► Size effect of abrasive particles examined for WC-based coating and sintered WC. ► Influential parameters affecting the wear mechanisms have been examined and identified. ► Transition from plastic ...deformation to a more fracture related material removal observed. ► Parameters such as ‘severity of contact’ and ‘brittleness factor’ are defined to explain the behavior.
Downhole drilling operations expose tungsten carbide based sintered (WC–5.7Co–0.3Cr) and sprayed (WC–10Co–4Cr) hardmetals to abrasives of different sizes. Although the effect of abradant size on the abrasive wear of metals has been widely studied, the effect of particle size on the abrasive wear of sintered and sprayed tungsten carbide-based hardmetals has not been examined previously. The abrasion of hardmetal composite surfaces is complex due to the presence of hard and soft phases which respond differently during abrasive wear, where an increase in abrasive size leads to a change in the wear mechanism which significantly affects the overall wear rates. Three different abrasive sizes, 4.5μm, 17.5μm and 180μm, were used in a modified ASTM G65 rubber wheel abrasion test to examine the effects of abrasive size on wear in a sintered WC and a D-gun sprayed WC-based coating. Uniquely, influential parameters affecting the wear mechanisms have been examined and identified with the fundamental material properties of both abrasives and the multi-phase materials. As a unique way of mapping abrasion performance, a parameter previously developed for the micro-abrasion tester, ‘severity of contact’, has been reworked and plotted against a ‘brittleness factor’ parameter developed in this work. Plotting these parameters can explain the sharp rise in wear rates associated with the transition from ductile, plastic deformation dominated material removal to a more fracture-related material removal as the size of abrasives increases. This work has developed new insights into how hardmetal composites respond to change in abrasive size and provides a basis for controlling the abrasive particle size.
The Antarctic nematode Panagrolaimus sp. DAW1 is one of the only organisms known to survive extensive intracellular freezing throughout its tissues. Although the physiological mechanisms of this ...extreme adaptation are partly understood, the molecular mechanisms remain largely unknown. RNAi is a method that allows the examination of gene function in a direct, targeted manner, by knocking out specific mRNAs and revealing the effects on the phenotype. In this study we have explored the viability of RNAi in Panagrolaimus sp. DAW1. In the first trial, nematodes were fed E. coli expressing Panagrolaimus sp. DAW1 dsRNA of the embryonic lethal genes rps-2 and dhc, and the blister gene duox. Pd-rps-2(RNAi)-treated nematodes showed a significant decrease in larval hatching. However, qPCR showed no significant decrease in the amount of rps-2 mRNA in Pd-rps-2(RNAi)-treated animals. Several soaking protocols for dsRNA uptake were investigated using the fluorescent dye FITC. Desiccation-enhanced soaking showed the strongest uptake of FITC and resulted in a significant and consistent decrease of mRNA levels of two of the four tested genes (rps-2 and tps-2a), suggesting effective uptake of dsRNA-containing solution by the nematode. These findings suggest that RNAi by desiccation-enhanced soaking is viable in Panagrolaimus sp. DAW1 and provide the first functional genomic approach to investigate freezing tolerance in this non-model organism. RNAi, in conjunction with qPCR, can be used to screen for candidate genes involved in intracellular freezing tolerance in Panagrolaimus sp. DAW1.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The charge density mismatch concept was applied to the synthesis of high‐charge‐density silicoaluminophosphate SAPO‐69 (OFF) and SAPO‐79 (ERI) and zincoaluminophosphate PST‐16 (CGS), PST‐17 (BPH), ...PST‐19 (SBS), and ZnAPO‐88 (MER) molecular sieves. Combined alkali‐organoammonium structure direction in these systems is thus enabled. Structure direction is treated from the perspective of stabilizing an ionic framework, the relationships between reaction charge density (OH−/H3PO4), alkali and organoammonium content, and ionicity of tetrahedral framework atoms in successful structure direction are presented.
The missing link: Introduction of combined alkali‐organoammonium structure direction allows access to high charge density ZnAPO and SAPO molecular sieves, including PST‐16 (CGS), PST‐17 (BPH), PST‐19 (SBS), ZnAPO‐88 (MER), SAPO‐69 (OFF), and SAPO‐79 (ERI).
Entomopathogenic nematodes are effective biological control agents against insect pests but their commercial application is restricted by their limited shelf life. This study applies our knowledge of ...the cold tolerance of nematodes to this problem and investigates further the cold tolerance mechanisms of Steinernema feltiae and Heterorhabditis bacteriophora infective juveniles. When frozen using a fast freezing regime these nematodes are moderately freezing tolerant, with a lower lethal temperature of −5°C. Survival is significantly enhanced by slow freezing overnight (at −1°C), with a decrease in the lower lethal temperature to −14°C. This may indicate that these nematodes are capable of cryoprotective dehydration. Acclimation at 5°C further enhanced freezing survival in S. feltiae but only by a small amount. Nematodes that had survived freezing to −13°C retained their pathogenicity to an insect host. Rapid cold hardening or exposure to a cold shock had no significant effect on freezing survival. The further development of methods based on cryoprotective dehydration may result in a method for the commercial storage of these nematodes.
Capillary electrophoresis (CE) is a technique which uses an electric field to separate a mixed sample into its constituents. Portable CE systems enable this powerful analysis technique to be used in ...the field. Many of the challenges for portable systems are similar to those of autonomous in-situ analysis and therefore portable systems may be considered a stepping stone towards autonomous in-situ analysis. CE is widely used for biological and chemical analysis and example applications include: water quality analysis; drug development and quality control; proteomics and DNA analysis; counter-terrorism (explosive material identification) and corrosion monitoring. The technique is often limited to laboratory use, since it requires large electric fields, sensitive detection systems and fluidic control systems. All of these place restrictions in terms of: size, weight, cost, choice of operating solutions, choice of fabrication materials, electrical power and lifetime. In this review we bring together and critique the work by researchers addressing these issues. We emphasize the importance of a holistic approach for portable and in-situ CE systems and discuss all the aspects of the design. We identify gaps in the literature which require attention for the realization of both truly portable and in-situ CE systems.
This commentary focuses on the emerging intersection between BMP/TGF‐β signaling roles in nervous system function and the amyotrophic lateral sclerosis (ALS) disease state. Future research is ...critical to elucidate the molecular underpinnings of this intersection of the cellular processes disrupted in ALS and those influenced by BMP/TGF‐β signaling, including synapse structure, neurotransmission, plasticity, and neuroinflammation. Such knowledge promises to inform us of ideal entry points for the targeted modulation of dysfunctional cellular processes in an effort to abrogate ALS pathologies. It is likely that different interventions are required, either at discrete points in disease progression, or across multiple dysfunctional processes which together lead to motor neuron degeneration and death. We discuss the challenging, but intriguing idea that modulation of the pleiotropic nature of BMP/TGF‐β signaling could be advantageous, as a way to simultaneously treat defects in more than one cell process across different forms of ALS.
Key Findings
Gene mutations and environmental triggers of ALS primarily perturb protein homeostasis, RNA function, and cytoskeletal dynamics.
Emerging data reveal specific molecular links between BMP/TGF‐β signaling and dysfunctional cellular processes in ALS.
The pleiotropic nature of BMP/TGF‐β signaling may prove advantageous as a pathway whose modulation will impact multiple processes simultaneously versus the need to develop multiple interventions to slow or prevent motor decline in ALS.
Although structurally similar to type II counterparts, type I or activin receptor-like kinases (ALKs) are set apart by a metastable helix-loop-helix (HLH) element preceding the protein kinase domain ...that, according to a longstanding paradigm, serves passive albeit critical roles as an inhibitor-to-substrate-binding switch. A single recurrent mutation in the codon of the penultimate residue, directly adjacent the position of a constitutively activating substitution, causes milder activation of ACVR1/ALK2 leading to sporadic heterotopic bone deposition in patients presenting with fibrodysplasia ossificans progressiva, or FOP. To determine the protein structural-functional basis for the gain of function, R206H mutant, Q207D (aspartate-substituted caALK2) and HLH subdomain-truncated (208 Ntrunc) forms were compared to one another and the wild-type enzyme through in vitro kinase and protein-protein interaction analyses that were complemented by signaling read-out (p-Smad) in primary mouse embryonic fibroblasts and
S2 cells. Contrary to the paradigm, the HLH subdomain actively suppressed the phosphotransferase activity of the enzyme, even in the absence of FKBP12. Unexpectedly, perturbation of the HLH subdomain elevated kinase activity at a distance, i.e., allosterically, at the ATP-binding and polypeptide-interacting active site cleft. Accessibility to polypeptide substrate (BMP Smad C-terminal tails) due to allosterically altered conformations of type I active sites within heterohexameric cytoplasmic signaling complexes-assembled noncanonically by activin-type II receptors extracellularly-is hypothesized to produce a gain of function of the R206H mutant protein responsible for episodic heterotopic ossification in FOP.
This study aims to investigate the synergistic effects of corrosion and wear of artificial human joints made from a surgical grade cast F-75 cobalt–chromium–molybdenum (CoCrMo) alloy. Both ...electrochemical and gravimetric measurements have been used to determine the performance of CoCrMo samples in static environments and under predominantly three-body abrasive wear conditions using the micro-abrasion test method. Electrochemical measurements are presented from embedded corrosion cells within a micro-abrasion rig. Micro-abrasion–corrosion has been studied using an aggressive abrasive slurry (SiC/Ringer's) to identify depassivation and repassivation processes. These initial conditions are an attempt to simulate worst-case scenarios where wear, cement or bone debris are entrained into the contact. The in situ wear-corrosion measurements have been used to identify the implications of wear and corrosion on both the implant and tentative implications for the patient over the long term. Results show strong synergistic effects occur ranging from negative to positive (i.e. beneficial to accelerated surface removal rates). The synergistic levels appear to be dependent on the integrity of the passive films and the repassivation kinetics. Corrosion potentials are presented which corroborate depassivation within the scar.
This work has developed numerical models simulating steel plate corrosion degradation and presents a series of novel finite element modeling to assess the influence of localized pit distribution and ...bench-shaped pits, which are often observed in long-term exposures. Four location patterns of one-sided corroded shipping steel plates have been considered, which include both geometric and material non-linearities. Validation of the modeling method is achieved by a thermoelastic stress analysis, which provides the principal stress distribution over the plate surface. The modeling results demonstrate that the frequently detected localized corrosion may reduce the ultimate strength by up to 20% compared to uniformly corroded plate. In addition, bench-shaped pits may further decrease the ultimate strength by up to 14% compared to the no-bench condition with the same degree of pitting.
Combinatorial signaling is key to instruct context-dependent cell behaviors. During embryonic development, adult homeostasis, and disease, bone morphogenetic proteins (BMPs) act as dimers to instruct ...specific cellular responses. BMP ligands can form both homodimers or heterodimers; however, obtaining direct evidence of the endogenous localization and function of each form has proven challenging. Here, we make use of precise genome editing and direct protein manipulation via protein binders to dissect the existence and functional relevance of BMP homodimers and heterodimers in the Drosophila wing imaginal disc. This approach identified in situ the existence of Dpp (BMP2/4)/Gbb (BMP5/6/7/8) heterodimers. We found that Gbb is secreted in a Dpp-dependent manner in the wing imaginal disc. Dpp and Gbb form a gradient of heterodimers, whereas neither Dpp nor Gbb homodimers are evident under endogenous physiological conditions. We find that the formation of heterodimers is critical for obtaining optimal signaling and long-range BMP distribution.
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•Endogenous tagging combined with synthetic traps identifies BMP dimer composition in situ•Gbb secretion is dependent on Dpp expression•Gbb/Dpp heterodimers are the only BMP ligands secreted in the imaginal wing disc•Heterodimers trigger signaling at higher levels than would the Dpp homodimers
Bone morphogenetic proteins (BMPs) can potentially form both heterodimers or homodimers. Bauer et al. identify that in the Drosophila imaginal wing disc, heterodimers are the only secreted and fully active ligand species. In this tissue, the secretion of Gbb depends on its heterodimerization with Dpp.
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