2,415 research outputs found
Spectrophotometer for atmospheric ozone research – receiver reaction of irradiation with complex spectral composition
One of the basic problems in elaboration of spectro-photometer for atmospheric ozone research at the Space Research and Technologies Institute – Bulgarian Academy of Sciences seems to be the necessity of calculation of output signal of the irradiating receiver by fixed spectral composition and intensity. The calculation wouldn’t be difficult if the intensity values range is situated on the linear part of the irradiating receiver energetic characteristic. To the end, the absolutely spectral characteristic of receiver sensibility and spectral density of the treated receiver intensity has to be known.
The paper is dedicated to the elaboration and the obtained results by offering and creating a method for definition of the irradiating receiver output signal by fixed spectral composition and intensity
In the paper presents the obtained schemes and equations in the process of elaboration characterizing the reaction of the photo-receiver complex spectral composition with nonlinear energetic characteristic
An ultra melt-resistant hydrogel from food grade carbohydrates
© 2017 The Royal Society of Chemistry. We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agar-MC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agar-MC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agar-MC hydrogel has enhanced mechanical properties over the temperature range 25-85 °C and a maximum storage modulus at 55 °C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a sol-gel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agar-MC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agar-MC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 °C its structure was retained without melting. The produced highly thermally stable hydrogel shows melt resistance which may find application in high temperature food processing and materials templating
Scaling properties of step bunches induced by sublimation and related mechanisms: A unified perspective
This work provides a ground for a quantitative interpretation of experiments
on step bunching during sublimation of crystals with a pronounced
Ehrlich-Schwoebel (ES) barrier in the regime of weak desorption. A strong step
bunching instability takes place when the kinetic length is larger than the
average distance between the steps on the vicinal surface. In the opposite
limit the instability is weak and step bunching can occur only when the
magnitude of step-step repulsion is small. The central result are power law
relations of the between the width, the height, and the minimum interstep
distance of a bunch. These relations are obtained from a continuum evolution
equation for the surface profile, which is derived from the discrete step
dynamical equations for. The analysis of the continuum equation reveals the
existence of two types of stationary bunch profiles with different scaling
properties. Through a mathematical equivalence on the level of the discrete
step equations as well as on the continuum level, our results carry over to the
problems of step bunching induced by growth with a strong inverse ES effect,
and by electromigration in the attachment/detachment limited regime. Thus our
work provides support for the existence of universality classes of step
bunching instabilities [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103
(2002)], but some aspects of the universality scenario need to be revised.Comment: 21 pages, 8 figure
Simulation and beyond – Principles of effective obstetric training
Simulation training provides a safe, non-judgmental environment where members of the multi-professional team can practice both their technical and non-technical skills. Poor teamwork and communication are recurring contributing factors to adverse maternal and neonatal outcomes. Simulation can improve outcomes and is now a compulsory part of the national training matrix. Components of successful training include involving the multi-professional team, high fidelity models, keeping training on-site, and focussing on human factors training; a key factor in adverse patient outcomes. The future of simulation training is an exciting field, with the advent of augmented reality devices and the use of artificial intelligence
Instabilities at vicinal crystal surfaces - competition between the electromigration of the adatoms and the kinetic memory effect
We studied the step dynamics during sublimation and growth in the presence of
electromigration force acting on the adatoms. In the limit of fast surface
diffusion and slow kinetics of atom attachment-detachment at the steps we
formulate a model free of the quasi-static approximation in the calculation of
the adatom concentration on the terraces. Numerical integration of the
equations for the time evolution of the adatom concentrations and the equations
of step motion reveals two different step bunching instabilities: 1) step
density waves (small bunches which do not manifest any coarsening) induced by
the kinetic memory effect and 2) step bunching with coarsening when the
dynamics is dominated by the electromigration. The model developed in this
paper also provides very instructive illustrations of the Popkov-Krug dynamical
phase transition during sublimation and growth of a vicinal crystal surface.Comment: 15 pages, 6 figure
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