5,734 research outputs found
Two-Pulse Ionization Injection into Quasi-Linear Laser Wakefields
We describe a scheme for controlling electron injection into the quasi-linear
wakefield driven by a guided drive pulse via ionization of a dopant species by
a collinear injection laser pulse with a short Rayleigh range. The scheme is
analyzed by particle in cell simulations which show controlled injection and
acceleration of electrons to an energy of 370 MeV, a relative energy spread of
2%, and a normalized transverse emittance of 3.0 {\mu}m.
This is an arXiv version of the original APS paper. It should be cited as N.
Bourgeois, J. Cowley, and S. M. Hooker, Phys. Rev. Lett. 111, 155004 (2013).
APS link here: http://link.aps.org/doi/10.1103/PhysRevLett.111.155004Comment: 5 pages, 4 figure
Lagrangian Cobordisms via Generating Families: Constructions and Geography
Embedded Lagrangian cobordisms between Legendrian submanifolds are produced
from isotopy, spinning, and handle attachment constructions that employ the
technique of generating families. Moreover, any Legendrian with a generating
family has an immersed Lagrangian filling with a compatible generating family.
These constructions are applied in several directions, in particular to a
non-classical geography question: any graded group satisfying a duality
condition can be realized as the generating family homology of a connected
Legendrian submanifold in R^{2n+1} or in the 1-jet space of any compact
n-manifold with n at least 2.Comment: 34 pages, 11 figures. v2: corrected a referenc
The Omega Counter, a Frequency Counter Based on the Linear Regression
This article introduces the {\Omega} counter, a frequency counter -- or a
frequency-to-digital converter, in a different jargon -- based on the Linear
Regression (LR) algorithm on time stamps. We discuss the noise of the
electronics. We derive the statistical properties of the {\Omega} counter on
rigorous mathematical basis, including the weighted measure and the frequency
response. We describe an implementation based on a SoC, under test in our
laboratory, and we compare the {\Omega} counter to the traditional {\Pi} and
{\Lambda} counters. The LR exhibits optimum rejection of white phase noise,
superior to that of the {\Pi} and {\Lambda} counters. White noise is the major
practical problem of wideband digital electronics, both in the instrument
internal circuits and in the fast processes which we may want to measure. The
{\Omega} counter finds a natural application in the measurement of the
Parabolic Variance, described in the companion article arXiv:1506.00687
[physics.data-an].Comment: 8 pages, 6 figure, 2 table
The Parabolic variance (PVAR), a wavelet variance based on least-square fit
This article introduces the Parabolic Variance (PVAR), a wavelet variance
similar to the Allan variance, based on the Linear Regression (LR) of phase
data. The companion article arXiv:1506.05009 [physics.ins-det] details the
frequency counter, which implements the LR estimate.
The PVAR combines the advantages of AVAR and MVAR. PVAR is good for long-term
analysis because the wavelet spans over , the same of the AVAR wavelet;
and good for short-term analysis because the response to white and flicker PM
is and , same as the MVAR.
After setting the theoretical framework, we study the degrees of freedom and
the confidence interval for the most common noise types. Then, we focus on the
detection of a weak noise process at the transition - or corner - where a
faster process rolls off. This new perspective raises the question of which
variance detects the weak process with the shortest data record. Our
simulations show that PVAR is a fortunate tradeoff. PVAR is superior to MVAR in
all cases, exhibits the best ability to divide between fast noise phenomena (up
to flicker FM), and is almost as good as AVAR for the detection of random walk
and drift
Fast algorithms for min independent dominating set
We first devise a branching algorithm that computes a minimum independent
dominating set on any graph with running time O*(2^0.424n) and polynomial
space. This improves the O*(2^0.441n) result by (S. Gaspers and M. Liedloff, A
branch-and-reduce algorithm for finding a minimum independent dominating set in
graphs, Proc. WG'06). We then show that, for every r>3, it is possible to
compute an r-((r-1)/r)log_2(r)-approximate solution for min independent
dominating set within time O*(2^(nlog_2(r)/r))
Variety and the evolution of refinery processing
Evolutionary theories of economic development stress the role of variety as both a determinant and a result of growth. In this paper we develop a measure of variety, based on Weitzman's maximum likelihood procedure. This measure is based on the distance between products, and indicates the degree of differentiation of a product population. We propose a generic method, which permits to regroup the products with very similar characteristics values before choosing randomly the product models to be used to calculate Weitzman's measure. We apply the variety measure to process characteristics of oil refining. The results obtained for this technology show classic evolutionary specialization patterns that can be understood on the basis of niche theory. Here the changes in variety are related to changes in the range of the services the technology considered can deliver, range which plays a role similar to that of the size of the habitat of a biological species.TECHNOLOGICAL EVOLUTION; REFINERY PROCESSES; NICHE THEORY; WEITZMAN MEASURE
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