Softening Kinetics of Plain Carbon Steels Containing Dilute Nb Additions

The recrystallisation and precipitation kinetics of a plain carbon steel with 0.017 % Nb were studied using the double-hit deformation technique for interpass holding of 5 and 20s. The present study focuses on the effect of prestrain and deformation temperature on recrystallisation behaviour of the investigated steel. The fractional softening was calculated based on the percentage difference between the areas under the interrupted and uninterrupted deformations flow curves. The T5% and T95%, marking the beginning and end of recrystallisation, respectively, are determined as a function of strain. Quantitative microstructural studies validated the findings from the softening studies. The predicated results of recrystallisation regime are found to be in agreement with industrial observation and other experimental measurement for this steel. It can be seen that the dilute additions of Nb can influence the static recrystallisation of austenite under certain rolling condition which may lead to improved mechanical properties of steel

Microstructural evaluation in structural steels containing dilute niobium concentrations

The thermomechanical processing of microalloyed steels has been instrumental in the successful development of HSLA steel plate and strip products with enhanced property combinations. Microalloying additions of niobium (Nb) have the most potent effect in retarding the static recrystallisation of austenite during interpass times by solute drag and precipitate pinning mechanism. However, published research on the use of Nb in carbon steel long products (C > 0.20 wt.%) is somewhat limited due to the low solubility of Nb in austenite at such carbon levels. Such steels represent well over 50 % of overall world steel consumption primarily intended for the construction sector and therefore represent an essential area for cost efficiencies. This research aimed to understand the influence of dilute niobium concentrations (50-200 ppm) on microstructural evaluation in structural steels. The investigation involved three low carbon steels with varying Nb concentration at constant C (0.20%) and N (0.007%) levels. Isothermal double-hit deformation technique led to the determination of T5% and T95% (beginning and end of recrystallisation, respectively) as a function of strain and interpass time. The results indicate that the T5% increases with increasing Nb supersaturation in austenite at a rate of 40°C per 0.006% Nb supersaturation for a true stain ε=0.40. The Nb supersaturation ratio ≥ 6 resulted in an unrecrystallised microstructure at respective T5% for all tested steels. A high, localised strain-induced precipitation of Nb(CN) was observed at the austenite subgrain boundaries. This translated into higher values for local precipitate pinning force (FPIN), which were significantly higher than one predicted from equilibrium thermodynamics. The critical FPIN for retardation of static recrystallisation was found to be 1.8 MPa at respective T5% for each steel. The present study has contributed to advancing our knowledge of the interplay between solute supersaturation and volume fraction of Nb(CN) precipitation. Even the lowest addition of 66 ppm Nb could retard the recrystallisation at certain rolling conditions and raised T5% temperature over base steel composition. It is possible to develop a viable TMCP deformation schedule to best benefit from dilute Nb additions. The better control of austenite microstructure will improve the mechanical properties of existing low value-added products through ferrite grain refinement. The dilute Nb additions might permit the reduction in other substitutional alloying elements such as Mn as the Nb provides a more strengthening effect at low cost

On the Synergistic Catalytic Properties of Bimetallic Mesoporous Materials Containing Aluminum and Zirconium: The Prins Cyclisation of Citronellal

Bimetallic three-dimensional amorphous mesoporous materials, Al-Zr-TUD-1 materials, were synthesised by using a surfactant-free, one-pot procedure employing triethanolamine (TEA) as a complexing reagent. The amount of aluminium and zirconium was varied in order to study the effect of these metals on the Brønsted and Lewis acidity, as well as on the resulting catalytic activity of the material. The materials were characterised by various techniques, including elemental analysis, X-ray diffraction, high-resolution TEM, N2 physisorption, temperature-programmed desorption (TPD) of NH3, and 27Al MAS NMR, XPS and FT-IR spectroscopy using pyridine and CO as probe molecules. Al-Zr-TUD-1 materials are mesoporous with surface areas ranging from 700–900 m2 g−1, an average pore size of around 4 nm and a pore volume of around 0.70 cm3 g−1. The synthesised Al-Zr-TUD-1 materials were tested as catalyst materials in the Lewis acid catalysed Meerwein–Ponndorf–Verley reduction of 4-tert-butylcyclohexanone, the intermolecular Prins synthesis of nopol and in the intramolecular Prins cyclisation of citronellal. Although Al-Zr-TUD-1 catalysts possess a lower amount of acid sites than their monometallic counterparts, according to TPD of NH3, these materials outperformed those of the monometallic Al-TUD-1 as well as Zr-TUD-1 in the Prins cyclisation of citronellal. This proves the existence of synergistic properties of Al-Zr-TUD-1. Due to the intramolecular nature of the Prins cyclisation of citronellal, the hydrophilic surface of the catalyst as well as the presence of both Brønsted and Lewis acid sites synergy could be obtained with bimetallic Al-Zr-TUD-1. Besides spectroscopic investigation of the active sites of the catalyst material a thorough testing of the catalyst in different types of reactions is crucial in identifying its specific active sites

Detection of transcriptional triggers in the dynamics of microbial growth: application to the respiratorily versatile bacterium Shewanella oneidensis

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nucleic Acids Research 40 (2012): 7132-7149, doi:10.1093/nar/gks467.The capacity of microorganisms to respond to variable external conditions requires a coordination of environment-sensing mechanisms and decision-making regulatory circuits. Here, we seek to understand the interplay between these two processes by combining high-throughput measurement of time-dependent mRNA profiles with a novel computational approach that searches for key genetic triggers of transcriptional changes. Our approach helped us understand the regulatory strategies of a respiratorily versatile bacterium with promising bioenergy and bioremediation applications, Shewanella oneidensis, in minimal and rich media. By comparing expression profiles across these two conditions, we unveiled components of the transcriptional program that depend mainly on the growth phase. Conversely, by integrating our time-dependent data with a previously available large compendium of static perturbation responses, we identified transcriptional changes that cannot be explained solely by internal network dynamics, but are rather triggered by specific genes acting as key mediators of an environment-dependent response. These transcriptional triggers include known and novel regulators that respond to carbon, nitrogen and oxygen limitation. Our analysis suggests a sequence of physiological responses, including a coupling between nitrogen depletion and glycogen storage, partially recapitulated through dynamic flux balance analysis, and experimentally confirmed by metabolite measurements. Our approach is broadly applicable to other systems.Office of Science (BER), U.S. Department of Energy [DE-FG02-07ER64388 to D.S. and DE-FG02- 08ER64511 to M.H.S.]; National Aeronautics and Space Administration, NASA Astrobiology Institute [NNA08CN84A to D.S.]

Shape-specific Effects of Cerium Oxide Nanoparticles (CNPs) on Macrophage Polarization

Immunotherapy is gaining traction in healthcare research where immune activation is central to the therapeutic interventions. The field of immunotherapy is expected to grow at 15% annually and surpass $100 billion by 2022. The mainstay of immunotherapy revolves around monoclonal antibodies, cytokines, immune-modulators, and checkpoint inhibitors. Fast track approval of newer drugs like Keytruda® (Pembrolizumab, Merck) reveals the need and potential of such medications. Evidence suggests that the activated macrophages by themselves are capable of identifying and alleviating viral infections. Macrophages display remarkable plasticity and change their phenotype in response to environmental cues. These changes give rise to different populations of cells with distinct functions namely M1 and M2. The goal of the current clinical trials involving lipopolysaccharide (LPS) or muramyldipeptide (MDP) or cytokines such as interferon-γ (IFN-γ) and granulocyte-macrophage colony-stimulating factor (GM-CSF) is to activate macrophages as a novel immunotherapeutic approach. However, inability of LPS to be systemically administered without causing toxicity in vivo or short duration of action of MDP and IFN-γ due to rapid clearance has limited their transition as effective clinical alternatives. Cerium oxide NPs (CNPs) are known to mitigate oxidative stress and alter the free radical balance. Some recent studies suggest that microenvironmental factors such as free radicals can affect macrophage polarization. On the other hand, various nanoparticles (NPs) have shown to modulate Shape-specific Effects of Cerium Oxide Nanoparticles (CNPs) on Macrophage Polarization Vishal Prabhakar Rakshe, B. Pharm. University of Pittsburgh, 2018 macrophage activation by virtue of their shape. However, interplay between NP shape effects and free radical modulating activity on the macrophage polarization is not known. Thus, we hypothesized that the shape specific CNPs can influence the macrophage phenotypes through their dual attributes: free radical modulating ability and their shapes with various aspect ratios. We used THP-1 human monocyte cell line as an in vitro model. THP-1 monocytes were pre-differentiated to M1 and M2 macrophage phenotypes using appropriate stimuli. Measurement of reactive oxygen and nitrogen species provided an early indication that CNP shape and duration of treatment influenced the inflammatory status of the macrophages. Quantification of mRNA levels of selected M1 and M2 markers revealed shape-dependent effect of CNPs on driving macrophage polarization towards a particular phenotype. Isotropic shape such as Sphere CNPs did not show tendency to drive phenotypic changes. However, anisotropic shapes with different aspect ratios such as Cube (1:1) and Rod (21:1) CNPs showcased a high proclivity to induce an inflammatory M1 phenotype. The ability of Cube and Rod CNPs to increase reactive oxygen and nitrogen species and simultaneously drive M1 phenotype evident from gene expression profiles suggested possible link between these two phenomena. We further confirmed link between CNP shape and free radical modulating activity to drive macrophage polarization through pharmacological inhibition of oxygen and nitrogen radicals. Overall, our results suggest that the biophysical characteristics such as shape of NPs play an important role in dictating macrophage polarization and can be exploited to design better delivery systems for drugs targeting macrophages. Keywords: Cerium oxide, nanomaterial, free radical modulation, macrophage polarization, M1 and M2 phenotype, reactive oxygen species, reactive nitrogen species, macrophage priming, macrophage re-programmin

Effect of niobium supersaturation in austenite on the static recrystallization behavior of carbon structural steels

This work describes the effect of Nb supersaturation in austenite on the suppression of static recrystallization of austenite during an isothermal holding period following hot deformation. The investigation involved three carbon structural steels with varying Nb concentration at constant C (0.20 pct) and N (0.007 pct) levels. The isothermal double-hit deformation technique led to the determination of T5 pct and T95 pct (recrystallization-stop and full recrystallization temperatures, respectively) as a function of a true strain and interpass time. The results indicate that the T5 pct increases with increasing Nb supersaturation in austenite at a rate of 40 °C per 0.006 pct Nb supersaturation for a true stain ε=0.40. At each respective T5 pct, all tested steels exhibited an Nb supersaturation ratio ≥ 7.5 in austenite. A high, localized strain-induced precipitation of Nb(CN) was observed at the austenite subgrain boundaries in the unrecrystallized microstructure. This translated into higher values for local precipitate-pinning forces (FPIN), which were significantly higher than that predicted from equilibrium thermodynamics. The critical FPIN for retardation of static recrystallization was found to be 1.6 MPa at the respective T5 pct for each steel. The present study has contributed to advancing our knowledge of the interplay between Nb solute supersaturation and volume fraction of Nb(CN) precipitation in particular for carbon structural steels. It has also highlighted an opportunity to apply niobium, even an ultra-low addition (i.e., < 100 ppm) to commodity-grade structural steels to reduce overall alloying costs