760 research outputs found
A high pass, mechanical velocity filter for fast neutral molecular beams
Design and transmission characteristics of high pass, mechanical velocity filter for fast neutral molecular or atomic beam
Flight dynamics analysis and simulation of heavy lift airships. Volume 1: Executive summary
A generic, yet comprehensive mathematical model and computer simulation of the HLA flight dynamics over its entire flight envelope was developed. Implicit in this simulation development are the data reviews and analyses which support the equations of motion and the calculation of forces and moments acting on the vehicle. The simulation, HYBRDS, is addressed to the broad requirements and is intended for use as a synthesis and analysis tool for the evaluation of competing HLA design concepts
Flight dynamics analysis and simulation of heavy lift airships. Volume 5: Programmer's manual
The Programmer's Manual contains explanations of the logic embodied in the various program modules, a dictionary of program variables, a subroutine listing, subroutine/common block/cross reference listing, and a calling/called subroutine cross reference listing
Dynamical Belyi maps
We study the dynamical properties of a large class of rational maps with
exactly three ramification points. By constructing families of such maps, we
obtain infinitely many conservative maps of degree ; this answers a question
of Silverman. Rather precise results on the reduction of these maps yield
strong information on the rational dynamics.Comment: 21 page
Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects
We analyze the influence of spatial orientation on the optical response of
hydrogenated silicon quantum wires. The results are relevant for the
interpretation of the optical properties of light emitting porous silicon. We
study (111)-oriented wires and compare the present results with those
previously obtained within the same theoretical framework for (001)-oriented
wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In
analogy with the (001)-oriented wires and at variance with crystalline bulk
silicon, we find that the (111)-oriented wires exhibit a direct gap at whose value is largely enhanced with respect to that found in bulk
silicon because of quantum confinement effects. The imaginary part of the
dielectric function, for the external field polarized in the direction of the
axis of the wires, shows features that, while being qualitatively similar to
those observed for the (001) wires, are not present in the bulk. The main
conclusion which emerges from the present study is that, if wires a few
nanometers large are present in the porous material, they are
optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte
Livestock Selective Behaviour in Natural Grasslands Challenges the Concept of Plant Preference in the Elaboration of a Successful Diet
Conciliating livestock production and conservation of grassland biodiversity is now an imperative. We propose that a way to reach that goal is to take advantage of the natural tendency of herbivores to exploit environmental heterogeneity. However, it would go against the well-rooted concept that mammalian herbivores have invariable preference for some plants. Preference was defined as being āwhat the animal selects when given the minimum of physical constraintsā (Parsons et al. 1994). But after decades of studies, the concept of preference remains particularly inefficient in predicting observed patterns of selection by herbivores (e.g. Newman et al. 1992; Parsons et al. 1994; Provenza 2006). We performed detailed descriptions of cattle diet composition and foraging strategy in highly diversified natural pasture of South Brazil. We present here preliminary results that seriously question the concept of plant preference
Sensitivity and Estimation of Flying-Wing Aerodynamic, Propulsion, and Inertial Parameters Using Simulation
This paper explores the difficulties of aircraft system identification, specifically parameter estimation, for a rudderless aircraft. A white box method is used in conjunction with a nonlinear six degree-of-freedom aerodynamic model for the equations of motion in order to estimate 33 parameters that govern the aerodynamic, inertial, and propulsion forces within the mathematical model. The analysis is conducted in the time-domain of system identification. Additionally, all the parameters are estimated using a single flight rather than a series of shorter flights dedicated to estimating specific sets of parameters as is typically done. A final flight plan is developed with a mixture of lateral maneuvers interspersed throughout the flight to accentuate the significance of the lateral parameters during estimation. Certain parameters were ill-conditioned for parameter estimation using the mathematical model and final flight plan derived in this paper. The gradient-based optimization technique used in the estimation algorithm struggled to accurately estimate all 33 in a single flight due to the abundance of local minima within the solution space. The results of this work may provide a few insights for parameter estimation. First, to understand why system identification is performed the way it is currently done through multiple different flight maneuvers. Second, to gain some visual insight to the behavior of the nonlinear six degree-of-freedom aerodynamic model that describes the motion of fixed wing aircraft. This work may also be helpful in determining which parameters might likely be estimated together and which may struggle due to coupled dynamic relations within the mathematical model
The role of angular momentum in the construction of electromagnetic multipolar fields
Multipolar solutions of Maxwell's equations are used in many practical
applications and are essential for the understanding of light-matter
interactions at the fundamental level. Unlike the set of plane wave solutions
of electromagnetic fields, the multipolar solutions do not share a standard
derivation or notation. As a result, expressions originating from different
derivations can be difficult to compare. Some of the derivations of the
multipolar solutions do not explicitly show their relation to the angular
momentum operators, thus hiding important properties of these solutions. In
this article, the relation between two of the most common derivations of this
set of solutions is explicitly shown and their relation to the angular momentum
operators is exposed.Comment: 13 pages, 2 figure
SIMAPāstructuring the network of protein similarities
Protein sequences are the most important source of evolutionary and functional information for new proteins. In order to facilitate the computationally intensive tasks of sequence analysis, the Similarity Matrix of Proteins (SIMAP) database aims to provide a comprehensive and up-to-date dataset of the pre-calculated sequence similarity matrix and sequence-based features like InterPro domains for all proteins contained in the major public sequence databases. As of September 2007, SIMAP covers ā¼17 million proteins and more than 6 million non-redundant sequences and provides a complete annotation based on InterPro 16. Novel features of SIMAP include a new, portlet-based web portal providing multiple, structured views on retrieved proteins and integration of protein clusters and a unique search method for similar domain architectures. Access to SIMAP is freely provided for academic use through the web portal for individuals at http://mips.gsf.de/simap/and through Web Services for programmatic access at http://mips.gsf.de/webservices/services/SimapService2.0?wsdl
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio
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