The Experts below are selected from a list of 38697 Experts worldwide ranked by ideXlab platform
Marloes H Maathuis - One of the best experts on this subject based on the ideXlab platform.
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order Independent Constraint based causal structure learning
Journal of Machine Learning Research, 2014Co-Authors: Diego Colombo, Marloes H MaathuisAbstract:We consider Constraint-based methods for causal structure learning, such as the PC-, FCI-, RFCI- and CCD- algorithms (Spirtes et al., 1993, 2000; Richardson, 1996; Colombo et al., 2012; Claassen et al., 2013). The first step of all these algorithms consists of the adjacency search of the PC-algorithm. The PC-algorithm is known to be order-dependent, in the sense that the output can depend on the order in which the variables are given. This order-dependence is a minor issue in low-dimensional settings. We show, however, that it can be very pronounced in high-dimensional settings, where it can lead to highly variable results. We propose several modifications of the PC-algorithm (and hence also of the other algorithms) that remove part or all of this order-dependence. All proposed modifications are consistent in high-dimensional settings under the same conditions as their original counterparts. We compare the PC-, FCI-, and RFCI-algorithms and their modifications in simulation studies and on a yeast gene expression data set. We show that our modifications yield similar performance in low-dimensional settings and improved performance in high-dimensional settings. All software is implemented in the R-package pcalg.
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order Independent Constraint based causal structure learning
arXiv: Machine Learning, 2012Co-Authors: Diego Colombo, Marloes H MaathuisAbstract:We consider Constraint-based methods for causal structure learning, such as the PC-, FCI-, RFCI- and CCD- algorithms (Spirtes et al. (2000, 1993), Richardson (1996), Colombo et al. (2012), Claassen et al. (2013)). The first step of all these algorithms consists of the PC-algorithm. This algorithm is known to be order-dependent, in the sense that the output can depend on the order in which the variables are given. This order-dependence is a minor issue in low-dimensional settings. We show, however, that it can be very pronounced in high-dimensional settings, where it can lead to highly variable results. We propose several modifications of the PC-algorithm (and hence also of the other algorithms) that remove part or all of this order-dependence. All proposed modifications are consistent in high-dimensional settings under the same conditions as their original counterparts. We compare the PC-, FCI-, and RFCI-algorithms and their modifications in simulation studies and on a yeast gene expression data set. We show that our modifications yield similar performance in low-dimensional settings and improved performance in high-dimensional settings. All software is implemented in the R-package pcalg.
Hongyang Jing - One of the best experts on this subject based on the ideXlab platform.
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two parameter approach of creep crack initiation times considering the Constraint effect induced by specimen geometry
Theoretical and Applied Fracture Mechanics, 2018Co-Authors: Dongquan Wu, Hongyang Jing, Lianyong Xu, Lei ZhaoAbstract:Abstract In this paper, a two-parameter approach and finite element method were conducted to investigate the Constraint effect of six different types of cracked specimen geometries on the creep crack initiation (CCI) time. The theoretical enhanced model of the C∗–Q∗ approach, which considers the load-Independent Constraint parameter Q∗, was proposed to predict the CCI time around a sharp crack tip. The order of Q∗ values and the creep damage accumulation rate for the different specimen geometries was C(T) > CS(T), SEN(B) > SEN(T) > DEN(T) > M(T). Whereas the CCI times were ordered conversely. The influence of the Constraint on hydrostatic stresses, triaxiality and multiaxial strain factor was discussed. The suitability of the two-parameter approach was verified due to the comparison of CCI times between theoretical and simulated results, which demonstrated that the C∗–Q∗ two-parameter prediction approach under stress intensity factor—Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) and Hutchinson–Rice–Rosengren—Riedel–Rice (HRR-RR) control (initially by plastic HRR control, then by RR conditions) could conservatively and effectively predict the CCI times. The K-RR solutions were more accurate when initial stress intensity factor K 6 MPa m1/2.
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analytical and numerical investigations of creep crack initiation considering the load Independent Constraint parameter varvec q q
Archive of Applied Mechanics, 2018Co-Authors: Hongyang Jing, Lei Zhao, Yongdian HanAbstract:The numerical simulation and a new theoretical approach were conducted to investigate the creep crack initiation (CCI) time and the effect of Constraints induced by the specimen thickness of P92 steel. The theoretical enhanced $$C^{*}-Q^{*}$$ approach, which considered the load-Independent Constraint parameter $$Q^{*}$$ , was proposed to predict the CCI time around a sharp crack tip. Moreover, finite element analysis was used to verify the load independence of parameter $$Q^{*}$$ as the value of $${C}^{*}$$ varied. The larger thickness of the compact tension (CT) specimen contributed to a larger Constraint parameter $$Q^{*}$$ , and the highly constrained CT specimens with larger thicknesses observably showed lower CCI times. The variation of hydrostatic stresses, triaxiality and multiaxial strain factor considering the Constraint was discussed. The suitability of the analytical approach was verified to predict CCI, and the comparison between analytical and simulated results demonstrated that the $$C^{*}-Q^{*}$$ two-parameter prediction approach under stress intensity factor and Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) and Hutchinson–Rice–Rosengren and Riedel–Rice (HRR-RR) control (initially by plastic HRR control, then by RR conditions) could conservatively and effectively characterize the CCI times. The K-RR solutions were more accurate when initial stress intensity factor $${K}<6\,\hbox {MPam}^{1/2}$$ , and the HRR-RR solutions were more appropriate when $${K}>6\,\hbox {MPam}^{1/2}$$ .
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theoretical and numerical analysis of the creep crack initiation time considering the Constraint effects for pressurized pipelines with axial surface cracks
International Journal of Mechanical Sciences, 2018Co-Authors: Hongyang Jing, Lei Zhao, Yongdian HanAbstract:Abstract A theoretical approach and numerical simulation were conducted to investigate the creep crack initiation (CCI) time and the effect of Constraints induced by the geometrical sizes of pipelines with axial surface cracks. The theoretical enhancement model of the C*–Q* approach under the transient creep condition, which considers the load-Independent Constraint parameter Q*, was proposed to predict the CCI time around the crack front. The results revealed that the distribution regulation of Q* along the crack front for circumferential internal surface cracks and external surface cracks was similar. The maximum Constraint level occurred near the deepest crack front part for cracks with small a/c (a/c 0.4). The Constraint values at the same position (2Φ/π) increased with the increasing of the crack depth when a/c kept constant. In addition, the axial internal surface cracks of pipelines were proved more dangerous than the external surface cracks with the same geometrical size. Furthermore, the CCI times were decided by the peak values of Constraint, or the CCI firstly occurred at the position where the Constraint level was maximum. Additionally, the variation of hydrostatic stresses and triaxiality considering the Constraint was discussed. The suitability of the analytical C*–Q* approach was verified to predict CCI. The comparison of CCI times between the analytical approach and the BS 7910 as well as the FE results demonstrated that the solutions under stress intensity factor—Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) were more accurate when internal pressure P 15 MPa.
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characterizing crack growth behavior and damage evolution in p92 steel under creep fatigue conditions
International Journal of Mechanical Sciences, 2017Co-Authors: Lei Zhao, Hongyang Jing, Yongdian Han, Zhifang GaoAbstract:Abstract The present paper characterized crack growth behavior and damage evolution in P92 steel under creep-fatigue interaction conditions. Creep-fatigue crack growth tests were conducted at a constant load amplitude with various hold times. To reveal the role of Constraint in creep-fatigue regime, specimens with different crack depths and thicknesses were used. Combination with a non-linear creep-fatigue interaction damage constitutive model, the crack growth and damage evolution behaviors were simulated using finite element method. Under creep-fatigue condition, time dependent crack growth rate increased as the duration period was reduced. This was attributed to the role of enhanced fatigue damage with the decreasing of the dwell time. Moreover, the deviation of crack growth rate with different dwell times became small as crack grew. With the crack length increasing, the creep damage level was improved regardless the dwell time, which may be due to the fact that the creep damage dominated crack growth in this stage. Furthermore, the crack growth rate increased as the crack depth became deep and the specimen thickness became large, as a result of the increased Constraint level. A load-Independent Constraint parameter Q * was introduced to correlate the crack growth rate, which provided a good prediction for specimens under different Constraint conditions.
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quantifying the creep crack tip Constraint effects using a load Independent Constraint parameter q
International Journal of Mechanical Sciences, 2016Co-Authors: Xingfu Zhang, Yongdian Han, Lei Zhao, Hongyang JingAbstract:Abstract In this work, a load-Independent creep Constraint parameter Q* was introduced, and its load-independence was confirmed by 3D finite element analyses of six different cracked specimens. A fixed distance r=0.2 mm ahead of crack tips was chosen to define the Q*. In addition, the parameter Q* was used to quantify the in-plane Constraint induced by crack depths, specimen widths and loading configurations and the Constraint effects induced by specimen thicknesses. The results revealed that the values of Q* increased with increasing the crack depths (a/W ≤0.5) and specimen thicknesses and decreased with increasing the width-thickness ratio W/B of specimens. Furthermore, the highest Constraint level occurred in the CT specimen while the lowest occurred in the CCT specimen.
Matias Zaldarriaga - One of the best experts on this subject based on the ideXlab platform.
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combining full shape and bao analyses of galaxy power spectra a 1 6 cmb Independent Constraint on h0
Journal of Cosmology and Astroparticle Physics, 2020Co-Authors: Oliver H E Philcox, Mikhail M Ivanov, Marko Simonovic, Matias ZaldarriagaAbstract:We present cosmological Constraints from a joint analysis of the pre- and post-reconstruction galaxy power spectrum multipoles from the final data release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric Constraints are obtained from the positions of BAO peaks in reconstructed spectra, analyzed in combination with the unreconstructed spectra in a full-shape (FS) likelihood using a joint covariance matrix, giving stronger parameter Constraints than FS-only or BAO-only analyses. We introduce a new method for obtaining Constraints from reconstructed spectra based on a correlated theoretical error, which is shown to be simple, robust, and applicable to any flavor of density-field reconstruction. Assuming $\Lambda$CDM with massive neutrinos, we analyze data from two redshift bins $z_\mathrm{eff}=0.38,0.61$ and obtain $1.6\%$ Constraints on the Hubble constant $H_0$, using only a single prior on the current baryon density $\omega_b$ from Big Bang Nucleosynthesis (BBN) and no knowledge of the power spectrum slope $n_s$. This gives $H_0 = 68.6\pm1.1\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$, with the inclusion of BAO data sharpening the measurement by $40\%$, representing one of the strongest current Constraints on $H_0$ Independent of cosmic microwave background data. Restricting to the best-fit slope $n_s$ from Planck (but without additional priors on the spectral shape), we obtain a $1\%$ $H_0$ measurement of $67.8\pm 0.7\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$. We find strong Constraints on the cosmological parameters from a joint analysis of the FS, BAO, and Planck data. This sets new bounds on the sum of neutrino masses $\sum m_\nu < 0.14\,\mathrm{eV}$ (at $95\%$ confidence) and the effective number of relativistic degrees of freedom $N_\mathrm{eff} = 2.90^{+0.15}_{-0.16}$, though contours are not appreciably narrowed by the inclusion of BAO data.
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combining full shape and bao analyses of galaxy power spectra a 1 6 cmb Independent Constraint on h0
Journal of Cosmology and Astroparticle Physics, 2020Co-Authors: Oliver H E Philcox, Mikhail M Ivanov, Marko Simonovic, Matias ZaldarriagaAbstract:We present cosmological Constraints from a joint analysis of the pre- and post-reconstruction galaxy power spectrum multipoles from the final data release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric Constraints are obtained from the positions of BAO peaks in reconstructed spectra, which are analyzed in combination with the unreconstructed spectra in a full-shape (FS) likelihood using a joint covariance matrix, giving stronger parameter Constraints than FS-only or BAO-only analyses. We introduce a new method for obtaining Constraints from reconstructed spectra based on a correlated theoretical error, which is shown to be simple, robust, and applicable to any flavor of density-field reconstruction. Assuming ΛCDM with massive neutrinos, we analyze clustering data from two redshift bins zeff=0.38,0.61 and obtain 1.6% Constraints on the Hubble constant H0, using only a single prior on the current baryon density ωb from Big Bang Nucleosynthesis (BBN) and no knowledge of the power spectrum slope ns. This gives H0 = 68.6±1.1 km s−1Mpc−1, with the inclusion of BAO data sharpening the measurement by 40%, representing one of the strongest current Constraints on H0 Independent of cosmic microwave background data, comparable with recent Constraints using BAO data in combination with other data-sets. Restricting to the best-fit slope ns from Planck (but without additional priors on the spectral shape), we obtain a 1% H0 measurement of 67.8± 0.7 km s−1Mpc−1. Finally, we find strong Constraints on the cosmological parameters from a joint analysis of the FS, BAO, and Planck data. This sets new bounds on the sum of neutrino masses ∑ mν < 0.14 eV (at 95% confidence) and the effective number of relativistic degrees of freedom Neff = 2.90+0.15−0.16, though contours are not appreciably narrowed by the inclusion of BAO data.
Yongdian Han - One of the best experts on this subject based on the ideXlab platform.
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analytical and numerical investigations of creep crack initiation considering the load Independent Constraint parameter varvec q q
Archive of Applied Mechanics, 2018Co-Authors: Hongyang Jing, Lei Zhao, Yongdian HanAbstract:The numerical simulation and a new theoretical approach were conducted to investigate the creep crack initiation (CCI) time and the effect of Constraints induced by the specimen thickness of P92 steel. The theoretical enhanced $$C^{*}-Q^{*}$$ approach, which considered the load-Independent Constraint parameter $$Q^{*}$$ , was proposed to predict the CCI time around a sharp crack tip. Moreover, finite element analysis was used to verify the load independence of parameter $$Q^{*}$$ as the value of $${C}^{*}$$ varied. The larger thickness of the compact tension (CT) specimen contributed to a larger Constraint parameter $$Q^{*}$$ , and the highly constrained CT specimens with larger thicknesses observably showed lower CCI times. The variation of hydrostatic stresses, triaxiality and multiaxial strain factor considering the Constraint was discussed. The suitability of the analytical approach was verified to predict CCI, and the comparison between analytical and simulated results demonstrated that the $$C^{*}-Q^{*}$$ two-parameter prediction approach under stress intensity factor and Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) and Hutchinson–Rice–Rosengren and Riedel–Rice (HRR-RR) control (initially by plastic HRR control, then by RR conditions) could conservatively and effectively characterize the CCI times. The K-RR solutions were more accurate when initial stress intensity factor $${K}<6\,\hbox {MPam}^{1/2}$$ , and the HRR-RR solutions were more appropriate when $${K}>6\,\hbox {MPam}^{1/2}$$ .
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theoretical and numerical analysis of the creep crack initiation time considering the Constraint effects for pressurized pipelines with axial surface cracks
International Journal of Mechanical Sciences, 2018Co-Authors: Hongyang Jing, Lei Zhao, Yongdian HanAbstract:Abstract A theoretical approach and numerical simulation were conducted to investigate the creep crack initiation (CCI) time and the effect of Constraints induced by the geometrical sizes of pipelines with axial surface cracks. The theoretical enhancement model of the C*–Q* approach under the transient creep condition, which considers the load-Independent Constraint parameter Q*, was proposed to predict the CCI time around the crack front. The results revealed that the distribution regulation of Q* along the crack front for circumferential internal surface cracks and external surface cracks was similar. The maximum Constraint level occurred near the deepest crack front part for cracks with small a/c (a/c 0.4). The Constraint values at the same position (2Φ/π) increased with the increasing of the crack depth when a/c kept constant. In addition, the axial internal surface cracks of pipelines were proved more dangerous than the external surface cracks with the same geometrical size. Furthermore, the CCI times were decided by the peak values of Constraint, or the CCI firstly occurred at the position where the Constraint level was maximum. Additionally, the variation of hydrostatic stresses and triaxiality considering the Constraint was discussed. The suitability of the analytical C*–Q* approach was verified to predict CCI. The comparison of CCI times between the analytical approach and the BS 7910 as well as the FE results demonstrated that the solutions under stress intensity factor—Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) were more accurate when internal pressure P 15 MPa.
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characterizing crack growth behavior and damage evolution in p92 steel under creep fatigue conditions
International Journal of Mechanical Sciences, 2017Co-Authors: Lei Zhao, Hongyang Jing, Yongdian Han, Zhifang GaoAbstract:Abstract The present paper characterized crack growth behavior and damage evolution in P92 steel under creep-fatigue interaction conditions. Creep-fatigue crack growth tests were conducted at a constant load amplitude with various hold times. To reveal the role of Constraint in creep-fatigue regime, specimens with different crack depths and thicknesses were used. Combination with a non-linear creep-fatigue interaction damage constitutive model, the crack growth and damage evolution behaviors were simulated using finite element method. Under creep-fatigue condition, time dependent crack growth rate increased as the duration period was reduced. This was attributed to the role of enhanced fatigue damage with the decreasing of the dwell time. Moreover, the deviation of crack growth rate with different dwell times became small as crack grew. With the crack length increasing, the creep damage level was improved regardless the dwell time, which may be due to the fact that the creep damage dominated crack growth in this stage. Furthermore, the crack growth rate increased as the crack depth became deep and the specimen thickness became large, as a result of the increased Constraint level. A load-Independent Constraint parameter Q * was introduced to correlate the crack growth rate, which provided a good prediction for specimens under different Constraint conditions.
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quantifying the creep crack tip Constraint effects using a load Independent Constraint parameter q
International Journal of Mechanical Sciences, 2016Co-Authors: Xingfu Zhang, Yongdian Han, Lei Zhao, Hongyang JingAbstract:Abstract In this work, a load-Independent creep Constraint parameter Q* was introduced, and its load-independence was confirmed by 3D finite element analyses of six different cracked specimens. A fixed distance r=0.2 mm ahead of crack tips was chosen to define the Q*. In addition, the parameter Q* was used to quantify the in-plane Constraint induced by crack depths, specimen widths and loading configurations and the Constraint effects induced by specimen thicknesses. The results revealed that the values of Q* increased with increasing the crack depths (a/W ≤0.5) and specimen thicknesses and decreased with increasing the width-thickness ratio W/B of specimens. Furthermore, the highest Constraint level occurred in the CT specimen while the lowest occurred in the CCT specimen.
Mikhail M Ivanov - One of the best experts on this subject based on the ideXlab platform.
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combining full shape and bao analyses of galaxy power spectra a 1 6 cmb Independent Constraint on h0
Journal of Cosmology and Astroparticle Physics, 2020Co-Authors: Oliver H E Philcox, Mikhail M Ivanov, Marko Simonovic, Matias ZaldarriagaAbstract:We present cosmological Constraints from a joint analysis of the pre- and post-reconstruction galaxy power spectrum multipoles from the final data release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric Constraints are obtained from the positions of BAO peaks in reconstructed spectra, analyzed in combination with the unreconstructed spectra in a full-shape (FS) likelihood using a joint covariance matrix, giving stronger parameter Constraints than FS-only or BAO-only analyses. We introduce a new method for obtaining Constraints from reconstructed spectra based on a correlated theoretical error, which is shown to be simple, robust, and applicable to any flavor of density-field reconstruction. Assuming $\Lambda$CDM with massive neutrinos, we analyze data from two redshift bins $z_\mathrm{eff}=0.38,0.61$ and obtain $1.6\%$ Constraints on the Hubble constant $H_0$, using only a single prior on the current baryon density $\omega_b$ from Big Bang Nucleosynthesis (BBN) and no knowledge of the power spectrum slope $n_s$. This gives $H_0 = 68.6\pm1.1\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$, with the inclusion of BAO data sharpening the measurement by $40\%$, representing one of the strongest current Constraints on $H_0$ Independent of cosmic microwave background data. Restricting to the best-fit slope $n_s$ from Planck (but without additional priors on the spectral shape), we obtain a $1\%$ $H_0$ measurement of $67.8\pm 0.7\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$. We find strong Constraints on the cosmological parameters from a joint analysis of the FS, BAO, and Planck data. This sets new bounds on the sum of neutrino masses $\sum m_\nu < 0.14\,\mathrm{eV}$ (at $95\%$ confidence) and the effective number of relativistic degrees of freedom $N_\mathrm{eff} = 2.90^{+0.15}_{-0.16}$, though contours are not appreciably narrowed by the inclusion of BAO data.
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combining full shape and bao analyses of galaxy power spectra a 1 6 cmb Independent Constraint on h0
Journal of Cosmology and Astroparticle Physics, 2020Co-Authors: Oliver H E Philcox, Mikhail M Ivanov, Marko Simonovic, Matias ZaldarriagaAbstract:We present cosmological Constraints from a joint analysis of the pre- and post-reconstruction galaxy power spectrum multipoles from the final data release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric Constraints are obtained from the positions of BAO peaks in reconstructed spectra, which are analyzed in combination with the unreconstructed spectra in a full-shape (FS) likelihood using a joint covariance matrix, giving stronger parameter Constraints than FS-only or BAO-only analyses. We introduce a new method for obtaining Constraints from reconstructed spectra based on a correlated theoretical error, which is shown to be simple, robust, and applicable to any flavor of density-field reconstruction. Assuming ΛCDM with massive neutrinos, we analyze clustering data from two redshift bins zeff=0.38,0.61 and obtain 1.6% Constraints on the Hubble constant H0, using only a single prior on the current baryon density ωb from Big Bang Nucleosynthesis (BBN) and no knowledge of the power spectrum slope ns. This gives H0 = 68.6±1.1 km s−1Mpc−1, with the inclusion of BAO data sharpening the measurement by 40%, representing one of the strongest current Constraints on H0 Independent of cosmic microwave background data, comparable with recent Constraints using BAO data in combination with other data-sets. Restricting to the best-fit slope ns from Planck (but without additional priors on the spectral shape), we obtain a 1% H0 measurement of 67.8± 0.7 km s−1Mpc−1. Finally, we find strong Constraints on the cosmological parameters from a joint analysis of the FS, BAO, and Planck data. This sets new bounds on the sum of neutrino masses ∑ mν < 0.14 eV (at 95% confidence) and the effective number of relativistic degrees of freedom Neff = 2.90+0.15−0.16, though contours are not appreciably narrowed by the inclusion of BAO data.
