Modeling enzymatic reactions involving transition metals

High-accuracy quantum chemistry has now been applied for almost 10 years to biological problems involving transition metal active sites. The leading theoretical method is hybrid density functional theory (DFT), usually with the B3LYP functional. The chemical models vary in size, commonly from 30 to 100 atoms treated fully quantum mechanically. Two schools exist, one using the smallest possible adequate models and the other using as large models as possible and sometimes including the entire enzyme by combining quantum mechanics with molecular mechanics. In our group, we have found that the latter approach, which is much more time-consuming and error prone, is seldom needed. In this Account, methods and models will be described and examples of recent applications given. The examples are chosen to illustrate trends and to show cases where theory has predicted new mechanisms not suggested previously.     

EPR/alanine dosimetry in LDR brachytherapy--a feasibility study

In this study, we present the results of in vivo dosimetry, using electron paramagnetic resonance in l-alanine, performed on 13 patients treated for gynaecological cancers. The doses from (137)Cs (12 samples) and (192)Ir (one sample) brachytherapy sources were determined inside vagina. The detectors had a form of small cellulose capsules tightly filled with crystalline alanine. The positions of the detectors were reconstructed from two orthogonal radiographs. The planned doses were calculated with a computer planning system (PLATO, Nucletron). The relative deviations between planned and measured doses ranged from -23 to +14%. The mean deviation from the prescribed dose was relatively low (-5%) with SD of 10%. The main sources of differences between the measured and calculated doses were attributed to uncertainty in the determination of the detector position inside the patient's body and to uncontrolled changes in the detector position during the treatment.     

Complex permittivity measurements of ferroelectrics employing composite dielectric resonator technique

Composite cylindrical TE(0n1) mode dielectric resonator has been used for the complex permittivity measurements of ferroelectrics at frequency about 8.8 GHz. Rigorous equations have been derived that allowed us to find a relationship between measured resonance frequency and Q-factor and the complex permittivity. It has been shown that the choice of appropriate diameter of a sample together with rigorous complex angular frequency analysis allows precise measurements of various ferroelectric. Proposed technique can be used for materials having both real and imaginary part of permittivity as large as a few thousand. Variable temperature measurements were performed on a PbMg(1/3)Nb(2/3)O3 (PMN) ceramic sample, and the measured complex permittivity have shown good agreement with the results of measurements obtained on the same sample at lower frequencies (0.1-1.8 GHz).     

The titanium structure after a thermoplastic compression at elevated temperatures

In the biomedicine, titanium with the refined grain is of great demand. The microstructure of the Grade 2 titanium samples was produced by the plastic forming at elevated temperatures and with different strain rates. Sellers–Tegartt equation was applied to verify that plastic forming stresses required to achieve the desired structure. Microstructure was observed with scanning electron and transmission electron microscopes. To characterise the elements of the structure, the electron backscatter diffraction was used. Grains were fragmented mostly with a twinning mechanism. Observations of strain–stress graphs obtained during the deformation indicate that the equilibrium between flow stress and loaded strain was achieved after the processes of dynamic polygonisation and/or recrystallisation.     

Optimization of Two‐Strand Industrial Tundish Work with Use of Turbulence Inhibitors: Physical and Numerical Modeling

The paper shows the results of the research obtained by physical and mathematical modeling of steel flow and mixing in the tundish. Two‐strand continuous casting tundish was under consideration. It has been working in one of polish steel plants. The change of concast slab assortment was caused by the changeable market terms. So, the tundish with the new system of steel flow controller was needed. Up to now baffles with the notch have played this role. Their placement cause the excessive consumption of the lining of the tundish front line. As a consequence the turbulence inhibitor (TI) was applied. Four different types of this inhibitor were designed. As a result of the experimental measurements and numerical simulations, the RTD curves of F‐type were obtained. Basing on these curves time constants for examined types were determined. Additionally, the research results were complemented by the E‐type curves. The percentage participations of dead volume flow, dispersed plug flow, and well‐mixed volume flow were calculated. The research gives possibility to estimate the designed TIs and their influence on the tundish work.     

Selection of pneumatic control valves from catalogues

In a case of computer simulation used for the verification of pneumatic system performance, one of the main problems is that various parameters can be used to describe flow characteristics of the system components. Although the Standard ISO 6358 offers two parameters: the sonic conductance C and the critical static pressure ratio b, these cannot be directly utilised in the selection of elements comprising a pneumatic system. In this paper, we present two algorithms for calculating the volumetric flow rate Q _N and the flow coefficient K _V as a function of sonic conductance C and critical pressure ratio b (recommended by the standard) toward the improved selection of pneumatic control valves.     

Längenabhängigkeit des Beulwiderstandes umfangsdruckbeanspruchter stählerner Kreiszylinderschalen

Das Versagen von Silos und Tanks wird häufig durch Druckunterschiede zwischen Außen‐ und Innendruck verursacht. Obwohl es sich beim Lastfall konstanter Umfangsdruck um einen Basisbeulfall der Kreiszylinderschale handelt, sind selbst hierbei einige Fragen noch nicht geklärt. Vergleicht man die Beulwiderstände, die sich in den technischen Regelwerken nach dem experimentell gestützten spannungsbasierten Beulsicherheitsnachweis ergeben, mit den Versagenslasten, die man bei einem numerisch gestützten Beulsicherheitsnachweis unter Einbeziehung von geometrischen Ersatzimperfektionen ermittelt, ergeben sich Diskrepanzen im Bereich langer Schalen. Im Beitrag werden experimentelle Ergebnisse eines deutsch‐polnischen Kooperationsprojektes vorgestellt, das diesen Widersprüchen nachgeht. Die Auswertung der Ergebnisse zeigt, dass der Beulwiderstand dünnwandiger Schalen unter Umfangsdruck auch von der geometrischen Schalenschlankheit abhängt. Das wird gegenwärtig von den Vorschriften noch nicht erfasst, so dass lange Schalen konservativer als kurze Schalen bemessen werden. Influence of the length‐to‐radius ratio on the buckling resistance of cylindrical steel shells subject to hoop compression. The failure of silos and tanks is often caused by differences between outer and inner pressure. Although the load case hoop compression is a basic buckling case of cylindrical shells, there are still some problems that have to be tackled. For long cylinders, discrepancies arise when comparing the buckling resistances calculated from the experimentally based stress design of current design rules with the resistances derived from numerical buckling strength verifications using equivalent geometric imperfections. In the contribution, the experimental results of a German‐Polish research project, concerning that problem, are presented. The evaluation of the results reveals that the buckling resistance of thin‐walled cylindrical steel shells subject to hoop compression also depends on the geometrical slenderness. This fact is neglected in current design rules. Therefore, long cylinders are designed more conservatively than short cylinders.     

Influence of Gaseous Media Flow in the Dual Ar-H<Subscript>2</Subscript>-H<Subscript>2</Subscript>O/air Atmosphere Setup on the Scale Growth Kinetics of Crofer 22APU Ferritic Stainless Steel

The problem of gaseous media distribution within the metallic interconnects in solid oxide fuel cells (SOFCs) and its influence on the oxidation resistance of the applied materials is currently of great interest. In the presented work, an influence of gas flow within the dual Ar-H₂-H₂O/air atmosphere experimental setup on the oxidation behavior of the Crofer 22APU ferritic stainless steel was investigated. Examination of the sample oxidized for 1000 h in temperature of 800 °C revealed the presence of coaxial regions on the scale surface, with the differences in scale’s thicknesses in those regions being clearly visible. Additionally, the morphology of the surface changed significantly in a function of the radial distance from the sample’s center. To further examine the phenomena of uneven gas distribution, a model of the dual-atmosphere setup was created, using Ansys Workbench software. Obtained results suggest that the correlation between scale morphology and distribution of temperature and pressure on the sample’s surface, created by gas flow in the system, can be justified.