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| 2. |
- Zhou, Xin, et al.
(författare)
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3D-imaging of selective laser melting defects in a Co-Cr-Mo alloy by synchrotron radiation micro-CT
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 98, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure defects set the mechanical property limits for solid Co-Cr-Mo alloy prepared by selective laser melting (SLM). Previous studies were mainly based on 2D SEM images and thus not able to provide information of the 3D morphologies of the complex defects. In this paper, the remaining porosities in Co-Cr-Mo alloy parts prepared by selective laser melting were presented in relation to the laser processing parameters. In order to understand the defect forming mechanism, accurate 3D images of defects inside SLM fabricated Co-Cr-Mo samples were provided by synchrotron radiation micro-CT imaging of 300 pm thick slices cut from a 10 mm cube. With 3D reconstructed images distinctive morphologies of SLM defects spanning across the consolidated powder layers were generated. The faults can be classified as single layer or multi-layers defects. The accidental single layer defects form as gaps between adjacent laser melt tracks or melt track discontinuousness caused by inherent fluid instability under various disturbances. The first formed single layer defect generates often a multi-layer defect spanning for 2-3 subsequent powder layers. By stabilizing the melt pool flow and by reducing the surface roughness through adjusting processing parameters it appears possible to reduce the defect concentrations.
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| 3. |
- Zhou, Xin, et al.
(författare)
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Balling phenomena in selective laser melted tungsten
- 2015
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 222, s. 33-42
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) of pure tungsten was carried out and the relevant consolidation issues were investigated. It was observed that balling of melted droplets at the laser focal points and entrapped cavities hindered the preparation of fully dense parts. An analysis of the balling mechanism reveals that SLM of tungsten is a process where melt spreading and solidification compete with each other and the final result is determined by intrinsic tungsten properties and the set laser processing parameters. Melted tungsten droplets wetted its own solid substrate at a low speed driven by capillary force, but solidified simultaneous at a high speed driven by the existing steep temperature gradient. Melted droplets solidified before spreading completely and kept their globular geometry instead of creating a flat layer. Tungsten bodies reaching a density of 14.8-15.2 g/cm(3) were prepared with an open irregular porosity and surface roughness. With a second laser scanning the balling W droplets were remelted at the building surface resulting in a much smoother appearance with less porosity and indicated a way to further improve relative density, near 16 g/cm(3) (82.9% theoretical density). Oxidation must be avoided, as any oxide contamination enriched preferably around the melt pool edge, changing the surface tension gradient and the thermocapillary convection thereby increasing balling.
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| 4. |
- Zhou, Xin, et al.
(författare)
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Textures formed in a CoCrMo alloy by selective laser melting
- 2015
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 631, s. 153-164
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Tidskriftsartikel (refereegranskat)abstract
- Unique crystal textures formed by selective laser melting of a CoCrMo alloy were characterized by electron backscattered diffraction. Preferred crystallographic orientations were found for individual grains in the solid alloy microstructure. Along the building or radial grain growth direction in the rapidly cooling melt pool the formed columnar grains were not purely < 001 > or < 111 >, as reported before, but a concurrence of < 001 > and < 011 >. Along the scanning direction, a (011) < 100 > texture was limited to the outmost surface whereas in the solid bulk the preferred orientation was a < 001 > fiber texture.
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| 5. |
- Chen, Yundai, et al.
(författare)
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Treatment Trends, Effectiveness, and Safety of Statins on Lipid Goal Attainment in Chinese Percutaneous Coronary Intervention Patients : a Multicenter, Retrospective Cohort Study
- 2017
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Ingår i: Clinical Therapeutics. - : ELSEVIER. - 0149-2918 .- 1879-114X. ; 39:9, s. 1827-1839
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Limited data exist on the use of statins in Chinese patients with coronary artery disease (CAD) treated with percutaneous coronary intervention (PCI). We therefore conducted this study to observe the usage trend and the effectiveness of statins on LDL-C goal attainment and other lipid parameters among PCI-treated patients.Methods: This multicenter, retrospective, observational, longitudinal cohort study was conducted in PCI-treated patients with CAD between July 1, 2011, and February 28, 2015. Primary study outcomes included statin treatment pattern after PCI and proportion of patients achieving target (LDL-C) levels 1 month after PCI and initiating statin therapy.Findings: Data were analyzed for 2708 patients (mean age, 59 [10] years; median body mass index, 25.6 [4.0] kg/m(2)). From baseline to the end of 1 month, atorvastatin and rosuvastatin were the most prescribed statins; 20 mg and 10 mg were the most prescribed doses and therefore chosen for efficacy comparisons. In patients without dose changes, LDL-C reduction with rosuvastatin 10 mg was significantly greater compared with atorvastatin 20 mg (-0.67 mmol/L [from 2.44 mmol/L to 1.77 mmol/L] vs 0.54 mmol/L [from 2.40 mmol/L to 1.86 mmol/L]; P = 0.008). However, there was no difference in HDL-C, triglyceride, or total cholesterol values between groups. Age and LDL-C levels at baseline were significantly associated with target LDL-C achievement.
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| 6. |
- Gifford, Katherine A, et al.
(författare)
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The 12-Word Philadelphia Verbal Learning Test Performances in Older Adults: Brain MRI and Cerebrospinal Fluid Correlates and Regression-Based Normative Data.
- 2018
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Ingår i: Dementia and geriatric cognitive disorders extra. - : S. Karger AG. - 1664-5464. ; 8:3, s. 476-491
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluated neuroimaging and biological correlates, psychometric properties, and regression-based normative data of the 12-word Philadelphia Verbal Learning Test (PVLT), a list-learning test.Vanderbilt Memory and Aging Project participants free of clinical dementia and stroke (n = 230, aged 73 ± 7 years) completed a neuropsychological protocol and brain MRI. A subset (n = 111) underwent lumbar puncture for analysis of Alzheimer's disease (AD) and axonal integrity cerebrospinal fluid (CSF) biomarkers. Regression models related PVLT indices to MRI and CSF biomarkers adjusting for age, sex, race/ethnicity, education, APOE-ε4 carrier status, cognitive status, and intracranial volume (MRI models). Secondary analyses were restricted to participants with normal cognition (NC; n = 127), from which regression-based normative data were generated.Lower PVLT performances were associated with smaller medial temporal lobe volumes (p < 0.05) and higher CSF tau concentrations (p < 0.04). Among NC, PVLT indices were associated with white matter hyperintensities on MRI and an axonal injury biomarker (CSF neurofilament light; p < 0.03).The PVLT appears sensitive to markers of neurodegeneration, including temporal regions affected by AD. Conversely, in cognitively normal older adults, PVLT performance seems to relate to white matter disease and axonal injury, perhaps reflecting non-AD pathways to cognitive change. Enhanced normative data enrich the clinical utility of this tool.
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| 7. |
- Osborn, Katie E, et al.
(författare)
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Cerebrospinal fluid and plasma neurofilament light relate to abnormal cognition.
- 2019
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Ingår i: Alzheimer's & dementia. - : Wiley. - 2352-8729. ; 11:C, s. 700-709
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Tidskriftsartikel (refereegranskat)abstract
- Neuroaxonal damage may contribute to cognitive changes preceding clinical dementia. Accessible biomarkers are critical for detecting such damage.Plasma and cerebrospinal fluid (CSF) neurofilament light (NFL) were related to neuropsychological performance among Vanderbilt Memory & Aging Project participants (plasma n=333, 73±7years; CSF n=149, 72±6years) ranging from normal cognition (NC) to mild cognitive impairment (MCI). Models adjusted for age, sex, race/ethnicity, education, apolipoprotein E ε4 carriership,and Framingham Stroke Risk Profile.Plasma NFL was related to all domains (P values ≤ .008) except processing speed (P values ≥ .09). CSF NFL was related to memory and language (P values ≤ .04). Interactions with cognitive diagnosis revealed widespread plasma associations, particularly in MCI participants, which were further supported in head-to-head comparison models.Plasma and CSF NFL (reflecting neuroaxonal injury) relate to cognition among non-demented older adults albeit with small to medium effects. Plasma NFL shows particular promise as an accessible biomarker with relevance to cognition in MCI.
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| 8. |
- Zhao, Dandan, et al.
(författare)
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Investigation of ion irradiation hardening behaviors of tempered and long-term thermal aged T92 steel
- 2018
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 511, s. 191-199
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Tidskriftsartikel (refereegranskat)abstract
- 9Cr ferritic/martensitic steels are promising materials for in-core components in advanced Gen-IV reactors. In these applications, their long-term microstructural stability under thermal exposure and resistance to neutron irradiation are essential. Tempered (unaged) and long-term thermal aged T92 samples were used to evaluate the effects of thermal aging and ion irradiation on the microstructure and micromechanical properties of the steel. Both the tempered and aged samples were irradiated with 3 MeV Fe11+ions to 0.25, 0.50, 1.00 and 5.00 dpa at room temperature. Using the nanoindentation technique, the irradiation hardening behaviors of T92 steel were investigated. The irradiation hardening effect was observed in both the tempered and aged T92 samples. To eliminate the soft substrate effect, the critical indentation depth was determined using the ratio of the average hardness of irradiated and unirradiated samples at the same depth. Under the same irradiation conditions, the macroscopic hardness values of the aged T92 samples after irradiation were lower than those of the tempered samples. The irradiation hardening effect was more significant in the aged T92 due to the decreased dislocation density and the coarsened martensitic lath after long-term thermal aging.
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| 9. |
- Zhao, Dandan, et al.
(författare)
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Proton irradiation induced defects in T92 steels: An investigation by TEM and positron annihilation spectroscopy
- 2019
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 442, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate proton irradiation damage on ferritic/martensitic T92 steels, both the unaged and aged (650 °C for 15,000 h) T92 steels were irradiated with 250 keV protons to 0.01, 0.05 and 0.20 dpa at room temperature due to the lower dose rate of protons compared with heavy-ions. The microstructural evolution induced by thermal aging and proton irradiation was studied by transmission electron microscopy and positron annihilation spectroscopy, and the corresponding micromechanical property changes were investigated by nano-indentation. After 0.20 dpa proton irradiation, the dominant irradiation-induced dislocation loops were a0100 type loops for both the unaged and aged samples. The dislocation-type defects in the aged T92 sample were larger in size and higher in number density, compared with those in the unaged samples. Less vacancy-type defects induced by protons were detected in the aged than the unaged T92 samples under the same irradiation conditions. The higher number density of dislocation-type defects led to more severe irradiation hardening in the aged T92 samples.
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