Quantitative description of 3D vascularity images: texture-based approach and its verification through cluster analysis

El propósito de este artículo es describir la poética de Teillier durante los años 60 y 70 en poemas breves, muchos de los cuales se revelan como haikús. Este aspecto de la obra de Teillier es poco atendido por la crítica y no solamente se verifica a través en textos que en gran medida se asimilan al haikú japonés clásico. Así este autor encuentra una consonancia más profunda y con el término “morada irreal” de Basho, que expresa la fragmentariedad de lo real, al menos de esa parte del mundo circundante que revela insospechadas conexiones con otro tiempo y lugar. The objective of this article is to describe Teillier's poetics during the 1960s and 1970s in short poems, many of which are revealed as haiku. This aspect of Teillier's work is poorly served by criticism and is not only verified through texts that are largely assimilated to classical Japanese haiku. Thus this author finds a deeper consonance and with the term "morada irreal" of Basho, which expresses the fragmentarity of the real, at least of that part of the surrounding world that reveals unsuspected connections with another time and place.El propòsit d'aquest article es descriure la poètica de Teillier durant els anys 60 y 70 en poemes breus, molts dels quals es revelen com haikus. Aquest aspecte de l'obra de Teillier és poc atès per la crítica i no solament es verifica a través de textos que en gran mesura s'asimilen al haiku japonès clàssic. Així aquest autor troba una consonància més profunda i amb el terme “morada irreal” de Basho, que expressa la fragmentarietat d'allò real, almenys d'aquella part del món circumdant que revela insospitades connexions amb un altre temps i lloc

Healthy kidney segmentation in the dce-mr images using a convolutional neural network and temporal signal characteristics

Quantification of renal perfusion based on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) requires determination of signal intensity time courses in the region of renal parenchyma. Thus, selection of voxels representing the kidney must be accomplished with special care and constitutes one of the major technical limitations which hampers wider usage of this technique as a standard clinical routine. Manual segmentation of renal compartments—even if performed by experts—is a common source of decreased repeatability and reproducibility. In this paper, we present a processing framework for the automatic kidney segmentation in DCE-MR images. The framework consists of two stages. Firstly, kidney masks are generated using a convolutional neural network. Then, mask voxels are classified to one of three regions—cortex, medulla, and pelvis–based on DCE-MRI signal intensity time courses. The proposed approach was evaluated on a cohort of 10 healthy volunteers who underwent the DCE-MRI examination. MRI scanning was repeated on two time events within a 10-day interval. For semantic segmentation task we employed a classic U-Net architecture, whereas experiments on voxel classification were performed using three alternative algorithms—support vector machines, logistic regression and extreme gradient boosting trees, among which SVM produced the most accurate results. Both segmentation and classification steps were accomplished by a series of models, each trained separately for a given subject using the data from other participants only. The mean achieved accuracy of the whole kidney segmentation was 94% in terms of IoU coefficient. Cortex, medulla and pelvis were segmented with IoU ranging from 90 to 93% depending on the tissue and body side. The results were also validated by comparing image-derived perfusion parameters with ground truth measurements of glomerular filtration rate (GFR). The repeatability of GFR calculation, as assessed by the coefficient of variation was determined at the level of 14.5 and 17.5% for the left and right kidney, respectively and it improved relative to manual segmentation. Reproduciblity, in turn, was evaluated by measuring agreement between image-derived and iohexol-based GFR values. The estimated absolute mean differences were equal to 9.4 and 12.9 mL/min/1.73 m2 for scanning sessions 1 and 2 and the proposed automated segmentation method. The result for session 2 was comparable with manual segmentation, whereas for session 1 reproducibility in the automatic pipeline was weaker.publishedVersio

Constitutive relations in 3-D for a wide range of strain rates and temperatures: Application to mild steels

24 pages, 13 figures.-- MSC2000 codes: 74C10, 74F05, 74-05.Zbl#: Zbl 1178.74024An original phenomenological thermo-visco-plastic model is reported that encompasses strain hardening, strain rate and temperature sensitivity. The model is based to some extent on the concept of physical modeling proposed earlier by Klepaczko [Klepaczko, J.R. 1975. Thermally activated flow and strain rate history effects for some polycrystalline FCC metals. Mater. Sci. Engng. 18, 121–135] , and also by different authors, for example: [Becker, R. 1925. Uber die plastizitat amorpher und kristalliner fester korper. Z. Physik 26, 919–925; Seeger, A., 1957. Dislocations and Mechanical Properties of Crystals, Wiley, New York; Conrad, H., 1964. Thermally activated deformation of metals J. Metals 16, 582; Gilman, J.J. 1968. Dislocation dynamics and response of materials to impact Appl. Mech. Rev. 21, 767–783; Gibbs, G.B., 1969. Thermodynamic analysis of dislocation glide controlled by dispersed local obstacles. Mater. Sci. Engng. 4, 313–328; Kocks, U.F., Argon, A.S., Ashby, M.F., 1975. Thermodynamics and kinetics of slip. In: Progress in Materials Science, vol. 19. Pergamon Press, New York, p. 19; Kocks, U.F. 1976. Laws for work-hardening and low-temperature creep. J. Eng. Mater. Technol. 98, 76–85, and later by many others.The thermo-visco-plastic formulation, called RK and applied in this paper, has been verified experimentally for strain rates of 10-4 s-1 ≤ εp ≤ 5x10^3 s-1 and temperatures 213 K ≤ T ≤ 393 K, it covers the range of dynamic loadings observed during crash tests and other impact problems. In order to implement the RK constitutive relation, a thermo-visco-plastic algorithm based on the J2 theory of plasticity is constructed. The type of algorithm is a return mapping one that introduces the consistency condition (f = overbar-σ - σy, f = 0), without the overstress state proposed by Perzyna [Perzyna, P. 1966. Fundamental problems in viscoplasticity. Advances in Applied Mechanics, vol. 9. Academic Press, New York, pp. 243–377]. The coupling of the RK constitutive relation with the integration scheme of the thermo-visco-plastic algorithm has demonstrated its efficiency for numerical analyses of different dynamic processes such as Taylor test [Zaera, R., Fernández-Sáez, J. 2006. An implicit consistent algorithm for the integration of thermoviscoplastic constitutive equations in adiabatic conditions and finite deformations. Int. J. Solids Struct., 43, 1594–1612.], ring expansion [Rusinek, A., Zaera, R., 2007. Finite element simulation of steel ring fragmentation under radial expansion. Int. J. Impact Eng. 34, 799–822], dynamic tension test [Rusinek, A., Zaera, R., Klepaczko, J.R., Cherigueme, R., 2005. Analysis of inertia and scale effects on dynamic neck formation during tension of sheet steel. Acta Mater. 53, 5387-5400], perforation of metallic sheets [Rusinek, A., 2000, Modélisation thermoviscoplastique d’une nuance de tôle d’acier aux grandes vitesses de déformation. Etude expérimentale et numérique du cisaillement, de la traction et de la perforation, Ph.D. thesis, University of Metz, France], and other cases. All the equations are implemented via the user subroutine VUMAT in the ABAQUS/Explicit code for adiabatic conditions of plastic deformation.Publicad

Identification of damage mechanism and validation of a fracture model based on mesoscale approach in spalling of titanium alloy

AbstractThe subject of this paper is identification of the physical mechanisms of spalling at low impact velocities for Ti–6Al–4V alloy and determination of the macroscopic stress of spalling via meso-macro approach. Spalling is a specific mode of fracture which depends on the loading history. The aspects of the initial microstructure and its evolution during plastic deformation are very important. In order to identify the spalling physical mechanisms in titanium alloy, numerous pictures by the optical microscopy of the spall surfaces created by plate impact technique have been taken. The scenario of failure observed is in complete agreement with known physical micro-mechanisms: namely nucleation, propagation and coalescence by adiabatic shearing of micro-voids. The most interesting point in spall fracture of Ti–6Al–4V alloy is the nucleation of micro-voids. A significant amount of small micro-voids in the region of the expected spall plane has been observed. It appears that microstructural effects are important due to dual α–β phase microstructure, called Widmanstätten structure. The orientation of microstructure has a direct influence on nucleation mechanism by means of distribution of nucleation sites and decohesion between the softer particles (α-phase lamellae) and the harder lattice (β-phase). According to these observations, a fracture model has been developed. This model is based on the numerous post-mortem microscopic observations of spall specimens. The goal is to determine the macroscopic stress of spalling in function of loading time and damage level via a meso-macro approach

Analysis of inertia and scale effects on dynamic neck formation during tension of sheet steel

14 pages, 17 figures.It is well known that a specimen for impact testing must be optimized in terms of its dimensions. The main reason is to reduce strain gradients due to the effects of elastic–plastic wave propagation. On the other hand, when a split Hopkinson bar in tension is applied, the net displacement of the specimen ends is very limited, usually from 2.0 to 3.0 mm. Thus, to reach a maximum strain of 0.5 the specimen length must be reduced in dimensions from 4.0 to 6.0 mm. Consequently, small diameters or lateral dimensions and lengths must be applied to assure one-dimensional deformation. Such small lengths substantially perturb the determination of real material behavior. So the main motivation of this study was to perform a systematic analysis, numerical and analytical, to find differences in the behavior of short and long specimens loaded in impact tension. The finite element code ABAQUS/Explicit has been used to simulate several specimen lengths from 10 to 40 mm submitted to impact velocities ranging from 10 to 100 m/s.Publicad

Effect of projectile nose shape on ballistic resistance of interstitial-free steel sheets

In this paper an experimental and numerical work is reported concerning the process of perforation of thin steel plates using different projectile nose shapes. The main goal is to analyze how the projectile shape may change the ballistic properties of materials. A wide range of impact velocities from 35 to 180 m/s has been covered during the tests. All the projectiles were 13 mm in diameter and the targets were 1 mm thick, as such the projectile can be regarded as rigid and the target sheets were of interstitial-free (IF) steel. The mass ratio (projectile mass/steel sheet mass) and the ratio between the span of the steel sheet and the diameter of the projectile were kept constant, equal to 0.38 and 3.85 respectively. To define the thermoviscoplastic behavior of the target material, the Rusinek-Klepaczko (RK) constitutive model [1] was used. The complete identification of the material constants was done based on a rigorous material characterization. Numerical simulations of some experimental tests were carried out using a non-linear finite element code ABAQUS/Explicit. It was found that the numerical models are able to describe the physical mechanisms in the perforation process with a good accuracy.The National Centre of Research and Development under the grant WND-DEM-1-203/00

Effect of plastic deformation and boundary conditions combined with elastic wave propagation on the collapse site of a crash box

21 pages, 22 figures.Several papers have been published recently on the crashworthiness studies. The main task was to predict the energy absorption Wp and average collapse force overbar-F in time of sheet steel structures. The main objective of this contribution is to design a component that allows absorbing and dissipating a high energy Wp allowing improvements of the survivability of passengers in vehicles. However, the range of applications is larger since it includes all civil and military applications related to safety of components, or more generally of construction elements being loaded by impacts or explosions. In the present 3D case, the aim of this numerical study on dynamic loading in adiabatic conditions of deformation is to analyze the effect of elastic wave propagation combined with plastic behavior on the collapse site of a rectangular tubular structure made of steel sheet. To demonstrate the strong coupling between the effects of strain-rate sensitivity, accounted for in the constitutive relation that is used in numerical simulations, with the process of elastic wave reflection on the boundary conditions, a series of numerical simulation was performed. It is shown in this numerical study that the strain-rate sensitivity influences the position of the first collapse site. Moreover, the first collapse initiation of a structure defines the level of power absorption. Since the process of folding may be combined with bending of the structure (in particular when a local buckling appears close to the opposite side of impact), in this non-axial case the energy absorption Wp decreases and the effectiveness of the structure to the energy absorption is insufficient.The researchers of the University Carlos III of Madrid are indebted to the Spanish Ministry of Education (project DPI2005-06769), and to the Region of Madrid (project CCG06-UC3M/DPI-0796) for the financial support that allowed to perform a part of the numerical simulations.Publicad

Modelling of thermo-viscoplastic behaviour of DH-36 and Weldox 460-E structural steels at wide ranges of strain rates and temperatures, comparison of constitutive relations for impact problems

In this paper, the thermo-viscoplastic behaviour of DH-36 and Weldox-460-E steels is analyzed at wide ranges of strain rates and temperatures. These materials are commonly used for naval applications. Thus, they may be subjected to a wide range of exploitation temperatures and at the same time to high strain rates due to accidental impact or explosion. The thermo-viscoplastic behaviour of these materials has been modeled by application of RK (Rusinek-Klepaczko) constitutive relation. The predictions obtained using RK constitutive relation have been compared with JC (Johnson-Cook) and PB (Physical Base) constitutive relations with use of the experimental results reported in the works of Nemat-Nasser and Guo [Nemat-Nasser, S., Guo, W.G., 2003. Thermomechanical response of DH-36 structural steel over a wide range of strain rates and temperatures. Mech. Mat. 35, 1023-1047] and Borvik et al. [Borvik, T., Hopperstad, O.S., Berstad, T., Langseth, M., 2001. A computational model of viscoplasticity and ductile damage for impact and penetration. Eur. J. Solid. Mech. A. 20, 685-712]. For both metals, a satisfactory agreement is reported between the experimental results and the analytical predictions using RK model at wide ranges of strain rates and temperatures (10-3 s-1 to 104 s-1, and 77 K to about 1000 K). Especially for high strain rate level, the predictions of RK model are notably more precise than those predictions obtained using PB and JC models. This proof converts RK model in suitable for modeling impact problems. Finally, numerical simulations of perforation process of DH-36 and Weldox 460-E steel plates impacted by conical non-deformable projectiles have been carried out using RK and JC models. Numerical results using FE simulations have revealed substantial influence of the constitutive relation concerning the ballistic limit, residual velocity and failure time predictions for the same initial and boundary conditions.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project UC3M/DPI 3395) and to the Ministerio de Educatión y Ciencia de España (Project DPI/2005 06769)Publicad

Estudio experimental y numérico del comportamiento de láminas de acero sometidas a impacto de media y alta velocidad

6 pages, 14 figures.-- Contributed to: "XXV Encuentro del Grupo Español de Fractura" (Sigüenza, Spain, Mar 5-7, 2008).[EN] In the present work it is experimentally and numerically analyzed the mechanical response of steel sheets subjected to medium and high impact velocity (40 m/s – 300 m/s). The experimental device developed, based on the Hopkinson bar technique, has allowed to evaluate the influence of friction in the fracture mechanics of the steel sheets. The material behaviour has been modelled using the Rusinek-Klepaczko constitutive relation which has been implemented into the FE code ABAQUS/Explicit via user subroutine. The validation of the results obtained from the numerical simulations has been made in terms of failure time, force-time history, ballistic limit and failure mode. The numerical simulations consider the influence of the projectile shape in the failure mode and particularly the petalling process apparition. The use of 3D simulation technique has permitted to reproduce accurately the asymmetry of this kind of processes.[ES] En este trabajo se ha analizado experimental y numéricamente la respuesta mecánica de láminas de acero de bajo contenido en carbono (mild steel ES) sometidas a impacto de media y alta velocidad (40 m/s-300 m/s). El dispositivo experimental desarrollado, basado en la técnica de la barra Hopkinson, ha permitido constatar la influencia de la fricción en los mecanismos de fallo del componente. El comportamiento del material se ha modelizado mediante la ecuación constitutiva de Rusinek-Klepaczko, implementada a tal efecto en el código de elementos finitos ABAQUS/Explicit. La validación de los resultados numéricos con los datos de los ensayos experimentales realizados se ha llevado a cabo en términos de tiempo de fractura, evolución fuerza-tiempo, límite balístico y modo de fallo. Las simulaciones numéricas consideran la influencia de la forma del proyectil en el modo de fallo y en particular en la aparición del fenómeno de "petalling". La utilización de simulaciones 3D ha permitido reproducir con precisión la asimetría característica de este tipo de procesos.Los investigadores de la Universidad Carlos III de Madrid desean agradecer al Ministerio de Educación (proyecto DPI2005-06769) y a la Comunidad Autónoma de Madrid (proyecto CCG06-UC3M/DPI-0796) por el soporte económico que ha permitido la realización de este proyecto. Los investigadores de la Universidad Paul Verlaine de Metz (LPMM) desean agradecer el soporte financiero recibido del CNRS-France.Publicad

Influence of conical projectile diameter on perpendicular impact oh thin steel plate

A numerical study of conical projectiles for perpendicular impact on a thin steel plate is reported. The target material considered, Weldox 460 E steel, is frequently used for this kind of application and several results of experiments are available in the international literature to verify numerical simulations. The Johnson-Cook constitutive relation coupled with the Johnson-Cook failure criterion have been applied to analyse penetration of the target and also the failure process. The analysis has been focussed on the influence of the projectile diameter on the perforation process, assuming the same projectile mass. The aim was to preserve the same initial kinetic energy and identical nose angle. The goal is to estimate the ballistic limit, the residual velocity, the plastic work, and the temperature levels produced during the penetration process. The analysis has shown a linear increase of the ballistic limit with the projectile diameter.Publicad