cruzi, the causative agent of Chagas disease, constitutes one of the strategies for the search of antichagasic agents. In this context, we have proposed, through docking and MPBSA studies, quinoxalinic compounds that could be inhibitors of the enzyme. These compounds were designed through its possible interaction in a site (AS2) close to S2 region. This site has been indicated as a target for antichagasic drug design.1 Numerous derivatives were synthesized and evaluated on endogenous CZP, using as substrate Z-FR-AMC. All the evaluated compounds were inactive until concentrations of 10-4 M, but in major concentrations they increased considerably the catalytic activity of the enzyme. Although these results did not lead to the expected inhibitory effect, they seemed to indicate that the designed compounds interacted with the enzyme according to that predicted by the computational studies. In order to shed light the experimental results in a molecular approach, we decided to extend the theoretical studies using molecular dynamics simulations, to evaluate greater degrees of freedom and collective interactions of the system. We studied the behaviour of the enzyme in the absence and presence of a quinoxaline derivative, a recognized inhibitor and a substrate. The studies carried out, allow us to understand the experimental results, based on structural and differential changes of the enzyme in different points of the active site, for each type of compound tested. These changes compromise the geometry of the catalytic site. In the particular case of quinoxaline, the conformation of the enzyme stabilized is similar as that in the presence of substrate, allowing a molecular approximation to the experimental results obtained.Fil: Martini, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Fabian, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Moglioni, Albertina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaDrug Discovery for Neglected Diseases International Congress 2018CABAArgentinaUniversidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármac

More Roads or Public Transit? Insights from Measuring City-Center Accessibility

We propose a theory-inspired measure of the accessibility of a city’s center: the size of the surrounding area from which it can be reached within a specific time. Using publicly-available optimal routing software, we compute these ”accessibility zones” for the 109 largest American and European cities, separately for cars and public transit commutes. Compared to European cities, US cities are half as accessible via public transit and twice as accessible via cars. Car accessibility zones are always larger than public transit zones, making US cities more accessible overall. However, US cities’ car orientation comes at the cost of less green space, more congestion, and worse health and pollution externalities

Diseño y síntesis de análogos quinoxalínicos con potencial actividad quimioterápica

Quinoxaline compounds form a family of heterocyclic compounds present in many compounds with demonstrated and varied biological activity. \nIn order to contribute to the design of new compounds with anti-HIV activity and / or anti-Trypanosoma cruzi activity, either through its inhibitory action on the reverse transcriptase of human immunodeficiency virus or its inhibition of cruzipain, essential enzyme for development life cycle of Trypanosoma cruzi in this PhD thesis it has been employed various strategies of aided drug design computer, to design potential inhibitors of the above enzyme systems with quinoxaline structure.\nFrom the results achieved by through virtual screening of reverse transcriptase inhibitors and by the novo design or cruzipain inhibitors, the synthesis of 25 compounds containing a quinoxaline ring were proposed. These compounds were synthesized using some common methodologies for the synthesis of quinoxaline system to which modifications were introduced that allowed optimization of them, such as the use of microwave radiation as an energy source. Thus a linear, simple and efficient synthetic route is provided for obtaining 29 quinoxaline compounds, some of them not described before in the literature.\nInitial studies of the anti-Trypanosoma cruzi activity of the designed and synthesized compounds raise the possibility that subsequent assays demonstrate the activity of them and with this, the utility of the computational methods in the design of new active compounds.\nFil: Fabian, Lucas Manuel. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; ArgentinaLas quinoxalinas constituyen un sistema heterocíclico presente en numerosos compuestos con demostrada y variada actividad biológica. \nCon el fin de contribuir al diseño de nuevos compuestos con potencial actividad anti-HIV y/o antichagásica, ya sea a través su acción inhibitoria sobre la transcriptasa reversa del virus de la inmunodeficiencia humana o su inhibición de la cruzipaína, enzima esencial para el desarrollo del ciclo de vida del Trypanosoma cruzi, en este trabajo de Tesis Doctoral de han empleado varias estrategias de diseño de fármacos asistido por computadora para diseñar posibles inhibidores de los mencionados sistemas enzimáticos con estructura quinoxalínica.\nA partir de los resultados alcanzados mediante el diseño de novo o a través del cribado virtual se propusieron un total de 25 compuestos quinoxalínicos que podrían resultar inhibidores de la transcripsa reversa y/o de la cruzipaína. Estos compuestos fueron sintetizados empleando algunas metodologías habituales para la síntesis de quinoxalinas a las cuales se les introdujeron modificaciones que permitieran su optimización, tales como el empleo de radiación microondas como fuente de energía. De esta manera se aporta una ruta sintética lineal, sencilla y eficiente para la obtención de 29 compuestos quinoxalínicos, muchos de ellos no descriptos previamente en la bibliografía.\nSe iniciaron los estudios de la potencial actividad antichagásica de los compuestos diseñados y sintetizados dejando planteada la posibilidad de que ensayos posteriores contribuyan a demostrar la actividad de los mismos y la utilidad de los métodos computacionales en el diseño de nuevos compuestos quinoxalínicos activos