| 21. |
- Adare, A., et al.
(författare)
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Scaling properties of fractional momentum loss of high- pT hadrons in nucleus-nucleus collisions at sNN from 62.4 GeV to 2.76 TeV
- 2016
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Ingår i: Physical Review C. - 2469-9985. ; 93:2
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the fractional momentum loss (Sloss≡δpT/pT) of high-transverse-momentum-identified hadrons in heavy-ion collisions are presented. Using π0 in Au+Au and Cu+Cu collisions at sNN=62.4 and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb+Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of Sloss as a function of a number of variables: the number of participants, Npart, the number of quark participants, Nqp, the charged-particle density, dNch/dη, and the Bjorken energy density times the equilibration time, Bjτ0. We find that the pT, where Sloss has its maximum, varies both with centrality and collision energy. Above the maximum, Sloss tends to follow a power-law function with all four scaling variables. The data at sNN=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of Sloss with dNch/dη and Bjτ0, lending insight into the physics of parton energy loss.
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| 22. |
- Adare, A., et al.
(författare)
-
Search for dark photons from neutral meson decays in p plus p and d plus Au collisions at root s(NN)=200 GeV
- 2015
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:3
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Tidskriftsartikel (refereegranskat)abstract
- The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g - 2)mu deviates from SM calculations by 3.6 sigma. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in pi(0), eta -> gamma e(+)e(-) decays and obtained upper limits of O(2 x 10(-6)) on U-gamma mixing at 90% C.L. for the mass range 30 < m(U) < 90 MeV/c(2). Combined with other experimental limits, the remaining region in the U-gamma mixing parameter space that can explain the (g - 2)(mu) deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29 < m(U) < 32 MeV/c(2) remaining.
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| 23. |
- Adare, A., et al.
(författare)
-
Systematic study of azimuthal anisotropy in Cu plus Cu and Au plus Au collisions at root s(NN)=62.4 and 200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:3
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the dependence of azimuthal anisotropy nu(2) for inclusive and identified charged hadrons in Au + Au and Cu + Cu collisions on collision energy, species, and centrality. The values of nu(2) as a function of transverse momentum pT and centrality in Au + Au collisions at root s(NN) = 200 and 62.4 GeV are the same within uncertainties. However, in Cu + Cu collisions we observe a decrease in nu(2) values as the collision energy is reduced from 200 to 62.4 GeV. The decrease is larger in the more peripheral collisions. By examining both Au + Au and Cu + Cu collisions we find that nu(2) depends both on eccentricity and the number of participants, N-part. We observe that nu(2) divided by eccentricity (epsilon) monotonically increases with N-part and scales as N-part(1/3). The Cu + Cu data at 62.4 GeV falls below the other scaled nu(2) data. For identified hadrons, nu(2) divided by the number of constituent quarks n(q) is independent of hadron species as a function of transverse kinetic energy K E-T = m(T) - m between 0.1 < K E-T / n(q) < 1 GeV. Combining all of the above scaling and normalizations, we observe a near-universal scaling, with the exception of the Cu + Cu data at 62.4 GeV, of nu(2)/(nq center dot e center dot N-part(1/3)) vs K E-T / n(q) for all measured particles.
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| 24. |
- Adare, A., et al.
(författare)
-
Systematic study of charged-pion and kaon femtoscopy in Au plus Au collisions at root s(NN)=200 GeV
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:3
-
Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of charged-pion and kaon interferometry in Au + Au collisions at root s(NN) = 200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.
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| 25. |
- Gustafsson, Gustaf, et al.
(författare)
-
Fracture probability modelling of impact-loaded iron ore pellets
- 2017
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Ingår i: International Journal of Impact Engineering. - : Elsevier. - 0734-743X .- 1879-3509. ; 102, s. 180-186
-
Tidskriftsartikel (refereegranskat)abstract
- Blast furnace iron ore pellets are sintered, centimetre-sized ore spheres with a high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In transporting pellets from pelletizing plants to customers, iron ore pellets are exposed to different static and dynamic loading situations, resulting in strength degradation and, in some cases, fragmentation. This can lead to a reduced gas flow in the blast furnace, which causes reduced quality in steel production. Reliable numerical simulations that can predict the ability of the pellets to endure their handling are important tools for optimizing the design of equipment for iron ore handling. This paper describes the experimental and numerical work performed to investigate the impact fracture behaviour of iron ore pellets at different strain rates. A number of split Hopkinson pressure bar tests with different striker velocities are carried out and analysed to investigate the strain rate dependency of the fracture strength of iron ore pellets. Fracture data for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. A stress based, strain-rate dependent fracture model that takes triaxiality into account is suggested. The fracture model is used and validated with impact tests of iron ore pellets. In the validation experiment, iron ore pellets are fired against a steel plate, and the percentage of fractured pellets at different impact velocities are measured. Finite element simulations of the experiment are carried out and the probability of pellets fracturing during impact are calculated and compared with the experimental results. The agreement between the experiments and numerical simulations shows the validity of the model.
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| 26. |
- Gustafsson, Gustaf, et al.
(författare)
-
High-rate behaviour of iron ore pellet
- 2015
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different loading situations, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental work to investigate the dynamic mechanical properties of blast furnace iron ore pellets. To study the dynamic fracture of iron ore pellets a number of split Hopkinson pressure bar tests are carried out and analysed
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| 27. |
- Gustafsson, Gustaf, et al.
(författare)
-
Mechanical characterization and modelling of the temperature-dependent impact behaviour of a biocompatible poly(L-lactide)/poly(ε-caprolactone) polymer blend
- 2015
-
Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 51, s. 279-290
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(ε-caprolactone) (PCL) is a ductile, bioabsorbable polymer that has been employed as a blend partner for poly(L-lactic acid) (PLLA). An improvement of the material strength and impact resistance of PLLA/PCL polymer blends compared to pure PLLA has been shown previously. To use numerical simulations in the design process of new components composed of the PLLA/PCL blend, a constitutive model for the material has to be established. In this work, a constitutive model for a PLLA/PCL polymer blend is established from the results of compressive tests at high and low strain rates at three different temperatures, including the body temperature. Finite element simulations of the split Hopkinson pressure bar test using the established constitutive model are carried out under the same condition as the experiments. During the experiments, the changes in the diameter and thickness of the specimens are captured by a high-speed video camera. The accuracy of the numerical model is tested by comparing the simulation results, such as the stress, strain, thickness and diameter histories of the specimens, with those measured in the experiments. The numerical model is also validated against an impact test of non-homogenous strains and strain rates. The results of this study provide a validated numerical model for a PLLA/PCL polymer blend at strain rates of up to 1800 s−1 in the temperature range between 22 °C and 50 °C.
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| 28. |
- Gustafsson, Gustaf, et al.
(författare)
-
Numerical Prediction of Fracture in Iron Ore Pellets During Handling and Transportation
- 2017
-
Konferensbidrag (refereegranskat)abstract
- Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. During transportation and handling of iron ore pellets they are exposed to different loads, resulting in degradation of the strength and in some cases fragmentation. The aim of this work is to increase the knowledge of how to design the handling systems for iron ore pellets to decrease the amount of fractured materials in the flows. A numerical finite element model for iron ore pellets fracture probability analysis is presented with a stress based fracture criterion. The model is used to simulate different flows of iron ore pellets hitting guide plates and to predict the proportion of fractured iron ore pellets in the flow. The amount of fractured iron ore pellets are predicted at different flow velocities, showing good agreement with experimental measurements.
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| 29. |
- Gustafsson, Gustaf, et al.
(författare)
-
Smoothed particle simulation and validation of powder filling
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Powder pressing is often a complicated process as the behaviour of the powder material changes with increasing density. Manufactures tend to produce components with more complicated shapes which demand complex pressing equipment and methods. Mechanical properties of powder materials changes dramatically from the beginning to the end of the compaction phase. Previous investigations have shown that powder transfer and high powder flow during filling affects the strength of the final component significantly. Experimental studies combined with simulations is likely to improve the understanding of the filling stage, e.g. to explain the non-homogeneity of the density of powder pressed parts. This work covers both experimental measurements and umerical modelling of powder filling. Experimental measurements with digital speckle photography (DSP) is used to study the powder behaviour and for the characterisation of the die filling as part of the process in powder pressing. TheDSP measurements are carried out by recording the powder filling process with a high speed video camera. The image series are then evaluated using an image correlation technique. By this, field data during the filling process can be visualised such as velocity fields and strain fields. These measurements are also supporting the development of a numerical model of the process. In this workthe smoothed particle method (SPH) is used to model the powder filling process. The numerical results are compared with the DSP measurements. The validated model is then used to study the process in more detail, e.g. to evaluate the density distribution after filling. The comparison of DPS measurements and simulations gives similar flow characteristics. Experimental measurements with DSP together with numerical simulation with the SP method are powerful tools to increase the knowledge of powder filling and to improve the process in the future is concluded.
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| 30. |
- Häggblad, Hans-åke, et al.
(författare)
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Modelling And Simulation The Cracking Of Green Metal Powder Body
- 2016
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Ingår i: Proceedings World PM2016 Congress. - : European Powder Metallurgy Association. - 9781899072484
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Konferensbidrag (refereegranskat)abstract
- During the ejection stage of the powder metallurgy (PM) pressing process the elastic behaviour is important. Especially, if the in the powder compact is unloaded in a non-beneficially manner crack formation can occur. Experiments show a non-linear and also stress dependent elastic behaviour of green bodies. Calibrated against experimental data, a fracture model controlling the stress versus crack-width relationship is used. The softening rate of the fracture model is obtained from the corresponding rate of the dissipated energy. The model is implemented with a smeared crack approach in a finite element code and tested in simulation of a diametral compression testing. Results from simulations correlates well with experimental results. The smeared crack method combined with a cohesive fracture model is an interesting tool for predicting fracture in powder compacts.
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