1,231 research outputs found
A 2D systems approach to iterative learning control for discrete linear processes with zero Markov parameters
In this paper a new approach to iterative learning control for the practically relevant case of deterministic discrete linear plants with uniform rank greater than unity is developed. The analysis is undertaken in a 2D systems setting that, by using a strong form of stability for linear repetitive processes, allows simultaneous con-sideration of both trial-to-trial error convergence and along the trial performance, resulting in design algorithms that can be computed using Linear Matrix Inequalities (LMIs). Finally, the control laws are experimentally verified on a gantry robot that replicates a pick and place operation commonly found in a number of applications to which iterative learning control is applicable
Svestka's Research: Then and Now
Zdenek Svestka's research work influenced many fields of solar physics,
especially in the area of flare research. In this article I take five of the
areas that particularly interested him and assess them in a "then and now"
style. His insights in each case were quite sound, although of course in the
modern era we have learned things that he could not readily have envisioned.
His own views about his research life have been published recently in this
journal, to which he contributed so much, and his memoir contains much
additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour
of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a
contribution to a Topical Issue in Solar Physics, based on the presentations
at this meeting (Editors Lyndsay Fletcher and Petr Heinzel
Iteration of Planar Amplitudes in Maximally Supersymmetric Yang-Mills Theory at Three Loops and Beyond
We compute the leading-color (planar) three-loop four-point amplitude of N=4
supersymmetric Yang-Mills theory in 4 - 2 epsilon dimensions, as a Laurent
expansion about epsilon = 0 including the finite terms. The amplitude was
constructed previously via the unitarity method, in terms of two Feynman loop
integrals, one of which has been evaluated already. Here we use the
Mellin-Barnes integration technique to evaluate the Laurent expansion of the
second integral. Strikingly, the amplitude is expressible, through the finite
terms, in terms of the corresponding one- and two-loop amplitudes, which
provides strong evidence for a previous conjecture that higher-loop planar N =
4 amplitudes have an iterative structure. The infrared singularities of the
amplitude agree with the predictions of Sterman and Tejeda-Yeomans based on
resummation. Based on the four-point result and the exponentiation of infrared
singularities, we give an exponentiated ansatz for the maximally
helicity-violating n-point amplitudes to all loop orders. The 1/epsilon^2 pole
in the four-point amplitude determines the soft, or cusp, anomalous dimension
at three loops in N = 4 supersymmetric Yang-Mills theory. The result confirms a
prediction by Kotikov, Lipatov, Onishchenko and Velizhanin, which utilizes the
leading-twist anomalous dimensions in QCD computed by Moch, Vermaseren and
Vogt. Following similar logic, we are able to predict a term in the three-loop
quark and gluon form factors in QCD.Comment: 54 pages, 7 figures. v2: Added references, a few additional words
about large spin limit of anomalous dimensions. v3: Expanded Sect. IV.A on
multiloop ansatz; remark that form-factor prediction is now confirmed by
other work; minor typos correcte
The Impact of Counterstereotypic Training and Related Correction Processes on the Application of Stereotypes
Two-Loop Correction to Bhabha Scattering
We present the two-loop virtual QED corrections to e^+ e^- to mu^+ mu^- and
Bhabha scattering in dimensional regularization. The results are expressed in
terms of polylogarithms. The form of the infrared divergences agrees with
previous expectations. These results are a crucial ingredient in the complete
next-to-next-to-leading order QED corrections to these processes. A future
application will be to reduce theoretical uncertainties associated with
luminosity measurements at e^+ e^- colliders. The calculation also tests
methods that may be applied to analogous QCD processes.Comment: Latex, 22 pages, 1 figur
Correlation property of length sequences based on global structure of complete genome
This paper considers three kinds of length sequences of the complete genome.
Detrended fluctuation analysis, spectral analysis, and the mean distance
spanned within time are used to discuss the correlation property of these
sequences. The values of the exponents from these methods of these three kinds
of length sequences of bacteria indicate that the long-range correlations exist
in most of these sequences. The correlation have a rich variety of behaviours
including the presence of anti-correlations. Further more, using the exponent
, it is found that these correlations are all linear (). It is also found that these sequences exhibit noise in some
interval of frequency (). The length of this interval of frequency depends
on the length of the sequence. The shape of the periodogram in exhibits
some periodicity. The period seems to depend on the length and the complexity
of the length sequence.Comment: RevTex, 9 pages with 5 figures and 3 tables. Phys. Rev. E Jan. 1,2001
(to appear
Iterative Learning Control Based on Relaxed 2D Systems Stability Criteria
This paper develops significant new results on the design of Iterative Learning Control (ILC) schemes based on treating the problem within the framework of the stability/control theory for linear repetitive processes. These processes propagate in two independent directions and arise in the modeling of a number of physical processes. The duration of information propagation in one of the two directions is finite, and this is a key link to ILC which has been developed as a technique for controlling systems which are required to repeat the same operation over a finite duration known as the trial length and information from previous executions is used to update the control input for the next trial and thereby sequentially improve performance. The experimental performance of the new algorithms on a gantry robot is reported, including a comparison with alternative designs
Cardiac Glycosides Induce Cell Death in Human Cells by Inhibiting General Protein Synthesis
BACKGROUND: Cardiac glycosides are Na(+)/K(+)-pump inhibitors widely used to treat heart failure. They are also highly cytotoxic, and studies have suggested specific anti-tumor activity leading to current clinical trials in cancer patients. However, a definitive demonstration of this putative anti-cancer activity and the underlying molecular mechanism has remained elusive. METHODOLOGY/PRINCIPAL FINDINGS: Using an unbiased transcriptomics approach, we found that cardiac glycosides inhibit general protein synthesis. Protein synthesis inhibition and cytotoxicity were not specific for cancer cells as they were observed in both primary and cancer cell lines. These effects were dependent on the Na(+)/K(+)-pump as they were rescued by expression of a cardiac glycoside-resistant Na(+)/K(+)-pump. Unlike human cells, rodent cells are largely resistant to cardiac glycosides in vitro and mice were found to tolerate extremely high levels. CONCLUSIONS/SIGNIFICANCE: The physiological difference between human and mouse explains the previously observed sensitivity of human cancer cells in mouse xenograft experiments. Thus, published mouse xenograft models used to support anti-tumor activity for these drugs require reevaluation. Our finding that cardiac glycosides inhibit protein synthesis provides a mechanism for the cytotoxicity of CGs and raises concerns about ongoing clinical trials to test CGs as anti-cancer agents in humans
Asymmetric WIMP dark matter
In existing dark matter models with global symmetries the relic abundance of
dark matter is either equal to that of anti-dark matter (thermal WIMP), or
vastly larger, with essentially no remaining anti-dark matter (asymmetric dark
matter). By exploring the consequences of a primordial asymmetry on the coupled
dark matter and anti-dark matter Boltzmann equations we find large regions of
parameter space that interpolate between these two extremes. Interestingly,
this new asymmetric WIMP framework can accommodate a wide range of dark matter
masses and annihilation cross sections. The present-day dark matter population
is typically asymmetric, but only weakly so, such that indirect signals of dark
matter annihilation are not completely suppressed. We apply our results to
existing models, noting that upcoming direct detection experiments will
constrain a large region of the relevant parameter space.Comment: 32 pages, 6 figures, updated references, updated XENON100 bounds,
typo in figure caption correcte
X-ray, Optical, and Radio Observations of the Type II Supernovae 1999em and 1998S
Observations of the Type II-P (plateau) Supernova (SN) 1999em and Type IIn
(narrow emission line) SN 1998S have enabled estimation of the profile of the
SN ejecta, the structure of the circumstellar medium (CSM) established by the
pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the
first Type II-P detected at both X-ray and radio wavelengths. The Chandra X-ray
data indicate non-radiative interaction of SN ejecta with a power-law density
profile (rho \propto r^{-n} with n ~ 7) with a pre-SN wind with a low mass-loss
rate of ~2 \times 10^{-6} M_sun/yr for a wind velocity of 10 km/sec, in
agreement with radio mass-loss rate estimates. The Chandra data show an
unexpected, temporary rise in the 0.4--2.0 keV X-ray flux at ~100 days after
explosion. SN 1998S, at an age of >3 years, is still bright in X-rays and is
increasing in flux density at cm radio wavelengths. Spectral fits to the
Chandra data show that many heavy elements (Ne, Al, Si, S, Ar, and Fe) are
overabundant with respect to solar values. We compare the observed elemental
abundances and abundance ratios to theoretical calculations and find that our
data are consistent with a progenitor mass of approximately 15-20 M_sun if the
heavy element ejecta are radially mixed out to a high velocity. If the X-ray
emission is from the reverse shock wave region, the supernova density profile
must be moderately flat at a velocity ~10^4 km/sec, the shock front is
non-radiative at the time of the observations, and the mass-loss rate is 1-2
\times 10^{-4} M_sun/yr for a pre-supernova wind velocity of 10 km/sec. This
result is also supported by modeling of the radio emission which implies that
SN 1998S is surrounded by a clumpy or filamentary CSM established by a high
mass-loss rate, ~2 \times 10^{-4} M_sun/yr, from the pre-supernova star.Comment: 14 pages, 10 figures, accepted by ApJ, includes new data (one new
obs. each of SN 1999em and SN 1998S), expanded discussion of spectral fit
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