Optical Diagnostic Methods Research Articles

Detecting Plant Infections: Prospects for Chlorophyll Fluorescence Imaging

Phytopathogens are a significant challenge to agriculture and food security. In this regard, methods for the early diagnosis of plant diseases, including optical methods, are being actively developed. This review focuses on one of the optical diagnostic methods, chlorophyll fluorescence (ChlF) imaging. ChlF reflects the activity of photosynthetic processes and responds subtly to environmental factors, which makes it an excellent tool for the early detection of stressors, including the detection of pathogens at a pre-symptomatic stage of disease. In this review, we analyze the peculiarities of changes in ChlF parameters depending on the type of pathogen (viral, bacterial, or fungal infection), the terms of disease progression, and its severity. The main mechanisms responsible for the changes in ChlF parameters during the interaction between pathogen and host plant are also summarized. We discuss the advantages and limitations of ChlF imaging in pathogen detection compared to other optical methods and ways to improve the sensitivity of ChlF imaging in the early detection of pathogens.

Detection of Nickel Atoms Released from Electrodes in Spark Discharges Using Laser-Induced Fluorescence.

The reduction of greenhouse gas emissions and the effort of carbon neutrality require the improvement of spark-ignition engines in terms of efficiency and capability to operate on renewable fuels. The electrode wear of spark plugs, used for ignition of novel fuels and lean mixtures, emerges as a significant challenge in this transition. Understanding the physical mechanism and influence of spark operation parameters of the wear process is thus important. Compared to the conventional methodology of performing long-term wear tests, laser-based optical diagnostics methods are capable of assessing electrode wear during one single or a few spark discharges. In this work, the necessary initial steps required for performing optical investigations using laser-induced fluorescence (LIF) are presented. Several excitation pathways of nickel atoms were investigated, and 336.96 nm was identified as the optimal one. This excitation approach yielded emissions between 338.75 and 353.58 nm, effectively avoiding the major interference from N2 plasma emission in spark discharges. Additionally, a linear relationship in fluorescence signal intensity with excitation energy up to 400 µJ was observed. These findings indicate the potential of LIF for in situ diagnostics of electrode wear, contributing to engine development in both efficiency and compatibility with sustainable fuels.

First spectroscopic studies in the plasma-beam installation

This paper presents the results of spectroscopic measurements of plasma in a linear simulator of a plasma-beam installation (PBI) for conducting materials science research. For the first time, non-contact optical diagnostic methods were employed to measure the plasma parameters in the PBI. These measurements were allowed for the clarification of the PBI plasma parameters and the identification of transition zones in different operational modes. Analysis of the plasma emission spectrum enabled the identification of impurity spectral lines and the estimation of key plasma parameters under varying experimental conditions. The spectra were recorded using two optical spectrometers covering a wavelength range of 200–800 nm. The experimental conditions varied in terms of electron beam accelerating voltage (1–5 kV), working gas pressure (1–6 mTorr), and target bias voltage (from −500 to −100 V). The Boltzmann plot method and Stark broadening of the Balmer lines were used to estimate electron temperature and density. Based on the obtained spectroscopic data, the electron density and the electron temperature were determined. The methods described in this study are applicable to linear plasma devices.

Estimation of the Global Equivalence Ratio of a Swirl Combustor from a Small Number of Absorption Spectra Using Machine Learning.

A new optical diagnostic method that predicts the global fuel-air equivalence ratio of a swirl combustor using absorption spectra from only three optical paths is proposed here. Under normal operation, the global equivalence ratio and total flow rate determine the temperature and concentration fields of the combustor, which subsequently determine the absorption spectra of any combustion species. Therefore, spectra, as the fingerprint for a produced combustion field, were employed to predict the global equivalence ratio, one of the key operational parameters, in this study. Specifically, absorption spectra of water vapor at wavenumbers around 7444.36, 7185.6, and 6805.6 cm-1 measured at three different downstream locations of the combustor were used to predict the global equivalence ratio. As it is difficult to find analytical relationships between the spectra and produced combustion fields, a predictive model was a data-driven acquisition. The absorption spectra as an input were first feature-extracted through stacked convolutional autoencoders and then a dense neural network was used for regression prediction between the feature scores and the global equivalence ratio. The model could predict the equivalence ratio with an absolute error of ±0.025 with a probability of 96%, and a gradient-weighted regression activation mapping analysis revealed that the model leverages not only the peak intensities but also the variations in the shape of absorption lines for its predictions.

Optical study of combustion stability in dual fuel approach using ammonia and high reactivity fuel

Ammonia, as a zero-carbon fuel, is considered to be an ideal alternative fuel for a reduction of carbon dioxide emissions. Owing to low laminar flame speed and high ignition energy, the utilization of pure ammonia in powerplant system still presents severe challenges. To solve these issues, the dual fuel combustion of high reactivity fuel and ammonia is a promising solution. However, the dual fuel combustion stability of ammonia and high reactivity fuel has not been clearly understood. In present study, the misfire reasons are investigated using various optical diagnostic methods. Results demonstrate that the misfire reasons are divided into two aspects. One is that the addition of ammonia increases the temperature and pressure required for direction injection fuel auto-ignition, which makes it difficult to generate auto-ignition site, resulting in misfire. The other is that the low flame development speed and degradation of the in-cylinder temperature and pressure causes the difficulty in the further flame development, which results in misfire. A collaborative regulation approach of engine operating condition and direction injection fuel reactivity is proposed to improve combustion stability, which achieves 93% ammonia energy ratio. At 93% ammonia energy ratio, increasing direction injection pressure from 600 bar to 1000 bar decrease combustion stability. The local equivalence ratio of direction injection fuel that can ignite ammonia stably is mainly concentrated between 0.56 and 0.86 in the conditions of 93% ammonia energy ratio and 22 bar in-cylinder pressure. Compared with the in-cylinder temperature, the main factor in determining combustion stability is local equivalence ratio of direction injection fuel. The addition of ammonia prolongs the low temperature reaction and constrains the high temperature reaction of direction injection fuel. In brief, the combustion stability and ammonia energy ratio can be improved simultaneously using the collaborative regulation.

Development of a biotechnical system for intraoperative diagnosis of perfusion and metabolic parameters of biological tissues during minimally invasive surgical interventions

The development of modern technologies, tendencies to reduce traumatization and extent of surgical interventions have created conditions for intensive implementation and widespread use of minimally invasive surgery (MIS). For all their advantages, MIS interventions have a number of peculiarities, primarily related to limited access to the organ. This drives the need to improve and expand the range of technologies used in MIS to provide additional diagnostic information about the functional state of biological tissues. The indications for MIS interventions are very broad, but from the pathophysiological point of view, many diseases, syndromes and conditions can be described in terms of unified disorders of perfusion and metabolic parameters of biological tissues. There is no alternative to optical diagnostic methods for the determination of perfusion and metabolic parameters of biological tissues in vivo, thus making it possible to obtain additional diagnostic information in MIS practice. In particular, diffuse reflectance spectroscopy is used to measure the absorption and scattering properties of optically inhomogeneous media, such as biological tissues, and to estimate their structural and biochemical properties. Fluorescence spectroscopy is based on the registration of the autofluorescence of biological tissues when excited by optical radiation. Most endogenous fluorophores are related to the structure or to various metabolic processes responsible for the functional state of biological tissues. The main method of studying blood microcirculation is laser Doppler flowmetry – a technology based on the analysis of laser radiation reflected from the surface layer of biological tissues. Another method for assessing perfusion disorders in clinical medicine is laser speckle contrast imaging, which is based on the registration of a random interference pattern that is formed on a camera detector when an object is illuminated by coherent laser radiation. The aim of the study is to develop a biotechnical system (BTS) for intraoperative diagnostics of perfusion and metabolic parameters of biological tissues during MIS interventions based on optical diagnostic methods, which enables surgeons to obtain additional diagnostic information about the state of operated organs and tissues in real time. To achieve this goal, the possibility of assessing perfusion and metabolic disorders of biological tissues using optical diagnostic methods was scientifically substantiated. A formalized scheme of BTS for intraoperative diagnostics of perfusion and metabolic parameters of biological tissues was developed. Fiber optic probes of different designs compatible with instruments for MIS interventions were described. An example of the implementation of intraoperative optical diagnostics in gynecology based on the developed BTS is presented. A study of changes in the perfusion and metabolic characteristics of the myometrium, myoma, and pseudocapsule during myomectomy is described. It is shown that the pseudocapsule is better supplied with blood than the myoma and the myometrium, confirming the data that this structure is a vascular capsule that surrounds and nourishes the myoma. The use of modern methods of optical diagnostics based on the analysis of the interaction of optical radiation with biological tissues, together with the integration of optical technologies into modern surgical equipment, is the next technological innovation in the era of MIS development. The proposed and described methodology of building BTS of intraoperative diagnostics of perfusion and metabolic parameters of biological tissues is the basis for creating new-generation medical systems, which provide the possibility of obtaining reliable diagnostic data in conditions of limited access to biological tissues associated with the specifics of MIS interventions and allow to improve the quality and safety of surgical care.

A novel state-resolved actinometry method to determine the nitrogen atom number density in the ground state and intra-shell excited states in low-pressure electron cyclotron resonance plasmas

The active-particle number density is a key parameter for plasma material processing, space propulsion, and plasma-assisted combustion. The traditional actinometry method focuses on measuring the density of the atoms in the ground state, but there is a lack of an effective optical emission spectroscopy method to measure intra-shell excited-state densities. The latter atoms have chemical selectivity and higher energy, and they can easily change the material morphology as well as the ionization and combustion paths. In this work, we present a novel state-resolved actinometry (SRA) method, supported by a krypton line-ratio method for the electron temperature and density, to measure the number densities of nitrogen atoms in the ground and intra-shell excited states. The SRA method is based on a collisional-radiative model, considering the kinetics of atomic nitrogen and krypton including their excited states. The densities measured by our method are compared with those obtained from a dissociative model in a miniature electron cyclotron resonance (ECR) plasma source. Furthermore, the saturation effect, in which the electron density remains constant due to the microwave propagation in an ECR plasma once the power reaches a certain value, is used to verify the electron density measured by the line-ratio method. An ionization balance model is also presented to examine the measured electron temperature. All the values obtained with the different methods are in good agreement with each other, and hence a set of verified rate coefficient data used in our method can be provided. A novel concept, the ‘excited-state system’, is presented to quickly build an optical diagnostic method based on the analysis of quantum number propensity and selection rules.

Impacts of flash boiling plume interactions on atomization evaluated using two-dimensional optical slit nozzles

Flash boiling atomization is a promising approach for liquid fuel energy conversion purposes, especially for alternative fuels and zero-carbon fuels. However, the fundamental mechanisms of flash boiling atomization is quite different from typical sub-cooled atomization both in the primary breakup mechanisms and plume interference principles. This work aims to investigate the spray plume interaction impacts under flash boiling injection schemes. To reduce the complexity in handling the dense spray regime for practical spray injectors, two-dimensional slit nozzles created by quartz blocks and thin channels are employed. Divergent, straight, and converge nozzles are designed and examined to evaluate the impact of nozzle design under the same thermodynamic conditions. Nozzles with a 2D expansion cavity are also tested to further reduce the optical depth in the observation direction. Various optical diagnostics methods including backlit measurement, phase Doppler interferometry, and the optical flow method are used to investigate different characteristics of the resultant superheat flows from different perspective. The experimental investigations reveal the interference mechanism of the two-plume nozzle with the increment of fuel temperature, as well as its impacts on atomization efficiency from the perspective of droplet sizes.

Exploring approaches to pulp vitality assessment: A scoping review of nontraditional methods.

Diagnostic procedures for pulp vitality assessment are a crucial aspect of routine dental practice. This review aims to provide a comprehensive overview of nontraditional techniques and methodologies for assessing pulp vitality, specifically exploring promising approaches that are currently not used in dental practice. The study protocol was registered a priori (https://osf.io/3m97z/). An extensive electronic search was conducted across multiple databases, including MEDLINE via PubMed, Scopus, Web of Science, and Embase. Inclusion criteria were guided by the research question based on the PCC model as follows: "What are the potential nontraditional techniques (Concept) for assessing pulp vitality (Population) in the field of endodontics or clinical practice (Context)?" Studies were included that explored possible approaches to pulp vitality assessment, utilizing a range of techniques, whilst any studies using traditional pulp tests (cold, heat, and electric stimulation) or well-known methods (pulse oximetry and laser Doppler flowmetry) were excluded. Reviewers independently screened articles and extracted data. A patent search was also performed. Of 3062 studies, 65 were included that described nontraditional approaches for assessing pulp vitality. These included a range of optical diagnostic methods, ultrasound Doppler flowmetry (UDF), magnetic resonance imaging (MRI), terahertz imaging, tooth temperature measurements, as well as invasive methodologies, including 133xenon washout, radioisotope-labelled tracers, hydrogen gas desaturation, intravital microscopy and fluorescent microspheres isotope clearance. The patent search included artificial intelligence and biomarkers methods. This review provides details for potential innovative tests that may directly describe pulp vitality. Importantly, these methods range from clinically impractical through to promising methods that may transform clinical practice. Several nontraditional techniques have the potential to enhance diagnostic accuracy and could provide valuable insights into the assessment of pulp vitality in challenging clinical scenarios.

Fluorescence spectral analysis and logistic regression modeling for diagnosing basal cell carcinoma on head and neck

The optical fluorescence method is distinguished by key features such as non-invasiveness, high sensitivity, and resolution, which are superior to traditional diagnostic approaches. Unlike histopathological examinations and biochemical analyses, optical diagnostic methods obviate the need for tissue sampling, enabling the analysis of virtually unlimited material.The research aims to examine the effectiveness of emission spectra analysis in the diagnosis of basal cell carcinoma (BCC) of the scalp and neck. The analysis was based on data provided by Specialized Hospital No. 2 in Bytom comprising a study sample of 10 patients. For each patient, fluorescence emission spectra were recorded from each of 512 points along a 5 mm line.The results obtained from the histopathological examination, the analysis and morphological evaluation of the tissue, and the diagnosis through microscopic observation were used to define a dichotomous variable (presence or absence of a cancerous lesion), adopted in the study as the modeled variable. The next step of the presented study involved constructing a logistic regression model for identifying cancerous lesions depending on the biochemical indicator's relative fluorescence value (RFV) and emission wavelength (ELW) within the 620 nm to 730 nm range. This wavelength range is often used in fluorescence diagnostics to detect various pathologies, including cancerous lesions.The resulting binary logistic regression model, logit(p)=−33.17+0.04ELW+0.01RFV, indicates a statistically significant relationship between wavelength and relative fluorescence values with the probability of detecting cancer. The estimated model exhibits a good fit and high predictive accuracy. The overall model accuracy is 84.8 %, with the correct classification rates at approximately 96 % for healthy individuals and 74 % for individuals with cancer. These findings underscore the potential of photodynamic diagnostics in cancer detection and monitoring.

Modern diagnostic technologies in oncodermatology

Skin tumors occupy the first place in terms of incidence in the structure of oncological neoplasms. The WHO estimates that 60,000 people die each year from malignant neoplasms of the skin: 48,000 from melanoma and 12,000 from skin cancer. Timely diagnosis of skin cancer makes it possible to achieve a cure for cancer patients with long periods of relapse-free follow-up after the completion of specialized treatment. The introduction of high-tech optical methods for diagnosing skin neoplasms into clinical practice has significantly increased the specificity, sensitivity, and accuracy of diagnostics. The review is devoted to a discussion of such methods for diagnosing skin neoplasms as fluorescent diagnostics, digital dermatoscopy, SIA-scopy, and confocal microscopy. The features of the application of each of the methods are discussed, the results of the most significant Russian and foreign studies in this field are presented, as well as our own results of the practical application of a number of high-tech optical diagnostic methods at the P.A. Herzen Moscow Oncology Research Center

Investigation of small-fraction molecular impurities in high-pressure helium plasmas using optical plasma diagnostic methods

In high-pressure plasmas using gases diluted via a rare gas, small-fraction impurities in the discharge space significantly impact the basic plasma parameters and excited-species generation processes. This study investigated the behaviors of molecular impurities in a dielectric barrier discharge (DBD) generated in a flow of high-purity He gas using optical plasma diagnostic methods. The optical emission spectra obtained under various discharge conditions (pressure, flow rate, and voltage frequency) indicated that the major impurity species in the He DBD was the H2O molecule, and the DBD decomposed the H2O before reaching the measurement spot. To quantitatively analyze the H2O fraction, time-resolved laser absorption spectroscopy was performed to measure the exponential decay time of He metastable (Hem) atoms in the He-DBD. The H2O fraction in the He gas flow was derived from the dependence of Hem lifetime decay on the voltage frequency. In addition, a model was proposed to estimate the H2O fraction under various He pressure and flow rate conditions from reference data. The procedures to perform optical plasma diagnostics and evaluate the fraction and behavior of H2O impurities are expected to facilitate a better understanding and control of high-pressure plasmas.

The Predicting the Value of Local Individual Minimal Erythema Dose without Test Ultraviolet Irradiation

The article substantiates the need for a prognostic approach and formulates the problem to assessing minimal erythema dose (MED) in dermatology without UV test exposure. Arguments are given in favor of using a number of optical non-invasive diagnostic methods for this purpose. The photosensitivity of human skin to ultraviolet radiation is determined by its optical and morphological parameters, as well as the reactivity of the skin microvasculature. These values can be determined before treatment; therefore, it is theoretically possible to predict an individual MED for healthy and psoriasis-affected skin. The article substantiates possible methods and approaches for solving this problem, proposes an optical model of the skin, and describes the proposed research protocol.

HYBRID MINIMALLY INVASIVE TECHNOLOGIES IN DIAGNOSING AND ASSESSING THE PROGNOSIS FOR THE COURSE OF THE DISEASE IN PATIENTS WITH BREAST CANCER: PUNCTURE-NEEDLE BIOPSY USING OZONE-OXYGEN MIXTURE AND TISSUE SPECTROPHOTOMETRY TECHNIQUE

Breast cancer is the most common malignant disease in women worldwide. According to the World Health Organization and the International Agency for Research on Cancer, it accounts for 25.1% of all cancer cases in women. Intracystic breast cancer is one of the most rare and difficult to diagnose forms of this disease. Due to this improving existing methods of breast cancer diagnosis and developing new ways for the early detection of this pathology are of great importance. The aim of the study is to evaluate the effectiveness of new methods for breast cancer diagnosis – an improved technique of puncture–needle biopsy under ultrasound control and a hybrid technology for assessing the local metabolism of mammary tumors. Materials and methods. The article presents the results of examining 67 female patients with intracystic breast cancer using the traditional technique of puncture-needle biopsy and a new method of cytological diagnosis of this disease. The article presents the pilot results of using the hybrid technology for evaluating local metabolism of mammary gland tumors in 22 patients with suspected breast cancer to clarify the diagnosis and assess the prognosis using optical diagnostic methods: fluorescence spectroscopy (at wavelengths of fluorescence excitation of 365 and 450 nm) and diffuse reflectance spectroscopy (with a source of polychromatic radiation). Results. The sensitivity of puncture-needle biopsy performed according to the traditional method in the diagnosis of intracystic breast cancer was 81.8%, and the sensitivity of the improved method was 97.06% (p < 0.05). To asses reliably the effectiveness of the hybrid technology for determining the local metabolism of tumors in the diagnosis of breast cancer, examination of a larger number of patients is required. Among the patients examined using the optical diagnostic methods, the following data were obtained: the redox index in the tumor was 0.67±0.10 relative units, in the surrounding tissue – 0.77±0.14, tissue saturation in the tumor – 64±14%, in the surrounding tissue – 68±9%. Two cases of breast cancer in patients prior to the start of treatment and after 6 courses of neoadjuvant polychemotherapy are considered separately. The following data were obtained: the redox index in the tumor in the patient without treatment was 0.53± 0.01 relative units, in the patient after 6 courses of neoadjuvant therapy – 0.81±0.01 relative units; the value of tissue saturation in the tumor in the patient without treatment – 71±1%, in the patient after 6 courses of neoadjuvant therapy – 64± 2%. To asses reliably the effectiveness of the hybrid technology for determining the local metabolism of tumors in the diagnosis of breast cancer and to have the opportunity to assess the prognosis for the disease course, examination of a larger number of patients is required. Conclusions. A new method of cytological diagnosis of cancer in a breast cyst using ozone-oxygen mixture proved to be more effective than the traditional method, which proves the expediency of its use in order to improve the diagnosis of this pathology at the preoperative stage. To solve the question of the expediency of using the technique of spectrophotometry of tumor tissues in patients with breast cancer in order to assess the effectiveness of chemotherapy, a larger number of women under examination and a period of their follow-up for 3–5 years are required.

Effect of gas additives on soot formation in flat laminar premixed ethylene/air flames under low pressure

This study reports on the effect of the additive gases, namely N2, CO2, and Ar, on the soot formation in laminar premixed C2H4/air flames at low pressure of 40 kPa. The flames blended with N2, CO2, or Ar were experimentally investigated, where the emission spectra of CH* and C2*, qualitative concentration of PAHs, and soot volume fraction (fv) were measured using laser and optical diagnostic methods. The flame temperature was measured using a thermocouple. The results reveal that additive gases significantly influence flame height above the burner and fuel combustion as well as reduce soot formation and flame temperature. With respect to N2 and CO2, Ar proves the most effective in reducing soot volume fraction, achieving a 100-fold reduction compared to the reference flame. Moreover, the additive gases were found to delay the ignition, leading to a 5 mm downstream shift in soot inception. Despite the difference in the properties of the three gas additives, it was found the first incepted soot particles were detected at a common temperature, Tinception, of 1515 ± 70 K. Three regimes related to the soot appearance rate were identified, which are the fast-increasing range from the soot inception location, the plateau region, and the decreasing range to the flame front of 20 mm. According to the Lagrangian time-derivative of soot volume fraction (dfv/dt) as a function of fv, the constant of surface growth (kSG) was determined to be 170 s−1 in the flame with additives of CO2 and Ar, measured at 40 kPa. The identified turning point between the plateau region and the negative soot increase regions can be used as an indicator of the transition from higher to lower soot formation rates in soot modeling.

Validation of a new optical diagnosis training module to improve dysplasia characterization in inflammatory bowel disease: a multicenter international study

Background and aimsInflammatory bowel disease (IBD) increases risk of dysplasia and colorectal cancer. Advanced endoscopic techniques allow for the detection and characterization of IBD dysplastic lesions, but specialized training is not widely available. We aim to develop and validate an online training platform to improve the detection and characterization of colonic lesions in IBD: OPTIC-IBD. MethodsWe designed a web-based learning module that includes surveillance principles, optical diagnostic methods, approach to characterization, classifications of colonic lesions, utilizing still images and videos. We invited gastroenterologists from Canada, Italy, and the UK, with a wide range of experience. Participants reviewed 24 educational videos of IBD colonic lesions, predicted histology, and rated their confidence. The primary endpoint was to improve accuracy in detecting dysplastic lesions following training on the platform. Furthermore, participants were randomized 1:1 to get additional training or not, with a final assessment occurring after 60 days. Diagnostic performance for dysplasia and rater confidence were measured. ResultsOne hundred seventeen participants completed the study and were assessed for the primary endpoint. Diagnostic accuracy improved from 70.8% to 75.0% (p 0.002) following training, with the greatest improvements seen in less experienced endoscopists. Improvements in both accuracy and confidence were sustained after 2 months of assessment, although the group randomized to receive additional training did not improve further. Similarly, participants’ confidence in characterizing lesions significantly improved between pre- and post-course (p<0.001), and it was sustained after 2 months of assessment. ConclusionsThe OPTIC-IBD training module demonstrated that an online platform could improve participants’ accuracy and confidence in the optical diagnosis of dysplasia in patients with IBD. The training platform can be widely available and improve endoscopic care for people with IBD. Clinicaltrials.gov NCT04924543.

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.

Numerical study of CH* chemiluminescence and heat release rate in methane inverse diffusion flame

Flame optical diagnostic method based on CH* chemiluminescence is often used in the combustion process monitoring. In this work, a numerical study of CH* chemiluminescence was conducted for the laminar methane inverse diffusion flame with a range of global oxygen/fuel equivalence ratios. CH* chemiluminescence is mainly distributed in the upstream of the inverse diffusion flame and the CH* concentration increases with the global oxygen/fuel equivalence ratio. CH* is generated by C2H, which mainly comes from the reactions OH + C2H2<=>C2H + H2O and H + C2H2<=>C2H + H2. In addition, most CH* is quenched by collisions with H2O, CO, CO2 and H2, and the CH* collision quench is enhanced with increasing global oxygen/fuel equivalence ratios. The CH* generated in the peak reaction zone will diffuse to the fuel and oxidizer sides due to the mass diffusion and the thermal diffusion. Moreover, the correlation between CH* and local heat release rate distribution is explored and CH* can characterize the local heat release rate on the fuel side.

Pattern analysis of fractal-like systems

The features of the Fourier spectra of fractal-like systems are studied. On the basis of theoretical studies, the features of the scaling invariants of the objects under consideration in light fields are determined, which manifest themselves in the form of stable local formations — patterns. Particular attention is paid to the problem of stability of the ratios of the scaling characteristics of the analyzed systems and their Fourier transforms. The possibility of identifying and systematizing various fractal systems based on the estimation of their scaling parameters is considered. An analysis of the stability of the scaling parameters of the probing radiation to changes in the parameters of the systems under study indicates that the pattern approach to improving the methods of optical diagnostics is promising.

Effect of a dynamic axial magnetic field on a preconditioned single-wire Z-pinch

In this study, the effect and mechanism of a dynamic axial magnetic field on a preconditioned single-wire Z-pinch were investigated experimentally and theoretically. Optical diagnostic methods, including shadowgraphy, interferometry, Faraday rotation, and Thomson scattering, have been used to measure the parameters of magnetized plasmas. Compression of the azimuthal and axial magnetic fields was observed, and the suppression of the plasma instability was recorded and analyzed. The results showed that an external axial magnetic field could reduce the plasma instability and non-uniformity, but prolong the implosion time and weaken the compression ratio. In the implosion process with an axial magnetic field, the plasma rotated at a speed similar to that of imploding, which could be regarded as a stabilization method. A simplified model of the diffusion and compression processes of a dynamic axial magnetic field was developed to investigate the conditions for maximizing the amplitude of the axial magnetic field. Subsequently, the snowplow model was used to calculate the effect of axial magnetic fields on the implosion process and energy conversion.