All-Russian Research Institute for Optical and Physical Measurements

the estimation of body fat mass (FM) can be performed using different methods. Although Dual-Energy X-ray Absorptiometry (DXA) is considered the reference technique due to its precision and reproducibility, its high cost and limited accessibility restrict its widespread use. Moreover, its application requires standardized hydration conditions and trained personnel, which makes its implementation difficult in field settings or for frequent assessments of athletes. More accessible methods, such as Bioelectrical Impedance Analysis (BIA) and Anthropometry (ANT), present validity limitations when applied to Mexican athletes. to compare the body fat mass of Mexican triathletes obtained by BIA and ANT versus DXA, in order to evaluate the reliability of the equations used in these methods. an exploratory, observational, cross-sectional study was conducted with 30 Mexicans triathletes (10 women, 20 men), between 18 and 40 years of age, who met the inclusion criteria were studied. The BIA equation used was Macias (2007) and the anthropometric equations were those of Durnin & Womersley with Siri. different average values of body fat percentage were obtained in the methods used (DXA 24.91 %; BIA 22.18 %; ANT 21.83 %), but they did not present significant differences (one-way ANOVA, post hoc Scheffe & Bonferroni, p > 0.05). A positive correlation was obtained between DXA and the other methods (BIA r = 0.697, ANT r = 0.876, p > 0.05), with anthropometry being the strongest. the methods used estimate different values of body fat percentage in the studied population, but without statistically significant differences. The method that showed the best results in the studied population when compared to DXA was the anthropometric method.

ABSTRACT This article presents a three autocollimation method (TAM) for measuring the refractive index (RI) of optical glass. The popular minimum deviation method (MDM) for RI measurement is accurate, but it is very laborious, since the procedure of determining the minimum possible angle requires many iterations. TAM allows the calculation of RI based on the measurement of the angles of incidence of the beam corresponding to the autocollimation from the mirror located behind the investigated prism, parallel to the entrance face. Measurements must be carried out for all three faces, but it is not necessary to measure the prism angles, since the RI is calculated by solving a system of equations relating the values of unknown parameters. A comparative analysis showed that the accuracy of the proposed method is about 20% higher than the accuracy of classical MDM under the same conditions. A limitation of TAM is the phenomenon of total internal reflection, which limits the measurement range. To implement TAM, a goniometric system with a photoelectric encoder and a set of three reference prisms made of optical glass is used. The experimental absolute error does not exceed ±1·10 −5 , which proves the prospect of using the method for high‐precision RI measurements. TAM can also be used to study the dispersion characteristics of triangular prisms made of optically transparent materials. TAM increases the accuracy and simplifies the RI measurement process compared to MDM.

Raman spectroscopy is mainly used for qualitative analysis, since the intensity of Raman lines is instrument dependent. At the same time, the high selectivity of Raman spectra stimulates interest in finding ways to use them for quantitative analysis as well, and the development of methods to effectively apply Raman spectroscopy for quantitative analysis is quite relevant.The aim of the study was to investigate the possibilities of using the measure developed at the All-Russian Scientific Research Institute for Optical and Physical Measurements and designed for calibration of Raman instruments on the Raman shift wavenumber scale for quantitative analysis from Raman spectra.The developed measure (registration number in the Federal Information Fund for Ensuring Uniformity of Measurements 93847-24) is a polymer film made of polystyrene with sulfur addition and allows storing and transmitting a unit of Raman shift wavenumber for Raman scattering excitation wavelengths of 532, 633 and 785 nm.The possibility of using this measure for quantitative analysis of substances by measuring the intensity of Raman lines in instrument-independent units is considered. It was found that the use of the measure allows to determine the volume fraction of individual substances (ethanol) with relative random error less than 3 % and relative systematic error less than 6 %. To analyze multicomponent mixtures (alcohols, sugars) with the help of the measure, a multivariate calibration was constructed using the Partial Least Squares method. In this case, the volume fraction of components in an unknown sample was determined with a relative error not exceeding 15 %.The practical significance of the obtained study results allows to calibrate Raman microscopes and spectrometers on the Raman shift wavenumber scale, as well as to carry out quantitative analysis of individual substances and multicomponent systems using Raman spectroscopy.

The accuracy of determining the physical and chemical properties of a liquid, in particular, assessing the viscosity of the liquid used, is considered an important technical problem in medicine, food, oil, chemical industries, as well as in other areas that determine the quality and safety of human life and activity. For example, assessing the viscosity of the liquid used is a key stage in the design of hydraulic systems. Today, the improvement of methods for determining the viscosity of a liquid is on the path to automation (digitalization) of measurement instruments and methods. In this area, the activities of metrologists and engineers are consistent with the national program «Digital Economy of the Russian Federation» adopted in 2017. The article discusses the capillary method for determining the kinematic viscosity of a liquid as the most accurate of all possible methods at present. The method is based on determining the time of liquid flow between two marks, which are applied to the walls of a glass capillary viscometer forming a measuring tank. One of the main problems of this method is that all stages of measurement are performed by a person, even recording the moment when the liquid meniscus crosses the mark, which is a violation of one of the key principles of process automation – independence of execution, which only implies monitoring the operation of the system. Since ready-made solutions do not fit the laboratory’s measurement tasks, the management decided to develop and conduct a study of an information and measuring system that will carry out the process of detecting the liquid meniscus at the mark level, as well as recalculate the measured time interval into the kinematic viscosity value. The key decision in this development is the choice of a sensor for detecting the liquid meniscus. Based on the literature review, it was decided to use a photoelectric sensor. A study of the transmission spectra of liquids used in this method was conducted to select the wavelength at which the sensor will operate. Thus, a type of photoelectric sensor designed to operate in the UV range has been selected to automate the method of detecting the liquid meniscus when it crosses a mark applied to a capillary tube. The article is addressed to metrologists who perform verification and calibration of glass capillary viscometers, specialists in the field of experimental and theoretical viscometry. The method proposed by the authors can become the basis for further improvement of the method for measuring the kinematic viscosity of a liquid.

The issues of correspondence of the results of direct and indirect measurements of optical density in a narrow wavelength band are considered. The optical density in a narrow wavelength band was measured by filtering the luminous flux according to the international standard ISO 5-3:2009 “Photography and graphic technology – Density measurements. Part 3: Spectral conditions” (direct measurement) and spectral method (indirect measurement). In order to ensure the uniformity of optical density measurements in a narrow wavelength band and establish the traceability of measurement results to the State Primary Standard of optical density units GET 206-2016, the degree of conformity of the results obtained by two methods was investigated. The techniques of measuring optical density in a narrow wavelength band for each method are described. The method of fi ltering the luminous flux was implemented using GET 206-2016, namely using a complex for measuring diffuse optical transmittance density. The Cary 7000 spectrophotometer (Agilent, USA) was used to implement the spectral method. Data on measuring the optical density of glass light fi lters by two methods are presented. A method for correcting the results of spectral measurements has been developed and a correction to the results of spectral measurements has been determined. The developed method and the correction make it possible to establish the correspondence of the results of spectral measurements to the results of measurements by fi ltering the luminous fl ux. Also, the described method for correcting the results of spectral measurements makes it possible to establish the traceability of the results of optical density measurements by the spectral method to the measurement results using GET 206-2016.

The current state of metrological support for precision optical density measurements is described. In order to analyze the principles of building optical schemes, structural, constructive and functional features of the blocks included in the standards, and metrological characteristics of national standards of optical density units, high-precision optical density measuring instruments developed by national metrological institutes of Russia, Germany, China, and the USA are considered. The equations of optical density measurements are presented, which are a mathematical model of the process of measuring the optical transmittance density of materials. The principles of operation of optical transmittance density unit standards based on light fl fi ration are described. The data of studies of geometric and spectral characteristics of fi national standards of optical density units of four countries are presented, as well as optical schemes and characteristics of standards in the following areas are analyzed: compliance with international standards; features of optical schemes; methods of fi the luminous fl and creating scattered radiation; features of object positioning; type of radiation receiver; metrological characteristics. Information is provided on the participation of national standards in international comparisons. The metrological characteristics of these national standards are summarized in a table. Taking into account and using the considered features of optical schemes, design solutions in conjunction with the metrological characteristics of the described devices contributes to an increase in the level of development while improving the State primary standard of the unit of optical density GET 206-2016.