1,528 research outputs found
Predicting Fracture in the Proximal Humerus using Phase Field Models
Proximal humerus impacted fractures are of clinical concern in the elderly
population. Prediction of such fractures by CT-based finite element methods
encounters several major obstacles such as heterogeneous mechanical properties
and fracture due to compressive strains. We herein propose to investigate a
variation of the phase field method (PFM) embedded into the finite cell method
(FCM) to simulate impacted humeral fractures in fresh frozen human humeri. The
force-strain response, failure loads and the fracture path are compared to
experimental observations for validation purposes. The PFM (by means of the
regularization parameter ) is first calibrated by one experiment and
thereafter used for the prediction of the mechanical response of two other
human fresh frozen humeri. All humeri are fractured at the surgical neck and
strains are monitored by Digital Image Correlation (DIC). Experimental strains
in the elastic regime are reproduced with good agreement (),
similarly to the validated finite element method [9]. The failure pattern and
fracture evolution at the surgical neck predicted by the PFM mimic extremely
well the experimental observations for all three humeri. The maximum relative
error in the computed failure loads is . To the best of our knowledge
this is the first method that can predict well the experimental compressive
failure pattern as well as the force-strain relationship in proximal humerus
fractures
Characterizing galaxy clusters by their gravitational potential: systematics of cluster potential reconstruction
Context. Biases in mass measurements of galaxy clusters are one of the major
limiting systematics in constraining cosmology with clusters. Aims. We aim to
demonstrate that the systematics associated with cluster gravitational
potentials are smaller than the hydrostatic mass bias and that cluster
potentials could therefore be a good alternative to cluster masses in
cosmological studies. Methods. Using cosmological simulations of galaxy
clusters, we compute the biases in the hydrostatic mass (HE mass) and those in
the gravitational potential, reconstructed from measurements at X-ray and
millimeter wavelengths. In particular, we investigate the effects of the
presence of substructures and of non-thermal pressure support on both the HE
mass and the reconstructed potential. Results. We find that the bias in the
reconstructed potential (6%) is less than that of the HE mass (13%), and that
the scatter in the reconstructed potential decreases by about 35% with respect
to that in the HE mass. Conclusions. This study shows that characterizing
galaxy clusters by their gravitational potential is a promising alternative to
using cluster masses in cluster cosmology.Comment: submitted to the journal A&A, 16 pages, 26 figure
On the statistical evaluation of dose-response functions
The linear-quadratic dependence of effect on the dose of ionizing radiation and its biophysical implications are considered. The estimation of the parameters of the response function and the derivation of the joint confidence region of the estimates are described. The method is applied to the induction of pink mutations inTradescantia which follows the linear-quadratic model. The statistical procedure is also suitable for other response functions
Characterization of ellipses as uniformly dense sets with respect to a family of convex bodies
Let K \subset R^N be a convex body containing the origin. A measurable set G
\subset R^N with positive Lebesgue measure is said to be uniformly K-dense if,
for any fixed r > 0, the measure of G \cap (x + rK) is constant when x varies
on the boundary of G (here, x + rK denotes a translation of a dilation of K).
We first prove that G must always be strictly convex and at least C1,1-regular;
also, if K is centrally symmetric, K must be strictly convex, C1,1-regular and
such that K = G - G up to homotheties; this implies in turn that G must be
C2,1- regular. Then for N = 2, we prove that G is uniformly K-dense if and only
if K and G are homothetic to the same ellipse. This result was already proven
by Amar, Berrone and Gianni in [3]. However, our proof removes their regularity
assumptions on K and G and, more importantly, it is susceptible to be
generalized to higher dimension since, by the use of Minkowski's inequality and
an affine inequality, avoids the delicate computations of the higher-order
terms in the Taylor expansion near r = 0 for the measure of G\cap(x+rK) (needed
in [3])
Bimodal magnetic force microscopy with capacitive tip-sample distance control
A single-passage, bimodal magnetic force microscopy technique optimized for scanning samples with arbitrary topography is discussed. A double phase-locked loop (PLL) system is used to mechanically excite a high quality factor cantilever under vacuum conditions on its first mode and via an oscillatory tip-sample potential on its second mode. The obtained second mode oscillation amplitude is then used as a proxy for the tip-sample distance, and for the control thereof. With appropriate z-feedback parameters two data sets reflecting the magnetic tip-sample interaction and the sample topography are simultaneously obtained
Growth and texture of Spark Plasma Sintered Al2O3 ceramics: a combined analysis of X-rays and Electron Back Scatter Diffraction
Textured alumina ceramics were obtained by Spark Plasma Sintering (SPS) of
undoped commercial a-Al2O3 powders. Various parameters (density, grain growth,
grain size distribution) of the alumina ceramics, sintered at two typical
temperatures 1400{\deg}C and 1700{\deg}C, are investigated. Quantitative
textural and structural analysis, carried out using a combination of Electron
Back Scattering Diffraction (EBSD) and X-ray diffraction (XRD), are represented
in the form of mapping, and pole figures. The mechanical properties of these
textured alumina ceramics include high elastic modulus and hardness value with
high anisotropic nature, opening the door for a large range of applicationsComment: 16 pages, 6 figures, submitted to J. Appl. Phy
Classical double-layer atoms: artificial molecules
The groundstate configuration and the eigenmodes of two parallel
two-dimensional classical atoms are obtained as function of the inter-atomic
distance (d). The classical particles are confined by identical harmonic wells
and repel each other through a Coulomb potential. As function of d we find
several structural transitions which are of first or second order. For first
(second) order transitions the first (second) derivative of the energy with
respect to d is discontinuous, the radial position of the particles changes
discontinuously (continuously) and the frequency of the eigenmodes exhibit a
jump (one mode becomes soft, i.e. its frequency becomes zero).Comment: 4 pages, RevTex, 5 ps figures, to appear in Phys.Rev.Let
Studies of the dose-effect relation
Dose-effect relations and, specifically, cell survival curves are surveyed with emphasis on the interplay of the random factors — biological variability, stochastic reaction of the cell, and the statistics of energy deposition —that co-determine their shape. The global parameters mean inactivation dose, , and coefficient of variance, V, represent this interplay better than conventional parameters. Mechanisms such as lesion interaction, misrepair, repair overload, or repair depletion have been invoked to explain sigmoid dose dependencies, but these notions are partly synonymous and are largely undistinguishable on the basis of observed dose dependencies. All dose dependencies reflect, to varying degree, the microdosimetric fluctuations of energy deposition, and these have certain implications, e.g. the linearity of the dose dependence at small doses, that apply regardless of unresolved molecular mechanisms of cellular radiation action
Minkowski Tensors of Anisotropic Spatial Structure
This article describes the theoretical foundation of and explicit algorithms
for a novel approach to morphology and anisotropy analysis of complex spatial
structure using tensor-valued Minkowski functionals, the so-called Minkowski
tensors. Minkowski tensors are generalisations of the well-known scalar
Minkowski functionals and are explicitly sensitive to anisotropic aspects of
morphology, relevant for example for elastic moduli or permeability of
microstructured materials. Here we derive explicit linear-time algorithms to
compute these tensorial measures for three-dimensional shapes. These apply to
representations of any object that can be represented by a triangulation of its
bounding surface; their application is illustrated for the polyhedral Voronoi
cellular complexes of jammed sphere configurations, and for triangulations of a
biopolymer fibre network obtained by confocal microscopy. The article further
bridges the substantial notational and conceptual gap between the different but
equivalent approaches to scalar or tensorial Minkowski functionals in
mathematics and in physics, hence making the mathematical measure theoretic
method more readily accessible for future application in the physical sciences
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