3,353 research outputs found
Probabilistic sequence alignments: realistic models with efficient algorithms
Alignment algorithms usually rely on simplified models of gaps for
computational efficiency. Based on an isomorphism between alignments and
physical helix-coil models, we show in statistical mechanics that alignments
with realistic laws for gaps can be computed with fast algorithms. Improved
performances of probabilistic alignments with realistic models of gaps are
illustrated. Probabilistic and optimization formulations are compared, with
potential implications in many fields and perspectives for computationally
efficient extensions to Markov models with realistic long-range interactions
Intersection numbers of Riemann surfaces from Gaussian matrix models
We consider a Gaussian random matrix theory in the presence of an external
matrix source. This matrix model, after duality (a simple version of the
closed/open string duality), yields a generalized Kontsevich model through an
appropriate tuning of the external source. The n-point correlation functions of
this theory are shown to provide the intersection numbers of the moduli space
of curves with a p-spin structure, n marked points and top Chern class. This
sheds some light on Witten's conjecture on the relationship with the pth-KdV
equation
Flexible-Link Robot Control Using a Linear Parameter Varying Systems Methodology
This paper addresses the issues of the Linear Parameter Varying (LPV) modelling and control of flexible-link robot manipulators. The LPV formalism allows the synthesis of nonlinear control laws and the assessment of their closed-loop stability and performances in a simple and effective manner, based on the use of Linear Matrix Inequalities (LMI). Following the quasi-LPV modelling approach, an LPV model of a flexible manipulator is obtained, starting from the nonlinear dynamic model stemming from Euler-Lagrange equations. Based on this LPV model, which has a rational dependence in terms of the varying parameters, two different methods for the synthesis of LPV controllers are explored. They guarantee the asymptotic stability and some level of closed-loop â„’ 2 -gain performance on a bounded parametric set. The first method exploits a descriptor representation that simplifies the rational dependence of the LPV model, whereas the second one manages the troublesome rational dependence by using dilated LMI conditions and taking the particular structure of the model into account. The resulting controllers involve the measured state variables only, namely the joint positions and velocities. Simulation results are presented that illustrate the validity of the proposed control methodology. Comparisons with an inversion-based nonlinear control method are performed in the presence of velocity measurement noise, model uncertainties and high-frequency inputs
Human telomerase RNA and box H/ACA scaRNAs share a common Cajal body–specific localization signal
Telomerase is a ribonucleoprotein reverse transcriptase that uses its RNA component as a template for synthesis of telomeric DNA repeats at the ends of linear eukaryotic chromosomes. Here, fluorescence in situ hybridization demonstrates that in HeLa cancer cells, human telomerase RNA (hTR) accumulates in the nucleoplasmic Cajal bodies (CBs). Localization of transiently expressed hTR to CBs is supported by a short sequence motif (411-UGAG-414) that is located in the 3′-terminal box H/ACA RNA-like domain of hTR and that is structurally and functionally indistinguishable from the CB-specific localization signal of box H/ACA small CB-specific RNAs. In synchronized HeLa cells, hTR shows the most efficient accumulation in CBs during S phase, when telomeres are most likely synthesized. CBs may function in post-transcriptional maturation (e.g., cap hypermethylation of hTR), but they may also play a role in the assembly and/or function of telomerase holoenzyme
Characteristic polynomials of random matrices at edge singularities
We have discussed earlier the correlation functions of the random variables
\det(\la-X) in which is a random matrix. In particular the moments of the
distribution of these random variables are universal functions, when measured
in the appropriate units of the level spacing. When the \la's, instead of
belonging to the bulk of the spectrum, approach the edge, a cross-over takes
place to an Airy or to a Bessel problem, and we consider here these modified
classes of universality.
Furthermore, when an external matrix source is added to the probability
distribution of , various new phenomenons may occur and one can tune the
spectrum of this source matrix to new critical points. Again there are
remarkably simple formulae for arbitrary source matrices, which allow us to
compute the moments of the characteristic polynomials in these cases as well.Comment: 22 pages, late
The environmental and health impacts of tobacco agriculture, cigarette manufacture and consumption.
The health consequences of tobacco use are well known, but less recognized are the significant environmental impacts of tobacco production and use. The environmental impacts of tobacco include tobacco growing and curing; product manufacturing and distribution; product consumption; and post-consumption waste. The World Health Organization's Framework Convention on Tobacco Control addresses environmental concerns in Articles 17 and 18, which primarily apply to tobacco agriculture. Article 5.3 calls for protection from policy interference by the tobacco industry regarding the environmental harms of tobacco production and use. We detail the environmental impacts of the tobacco life-cycle and suggest policy responses
Visual Masking: A Reliable Measure for the Assessment of Cognitive Dysfunction in the Elderly?
Reliable assessment of cognitive dysfunction in the elderly is a prerequisite for the evaluation of treatment of age-related cognitive decline. Psychophysical thresholds are known to be more reliable than psychometric tests, as assessed by stability of performance in visual masking. A backward (Till & Franklin, 1981) and a forward masking study (Coyne, 1981) were replicated. Thereafter, the same volunteers carried out a backward and forward masking task adapted to minimize noncognitive age-related influences: target and mask duration were individually adjusted to control for reduced eye transmissiveness. Attention was assessed with the electrooculogram; a dependent variable insensitive to sporadic decreases of attention was selected. Test-retest stability in the elderly after 2-4 weeks was r = .97 in backward and r = .86 in forward masking. As Alzheimer's disease mainly affects the cortex, backward masking, which is primarily cortical, may be useful to assess aspects of cognitive dysfunctio
Properties of two biological glasses used as metallic prosthesis coatings and after an implantation in body
présentation faite par Y. Barbottea
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