The evolution of microstructures with thermal cycles was studied for wire-arc additive manufacturing of duplex stainless steel blocks. To produce samples, arc energy of 0.5 kJ/mm and interlayer ...temperature of 150 °C were used as low heat input–low interlayer temperature (LHLT) and arc energy of 0.8 kJ/mm and interlayer temperature of 250 °C as high heat input–high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers—4 beads in each layer—for LHLT and 15 layers—3 beads in each layer—for HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 °C, compared with HHHT. A higher austenite fraction (+ 8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 °C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-arc additively manufactured duplex stainless steel samples (35–60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800–1200 °C).
Since the advent of 3D printing in the mid-1980s, additive manufacturing has grown steadily and found numerous applications across all types of industries. More recently, the industry has seen a spur ...of growth as the terms of the original patents expired and new companies entered the market. While there exist several different methods of additive manufacturing, polymer-based material extrusion 3D printing (also known as fused filament fabrication) has become one of the most widely used ones due to its lower cost, ease of use, and versatility. While development has greatly expanded the material availability and improved the quality of prints, material extrusion 3D printers have often faced a challenge in physical scaling. There are inherent design hurdles to the extrusion process when the print starts to grow larger. This paper aims to study the market landscape of extrusion-based 3D printing technology for polymer-based material as well as challenges faced in upscaling this technology for industrial applications. A prototype large-scale material extrusion 3D printer has been designed, constructed, and then tested to gain experimental data on large-scale 3D printing using thermoplastic polymers as a printing material. Results of testing and experimentation verified certain key design elements and how they can improve large-scale 3D printing. Testing also revealed how large diameter nozzles for the hot end introduce challenges not seen in small-scale 3D printers. This paper also seeks to consolidate available information pertaining to large-scale 3D printing into one comprehensive document.
There still is little treatment available for amyloid diseases, despite their significant impact on individuals and the social and economic implications for society. One reason for this is that the ...physical nature of amyloid formation is not understood sufficiently well. Therefore, fundamental research at the molecular level remains necessary to support the development of therapeutics. A few structures of short peptides from amyloid-forming proteins have been determined. These can in principle be used as scaffolds for designing aggregation inhibitors. Attempts to this end have often used the tools of computational chemistry, in particular molecular simulation. However, few simulation studies of these peptides in the crystal state have been presented so far. Hence, to validate the capability of common force fields (AMBER19SB, CHARMM36m, and OPLS-AA/M) to yield insight into the dynamics and structural stability of amyloid peptide aggregates, we have performed molecular dynamics simulations of twelve different peptide crystals at two different temperatures. From the simulations, we evaluate the hydrogen bonding patterns, the isotropic B-factors, the change in energy, the Ramachandran plots, and the unit cell parameters and compare the results with the crystal structures. Most crystals are stable in the simulations but for all force fields there is at least one that deviates from the experimental crystal, suggesting more work is needed on these models.
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•Plate showed more Cr and Fe phase separation, increase in ferrite microhardness, and drop in toughness compared to the welds.•Plate-surface with smaller austenite spacing and higher ...level misorientation and mean angular deviation had more phase separation than plate-center.•Higher Ni content super duplex stainless steel welds caused more phase separation than the hyper duplex stainless steel weld.•Processing history was more impactful on kinetics of 475˚C-embrittlement than slight variations in composition.
Fe and Cr phase separation in ferrite, causing 475 °C-embrittlement, was studied after very short aging times in super duplex stainless steel (SDSS) and hyper duplex stainless steel (HDSS) plates and welds. Atom probe tomography showed that hot-rolled SDSS, experiencing significant metal working, had faster kinetics of phase separations compared to the SDSS and HDSS welds after 5 min aging at 475 °C. The surface of the 33-mm SDSS plate had faster Fe and Cr phase separation and larger toughness drop. A higher density of dislocations next to the austenite phase boundary in ferrite, detected by electron channeling contrast, can promote the phase separation at the surface of the plate with lower austenite spacing. The toughness dropped in HDSS welds after aging, but SDSS welds maintained their toughness. An inverse simulation method considering an initial sinusoidal nanometric Cr and Fe fluctuation showed that Ni increases the interdiffusion of Cr in the system, resulting a higher degree of phase separation in SDSS welds than the HDSS weld. Within the composition range of the studied SDSS and HDSS materials, the processing influences the Fe and Cr phase separation more than the variation in composition during short aging or typical fabrication times.
This article presents a study on the capability of the time domain OMA method, NExT-ERA, to identify closely spaced structural dynamic modes. A survey in the literature reveals that few experimental ...studies have been conducted on the effectiveness of the NExT-ERA methodology in case of closely spaced modes specifically. In this paper we present the formulation for NExT-ERA. This formulation is then implemented in an algorithm and a code, developed in house to identify the modal parameters of different systems using their generated time history data. Some numerical models are firstly investigated to validate the code. Two different case studies involving a plate with closely spaced modes and a pulley ring with greater extent of closeness in repeated modes are presented. Both structures are excited by random impulses under the laboratory condition. The resulting time response acceleration data are then used as input in the developed code to extract modal parameters of the structures. The accuracy of the results is checked against those obtained from experimental tests.
The present study aims at investigating bead geometry and the evolution of microstructure with thermal cycles in multipass shielded metal arc welding of a V-groove 13-mm type-2507 super-duplex ...stainless steel (SDSS) plate. The weld consisted of 4 beads produced with arc energies of 0.81–1.06 kJ/mm. The upper beads showed lower base metal (BM) dilution than the first bead. Thermal cycles were recorded with thermocouples, indicating that the cooling rate decreased in the as-deposited weld zone when adding a new bead. Ferrite fraction in the as-welded condition was lower for the upper beads. The austenite grain morphology in reheated passes varied depending on the local peak temperatures and the number of reheating passes. Sigma phase precipitated in a location reheated by the third and fourth passes that was subjected to a critical peak temperature for sigma precipitation. Ferrite content, measured using image analysis and Fisher FERITSCOPE technique, showed that the ferrite fraction moved toward 50/50% in the weld metal with an increasing number of reheating cycles. Finally, a schematic map showing an overview of the microstructure in the multipass SDSS weld was introduced.
Toxoplasma gondii (T. gondii) as an obligate intracellular protozoan with a worldwide distribution can infect virtually all warm-blooded animals and humans. This study aims to provide a summary of ...the available data on genotypes of T. gondii in human. Five databases including MEDLINE in PubMed, Scopus, Science Direct, Web of Science and Google Scholar were searched for the T. gondii genotyping in human during 1995-August 2017. Next, we screened all the articles based on the inclusion and exclusion criteria. Overall, 26 studies were eligible regarding genotyping T. gondii in human samples. In clonal genotyping, 167 out of 286 cases (58%) were infected with type II. Genetic characterisation of T. gondii isolates displayed that type II was the most predominant genotype in human with the prevalence of 64.3%, 62.1% and 41.7% in patients with AIDS, congenital and ocular toxoplasmosis, respectively. In ToxoDB genotyping, most individuals were infected with genotypes #9 and #65 (21.2%). Based on these results, genotype profile of T. gondii isolates is different throughout the world. The strains in Asian and African countries are characterised by low genetic diversity, while in North and South America a wide diversity of this parasite is found. In countries without any data (e.g. Australia, Western and Southern Africa and Western Asia), identification of T. gondii genotypes might discover higher genetic diversity.
Let
M
be a von Neumann algebra, and let
T
:
M
→
M
be a bounded linear map satisfying
T
(
P
2
)
=
T
(
P
)
P
+
Ψ
(
P
,
P
)
for each projection
P
of
M
, where
Ψ
:
M
×
M
→
M
is a bi-linear map. If
Ψ
is a ...bounded
l
-semi Hochschild 2-cocycle, then
T
is a left centralizer associated with
Ψ
. By applying this conclusion, we offer a characterization of left
σ
-centralizers, generalized derivations and generalized
σ
-derivations on von Neumann algebras. Moreover, it is proved that if
M
is a commutative von Neumann algebra and
σ
:
M
→
M
is an endomorphism, then every bi-
σ
-derivation
D
:
M
×
M
→
M
is identically zero.
Previous studies have shown the role of silicon (Si) in mitigating the adverse effect of drought stress in different crop species. However, data are lacking on a comparison of drought tolerant and ...drought sensitive crop cultivars in response to Si nutrition. Therefore, the aim of this study was to elucidate the mechanism (s) by which two contrasting tomato genotypes respond to Si nutrition under osmotic stress condition. Two tomato lines contrasting in their response to drought stress were hydroponically grown under polyethylene glycol (PEG, 6000) and two regimes of Si (0 and 1.5 mM). Metabolite profiling was performed in two lines. Growth and relevant physiological parameters, and expression levels of selected genes were also measured. Si application resulted in improved osmotic stress tolerance in both drought tolerant line LA0147 and drought sensitive line FERUM. In the drought tolerant line, Si enhanced uptake of sulfur (S) and ammonium (
) which led to a significantly higher production of amino acids arginine, methionine, serine, and glycine. While in the drought sensitive line, Si significantly increased production of amino acids proline and GABA which further lowered the level of GSSG to GSH ratio and thus balanced the redox homeostasis under osmotic stress. The higher significant production of amino acids arginine, methionine, GABA, and proline enhanced production of free polyamines putrescine and spermidine and improved osmotic stress tolerance. Therefore, we conclude that Si distinctively regulated osmotic stress tolerance in two contrasting tomato genotypes by differential accumulation of relevant amino acids which eventually led to enhanced polyamine metabolism.
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