Pressureless sintering and properties of boron carbide composite materials

Boron carbide and Tantalum boride composites were prepared by pressureless sintering of B₄C with addition of TaC powder. The effect of TaC addition on the sinterability of boron carbide was studied. High densified ceramic with a relative density of 98.7% was obtained at sintering temperature of 2250°C. The composition and the microstructure of the dense composites are characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). The studies show that the composites contain boron carbide, TaB₂, and carbon phases with a homogeneous structure. In addition, the correlation between the composition and the electrical conductivity was investigated. The electrical conductivity of the composite increased with increasing addition of TaC, and a change in conduction behavior from semiconducting to metallic was observed. High hardness value of 28.49 ± 1.33 GPa was obtained by the sample with 30 wt% TaC addition.     

Structural Consequences of the 1,2,3-Triazole as an Amide Bioisostere in Analogues of the Cystic Fibrosis Drugs VX-809 and VX-770

Although the 1,2,3-triazole is a commonly used amide bioisostere in medicinal chemistry, the structural implications of this replacement have not been fully studied. Employing X-ray crystallography and computational studies, we report the spatial and electronic consequences of replacing an amide with the triazole in analogues of cystic fibrosis drugs in the VX-770 and VX-809 series. Crystallographic analyses quantify subtle differences in the relative positions and conformational preferences of the R¹ and R² substituents attached to the amide and triazole bioisosteres. Computational studies derived from the X-ray data highlight the improved hydrogen bonding donor and acceptor capabilities of the amide in comparison to the triazole. This analysis of the spatial and electronic differences between the amide and 1,2,3-triazole will inform medicinal chemists as they consider using the triazole as an amide bioisostere.     

Decision rules for determining terrestrial movement and the consequences for filtering high-resolution global positioning system tracks: a case study using the African lion (Panthera leo)

The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement.     

Aurora Kinase A Is Involved in Controlling the Localization of Aquaporin-2 in Renal Principal Cells

The cAMP-dependent aquaporin-2 (AQP2) redistribution from intracellular vesicles into the plasma membrane of renal collecting duct principal cells induces water reabsorption and fine-tunes body water homeostasis. However, the mechanisms controlling the localization of AQP2 are not understood in detail. Using immortalized mouse medullary collecting duct (MCD4) and primary rat inner medullary collecting duct (IMCD) cells as model systems, we here discovered a key regulatory role of Aurora kinase A (AURKA) in the control of AQP2. The AURKA-selective inhibitor Aurora-A inhibitor I and novel derivatives as well as a structurally different inhibitor, Alisertib, prevented the cAMP-induced redistribution of AQP2. Aurora-A inhibitor I led to a depolymerization of actin stress fibers, which serve as tracks for the translocation of AQP2-bearing vesicles to the plasma membrane. The phosphorylation of cofilin-1 (CFL1) inactivates the actin-depolymerizing function of CFL1. Aurora-A inhibitor I decreased the CFL1 phosphorylation, accounting for the removal of the actin stress fibers and the inhibition of the redistribution of AQP2. Surprisingly, Alisertib caused an increase in actin stress fibers and did not affect CFL1 phosphorylation, indicating that AURKA exerts its control over AQP2 through different mechanisms. An involvement of AURKA and CFL1 in the control of the localization of AQP2 was hitherto unknown.     

A Toxoplasma gondii Oxopurine Transporter Binds Nucleobases and Nucleosides Using Different Binding Modes

Toxoplasma gondii is unable to synthesize purines de novo, instead salvages them from its environment, inside the host cell, for which they need high affinity carriers. Here, we report the expression of a T. gondii Equilibrative Nucleoside Transporter, Tg244440, in a Trypanosoma brucei strain from which nucleobase transporters have been deleted. Tg244440 transported hypoxanthine and guanine with similar affinity (K_m ~1 µM), while inosine and guanosine displayed K_i values of 4.05 and 3.30 µM, respectively. Low affinity was observed for adenosine, adenine, and pyrimidines, classifying Tg244440 as a high affinity oxopurine transporter. Purine analogues were used to probe the substrate-transporter binding interactions, culminating in quantitative models showing different binding modes for oxopurine bases, oxopurine nucleosides, and adenosine. Hypoxanthine and guanine interacted through protonated N1 and N9, and through unprotonated N3 and N7 of the purine ring, whereas inosine and guanosine mostly employed the ribose hydroxy groups for binding, in addition to N1H of the nucleobase. Conversely, the ribose moiety of adenosine barely made any contribution to binding. Tg244440 is the first gene identified to encode a high affinity oxopurine transporter in T. gondii and, to the best of our knowledge, the first purine transporter to employ different binding modes for nucleosides and nucleobases.     

Vortex characteristics due to nozzle clogging in water caster mould: modelling and validation

In continuous slab casting, clogging in the submerged entry nozzle (SEN) ports leads to flow asymmetry and vortex formation in the mould. Knowledge of vortexing and its influence on product quality is fundamental for defect-free production. In this study, the interconnected effects of nozzle clogging and SEN submergence depth, variation on flow asymmetry and vortex characteristics in a 0.4 scale water caster have been characterised by CFD investigation and validated with experimental results from the authors’ previous work. Mean flow velocities at the sub-meniscus and near the port exit predicted by the computational model are compared with the time-averaged values of the impeller probe velocity measurements and found to be in reasonable agreement. Three different clogging conditions (0, 33 and 66% in the left port of the SEN) for SEN submergence depth of 60?mm are studied and the 66% clogging produced vortices having largest diameter, which is consistent with the experimental observations. The effects of SEN submergence depth on flow asymmetry and vortexing are investigated with three different conditions – 40, 60 and 80?mm. It is found that the shallow SEN submergence depth (40?mm) produces vortices of largest diameter and the flow is most stable for a SEN submergence depth of 60?mm among the three cases. Vortex bending towards the SEN as noticed in the experimental observations is also observed in the computational study. This work illustrates the possibility of capturing features of vortexing using validated CFD model.     

Reduced chemistries with the Quantemol database (QDB)

Typical feed gas mixtures used in technological and other plasmas may give rise to reaction networks involving several hundred reactions. Such chemistries are often too large to be used in full reactor simulations and it is therefore desirable to construct reduced chemistry networks which mimic as closely as possible the behavior of the full chemistry but employ far fewer individual reactions and species. Constructed chemistries are available from the Quantemol database (QDB) and two approaches to constructing reduced chemistry from these chemistries based on (a) physical intuition and (b) sensitivity analysis of dominant reaction pathways, are explored. In doing this it is necessary to consider different pressure and power regimes. Reduced chemistry sets are presented for CF₄ /O₂/N₂/H₂, for which 396 reactions and 52 species are reduced to 71 reactions and 26 species, and for pure O₂, for which 45 reactions and 10 species are reduced to 34 reactions.     

Acylierung von Heterocyclen mit Kohlensäurederivaten. I. Kinetik und Mechanismus der Reaktion von 2-Aminobenzimidazolen mit Arylcyanaten

Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.