Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers

Controlled chemical modification of enzymes, targeting groups not involvedin the active site, can lead to modified catalysts that are intrinsicallymore efficient and resistant to heat and denaturing agents. Bovinepancreatic trypsin was covalently modified up to 75-85% with monomericglutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose andoxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss inactivity occurred upon modification. Temperature optima of trypsin shiftsfrom 45-76 degrees C and T50 from 54-76 degrees C for the best modifiedsample made with OSP. The efficiency of the modifiers in stabilization wasranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T >Sucrose-T. Half-life of modified enzymes also followed the same trend. Bothstabilization factor and t1/2 decreased with increasing temperatures. Thefree energy of activation for inactivation delta(deltaG*) varies from 12-20kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsinby 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsinby urea is less noticeable. The character of the two-step inactivationprocess of trypsin changes with the degree of stabilization in that theduration of phase I one increased noticeably as stabilization increases.Native trypsin fluoresces less intensely showing a red shift under theinfluence of denaturation. Such a fluorescence change is not so obvious forthe modified enzymes indicating conformational stability acquired bymodification.     

Machining High-Temperature Alloys by Means of Solid Ceramic End Mills

Russian Engineering Research - The cutting of high-temperature alloys is considered. The performance of solid ceramic end mills is assessed by experimental comparison of five different designs with...     

Solid Ceramic Toroidal End Mill

Russian Engineering Research - The possibility of designing solid ceramic end mills with different geometry is considered. A mathematical model is developed for the cutting section of the mill on...     

Investigation of buried quantum dots using grazing incidence X-ray diffraction

Self-organized, buried InAs quantum dots covered by an AlAs diffusion barrier were investigated under UHV conditions using grazing incidence X-ray diffraction. The experimental data is compared to the simulated results obtained by Finite Element Method and Distorted Wave Born Approximation. We have found that the simulated data could be compared to the experimental one only after convolution by the resolution element which can be estimated from the experiment. By adjusting the simulation parameters we were able to find good agreement between the simulated and the measured data.     

On the mechanism of encapsulated particle formation during pulsed laser deposition of WSe x thin-film coatings

We have studied factors influencing the formation of particles with the structure of a spherical metal W core inside a WSe₂ shell during pulsed laser deposition (PLD) of thin films of tungsten diselenide under variable conditions (buffer gas (Ar) pressure, substrate temperature). It is established that the metal core is formed at the stage of laser ablation of a synthesized WSe₂ target, while the shell grows as a result of condensation, migration, and redistribution of atoms during deposition of a laser-initiated atomic flow on the surface of a growing film. Retardation of the atomic flow by a buffer gas at pressures within 2–10 Pa does not ensure activation of the shell condensation process on the metal core in the gas phase. Increasing the substrate temperature from room temperature up to 250°C leads to transformation of the shell structure from amorphous into laminar.     

Normalization of precision and conformance confirmation in radiation monitoring

The concept of precision standard for the domain of radiation measurements is formulated. In accordance with international recommendations for the quantitative expression of the precision of measurements, the concept of the uncertainty of results is used and its application to problems of radiation monitoring of objects is demonstrated. The basic principles underlying the application of criteria that define the conformance of results to safety standards are formulated. An example of a conformance criterion for a typical situation of radiation monitoring is given.     

An estimate of the error of measuring sensitivity by the SINAD method

The limits of applicability of the SINAD method when measuring the signal-to-noise ratio, often used to estimate the sensitivity of receivers, are investigated. It is shown that if the systematic component of the error in measuring the harmonic coefficients of the generator being measured – the signal source – and of the high-frequency part of the receiver is ignored, there will be an unlimited increase in the error in measuring the sensitivity when the signal-to-noise ratio approaches the limiting value. The approach described enables the contribution to this error of components arising from distortions and noise of different origin to be separated.     

Specific features of ion-initiated processes during pulsed laser deposition of MoSe2 coatings in pulsed electric fields

Experimental data and results of mathematical modeling have been used to determine the energy characteristics of an ion beam used to assist pulsed laser deposition (PLD) of MoSe₂ layers under conditions of positive high-voltage pulses applied to a laser-ablated target. It is shown that PLD assisted by implantation of ions at energies up to 100 keV can be used to obtain MoSe2 coatings on ⁵⁷Fe-containing substrates. Analysis of the concentration-depth profiles of Mo, Se, and ⁵⁷Fe atoms and the phase composition of a near-surface layer in samples shows evidence for mass transfer domination in thermal spikes and a significant influence of ion impact on the structure of this layer at the nanoscale. These features are manifested by the formation of a nanocomposite structure with inclusions of a specific hexagonal FeSe phase. The obtained results demonstrate the existence of principally new possibilities of using the proposed modified PLD method for controlled formation of solid lubricant coatings with improved properties.     

Influence of hydrogen on the thermoelectric voltage signal in a Pt/WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/6<Emphasis Type="Italic">H</Emphasis>-SiC/Ni/Pt layered structure

The possibility of detecting H₂ by registering the thermal electromotive force signal, which arises between the surfaces of 6H-SiC plates with a thickness of 400 μm, is established. The working surface of the plates is modified by deposition of a WO _x film and catalytic Pt. An ohmic contact (Ni/Pt) is created on the rear surface of the plate, and this surface is maintained at a stabilized temperature of 350°C. The temperature gradient through the plate thickness arises due to the cooling of the working surface with the air medium. The delivery of H₂ into this medium up to a concentration of 2% gives rise to a 15-fold increase in the electric signal, which considerably exceeds the Pt/WO _x /SiC/Ni/Pt system’s response registered in the usual way by measuring the current–voltage dependence. In this case, an additional power source for the registration of the thermal electromotive force is not required.