24,076 research outputs found
The categorical limit of a sequence of dynamical systems
Modeling a sequence of design steps, or a sequence of parameter settings,
yields a sequence of dynamical systems. In many cases, such a sequence is
intended to approximate a certain limit case. However, formally defining that
limit turns out to be subject to ambiguity. Depending on the interpretation of
the sequence, i.e. depending on how the behaviors of the systems in the
sequence are related, it may vary what the limit should be. Topologies, and in
particular metrics, define limits uniquely, if they exist. Thus they select one
interpretation implicitly and leave no room for other interpretations. In this
paper, we define limits using category theory, and use the mentioned relations
between system behaviors explicitly. This resolves the problem of ambiguity in
a more controlled way. We introduce a category of prefix orders on executions
and partial history preserving maps between them to describe both discrete and
continuous branching time dynamics. We prove that in this category all
projective limits exist, and illustrate how ambiguity in the definition of
limits is resolved using an example. Moreover, we show how various problems
with known topological approaches are now resolved, and how the construction of
projective limits enables us to approximate continuous time dynamics as a
sequence of discrete time systems.Comment: In Proceedings EXPRESS/SOS 2013, arXiv:1307.690
Turbulence Time Series Data Hole Filling using Karhunen-Loeve and ARIMA methods
Measurements of optical turbulence time series data using unattended
instruments over long time intervals inevitably lead to data drop-outs or
degraded signals. We present a comparison of methods using both Principal
Component Analysis, which is also known as the Karhunen--Loeve decomposition,
and ARIMA that seek to correct for these event-induced and mechanically-induced
signal drop-outs and degradations. We report on the quality of the correction
by examining the Intrinsic Mode Functions generated by Empirical Mode
Decomposition. The data studied are optical turbulence parameter time series
from a commercial long path length optical anemometer/scintillometer, measured
over several hundred metres in outdoor environments.Comment: 8 pages, 9 figures, submitted to ICOLAD 2007, City University,
London, U
Humidity contribution to C_n^2 over a 600m pathlength in a tropical marine environment
We present new optical turbulence structure parameter measurements, C_n^2,
over sea water between La Parguera and Magueyes Island (17.6N 67W) on the
southwest coast of Puerto Rico. The 600 meter horizontal paths were located
approximately 1.5 m and 10 m above sea level. No data of this type has ever
been made available in the literature. Based on the data, we show that the
C_n^2 measurements are about 7 times less compared to equivalent land data.
This strong evidence reinforces our previous argument that humidity must be
accounted for to better ascertain the near surface atmospheric turbulence
effects, which current visible / near infrared C_n^2 bulk models fail to do. We
also explore the generalised fractal dimension of this littoral data and
compare it to our reference land data. We find cases that exhibit monofractal
characteristics, that is to say, the effect of rising temperatures during the
daylight hours upon turbulence are counterbalanced by humidity, leading to a
single characteristic scale for the measurements. In other words, significant
moisture changes in the measurement volume cancels optical turbulence increases
due to temperature rises. Figures available as JPG only.Comment: 7 pages, 4 figures, 1 table, SPIE Photonics West 2007, paper 6457B-2
SPEKTRALE IJNTERSUCHUNG DER ABBILDUNG 5)'( 'X-N X -L XNT • - p- I - q
SPECTRAL ANALYSIS OF MAPPING ~l:X .. N-X XNI - Description is given
of the spectral analysis of mapping ~(:X .-- NqX XN,q interpreted in the space of p .q-
type matrices of complex elements where Np [Gi.j-I]' 1, ] L .... p, is a nilpotent matrix
of order p, and Nl is the tramposed of Nq• ?Je is shown to be a nilpotent operator with the ex-
ponent p q 1: hence its eigenvectors are solutions of matrix equation NpX + XNJ ~~O
For linearly independent eigenvectors Xrl; = [( _1)i Tl Gi+ j'f+ rl. i= L .... p, j = L ... , q a
Jordan's chain of principal yectors is produced, demonstrating them to be of maximum
length
Applying the Hilbert--Huang Decomposition to Horizontal Light Propagation C_n^2 data
The Hilbert Huang Transform is a new technique for the analysis of
non--stationary signals. It comprises two distinct parts: Empirical Mode
Decomposition (EMD) and the Hilbert Transform of each of the modes found from
the first step to produce a Hilbert Spectrum. The EMD is an adaptive
decomposition of the data, which results in the extraction of Intrinsic Mode
Functions (IMFs). We discuss the application of the EMD to the calibration of
two optical scintillometers that have been used to measure C_n^2 over
horizontal paths on a building rooftop, and discuss the advantage of using the
Marginal Hilbert Spectrum over the traditional Fourier Power Spectrum.Comment: 9 pages, 11 figures, proc. SPIE 626
Low variability of single-molecule conductance assisted by bulky metal-molecule contacts
A detailed study of the trimethylsilylethynyl moiety, –C[triple bond]CSiMe3 (TMSE) , as an anchoring group in metalmoleculemetal junctions, using a combination of experiment and density functional theory is presented. It is shown that the TMSE anchoring group provides improved control over the molecule-substrate arrangement within metalmoleculemetal junctions, with the steric bulk of the methyl groups limiting the number of highly transmissive binding sites at the electrode surface, resulting in a single sharp peak in the conductance histograms recorded by both the in situ break junction and I(s) STM techniques. As a consequence of the low accessibility of the TMSE group to surface binding configurations of measurable conductance, only about 10% of gold break junction formation cycles result in the clear formation of molecular junctions in the experimental histograms. The DFT-computed transmission characteristics of junctions formed from the TMSE-contacted oligo(phenylene)ethynylene (OPE)-based molecules described here are dominated by tunneling effects through the highest-occupied molecular orbitals (HOMOs). This gives rise to similar conductance characteristics in these TMSE-contacted systems as found in low conductance-type junctions based on comparably structured OPE-derivatives with amine-contacts that also conduct through HOMO-based channels.R. R. F. thanks the Consejería de Educación del Principado de Asturias for a Severo Ochoa grant (BP11-069). V. M. G.-S. thanks the Spanish Ministerio de Economía y Competitividad for a Ramón y Cajal fellowship (RYC-2010-06053). R. R. F., J. F. and
V. M. G.-S. wish to acknowledge financial support from the Spanish grant FIS2012-34858 and the Marie Curie Network MOLESCO. P. C. and S. M. are grateful for financial assistance from the Ministerio de Economía y Competitividad of Spain in the
framework of the project CTQ2012-33198 as well as the award of the CTQ2013-50187-EXP grant. H. M. O., P. C., and S. M. thank the support from DGA and Fondos FEDER for funding through the Platon research group. H. M. O. is also grateful for financial assistance from the Secretaría Nacional de Educación Superior, Ciencia, Tecnología e Innovaciín from Ministerio de Educación (Ecuador). S. M. thanks the Ministerio de Educación from Spain for financial support through the framework of the Campus de Excelencia Internacional, CEI Iberus. S. J. H., R. J. N., P. J. L. and S. M.-G. thank the EPSRC for funding (EPSRC grants EP/K007785/1, EP/H035184/1, EP/K007548/1, EP/H005595/1). P. J. L. holds an Australian Research Council Future Fellowship (FT120100073) and gratefully acknowledges funding for this work from the ARC (DP140100855).Peer Reviewe
Mashairi ya waadhi `verses of admonition`:
Aliyetunga kasiga hii, Sheikh Abgallah al-Husni, alikuwa ni mtu maarufu sana Mombasa .. Kwa muda wa myaka arobaini takriban alikuwa akisomesha elimu za gini, msikiti wa Anisa, Mjuwakale; piya alikuwa akitoa waadhi msikiti huu na mahali pengine .. Antunga kasiga mbili za waadhi, moja katika hizo ndiyo hii tuliyoishereheya katika makala haya .. W akati wa kutungwa waadhi huu - 1368 (mwaka 1948 wa milagi) - Mombasa ilikuwa ikali mji wa kiSawahili, yaani mji wa kilsilamu; lakini kulikuwa kuna mabadiliko makubwa yaanza, mabadiliko ambayo mwisho yanaondowa sura za uSawahili katika Mombasa na pwani nzima ya Afrika ya mashariki
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