| 1. |
- Danilovich, I. L., et al.
(författare)
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Co(NO3)(2) as an inverted umbrella-type chiral noncoplanar ferrimagnet
- 2020
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:9
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Tidskriftsartikel (refereegranskat)abstract
- The low-dimensional magnetic systems tend to reveal exotic spin-liquid ground states or form peculiar types of long-range order. Among systems of vivid interest are those characterized by the triangular motif in two dimensions. The realization of either ordered or disordered ground state in triangular, honeycomb, or kagome lattices is dictated by the competition of exchange interactions, also being sensitive to anisotropy and the spin value of magnetic ions. While the low-spin Heisenberg systems may arrive to a spin-liquid long-range entangled quantum state with emergent gauge structures, the high-spin Ising systems may establish the rigid noncollinear structures. Here, we present the case of chiral noncoplanar inverted umbrella-type ferrimagnet formed in cobalt nitrate Co(NO3)(2) below T-C = 3 K with the comparable spin and orbital contributions to the total magnetic moment.
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| 2. |
- Grubova, I. Y., et al.
(författare)
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Process window for electron beam melting of Ti–42Nb wt.%
- 2023
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 25, s. 4457-4478
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Tidskriftsartikel (refereegranskat)abstract
- Pre-alloyed β-phase Ti˗42Nb alloy was successfully produced for the first time by E-PBF. The study focuses on the determination of the processing parameter window by varying the beam current, beam speed, layer thickness, and line offset to achieve the defect-free manufacturing of new material with desired properties. Overall, 49 regimes were investigated. The Ti˗42Nb powder were characterized using the DSC/TG, XRD, and SEM/EDX analyses to evaluate its suitability for E-PBF manufacturing. The alloys with the best-built quality fall into the narrow zone between the line energies of 0.30 and 0.34 J/mm. The predicted optimal process parameters were I = 4 mA, v = 700–800 mm/s, h = 100 μm, U = 60 kV, and t = 100 μm. Detailed microstructural characterization was carried out to gain insights into the fundamental mechanisms that govern the behavior of the studied alloys. TEM identified the α'' martensitic phase nucleation occurred preferentially at the β grain boundaries. Un-melted ellipsoidal NbC (∼10 μm) particles were detected with no preferential segregation sites. EBSD revealed coarse microstructures and <001> fiber texture, as well as epitaxial grain growth of columnar grains of about 300 μm. The optimal regime demonstrated a texture composed of a high amount of low aspect ratio grains (50%), which yielded a microindentation hardness of 3.0 GPa and a low elastic modulus of 68 GPa. Hence, these results provide opportunities to design novel alloys to be of interest for biomedical applications. Moreover, this study extends the scope of AM by establishing the process parameter window that yields a material with favorable mechanical properties.
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| 3. |
- Surmeneva, M. A., et al.
(författare)
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The influence of chemical etching on porous structure and mechanical properties of the Ti6AL4V Functionally Graded Porous Scaffolds fabricated by EBM
- 2022
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 275
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Tidskriftsartikel (refereegranskat)abstract
- Functionally Graded Porous Scaffolds (FGPS) manufactured from Ti and Ti alloys such as Ti6Al4V is an attractive candidate for mimicking host bone tissue. Porous specimens manufactured by powder-bed fusion additive manufacturing (PBF-AM) methods always contain some amount of powder attached to the surfaces of the outer or the inner parts. Powder removal is an important issue for the porous structures with high relative density designed for biomedical applications. In some cases, traditional powder removal methods such as standard powder recovery systems (PRS) become ineffective. Chemical and electrochemical etching is one of the possible solutions for effective residual powder removal from PBF-AM structures. Traditional single-stage HF/HNO3 chemical etching protocols of the Ti6Al4V often leads to the overetching of the periphery of the porous samples leaving inner parts untouched. The aim of present research was to determine if fractionated chemical etching of porous Ti6Al4V Functionally Graded Porous Scaffolds (FGPS) with multiple immersions could facilitate trapped powder removal and reduction the surface roughness without critical degradation of the mechanical properties. Protocols with different number and time of immersions were studied. Mechanical properties and fracture modes of as manufactured and chemically etched Ti6Al4V FGPS were investigated. Results clearly illustrate that fractionating of the etching times have positive effect. It is possible to achieve more uniform etching of the thin structures at the periphery and inside porous structures, facilitate removal of the powder particles attached to the surfaces, and removal of the powder trapped inside the structures without serious degradation of the mechanical properties.
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| 4. |
- Chudinova, E., et al.
(författare)
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Functionalization of additive-manufactured Ti6Al4V scaffolds with poly(allylamine hydrochloride)/poly(styrene sulfonate) bilayer microcapsule system containing dexamethasone
- 2021
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 273
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Tidskriftsartikel (refereegranskat)abstract
- Porous titanium alloy Ti6Al4V scaffolds manufactured via electron beam melting (EBM®) reveal broad prospects for applications in bone tissue engineering. However, local inflammation and even implant failure may occur while placing an implant into the body. Thus, the application of drug carriers to the surface of a metallic implant can provide treatment at the inflammation site. In this study, we propose to use polyelectrolyte (PE) microcapsules formed by layer-by-layer (LbL) synthesis loaded with both porous calcium carbonate (CaCO3) microparticles and the anti-inflammatory drug dexamethasone (DEX) to functionalize implant surfaces and achieve controlled drug release. Scanning electron microscopy indicated that the CaCO3 microparticles coated with PE bilayers loaded with DEX had a spherical shape with a diameter of 2.3 ± 0.2 μm and that the entire scaffold surface was evenly coated with the microcapsules. UV spectroscopy showed that LbL synthesis allows the manufacturing of microcapsules with 40% DEX. According to high performance liquid chromatography (HPLC) analysis, 80% of the drug was released within 24 h from the capsules consisting of three bilayers of polystyrene sulfonate (PSS) and poly(allylamine)hydrochloride (PAH). The prepared scaffolds functionalized with CaCO3 microparticles loaded with DEX and coated with PE bilayers showed hydrophilic surface properties with a water contact angle below 5°. Mouse embryonic fibroblast cells were seeded on Ti6Al4V scaffolds with and without LbL surface modification. The surface modification with LbL PE microcapsules with CaCO3 core affected cell morphology in vitro. The results confirmed that DEX had no toxic effect and did not prevent cell adhesion and spreading, thus no cytotoxic effect was observed, which will be further studied in vivo.
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| 5. |
- Grubova, Irina Yu., et al.
(författare)
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Combined First-Principles and Experimental Study on the Microstructure and Mechanical Characteristics of the Multicomponent Additive-Manufactured Ti-35Nb-7Zr-5Ta Alloy
- 2023
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:30, s. 27519-27533
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Tidskriftsartikel (refereegranskat)abstract
- New & beta;-stabilizedTi-based alloys are highly promising forbone implants, thanks in part to their low elasticity. The natureof this elasticity, however, is as yet unknown. We here present combinedfirst-principles DFT calculations and experiments on the microstructure,structural stability, mechanical characteristics, and electronic structureto elucidate this origin. Our results suggest that the studied & beta;Ti-35Nb-7Zr-5Ta wt % (TNZT) alloy manufacturedby the electron-beam powder bed fusion (E-PBF) method has homogeneousmechanical properties (H = 2.01 & PLUSMN; 0.22 GPa and E = 69.48 & PLUSMN; 0.03 GPa) along the building direction,which is dictated by the crystallographic texture and microstructuremorphologies. The analysis of the structural and electronic properties,as the main factors dominating the chemical bonding mechanism, indicatesthat TNZT has a mixture of strong metallic and weak covalent bonding.Our calculations demonstrate that the softening in the Cauchy pressure(C & PRIME; = 98.00 GPa) and elastic constant C ̅ ( 44 ) = 23.84 GPa is the originof the low elasticity of TNZT. Moreover, the nature of this softeningphenomenon can be related to the weakness of the second and thirdneighbor bonds in comparison with the first neighbor bonds in theTNZT. Thus, the obtained results indicate that a carefully designedTNZT alloy can be an excellent candidate for the manufacturing oforthopedic internal fixation devices. In addition, the current findingscan be used as guidance not only for predicting the mechanical propertiesbut also the nature of elastic characteristics of the newly developedalloys with yet unknown properties.
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| 6. |
- Lett, Signe, et al.
(författare)
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Can bryophyte groups increase functional resolution in tundra ecosystems?
- 2022
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Ingår i: Arctic Science. - Ottawa : Canadian Science Publishing. - 2368-7460. ; 8:3, s. 609-637
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Tidskriftsartikel (refereegranskat)abstract
- The relative contribution of bryophytes to plant diversity, primary productivity, and ecosystem functioning increases towards colder climates. Bryophytes respond to environmental changes at the species level, but because bryophyte species are relatively difficult to identify, they are often lumped into one functional group. Consequently, bryophyte function remains poorly resolved. Here, we explore how higher resolution of bryophyte functional diversity can be encouraged and implemented in tundra ecological studies. We briefly review previous bryophyte functional classifications and the roles of bryophytes in tundra ecosystems and their susceptibility to environmental change. Based on shoot morphology and colony organization, we then propose twelve easily distinguishable bryophyte functional groups. To illustrate how bryophyte functional groups can help elucidate variation in bryophyte effects and responses, we compiled existing data on water holding capacity, a key bryophyte trait. Although plant functional groups can mask potentially high interspecific and intraspecific variability, we found better separation of bryophyte functional group means compared with previous grouping systems regarding water holding capacity. This suggests that our bryophyte functional groups truly represent variation in the functional roles of bryophytes in tundra ecosystems. Lastly, we provide recommendations to improve the monitoring of bryophyte community changes in tundra study sites.
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| 7. |
- Volkova, A., et al.
(författare)
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5th generation district heating and cooling (5GDHC) implementation potential in urban areas with existing district heating systems
- 2022
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Ingår i: Energy Reports. - : Elsevier BV. - 2352-4847. ; 8, s. 10037-10047
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Tidskriftsartikel (refereegranskat)abstract
- The 5th Generation District Heating and Cooling (5GDHC) network has great advantages in terms of integration of low-temperature resources, bi-directional operation, decentralised energy flows, and possible energy sharing. One way to develop the idea and concept of 5GDHC is to identify potential agents, including residential buildings, office buildings, shopping malls, data centres, electrical transformers, and so on, in 5GDHC in each target context. The prospects for 5GDHC have been assessed in light of the conditions in the Baltics. The multi-criteria analysis method was used to quantify the main identified barriers and drivers behind the implementation of 5GDHC systems. It should be noted that new urban areas in the Baltic states are being actively developed with low-energy buildings, so 5GDHS can be integrated to supply heat to these areas. The highest score in the multi-criteria assessment was achieved by Lithuania due to support availability and open heating market conditions. When all applied criteria are weighted equally, Estonia has the most favourable conditions for 5GDHC systems due to widespread use of heat pumps and greater excess heat potential. © 2022 The Author(s)
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