3,040 research outputs found
The design concept of the 6-degree-of-freedom hydraulic shaker at ESTEC
The European Space Agency (ESA) has decided to extend its test facilities at the European Space and Technology Center (ESTEC) at Noordwijk, The Netherlands, by implementing a 6-degree-of-freedom hydraulic shaker. This shaker will permit vibration testing of large payloads in the frequency range from 0.1 Hz to 100 Hz. Conventional single axis sine and random vibration modes can be applied without the need for a configuration change of the test set-up for vertical and lateral excitations. Transients occurring during launch and/or landing of space vehicles can be accurately simulated in 6-degrees-of-freedom. The performance requirements of the shaker are outlined and the results of the various trade-offs, which are investigated during the initial phase of the design and engineering program are provided. Finally, the resulting baseline concept and the anticipated implementation plan of the new test facility are presented
Thermodynamics of an incommensurate quantum crystal
We present a simple theory of the thermodynamics of an incommensurate quantum
solid. The ground state of the solid is assumed to be an incommensurate
crystal, with quantum zero-point vacancies and interstitials and thus a
non-integer number of atoms per unit cell. We show that the low temperature
variation of the net vacancy concentration should be as , and that the
first correction to the specific heat due to this varies as ; these are
quite consistent with experiments on solid He. We also make some
observations about the recent experimental reports of ``supersolidity'' in
solid He that motivate a renewed interest in quantum crystals.Comment: revised, new title, somewhat expande
COPTRAN - A method of optimum communication systems design
Single set of mathematical expressions describes system cost and probability of error of data transmission in terms of four basic parameters in the link equation. A Lagrange multiplier sets up equations whose solutions yield the optimum values for system design considerations and weight and cost values
Marine Protected Areas and commercial fisheries: the existing fishery in potential protected areas, and a modelling study of the impact of protected areas on North Sea Plaice
Dit rapport presenteert resultaten van onderzoek, dat in 2005/2006 is uitgevoerd. In het kader van de Europese Vogel en Habitat Richtlijnen dienen lidstaten te beschermen gebieden op zee aan te wijzen, wat mogelijk zou leiden tot beperkingen van visserijactiviteiten in deze gebieden. De vraag was, welke invloed dit zou hebben op de vis en visserij. In dit onderzoek is enerzijds een statische beschrijving opgesteld van de visserijinspanning en de vangsten in de voorgestelde gebieden, en is anderzijds een eerste analyse (simulatie-model) opgezet van het lange-termijn effect op migrerende vis (schol). Dit onderzoek werd eind 2006 afgerond met een concept-rapport
On the Use and Development of the Pentatonic Scale Through the Works of AntonÃn Dvořák
Concepts related to style change have been discussed thoroughly by theorists such as Leonard Meyer and others. In the case of Czech scholar, AntonÃn Dvořák, this change relates directly to his pentatonic style. While many musicologists suggest that the composer\u27s travels to the United States in the early 1890\u27s had a profound effect on the birth of his pentatonic style, this thesis posits that Dvořák\u27s pentatonicism is apparent from even his earliest works. In examining evidence of this pentatonicism it becomes clear that, for Dvořák, there are two types: thematic and cadential. Thematic pentatonicism arises from themes of works or movements which only include pitches found within the traditional Western pentatonic scale (scale degrees 1, 2, 3, 5, and 6). Cadential pentatonicism is more abstract in that it only makes an appearance during the close of phrases, sections, or melodic gestures. In these moments, often a rising or falling pentatonic scale will be heard in one or more melody instruments with a harmonic accompaniment that moves towards a tonic structure. In order to better understand and find these two factors, a corpus study was used along with various statistical and programming tools. The use of these tools allowed for a quicker and more thorough examination of various themes and figures for elements of pentatonicism. The results of this corpus study hint towards further research into the fields of pentatonic structure, Czech folk music, and the composer himself, AntonÃn Dvořá
Preferential adsorption of high density lipoprotein (HDL) in blood plasma/polymer interaction
A few studies on the adsorption of plasma proteins to polymeric surfaces show that major plasma proteins: albumin (Alb), fibrinogen (Fb) and immunoglobulin (IgG) are adsorbed in much smaller quantities from plasma than from protein solutions (1,2). Present results show that this difference in adsorption is due to the preferential adsorption of high density lipoprotein from plasma onto the material surfaces studied (PVC and PS)
Study and development of a mathematical analysis for the performance assessment of space communication system parameters
Electronic computer program user manual for optimum design of space communication syste
User's manual for COPTRAN, a method of optimum communication system design
User manual for COPTRAN /communication system optimization program translator
Non-perturbative renormalization group analysis of nonlinear spiking networks
The critical brain hypothesis posits that neural circuits may operate close
to critical points of a phase transition, which has been argued to have
functional benefits for neural computation. Theoretical and computational
studies arguing for or against criticality in neural dynamics largely rely on
establishing power laws or scaling functions of statistical quantities, while a
proper understanding of critical phenomena requires a renormalization group
(RG) analysis. However, neural activity is typically non-Gaussian, nonlinear,
and non-local, rendering models that capture all of these features difficult to
study using standard statistical physics techniques. Here, we overcome these
issues by adapting the non-perturbative renormalization group (NPRG) to work on
(symmetric) network models of stochastic spiking neurons. By deriving a pair of
Ward-Takahashi identities and making a ``local potential approximation,'' we
are able to calculate non-universal quantities such as the effective firing
rate nonlinearity of the network, allowing improved quantitative estimates of
network statistics. We also derive the dimensionless flow equation that admits
universal critical points in the renormalization group flow of the model, and
identify two important types of critical points: in networks with an absorbing
state there is Directed Percolation (DP) fixed point corresponding to a
non-equilibrium phase transition between sustained activity and extinction of
activity, and in spontaneously active networks there is a \emph{complex valued}
critical point, corresponding to a spinodal transition observed, e.g., in the
Lee-Yang model of Ising magnets with explicitly broken symmetry. Our
Ward-Takahashi identities imply trivial dynamical exponents in
both cases, rendering it unclear whether these critical points fall into the
known DP or Ising universality classes
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