137 research outputs found
Spiral Disk Instability Can Drive Thermonuclear Explosions in Binary White Dwarf Mergers
Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion
of carbon--oxygen white dwarfs, and serve as standardizable cosmological
candles. However, despite their importance, the nature of the progenitor
systems that give rise to SNe Ia has not been hitherto elucidated.
Observational evidence favors the double-degenerate channel in which merging
white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies
exist between observations and theory, and to date, there has been no
self-consistent merger model that yields a SNe Ia. Here we show that a spiral
mode instability in the accretion disk formed during a binary white dwarf
merger leads to a detonation on a dynamical timescale. This mechanism sheds
light on how white dwarf mergers may frequently yield SNe Ia.Comment: Final version (as in ApJL) with minor edit
Structural selective charge transfer in iodine-doped carbon nanotubes
We have investigated iodine intercalated carbon nanostructures by extended X-ray absorption fine structure (EXAFS) and Raman spectroscopies. We discuss here the charge transfer and the iodineâcarbon interaction as a function of the carbon nanostructures (graphite, multi-walled, double-walled and single walled nanotubes). The results show that iodine is weakly adsorbed on the surface of all multi-walled nanotubes. By contrast, a charge transfer between iodine and single walled nanotubes is evidenced
CYCLONE Unified Deployment and Management of Federated, Multi-Cloud Applications
Various Cloud layers have to work in concert in order to manage and deploy
complex multi-cloud applications, executing sophisticated workflows for Cloud
resource deployment, activation, adjustment, interaction, and monitoring. While
there are ample solutions for managing individual Cloud aspects (e.g. network
controllers, deployment tools, and application security software), there are no
well-integrated suites for managing an entire multi cloud environment with
multiple providers and deployment models. This paper presents the CYCLONE
architecture that integrates a number of existing solutions to create an open,
unified, holistic Cloud management platform for multi-cloud applications,
tailored to the needs of research organizations and SMEs. It discusses major
challenges in providing a network and security infrastructure for the
Intercloud and concludes with the demonstration how the architecture is
implemented in a real life bioinformatics use case
The Koch monopole: a small fractal antenna
Fractal objects have some unique geometrical properties. One of them is the possibility to enclose in a finite area an infinitely long curve. The resulting curve is highly convoluted being nowhere differentiable. One such curve is the Koch curve. In this paper, the behavior the Koch monopole is numerically and experimentally analyzed. The results show that as the number of iterations on the small fractal Koch monopole are increased, the Q of the antenna approaches the fundamental limit for small antennas.Peer Reviewe
Sports Scene Searching, Rating & Solving using AI
This work shows the application of artificial intelligence (AI) on invasion game tracking data to realize a fast (sub-second) and adaptable search engine for sports scenes, scene ratings based on machine learning (ML) and computer-generated solutions using reinforcement learning (RL). We provide research results for all three areas. Benefits are expected for accelerated video analysis at professional sports clubs.Diese Arbeit zeigt die Anwendung von kĂŒnstlicher Intelligenz (KI) auf Invasionsspielverfolgungsdaten, um eine schnelle (unter einer Sekunde) und anpassungsfĂ€hige Suchmaschine fĂŒr Sportszenen zu realisieren, Szenenbewertungen auf der Grundlage von maschinellem Lernen (ML) und computergenerierte Lösungen unter Verwendung von VerstĂ€rkungslernen (RL). Wir stellen Forschungsergebnisse fĂŒr alle drei Bereiche vor. Es werden Vorteile fĂŒr eine beschleunigte Videoanalyse in Profisportvereinen erwartet
Activation of G proteins by GIV-GEF is a pivot point for insulin resistance and sensitivity.
Insulin resistance (IR) is a metabolic disorder characterized by impaired insulin signaling and cellular glucose uptake. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the sole conduit for postreceptor signaling. Here we challenge that paradigm and show that GIV/Girdin, a guanidine exchange factor (GEF) for the trimeric G protein Gαi, is another major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind InsR, IRS1, and phosphoinositide 3-kinase, GIV serves as a key hub in the immediate postreceptor level, which coordinately enhances the metabolic insulin response and glucose uptake in myotubes via its GEF function. Site-directed mutagenesis or phosphoinhibition of GIV-GEF by the fatty acid/protein kinase C-theta pathway triggers IR. Insulin sensitizers reverse phosphoinhibition of GIV and reinstate insulin sensitivity. We also provide evidence for such reversible regulation of GIV-GEF in skeletal muscles from patients with IR. Thus GIV is an essential upstream component that couples InsR to G-protein signaling to enhance the metabolic insulin response, and impairment of such coupling triggers IR. We also provide evidence that GIV-GEF serves as therapeutic target for exogenous manipulation of physiological insulin response and reversal of IR in skeletal muscles
On the behavior of the Sierpinski multiband fractal antenna
The multiband behavior of the fractal Sierpinski antenna is described. Due to its mainly triangular shape, the antenna is compared to the well-known single-band bow-tie antenna. Both experimental and numerical results show that the self-similarity properties of the fractal shape are translated into its electromagnetic behavior. A deeper physical insight on such a behavior is achieved by means of the computed current densities over the antenna surface, which also display some similarity properties through the bands.Peer Reviewe
Low cost transmission line demonstrator for a novel intermediate level communication engineering laboratory
This paper is devoted to the description of a transmission line laboratory demonstrator for intermediate level communication engineering students, within a course on radiation and guided waves. Student activities have been organized according to the needs of intermediate level students and the objectives of an introductory laboratory, which are substantially different from those of specialized laboratory activities aimed at higher level students and placed just before graduation. Since a large number of students attend these laboratory sessions before they choose their specialty, low cost is an unavoidable requirement to be considered. For this reason, the measurement set-up makes use of standard instrumentation, usually available in a basic electronic laboratory, which allows multiplication of work places at a reasonable cost. Both time domain reflectometry and sinusoidal steady state measurements are presented to characterize the main parameters of a coaxial line. However, discussions are mainly focused on sinusoidal measurements, which are scarce in the literature and exclusively devoted to slotted line measurements. The experimental work undertaken by the students gives them insight into main transmission line parameter and features: line impedance, propagation speed, its behavior as an impedance transformer, the complex nature of the measured magnitudes and the standing wave behavior of voltage and attenuation.Peer Reviewe
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