1,893 research outputs found
Optimization of a Classical Stamping Progression by Modal Correction of Anisotropy Ears
This work is a development from the Inetforsmep European project. We proposed
to realize a global optimization of a deep drawing industrial progression (made
of several stages) for a cup manufacture. The objectives of the process were
the thickness decrease and the geometrical parameters (especially the height).
This paper improves on this previous work in the aim of mastering the contour
error. From the optimal configuration, we expect to cut down the amount of the
needed material and the number of forming operations. Our action is focused on
the appearance of unexpected undulations (ears) located on the rim of the cups
during forming due to a nonuniform crystallographic texture. Those undulations
can cause a significant amount of scraps, productivity loss, and cost during
manufacture. In this paper, this phenomenon causes the use of four forming
operations for the cup manufacture. The aim is to cut down from four to two
forming stages by defining an optimal blank (size and shape). The advantage is
to reduce the cost of the tool manufacturing and to minimize the needed
material (by suppressing the part flange). The chosen approach consists in
defining a particular description of the ears' part by modal decomposition and
then simulating several blank shapes and sizes generated by discrete cosine
transformation (DCT). The use of a numerical simulation for the forming
operation and the design of an experiment technique allow mathematical links
between the ears' formation and the DCT coefficients. An optimization is then
possible by using mathematical links. This original approach leads the ears'
amplitude to be reduced by a factor of 10, with only 15 numerical experiments.
Moreover, we have limited the number of forming stages from 4 to 2 with a
minimal material use
Putting fear in its place: remapping of hippocampal place cells during fear conditioning
We recorded hippocampal place cells in two spatial environments: a training environment in which rats underwent fear conditioning and a neutral control environment. Fear conditioning caused many place cells to alter ( or remap) their preferred firing locations in the training environment, whereas most cells remained stable in the control environment. This finding indicates that aversive reinforcement can induce place cell remapping even when the environment itself remains unchanged. Furthermore, contextual fear conditioning caused significantly more remapping of place cells than auditory fear conditioning, suggesting that place cell remapping was related to the rat's learned fear of the environment. These results suggest that one possible function of place cell remapping may be to generate new spatial representations of a single environment, which could help the animal to discriminate among different motivational contexts within that environment
Fatigue analysis-based numerical design of stamping tools made of cast iron
This work concerns stress and fatigue analysis of stamping tools made of cast iron with an essentially pearlitic matrix and containing foundry defects. Our approach consists at first, in coupling the stamping numerical processing simulations and structure analysis in order to improve the tool stiffness geometry for minimizing the stress state and optimizing their fatigue lifetime. The method consists in simulating the stamping process by considering the tool as a perfect rigid body. The estimated contact pressure is then used as boundary condition for FEM structure loading analysis of the tool. The result of this analysis is compared with the critical stress limit depending on the automotive model. The acceptance of this test allows calculating the fatigue lifetime of the critical zone by using the S–N curve of corresponding load ratio. If the prescribed tool life requirements are not satisfied, then the critical region of the tool is redesigned and the whole simulation procedures are reactivated. This method is applied for a cast iron EN-GJS-600-3. The stress-failure (S–N) curves for this material is determined at room temperature under push pull loading with different load ratios R0σmin/σmax0−2, R0−1 and R00.1. The effects of the foundry defects are determined by SEM observations of crack initiation sites. Their presence in tested specimens is associated with a reduction of fatigue lifetime by a factor of 2. However, the effect of the load ratio is more important
The central limit problem for random vectors with symmetries
Motivated by the central limit problem for convex bodies, we study normal
approximation of linear functionals of high-dimensional random vectors with
various types of symmetries. In particular, we obtain results for distributions
which are coordinatewise symmetric, uniform in a regular simplex, or
spherically symmetric. Our proofs are based on Stein's method of exchangeable
pairs; as far as we know, this approach has not previously been used in convex
geometry and we give a brief introduction to the classical method. The
spherically symmetric case is treated by a variation of Stein's method which is
adapted for continuous symmetries.Comment: AMS-LaTeX, uses xy-pic, 23 pages; v3: added new corollary to Theorem
Dynamical evolution and leading order gravitational wave emission of Riemann-S binaries
An approximate strategy for studying the evolution of binary systems of
extended objects is introduced. The stars are assumed to be polytropic
ellipsoids. The surfaces of constant density maintain their ellipsoidal shape
during the time evolution. The equations of hydrodynamics then reduce to a
system of ordinary differential equations for the internal velocities, the
principal axes of the stars and the orbital parameters. The equations of motion
are given within Lagrangian and Hamiltonian formalism. The special case when
both stars are axially symmetric fluid configurations is considered. Leading
order gravitational radiation reaction is incorporated, where the quasi-static
approximation is applied to the internal degrees of freedom of the stars. The
influence of the stellar parameters, in particular the influence of the
polytropic index , on the leading order gravitational waveforms is studied.Comment: 31 pages, 7 figures, typos correcte
Maximum gradient embeddings and monotone clustering
Let (X,d_X) be an n-point metric space. We show that there exists a
distribution D over non-contractive embeddings into trees f:X-->T such that for
every x in X, the expectation with respect to D of the maximum over y in X of
the ratio d_T(f(x),f(y)) / d_X(x,y) is at most C (log n)^2, where C is a
universal constant. Conversely we show that the above quadratic dependence on
log n cannot be improved in general. Such embeddings, which we call maximum
gradient embeddings, yield a framework for the design of approximation
algorithms for a wide range of clustering problems with monotone costs,
including fault-tolerant versions of k-median and facility location.Comment: 25 pages, 2 figures. Final version, minor revision of the previous
one. To appear in "Combinatorica
Spallation Neutron Production by 0.8, 1.2 and 1.6 GeV Protons on various Targets
Spallation neutron production in proton induced reactions on Al, Fe, Zr, W,
Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at
the SATURNE accelerator in Saclay is reported. The experimental
double-differential cross-sections are compared with calculations performed
with different intra-nuclear cascade models implemented in high energy
transport codes. The broad angular coverage also allowed the determination of
average neutron multiplicities above 2 MeV. Deficiencies in some of the models
commonly used for applications are pointed out.Comment: 20 pages, 32 figures, revised version, accepted fpr publication in
Phys. Rev.
Cognitive appraisal of environmental stimuli induces emotion-like states in fish
The occurrence of emotions in non-human animals has been the focus of debate over the years. Recently, an interest in expanding this debate to non-tetrapod vertebrates and to invertebrates has emerged. Within vertebrates, the study of emotion in teleosts is particularly interesting since they represent a divergent evolutionary radiation from that of tetrapods, and thus they provide an insight into the evolution of the biological mechanisms of emotion. We report that Sea Bream exposed to stimuli that vary according to valence (positive, negative) and salience (predictable, unpredictable) exhibit different behavioural, physiological and neuromolecular states. Since according to the dimensional theory of emotion valence and salience define a two-dimensional affective space, our data can be interpreted as evidence for the occurrence of distinctive affective states in fish corresponding to each the four quadrants of the core affective space. Moreover, the fact that the same stimuli presented in a predictable vs. unpredictable way elicited different behavioural, physiological and neuromolecular states, suggests that stimulus appraisal by the individual, rather than an intrinsic characteristic of the stimulus, has triggered the observed responses. Therefore, our data supports the occurrence of emotion-like states in fish that are regulated by the individual's perception of environmental stimuli.European Commission [265957 Copewell]; Fundacao para a Ciencia e Tecnologia [SFRH/BD/80029/2011, SFRH/BPD/72952/2010]info:eu-repo/semantics/publishedVersio
Convex recovery of a structured signal from independent random linear measurements
This chapter develops a theoretical analysis of the convex programming method
for recovering a structured signal from independent random linear measurements.
This technique delivers bounds for the sampling complexity that are similar
with recent results for standard Gaussian measurements, but the argument
applies to a much wider class of measurement ensembles. To demonstrate the
power of this approach, the paper presents a short analysis of phase retrieval
by trace-norm minimization. The key technical tool is a framework, due to
Mendelson and coauthors, for bounding a nonnegative empirical process.Comment: 18 pages, 1 figure. To appear in "Sampling Theory, a Renaissance."
v2: minor corrections. v3: updated citations and increased emphasis on
Mendelson's contribution
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