7,545 research outputs found
Stochastic sensitivity measure for mistuned high-performance turbines
A stochastic measure of sensitivity is developed in order to predict the effects of small random blade mistuning on the dynamic aeroelastic response of turbomachinery blade assemblies. This sensitivity measure is based solely on the nominal system design (i.e., on tuned system information), which makes it extremely easy and inexpensive to calculate. The measure has the potential to become a valuable design tool that will enable designers to evaluate mistuning effects at a preliminary design stage and thus assess the need for a full mistuned rotor analysis. The predictive capability of the sensitivity measure is illustrated by examining the effects of mistuning on the aeroelastic modes of the first stage of the oxidizer turbopump in the Space Shuttle Main Engine. Results from a full analysis mistuned systems confirm that the simple stochastic sensitivity measure predicts consistently the drastic changes due to misturning and the localization of aeroelastic vibration to a few blades
Discourse comprehension and simulation of positive emotions
Recent research has suggested that emotional sentences are understood by constructing an emotion simulation of the events being described. The present study aims to investigate whether emotion simulation is also involved in online and offline comprehension of larger language segments such as discourse. Participants read a target text describing positive events while their facial postures were manipulated to be either congruent (matching condition) or incongruent (mismatching condition) with emotional valence of the text. In addition, a control condition was included in which participants read the text naturally (without a manipulation of facial posture). The influence of emotion simulation on discourse understanding was assessed by online (self-paced reading times) and offline (verbatim and inference questions) measures of comprehension. The major result was that participants read faster the target text describing positive emotional events while their bodily systems were prepared for processing of positive emotions (matching condition) rather than unprepared (control condition) or prevented from positive emotional processing (mismatching condition). Simulation of positive emotions did not have a significant impact on offline explicit and implicit discourse comprehension. This pattern of results suggests that emotion simulation has an impact on online comprehension, but may not have any effect on offline discourse processing
First CMB Constraints on the Inflationary Reheating Temperature
We present the first Bayesian constraints on the single field inflationary
reheating era obtained from Cosmic Microwave Background (CMB) data. After
demonstrating that this epoch can be fully characterized by the so-called
reheating parameter, we show that it is constrained by the seven years
Wilkinson Microwave Anisotropies Probe (WMAP7) data for all large and small
field models. An interesting feature of our approach is that it yields lower
bounds on the reheating temperature which can be combined with the upper bounds
associated with gravitinos production. For large field models, we find the
energy scale of reheating to be higher than those probed at the Large Hadron
Collider, Ereh > 17.3 TeV at 95% of confidence. For small field models, we
obtain the two-sigma lower limits Ereh > 890 TeV for a mean equation of state
during reheating = -0.3 and Ereh > 390 GeV for = -0.2. The
physical origin of these constraints is pedagogically explained by means of the
slow-roll approximation. Finally, when marginalizing over all possible
reheating history, the WMAP7 data push massive inflation under pressure (p <
2.2 at 95% of confidence where p is the power index of the large field
potentials) while they slightly favor super-Planckian field expectation values
in the small field models.Comment: 18 pages, 15 figures, uses RevTeX. References added, matches
published versio
Renormalization Group Scaling of Higgs Operators and \Gamma(h -> \gamma \gamma)
We compute the renormalization of dimension six Higgs-gauge boson operators
that can modify \Gamma(h -> \gamma \gamma) at tree-level. Operator mixing is
shown to lead to an important modification of new physics effects which has
been neglected in past calculations. We also find that the usual formula for
the S oblique parameter contribution of these Higgs-gauge boson operators needs
additional terms to be consistent with renormalization group evolution. We
study the implications of our results for Higgs phenomenology and for new
physics models which attempt to explain a deviation in \Gamma(h -> \gamma
\gamma). We derive a new relation between the S parameter and the \Gamma(h ->
\gamma \gamma) and \Gamma(h ->Z \gamma) decay rates.Comment: 20 pp. 2 fi
Exponential number of equilibria and depinning threshold for a directed polymer in a random potential
By extending the Kac-Rice approach to manifolds of finite internal dimension,
we show that the mean number
of all possible equilibria
(i.e. force-free configurations, a.k.a. equilibrium points) of an elastic line
(directed polymer), confined in a harmonic well and submitted to a quenched
random Gaussian potential in dimension , grows exponentially
with its
length . The growth rate is found to be directly related to the
generalised Lyapunov exponent (GLE) which is a moment-generating function
characterising the large-deviation type fluctuations of the solution to the
initial value problem associated with the random Schr\"odinger operator of the
1D Anderson localization problem. For strong confinement, the rate is small
and given by a non-perturbative (instanton, Lifshitz tail-like) contribution to
GLE. For weak confinement, the rate is found to be proportional to the
inverse Larkin length of the pinning theory. As an application, identifying the
depinning with a landscape "topology trivialization" phenomenon, we obtain an
upper bound for the depinning threshold , in the presence of an applied
force, for elastic lines and -dimensional manifolds, expressed through the
mean modulus of the spectral determinant of the Laplace operators with a random
potential. We also discuss the question of counting of stable equilibria.
Finally, we extend the method to calculate the asymptotic number of equilibria
at fixed energy (elastic, potential and total), and obtain the (annealed)
distribution of the energy density over these equilibria (i.e. force-free
configurations). Some connections with the Larkin model are also established.Comment: v1: 6 pages main text + 14 pages supplemental material, 10 figures.
v2: LaTeX, 79 pages, 18 eps figures, new material (Sections 6, 10, 11 &
Appendices C, E, F, G
Localization of aeroelastic modes in mistuned high-energy turbines
The effects of blade mistuning on the aerodynamic characteristics of a class of bladed-disk assemblies, namely high energy turbines, are discussed. The specific rotor analyzed is the first stage of turbine blades of the oxidizer turbopump in the Space Shuttle Main Engine. The common occurrence of fatigue cracks for these turbine blades indicates the possibility of high dynamic loading. Since mistuning under conditions of weak interblade coupling has been shown to increase blade response amplitudes drastically for simple structural models of blade assemblies, it provides a plausible explanation for the occurrence of cracks. The focus here is on the effects of frequency mistuning on the aeroelastic stability of the assembly and on the aeroelastic mode shapes
Multiscale Finite Element Modeling of Nonlinear Magnetoquasistatic Problems Using Magnetic Induction Conforming Formulations
In this paper we develop magnetic induction conforming multiscale
formulations for magnetoquasistatic problems involving periodic materials. The
formulations are derived using the periodic homogenization theory and applied
within a heterogeneous multiscale approach. Therefore the fine-scale problem is
replaced by a macroscale problem defined on a coarse mesh that covers the
entire domain and many mesoscale problems defined on finely-meshed small areas
around some points of interest of the macroscale mesh (e.g. numerical
quadrature points). The exchange of information between these macro and meso
problems is thoroughly explained in this paper. For the sake of validation, we
consider a two-dimensional geometry of an idealized periodic soft magnetic
composite.Comment: Paper accepted for publication in the SIAM MMS journa
Competence, specification and induction of Pax-3 in the trigeminal placode
Placodes are discrete regions of thickened ectoderm that contribute extensively to the peripheral nervous system in the vertebrate head. The paired-domain transcription factor Pax-3 is an early molecular marker for the avian ophthalmic trigeminal (opV) placode, which forms sensory neurons in the ophthalmic lobe of the trigeminal ganglion. Here, we use collagen gel cultures and heterotopic quail-chick grafts to examine the competence, specification and induction of Pax-3 in the opV placode. At the 3-somite stage, the whole head ectoderm rostral to the first somite is competent to express Pax-3 when grafted to the opV placode region, though competence is rapidly lost thereafter in otic-level ectoderm. Pax-3 specification in presumptive opV placode ectoderm occurs by the 8-somite stage, concomitant with robust Pax-3 expression. From the 8-somite stage onwards, significant numbers of cells are committed to express Pax-3. The entire length of the neural tube has the ability to induce Pax-3 expression in competent head ectoderm and the inductive interaction is direct. We propose a detailed model for Pax-3 induction in the opV placode
Silicon carbide equipments for process intensification of silicon reactions.
Bluestar Silicones, one of the worldwide leaders in silicones chemistry, proposes a
R&D project, aiming to design new equipment for the transposition of batch to continuous
processes. The safety and environmental issues linked to this type of chemicals, and the
productivity targets as well require innovative technologies characterized by a fair corrosion
resistance and high heat and mass transfer performances. A preliminary prototype of heat
exchanger reactor made of silicon carbide plates has been developed by the LGC in
collaboration with a SME specialist of SiC, Boostec. It has allowed the pilot feasibility with
some reactions of industrial interest for a Bluestar Silicones to be highlighted. Now, it is
necessary to pursue this effort and beyond the feasibility step to go on up to the design of an
industrial reactor. This project corresponds to a programme of innovative process development
in order to design cleaner, safer and less consuming devices
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