Search

We analyze the effect of the stochastic growth rates, which may originate from heterogeneity of resource distribution on the average unrestricted growth of an ensemble of non-interacting sub-populations of consumers with Holling I and II functional responses, assuming normal (Gaussian) and anomalous (Tweedie) density distributions of resources. We show that the variation in the resource availability between the sub-population habitats leads to a non-Malthusian dynamics of the initial phase of the average biomass growth, and that this phase of growth can be successfully approximated using quasi-Gaussian approach. This conclusion is illustrated by numerical simulations. [ABSTRACT FROM AUTHOR]

We propose an approach to the fast numerical evaluation of the continuous wavelet transform with the Morlet wavelet based on the replacement of the Gaussian factor in the latter by a hierarchical sequence of B-splines and their application to the image formed by the analyzed signal multiplied by a set of periodic functions. We show that the suggested approach results in a significant reduction of the resulting data storage (almost linear dependence on the sample length vs. the quadratic one required by conventional methods). In order to illustrate the workability of the proposed technique we applied it to the analysis of the data on the blood flow velocity data obtained in vivo from chorioallantoic membrane of chicken embryo, which exhibit non-stationarity, bi- or multirhythmicity. [ABSTRACT FROM AUTHOR]

Recently, it has been proven Lebedeva and Postnikov (2014) that the continuous wavelet transform with non-admissible kernels (approximate wavelets) allows an existence of the exact inverse transform. Here, we consider the computational possibility for the realization of this approach. We provide a modified simpler explanation of the reconstruction formula, restricted on the practical case of real valued finite (or periodic/periodized) samples and the standard (restricted) Morlet wavelet as a practically important example of an approximate wavelet. The provided examples of applications include the test function and the non-stationary electro-physical signals arising in the problem of neuroscience. [ABSTRACT FROM AUTHOR]

We explore the behaviour of the inverse reduced density fluctuations and the isobaric expansion coefficient using α , ω -dibromoalkanes as an example. Two different states are revealed far from the critical point: the region of exponentially decaying fluctuations near the coexistence curve and the state with longer correlations under sufficiently high pressures. The crossing of the isotherms of the isobaric expansion coefficient occurs within the PVT range of the mentioned transition. We discuss the interplay of this crossing with the changes in molecular packing structure connected with the analysed function of the density, which represents inverse reduced volume fluctuations. [ABSTRACT FROM AUTHOR]

In this work, we argue that the SERS technique allows distinguishing between drug-sensitive and drug-resistant strains on the level of resolution of individual mycobacteria. This result is based on the experimental investigations of deactivated M. tuberculosis strains by the Raman spectroscopy in high-wavenumber region. A discussion of drug resistance-related complexity of emerging specific vibrational bands for proteins and lipids forming a cell's wall is provided. • Surface enhanced Raman spectra of single mycobacteria are obtained. • Complexity of SERS spectra grows with drug resistance. • Drug resistance can be related to complexity of cell wall topology. [ABSTRACT FROM AUTHOR]

We consider the problem of linear fitting of noisy data in the case of broad (say α -stable) distributions of random impacts (“noise”), which can lack even the first moment. This situation, common in statistical physics of small systems, in Earth sciences, in network science or in econophysics, does not allow for application of conventional Gaussian maximum-likelihood estimators resulting in usual least-squares fits. Such fits lead to large deviations of fitted parameters from their true values due to the presence of outliers. The approaches discussed here aim onto the minimization of the width of the distribution of residua. The corresponding width of the distribution can either be defined via the interquantile distance of the corresponding distributions or via the scale parameter in its characteristic function. The methods provide the robust regression even in the case of short samples with large outliers, and are equivalent to the normal least squares fit for the Gaussian noises. Our discussion is illustrated by numerical examples. [ABSTRACT FROM AUTHOR]

During this research, we present an acoustic method used for determination of the thermal properties, such as the thermal expansivities and heat capacities from 293.15 K to 313.15 K of compressed liquid α,ω-dibromoalkanes. A designed in our lab experimental apparatus has been used to measure the speed of sound in liquid dibromoalkanes on five isotherms between 293 and 313 K and at pressures up to 100 MPa. The measurement technique is based on a traditional single-reflector pulse-echo method with a single piezoceramic transducer. The speed of sound data were combined with values of density and isobaric heat capacity along one isobar at atmospheric pressure to calculate the density, thermal expansivity and heat capacity over the whole temperature and pressure range by means of the acoustic numerical method. To explore the possibility of analytical description of the data, we propose the method based on the continuation of inverse reduced volume fluctuations into a single-phase region. The resulting expression contains two parameters characterizing the inverse volume fluctuations in the liquid and the isobaric heat capacity along the referent line and allows to predict the density and the isobaric heat capacity for the whole studied region with the accuracy, which does not exceed 0.1% and 1% correspondingly. [ABSTRACT FROM AUTHOR]

Highlights: [•] SIRS equations with variable reaction rate represented as ODE with outer excitation. [•] We explain a crucial property of epidemic behavior: 1:1 dynamical resonance. [•] We propose the model for prediction of flu activity based on the weather forecast. [•] This approach is confirmed via the comparison with real epidemiological data. [Copyright &y& Elsevier]

Abstract: In this paper we study the numerical solution of singular Abel–Volterra integro-differential equations, which are typical for the theory of anomalous diffusion and viscoelastic delayed stresses. The proposed method is based on application of the operational and almost operational matrices to derivatives and integrals in a vicinity of the kernel’s singular point. As examples, two orthonormal systems are considered: Bernstein polynomials and Legendre wavelets. The methods convert the singular integro-differential equation in to a system of algebraic equations that implies two advantages: (i) one does not need to introduce artificial smoothing factors into the singular integrand and (ii) the direct estimation of computational error around singular point is possible via the obtained explicit expression. The examples of numerical solution and their discussion are presented. [Copyright &y& Elsevier]

Abstract: We consider the diffusion of markers in a layered medium, with the lateral diffusion coefficient being the function of hight. We show that the probability density of the lateral displacements follows a one-dimensional Batchelor’s equation with time-dependent diffusion coefficient governed by the particles’ redistribution in height. For the film of a finite thickness the resulting mean squared displacement exhibits superdiffusion at short times and crosses over to normal diffusion at long times. The approach is used for a description of experimental results on inhomogeneous molecular diffusion in thin liquid films deposited on solid surfaces. [Copyright &y& Elsevier]

We propose two approaches to the analysis of sparse stochastic data, which exhibit a power-law dependence between their first and second moments (Taylor's law), and determining the respective power index, when it has a value between 1 and 2. They are based on the analysis of components of the Haar wavelet expansion. The first method uses a dependence between the first iterations of averaging and wavelet coefficients with the subsequent studying the statistics of zero paddings on the line, which corresponds the linear dependence between two first moments of the analysed distributions. The second method refers to Taylor's plot formed by the full set of wavelet coefficients. It is discussed that such representations provide also an opportunity to check time–scale stability of analysed data and distinguish between particular cases of the Tweedie probabilistic distribution. Both simulated series and real marine species abundance data for five spatial regions of the Pacific are used as example illustrating an applicability of these approaches. • The Haar wavelet transform allow calculating the Tweedie power index. • Taylor(Tweedie)'s law can be distinguished from the Gamma-distributed data with zeros. • Real fish abundance data are analysed as an example. [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 propose an approach to analysing single trajectories of a particle, which moves randomly on a landscape distinct parts of which result in sufficiently various diffusion coefficients. The method based on the mapping the cumulative sum of step-wise elementary displacement squared into a complex oscillating function with the subsequent continuous wavelet analysis of the later allows the localization of relatively homogeneous sub-regions and determining values of the diffusion coefficient within each such sub-region. This approach is applied to demonstrable test examples as well as to the reconstruction of the biological membrane's properties from the real data of single molecule walk tracing. • Revealing patches with different diffusivity from a single particle track. • An improved continuous wavelet transform for exploring random walks. • Processing a case study of real biological membrane visited by a walking molecule. [ABSTRACT FROM AUTHOR]

Here we report the results of ultrasound measurements for liquid bromobenzene in the temperature range of (293.15 − 473.15) K and the pressure range (0.1 − 600) MPa : the speed of sound and the density, which was determined via the acoustic route. This data allows us to confirm that the density of this highly pressurized liquid can be accurately predicted with the combination of Tait's and Murnaghan's equations with parameters determined using only the data obtained at ambient atmospheric pressure. It is also shown that the frequency of intermolecular oscillations, which follows from the Raman-Kerr spectrum, can be corresponded to the combination of macroscopic speed of sound and density; this confirms ideas of the phonon theory of liquid thermodynamics and provides the parameter of isotherms nonlinearity required for predictive calculations. Finally, this approach was applied to determine pressures achieved by the shock wave compression of bromobenzene when the density is determined from the X-ray pictures. • Acoustic measurements up to 600 MPa and the density determined on their base. • Correspondence between the speed of sound and the Raman-Kerr spectrum. • Predictive calculations of the density as a function of the pressure and vice versa. [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]

This work reports new experimental data for the viscosity of 1-bromopenthane (within the temperature range (253.15–298.15) K), 1-bromohexane ((263.15–293.15) K), 1-bromoheptane ((263.15–298.15) K), 1-bromooctane ((253.15–293.15) K), 1-bromononane ((253.15–413.15) K), 1-bromodecane ((253.15–423.15) K), 1-bromoundecane ((283.15–423.15) K), 1-bromododecane ((273.15–293.15) K), and 1-bromohexadecane ((298.15–423.15) K). Considering them in combination with previously known data for these substances, it is shown that the viscosity of this series of 1-bromoalkanes accurately satisfies the Bingham-Coombs model based on the free volume approach. The quantitative connection of the excluded volume with the van der Waals volume and the packing fraction is revealed. • New data in unexplored before temperature regions are provided. • Applicability of Bingham-Coombs model is confirmed. • Physical interpretation of free volume parameters is proposed. [ABSTRACT FROM AUTHOR]

In this paper, the high-pressure calorimetry was used to monitor the heat of the polymerization of bisphenol-A diglycidyl ether (DGEBA) mixed with a stoichiometric amount of aniline over a wide range of pressure (p = 0.1–350 MPa at T = 298.15 K). To the best of our knowledge, this is the first high-pressure calorimetric study of the reaction kinetics of the epoxy resin curing processes. The collected novel experimental data were analysed with two models: the original Kamal and its modified version taking into account the real monomer conversion, which provides insight into the progress of two subsequent non-catalyzed and catalyzed reactions occurring during the step growth polymerization. It was found that the determined rate constants are sensitive to pressure and model dependent, resulting in different activation volumes, which fall within the range from −16 cm3/mol to −26 cm3/mol. Interestingly, these values are similar to those reported for the epoxide ring-opening polymerization reaction, which changes in the range between −15 cm3/mol to −20 cm3/mol. In addition, the analysis of the high-pressure data revealed that the original Kamal model fails to describe kinetic curves obtained for the polymerization reaction, where the monomer conversion is far below 100%. Interestingly, such effects are considered to be due to the change in the mechanism of the reaction from mass to the diffusion-controlled regime. Here, we explicitly have shown that it has nothing to do with this phenomenon since after considering solely the real monomer conversion in the Kamal model fits, quality has been significantly improved. As a consequence, estimated rate constants are more reliable. Results presented herein clearly indicated that high-pressure experiments provide a new perspective to understand the progress of the classical reactions, as step-growth polymerization that has mainly been studied as a function of the chemical composition and temperature. Image 1 - High-pressure calorimetric data for step-growth polymerization (SGP) are presented - Original Kamal and modified version considering the monomer conversion were tested - Original model fails if the real monomer conversion is far below 100% - Rate constants are sensitive to pressure and model dependent - Activation volumes of catalyzed and non-catalyzed reactions in SGP are different [ABSTRACT FROM AUTHOR]

Presented here are the thermophysical characterization and thermodynamic modelling of RAVENOL Calibration Fluid 2.5 which is used for the calibration and preservation of diesel engine fuel injectors. Accurate knowledge of the standardized fluid properties is an important component for engineering modelling to deliver the correct dose of fuel into the combustion chamber of diesel engines while reducing the occurrence of cavitation phenomena. The liquid density and specific isobaric heat capacity measurements were carried out up to T = 423 K at ambient pressure. The speed of sound moving through the liquid was measured from T = (300 to 423) K from ambient pressure up to p = 200 MPa. This plays a crucial role in fuel injection timing. With the combination of these data with high pressure, it is possible to accurately calculate the liquid density, specific isobaric heat capacity, coefficient of isobaric thermal expansion and isothermal compressibility at elevated pressures. The data obtained at ambient pressure were used to confirm the accuracy of the high-pressure experimental data by comparing them with the predictions of the Fluctuation-Theory Equation-of-State. The calibration fluid has become the second ISO 4113 fluid to be characterized in this fashion. • Thermophysical characterization of an ISO 4113 calibration standard • High-pressure speed of sound measurements up to 200 MPa • Iterative calculation of high-pressure volumetric properties and heat capacity • Accurate density predictions derived from atmospheric pressure data with FT-EoS [ABSTRACT FROM AUTHOR]