70,452 research outputs found
Face identification by deformation measure
This paper studies the problem of face identification for the particular application of an automatic cash machine withdrawal: the problem is to decide if a person identifying himself by a secret code is the same person registered in the data base. The identification process consists of three main stages. The localization of salient features is obtained by using morphological operators and spatio-temporal information. The location of these features are used to achieve a normalization of the face image with regard to the corresponding face in the data base. Facial features, such as eyes, mouth and nose, are extracted by an active contour model which is able to incorporate information about the global shape of each object. Finally the identification is achieved by face warping including a deformation measure. 1
3-D Face Analysis and Identification Based on Statistical Shape Modelling
This paper presents an effective method of statistical shape representation for automatic face analysis and identification in 3-D. The method combines statistical shape modelling techniques and the non-rigid deformation matching scheme. This work is distinguished by three key contributions. The first is the introduction of a new 3-D shape registration method using hierarchical landmark detection and multilevel B-spline warping technique, which allows accurate dense correspondence search for statistical model construction. The second is the shape representation approach, based on Laplacian Eigenmap, which provides a nonlinear submanifold that links underlying structure of facial data. The third contribution is a hybrid method for matching the statistical model and test dataset which controls the levels of the model’s deformation at different matching stages and so increases chance of the successful matching. The proposed method is tested on the public database, BU-3DFE. Results indicate that it can achieve extremely high verification rates in a series of tests, thus providing real-world practicality
Degenerations of ideal hyperbolic triangulations
Let M be a cusped 3-manifold, and let T be an ideal triangulation of M. The
deformation variety D(T), a subset of which parameterises (incomplete)
hyperbolic structures obtained on M using T, is defined and compactified by
adding certain projective classes of transversely measured singular
codimension-one foliations of M. This leads to a combinatorial and geometric
variant of well-known constructions by Culler, Morgan and Shalen concerning the
character variety of a 3-manifold.Comment: 31 pages, 11 figures; minor changes; to appear in Mathematische
Zeitschrif
Identification of plastic constitutive parameters at large deformations from three dimensional displacement fields
The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated
3D Residual Stress Field in Arteries: Novel Inverse Method Based on Optical Full-field Measurements
Arterial tissue consists of multiple structurally important constituents that
have individual material properties and associated stress-free configurations
that evolve over time. This gives rise to residual stresses contributing to the
homoeostatic state of stress in vivo as well as adaptations to perturbed loads,
disease or injury. The existence of residual stresses in an intact but
load-free excised arterial segment suggests compressive and tensile stresses,
respectively, in the inner and outer walls. Accordingly, an artery ring springs
open into a sector after a radial cut. The measurement of the opening angle is
commonly used to deduce the residual stresses, which are the stresses required
to close back the ring. The opening angle method provides an average estimate
of circumferential residual stresses but it gives no information on local
distributions through the thickness and along the axial direction. To address
this lack, a new method is proposed in this article to derive maps of residual
stresses using an approach based on the contour method. A piece of freshly
excised tissue is carefully cut into the specimen, and the local distribution
of residual strains and stresses is determined from whole-body digital image
correlation measurements using an inverse approach based on a finite element
model
Quasi-static and Dynamic Behavior of Additively Manufactured Metallic Lattice Cylinders
Lattice structures have tailorable mechanical properties which allows them to
exhibit superior mechanical properties (per unit weight) beyond what is
achievable through natural materials. In this paper, quasi-static and dynamic
behavior of additively manufactured stainless steel lattice cylinders is
studied. Cylindrical samples with internal lattice structure are fabricated by
a laser powder bed fusion system. Equivalent hollow cylindrical samples with
the same length, outer diameter, and mass (larger wall thickness) are also
fabricated. Split Hopkinson bar is used to study the behavior of the specimens
under high strain rate loading. It is observed that lattice cylinders reduce
the transmitted wave amplitude up to about 21% compared to their equivalent
hollow cylinders. However, the lower transmitted wave energy in lattice
cylinders comes at the expense of a greater reduction in their stiffness, when
compared to their equivalent hollow cylinder. In addition, it is observed that
increasing the loading rate by five orders of magnitude leads to up to about
36% increase in the peak force that the lattice cylinder can carry, which is
attributed to strain rate hardening effect in the bulk stainless steel
material. Finite element simulations of the specimens under dynamic loads are
performed to study the effect of strain rate hardening, thermal softening, and
the failure mode on dynamic behavior of the specimens. Numerical results are
compared with experimental data and good qualitative agreement is observed.Comment: 20th Biennial Conference of the APS Topical Group on Shock
Compression of Condensed Matte
Experimental analysis and modeling of orthogonal cutting using material and friction models
In this study, a process model for orthogonal cutting processes is proposed. The model involves the primary and secondary deformation zones. The primary shear zone is modeled by a Johnson-Cook constitutive relationship and a shear plane having constant thickness. The secondary deformation zone is modeled semi-analytically, where the coefficient of friction is calibrated experimentally. The cutting forces predicted using the calibrated sliding friction coefficients are in good agreement with the measurements. The experimental investigation of sliding friction coefficients also show promising results for the proposed model, which is still under development
Explicit Formulas for Relaxed Disarrangement Densities Arising from Structured Deformations
Structured deformations provide a multiscale geometry that captures the
contributions at the macrolevel of both smooth geometrical changes and
non-smooth geometrical changes (disarrangements) at submacroscopic levels. For
each (first-order) structured deformation of a continuous body, the
tensor field is known to be a measure of deformations without
disarrangements, and is known to be a measure of deformations
due to disarrangements. The tensor fields and together deliver not only
standard notions of plastic deformation, but and its curl deliver the
Burgers vector field associated with closed curves in the body and the
dislocation density field used in describing geometrical changes in bodies with
defects. Recently, Owen and Paroni [13] evaluated explicitly some relaxed
energy densities arising in Choksi and Fonseca's energetics of structured
deformations [4] and thereby showed: (1) , the positive part of
, is a volume density of disarrangements due to submacroscopic
separations, (2) , the negative part of , is a volume density
of disarrangements due to submacroscopic switches and interpenetrations, and
(3) , the absolute value of , is a volume density of all three of
these non-tangential disarrangements: separations, switches, and
interpenetrations. The main contribution of the present research is to show
that a different approach to the energetics of structured deformations, that
due to Ba\'ia, Matias, and Santos [1], confirms the roles of ,
, and established by Owen and Paroni. In doing so, we give
an alternative, shorter proof of Owen and Paroni's results, and we establish
additional explicit formulas for other measures of disarrangements.Comment: 17 pages; http://cvgmt.sns.it/paper/2776
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