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The resazurin test is one of the most widespread approaches for studying the growth and metabolic activity of microorganisms. It is based on the colour change of the blue indicator, resazurin, to its pink reduced form, resorufin due to the reduction process catalyzed by the metabolic activity. At the same time, the quantitative characterization of the process needs to take into account the fact that one registers the results of the chemical transformation, which can differ from the underlying kinetics of the population growth. Purpose. The principal goal of this work is a sequential modelling of both coupled nonlinear growth processes aimed at obtaining the closed-form solution depending on the specificity and parameters of biological and chemical counterparts and its comparison with the curves obtained experimentally. Methods. The indicator concentration change is derived under the assumption of the logistic bacterial growth catalyzing the unidirectional chemical reaction considered and compared with the photometrically registered growth curve for a population of lactobacteria. Results. It is revealed that the biochemical growth curve will be logistic too only in the case of specially coordinated kinetic parameters and the systems’ carrying capacity. Otherwise, another functional form should be used to approximate the observable dynamics. Conclusion. Thus, the main conclusion consists of drawing attention to the importance of distinguishing between the underlying microbial and observable chemical growth curves. Their difference affects the value of the population growth rate, which is the target of such tests, and, therefore, the proper functional form should be used for the experimental data regression.

The nonlinearity parameter B/A is a characteristic of liquids and soft matter, which gains growing attention due to its sensibility to the composition of materials. This makes it a prospective indicator for nondestructive testing applications based on the ultrasound sounding suitable for a variety of applications from physic chemistry to biomedical studies. At the same time, the thermodynamic definition of the nonlinearity parameter requires extensive measurements at elevated pressures that are not always available; in addition, there are known certain contradiction of such data with the data obtained by methods of nonlinear acoustics. Objective. In this work, we consider a recently proposed approach to the prediction of the speed of sound at high pressures, which uses the property of invariance of the reduced pressure fluctuations and the data obtained at normal ambient pressure only. The method generalises the classic Nomoto model, which however gives only a qualitative picture, and results in the quantitative correspondence to the experimental values within their range of uncertainty. Methods. Analytical methods of the theory of thermodynamic fluctuations applied to the parameters of equations of nonlinear acoustics as well as numerical simulation in the COMSOL Multiphysics® environment. Results. Expressions for calculating the nonlinearity parameter with acceptable accuracy were obtained using thermodynamic data obtained only at atmospheric pressure. Numerical calculations were performed for toluene. In addition, the discrepancy between values of the nonlinear parameter obtained via the thermodynamic and nonlinear acoustic routes is analysed based on the numerical solution of the Westervelt equation; it is revealed that this deviation emerges when the effects of absorption of finite-amplitude waves were not properly taken into account.

We report a workflow and a software description for digital image colorimetry aimed at obtaining a quantitative dose–response curve and the minimal inhibitory concentration in the Resazurin Microtiter Assay (REMA) test of the activity of antimycobacterial drugs. The principle of this analysis is based on the newly established correspondence between the intensity of the a * channel of the CIE L*a*b* colour space and the concentration of resorufin produced in the course of this test. The whole procedure can be carried out using free software. It has sufficiently mild requirements for the quality of colour images, which can be taken by a typical smartphone camera. Thus, the approach does not impose additional costs on the medical examination points and is widely accessible. Its efficiency is verified by applying it to the case of two representatives of substituted 2-(quinolin-4-yl) imidazolines. The direct comparison with the data on the indicator's fluorescence obtained using a commercial microplate reader argues that the proposed approach provides results of the same range of accuracy on the quantitative level. As a result, it would be possible to apply the strategy not only for new low-cost studies but also for expanding databases on drug candidates by quantitatively reprocessing existing data, which were earlier documented by images of microplates but analysed only qualitatively. [ABSTRACT FROM AUTHOR]

Recent studies of the spread of substances penetrating the disrupted blood–brain barrier have revealed that the spread in the parenchyma surrounding a vessel has a complex character. In particular, a flow-like motion occurred for a short time that exhibits a smooth transition to diffusional spread. To address the possible physical background of such behavior, we created a system formed by a hydrogel medium with a channel filled by a marker solution, which can serve as a physical model mimicking the process of a substance passively spreading to the brain's parenchyma when the blood–brain barrier is disrupted. The key result obtained in this work consists of the conclusion that the above-mentioned two-stage character of the spread process discovered in a previous biophysical experiment on the blood–brain opening in a living mouse may originate from the specificity of transport in porous soft matter with relaxation. We propose a mathematical model based on the extended Cattaneo equation, which reproduces our experimental data; determines the crossover time coinciding with that found in the biological system; and, therefore, provides a means of interpretation of this phenomenon. [ABSTRACT FROM AUTHOR]

Determining the isothermal and adiabatic nonlinearity parameters of liquids and soft matter is crucially important for a variety of engineering applications requiring operations under high pressures, nondestructive testing, exploring the propagation of finite amplitude and shock waves, etc. It has been shown recently that mathematically this problem can be reduced to the initial value problem for an ODE build based on the linear response theory for thermodynamic equalities. The required initial conditions should be determined from thermodynamic measurements at ambient pressure (or along the saturation curve). From the physical point of view, the required regression leading to the determining nonlinearity parameters originates from certain regularities in the response of molecular oscillations to the density changes. In this work, we explore how this regression procedure should be optimized computationally with respect to temperature ranges, which exclude anomalies affecting parameters of equations used for the required predictive calculations under high pressures. The validity of the proposed approach is tested by case studies of the propagation of weakly non-linear waves with finite amplitudes and density changes due to shock waves under the Rankine-Hugoniot jump conditions. [ABSTRACT FROM AUTHOR]

This work explores the thermophysical properties of the SPC/E model of water at temperatures between 250 and 400 K and at pressure from 0.1 to 1000 MPa. From a series of Molecular Dynamics simulations (in the NPT ensemble and also in the NVT ensemble), the constant pressure and constant volume heat capacity, the isobaric expansion coefficient, the isothermal compressibility, and the speed of sound are obtained from fluctuation formulas and thermodynamic numerical derivatives and compared with available experimental data. [Display omitted] • Thermophysical properties of water over a wide temperature and pressure range. • Confrontation of a common water model with experimental results. • Benchmark data for molecualr dynamics simulations. [ABSTRACT FROM AUTHOR]

We report new experimental data of the ultrasonic measurements in three ionic liquids with triflate anion: 1-ethylpyridinium triflate, 1-butyl-3-methylimidazolium triflate, diethylmethylammonium triflate. The speed of sound was determined in the temperature range of (297 – 374) K and the pressure range of (0. 1 – 196. 2) MPa. In addition, the respective densities in this range were found using the acoustic route. For the first two substances, the effect of pressure-induced solidification is detected. It is shown that the high-pressure data on the sound velocity can be accurately predicted by applying the pressure fluctuation theory-based model using parameters, which requires only the data determined at the ambient atmospheric pressure. In turn, the density can be predicted using the Fluctuation Theory-based Equation of State (FT-EoS), which includes the isothermal nonlinearity parameter, which is argued as related to the frequency of interparticle oscillations. This interdependence is confirmed by the comparative analysis with the respective peak in the low-frequency Raman–Kerr spectrum. • The speed of sound is measured and the density is determined to 196. 1 MPa. • Pressure-induced freezing of ionic liquids at macroscopic volumes is detected. • Interplay of thermodynamics and microscopic interparticle oscillations is discussed. [ABSTRACT FROM AUTHOR]

We consider subdiffusive motion, modeled by the generalized Langevin equation in an equilibrium setting, of tracer particles in channels of indefinite length in the x direction: the channels of varying width and the channels with sinusoidally meandering midline. The subdiffusion in the x direction is not affected by constraints put by the channel. This is especially astonishing for meandering channels whose centerline might be quite long. The same behavior is seen in a holonomic model of a bead on a sinusoidal and meandering wire, where some analytic insights are possible.