876 research outputs found
Katalog der Musikbibliothek Peters ...
No full textClassified, with author indexes.Preface signed: C.F. Peters. Dr. Emil Vogel, bibliothekar.Abth. 1. Theoretische Werke.--Abth. 2. Praktische Werke.Mode of access: Internet
Motion of quantum vortex lines near realistic rough boundaries
No full textWe numerically solve the three--dimensional, time--dependent Gross--Pitaevskii equation to model a superfluid flowing over a realistic rough boundary. Our model for the boundary is based on the atom--force microscope image of a NbTi vibrating wire used to generate turbulence in actual experiments. We find that near the boundary a dense region of quantum vortices is created, which forms a kind of `superfluid boundary layer'
Wave excitations in adjacent vortex filaments
No full textThe interactions of the nearest neighbour vortices are argued to play a significant role in the crossover range of scales that lies between the Kolmogorov-Richardson cascade and the Kelvin wave driven cascade in superfluid turbulence. In this work, we study how a wave excitation (a Kelvin wave or a soliton) on a vortex affects a nearby straight vortex. Our numerical simulations reveal that coherent excitations can hop from one vortex filament to another whilst retaining their coherent properties
Spectral properties of Andreev reflection from quantum turbulence in 3He-B: What do they tell about turbulent fluctuations?
No full textOne of the experimental techniques developed to measure quantum turbulence at low temperatures in 3He-B utilizes the Andreev reflection of thermal quasiparticle excitations from quantized vortices and vortex structures. We present the results of theoretical, numerical, and experimental study of Andreev scattering from quantum turbulence in 3He-B. We analyze the spectral properties of the Andreev reflection and compare these with the spectral properties of superfluid turbulence, and discuss the physical mechanisms responsible for the scaling of spectral densities. Finally, we discuss the relation between our findings and related observables in ordinary turbulence
Evaluación in vitro del efecto del mercurio sobre la movilidad y velocidad espermática individual de la barbilla (Rhamdia sebae c.f)
No full textLos residuos de metales pesados liberados en los sistemas acuáticos ocasionan contaminación en el medio ambiente los cuales progresivamente se van biocumulando en ecosistemas. El mercurio (Hg) como parte de estos elementos contaminantes, se presenta en diferentes formas orgánicas e inorgánicas que son fácilmente asimilables en el agua y dentro de los organismos acuáticos, magnificándose a medida que la cadena trófica crece. En Colombia muchos de los afluentes de las principales cuencas, ya presentan contaminación con mercurio principalmente cerca de zonas de explotación aurífera, ya que esta tipo de actividad necesita de este metal para la extracción de oro, Uno de los muchos efectos del mercurio esta estrechamente relacionado con la disrupción endocrina, por lo cual el presente estudio fue orientado en determinar la movilidad y velocidad espermática individual del semen de barbilla (Rhamdia sebae c.f) expuesto a mercurio bajo condiciones in vitro.
El presente estudio se realizó en el Instituto de Acuicultura de los Llanos en el departamento del Meta- Colombia. La barbilla (Rhamdia sebae c.f) es una especie endémica de la región de la Orinoquia (Meta). Se utilizaron ocho machos adultos de Rhamdia sebae c.f (86,85 ± 4,29 g; 22,32 ± 1,44 cm). En cada una de las muestras seminales como parte de la metodología experimental, se evaluaron las características macroscópicas (volumen, color, viscosidad) y microscópicas del semen (concentración espermática, espermatocrito y movilidad masal). Y para el análisis de las variables respuesta se procedió a la evaluación de movilidad y velocidad espermática utilizando un sistema de análisis espermático asistido (CASA). La movilidad fue activada utilizando concentraciones de 0 (control) 10, 100, 500, 1.000, 10.000 y 100.000 µg.L-1 de cloruro de mercurio (HgCL2). Se determinó la movilidad progresiva rápida lineal (WHOa), movilidad progresiva lenta lineal (WHOb), movilidad circular (WHOc) y amótiles (WHOd) y variables de velocidad como: velocidad en línea recta (VSL), velocidad curvilínea (VCL) y velocidad angular promedio (VAP).
Los resultados arrojaron que concentraciones de 10.000 y 100.000 µg.L-1 de cloruro de mercurio disminuyen y afectan las variables de movilidad y velocidad espermática, mientras que en concentraciones mas bajas de 10, 100, 500 y 1000 µg.L-1 no existe un efecto significativo sobre las variables de movilidad y velocidad espermática en Rhamdia sebae c.f . Se determino que existe un efecto del mercurio sobre la movilidad y velocidad espermática de la barbilla (Rhamdia sebae c.f) a medida que las concentraciones aumentan; por lo tanto se puede inferir que bajo estas condiciones el mercurio puede afectar la reproducción de peces en ambientes acuáticos contaminados con este metal
A Fuzzy-based Scoring Rule for Author Ranking: an alternative to h-index
No full textThe measurement of the quality of research has reached nowadays an increasing interest not only for scientific reasons but also for the critical problem of researchers' ranking, due to the lack of grant assignments. The most commonly used approach is based on the so-called h-index, even if the current literature debated a lot about its pros and cons. This paper, after a brief review of the h-index and of alternative models, focuses on the characterization and the implementation of a modified scoring rule approach by means of a fuzzy inference system a là Sugeno
Tips for TIPS
No full textThe transjugular intrahepatic portosystemic shunt (TIPS) procedure is one of the most technically challenging procedures in interventional radiology. During the procedure, interventional radiologists (IRs) insert very thin and long instruments through a little incision in the patient’s neck. They then navigate the instruments through the blood vessels towards the liver to create a shunt in the liver. The most difficult step of the procedure is to puncture through the liver into to the portal vein, often referred to as the intrahepatic puncture. The difficulty of the puncture lies in the limited availability of real-time three-dimensional (3D) information about the anatomy and instruments during the puncture. IRs do get information to navigate, for example from X-ray imaging modalities, but insufficient. A promising technique to provide IRs the required information is by using three-dimensional ultrasound (3D US). However, the user interfaces (UI) of current 3D US machines are complicated and do not meet IRs’ expectations. The goal of this research is to design a real-time 3D US based UI for IRs to minimize the number of punctures during the TIPS procedure. To do so, the main objective of this thesis was to discover what information should be presented in an interactive 3D US based UI to minimize the number of intrahepatic punctures in the TIPS procedure. By using co-design research, the author was able to create an overview of the TIPS procedure, identify the related challenges and UI needs, and investigate the possibilities of using 3D US technology to improve the procedure. She found that IRs mainly miss information to perform the elementary cognitive actions and have limited possibility to create and maintain proper situation awareness, to predict the consequence of actions, and to learn from previous attempts. Based on the insights, two 3D US based UIs were designed to plan and perform the intrahepatic puncture, respectively. The UIs were tested with IRs and the results showed that both UIs provided the participating IRs with 3D information, feedback and navigation support in a more effective and efficient manner.Design EngineeringIndustrial Design Engineerin
Análisis no destructivo, mediante haces de iones, de joyas y ornamentos propios de la metalurgia del oro de América prehispánica
No full textLa metalurgia del oro en América nació hace más de 3.500 años en Perú (Lechtman, 1988: 344). Los conocimientos metalúrgicos comenzaron a desarrollarse paulatinamente y a propagarse hasta llegar a Mesoamérica a principios del período posclásico. Los conceptos del universo y de la relación hombre-naturaleza, los símbolos y los significados asociados a los metales preciosos, los recursos naturales y el papel del metal en la sociedad en los ámbitos religioso, político y social, determinaron el uso de los metales preciosos y el desarrollo de la tecnología metalúrgica de una manera muy particular y única en el mund
Formal synthesis of analytic controllers for sampled-data systems via genetic programming
No full textThis paper presents an automatic formal controller synthesis method for nonlinear sampled-data systems with safety and reachability specifications. Fundamentally, the presented method is not restricted to polynomial systems and controllers. We consider a periodically switched controllers based on a Control Lyapunov Barrier-like function. The proposed method utilizes genetic programming to synthesize these function in analytic form, as well as the controller modes. Correctness of the controller are subsequently verified by means of a Satisfiability Modulo Theories solver. Effectiveness of the proposed methodology is demonstrated on multiple systems.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Tamas Keviczk
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