Base excision repair (BER) removes damaged bases by generating single‐strand breaks (SSBs), gap‐filling by DNA polymerase β (POLβ), and resealing SSBs. A base‐damaging agent, MMS is widely used to study BER. BER increases cellular tolerance to MMS, anti‐cancer base‐damaging drugs, Temozolomide, Carmustine, and Lomustine, and to clinical poly(ADP ribose)polymerase (PARP) poisons, Olaparib and Talazoparib. The poisons stabilize PARP1/SSB complexes, inhibiting access of BER factors to SSBs. PARP1 and XRCC1 collaboratively promote SSB resealing by recruiting POLβ to SSBs, but XRCC1‐/‐ cells are much more sensitive to MMS than PARP1‐/‐ cells. We recently report that the PARP1 loss in XRCC1‐/‐ cells restores their MMS tolerance and conclude that XPCC1 facilitates the release of PARP1 from SSBs by maintaining its autoPARylation. We here show that the PARP1 loss in XRCC1‐/‐ cells also restores their tolerance to the three anti‐cancer base‐damaging drugs, although they and MMS induce different sets of base damage. We reveal the synthetic lethality of the XRCC1‐/‐ mutation, but not POLβ‐/‐, with Olaparib and Talazoparib, indicating that XRCC1 is a unique BER factor in suppressing toxic PARP1/SSB complex and can suppress even when PARP1 catalysis is inhibited. In conclusion, XRCC1 suppresses the PARP1/SSB complex via PARP1 catalysis‐dependent and independent mechanisms.
Among post-translational modifications of proteins, ADP-ribosylation has been studied for over fifty years, assigning to this post-translational modification (PTM) a large set of functions, including DNA repair, transcription and cell signaling. This review presents an update on the function of a large set of enzyme writers, the readers that are recruited by the modified targets, and the erasers that reverse the modification to the original amino acid residue, removing the covalent bonds formed. In particular, the review provides details on the involvement of the enzymes performing monoADP-ribosylation/ polyADP-ribosylation (MAR/PAR) cycling in cancers. Of note, there is potential for application of the inhibitors developed for cancer also in the therapy of non-oncological diseases such as the protection against oxidative stress, suppression of inflammatory responses, and the treatment of neurodegenerative diseases. This field of studies is not concluded, since novel enzymes are being discovered at a rapid pace.
Annually over 500 million tons worldwide of flat and long commodity grade structural steel products are produced for applications in the construction sector. Major costs to produce these commodity grade structural steels lies in alloys, energy and depending on region labor. Production costs for these commodity grades, which typically have low margins for profits, continue to rise worldwide driven by ferro alloy costs. Improved operational efficiencies (productivity, reduced energy consumption, improved melt to finished yields, reduced consumable consumption, etc.) can be realized along with lowered alloy costs with a proper understanding of a new metallurgical strategy to alloy design. These operational efficiencies along with cost savings can be accomplished with proper alloy design in conjunction with the mills processing capabilities to achieve the desired end metallurgy/mechanical properties. Requirements of strength and ductility for any given structural steel microstructure are obtained from three metallurgical mechanisms or "building blocks": a) grain size refinement, b) solid solution and c) precipitation. Overall operation costs including alloy costs can be minimized if better engineering of these contributions can be realized. The correct use of these factors brings improved process/mechanical property stability. Use of practical metallurgical modeling tools along with mill data to determine process control capabilities can also assist in optimization of the metallurgical designs for cost effective structural steel production.
Abrasion resistant steel plates with hardness equal to or greater than 360 BHN and high strength structural steel plates/coils with yield strength requirements equal to or greater than 690 MPa are typically produced by the quench and tempering (Q&T) process. The Q&T microstructures thus produced by either reheating, quench or tempering (RQT) or direct quench and/or tempering (DQ and/or DQT) lead to very high hardness and strength levels as a result of tempered martensite/bainite or auto-tempered and/or lower bainite microstructures. Using these steels in the earth moving, mining equipment and in the general materials processing industry, in addition to strength and toughness other major requirements are weldability (low CE), good elongation and formability. Hence, to achieve optimum balance of properties in these steels, it is very important to understand the microstructural evolution from the interaction of thermo-mechanical control rolling of plate/coil followed by the RQT/DQ/DQT processes. It is shown in the present paper that with careful design of the steel chemistry (C, Mn, Si, Cr, Mo) while utilising optimized microalloying, especially niobium, titanium and boron complemented by proper rolling, cooling, and Q&T process design, uniform cross sectional microstructure and optimum balance of strength, hardness, toughness, ductility and weldability are achieved.
The objective of this work was to observe the significant factors for the dehydration reaction of xylose to furfural and to optimize the processes using experimental design. The studied variables were temperature, time, initial percentage of xylose mass, and catalyst/xylose ratio. Temperature and initial percentage of xylose mass were considered statistically significant, while the maximum point for furfural selectivity was at 160 °C and 2% of initial xylose mass. Using niobic acid and niobium phosphate (1:1) (NbP/NbA), 44.05% xylose conversion and 74.71% furfural selectivity were obtained. The results showed that the mixture of catalysts with Brönsted acid and Lewis acid sites improved the selectivity of furfural from the xylose dehydration reaction. NbP/NbA catalysts were very stable under the investigated condition after 5 continuous recycles.
5-Hydroxymethylfurfural (HMF) production from fructose was studied by using niobium phosphate as solid acid catalyst. HMF selectivity was optimized in a water-acetone system and compared to a water system. The HMF optimal selectivity for process carried out in the water-acetone system was 62.94%. When the process was performed in water, the HMF selectivity achieved 55.73%. These results were used in a large-scale simulation and economic analysis of the two processes. The higher selectivity of system water-acetone affected the HMF minimum selling price (MSP). The MSP value was 2.21 USD/kg for process performed in water-acetone and 3.05 USD/kg for process in water. In the sensitivity analysis, we have found that in addition to process selectivity, the fructose cost was the most significant factor affecting HMF price.
PdxNby/C binary electrocatalysts supported on Vulcan carbon XC72 were prepared by the sol-gel method. The materials are characterized by transmission electron microscopy, X-ray diffraction analysis, inductively coupled plasma–mass spectrometry and contact angle measurements. The electrocatalytic activity for ethanol electrooxidation reaction was studied by cyclic voltammetry, chronoamperometry, Tafel slope and accelerated durability testing. The direct ethanol performance and the products after the experiments were studied by Fourier transform infrared spectroscopy. Pd1Nb1/C (50:50 wt%) shows superior activity for ethanol oxidation compared to the other electrocatalysts prepared in this work. All electrocatalysts containing Nb show the highest current exchange density. The Tafel slope results suggest that the Nb modified the Pd-electrocatalyst to obtain a reaction path with high selectivity with only a single determining step with low production of the intermediates for the ethanol oxidation reaction. The best performance is obtained using Pd1Nb1/C 18.11 mW cm⁻². The Pd1Nb1/C electrocatalyst displays the highest production of CO2 and the lowest production of acetaldehyde. Pd1Nb1/C shows the highest peak current density during 1000 cycles of the experiment and the lowest mass loss of Pd after the cycling test. We find that the Nb modifies the Pd electrocatalysts from the bifunctional mechanism and reduces the loss of Pd during the accelerated durability test.
Resumo Os aços de alta resistência microligados ao nióbio têm mostrado ser uma boa opção para fabricação de perfis estruturais, utilizando os conceitos já desenvolvidos para a indústria de gás e óleo. Entretanto, a definição das reais necessidades em termos de soldagem desta família de aços não está bem descrita nas normas de soldagem mais utilizadas pelo setor. Este trabalho demonstra a construção e avaliação de um Atlas de Soldagem produzido através de simulações físicas (Gleeble e dilatometria) e ensaios mecânicos de amostras simuladas. O objetivo é que o atlas de soldagem seja uma ferramenta orientativa para melhor definição das faixas de parâmetros para soldagem desta classe de material. A metodologia proposta foi aplicada a um aço ARBL bainítico da classe 65 ksi. Foi possível determinar com mais segurança a faixa de energia de soldagem recomendada, inclusive quanto à necessidade ou não do uso de pré-aquecimento, e evidenciar que as simulações são comparáveis a soldas reais. Esta abordagem mostrou trazer benefícios, como redução de custos com processo de pré-aquecimento desnecessário.
29 Synopsis: Since the erection of the first modern cable-stayed bridge in 1956 in Sweden structural engineers have always looked for improved material performance, especially for the steel wire rod. This type of long-span bridge is increasing in popularity across the world and in particular in South East Asia and China. The world's longest cable-stay bridge is the 10 km (main span) JaiShao Bridge, completed in 2013 in China. In general, the steel used for stay-cables and pre-stressed concrete is characterised by its high carbon content which imparts tensile strengths nearing 1,800 MPa, however, this high carbon approach negatively impacts the desired elongation. This paper presents and provides metallurgical analysis on experimental data demonstrating that microalloying using niobium imparts significant microstructural refinement of high carbon steel wire rods; effectively reducing pearlite colony size and inter-lamellar spacing. This refinement not only leads to improvements in strength allowing for example, light-weighting of cables, but moreover and importantly improvements in ductility, %RA, and drawability for cold drawn wire. The overriding conclusion is that through very small additions of niobium to high carbon steel wire rod, notable product and operational cost benefits can be created for steelmakers, rod and wire rope producers generating improved productivity and quality in the cold drawing process and better final performance of the strand in applications such as wire rope for cable-stayed bridges.
Mathematical models have been used extensively in the optimization of hot rolling schedules. They are cost effective tools in reducing mill trials and give guidance in the directions to follow when either schedule parameters or chemical compositions are changed. However, the existing models were usually derived from laboratory parametric equations, obtained with the inherent limitations of attainable processing variables, in particular strain rates. The present paper introduces a model for austenite grain size evolution during thermomechanical processing in which the focus is hot deformation schedule optimization with lean chemistry designs. Very often, nowadays, expensive elements such as Cr, Mo and Ni, among others, have been used to promote adequate microstructure and mechanical properties. By using the model presented in this paper, a hot rolling schedule can be examined from the point of view of the fundamentals of physical metallurgy and, if possible, optimized both in terms of processing parameters and chemical composition. The model has been used to design a lean microalloyed chemistry which was then tested in an industry trial. Results showed that reasonable mechanical properties can be obtained and that the model can be used for the purpose of industry scale alloy designing.
This paper reports the synthesis of a new class of catalysts based on niobium using Filter Cake (FC) as precursor, which is more affordable economically than other niobium sources commonly used. FC is obtained before the necessary purification to obtain niobic acid (Nb2O5.nH2O), making the catalyst synthesis process less costly. Its modification by hydrothermal treatment in the presence of different agents (oxalic acid or hydrogen peroxide) allowed the obtention of nanostructured materials in the form of rods or spheres with larger BET area, crystallinity and acidity than the precursor. Their catalytic potential were evaluated in fructose dehydration reaction in aqueous media, aiming the obtention of 5-hydroxymethylfurfural (5-HMF). The production of furan compounds from sugars has become a process of great interest in recent years because it is related to the search for more sustainable sources of energy, since carbohydrates are the predominant part of biomass. In optimum conditions, it was possible to obtain 22% yield of 5-HMF in aqueous medium and 47% yield of 5-HMF using DMSO as solvent.
This paper presents an actual case of a new industrial building at CBMM’s plant in Araxá, Brazil as an example of lean design using microalloyed steels. The structure consists mostly of microalloyed ASTM A572 steel grades 65 and 50 instead of the conventional carbon manganese ASTM A36 steel. The application of grade 65 with more than 450 MPa of yield strength is an innovative solution for this type of construction in South America. A complete welding evaluation performed on the low carbon, niobium microalloyed grade 65 steel showed the welding properties and benefits. Niobium’s effect of increasing strength and toughness simultaneously resulted in relevant savings in total steel consumption for the project. The paper also quantifies the expected savings in costs, energy and carbon dioxide emissions.
This paper presents an actual case of a new industrial building at CBMM's plant in Araxá, Brazil as an example of lean design using microalloyed steels. The structure consists mostly of microalloyed ASTM A572 steel grades 65 and 50 instead of the conventional carbon manganese ASTM A36 steel. The application of grade 65 with more than 450 MPa of yield strength is an innovative solution for this type of construction in South America. A complete welding evaluation performed on the low carbon, niobium microalloyed grade 65 steel showed the welding properties and benefits. Niobium's effect of increasing strength and toughness simultaneously resulted in relevant savings in total steel consumption for the project. The paper also quantifies the expected savings in costs, energy and carbon dioxide emissions. © 2016 by The Minerals, Metals & Materials Society. All rights reserved.
Austenite grain growth and microalloy precipitate size and composition evolution during thermal processing were investigated in a carburizing steel containing various additions of niobium and molybdenum. Molybdenum delayed the onset of abnormal austenite grain growth and reduced the coarsening of niobium-rich precipitates during isothermal soaking at 1323 K, 1373 K, and 1423 K (1050 °C, 1100 °C, and 1150 °C). Possible mechanisms for the retardation of niobium-rich precipitate coarsening in austenite due to molybdenum are considered. The amount of Nb in solution and in precipitates at 1373 K (1100 °C) did not vary over the holding times evaluated. In contrast, the amount of molybdenum in (Nb,Mo)C precipitates decreased with time, due to rejection of Mo into austenite and/or dissolution of fine Mo-rich precipitates. In hot-rolled alloys, soaking in the austenite regime resulted in coarsening of the niobium-rich precipitates at a rate that exceeded that predicted by the Lifshitz-Slyozov-Wagner relation for volume-diffusion-controlled coarsening. This behavior is attributed to an initial bimodal precipitate size distribution in hot-rolled alloys that results in accelerated coarsening rates during soaking. Modification of the initial precipitate size distribution by thermal processing significantly lowered precipitate coarsening rates during soaking and delayed the associated onset of abnormal austenite grain growth. © 2015, The Minerals, Metals & Materials Society and ASM International.
The selection of the right materials to produce a vehicle, machinery, a steel building or structure provides an opportunity to improve quality, reduce costs and enable more efficient use of precious resources. A wide range of advantages can be realized through the use of optimized steel grades, such as weight and costs reduction, improved construction/manufacture time, production stability and quality variability. This paper will highlight case studies where the use of value-added steels is the path to improve the product life cycle by expanding the service life of a structure, reducing costs and potentially enhancing the profitability of the supply-chain by just using high strength Nb-microalloyed steels to replace conventional materials.
The effect of Nb microalloying on structure and physical properties of quenched and tempered 13%Cr martensitic stainless steel was investigated. Excellent strength and adequate toughness properties were obtained by 0.10 wt% Nb addition to low interstitial (N 0.01wt%, C < 0.02wt%) steel. The effect of Nb in 13%Cr steels with high N content was also studied in a commercial martensitic stainless steel sample containing higher levels of N and also alloyed with V. The microstructure, precipitate morphology and dispersion and volume fraction of reverse austenite were characterized. The strength properties obtained in the steel with 0.10%Nb are significantly higher than those of the V-containing steel. The study shows that whereas amount, size and dispersion of precipitates of microalloying elements contribute to enhanced strength, the optimum volume fraction of reverse austenite formed contributes to enhanced ductility and toughness properties. More importantly, high Nb additions to low N -13%Cr-1%Mo steel are found to improve significantly resistance against pitting corrosion significantly.
Molybdenum is known to affect microalloy precipitate evolution during processing in ferrite and austenite, but a unified explanation of the role of Mo in precipitate evolution is still lacking. Experiments and thermodynamic calculations indicate that Mo is incorporated into (Nb,Mo)(C,N) precipitates both in the hot-rolled condition and after reheating to 900 °C. Molybdenum enrichment is reduced after reheating and soaking at 1100 °C. No measurable segregation of Mo to the carbonitride–matrix interface was observed in any condition.
The aim of the study was to evaluate the seasonality of andrological characteristics and hormonal profile of captive maned wolves (Chrysocyon brachyurus, Illiger 1811). Three adult males were evaluated from the Companhia Brasileira de Metalurgia e Mineração Scientific Breeding Center in Araxá, MG, Brazil, over 13 months. Semen was collected 2-3 times weekly and analysed. Scrotal circumference, biometrics and testicular volume were measured. Stool samples were collected 2-3 times weekly to analyse corticosteroid and testosterone metabolite concentrations. A success rate of 100% was achieved in the collection attempts during the breeding season (BS) and 77.8% during the non-breeding season (NBS). The interval to achieve penile erection was 1-5 min in the BS and 6-10 in the NBS (p < 0.001). Of the ejaculates collected, 80.0% contained sperm during BS, while 28.6% did during the NBS. The ejaculate had only one fraction, was odourless, predominantly translucent (72.4%), with a watery appearance, pH 6.7 and osmolarity of 352.8 mOsmol. Seasonal influences were seen in ejaculate volume (1.3 ml vs 0.4 ml), number of spermatozoa per ejaculate (73.9 × 10(6) vs 6.1 × 10(6) ) and percentage of live sperm (82.0% vs 66.1%) between the BS and NBS (p < 0.05), respectively. A high percentage of major sperm defects were observed in both seasons (50.1% in BS; 65.7% in NBS). Testicular volume was larger (p < 0.05; right testicles 13.1 cm(3) in BS vs 4.0 cm(3) in NBS, while left testicles 12.9 cm(3) in BS vs 5.3 cm(3) in NBS) and testicular consistency increased in the BS. No difference was seen in the basal faecal metabolite concentrations of testosterone; however, the corticosteroid concentrations were higher in the BS. Based on these results, it is possible to conclude that the collection of semen is feasible in captive maned wolves without compromising libido, seminal characteristics and reproductive behaviour and that sperm production is influenced by seasonality; however, it appears that there is no seasonal influence on basal testosterone concentrations.
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