Modern Optical Methods Research Articles

Ultrastructural 3D Microscopy for Biomedicine: Principles, Applications, and Perspectives.

Modern biomedical research often requires a three-dimensional microscopic analysis of the ultrastructure of biological objects and materials. Conceptual technical and methodological solutions for three-dimensional structure reconstruction are needed to improve the conventional optical, electron, and probe microscopy methods, which to begin with allow one to obtain two-dimensional images and data. This review discusses the principles and potential applications of such techniques as serial section transmission electron microscopy; techniques based on scanning electron microscopy (SEM) (array tomography, focused ion beam SEM, and serial block-face SEM). 3D analysis techniques based on modern super-resolution optical microscopy methods are described (stochastic optical reconstruction microscopy and stimulated emission depletion microscopy), as well as ultrastructural 3D microscopy methods based on scanning probe microscopy and the feasibility of combining them with optical techniques. A comparative analysis of the advantages and shortcomings of the discussed approaches is performed.

Optical Methods for the Detection of Plant Pathogens and Diseases (Review)

Plant diseases of an infectious nature are the reason for major economic losses in agriculture throughout the world. The early, rapid and non-invasive detection of diseases and pathogens is critical for effective control. Optical diagnostic methods have a high speed of analysis and non-invasiveness. The review provides a general description of such methods and also discusses in more detail methods based on the scattering and absorption of light in the UV, Vis, IR and terahertz ranges, Raman scattering and LiDAR technologies. The application of optical methods to all parts of plants, to a large number of groups of pathogens, under various data collection conditions is considered. The review reveals the diversity and achievements of modern optical methods in detecting infectious plant diseases, their development trends and their future potential.

Optical methods for the management of progressive myopia

Introduction. Myopia is the main cause of preventable blindness and is widespread around the world at an alarming rate, especially in Asian countries. The age of the onset of myopia is getting younger. The prevalence of myopia and high myopia is sharply increasing, which requires clinicians to use new and safe methods of its stabilization. The main methods of correction are optical. This group is based on the hypothesis of induced peripheral myopic defocus.Aim: to study the domestic and international experience with the use of the optical methods in treatment of progressive myopia according to the literature and factors, as well as factors affecting their effectiveness.Materials and methods. More than 200 publications on PubMed, eLibrary, and Crossref Metadata over the past 10 years were analyzed. Our analysis includes a review of 60 publications.Results. Over the past years, there has been a strong interest of researchers in the problem of progressive myopia. This is reflected by a more than four-fold increase in the number of publications devoted to the causes and methods of treatment in patients with progressive myopia. Publications demonstrate the importance of using the modern optical methods, such as spectacle lenses, multifocal and bifocal soft contact lenses and orthokeratology in the routine practice of ophthalmologists and optometrists in order to stabilize the progression of myopia in children and adolescents. On the one hand, the results of analysis show their high efficiency. On the other hand, we need an individual approach in choosing the method for myopia control in each specific case. The factors influencing the result are identified: the diameter of the optical zone, the force of addition that creates the peripheral myopic defocus and the time of use myopia correction during the day.Conclusion. No method of treating progressive myopia demonstrates clear superiority. Orthokeratology, multifocal and bifocal soft contact lenses, special glasses and low doses atropine instillation demonstrates the similar effect with some clauses. When choosing optical methods for myopia control, the factors affecting their effectiveness should be taken into account.

Unusual phase transition in 1D localization and its observability in optics

Localization of electrons in 1D disordered systems is usually described in the random phase approximation, when distributions of phases φ and θ, entering the transfer matrix, are considered as uniform. In the general case, the random phase approximation is violated, and the evolution equations are written in terms of the Landauer resistance ρ and the combined phases ψ = θ − φ and χ = θ + φ. The distribution of the phase ψ is found to exhibit an unusual phase transition at the point when changing the electron energy , which manifests itself in the appearance of the imaginary part of ψ. The distribution of resistance P(ρ) has no singularity at the point , and the transition seems unobservable in the framework of condensed matter physics. However, the theory of 1D localization is immediately applicable to the scattering of waves propagating in a single-mode optical waveguide. Modern optical methods open a way to measure phases ψ and χ. As a result, the indicated phase transition becomes observable.

Comparative study of LDA and PIV methods for flow homogeneity measurements

Abstract In the Hydraulic Laboratory of the Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava the distribution of the flow velocity in a shaft intake structure was investigated on a physical model. The homogeneity of the flow velocity distribution in the intakes of turbines has a great influence on the turbine performance. Modern optical methods, particle image velocimetry and laser Doppler anemometry, were used to measure the flow velocity distribution in the model of the turbine intake. The particle image velocimetry method provides a record of the velocity field, while the laser Doppler anemometry method provides an accurate indication of the velocity at a given point. The flow velocity distributions in the examined profiles were measured by the particle image velocimetry and laser Doppler anemometry methods and the results were compared with each other.

Surgically induced astigmatism after cataract surgery – a vector analysis

Background: Surgically induced astigmatism (SIA) has been widely discussed in the literature as the change in corneal astigmatism resulting from corneal incision. The purpose of this study was to investigate the change in corneal refractive power preoperative to postoperative using a vector analysis of keratometry, total keratometry, and corneal back surface data from a modern optical biometer Methods: The analysis was based on a dataset of 122 eyes of 122 patients with preoperative and 1 month postoperative measurements performed with the IOLMaster 700 biometer from 1 clinical centre and a standardised surgical technique involving a corneal 2.5 mm 45°-incision made from the superior direction. Keratometry, total keratometry and corneal back surface data were processed in 3 vector components (spherical equivalent power SEQ and astigmatism considered in 0°/90° (C0°) and in 45°/135° (C45°) meridian), and the changes in corneal power vectors were analysed, comparing preoperative to postoperative values. Results: The mean corneal power of total keratometry reduced slightly after cataract surgery (-0.05 dpt), resulting mostly from a decrease in back surface power (-0.04 dpt). The astigmatism vector component C0° of total keratometry reduced by -0.28 dpt, mostly due to a decrease at the corneal front surface (-0.26 dpt). With the corneal incision at 12 o’clock position this flattening in the 90° meridian refers to a SIA of around ¼ dpt. The change in C0° and the C45° astigmatic vector components for both keratometry and total keratometry show a large variation ranging between 0.24 and 0.33 dpt (standard deviations), indicating a poor predictability of the change in astigmatism due to cataract surgery. Conclusion: Cataract surgery locally flattens the cornea in the incision meridian. This flattening shows a large individual variation and therefore a poor predictability. Our study indicates that SIA in modern cataract surgery with standardised corneal incision is in a range of 1/4 dpt.

Selective behavioral response of Trichoplax (Placozoa) to RGB-light stimuli

Introduction. The marine animal Trichoplax (Placozoa), which has the animalcular organization among invertebrates, but with outstanding social behaviour and specific movement of the body and its cells, is a model animal for studying various biophysical and chemical processes, including responses to external stimuli. In the articles of specialists from many universities, the problem of Trichoplax phototaxis (Placozoa) is covered in a hypothetical and declarative form. However, there are no specific studies on the behavioural response of these protozoa and their cells to monochrome light signals with different wavelengths that are characteristic of its light habitat at a depth of 5 to 20 meters. Materials and methods. The studies were conducted on laboratory animals Trichoplax sp. H2. Studies of the behavioural response of Trichoplax were performed using modern methods of optical microscopy: Nikon Eclipse Ts2R-Fl Optical Microscope; optical microscopes: Nikon SMZ-1270, Stemi 305; An optical microscope “Leonardo 3.0“(specially designed for the project) allows simultaneously observing the behaviour of a group of Trichoplax and each Trichoplax of this group at a low level of illumination and a stable temperature of its aquatic habitat. Two web cameras were used in the microscope-the upper one with a 1.9 Mp matrix and the lower one - 5 Mp). Results. The theoretical analysis of the spectral composition of light and the degree of its polarization in the marine habitat of the protozoan multicellular animal Trichoplax (Placozoa) and the features of its gene-cell structure is carried out. Based on the laws of hydrooptics and the survival strategy (“food-prey”), the coordinate axes of the light-medium for Trichoplax are determined (the light vertical (395 nm) and two horizontal light axes - the reflected horizontal light from the food (green - 532 nm) and the fluorescent light coming from the aragonite shell of the predator mollusc (red - 630 nm). Based on the animal’s responses to these RGB light stimuli, the hypothesis of RGB phototaxis in Trichoplax and the kinesis of its cells was expressed and confirmed. The monochrome light signals red - 630 nm, green - 532 nm and blue - 395 nm are selected for Trichoplax control. Limitations of the study. In the study of Trichoplax (Placozoa), the behavioural response of this animal and its cells to monochrome light signals with different wavelengths was studied using modern optical microscopy methods, which make it possible to simultaneously observe the behaviour of both the Trichoplax group and each animal of this group at a low level of illumination and stable temperature of its aquatic environment. Conclusion. For the first time, the behaviour of Trichoplax and its cells was controlled using light signals, and the presence of RGB phototaxis and kinesis in its cells was also proved in Trichoplax. The discovery of the RGB-taxis Trichoplax (Placozoa) changed the established scientific ideas in the evolution of colour vision in animals Trichoplax (Placozoa) and the human visual analyzer functioning of its pineal gland. The presented method can be used in hygienic studies of the influence of external pollutants on the environment and the effect of light on the human pineal gland.

Survey of experimental channels employed on investigation of a non-isothermal laminar flow and design requirements for a new experiment

In this article, a literature survey of the experimental channels used for investigation of a non-isothermal flow is presented. Particular interest is focused on the flow stability with a heated wall by a uniform heat flux. The aim of this work is to prepare a comprehensive overview of the technical design and experimental settings used in previous studies. Collected information shall help to design and manufacture new horizontal channel with a rectangular cross-section with a width of around 200 mm and a height of 20 mm. The channel will be equipped with a constant heat flux section on a bottom wall for investigation of the vortex structures and the flow instabilities using modern optical methods. The channel will operate with liquid (most probably water) in the range of low Reynolds numbers. Parallel laminar flow with Poiseuille velocity profile at the inlet of a heated section and a uniform heat flux predefine the essential requirements on the channel design.

Direct imaging of single-molecule electrochemical reactions in solution.

Chemical reactions tend to be conceptualized in terms of individual molecules transforming into products, but are usually observed in experiments that probe the average behaviour of the ensemble. Single-molecule methods move beyond ensemble averages and reveal the statistical distribution of reaction positions, pathways and dynamics1-3. This has been shown with optical traps and scanning probe microscopy manipulating and observing individual reactions at defined locations with high spatial resolution4,5, and with modern optical methods using ultrasensitive photodetectors3,6,7 that enable high-throughput single-molecule measurements. However, effective probing of single-molecule solution chemistry remains challenging. Here we demonstrate optical imaging of single-molecule electrochemical reactions7 in aqueous solution and its use for super-resolution microscopy. The method utilizes a chemiluminescent reaction involving a ruthenium complex electrochemically generated at an electrode8, which ensures minimal background signal. This allows us to directly capture single photons of the electrochemiluminescence of individual reactions, and to develop super-resolved electrochemiluminescence microscopy for imaging the adhesion dynamics of live cells with high spatiotemporal resolution. We anticipate that our method will advance the fundamental understanding of electrochemical reactions and prove useful for bioassays and cell-imaging applications.

Studies on the influence of speckle density on the accuracy of digital image correlation method based on numerical simulation

Digital image correlation method is a high-precision non-contact modern optical mechanics method whose measurement accuracy is directly affected by the quality of the speckle pattern used. In this paper, a numerical simulation experiment is designed to measure and analyze the accuracy of DIC method using speckle patterns which are generated with different speckle densities. The results show that the measurement error of DIC decreases first and then increases with the increase of speckle density, and the error is minimum when the duty ratio is about 60% to 70%. The result show that in practical application the duty ratio of speckle on the specimen surface should be appropriately high, preferably between 60% and 70%. This study is helpful for speckle selection and related research in practical application.

Современные методы оценки термоокислительной стабильности реактивных топлив в динамических условиях и перспективы их развития

The article discusses methods for assessing the thermal bonding stability (TOC) of jet fuels. The importance of determining this indicator for the design and operation of modern and advanced aircraft was noted. It is indicated that the methods used for assessing TOC are indirect, which limits their accuracy and reliability. The article gives the author's expert assessment of the correlation of the method indicators with the operational properties of fuels. Promising areas for the development of methods for measuring the amount of deposits include modern optical research methods: spectroscopic reflectometry, laser ellipsometry, as well as direct measurement of micro-amounts of deposits on control elements.

The Influence of Aggregate Microstructure on Tailings Behaviour

Conventional constitutive soil models applied in geotechnical engineering have been developed using the phenomenological approach from macroscopic observations and application of continuum mechanics. Despite the adopted simplification and homogenisation of complex interactions of soil particles, water and air, the phenomenological models and the underlying principles have been proven to satisfactorily describe the stress-strain conditions in most common soils. However, the application of the conventional soil behaviour models has been proven to be difficult in the mining industry and tailings storage facilities in particular, where the structural integrity of the storage facilities often depends on the performance of extensively altered materials (tailings) that are produced as a waste product from ore processing. The difficulties stem from the altered nature of the tailings and the inconsistencies in the tailings deposition, which may result in the formation of porous and brittle matrices of heterogeneous aggregates. Such matrices are susceptible to static and dynamic liquefaction whereby little changes in the stress-strain conditions can result in a sudden collapse of the soil structure. Sampling and preservation of intact delicate tailings is often unachievable, and the analyses of the laboratory tests are obscured by the simplifications, assumed homogenisation of the sample and the inherent influence of the testing apparatus on the measured properties. Therefore, the characterisation of the in situ conditions of the tailings and the prediction of the tailings performance for altering stress-strain conditions using conventional soil behaviour models is very difficult. Yet, understanding the delicate state of the brittle tailings is crucial for upstream and centrally raised tailings storage facilities. This is exemplified by the facility failures which featured devastating consequences in Brazil in 2015 and 2019. These failures were caused by liquefaction of tailings, which acted as foundations for the upstream raised embankments. This paper discusses the influence of the tailings micro-structure on the macroscopically observed behaviour. This paper also shows that, using modern optical and other testing methods, the micro-structure can be measured and then allowed for in the soil behaviour model with the aim to improve the reliability of tailings liquefaction assessment.

Utilization of Modern Optical Methods for Creation of Digital Model of Human

The aim of the paper is to describe the methodology of creating a digital model of human using an optical 3D scanner. This methodology consists of several main phases, such as preparing the scan for human movement, scanning in the shortest possible time, and processing the data obtained by scanning. The data processing itself is divided into other sub-phases, which describe the individual steps necessary to create a digital model. The paper describes obstacles that need to be eliminated or minimized during 3D scanning in order not to disrupt the integrity of the model and to create a digital model.

Effect of the mixture initial temperature on the velocity field in the swirling flame

The paper presents the results of an experimental study of the flow structure of a turbulent swirling flame of a methane-air and syngas-air mixture at elevated temperature using modern optical methods PIV (Particle Image Velocimetry) and PLIF (Planar Laser-Induced Fluorescence). A comparison of the averaged flow characteristics of a high-swirl flame with an equivalence ratio Φ = 0.45 for syngas-air and Φ = 0.7 for methane-air mixture are performed with preheating the mixture to a temperature of 300, 400 and 500 K. The distribution of the fluorescence signal showed that the longitudinal size of the region of hot combustion products decreases significantly with increasing temperature of the mixture for both syngas-air and methane-air flames. For the flame of a mixture of methane-air and syngas-air heated to a temperature of 500 K, the size of the recirculation zone and velocity pulsation distribution are very similar, in contrast to a methane flame at lower preheating temperatures of the mixture.

Experimental approbation of methodological and hardware-software speck-visualization in diagnosis of microcirculation of human surface biological tissues

In modern clinical practice, the assessment of the state of blood microcirculation and the diagnosis of microcirculatory disorders are extremely relevant in a variety of diseases: in cardiology, diabetology, oncology, dermatology, dentistry, surgery and resuscitation. Microcirculatory disorders are very diverse both in their pathogenesis and in clinical manifestations. Therefore, in the pattern of various diseases and extreme conditions, as well as in the correction of microcirculatory disorders the methods are needed for both operative assessment of the state of blood flow at tissue level and for its long-term monitoring. The interest in the study of the microvascular bed of the circulatory system is sparked by the significant role of capillaries in the implementation of the basic processes of the body's vital activity, in the trophic support of organs and their direct participation in tissue and cellular respiration. The health and life expectancy of a person depend on the coordinated work of the heart, large blood lines, and microcirculation vessels. The authors have studied modern optical methods for diagnosing microcirculation. The feasibility of using the speckle imaging method for noninvasive rapid assessment of the state of the microvasculature of human surface biological tissues has been substantiated. To implement the speckle-visualization method, methodological and software have been developed. The processing parameters that are most optimal from the point of view of the ratio of spatiotemporal resolution and computation time have been experimentally substantiated. The purpose of this work is the experimental testing of the developed methodological and hardware speckle imaging for the diagnosis of microcirculation of human surface biological tissues. The authors have carried out the studies of the state of microcirculation in the superficial blood vessels of the skin during physiotherapeutic procedures and in the imitation of pathology. The results of the studies have proved the feasibility of using the developed software for a high-quality diagnosis of the state of microcirculation of human surface biological tissues: primary changes in microcirculation are revealed, further changes to occur during physiotherapeutic procedures are visualized.

Development of the Device with a High Positioning Accuracy Serving for Residual Stress Quantification using Optical Methods

The paper describes some procedures required for functional verification of a newly designed unique positioning device developed to quantify residual stresses by modern optical methods with a combination of the hole-drilling method based on ASTM-E 837-13a American standard. The high precision of milling a circular groove or a hole belongs to essential requirements for achieving relevant results in the quantification of residual stresses using semi-destructive methods. At the beginning of the paper, the mechanical parts of the developed drilling device are briefly described. Subsequently, two analyses were realized and present in the paper. While the first one verifies the possibilities and accuracy of the cutter positioning in the vertical direction, the second one is focused on the investigation of the milled groove circularity. The results of both analyses are processed tabularly and prove the possibility to use the drilling device in residual stress analysis.

Modern optical methods of peripheral defocus correction

Experimental animal studies proved that by manipulating with the defocus one can slow down or speed up the eye growth. The leading mechanism among modern optical strategies of myopia progression treatment is to induce myopic defocus to retinal periphery or decrease the hyperopic defocus. This review sums up the data on peripheral refraction in orthokeratological, multifocal contact, and multifocal spectacle correction. The effectiveness of these methods in myopia control in children and teenagers is shown.

Structure of a reacting flow of a turbulent swirling jet during combustion of a syngas–air mixture

The paper presents the results of an experimental study of the flow structure and features of combustion in a turbulent swirling lean pre-mixed syngas flame using modern planar optical laser-based methods. The measurement of the instantaneous velocity field was carried out using the particle image velocimetry (PIV), and location of the OH radicals in the jet were determined by the method of laser-induced fluorescence (PLIF). A comparison of the averaged flow characteristics of a high-swirl flame with an equivalence ratio Φ = 0.45 for syngas and Φ = 0.7 for methane are performed. Presence of a recirculation zone in the jet core is typical of both cases, however, the size of the central recirculation zone for the methane flame are approximately 1.5 times larger than that for the synthesis gas flame in both dimensions. The average distributions of the intensity of fluorescence signal of the OH radical shows a good coincidence of the position of the flame front in both cases, and lower fluorescence signal intensity for the synthesis gas flame.

Study of liquid hydrocarbons atomization by supersonic air or steam jet

In this work, the gas-drop two-phase flow characteristics in a perspective atomizing burner were measured with respect to operating conditions. The liquid fuel (diesel fuel and waste engine oil) was sprayed by a superheated steam or air jet. Data on the main parameters of such a gas-fuel jet (dispersed composition, carrier and dispersed phase velocity, jet opening angle) were obtained for various operating conditions (steam/air and fuel temperatures and flow rates) using modern optical flow diagnostics methods (SP, IPI, PIV, PTV). The flow structure, characteristic of a supersonic submerged jet with an opening angle of 20°, was registered near the nozzle. Characteristic diameter of the identified drops in all investigated modes is 10–20 µm, which is sufficient for efficient fuel combustion that proves the advantages of the investigated method of liquid fuel atomization. It has been established that operating conditions (such as gas or fuel temperature and fuel rates, ratio of flow rates) in the studied range slightly affects the change in the droplet size distribution. The research results showed that the size distribution of fuel droplets depends weakly on the choice of atomizing phase (steam or air).

Development of a metrology technique suitable for in situ measurement and corrective manufacturing of freeform optics

Abstract The applications of freeform optical surfaces in modern optical systems are providing unique solutions over rotationally symmetric surfaces. These surfaces offer higher degrees of freedom to the designer to enhance the high-end performance of the optical system. The precise metrology of freeform optics is one of the major bottlenecks for its use in imaging applications. Modern optical fabrication methods (i.e. fast or slow tool servo configuration) are, in principle, capable to meet the challenges to generate complex freeform surfaces if supported by precise metrology feedback for error compensation. In the present work, we have developed a Shack-Hartmann sensor-based metrology technique that can be used for quantitative in situ measurement of freeform optics. The sensor head is used to measure freeform optics in the reflection mode by following the CNC tool path in the offline mode. The measurements are used as feedback for corrective machining. Quantitative analysis is also performed to estimate the error budget of the metrology system. Further, the proposed in situ metrology scheme is validated by measuring freeform surface using a coherence correlation interferometric optical profiler.