7,806 research outputs found
Successive Standardization of Rectangular Arrays
In this note we illustrate and develop further with mathematics and examples,
the work on successive standardization (or normalization) that is studied
earlier by the same authors in Olshen and Rajaratnam (2010) and Olshen and
Rajaratnam (2011). Thus, we deal with successive iterations applied to
rectangular arrays of numbers, where to avoid technical difficulties an array
has at least three rows and at least three columns. Without loss, an iteration
begins with operations on columns: first subtract the mean of each column; then
divide by its standard deviation. The iteration continues with the same two
operations done successively for rows. These four operations applied in
sequence completes one iteration. One then iterates again, and again, and
again,.... In Olshen and Rajaratnam (2010) it was argued that if arrays are
made up of real numbers, then the set for which convergence of these successive
iterations fails has Lebesgue measure 0. The limiting array has row and column
means 0, row and column standard deviations 1. A basic result on convergence
given in Olshen and Rajaratnam (2010) is true, though the argument in Olshen
and Rajaratnam (2010) is faulty. The result is stated in the form of a theorem
here, and the argument for the theorem is correct. Moreover, many graphics
given in Olshen and Rajaratnam (2010) suggest that but for a set of entries of
any array with Lebesgue measure 0, convergence is very rapid, eventually
exponentially fast in the number of iterations. Because we learned this set of
rules from Bradley Efron, we call it "Efron's algorithm". More importantly, the
rapidity of convergence is illustrated by numerical examples
Successive normalization of rectangular arrays
Standard statistical techniques often require transforming data to have mean
and standard deviation . Typically, this process of "standardization" or
"normalization" is applied across subjects when each subject produces a single
number. High throughput genomic and financial data often come as rectangular
arrays where each coordinate in one direction concerns subjects who might have
different status (case or control, say), and each coordinate in the other
designates "outcome" for a specific feature, for example, "gene," "polymorphic
site" or some aspect of financial profile. It may happen, when analyzing data
that arrive as a rectangular array, that one requires BOTH the subjects and the
features to be "on the same footing." Thus there may be a need to standardize
across rows and columns of the rectangular matrix. There arises the question as
to how to achieve this double normalization. We propose and investigate the
convergence of what seems to us a natural approach to successive normalization
which we learned from our colleague Bradley Efron. We also study the
implementation of the method on simulated data and also on data that arose from
scientific experimentation.Comment: Published in at http://dx.doi.org/10.1214/09-AOS743 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org). With Correction
Second post-Newtonian gravitational radiation reaction for two-body systems: Nonspinning bodies
Starting from the recently obtained 2PN accurate forms of the energy and
angular momentum fluxes from inspiralling compact binaries, we deduce the
gravitational radiation reaction to 2PN order beyond the quadrupole
approximation - 4.5PN terms in the equation of motion - using the refined
balance method proposed by Iyer and Will. We explore critically the features of
their construction and illustrate them by contrast to other possible variants.
The equations of motion are valid for general binary orbits and for a class of
coordinate gauges. The limiting cases of circular orbits and radial infall are
also discussed.Comment: 38 pages, REVTeX, no figures, to appear in Phys. Rev.
Localization and Fluctuations in Quantum Kicked Rotors
We address the issue of fluctuations, about an exponential lineshape, in a
pair of one-dimensional kicked quantum systems exhibiting dynamical
localization. An exact renormalization scheme establishes the fractal character
of the fluctuations and provides a new method to compute the localization
length in terms of the fluctuations. In the case of a linear rotor, the
fluctuations are independent of the kicking parameter and exhibit
self-similarity for certain values of the quasienergy. For given , the
asymptotic localization length is a good characteristic of the localized
lineshapes for all quasienergies. This is in stark contrast to the quadratic
rotor, where the fluctuations depend upon the strength of the kicking and
exhibit local "resonances". These resonances result in strong deviations of the
localization length from the asymptotic value. The consequences are
particularly pronounced when considering the time evolution of a packet made up
of several quasienergy states.Comment: REVTEV Document. 9 pages, 4 figures submitted to PR
FDM preparation of bio-compatible UHMWPE polymer for artificial implant
Due to its properties of high wear, creep resistance, high stiffness and strength, Ultra-High Molecular Weight Polyethylene (UHMWPE) was developed to eliminate most metallic wear in artificial implant, which conventionally found in stainless steel, Cobalt Chromium (Co-Cr) and Titanium (Ti) alloys. UHMWPE has an ultra-high viscosity that renders continuous melt-state processes including one of the additive manufacturing processes, Fused Deposition Modeling (FDM) ineffective for making UHMWPE implant. Attempt to overcome this problem and adapting this material to FDM is by blending UHMWPE with other polyethylene including High Density Polyethylene (HDPE) and Polyethylene-Glycol (PEG) which provide adequate mechanical properties for biomedical application along with the improvement in extrudability. It was demonstrated that the inclusion of 60% HDPE fraction has improved the flowability of UHMWPE in MFI test and showing adequate thermal stability in TGA
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Thaan Vuzha Nilam Tharisu: the land without a farmer becomes barren
This report forms a part of the international research project on policy and sustainable agriculture, Policies that Work for Sustainable Agriculture and Regenerated Rural Economies. The report details the findings of one of the constituent studies, undertaken by an Indian NGO, the Society for People's Education and Economic Change (SPEECH). The Importance of this project is that it concentrated on rainfed rather than irrigated agriculture - i.e. the sharp end of rural development in India, and that the focus was very much on the micro-level, looking at policy as seen from the ground. One of the recurring themes throughout the research was the importance of appreciating people as individuals, and in this spirit some of the personal qualities of the research team are shared. The research covers events in sites in the Virudhunagar district of Tamilnadu: Tiruchuli Panchayat Union and the Villur chain of tanks. This is an essentially rural area, where the need for sustainable forms of agriculture and rural livelihoods is clear. The political landscape is fractured and complex (§2.3), and the officials with the responsibility of implementing policy face significant obstacles and disincentives in doing so in response to the needs of local communities
High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects
A large magnetoresistance effect is obtained at room-temperature by using
p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is
the virtual elimination of thermal currents due to the presence of band gaps in
the contacts. The current at B=0T is greatly decreased while the current at
B>0T is relatively large due to the band-to-band tunneling effects, resulting
in a high magnetoresistance ratio, even at room-temperature. Moreover, we
explore the effects of edge-roughness, length, and width of GNR channels on
device performance. An increase in edge-roughness and channel length enhances
the magnetoresistance ratio while increased channel width can reduce the
operating bias.Comment: http://dx.doi.org/10.1063/1.362445
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