Special Issue: A,B and Z: The Structure,Function and Genetics of Z-DNA and Z-RNA

It is now difficult to believe that a biological function for the left-handed Z-DNA and Z-RNA conformations was once controversial. The papers in this Special Issue, “Z-DNA and Z-RNA: from Physical Structure to Biological Function”, are based on presentations at the ABZ2021 meeting that was held virtually on 19 May 2021 and provide evidence for several biological functions of these structures. The first of its kind, this international conference gathered over 200 scientists from many disciplines to specifically address progress in research involving Z-DNA and Z-RNA. These high-energy left-handed conformers of B-DNA and A-RNA are associated with biological functions and disease outcomes, as evidenced from both mouse and human genetic studies. These alternative structures, referred to as “flipons”, form under physiological conditions, regulate type I interferon responses and induce necroptosis during viral infection. They can also stimulate genetic instability, resulting in adaptive evolution and diseases such as cancer. The meeting featured cutting-edge science that was, for the most part, unpublished. We plan for the ABZ meeting to reconvene in 2022.     

Kr and N implantations in a stainless steel AISI304L: thermal evolution

The evolution of nitrides produced by N-implantation of stainless steel samples previously bombarded with Kr and annealed up to temperature corresponding to 0.5 of the melting point is studied. Transmission electron microscopy shows the size evolution of the bubbles. The dependence of the bubbles on the nitride evolution is established by conversion electron Mössbauer spectroscopy and a retention of -(Fe,Cr,Ni)_{2 + x}N up to 400°C was observed. Between 450 °C and 650 °C the presence of a magnetic field characteristic of the -Fe phase was observed. The evolution of the N-profile was obtained by nuclear reaction analysis.     

L-dopa enhances acquisition of an inhibitory avoidance response

The adult worms of Stilesia globipunctata, Avitellina centripunctata and Moniezia expansa with immature, mature and gravid proglottids and having almost the same length were collected simultaneously from the sheep intestine. Neutral lipid concentration is about 2.2, 1.24 and 18.4% of the dried worm tissue respectively. Cholesterol is 87.8, 85.7 and 88.0% of the unsaponifiable material respectively.     

Characteristics of low-energy ion beams extracted from a wire electrode geometry

Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm(2) with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm(2) for a 50 eV ion beam and 1.78 mA/cm(2) for a 100 eV ion beam.     

A comparative pitting corrosion study of mild steel in different alkaline solutions containing salts with sulphur-containing anions

The localized corrosion of mild steel in alkaline solutions containing a salt with a sulphurcontaining anion (sodium sulphate, sodium sulphite, sodium thiosulphate, potassium thiocyanate and sodium sulphide) is studied by using potentiostatic and potentiodynamic techniques complemented with scanning electron microscopy.Alkaline solutions containing one of those salts produce pitting of mild steel at potential values more positive than those of the active-passive transition of iron in base. In the presence of either thiocyanate or thiosulphate anion iron pitting takes place through sulphide formation which reacts at the electrode surface yielding poorly protective ferrous sulphide. At potential more positive than the breakdown potential the kinetic behaviour fits a competitive surface reaction mechanism involving the formation of the passive film and the nucleation and growth of a ferrous sulphide salt layer. The proposed reaction model reproduces the corresponding experimental current-transients.     

ANALYSIS OF RANDOM AND SYSTEMATIC ERROR EFFECTS ON UNCERTAINTY PROPAGATION IN PROCESS DESIGN AND SIMULATION USING DISTRIBUTION TAIL CHARACTERIZATION

An exponential and heavy tail analysis method is presented to study the effect of systematic and random errors present in thermodynamic data on chemical process design and simulation. The true distribution tail characteristics (important for high levels of quality assurance) can be far from the estimates obtained with typical Gaussian distribution analysis. Pareto (heavy) or exponential distributions may represent the tail behavior better under many circumstances. Heavy tails diminish at an algebraic rate rather than at an exponential rate. Different error types such as random and systematic error can potentially cause different effects in the behavior of probability distributions, particularly in the tails. In this work, we use the tail behavior of cumulative frequency distributions produced from uncertainty analyses to characterize the error propagation in process design and simulation. The diminishing rate of the tail of a given distribution can be related to the error types involved in the process and also can be used to determine which error exhibits stochastic dominance. Case studies of process performance evaluations for liquid-liquid extraction operations are presented to illustrate the approach. It is observed that random and systematic errors (coupled with typical nonlinear chemical engineering models) can cause the tails of the uncertainty probability distributions to be exponential.     

Study of the decomposition of a 0.62LiBH4–0.38NaBH4 mixture

This work highlights the dehydrogenation mechanisms of a 0.62LiBH₄–0.38NaBH₄ mixture in the range of 25–650 °C in flowing Ar. The dehydrogenation starts from 287 °C followed by two decomposition steps at 488 °C and 540 °C. These peak temperatures are in the range of 470 °C (for pure LiBH₄)–580 °C (for pure NaBH₄) due to different Pauling electronegativity values for Li⁺ (0.98) and Na⁺ (0.93) that affects the stability and decomposition temperatures. The 1^st step of dehydrogenation is accompanied with precipitation of LiH, Li₂B₁₂H₁₂ and B in between 287 and 520 °C; whilst the 2^nd step of dehydrogenation is mainly accompanied by the precipitation of Na and B when temperature is higher than 520 °C. The total amount of H₂ released is 10.8 wt.% that exceeds the estimated amount (8.9 wt.%), indicating less metal dodecaborate (than that for pure LiBH₄) is formed during the decomposition.     

Achieving Water Quality System Reliability Using Genetic Algorithms

This paper presents an efficient approach for obtaining wasteload allocation solutions that provide the optimal trade-off between treatment cost and reliability. This approach links a genetic algorithm (GA) with the first-order reliability method (FORM) for estimating the probability of system failure under a given wasteload allocation. The GA-FORM optimization approach is demonstrated for the case study of managing water quality in the Willamette River in Oregon. The objective function minimizes the sum of the treatment cost and the penalty associated with breaching a reliability target for meeting a water quality standard. The random variables used to generate the reliability estimates include streamflow, temperature, and reaeration coefficient values. The results obtained indicate that the GA-FORM approach is nearly as accurate as the approach that links the GA with Monte Carlo simulation and is far more efficient. The trade-off between total treatment cost and reliability becomes more pronounced at higher water quality standards and is most sensitive to the uncertainty in the reaeration coefficient. The sensitivity to the reaeration coefficient also increases at increased reliability levels.