1,540 research outputs found
Cosmological unparticle correlators
No full textAbstractWe introduce and study an extension of the correlator of unparticle matter operators in a cosmological environment. Starting from FRW spaces we specialize to a de Sitter space–time and derive its inflationary power spectrum which we find to be almost flat. We finally investigate some consequences of requiring the existence of a unitary boundary conformal field theory in the framework of the dS/CFT correspondence
Electron transport through single donors in silicon
No full text-Kavli Institute of Nanoscience DelftApplied Science
An analytical short- and long-term memory model of presynaptic plasticity
No full textA mathematical model, called the Learning Gate Model (LGM), that describes phenomena responsible for biological synaptic plasticity, is presented. The functionality of the model are mainly based on the work of Kandel and colleagues on the most elementary forms of learning observed in the Aplysia Californica marine mollusc. In particular, emphasis is placed on the double temporal dynamics of synaptic plasticity and the temporal specificity of classical conditioning. By properly modeling the effect of the binding of Ca++ ions to the serotonin-sensitive adenylate cyclase enzyme, it is shown how a positively accelerated learning curve can be obtained for sensitization and classical conditioning. Phenomena of spontaneous recovery and second-order conditioning are reproduced through simulations. Mathematical analyses of the temporal trace of conditioned stimulus and of the Short-Term Memory steady state are also given. © 1992 Springer-Verlag
New (Probabilistic) Derivation of Diaz-Metcalf and Pólya-Szegő Inequalities and Consequences
No full textClassical inequalities of Diaz - Metcalf and Pólya - Szegő are generalized to
probabilistic setting which covers the initial deterministic (both discrete and integral) variants.
From these two inequalities, by the probabilistic derivation method further well -
known inequalities are obtained (that ones by Kantorovich, Rennie and Schweitzer)
Vacuum energy and spectral function sum rules.
No full textWe reformulate the problem of the cancellation of the ultraviolet divergencies of the vacuum energy, particularly important at the cosmological level, in terms of a saturation of spectral function sum rules which leads to a set of conditions on the spectrum of the fundamental theory. We specialize the approach to both Minkowski and de Sitter space-times and investigate some examples
Second Order Gauge-Invariant Perturbations during Inflation
No full textThe evolution of gauge invariant second-order scalar perturbations in a general single field inflationary scenario are presented. Different second order gauge invariant expressions for the curvature are considered. We evaluate perturbatively one of these second order curvature fluctuations and a second order gauge invariant scalar field fluctuation during the slow-roll stage of a massive chaotic inflationary scenario, taking into account the deviation from a pure de Sitter evolution and considering only the contribution of super-Hubble perturbations in mode-mode coupling. The spectra resulting from their contribution to the second order quantum correlation function are nearly scale-invariant, with additional logarithmic corrections to the first order spectrum. For all scales of interest the amplitude of these spectra depend on the total number of e-folds. We find, on comparing first and second order perturbation results, an upper limit to the total number of e-folds beyond which the two orders are comparable
The electrons are waves: impossible interview to C.J. Davisson (1881-1958) and G.P. Thomson (1892-1975)
No full textThe author imagines to interview the Nobel Laureates in Physics of the year 1937, who turned upside-down modern physics, demonstrating the wave nature of matter. The answers of C. Davisson and G.P. Thomson are based on
the Nobel Lectures they delivered during the Nobel Prize Award Ceremony
The QCD odderon in elastic (anti)proton scattering
No full textThe C-odd amplitude for the elastic pp and scattering due to the exchange of the QCD odderon proposed by J. Bartels, L.N. Lipatov and G.P. Vacca is calculated with the Fukugita–Kwiecinski proton impact factor. The found amplitude is very small and cannot be felt in the differential cross-sections at 2.76 and 1.96 TeV respectively
Evaluatierapport “Powered by you”: Ontwikkeling Sustainable Energy Floor- energieopwekkende vloer
No full textOp weg naar rendabele energieopwekking door lopen. Er was een voorsprong in kennis en ervaring aangaande de techniek die nodig was een energie genererende loopvloer (de Sustainable Energy Floor – SEF) te realiseren. Specifieke aanpassingen moesten echter ontwikkeld worden in verband met de andere bewegingsvorm, de schaal die vele malen groter is en de andere installatie- en logistieke eisen. Het doel was om een pilot te doen op één of meer aansprekende locaties. Het project moest een belangrijke stap zijn op weg naar rendabele energieopwekking door lopen. Samen met de TU Delft, faculteit Industrieel Ontwerpen en Rinnic Vaude is onderzoek gedaan naar de haalbaarheid van het ontwikkelen van SEF, zijn prototypes en een pilotvloer gerealiseerd, tests gedaan en presentaties en demonstraties gegeven aan vele partijen en een breed publiek in Delft en Rotterdam. Vanwege technische knelpunten gedurende het project en de praktische haalbaarheid is er niet één grote pilot voor een langere periode gedaan, maar zijn er meerdere kortdurende pilots en tests gedaan. Het voordeel hiervan was dat we op basis van de analyses, tests en de feedback van gebruikers op verschillende versies prototypes, het ontwerp steeds verder konden verbeteren. Tenslotte heeft dit geresulteerd in het bouwen van de pilotvloer, waarmee de eindtest in De Kuip is uitgevoerd naar tevredenheid van alle betrokken partijen. Het project is succesvol afgerond en de doelstellingen zijn gehaald binnen het gestelde budget. Het project is uitgevoerd met steun van het programma Kansen voor West, wat valt onder het Europese Fonds voor Regionale Ontwikkeling.Industrial Design Engineerin
Decay of turbulence at high Reynolds numbers
No full textUsing the unique capabilities of the Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization, we investigated virtually homogeneous and isotropic grid turbulence over a wide range of Reynolds numbers, , between and . The choice of pressurizable Sulfur Hexafluoride as a working gas makes it possible to reach extremely high Reynolds numbers without changing boundary conditions. Indeed, the Reynolds number we reached were higher than any previous classical grid wind-tunnel experiment. In this talk, we focus on the fundamental question of how fast turbulent energy decays once it has been created, and show that the Reynolds number plays no important role in setting the decay rate if it is high enough
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