| 1. |
- Lindgren, Lars-Erik, et al.
(author)
-
Thermal stresses and computational welding mechanics
- 2019
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In: Journal of thermal stresses. - : Taylor & Francis. - 0149-5739 .- 1521-074X. ; 42:1, s. 107-121
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Journal article (peer-reviewed)abstract
- Computational welding mechanics (CWM) have a strong connection to thermal stresses, as they are one of the main issues causing problems in welding. The other issue is the related welding deformations together with existing microstructure. The paper summarizes the important models related to prediction of thermal stresses and the evolution of CWM models in order to manage the large amount of ‘welds’ in additive manufacturing.
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| 2. |
- Lindwall, Johan, et al.
(author)
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Efficiency and Accuracy in Thermal Simulation of Powder Bed Fusion of Bulk Metallic Glass
- 2018
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In: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 70:8, s. 1598-1603
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Journal article (peer-reviewed)abstract
- Additive manufacturing by powder bed fusion processes can be utilized to create bulk metallic glass as the process yields considerably high cooling rates. However, there is a risk that reheated material set in layers may become devitrified, i.e., crystallize. Therefore, it is advantageous to simulate the process to fully comprehend it and design it to avoid the aforementioned risk. However, a detailed simulation is computationally demanding. It is necessary to increase the computational speed while maintaining accuracy of the computed temperature field in critical regions. The current study evaluates a few approaches based on temporal reduction to achieve this. It is found that the evaluated approaches save a lot of time and accurately predict the temperature history.
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| 3. |
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| 4. |
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| 5. |
- Almqvist, Helena, et al.
(author)
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CETSA screening identifies known and novel thymidylate synthase inhibitors and slow intracellular activation of 5-fluorouracil
- 2016
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Journal article (peer-reviewed)abstract
- Target engagement is a critical factor for therapeutic efficacy. Assessment of compound binding to native target proteins in live cells is therefore highly desirable in all stages of drug discovery. We report here the first compound library screen based on biophysical measurements of intracellular target binding, exemplified by human thymidylate synthase (TS). The screen selected accurately for all the tested known drugs acting on TS. We also identified TS inhibitors with novel chemistry and marketed drugs that were not previously known to target TS, including the DNA methyltransferase inhibitor decitabine. By following the cellular uptake and enzymatic conversion of known drugs we correlated the appearance of active metabolites over time with intracellular target engagement. These data distinguished a much slower activation of 5-fluorouracil when compared with nucleoside-based drugs. The approach establishes efficient means to associate drug uptake and activation with target binding during drug discovery.
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| 6. |
- Babu, Bijish, Tec. Lic. 1979-, et al.
(author)
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Simulation of Ti-6Al-4V Additive Manufacturing Using Coupled Physically Based Flow Stress and Metallurgical Model
- 2019
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In: Materials. - : MDPI. - 1996-1944. ; 12:23
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Journal article (peer-reviewed)abstract
- Simulating the additive manufacturing process of Ti-6Al-4V is very complex due to the microstructural changes and allotropic transformation occurring during its thermomechanical processing. The α -phase with a hexagonal close pack structure is present in three different forms—Widmanstatten, grain boundary and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases was used here. Furthermore, a physically based flow-stress model coupled with the metallurgical model was applied in the simulation of an additive manufacturing case using the directed energy-deposition method. The result from the metallurgical model explicitly affects the mechanical properties in the flow-stress model. Validation of the thermal and mechanical model was performed by comparing the simulation results with measurements available in the literature, which showed good agreement
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| 7. |
- Charles Murgau, Corinne, et al.
(author)
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Temperature and Microstructure Evolution in Gas Tungsten Arc Welding Wire Feed Additive Manufacturing of Ti-6Al-4V
- 2019
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In: Materials. - : MDPI. - 1996-1944. ; 12:21
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Journal article (peer-reviewed)abstract
- In the present study, the gas tungsten arc welding wire feed additive manufacturing process is simulated and its final microstructure predicted by microstructural modelling, which is validated by microstructural characterization. The Finite Element Method is used to solve the temperature field and microstructural evolution during a gas tungsten arc welding wire feed additive manufacturing process. The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a density-based approach and coupled to a model that predicts the thickness of the α lath morphology. The work presented herein includes the first coupling of the process simulation and microstructural modelling, which have been studied separately in previous work by the authors. In addition, the results from simulations are presented and validated with qualitative and quantitative microstructural analyses. The coupling of the process simulation and microstructural modeling indicate promising results, since the microstructural analysis shows good agreement with the predicted alpha lath size.
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| 8. |
- Fisk, Martin, et al.
(author)
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Simulation of microstructural evolution during repair welding of an IN718 plate
- 2016
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In: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 120, s. 92-101
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Journal article (peer-reviewed)abstract
- A precipitate evolution model based on classical nucleation, growth and coarsening theory is adapted and solved using the multi-class approach for the superalloy IN718. The model accounts for dissolution of precipitates and is implemented in a finite element program. The model is used to simulate precipitate evolution in the fused zone and the adjacent heat affected zone for a welding simulation. The calculated size distribution of precipitates is used to predict Vickers hardness. The simulation model is compared with nanoindentation experiments. The agreement between simulated and measured hardness is good. (C) 2016 Elsevier B.V. All rights reserved.
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| 9. |
- Herold, Nikolas, et al.
(author)
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Targeting SAMHD1 with the Vpx protein to improve cytarabine therapy for hematological malignancies
- 2017
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In: Nature Medicine. - : Springer Science and Business Media LLC. - 1078-8956 .- 1546-170X. ; 23:2, s. 256-263
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Journal article (peer-reviewed)abstract
- The cytostatic deoxycytidine analog cytarabine (ara-C) is the most active agent available against acute myelogenous leukemia (AML). Together with anthracyclines, ara-C forms the backbone of AML treatment for children and adults'. In AML, both the cytotoxicity of ara-C in vitro and the clinical response to ara-C therapy are correlated with the ability of AML blasts to accumulate the active metabolite ara-C triphosphate (ara-CTP)(2-5), which causes DNA damage through perturbation of DNA synthesis(6). Differences in expression levels of known transporters or metabolic enzymes relevant to ara-C only partially account for patient-specific differential ara-CTP accumulation in AML blasts and response to ara-C treatment(7-9). Here we demonstrate that the deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAM domain and HD domain 1 (SAMHD1) promotes the detoxification of intracellular ara-CTP pools. Recombinant SAMHD1 exhibited ara-CTPase activity in vitro, and cells in which SAMHD1 expression was transiently reduced by treatment with the simian immunodeficiency virus (SIV) protein Vpx were dramatically more sensitive to ara-C-induced cytotoxicity. CRISPR-Cas9-mediated disruption of the gene encoding SAMHD1 sensitized cells to ara-C, and this sensitivity could be abrogated by ectopic expression of wild-type (WT), but not dNTPase-deficient, SAMHD1. Mouse models of AML lacking SAMHD1 were hypersensitive to ara-C, and treatment ex vivo with Vpx sensitized primary patient derived AML blasts to ara-C. Finally, we identified SAMHD1 as a risk factor in cohorts of both pediatric and adult patients with de novo AML who received ara-C treatment. Thus, SAMHD1 expression levels dictate patient sensitivity to ara-C, providing proof-of-concept that the targeting of SAMHD1 by Vpx could be an attractive therapeutic strategy for potentiating ara-C efficacy in hematological malignancies.
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| 10. |
- Karlsson, Dennis, et al.
(author)
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Binder jetting of the AlCoCrFeNi alloy
- 2019
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In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
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Journal article (peer-reviewed)abstract
- High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
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| 11. |
- Karlsson Tiselius, Andreas, 1977-, et al.
(author)
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Bryophyte community assembly on young land uplift islands : dispersal and habitat filtering assessed using species traits
- 2019
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In: Journal of Biogeography. - : John Wiley & Sons. - 0305-0270 .- 1365-2699. ; 46:10, s. 2188-2202
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Journal article (peer-reviewed)abstract
- Aim: To assess habitat filtering and dispersal limitation in spore plant community assembly using bryophytes on recently emerged land uplift islands as study system. Location Gulf of Bothnia, northern Europe. Taxa Bryophytes, including the spore plant phyla Bryophyta (mosses) and Marchantiophyta (liverworts).Methods: The species compositions of 20 coastal land uplift islands differing in age, area, connectivity and habitat composition were recorded in the field. In addition, we compiled a list of the regional species pool (446 species) and gathered data on species traits related to habitat affiliations (substrate, light, moisture, and pH) and dispersal capacity (regional abundance, spore size, sporophyte frequency, sexual system, vegetative propagules). For the 420 species with available trait data, we used multivariate generalized linear models to compare trait effects on species occurrence probabilities on the islands.Results: Occurrence probabilities depended strongly on habitat affiliations. In addition, occurrence probabilities were lower for predominantly asexual species than for sexual species and for regionally rare than for regionally abundant species. Having specialized asexual propagules increased occurrence probabilities, but compensated only partly for the reductions in asexual species. No effect of the size of sexually produced spores was detected. Comparison of trait effects across island size and connectivity gradients revealed (a) reduced habitat filtering on larger islands and (b) decreasing negative effects of being predominantly asexual with increasing island connectivity.Conclusions: Both habitat filtering and dispersal capacities affect the community assembly of spore plants on land uplift islands. Asexual mosses and liverworts show landscape scale (<= 10 km) dispersal limitation. The weak or absent relationships between island connectivity and the effects of dispersal traits suggest that colonization is regulated mainly by habitat availability and the abundance of each species in a "regional spore rain" from which colonists are recruited.
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| 12. |
- Lindgren, Lars-Erik, et al.
(author)
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Additive manufacturing and high performance applications
- 2018
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In: Proceedings Of The 3rd International Conference On Progress In Additive Manufacturing (PRO-AM 2018). - : Pro-AM. ; , s. 214-219
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Conference paper (peer-reviewed)abstract
- The requirement on life and robustness for aero-engine components poses obstacles to additive manufacturing. It is expected that increasing knowledge about the process and thereby its development together with adaption of existing alloys may improve this state. Simulations can contribute to understanding as well as be used in the design of process and components in order to reduce residual deformations and stresses as well as defects. Models for the latter are still not well established. The paper describes various existing approaches and also on-going developments at Luleå University of Technology that enable better descriptions in the near weld region for crack initiation.
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| 13. |
- Lindgren, Lars-Erik, et al.
(author)
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Approaches in computational welding mechanics applied to additive manufacturing : Review and outlook
- 2018
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In: Comptes rendus. Mecanique. - : Elsevier. - 1631-0721 .- 1873-7234. ; 346:11, s. 1033-1042
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Journal article (peer-reviewed)abstract
- The development of computational welding mechanics (CWM) began more than four decades ago. The approach focuses on the region outside the molten pool and is used to simulate the thermo-metallurgical-mechanical behaviour of welded components. It was applied to additive manufacturing (AM) processes when they were known as weld repair and metal deposition. The interest in the CWM approach applied to AM has increased considerably, and there are new challenges in this context regarding welding. The current state and need for developments from the perspective of the authors are summarised in this study.
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| 14. |
- Lindgren, Lars-Erik, et al.
(author)
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Modelling additive manufacturing of superalloys
- 2019
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In: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 35, s. 252-258
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Journal article (peer-reviewed)abstract
- There exist several variants of Additive Manufacturing (AM) applicable for metals and alloys. The two main groups are Directed Energy Deposition (DED) and Powder Bed Fusion (PBF). AM has advantages and disadvantages when compared to more traditional manufacturing methods. The best candidate products are those with complex shape and small series and particularly individualized product. Repair welding is often individualized as defects may occur at various instances in a component. This method was used before it became categorized as AM and in most cases, it is a DED process. PBF processes are more useful for smaller items and can give a finer surface. Both DED and PBF products require subsequent surface finishing for high performance components and sometimes there is also a need for post heat treatment. Modelling of AM as well as eventual post-processes can be of use in order to improve product quality, reducing costs and material waste. The paper describes the use of the finite element method to simulate these processes with focus on superalloys.
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| 15. |
- Lindgren, Lars-Erik, et al.
(author)
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Simulation of additive manufacturing using coupled constitutive and microstructure models
- 2016
-
In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 12:Part B, s. 144-158
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Journal article (peer-reviewed)abstract
- The paper describes the application of modeling approaches used in Computational Welding Mechanics (CWM) applicable for simulating Additive Manufacturing (AM). It focuses on the approximation of the behavior in the process zone and the behavior of the solid material, particularly in the context of changing microstructure. Two examples are shown, one for the precipitation hardening Alloy 718 and one for Ti-6Al-4V. The latter alloy is subject to phase changes due to the thermal cycling
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| 16. |
- Lindwall, Johan, et al.
(author)
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Boundary conditions for simulation of powder bed fusion for metallic glass formation: Measurements and calibrations
- 2019
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In: II International Conference on Simulation for Additive Manufacturing. ; , s. 51-59
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Conference paper (other academic/artistic)abstract
- A finite element model for prediction of the temperature field in the powder bed fusion process is presented and compared to measurements. Accurate temperature predictions at the base plate are essential to accurately predict the formation of crystals in a metallic glass forming material. The temperature measurements were performed by equipping the base plate with thermocouples during manufacturing of a cylinder with the glass forming alloy AMZ4. Boundary conditions for heat losses through the base plate/machine contact interfaces was calibrated to fit the measurements. Additional heat losses was used to account for radiation at the top surface and conduction through the powder bed. An interface boundary condition based on conservation of heat flux was examined to match the heat flow to the machine structure and the temperature predictions was satisfying. Still, temperature predictions with a constant heat transfer coefficient matched the measurements within 1.5oC during the entire building process of about 9 hours.
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| 17. |
- Lindwall, Johan
(author)
-
Modelling of Bulk Metallic Glass formation in Powder Bed Fusion
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- This thesis discusses a model for simulation of the Powder Bed Fusion (PBF) process of metallic powder with the capability to become amorphous. The temperature field in the PBF process is predicted by a three-dimensional thermal finite element model in three dimensions using a layer-by-layer approach, meaning that the scanning strategy of the moving laser spot is consolidated into a single heat source acting on the entire layer momentarily. This temporal reduction enables simulations of large domains and many layers while it becomes less computational demanding compared to a detailed transient model that incorporates a scanning sequence. Predictions of the amorphous and crys- talline phase fractions are performed with a phase model coupled to the temperature field simulation. The phase model is based on differential scanning calorimetry measure- ments and optimized to fit continuous heating transformation into a crystalline state of an amorphous sample. The simulations are performed on the commercial available glass forming alloy AMZ4.Bulk Metallic Glass (BMG) have an amorphous structure and possesses desirable me- chanical, magnetic and corrosion properties such as high yield stress, low magnetic losses and high corrosion resistance. Glass forming alloy has the potential to become amorphous provided that the solidification rate is rapid enough to avoid crystallization. However, traditional manufacturing techniques, such as casting, limits the cooling rates and size of components due to limited heat conduction in the bulk. With Additive Manufacturing (AM) on the other hand, it is possible to produce BMG’s as the melt pool is very small and solidification can be achieved very rapid to bypass crystallization. Yet, crystals may form by devitrification (crystal formation upon heating of the amorphous phase) because of thermal cycling in previous layers. Simulation of the process will aid the understanding of glass formation during AM and the development of process parameters to control the level of devitrification.
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| 18. |
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| 19. |
- Lindwall, Johan, et al.
(author)
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Thermal simulation and phase modeling of bulk metallic glass in the powder bed fusion process
- 2019
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In: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 345-352
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Journal article (peer-reviewed)abstract
- One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.
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| 20. |
- Llona-Minguez, Sabin, et al.
(author)
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Discovery of the First Potent and Selective Inhibitors of Human dCTP Pyrophosphatase 1
- 2016
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In: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 59:3, s. 1140-1148
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Journal article (peer-reviewed)abstract
- The dCTPase pyrophosphatase 1 (dCTPase) regulates the intracellular nucleotide pool through hydrolytic degradation of canonical and noncanonical nucleotide triphosphates (dNTPs). dCTPase is highly expressed in multiple carcinomas and is associated with cancer cell sternness. Here we report on the development of the first potent and selective dCTPase inhibitors that enhance the cytotoxic effect of cytidine analogues in leukemia cells. Boronate 30 displays a promising in vitro ADME profile, including plasma and mouse microsomal half-lives, aqueous solubility, cell permeability and CYP inhibition, deeming it a suitable compound for in vivo studies.
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| 21. |
- Llona-Minguez, Sabin, et al.
(author)
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Identification of Triazolothiadiazoles as Potent Inhibitors of the dCTP Pyrophosphatase 1
- 2017
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In: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 60:5, s. 2148-2154
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Journal article (peer-reviewed)abstract
- The dCTP pyrophosphatase 1 (dCTPase) is involved in the regulation of the cellular dNTP pool and has been linked to cancer progression. Here we report on the discovery of a series of 3,6-disubstituted triazolothiadiazoles as potent dCTPase inhibitors. Compounds 16 and 18 display good correlation between enzymatic inhibition and target engagement, together with efficacy in a cellular synergy model, deeming them as a promising starting point for hit -to-lead development.
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| 22. |
- Lundbäck, Andreas, et al.
(author)
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Finite Element Simulation to Support Sustainable Production by Additive Manufacturing
- 2016
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In: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 7, s. 127-130
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Journal article (peer-reviewed)abstract
- Additive manufacturing (AM) has been identified as a disruptive manufacturing process having the potential to provide a number of sustainability advantages. Functional products with high added value and a high degree of customization can be produced. AM is particularly suited for industries in which mass customization, light weighting of parts and shortening of the supply chain are valuable. Its applications can typically be found in fields such as the medical, dental, and aerospace industries. One of the advantages with AM is that little or no scrap is generated during the process. The additive nature of the process is less wasteful than traditional subtractive methods of production. The capability to optimize the geometry to create lightweight components can reduce the material use in manufacturing. One of the challenges is for designers to start using the power of AM. To support the designers and manufacturing, there is a need for computational models to predicting the final shape, deformations and residual stresses. This paper summarizes the advantages of AM in a sustainability perspective. Some examples of application of simulation models for AM are also given.
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| 23. |
- Lundbäck, Andreas, et al.
(author)
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Modeling and Experimental Measurement with Synchrotron Radiation of Residual Stresses in Laser Metal Deposited Ti-6Al-4V
- 2016
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In: Proceedings of the 13th World Conference on Titanium. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781119293668 - 9781119296126 ; , s. 1279-1282
-
Conference paper (peer-reviewed)abstract
- There are many challenges in producing aerospace components by additive manufacturing (AM). One of them is to keep the residual stresses and deformations to a minimum. Another one is to achieve the desired material properties in the final component. A computer model can be of great assistance when trying to reduce the negative effects of the manufacturing process. In this work a finite element model is used to predict the thermo-mechanical response during the AM-process. This work features a physically based plasticity model coupled with a microstructure evolution model for the titanium alloy Ti -6Al-4V. Residual stresses in AM components were measured non-destructively using high-energy synchrotron X-ray diffraction on beam line ID15A at the ESRF, Grenoble. The results are compared with FE model predictions of residual stresses. During the process, temperatures and deformations was continuously measured. The measured and computed thermal history agrees well. The result with respect to the deformations agrees well qualitatively. Meaning that the change in deformation in each sequence is well predicted but there is a systematic error that is summing so that the quantitative agreement is lost.
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| 24. |
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| 25. |
- Lundbäck, Andreas, et al.
(author)
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Modelling and Simulation of Metal Deposition on a Ti-6al-4v Plate
- 2015
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Conference paper (other academic/artistic)abstract
- There are many challenges in producing aerospace components by metal deposition (MD). One of them is to keep the residual stresses and deformations to a minimum. Anotherone is to achieve the desired material properties in the final component. A computer model can be of great assistance when trying to reduce the negative effects of the manufacturing process. In this work a finite element model is used to predict the thermo-mechanical response during the MD-process. This work features a pysically based plasticity model coupled with a microstructure evolution model for the titanium alloy Ti-6Al-4V. A thermally driven microstructure model is used to derive the evolution of the non-equilibrium compositions of α-phases and β-phase. Addition of material is done by activation of elements. The method is taking large deformations into consideration and adjusts the shape and position of the activated elements. This is particularilly important when adding material onto thin and flexible structures. The FE-model can be used to evaluate the effect of different welding sequenses. Validation of the model is performed by comparing measured deformations, strains, residual stresses and temperatures with the computed result. The deformations, strains and temepratures are measured during the process. The deformations are measured with a LVDT-gauge at one location. The strains are measured with a strain gauge at the same location as the deformations. The temperature is measured at five locations, close to the weld and with an increasing distance of one millimeter between each thermo couple. The residual stresses in MD component were measured non-destructively using high-energy synchrotron X-ray diffraction on beam line ID15A at the ESRF, Grenoble.
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| 26. |
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| 27. |
- Wärmefjord, Kristina, 1976, et al.
(author)
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Welding of non-nominal geometries : physical tests
- 2016
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In: Procedia CIRP. - : Elsevier BV. - 2212-8271 .- 2212-8271. ; 43, s. 136-141
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Journal article (peer-reviewed)abstract
- The geometrical quality of a welded assembly is to some extent depending part positions before welding. Here, a design of experiment is set up in order to investigate this relation using physical tests in a controlled environment. Based on the experimental results it can be concluded that the influence of part position before welding is significant for geometrical deviation after welding. Furthermore, a working procedure for a completely virtual geometry assurance process for welded assemblies is outlined. In this process, part variations, assembly fixture variations and welding induced variations are important inputs when predicting the capability of the final assembly.
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