| 1. |
- Adare, A., et al.
(författare)
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Measurement of K-S(0) and K*(0) in p plus p, d plus Au, and Cu plus Cu collisions at root s(NN)=200 GeV
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:5
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K-S(0) and K*(0) meson production at midrapidity in p + p, d + Au, and Cu + Cu collisions at root s(NN) = 200 GeV. The K-S(0) and K*(0) mesons are reconstructed via their K-S(0) -> pi(0)(-> gamma gamma) pi(0)(-> gamma gamma) and K*(0) -> K-+/-pi(-/+) decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K-S(0) and K*(0) mesons in d + Au and Cu + Cu collisions at different centralities. In the d + Au collisions, the nuclear modification factor of K-S(0) and K*(0) mesons is almost constant as a function of transverse momentum and is consistent with unity, showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu + Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the p + p yield scaled by the number of binary nucleon-nucleon collisions in the Cu + Cu system. In the p(T) range 2-5 GeV/c, the strange mesons (K-S(0), K*(0)) similarly to the phi meson with hidden strangeness, showan intermediate suppression between the more suppressed light quark mesons (pi(0)) and the nonsuppressed baryons (p, (p) over bar). At higher transverse momentum, p(T) > 5 GeV/c, production of all particles is similarly suppressed by a factor of approximate to 2.
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| 2. |
- Adare, A., et al.
(författare)
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Measurements of Elliptic and Triangular Flow in High-Multiplicity He-3 + Au Collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review Letters. - 1079-7114. ; 115:14
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Tidskriftsartikel (refereegranskat)abstract
- We present the first measurement of elliptic (v(2)) and triangular (v(3)) flow in high-multiplicity He-3 + Au collisions at root s(NN) = 200 GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in He-3 + Au and in p + p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the He-3 + Au system. The collective behavior is quantified in terms of elliptic v(2) and triangular v(3) anisotropy coefficients measured with respect to their corresponding event planes. The v(2) values are comparable to those previously measured in d + Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three He-3 nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
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| 3. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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A simple scalar directional hardening model for the Bauschinger effect compared with a tensorial model
- 2020
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Ingår i: Journal of Mechanics of Materials and Structures. - : Mathematical Sciences Publishers. - 1559-3959 .- 2157-5428. ; 15:4, s. 511-537
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Tidskriftsartikel (refereegranskat)abstract
- Modeling the Bauschinger effect is usually accomplished by introducing a second-order back-stress or directional hardening tensor. The objective of this paper is to propose a simpler scalar model of the Bauschinger effect based on a scalar directional hardening parameter that is determined by integration of an evolution equation. The behavior of this scalar model is compared to a tensorial model for a number of load cases. Strongly objective numerical algorithms are developed for integrating the evolution equations for both the tensorial and scalar models. Also, a consistent tangent is developed for both models. Obviously, the numerical implementation of the scalar model is significantly less complicated than for the tensorial model. Examples show that the tensorial and scalar models predict the same results for cyclic proportional triaxial extension and triaxial compression loadings. In contrast, the tensorial model predicts a Bauschinger effect for cyclic proportional pure torsion loading which is not predicted by the scalar model. More complicated examples with nonproportional loading paths and inhomogeneous deformations indicate that, relative to the tensorial model, the scalar model accounts for directional hardening fairly well and the simplicity of the model makes it an attractive option to add to isotropic hardening models.
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| 4. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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An Eulerian constitutive model for the inelastic finite strain behaviour of isotropic semi-crystalline polymers
- 2023
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 100
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for isotropic, semi-crystalline polymers is proposed. The model is Eulerian in the sense that it is independent of measures of total deformation and plastic/inelastic deformations. It is able to account for such essential phenomena as strain-rate dependence, work hardening, stress relaxation, volumetric inelastic deformations, and damage. The model was applied to uniaxial tension tests performed on polyoxymethylene (POM), which is a semi-crystalline polymer widely used in the industry. Three types of tests were conducted: monotonic tests at different strain rates, stress relaxation tests, and loading-unloading tests. The model was able to reproduce the experimental results well. The proposed model was also implemented as a VUMAT in Abaqus, and the deformation of a 3D geometry was simulated.
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| 5. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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An Eulerian model for orthotropic elasticity and inelasticity applied to injection-moulded low-density polyethylene
- 2022
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Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 167
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic elasticity and inelasticity is of relevance in many practical applications. The Eulerian formulation for anisotropic elastic and inelastic response based on microstructural vectors is used here to model an injection-moulded low-density polyethylene. In contrast with Lagrangian models of inelasticity, the Eulerian formulation is insensitive to arbitrariness of the reference and intermediate configurations as well as to measures of total and inelastic deformations. A specific strain-space-type anisotropic yield function is proposed that depends on anisotropic measures of elastic deformation and anisotropic hardening variables. Use is also made of a rate-independent model with a smooth elastic-inelastic transition. The material parameters were calibrated to reproduce uniaxial test data for loading in three directions in the moulding plane. In addition, a strongly objective numerical implementation is presented and used to simulate stretching of a plate with a circular hole. In contrast with metals, this polyethylene experiences elastic deformations of about 10%. Although the inelastic spin rate could not be determined by the available test data, simulations of loadings in different material directions yield observable influences of inelastic spin rate.
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| 6. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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An Eulerian thermomechanical elastic-viscoplastic model with isotropic and directional hardening applied to computational welding mechanics
- 2021
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Ingår i: Acta Mechanica. - : Springer. - 0001-5970 .- 1619-6937. ; 232, s. 189-218
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Tidskriftsartikel (refereegranskat)abstract
- An Eulerian thermomechanical elastic-viscoplastic model with isotropic and directional hardening is used to analyse the residual mechanical state resulting from the arc welding of a multi-pass weld. Details of the weld test plate, weld filler material, and numerical implementation of the model are provided, including integration algorithms and consistent tangent modulus. For the computational welding mechanics analyses, the austenitic ASME stainless steel grade 316L was considered so that no phase transformations of solid states needed to be considered. The maximum residual stresses were found to be about 500-600 MPa, which is of the order of the yield stress of the base material. Variations in the heat input and the resulting weld cooling time had a significant influence both on the residual stress state and on the resulting geometry of the weld. The predicted stress levels were compared to the experimental results. Overall, the proposed Eulerian framework seems to be a promising tool for analysing melting/solidification processes and residual mechanical states.
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| 7. |
- Kroon, Martin, 1974-, et al.
(författare)
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Influence of thermal recovery on predictions of the residual mechanical state during melting and solidification
- 2020
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Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 141:January, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- A thermomechanically consistent Eulerian plasticity model with work hardening is adopted for studying the residual mechanical state resulting from loading at elevated temperatures. The isotropic plasticity model includes the standard effect of thermal softening as well as specific modeling of thermal recovery. The model parameters and functions were calibrated to data for an austenitic stainless steel 316L. The model is applied in two numerical examples: a case of uniaxial tension and a circular disk that is exposed to a temperature load. The influence of thermal recovery is examined for each example by comparing the response of the complete model with thermal recovery to that when thermal recovery is omitted. The results of the second example indicate the importance of modeling thermal recovery for accurate prediction of residual stresses for problems dealing with melting and solidification.
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| 8. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Prediction of welding residual stresses using an Eulerian plasticity model
- 2022
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Ingår i: Proceedings M2D2022 - 9th International Conference on Mechanics and Materials in Design, Funchal/Portugal 26-30 June 2022. - 9789895475636 ; , s. 167-168
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Konferensbidrag (refereegranskat)abstract
- Solidification processes play an important role in several industrial processes, such as weldingand additive manufacturing, and the resulting residual stress state is often critical for thestructural integrity of the material. A thermomechanical model was developed for the analysisand prediction of such solidification processes. The approach is based on a model proposed byRubin (Int. J. Eng. Sci. 25, 1175-1191, 1987). This plasticity model was formulated for finitestrains using an Eulerian evolution equation for a unimodular elastic distortional deformationtensor. This evolution equation automatically ensures thermodynamic consistency andpreservation of isochoric inelastic deformations. A 2D problem in the form of a butt weld jointwas analyzed. The main outcome from the analyses were the residual stress distributions. Theresults are compared to experimental data from the literature.
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| 9. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Regularization of localization due to material softening using a nonlocal hardening variable in an Eulerian formulation of inelasticity
- 2022
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Ingår i: International Journal of Engineering Science. - : Elsevier. - 0020-7225 .- 1879-2197. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- It is known that damage or inelastic softening can cause an ill-posed problem leading to localization and mesh-dependence in finite element simulations. In this paper, a nonlocal hardening variable, ̄? , is introduced in a finite deformation Eulerian formulation of inelasticity with a rate-independent smooth elastic–inelastic transition. This nonlocal variable is defined over an Eulerian region of nonlocality, which is a sphere with radius equal to the characteristic length, ?c, defined in the current deformed geometry of the material. Two models of this nonlocal hardening variable are explored. One model where ̄ ? is the minimum value of the local hardening ? within the region of nonlocality, and another model where ̄? is the average of ? in the same region. The influence of the nonlocal hardening variable is studied using an example of a plate that is loaded by a prescribed boundary displacement causing formation of a shear band. Predictions of the applied load vs. displacement curves and contour plots of the total distortional deformation of the plate and the hardening variable ? are studied. The model based on the minimum value of ? in the nonlocal region predicts mesh-independent post-peak response of the load vs. displacement curve. Also, it is shown that the characteristic material length, ?c, controls the structure of the shear band developed in the plate.
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| 10. |
- Wetterskog, Daniel, 1978, et al.
(författare)
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Mutation profiling of adenoid cystic carcinomas from multiple anatomical sites identifies mutations in the RAS pathway, but no KIT mutations
- 2013
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Ingår i: Histopathology. - : Wiley. - 0309-0167. ; 62:4, s. 543-550
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Tidskriftsartikel (refereegranskat)abstract
- Aims The majority of adenoid cystic carcinomas (AdCCs), regardless of anatomical site, harbour the MYB–NFIB fusion gene. The aim of this study was to characterize the repertoire of somatic genetic events affecting known cancer genes in AdCCs. Methods and results DNA was extracted from 13 microdissected breast AdCCs, and subjected to a mutation survey using the Sequenom OncoCarta Panel v1.0. Genes found to be mutated in any of the breast AdCCs and genes related to the same canonical molecular pathways, as well as KIT, a proto-oncogene whose protein product is expressed in AdCCs, were sequenced in an additional 68 AdCCs from various anatomical sites by Sanger sequencing. Using the Sequenom MassARRAY platform and Sanger sequencing, mutations in BRAF and HRAS were identified in three and one cases, respectively (breast, and head and neck). KIT, which has previously been reported to be mutated in AdCCs, was also investigated, but no mutations were identified. Conclusions Our results demonstrate that mutations in genes pertaining to the canonical RAS pathway are found in a minority of AdCCs, and that activating KIT mutations are either absent or remarkably rare in these cancers, and unlikely to constitute a driver and therapeutic target for patients with AdCC.
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