On the mechanisms of secondary flows in a gas vortex unit

The hydrodynamics of secondary flow phenomena in a disc‐shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT^® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multivortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl‐decay mechanism in the exhaust line. Near‐wall jet formation in the boundary layers near the GVU end‐walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multivortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1859–1873, 2018     

Applying γ‐Substituted Prolines in the Foldon Peptide: Polarity Contradicts Preorganization

Rational choice of chemical modifications to proline residues allows the preorganization principle to be exploited for more stable assembly of the foldon domain as a tag for trimerization. With systematic knowledge of how chemical and steric variations of the ring substituents affect the relative stabilities of exo and endo puckers, the preorganization principle should then be usable in biotechnologically synthesized foldon mutants and applicable for protein tagging elsewhere.     

Exchange reactions control for selective separation of glyoxylic acid in technological mixtures of glyoxal oxidation

Separation of glyoxylic acid from unpurified multicomponent technological mixtures, resulting in the process of direct oxidation of glyoxal, and preparation of sodium glyoxylate are developed. The mixtures are treated with an optimal amount of CaCO_3, which has to be prespecified by acidic–basic titration of the technological mixtures. Both separation of glyoxylic acid and preparation of sodium glyoxylate take place owing to ionic exchange reactions: calcium glyoxylate is easily converted into glyoxylic acid by action of oxalic acid. Reaction with Na₂CO₃ leads to the formation of sodium glyoxylate.     

DNA-based materials as chemical reactors for synthesis of metal nanoparticles

In this minireview we highlight a recent progress in preparation of DNA-based matrices that can be used as reactors for templating of inorganic nanomaterials and, in particular, highlight catalytic applications of such hybrid materials. We also discuss advantages and disadvantages of DNA utilization as a material and outline prospects of DNA-based technologies in future.     

Effects of mutations in the calcium-binding sites of recoverin on its calcium affinity: evidence for successive filling of the calcium binding sites

A molecule of the photoreceptor Ca²⁺-binding protein recoverincontains four potential EF-hand Ca²⁺-binding sites, of whichonly two, the second and the third, are capable of binding calciumions. We have studied the effects of substitutions in the second,third and fourth EF-hand sites of recoverin on its Ca²⁺-bindingproperties and some other characteristics, using intrinsic fluorescence,circular dichroism spectroscopy and differential scanning microcalorimetry.The interaction of the two operating binding sites of wild-typerecoverin with calcium increases the protein's thermal stability,but makes the environment around the tryptophan residues moreflexible. The amino acid substitution in the EF-hand 3 (E121Q)totally abolishes the high calcium affinity of recoverin, whilethe mutation in the EF-hand 2 (E85Q) causes only a moderatedecrease in calcium binding. Based on this evidence, we suggestthat the binding of calcium ions to recoverin is a sequentialprocess with the EF-hand 3 being filled first. Estimation ofCa²⁺-binding constants according to the sequential binding schemegave the values 3.7 x 10⁶ and 3.1 x 10⁵ M^–1 for thirdand second EF-hands, respectively. The substitutions in theEF-hand 2 or 3 (or in both the sites simultaneously) do notdisturb significantly either tertiary or secondary structureof the apo-protein. Amino acid substitutions, which have beendesigned to restore the calcium affinity of the EF-hand 4 (G160D,K161E, K162N, D165G and K166Q), increase the calcium capacityand affinity of recoverin but also perturb the protein structureand decrease the thermostability of its apo-form.     

Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor Synthesis

Powders of nanocrystalline zirconia doped with 3–30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000°C for 1 h results in fully dense, transparent ceramics with grain sizes of 40–45 nm and homogeneous microstructures.     

Study of cryostructuration of polymer systems. XVI. Freeze–thaw‐induced effects in the low concentration systems amylopectin–water

Studies of the freeze–thaw behavior of low‐concentrated (0.01–0.25 g/dL) water solutions and dilute pastes (0.5–1.0 g/dL) of maize starch amylopectin showed that cryogenic treatment of these systems resulted in the formation of precipitated matter, whose yield and thermal characteristics (melting temperature and enthalpy) depended on the initial polymer concentration and conditions of freezing, frozen storage, and thawing. Research of the kinetic features of these cryoprecipitation events revealed at least two stages for this process: (i) a rapid stage, when the precipitation of virtually all of the dissolved polysaccharide occurred while the system was freezing, and (ii) a slower stage, the rate of which was mainly dependent on the thawing regimes or duration of the sample storage frozen at subzero temperatures. Cryoprecipitation phenomena were observed to be most extensive at temperatures 1–2° below the melting point of the frozen system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1740–1748, 2000     

Synthesis and electrorheological characteristics of titanate nanotube suspensions under oscillatory shear

In this study, titanate nanotubes (TNTs) were synthesized by hydrothermal treatment of TiO₂ powders (P25) in a NaOH solution. The as-synthesized TNTs exhibit high surface area and large aspect ratio. Rheological properties of TNTs suspensions were then investigated under oscillatory shear. The TNTs fluid shows the viscoelastic behavior and the dynamic moduli (G′, G″) increase significantly by about 4 orders of magnitude as the electric field strength is up to 2.0 kV/mm. Transient response under dynamic shear reveals different changes in the microstructure of TNTs fluid from steady shear. The complex modulus of TNTs fluids is sensitive to temperature while that of P25 fluid become insensitive at higher temperature. Dynamic viscoelastic behavior suggests that structure of P25 to TNTs transition merits the enhancement of ER activity of TNTs fluid.     

Causes of chatter in a hot strip mill: Observations, qualitative analyses and mathematical modelling

Severe vibrations, known as chatter, occur often in both hot and cold rolling of steel. A recent chatter outbreak at the second stand of hot strip mill in Hastings, Australia, prompted an investigation into the causes of chatter by a literature review, the development and deployment of mathematical models, and a rigorous analysis of plant observations. The investigation suggests that the frictional conditions in the roll gap are the principal cause of chatter in this mill, though residual chatter marks on work rolls can occasionally cause it. The frictional conditions appear to be associated with the thickness and properties of oxide formed on rolls.