simultaneous fitting
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2021 ◽  
Author(s):  
Hüsnü Dal ◽  
Kemal Açikgöz ◽  
Yashar Badienia

Abstract Besides the well-known landmark models for hyperelastic response of rubberlike materials, many new hyperelastic constitutive models heve emerged over the last decade. Despite many reviews on constitutive modelling or elastomers, it is still a challenging endeavor for engineers to decide for a constitutive model for the specific rubber compound and application. In this work, we have reviewed 44 hyperelastic constitutive models for elastomers and assessed their strength and weaknesses under uniaxial, pure shear, and (equi)biaxial deformations. To this end, we first present a novel parameter identification methodology based on various multi-objective optimization strategies for the selection of the best constitutive models from a given set of uniaxial tension, pure shear and (equi)biaxial tension experiments. We utilize a hybrid multi-objective optimization procedure using a genetic algorithm to generate multiple initial points for gradient based search algorithm, Fmincon utility in Matlab. The novelty of the approach is (i) simultaneous fitting with variable weight factors for uniaxial, equibiaxial, and pure shear data, and (ii) the sorting of the models based on an objective normalized quality of fit metric. For the models incapable of simultaneously fitting the three distinct deformation data, the validity range is assessed through a threshold value for the quality of fit measure. Accordingly, 44 hyperelastic models are sorted with respect to their simultaneous fitting performance to the experimental dataset of Treloar and Kawabata. Based on the number of material parameters, and their fitting performance to experimental data, a detailed discussion is carried out.


2021 ◽  
Vol 29 ◽  
pp. 179-203
Author(s):  
Irina V. Belova ◽  
Mohammad Afikuzzaman ◽  
Graeme E. Murch

A novel study of analysis interdiffusion in multicomponent alloys is investigated by means of closed form solutions and numerical simulations. Quaternary as well as selected CoCrFeMnNi (HEAs) quinary metallic systems are analysed using one, two and three diffusion couples with the full set of interdiffusion coefficients being calculated. A custom written Matlab fitting program (MFP) is used as the main tool for the simultaneous fitting into multiple composition profiles in both systems. The retrieved interdiffusion matrices are obtained using a newly developed approach that is interlinked with composition vectors, eigenvalues and eigenvector. On average, it can be concluded that the accuracy of the obtained matrices steadily improves with the increase of the number of couples used in the analysis.


2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Xue Wang ◽  
Jiao Song ◽  
Shengfa Zhou ◽  
Yi Lu ◽  
Wenxiao Lin ◽  
...  

Abstract Background To compare different fitting methods for determining IVIM (Intravoxel Incoherent Motion) parameters and to determine whether the use of different IVIM fitting methods would affect differentiation of cervix cancer from normal cervix tissue. Methods Diffusion-weighted echo-planar imaging of 30 subjects was performed on a 3.0 T scanner with b-values of 0, 30, 100, 200, 400, 1000 s/mm2. IVIM parameters were estimated using the segmented (two-step) fitting method and by simultaneous fitting of a bi-exponential function. Segmented fitting was performed using two different cut-off b-values (100 and 200 s/mm2) to study possible variations due to the choice of cut-off. Friedman’s test and Student’s t-test were respectively used to compare IVIM parameters derived from different methods, and between cancer and normal tissues. Results No significant difference was found between IVIM parameters derived from the segmented method with b-value cutoff of 200 s/mm2 and the simultaneous fitting method (P>0.05). Tissue diffusivity (D) and perfusion fraction (f) were significantly lower in cervix cancer than normal tissue (P< 0.05). Conclusions IVIM parameters derived using fitting methods with small cutoff b-values could be different, however, the segmented method with b-value cutoff of 200 s/mm2 are consistent with the simultaneous fitting method and both can be used to differentiate between cervix cancer and normal tissue.


2020 ◽  
Vol 499 (2) ◽  
pp. 3034-3045 ◽  
Author(s):  
J Daszyńska-Daszkiewicz ◽  
A A Pamyatnykh ◽  
P Walczak ◽  
W Szewczuk

ABSTRACT We present the results of complex seismic analysis of the prototype star SX Phoenicis. This analysis consists of a simultaneous fitting of the two radial-mode frequencies, the corresponding values of the bolometric flux amplitude (the parameter f) and of the intrinsic mode amplitude ε. The effects of various parameters as well as the opacity data are examined. With each opacity table it is possible to find seismic models that reproduce the two observed frequencies with masses allowed by evolutionary models appropriate for the observed values of the effective temperature and luminosity. All seismic models are in the post-main sequence phase. The OPAL and OP seismic models are in hydrogen shell-burning phase and the OPLIB seismic model has just finished an overall contraction and starts to burn hydrogen in a shell. The OP and OPLIB models are less likely due to the requirement of high initial hydrogen abundance (X0 = 0.75) and too high metallicity (Z ≈ 0.004) as for a Population II star. The fitting of the parameter f, whose empirical values are derived from multicolour photometric observations, provides constraints on the efficiency of convective transport in the outer layers of the star and on the microturbulent velocity in the atmosphere. Our complex seismic analysis with each opacity data indicates low to moderately efficient convection in the star’s envelope, described by the mixing length parameter of αMLT ∈ (0.0,  0.7), and the microturbulent velocity in the atmosphere of about ξt ∈ (4,  8) km s−1.


2019 ◽  
Vol 100 (5) ◽  
Author(s):  
Spencer Beloin ◽  
Sophia Han ◽  
Andrew W. Steiner ◽  
Khorgolkhuu Odbadrakh

2019 ◽  
Vol 134 ◽  
pp. 93-109 ◽  
Author(s):  
T. Rodrigues ◽  
J.-L. Dortet-Bernadet ◽  
Y. Fan
Keyword(s):  

2018 ◽  
Vol 28 (4) ◽  
pp. 311 ◽  
Author(s):  
Vi Ho Phong ◽  
Shunji Nishimura ◽  
Le Hong Khiem

This paper presents a Monte-Carlo code to simulate the time sequences of the \(\beta\)-decay following implantation of a continuous radioactive ion beam in to a segmented silicon detector. We extended our simulation to the \(\beta\)-delayed neutron process. Ananalis is procedure, which has been developed to obtain simultaneously the \(\beta\)-decay half-life and the \(\beta\)-delayed multi-neutron emission probability, was verified by the simulation data.


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