To evaluate the effect of preoperative neoadjuvant chemotherapy regimen of XELOX  on surgical condition and oncogene expression in advanced gastric cancer.From January 2015 to July 2016, 124 patients with advanced gastric cancer who were admitted to our hospital were selected. Random number table method was used to divide them into an observation group and a control group, 62 each group. The observation group received two courses of neoadjuvant chemotherapy (XELOX) before operation, and the control group received surgery. The operation condition, expression of oncogenes in gastric cancer lesions, occurrence of adverse reactions and the long-term prognosis were compared between the two groups.The R0 resection rate of the observation group was significantly higher than that of the control group, and the difference was statistically significant (P<0.05). The operation time of the observation group was shorter than that of the control group, the amount of intraoperative bleeding and the amount of postoperative drainage of the observation group were less than that of the control group, and the differences were statistically significant (P<0.05). The mRNA expression of gastrokine 1, multiple tumor suppressor protein, Wilms tumor gene on the X chromosome (WTX gene) and gene of phosphate and tension homology deleted on chromosome ten (PTEN gene) in the observation group after treatment was significantly higher than that in the control group before treatment, and the increase amplitude of the observation group was more obvious than that of the control group (P<0.05). There was no significant difference in the incidence of adverse reactions between the two groups (P>0.05). In terms of long-term prognosis, the disease-free survival time and average survival time of the observation group during the two-year follow-up period were significantly better than those of the control group, and the recurrence rate of the observation group was significantly lower than that of the control group; the differences were statistically significant (P<0.05).Preoperative XELOX for advanced gastric cancer patients can effectively increase the proportion of radical surgery, reduce the risk of surgery, and significantly regulate the expression of oncogene, thus improving the long-term prognosis of patients. Gastric cancer, one of the most common malignant tumors of digestive system. In recent years, due to the deterioration of the environment and the change of people’s lifestyle, the morbidity and mortality of gastric cancer remain high.5Neoadjuvant chemotherapy refers to systemic chemotherapy before local treatment such as surgery or radiotherapy, which aims at shrinking the mass and killing the invisible metastatic cells as early as possible to facilitate follow-up surgery and radiotherapy.In this study 124 patients with advanced gastric cancer who were admitted to our hospital were selected. This study was conducted after ethical approval between January 2015 to July 2016. 18 years old ≤ age ≤ 75 years old.Preoperative pathology indicated primary gastric cancer.Not undergoing treatment such as surgery, radiotherapy and chemotherapy.IIb-IIIcclinical stage of cancer.Karnofsky score ≥60 points.Expected survival time ≥3 months.Having other malignant tumors.Being allergic to oxaliplatin and capacitating.Having severe organ dysfunction.Undergoing preoperative chemotherapy.Having severe infectious or autoimmune diseases.The patients were divided into an observation group and a control group by random number table method, 62 each group. This study was approved by the ethics committee of our hospital. All the selected subjects signed the informed consent.2, from d1 to d14, 21 days as a course; oxaliplatin was intravenously dripped on the first day of each course, at a dose of 130 mg/m2, and 21 days was taken as a course. The observation group received surgery in the 4th week after the second course of chemotherapy, while the control group received surgery directly. The operation mode of the two groups was consistent. The operation was performed by the same operation team. The operation mode was radical mastectomy combined with D2 lymphadenectomy, and palliative operation was performed for patients who could not undergo radical mastectomy. After operation, adjuvant chemotherapy was given to both groups, for about eight cycles.The observation group was given two courses of XELOX neoadjuvant chemotherapy before operation: capacitating was given twice a day, after breakfast and dinner, at a dose of 2500 mg/mDuring the operation, the operation time, intraoperative bleeding volume and postoperative drainage volume were observed, and the R0 resection rate was judged according to the pathological results after resection of the tumours .Gastric cancer lesions which were taken for biopsy were taken before chemotherapy, and gastric cancer lesions which were surgically respected were taken after chemotherapy. RNA in the lesion tissues was isolated and purified using kit . Complementary DNA (cDNA) was obtained after performing inverse transcription on RNA, and the reaction system was prepared. The reaction was carried out according to the procedure of pre degeneration at 95°C for three minutes, pre degeneration at 95°C for 25 s, annealing at 60°C for 40 s and extension at 72°C for 35 s. The reaction curve generated in the software after reaction, and the mRNA expression quantity of atropine 1, multiple tumour suppressor protein (p16), Wilms tumour gene on the X chromosome (WTX gene) and gene of phosphate and tension homology deleted on chromosome ten (PTEN gene) was calculated according to the reaction curve.During the recovery, the occurrence of adverse reactions after operation was observed.At the end of the two-year follow-up, the long-term prognostic indicators such as disease-free survival time, survival time and recurrence rate were recorded.2 test. Difference was considered as statistically significant if the value of P was smaller than 0.05.All the data were analyzed by SPSS 22.0. The measurement data conformed to normal distribution. The independent sample t-test was used for statistical analysis, and the related data were expressed as Mean±Standard Deviation. The enumeration data were expressed as rate (%). The comparison between groups was performed using X2. As to the pathological stage, there were 15 cases of stage IIb, 11 cases of stage IIIa, 20 cases of stage IIIb, and 16 cases of stage IIIc; as to the location of tumors, there were 31 cases of cardia, 13 cases of pylorus, 16 cases of gastric body, and 2 cases of whole stomach. The control group consisted of 31 males and 31 females, with an average age of 57.31±13.69 years and BMI of 27.88±7.50 kg/m2. As to the pathological stage, there were 15 cases of stage IIb, 11 cases of stage IIIa, 20 cases of stage IIIb and 16 cases of stage IIIc. As to the location of tumors, there were 35 cases of cardia, 10 cases of pylorus, 14 cases of gastric body and 3 cases of whole stomach. There was no significant difference in general clinical data between the two groups (P > 0.05); hence the results were comparable.There were 32 males and 30 females in the observation group, with an average age of 58.41±12.30 years and body mass index (BMI) of 28.47±7.33 kg/m: The R0 resection rate of the observation group was significantly higher than that of the control group [91.94% (57/62) vs. 66.13% (41/62)], and the difference was statistically significant . The operation time of the observation group was shorter than that of the control group, and the amount of bleeding during operation and the amount of drainage after operation were less than that of the control group; the differences were statistically significant . The reason might be that the operation was performed at the 4th week after two cycles of preoperative chemotherapy, during which the physical condition and immunity of the patients recovered basically. It suggested that neoadjuvant chemotherapy was safe. However, Li et al. pointed out that neoadjuvant chemotherapy might increase the risk of surgery and lead to related postoperative complications.The over proliferation and invasion of gastric cancer cells are closely related to the activation of proto-ontogenesis and the inactivation of various anti-ontogenesis. Motilin 1 encodes a class of gastric mucosal protective proteins, which can repair and protect gastric mucosa, and its loss of expression will increase the damage of carcinogenic factors to gastric mucosal cells and promote malignant transformation.23By analyzing the changes of proto-oncogene expression in gastric cancer lesions, it was found that the mRNA expression quantity of motilin-1, p16, WTX and PTEN genes in gastric cancer lesions of the observation group increased more significantly than that of the control group. The result suggests that neoadjuvant chemotherapy before operation has a more prominent effect on tumour suppressor gene than radical operation alone. This result is also rarely reported in previous studies.24This study is a single-center, small-sample study, with a low level of evidence. How to maximize the advantages of preoperative chemotherapy and improve the long-term prognosis of patients still need to be further explored.Preoperative radiotherapy combined with neoadjuvant chemotherapy can improve the resection rate of advanced gastric cancer without increasing the incidence of adverse reactions. At the same time, combined therapy can significantly increase the expression of anti-ontogeny and prolong the survival of patients, which is worthy of promotion.GYS: Study design, data collection and analysis and is responsible and accountable for the accuracy or integrity of the work.GYS & SYW: Manuscript preparation, drafting and revising.GYS & GSL: Review and final approval of manuscript.


The contralateral secondary VCT was significantly higher and lower in the MD and tract volume, respectively (p < 0.05), compared to the ipsilateral VCT. Therefore, we believe that the results will be useful for future studies of the vestibular projection pathway in the human brain injury aspect of central vestibular syndrome.The vestibulocerebellar tract (VCT) is regarded as an important pathway of the central vestibular system. We identified the anatomical characteristics of the primary and secondary VCTs in a normal human brain using diffusion tensor imaging (DTI) tractography. Thirty-one healthy adults were recruited. A 1.5 T scanner was used for DTI tractography. A seed region of interest (ROI) was placed on the superior and medial vestibular nuclei at the pons level and a target ROI was placed on the uvula–nodulus of the cerebellum for reconstructing the primary VCT. In the secondary VCTs, the seed ROI was placed on the inferior and medial vestibular nuclei at the medulla oblongata level, and target ROIs were placed on the bilateral uvula–nodulus of the cerebellum. The primary VCT originated from the superior and medial vestibular nuclei at the pons level and terminated at the ipsilateral uvula–nodulus of the cerebellum. The component of the secondary VCTs originated from the inferior and medial vestibular nuclei at the level of the medulla oblongata and terminated at the bilateral uvula–nodulus of the cerebellum. Among them, 70.97% in the contralateral secondary VCT crossed at the vermis of the cerebellum. In addition, the fractional anisotropies (FAs) and mean diffusivity (MD) values of the primary VCT were significantly higher and lower, respectively, compared to those of the secondary VCTs ( The vestibular system is composed of the peripheral vestibular organs in the inner ear, the ocular system, and projections of the central nervous system ,2. PartiPrevious studies have suggested that the VCT is divided into primary and secondary projections and reported that primary and secondary VCTs connect the vestibular nucleus with the uvula–nodulus of the cerebellum ,4,8,9,10In the current study, we reconstructed the structures and identified the anatomical characteristics of the primary and secondary VCTs in the normal human brain using DTI tractography.This study recruited thirty-one healthy adults (aged 20–40 years) that did not have any history of neurological or musculoskeletal disease. The inclusion criteria were: (1) no diagnosis associated with vestibular function in the past, (2) no history of cerebellum injury, and (3) no history of neurological, cognitive, or musculoskeletal dysfunction. The exclusion criteria were: (1) participants who had been diagnosed with musculoskeletal and neurological problems in the past and (2) participants who had been diagnosed with a brain injury in the past. All participants provided informed consent prior to DTI tractography. The study was approved by the institutional review board of Dankook University (DKU 2020-07-009).The DTI data were acquired using a six-channel head coil on a 1.5 T Philips Gyroscan Intera  with single-shot echo-planar imaging. For each of the 32 non-collinear diffusion sensitizing gradients, this study collected 67 contiguous slices parallel to the anterior commissure–posterior commissure line. The imaging parameters used were: acquisition matrix = 96 × 96; reconstructed matrix = 192 × 192; field of view = 240 × 240 mm2; repetition time (TR) = 10,726 ms; echo time (TE) = 76 ms; parallel imaging reduction factor (SENSE factor) = 2; EPI factor = 49; b = 1000 s/mm2; NEX = 1; and a slice thickness of 2.5 mm with no gap (acquired voxel size: 1.3 × 1.3 × 2.5 mm3) .www.fmrib.ox.ac.uk/fsl). The head motion effect and image distortions due to eddy currents were corrected by affine multi-scale two-dimensional registration. Fiber tracking was performed using a probabilistic image method based on a multifiber model and by utilizing image routines implemented in FMRIB diffusion  [The diffusion-weighted imaging data were analyzed using the Oxford Center for Functional Magnetic Resonance Imaging of the Brain (FMRIB) Software Library  . The prid = 0.2) . In the d = 0.2) ,8. A totp-value of < 0.05 was considered to be statistically significant.This study analyzed the significance of differences in the DTI parameters between the three reconstructed VCTs using a one-way analysis of variance (ANOVA) with an Fisher’s least significant difference (LSD) post-hoc test. SPSS ver. 20.0  was used for the analysis. A Using the probabilistic DTI tractography, this study reconstructed the primary and secondary VCTs in the normal human brain . The prip < 0.05). However, there were no significant differences in the tract volume between the primary and secondary VCTs (p > 0.05). The contralateral secondary VCT was significantly higher and lower in the MD and tract volume, respectively (p < 0.05), compared to the ipsilateral VCT. In contrast, the FAs of the DTI parameters were not significantly different between the secondary VCTs (p > 0.05).The mean FAs, MD, and tract volumes of the primary, ipsilateral, and contralateral VCTs are shown in In the current study, we reconstructed the primary and secondary VCTs in the healthy human brain using DTI tractography. With our reconstruction of the VCTs, we found that: (1) The primary VCT originated from the pons level, passed through the inferior cerebellar peduncle, and terminated at the ipsilateral uvula–nodulus of the cerebellum; (2) the secondary VCTs originated from the medulla oblongata, crossed at the vermis of the cerebellum on the contralateral side, and terminated at the bilateral uvula–nodulus of the cerebellum. Regarding the FA and MD values of the primary VCT, they were significantly higher and lower, respectively, compared to those of the ipsilateral and contralateral secondary VCTs. The MD value of the contralateral secondary VCT was significantly higher than that of the ipsilateral secondary VCT. In contrast, the tract volume was not significantly different between the primary and secondary VCTs.Previous animal studies have shown that the brain anatomy of the primary VCT terminates at the ipsilateral uvula–nodulus of the cerebellum in cats, rabbits, monkeys, and pigeons ,20,21,22In the human brain, it is known that the primary VCT originates from the inferior cerebellar peduncle and terminates in the vestibulocerebellum of the ipsilateral side. It is also known that the secondary VCTs originate from the medial and inferior vestibular nuclei and terminate in the vestibulocerebellum  . Our finIn conclusion, based on the DTI tractography findings, we identified the anatomical characteristics of the primary and secondary VCTs in the human brain. We believe that the results of the current study will be clinically helpful in evaluating postural control impairment and central vestibular syndrome according to injuries of the vestibular projection pathway in patients with brain injuries, and particularly lesions of the VCT. However, some limitations of the study should be considered. First, the generalizability of our findings is difficult due to the limited age range of the subjects recruited (20–40 years), and thus, additional research needs to be performed in a population with a greater age range in order to generate standard data. Second, DTI may have difficulty in locating ROIs accurately due to the fiber tracts in regions of crossing and fiber complexity. Although DTI is a powerful anatomical imaging tool that can demonstrate a general fiber architecture, it can underestimate or overestimate all of the fibers. Therefore, we suggest that further studies be undertaken to demonstrate the reliability and validity of the VCT and of its clinical correlations.


The paper presents the assessment of the possibility and reliability of the digital image correlation (DIC) system for engineering and scientific purposes. The studies were performed with the use of samples made of the three different materials—mild S235JR + N steel, microalloyed fine-grain S355MC steel, and high strength 41Cr4 steel subjected to different heat-treatment. The DIC studies were focused on determinations of dangerous zones with large stress concentrations, plastic deformation growth, and prediction of the failure zone. Experimental tests were carried out for samples with different notches . With the use of the DIC system and microstructure analyses, the influence of different factors  on the material behavior were studied. For all studied cases, the stress concentration factors (SCF) were estimated with the use of the analytical formulation and the finite element analysis. It was observed that the theoretical models for calculations of the influence of the typical notches may result in not proper values of SCFs. Finally, the selected results of the total strain distributions were compared with FEM results, and good agreement was observed. All these allow the authors to conclude that the application of DIC with a common digital camera can be effectively applied for the analysis of the evolution of plastic zones and the damage detection for mild high-strength steels, as well as those normalized and quenched and tempered at higher temperatures. Emerging methods of manufacturing, new technologies in materials production ,2,3,4,5,In the area of the material production still, new materials are issued, starting from very modern composite materials and ending with the new steel alloys ,5,38,39.Recently, several non-destructive approaches for failure analysis and damage detection have been developed at the turn of the XX–XXI century. These are techniques based on acoustic emission, lamb wave propagation, application of thermography cameras, the Moire interferometry, or scanning electron microscopy . In the The above-mentioned problem of stress concentration analysis has attracted researchers for many years. The primary mathematical solutions for the notch problem within the elastic range was set for the infinite flat and thin infinite element with a circular hole and published by Kirsch , Kolosov(1)Verification of the theoretical models for typical openings by the experiments and FEM simulations; and(2)Evaluation of the influence of the different notches , manufacturing technologies (laser cutting), material type , and microstructure  on the structure and material behavior, plastic deformation growth, and failure mode.The main aim of this paper is the assessment of possibilities and reliability of the DIC system for the determinations of dangerous zones with large stress concentration, plastic deformation growth, and prediction of the failure zone and mode for different structural steels. For this reason, DIC analyses were performed for different steels with different notches and some of them were compared with the results obtained with the use of the classical FEM analysis. The other aims of the paper are as follows:The paper consists of eight sections. The introduction to the investigated problems and the literature review is described in To investigate the influence of the notch effect in structural elements as well as the possibilities of prediction of damage position and form, the three different materials  steelmaking process and hot-rolled with coils thickness 2 mm and tested after normalizing rolling (+N). The influence of normalization on the mechanical properties was discussed by Rdzawski et al. . Steel SThe investigated materials were certificated with respect to the recent standards ,80,81. TThe experimental tensile tests were performed for flat samples with different geometries and the three different materials mentioned above. The mechanical properties of the tested materials are described in The samples made of S355MC had rectangular shape b with sqThe thicknesses of the tested samples were set to 2 mm for S235JR + N and 41Cr4 and 4 mm for S355MC; more details are given in To get the experimental distribution of the displacements and strains using the DIC analysis, the surfaces of all investigated samples were coated by randomly distributed speckle patterns with various unique shapes . The firtK and calculated as the ratio of the maximal stress at the hole vicinity σnotch,MAX to the nominal stress σnotch,NOM, which is calculated with the well-known formulae as follow:The cutouts of various shapes, such as circular, rectangular, triangular, etc., often occur in the structural elements ,29,30,32For all considered samples, the value of the stress concentration factor was estimated using finite element method and Equation (1). In certain cases (a circular hole), detailed theoretical solutions are available ,19,70,76d is a diameter of the circular hole and W is a panel width. For infinity panel, tK is equal 3. Good agreement of the above solution was confirmed by many analytical and experimental studies [The values of SCFs can be identified for many practical applications with the use of the analytical formulas or with the use of graphical charts given in engineering handbooks ,76. Such studies . There a studies ,76.R is a radius of the filleted corner, b is the size of a hole measured in the direction parallel to tension, and a is a width of the hole in the direction perpendicular to tension. However, the application of the above solution for elements with finite width leads to the high overestimation of SCF. This can be observed in the diagram in The remaining two investigated examples with rectangular (square) and triangular holes with rounded corners are more complicated in the analysis. In the case of a rectangular hole with rounded corners subjected to in-plane tension, there are available mathematical or approximate experimental results for infinite panels ,68,72,731; and (2) vertical stress σY (Y is the direction of tensile load). Both dependencies are presented because the direction of the principal stress σ1 is rotated with respect to the tension load when moving along the hole edge. It was observed that, for both rectangular and triangular filleted holes, the maximum of the stress does not exactly appear in the point where the arc of the fillet starts but is slightly moved along the arc. These observations confirmed previous investigations [The FEM calculations of SCFs were performed by the authors in ANSYS 19R3 with the use of fine mesh and plane finite elements PLANE182 and linear elastic material behavior. Two different SCF curves were determined with the use of numerically calculated: (1) principal stress σigations ,29,30,31The option in the case of finite panels is the use of the FEM solutions ,22,23 orR/b and a/W, relative error was smaller than −10%. For a larger ratio, mainly when a/w ≈ 0.5, the error may achieve even −20%. A more complicated situation appears in the case of example with a triangular hole with rounded corners ); however, the value of the SCF is usually underestimated in relation to the FEM solution. For small ratios  corners c. There  corners . The cal corners  can be rb/w and R/w on the SCFs is given in R/w and b/w ratios lead to the smallest SCF. Increase of the R/w ratio results in decreasing in the SCF value. For ratios R/w higher than 0.0667, the increase of b/w has a beneficial influence on the SCF value. However, for small R/w ratios (0.0444 and lower), the trend of the SCF curve is changing. There can be found a suboptimal b/w ratio for which the SCF achieves its highest value . Moreover, in contrast to the other cases, for R/w = 0.0222, the optimal SCF was achieved for the smallest possible ratio b/w.The influence of the ratios tK, used for determination of the peak of the stress at the notch, fulfilled its function effectively for static loads. Unfortunately, tK usually gives overestimated results, such as the number of cycles to damage, for fatigue problems [fK, which is defined as the ratio between un-notched fatigue limit to the notch fatigue limit in the analyzed sample with a notch. fK is usually lower than tK, and the difference increases with the decrease of the characteristic size of the considered notch . Such discrepancy is explained by the plastic behavior of the material in the notch or by the stress field theory [tK. Next, the difference between tK and fK values exist due to the chemical composition and heat treatment applied for the steel used for the element. In the case of mild steel, the discrepancy is bigger than in the case of high strength and alloy steels. For the same geometry, notch type, and applied load and boundary condition, the zone of damage is lower in case of high strength steel application and it increases the average stress, which lowers fatigue endurance.The stress concentration factor problems ,85,86. Fd theory ,88,89. ItK and fK was proposed [q is known as the notch sensitivity factor and its value varies from 0.0 to 1.0. In the case of fully notch sensitive materials, q is equal to 1.0, while, for the notch insensitive materials, it drops down to 0.0. For a particular estimation of q values, several proposals have been introduced [q evaluation, are given in many handbooks of fatigue design and are still in use in practical use [Based on empirical tests simple relation between proposed :(5)Kf=1+troduced ,35,74. Ttroduced . It takeical use .eHY = 380 MPa and tensile strength mR = 472 MPa. The determined for normalized S235JR + N steel upper yield strength eHY varied within the range 317–323 MPa while the lower yield limit eLY varied from 294 to 299 MPa Nominal stress in non-weakened cross-section—(2)Nominal stress in cross-section weakened by a notch—(3)The estimated maximal stress in cross-section weakened by a notch—To understand the phenomena occurring in the investigated specimens with circular, square, and triangular notches subjected to tension, the following stresses have been considered:tK. The values of tK are given in notch,NOM = f(εTOT). In the first part of the σ–ε curves, for the nominal stress σnotch,NOM in the range 0–300 MPa, the particular curves can be interpolated by two linear functions. This effect is caused by the appearance of the first plastic strains around the notches. In the σ–ε curve, certain characteristic points are spotted. For example, the points in which plastic strains occur . In the case of the plate with the circular notch, a slight decrease of strength was observed for the nominal stress σnotch,NOM = 188 MPa; Point 2). The σ = f(εTOT) relationship was no longer linear when σnotch,NOM exceeded 284 MPa . In the investigated sample, the theoretical value of the maximum stress was closer to the observed one (plastification for 290 MPa). The hole manufacturing technology—water jet cutting—can be responsible for that, namely, a non-smooth transition between the straight part, and filleted corner was observed, which was the source of the future crack. At Point 2, the curve became no longer linear; this was for σnotch,NOM = 248 MPa.In the case of the plate with the square hole with fillet corners, the first bend of the curve is observed at Point 1 , and after that characteristic slight drop in stress value (like during the tension of standard non-weakened sample) appeared. During the further part of the test, the plastic flow took place along with the material hardening. In this way, Point 5 was reached, where the first crack on the edge appeared . The probable source of this was the presence of two severe notches on each side of the hole. At Point 3 b, the loappeared a. Shortlappeared b. Furtheappeared c.tK maximal vertical stress in notch reached σnotch,MAX = 293 MPa. The further increase of the external load caused the plastification in vertex V2 and V3. The estimated vertical stress values for these notches were equal to σnotch,MAX = 290 MPa. At Point 3, the plot became no longer linear . Further behavior of the sample is determined by the combination of elastic and plastic behavior. The full plastification of the sample is reached at Point 4, for which the nominal stress value was equal to σnotch,NOM = 318 MPa . The maximum load resulted in maximum stress equal to σnotch,NOM = 393 MPa, which was reached at Point 5 , a larger difference between higher and lower yield strength, and larger percentage yield point extension, whereas the tensile strength for both samples was almost the same .Similar, typical static tensile tests were performed for two specimens with dimensions given in notch,NOM = 409 MPa) and 2 ; more details in notch,NOM = 462 MPa) and 4 ; tK (2.25 for R4 and 2.59 for R2); no clear bends of σ–ε curves in the range below the plasticity in the whole cross-section is observed. Moreover, the values of σnotch,nom for yield limit and tensile strength are consistent with the limits obtained for samples without notches  and then no elements increasing hardenability are present in the microstructure and there is no risk of tough and brittle carbides formation.The influence of the stress concentrators was tested with the use of two samples with a square hole with filleted corners each. The dimensions of the square hole were the same in both specimens 15 mm × 15 mm. The different fillet radii were applied: 2 or 4 mm see b. The reches see , while tThese examples demonstrate that commonly used assumptions—i.e., larger radius leads to larger strength—may not always be right and are influenced by the notch sensitivity. To confirm this phenomenon, further studies will be performed.The static tensile tests for 41Cr4 steel were made for samples with a square hole 15 × 15 mm with a fillet radius of 2 mm. The geometries c, loadinNotched samples made of 41Cr4 + AC revealed significantly smaller yield limit (reduced about 50%) and ultimate tensile strength than notched samples made of 41Cr4 + QT and 41Cr4 + Q, but a much larger ultimate strain was observed in comparison to hardened or quenched and tempered 41Cr4 samples. However, it should be noted that, despite the smaller strength of spheroidized annealed samples (41Cr4 + AC), the tensile work until failure is significantly higher for normalized samples than for the quenched one (41Cr4 + Q). The cracks in samples made of 41Cr4 + AC were initiated at two points: the first inclined crack at the end of the fillet radius a and theThe notched sample subjected only to hardening 41Cr4 + Q revealed brittle behavior without visible plastic strains in the σ–ε curve. The cracks initiated in the points with the highest stress concentrations and no plastic deformation were observed around the hole area f.eY and mR in comparison with the non-tempered or tempered 41Cr4 steel at low temperatures [The notched sample subjected to the typical heat-treatment procedure 41Cr4 + QT (hardening and tempering), in the first part of the test, until the yield limit was reached, revealed almost the same slope of σ–ε curve as 41Cr4 + Q. The yield limit of 41Cr4 + QT was similar to the ultimate stress of 41Cr4 + Q. However, it can be observed in eratures . It meanThe damage caused by external loading can be detected, localized, and identified by the use of the different non-destructive methods. Different techniques based on acoustic emission, lamb wave propagation, or with the use of scanning electron microscopy, thermography camera, Moire interferometry, etc. are in use ,46. Thes(1)Detection and control of plastic strain zones growth;(2)Determination of the possibilities of DIC method in detection of damage and prediction of failure form; and(3)Verification of the DIC results by FEM analyses.In the investigated case, the DIC analyses were performed with the use of the GOM Software. The photographs were made by Nikon D90 camera with constant time intervals (6 s). The main aims of the DIC analyses were:It is obvious that the applied equipment (average high-resolution camera) does not give the same possibilities as professional DIC systems , but such instrumentation is widely available and accurate enough for the presented study. The input data to the DIC analysis were made by making a series of images of the investigated surface coated by randomly distributed speckle pattern. The first image was assumed as a reference one (unloaded sample) and the others were made in constant time-intervals with the increasing tensile load. After the tests, the images were processed with GOM Software , in whicsensGOM = 0.005 for the investigated sample. The first image . The d strains . In this strains d–f. Afte strains a, the ma strains b, which  strains c, in whiIn parallel, the respective finite element model was prepared. For that purpose, Ansys software  was usedThe distribution of total strains in the vertical direction was chosen for the comparison. In A similar study was performed for the structure with the square hole with rounded corners in the center part. Here, the results for the radii 5.0 mm and the distance 30.0 mm between the opposite sides of the square are shown. This means that the thinnest cross-section has the same area as in the previous study. However, the analytical results for the tensed thin plate with such a void result in the higher value of the stress concentration factor than for circular opening. This tendency is kept when going to the finite width of the plate. TOT = 0.41 On the V1 corner side: The shape and growth of the plastic zones is similar as for plate with the circular hole.(2)On the opposite side (Corners V2 and V3): The spread of the plastic zones is qualitatively similar to that one observed in the plate with the square hole.The final study for S235JR + N was performed for the plate with the triangular hole in the center part. The opening was cut with rounded corners with radii equal to 5.0 mm. The analyses of the vertical strains distribution for this plate and comparison of them with strains distributions for plates with circular and rectangular hole revealed the following conclusions:TOT = 3.28  and the sample with the square hole (Corners V2 and V3). Here, fairly good agreement of the result was also spotted.Similar analyses were performed for specimens with square holes made of S355MC and 41Cr4 steels. In these investigated examples, the different development of the plastic zones was observed for different materials. These distributions for the range of the strain hardening are presented in In the case of the high-strength steel 41Cr4, high strain concentrations occurred in the notches , similarThe significant differences in the plastic strain distributions in comparison with other investigated samples were observed for samples made of S355MC . In thesMaterials used in the experimental tests belong to different groups of steels. Therefore, an analysis of the microstructure of materials in the delivery condition was prepared. In the first step, the samples of material were cut out by mechanical cutting without providing heat, which saved the material from structural changes. In the next step, the samples were embedded in the duracryl polymer. The surfaces of metals were grinded by the sandpaper with gradation varying from 120 to 2500. After that, the polishing process was performed with the use of aluminum oxide . To expose microstructure features such as the size of grains and phases of material, 5% of the Nital solution was used, which is the typical reagent applied for revealing the microstructure of carbon steels. Microstructure photos were taken by metallurgical microscope MET-3 PZO with additional camera grip, and the results are presented in The microstructures presented in The surfaces of ruptures were observed for samples after heat treatment process, namely for 41Cr4 + Q and 41Cr4 + QT. The study was made with the use of the scanning electron microscope (SEM) JOEL JSM5510LV. The results for 41Cr4 + Q are presented in The result of the 41Cr4 + QT sample fracture see  investigThe presented study is focused on the two problems—determination and influence of the SCFs and notch sensitivity on the material behavior, plastic deformation growth, and failure mode, and possibilities of applying DIC in the experimental analyses of the recent materials. The presented analytical and numerical FE calculations demonstrate that there are still unsolved issues related to the stress concentrators with typical and common shapes of notches. The application of the finite-width correction factors also may not guarantee an accurate assessment of SCF. This can be seen on the example of a plate with a square hole in which the application of the theoretical formulas and the correction factor leads to the non-conservative estimation of the SCF . On the tK for the square hole (tK = 2.46) was larger from the SCF for the circular hole  close to the 300 MPa  and applicability only to the flat surfaces. Due to the resolution of the Nikon D90 camera, the DIC analyses were possible only after the occurrence of the considerable plastic deformations. Because of this, such system is practically not suitable to the hardened high-strength steels (such as 41Cr4 + Q) in which plastic strains practically did not occur. On the other hand, in the case of heat-treated (+QT) and softened (+AC) high-strength 41Cr4 steel, it is possible to determine the displacement and strain fields of the investigated surfaces with satisfactory accuracy. It should be also noted, that accuracy of the results for samples made of 41Cr4 was reduced due to the images being taken through the closed cover of the testing machine (safety requirements). In the case of the S355MC steel, the limit for DIC application was the chipping resistance of the paint to peel off from the tested surface. The microalloyed fine-grain structural S355MC steel exhibit significant thinning in the volumes weakened by hole, which can be attributed to its high ductility. This leads to the faster degradation of the varnish layer much earlier than the crack nucleation. From this moment, the DIC analyses calculate displacements related not only to the sample but also to the damaged varnish layer. Generally, in such zones, in which the varnish layer is peeled off from the surface the DIC analysis will reveal large deformations or failure. It remains in disagreement with the experiment and caused by the fact that the strain field calculation in the DIC method is based on the deformation of the surface coating. This effect also occurred in the final part of the test of the plate with a square hole made of S235JR + N. For the two remaining samples made of S235JR + N (circular and triangular holes), the DIC analyses were possible almost to the final failure of the samples. In these cases, it allows for correct detection and tracking crack initiation and growth.Except for the sample made of 41Cr4 + Q, the DIC method allows for the fairly good determination of plastic zone growth, the location of zones where the failure may occur, and in some cases, it even allows for the prediction of the final failure form. The obtained distributions of plastic zones were compared with the results of the FEM analyses. The largest difficulties with the FEM analysis were related to the modeling of the material behavior and the elaboration of the equivalent model in the range of the large plastic deformations. In addition, it should be noted that the simple, well-established material models are only applicable to a limited strain range . To obtaThe performed experimental tensile tests, microstructure analyses, and DIC studies revealed the disadvantageous influence of martensite structure after hardening on the structure strength and notch sensitivity. Such martensite structure, formed during the hardening process of the material, is very hard, by what is exposed for low-energy brittle fractures. However, it was also observed that martensite transformation may occur during a laser cutting of the hardenable steel (such as 41Cr4) and may significantly decrease their mechanical properties due to the increased sensitivity of the material for the notches. In the case of such material, it is important to start the laser cutting in an area where no stress concentration may appear It was also observed that the intensity of the laser cutting on notch sensitivity was much stronger in the softened 41Cr4 + AC steel than heat-treated 41Cr4 + QT one. On the other hand, there are also materials  that are insensitive for laser cutting. The remarks given in this paragraph are fully confirmed by the microstructure and fracture studies given in (1)The application of DIC with a common digital camera can be effectively applied for evolution of plastic zones and damage detection for mild, as well as normalized and quench and tempered in higher temperatures high-strength steels.(2)The effectiveness of the DIC usage increases with the decrease of the hardness  of the material.(3)In the case of the quenched steels, the resolution of the common camera seems to be too low, or the test should be made with much lower velocity of the tension.(4)The general forms of the plastic zone obtained from DIC were in good agreement with FE simulations.(5)DIC can be effectively used as an additional control measurement tool for experimental tests.(6)The disadvantage of DIC analyses is that the deformation of varnish layer is measured, if varnish layer peels off from the surface the method may lead to the misleading results.(7)It is possible to predict the dangerous zones in the structure, and it is often possible to predict the final fracture form before the crack would nucleate with the use of the DIC system as well.(8)The performed analytical and FE calculation revealed that theoretical models for calculations of the influence of typical notches may result in not proper values for SCF.(9)Microalloyed fine grain S355MC steel revealed very low sensitivity for notch presence.(10)Steel S355MC revealed no sensitivity for laser cutting.(11)Steel 41Cr4 revealed the strong local influence of the laser cutting on the microstructure , and laser significantly increases notch sensitivity of 41Cr4 when it is in softened state.The performed study was focused on the possibilities of application and the reliability of the DIC system for the investigations of different steels—mild S235JR+N steel, microalloyed fine-grain S355MC, and different heat-treated high-strength 41Cr4 steel subjected to tension. With the use of the DIC system, the influence of the notch presence and its geometry were studied. The studies were performed for thin flat samples with circular, square, and triangular openings. The following conclusions can be drawn:


We investigated the effect of reduced graphene oxide (rGO) doping on the birefringence of 5CB liquid crystal (LC). The characteristics of the synthesized rGO and LC-rGO composite with different rGO concentrations were analyzed by atomic force microscopy, X-ray photoelectron spectroscopy, white light polarized microscopy, voltage-dependent transmission measurement, and differential scanning calorimetry. We found that doping LC with an appropriate concentration of rGO enhances the birefringence of the LC. This is mainly due to the improved anisotropy of polarizability, which stems from the high shape anisotropy of rGO. However, the aggregation of rGO reduces the birefringence by decreasing the anisotropy of polarizability as well as the order parameter. Our study shows the promising potential of LC-rGO for developing various electro-optic devices that offer improved electro-optic effects. Various nanoparticles synthesized based on metals ,3,4,5,6,ge (Vth)  and a swh) [τon)  simultanRecently, graphene ,20,21,22In general, graphene is a hydrophobic material, thereby it has poor solubility in solvents. Graphene with very low concentration will disperse in LC due to the insufficient graphene-graphene interactions. At higher concentrations the graphene-graphene interaction becomes significant and facilitates aggregation, resulting in decreased nematic ordering of the LC. Therefore, surface modification is required to disperse graphene in LC.Here, we demonstrate the effect of chemically reduced graphene oxide (rGO) on the birefringence of the phase modulator fabricated using the homogeneously aligned LC doped with rGO (LC-rGO). Reduced graphene oxide is another form of graphene but it exhibits better dispersibility in solvents because of additional functional groups including carboxyl, epoxides and hydroxyl groups and is easier to mass-produce . We foun3), and 100 mL of sulfuric acid (H2SO4) with 95 wt% was prepared and stirred for 1 h. After cooling down the mixture in an ice bath, 10 g of potassium permanganate (KMnO4) was added and magnetically stirred until the solution became brown. Three hundred milliliter of deionized water was added to the solution slowly during the stirring. To remove excess KMnO4, 10 mL of hydrogen peroxide (H2O2) was added and stirred. Deionized (DI) water was then added and centrifuged. The supernatant was removed and residuals were washed using DI water and centrifuged five times. The GO solution was dried in the oven at 80 ℃ for 3 h to obtain the GO powder. One gram of GO were dissolved in 400 mL of DI water during sonication. After heating the GO solution up to 100 ℃, 10 mL of hydrazine was added and heated for 1 h. The resulting rGO was then washed using DI water and dried in the oven at 80 ℃ for 3 h. One gram of rGO was then dissolved in 100 mL of isopropyl alcohol and mixed using a rotating mixer for 10 min followed by the solution ball milling for 2 h. The rGO was prepared by reducing GO produced by the modified hummers method from the graphite powder. A mixture of 2 g of graphite having a mean size of 200 mesh and purity of 99%, 2 g of sodium nitrate  as shown in To quantify the changes in the birefringence by rGO doping, the voltage-dependent optical transmission measurement was performed. The birefringence of a nematic LC is determined by the order parameter and anisotropy of polarizability of the individual molecules. The relationship between the order parameter (S), the anisotropy of polarizability (pression :(3)SΔαα¯NIT) of the LC-rGO was measured using a differential scanning calorimeter as shown in NIT for all doping concentrations. The relationship between NIT and the order parameter (S) can be described by following Haller’s empirical expression [T is the temperature at which the measurement is made, and β is a unitless fitting parameter. Therefore, the decrease in NIT is attributed to the reduced-order parameter for all rGO concentrations. This result and Equation (3) imply that increased birefringence for the rGO concentration of 0.02 and 0.04 wt% is mainly due to the increased anisotropy of polarizability which compensates for the decreases in the order parameter. When subjected to an alternating electric field, rGO is polarized and both rGO and LC gain dipole moments. The torque exerted on rGO not only rotates the rGO itself but also facilitates the rotation of LC anchoring on both sides of the rGO surface. Thus, the increased anisotropy of polarizability of the LC-rGO results in increased birefringence of the LC-rGO composite. For higher doping concentrations, the aggregation of rGO lowers birefringence by decreasing both the order parameter and the anisotropy of polarizability. 11K) as shown in Equation (1). To investigate the effect of the order parameter and polarizability anisotropy on the threshold voltage, we described dielectric anisotropy and the splay elastic constant in terms of order parameter and anisotropy of polarizability by [N is the number density, h is the cavity field factor, F is the Onsager reaction field, kT is the thermal energy, 11C is the reduced splay elastic constant, and nV is the mole volume. Therefore, the threshold voltage can be described by the order parameter and dielectric anisotropy as follows:To investigate the effect of rGO doping on the order parameter, the nematic to isotropic phase transition temperature (pression :(4)S=(1−ility by ,47,48:(5We have demonstrated that the addition of an appropriate concentration of rGO enhances the birefringence of LC. It has been found that the enhancement of birefringence is mainly due to the increased anisotropy of polarizability, which compensates for the decrease in the order parameter. The high shape anisotropy of rGO provides improved anisotropy of polarizability. However, the aggregation of rGO reduces the birefringence by decreasing the anisotropy of polarizability as well as order parameter. Our study suggests that the LC doped with rGO can be potentially applied to a variety of electro-optic devices for an improved electro-optic effect and reduced device thickness.


They were selected because of their importance for numerous applications from climate and planetary research to natural gas exploration. Multiple measurements of single components in nitrogen and synthetic mixtures were conducted at room temperature and atmospheric pressure. Depending on the investigated hydrocarbon isotopologue, detection limits ranging from 0.043 ppmv to 3.4 ppmv were achieved. For a selective concentration determination, multivariate analysis (MVA) was applied. Partial least-squares regression (PLSR) was used to calculate concentrations from the PA spectra. The implementation of MVA has shown that the PA setup in principle works reliably and that the selective concentration determination of short-chained hydrocarbon isotopologues is possible.We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, served as light sources. The investigations comprised the main stable carbon isotopologues of methane ( Due to simplified news coverage, many people are not aware that atmospheric methane (CH4) plays a major role in the greenhouse effect as it has a considerably higher global warming potential compared to CO2, i.e., CH4 emission will have 28 times the impact on temperature of a CO2 emission of the same mass over the following 100 years [4 in the atmosphere can also affect the concentration of other greenhouse gases, such as tropospheric ozone (O3), water vapor, and CO2 [4 does not cause direct harm to human health or crop production, its role as precursor gas contributes significantly to the negative health and agricultural impacts of O3 [2, the climate system reacts rapidly to changes in CH4 emissions and reducing CH4 emissions could provide the opportunity to immediately achieve major benefits for global and regional climate as well as for human health and agriculture [In environmental policy discussions, people often only talk about the carbon dioxide CO emissionc ozone O, water vethane CH plays a iculture . A betteiculture .2 emissions, they may promote the use of NG to replace more carbon-intensive coal and liquid fuels. Again, the sensitive measurement of the stable carbon isotopic composition of NG plays a key role in the production of this energy source. The 13C/12C ratio of SC hydrocarbons is strongly related to the gas type or source  and to its maturity [A second application involving hydrocarbon isotopologue detection concerns natural gas (NG) exploration. Natural gas is the fastest growing fossil fuel on the global energy market and consumption of NG worldwide is projected to increase more than 40% between 2018 and 2050. Thus, total consumption will reach nearly 200 quadrillion British thermal units 1 Btu = 1055 J) by 2050, according to the International Energy Outlook 2019 . Asia es55 J by 2maturity . The iso2 by burning prior to analyses of the isotope ratio. Further development of alternative isotope ratio measurement techniques is thus highly desirable. An alternative measurement method can be based on spectroscopy. The mid infrared (IR) range has proven to be particularly suitable for hydrocarbon analysis, since many hydrocarbon molecules exhibit strong rotational vibration transitions that are characteristic of the respective molecule. In the mid IR region, several laser sources are available, which include CO and CO2 gas lasers, lead-salt diode lasers, coherent sources based on difference frequency generation, optical parametric oscillators, quantum cascade lasers, and interband cascade lasers (ICLs) [The standard technique for the measurement of carbon isotopes for the past 40 years has been the isotope ratio mass spectrometry (IRMS) together with the gas chromatography (GC) . This mes (ICLs) . Distribs (ICLs) . TogetheIn a previous study, IR absorption cross sections of the ethane and propane isotopologues were measured for the first time in the mid IR range using an FTIR spectrometer . SubsequPhotoacoustic spectroscopy (PAS) is based on the conversion of light to sound  and amon4), ethane (C2H6), and propane (C3H8) including their main stable 13C-isotopologues  by using two DFB-ICLs operating in the wavelength range from 3327.7 nm to 3334.7 nm  and from 3373.3 nm to 3396.7 nm , respectively. In order to obtain the concentrations of individual substances of a measured spectrum containing multiple substances, multivariate analysis (MVA) [In this work, we report the first PAS sensor for the detection of methane (CHis (MVA) ,22 can bis (MVA) . Well-knis (MVA) ,24. If tis (MVA) ,24. Here−1 W)) is known as the cell constant depending mainly on the cell geometry but also on the cell wall surface, beam profile, the modulation frequency, and the microphone sensitivity. 3), and the coefficients 2 molecule−1) of the substance of interest, respectively. The PA signal is directly proportional to the laser power, concentration of the absorbing molecules, and the cell constant. If the laser modulation frequency corresponds to an acoustical resonance frequency of the cell, a significant signal amplification can be obtained.The PAS technique uses the fact that absorbed electromagnetic radiation is partially converted into kinetic energy by inelastic molecular collisions. This corresponds to an increase in the temperature of the irradiated volume. If the radiation is modulated, this will lead to modulated heating and, thus, generate a pressure wave with an amplitude proportional to the concentration of the absorbing molecules, which can be recorded with a microphone. For a single absorbing compound and under the condition that the absorption is not saturated, the wavelength-dependent PA signal given as ,25(1)S and 3.38 μm , respectively, were selected as radiation sources for the isotope-selective detection of methane/ethane and propane. The laser sources (ICLs) were employed one after another. Each of them was operated by the same temperature controller  and current controller . The laser beam modulated by an optical chopper  and passes the H-shaped PA cell  before hAn overview of the PAS gas flow system is illustrated in 2) and three for sample gases, lead to a connecting tube, which is attached to a pressure meter, the inlet of the mixing cell (for preprocessing) and to the PA cell. The gas lines consist partly of polytetrafluoroethylene and partly of stainless-steel tubes. The cell pressure was measured using a ceramic pressure transducer (PM 3) connected to the vacuum gauge . The transducer exhibits a resolution of 0.1 hPa in the range between 0.1 hPa and 10 hPa and a resolution of 1 hPa for pressures higher than 10 hPa. The outlets of the cells were connected to the vacuum pump, a chemistry-hybrid pump , which enabled the evacuation of the gas lines including the cells down to 2.0 hPa. The sample mixtures were produced injecting a defined amount of one or more sample gases into the evacuated mixing cell and then adding N2 up to atmospheric pressure. Thereafter, the evacuated PA cell was filled with a small amount of the gas mixture from the mixing cell and, if required, additional amounts of different sample gases. Finally, the PA cell was filled with N2 up to atmospheric pressure to obtain the desired gas mixture. For some target concentrations, the usage of the mixing cell is not necessary. The concentrations, purities, and suppliers of the sample gases are listed in 4, C2H6, and C3H8 were each present at natural abundance (NA).Four gas lines, one for nitrogen  to be 12CH3-12CH3: 97.8% 13CH3-12CH3: 2.2%, 13CH3-13CH3: 0.013%, 12CH3-12CH2-12CH3: 96.7%, and 13CH3-12CH2-12CH3: 2.2%, respectively.Assuming that isotopes are randomly distributed throughout all isotopologues, the NA of the main methane isotopologues ectively . The NA 2 under ambient conditions. In total, 62 (43 with ICL 1541 and 19 with ICL 1638) different SC hydrocarbon measurements/spectra were recorded. It should be noted, that a considerably larger dataset is usually required to set up a reliable prediction model. However, the primary goal of this research project was to show the feasibility. The ICL 1541 was used for all methane and ethane measurements, and the ICL 1638 for all propane measurements. The concentrations of the hydrocarbon used vary between 50 ppmv and 1 vol%. The individual concentrations for each measurement are listed in Measurements were performed on single and multiple component mixtures of sample gas with NFurther details of the recording of the PA spectra with the ICLs and the processing of the spectra can be found elsewhere . The pro2 spectrum is perfectly suited to measure the background noise. The mean value of the PA signal during a N2 measurement represents an offset, e.g., due to window absorptions, and does not influence the SNR. The LOD is specified as the lowest quantity/concentration of a substance that can be distinguished from the absence of that substance. Here, the SNR shall be used for the calculation of the LOD of a substance:2 and measurements were conducted under ambient conditions with both ICLs. The standard deviations of the N2 spectrum are 1.1 × 10−5 V for the ICL 1541 and 7.9 × 10−6 V for the ICL 1638, respectively.The signal-to-noise ratio (SNR) is commonly defined as the ratio of the signal power to the background noise power and is often expressed in dB. In this work, the SNR is calculated as the highest possible PA signal Multicomponent measurements were processed with a PLSR model in the numerical software Matlab to evaluate the performance of the PA setup in detecting SC hydrocarbon isotopologue concentrations. The implementation of the PLSR method in Matlab is based on the SIMPLS algorithm developed by De Jong in 1993 . The Matr matrix ,24.The predictive accuracy, i.e., the standard/mean error of a multivariate calibration model, is expressed as the root-mean-square error (RMSE). For that, the predicted residual error sum of squares (PRESS) is calculated following the equation :(5)PRESS2H6 and C3H8 are shown in 2 = 0.991 (C2H6) and R2 = 0.997 (C3H8) and a small y-axis intercept of −0.162 V and −0.145 V, respectively. The linear behavior of the sensor was verified by evaluating the single-component gas measurements of the analytes. Representatively, the linearity of the single-component measurements of C2. The SNR and LOD of the PAS sensor are different for each individual species. The PA signal depends equally on the absorption of the sample and on the laser power. This explains the noticeably higher LOD of CH4, because CH4 has a lower absorption strength (approximately one magnitude) in the spectral region of the laser source compared to the other compounds. It should be noted that due to the varying power performance of the ICLs at different wavelengths, the highest absorption peaks do not necessarily result in the maximum PA signal.The SNR and the LOD of the PAS sensor are calculated for each measured SC hydrocarbon isotopologue and are summarized in n stands for the number of probes (spectra). Each model uses Y).The method of choice for the validation of the PLSR model was a full cross validation (CV). Usually, all measurements have to be divided into calibration measurements to train the PLSR model (as a reference) and test measurements to verify the validity of the model. The CV is one of the most frequently used and efficient validation methods because it uses all recorded data for calibration as well as for validation . In the 4 due to its comparably high concentration out, we get an RMSE of Mixture 29 of 13 ppmv and an RMSE of Mixture 40 of 98 ppmv. Hence, we consider a separation of the error into the respective components to be more informative, since, for example, larger concentrations were selected for CH4 (with possible larger errors) in order to obtain PA signals of the same magnitude as the other components. However, it is also possible for the PLSR to predict negative concentrations. Real concentrations are logically greater or equal to zero. Here, the negative predicted concentrations were set to zero. That way, the error (RMSECV0) could be slightly improved. In addition, in order to obtain a better understanding of the error in relation to the respective concentration, the CV mean relative residual (MRR) of the measurements of the individual components was determined. All the CV results are summarized in The standard approach to evaluate the prediction/quality of the model would be to specify the error (RMSE) according to Equations (5) and (6) of each individual calibration model and average it over all RMSE in the course of the CV (RMSECV). The RMSEs of Mixtures 29 and 40 equal 123 ppmv and 562 ppmv, respectively. If we leave CHThe concentrations retrieved by the PLRS models can be obtained from 13C12C2H8 measured with the ICL 1638. For the ICL 1541, the largest RMSECV (604 ppmv) and at the same time smallest MRR (9.7%) can be assigned to CH4. This proves that the RMSE is highly dependent on the concentration, which in the case of CH4 is, on average, one magnitude larger than the other hydrocarbons. The largest MMRs (15.6–17.6%) were found for the ethane isotopologues measured with the ICL 1541. These discrepancies between the expected and the regressed concentrations are too high to be attributed only to the regression algorithm. Moreover, the estimated errors for some concentration values such as the CH4 in Mixture 29 or the C2H6 in Mixture 40 appear to be too small to justify the difference with the retrieved concentration values. Additionally, the variation for retrieved concentrations where a gas component was absent is relatively large. For CH4, it varies between −756.2 ppmv in Mixture 4 and +1241 ppmv in Mixture 40. All these results point out an underlying problem with the gas line management and/or the recorded mixed sample spectra. Especially with a limited dataset, each single measurement has a significant influence on the model. The uncertainty of the results originates (in the sense of error propagation) from the uncertainty in the sample preparation as well as from all other influences of the experimental setup. The sample preparation is associated with a certain degree of inaccuracy. The method of preparing the gas mixtures results in an uncertainty of the partial pressures and, therefore, the concentrations. After inserting sample gas into the cell and closing the valves, the gas line between the cross-adaptor and the cell was still filled with this component. When the cell was subsequently filled up to ambient pressure with N2, this remainder was pushed into the cell, thus falsifying the sample gas concentration. In addition, the uncertainty in the sample preparation of multiple components is considerably higher because the determination is solely calculated out of the pressure readings of the gas system. Furthermore, it can be assumed that the different components are not particularly well mixed in the gas system and mixing cell and that unwanted remaining substances in the system cannot be completely excluded. In fact, the different components are linearly dependent of each other because all gases at NA include small proportions of their 13C isotopologues, which also increases the error. Considering the fact that in this work only a simple PA setup was realized without substantial efforts to maximize the SNR or LOD, these results are very promising, especially since many improvements are still possible, e.g., cell optimization, signal enhancement with optimized amplifier and LIA parameters, and the application of direct modulation of the ICL instead of using the mechanical chopper. In general, the quality of the MVA strongly depends on the applied calibration method as well as on the used spectra. The PLSR is applicable as long as the individual components contributing to the overall spectrum are linearly independent of each other and possess characteristic features with signals larger than the noise level. The recorded spectra depend on the experimental setup, the absorption strength of the investigated compounds, as well as their concentration. The smallest RMSECV (28 ppmv) and MRR (7.3%) were found for 4, C2H6, and C3H8 (each at NA) using QEPAS [Overall, the PA setup has demonstrated to work dependable in distinguishing SC hydrocarbon isotopologues and, in combination with the evaluation algorithm, enables an isotope-selective concentration determination of SC hydrocarbons. The current way of sample preparation offers room for improvement to minimize the concentration uncertainty. This can be achieved, for instance, with a suitable gas mixer, a system based on the combination of pressure controller and flow controller, and/or with the acquisition of hydrocarbon gas samples with accurate premixed concentrations. Afterwards, a proper design of experiment should be used for hydrocarbon concentration mixture combinations. This will help to plan necessary future measurements with synthetic multicomponent gas mixtures for the calibration model (required for the sensor’s concentration determination). In the future, the research will focus on several tasks concerning the optimization of the PA setup. The achievable LOD can be further enhanced by numerous experimental improvements. The used PA cell in this work has a relatively low Q-factor. An exchange of the current cell with an optimized PA cell with a higher Q-factor directly improves the PA signal and lowers the LOD. The feasibility of using a quartz tuning fork (QTF) as acoustic transducer will be further investigated, since QTFs can have Q values > 10,000 , which ing QEPAS . In adding QEPAS .


It has been suggested that a viable strategy to improve complexity estimation based on the assessment of pattern similarity is to increase the pattern matching rate without enlarging the series length. We tested this hypothesis over short simulations of nonlinear deterministic and linear stochastic dynamics affected by various noise amounts. Several transformations featuring a different ability to increase the pattern matching rate were tested and compared to the usual strategy adopted in sample entropy (SampEn) computation. The approaches were applied to evaluate the complexity of short-term cardiac and vascular controls from the beat-to-beat variability of heart period (HP) and systolic arterial pressure (SAP) in 12 Parkinson disease patients and 12 age- and gender-matched healthy subjects at supine resting and during head-up tilt. Over simulations, the strategies estimated a larger complexity over nonlinear deterministic signals and a greater regularity over linear stochastic series or deterministic dynamics importantly contaminated by noise. Over short HP and SAP series the techniques did not produce any practical advantage, with an unvaried ability to discriminate groups and experimental conditions compared to the traditional SampEn. Procedures designed to artificially increase the number of matches are of no methodological and practical value when applied to assess complexity indexes. In time series analysis, complexity markers are frequently computed to estimate the degree of irregularity in dynamics. For example, in cardiovascular control studies ,2,3,4, tThe aim of this study was to test these workarounds over short simulated series simulating partially predictable dynamics corrupted by increasing amounts of noise  and in tx = {n = 1, …, N}, where n is the progressive counter and N is the series length; x is first normalized by subtracting the mean and by dividing each resulting value by the standard deviation, thus obtaining a normalized series fluctuating about 0 with unit variance. Given the current value m − 1) consecutive past values of m − 1)-dimensional and m-dimensional embedding spaces built with the technique of time-delayed coordinates [We assign the series rdinates .C(·) subtracts from each component of the pattern the mean assessed over it, namely C(I(·) switches the sign of all pattern components by multiplying each coordinate by −1, namely I(R(·) reverts the flow of time within a given pattern in such a way that the most delayed sample becomes the first component and the most recent sample becomes the last component, namely R(IR(·) = I(R(·)) inverts the reverted pattern, namely I(R(I(RI(·) = R(I(·)), leading to reversion of the time flow of the inverted pattern, provides the same result as IR(·). Let us consider, as an example, the sine function n·f/sf), where f/sf represents the ratio of the frequency f of the sine to the sampling frequency sf with f/sf = 1/50. Assigned the pattern I [Two patterns are matched if the distance between them is smaller than an norm) ,10.x via the computation of the amount of information associated with r, computed by dividing the number of matches of n. After assigning r and N, increasing the number of matches could improve the robustness of the estimate of N and to the strict boundary condition in the definition of the neighborhood of SampEn assesses the complexity of computed  as(1)Sar to I(r to R(r to I(R(r to I(R(IR(r to Assigned the reference pattern rategies : (i) xm C; (ii) a realization of a stochastic linear process with a dominant spectral peak generated via a second-order autoregressive model featuring two complex and conjugate poles with modulus ρ = 0.92 and phases φ = ±π/5 and driven by Gaussian white noise with zero mean and unit variance (type-II simulation). The dynamic generated by the logistic map in the chaotic regime was chosen because of its nonlinear properties [We considered two types of dynamics : (i) a roperties  and diffoperties , both properties ,38. The operties , these bWe tested the null hypothesis that type-I simulations corrupted by noise are realizations of a linear process with a Gaussian distribution, possibly distorted via a nonlinear static invertible transformation. According to this null hypothesis, we built surrogate series with the same second-order statistical properties  and the same distribution  as the original ones but with random phases via iterated amplitude-adjusted Fourier transform procedure ,41. FourThe protocol was originally designed to typify cardiovascular control and its complexity in PD patients through HP and SAP variability analyses ,34. Brienth HP (HPn). The maximum arterial pressure within HPn was taken as the nth SAP (SAPn). Fiducial points were carefully checked to avoid erroneous detections or missed beats. If isolated ectopic beats affected HP and SAP values, these measures were linearly interpolated using the closest values unaffected by ectopic beats. Sequences of 256 consecutive HP and SAP values were randomly selected within REST and HUT sessions. The procedures for the extraction of physiological variables, strategy for correction of artifacts and duration of the frame are standard in short-term heart rate variability analysis [After detecting the QRS complex using a traditional method based on a threshold on the first derivative of the ECG and locating the R-wave peak with minimum jitters using parabolic interpolation, the temporal distance between two consecutive QRS apexes was computed and utilized as an approximation of the analysis ,25. Timeanalysis : brieflym = 2, r = 0.2 × the standard deviation of the series, N = 256, and Euclidean norm, to calculate distances among the patterns. SampEn was computed over simulated and real data after linear detrending. SampEn was calculated according to the different strategies designed to increase the number of matches, namely S, SI, SR, SIR and SIR2 and CS, CSI, CSR, CSIR and CSIR2. The difference between the 97.5th and the 2.5th percentiles of SampEn was taken as a measure of the SampEn dispersion about the median. This index was computed for all the strategies, and it was divided by that calculated via the S strategy, thus quantifying the variation of the SampEn variance induced by the adopted pattern matching approach compared to the S strategy. This ratio was labeled the variance reduction ratio (VRR). If the VRR was significantly below 1, the considered strategy reduced the variance of SampEn. The assessment of VRR was carried out over simulated signals and real series.SampEn was calculated according to the standard settings ,23,31, np < 0.05 was always considered significant.One-way repeated measures analysis of variance, or Friedman repeated measures analysis of variance on ranks when appropriate, was applied (Tukey’s test for multiple comparisons) to check whether the different strategies for the assessment of matches affected SampEn computed over type-I and type-II simulations corrupted by a minimal amount of noise . Two-way repeated measures analysis of variance  was performed to assess the significance of SampEn changes induced by the orthostatic challenge within the same population (H or PD group) and by the pathology within the same experimental condition (REST or HUT). The analysis was repeated with different pattern matching strategies to check for discrepancies among conclusions. Statistical analysis was carried out using a commercial statistical program . A type-I error probability The error bar graphs in In the case of type-I simulation a, the smm − 1 by CSIR and CSIR2 was so high that the increment at embedding dimension m was negligible compared to with the CSR strategy. Results obtained from type-II simulation . The departure of the mean VRR from 1 was more evident in the case of the type-II simulation, with the mean VRR equal to 0.81, 0.85, 0.76, and 0.77, respectively.In the case of the type-I simulation a,c,e,g,iIn the case of the type-II simulation b,d,f,h,jThe comparison is given as a function of the amplitude of the white noise contaminating the chaotic and autoregressive dynamics expressed as a percentage of the standard deviation of the uncorrupted series. The two (black or red) lines are relevant to the 2.5th and 97.5th percentiles of SampEn computed over the set of the 50 original or surrogate simulations. Nonlinear dynamics were detected until the 97.5th percentile of SampEn assessed over the original simulations surpassed the 2.5th percentile of SampEn computed over the surrogates. This situation was detected at percentages equal to 39, 39, 33, 33 and 31 in the case of S, SI, SR, SIR, and SIR2 approaches, respectively, and at percentages equal to 45, 41, 31, 35 and 33 in the cases of CS, CSI, CSR, CSIR and CSIR2 approaches, respectively, thus remarking that the ability of detecting nonlinear dynamics was negligibly altered by the pattern matching strategies compared to the S strategy. More specifically, the use of the traditional matching strategy over centered patterns  might even slightly improve the detection performance; namely, nonlinear dynamics were detected with larger levels of noise compared to with S , while the application of strategies inducing a more notable increase in the number of matches, such as, e.g., SIR, SIR2, CSIR and CSIR2, slightly reduced the ability to detect nonlinear dynamics relative to the S approach .The error bar graphs in The main methodological findings of the study can be summarized as follows: (i) the influence of the strategies favoring pattern matching over SampEn varied with the transformation exploited, type of dynamics and level of noise superposed on the data; (ii) the application of the strategies for increasing the number of matched patterns could lead to a reduction in the range of the SampEn values; (iii) the reduction in the SampEn variance was more evident over linear stochastic series and using transformations over centered patterns; (iv) strategies increasing the number of matches could lead to an overestimation of the level of regularity despite the stochastic nature of the series or the presence of noise; (v) the ability to detect nonlinear dynamics was generally poorly affected by the application of a pattern matching strategy.The main experimental findings of the study can be summarized as follows: (i) over both HP and SAP series, the impact of the adopted pattern matching strategies on SampEn depended on the exploited transformations; (ii) when the pattern matching strategy was applied to centered patterns, SampEn was significantly reduced compared to the standard application of SampEn, and this result held regardless of the series; (iii) strategies designed to raise the number of matches did not provide any additional advantage compared to the standard application of SampEn in separating group and experimental conditions, and this observation held for the assessment of the complexity of both cardiac and vascular controls.The application of transformations to the current pattern before assessing its similarity to the reference pattern has been suggested to improve pattern similarity in the computation of fuzzy entropy . Among tThe most relevant drawback of the techniques devised to increase the number of matches is that they mix different phases of the dynamic and merge classes of features that might indicate very peculiar behaviors. For example, if a pattern specifically typifies the ascending part of the positive half cycle of the sine curve, and the reverse pattern characterizes the descending part of the positive half cycle, the inverse pattern is found in the descending part of the negative half cycle and the inverted reverted pattern lies on the ascending part of the negative half cycle see also a–d. The The computation of SampEn assessed according to the usual pattern matching strategy  confirmed that (i) complexity of the cardiac control decreased during HUT compared to REST in H subjects ,34,43 whWe do not recommend the use of strategies artificially increasing the number of matches because of the inherent risk of destroying peculiar features of the dynamic, as suggested by simulations, and the null practical advantage, as suggested by the application to the analysis of the short-term cardiac and vascular neural controls. Given the inherent stochastic nature of the physiological series, the use of strategies increasing pattern matching rate is likely to underestimate their actual complexity, and this underestimation might offset the advantage that might be linked to the reduction in the variance of the complexity markers. Moreover, given that complexity indexes based on the computation of SampEn strongly depend on the strategy exploited to find matches, we stress the importance of clearly reporting it to favor future comparisons.


The oxidation of 15 Polish coals of various carbon contents was performed using a flow reactor technique. A chromatography method was applied to measure the changes of oxidation products concentrations with the increase of temperature. It has been determined that all the tested gases were generated at the initial temperature. The collected data indicated that CO2 was a major oxidation product in the entire temperature range, while the amounts of H2 produced did not exceed 0.49% volume. At the temperature of 323 K, the ratio of CO2/CO was in the range of 10–23 but along with the temperature increase the ratio range narrowed to 3–4. In this paper, a comparison of the physical-chemical properties of the tested coals and the emissions profile of the gases using, among others, the hierarchical clustering analysis showed that samples with higher oxygen, sulfur, and inertinite content as well as lower ash and carbon content formed larger amounts of fire gases.The self-heating phenomenon of coal leads to work safety hazards in underground mining. The quantitative analysis of gaseous products in mine atmosphere constitutes one of the detection methods of advanced coal heating. The article presents the results of tests on CO, CO The fires occur all over the world, mostly in major coal-producing countries—such as China, India, Russia, the United States, Australia, and South Africa—but also in a smaller scale in Germany, Poland, or the Czech Republic . For theer vapor . In realectively . Carbon 2 ratio is independent from airflow rates at the low initial temperature, but it decreases below 0.2 with the increase of temperature. The experimental findings of this work indicate also that carbon monoxide was detected earlier than carbon dioxide. The studies in works by Wang et al. [2 is greater than for CO. Additionally, the study by Zhang et al. [A number of studies have been conducted on the carbon dioxide and carbon monoxide emissions during the spontaneous heating of coal. Baris et al.  analyzedg et al. ,10 or Wog et al.  indicateg et al. ,12, the g et al.  showed tg et al. ,15. A deg et al. .Few studies on the hydrogen detection during spontaneous heating of coal were performed ,18,19, a2), and hydrogen (H2) released during the thermal oxidation of Polish coals in the temperature of 323, 373, 423, 473, and 523 K. In this paper, a chemometric method of hierarchical clustering analysis (HCA) was applied to investigate the correlation between coal parameters and gases concentrations at the outlet of the reactor. The findings of this study improve the knowledge in the field of the relationship between coal properties and carbon monoxide, carbon dioxide, and hydrogen emissions; in addition, they can find practical implications for work safety in the coal mining industry.The objective of the study was to investigate the influence of temperature and coal types on the amount of carbon monoxide (CO), carbon dioxide  was applied to monitor the value of the flow rate. Simultaneously, a crushed coal sample packed in the center of reactor was heated to the set temperature. The first gaseous mixture was collected at the temperature of 323 K. The tests were conducted up to the temperature of 523 K. Samples of the released gases were taken manually to an airtight Tedlar bag for the analyses. Carbon dioxide, carbon monoxide, and hydrogen concentrations in the multicomponent gaseous mixture in the outflow of the reactor and at the set temperature were measured with the application of gas chromatographs . A SRI 8610C chromatograph  was used for the quantitative analysis of carbon dioxide. The chromatograph is equipped with two packed columns, one of which is filled with a molecular sieve 5A and the other with Porapak Q material, whereas hydrogen content was measured with the application of Shimadzu GC 2014 chromatograph . The measurements were performed under isothermal conditions; the temperature of molecular sieve 5A packed column was programmed to 303 K. The above-mentioned chromatographs were equipped with thermal conductivity detectors. A gas chromatograph, model Shimadzu GC 17A, with flame ionization detector and 5A molecular sieve layer inside a capillary column (column temperature 357 K) was used for determining carbon monoxide. Gas samples were introduced in the volume of 120 mL each. In the case of hydrogen, pure argon was selected as a carrier gas. For the remaining gases, pure helium was chosen as a carrier medium. With this setup, the limit of carbon monoxide quantification was of 0.0001 vol %, carbon dioxide around 0.05 vol %, while hydrogen was 0.00005 vol %.During the experiment, a coal sample of a grain size below 2 mm and weight of 0.4 kg was placed on a steel mesh located 1 cm above the bottom of the reactor for better distribution of the synthetic air flow. The air from a gas cylinder was injected to the bottom of the reactor at the flow of 5 × 10The 15 different coals of relatively low , medium (70–80% w/w) and high (>80% w/w) carbon content, coming from active mines located in the area of the Upper Silesian Coal Basin (USCB), in the south of Poland, were selected as the tested samples. The coal samples were analyzed in terms of their proximate, ultimate and petrographic parameters according to relevant standards in an accredited laboratory of the Department of Solid Fuel Quality Assessment at the Central Mining Institute and the results in the analytical state are given in Detailed information concerning the analyzers and standards has been reported elsewhere ,28. SampSample no. 1 was an exception for which the oxygen content was at the level of 4.79% w/w. This sample is also characterized by the highest ash content (26.98% w/w) as well as the lowest sulfur and moisture contents. The carbon content of five bituminous coal samples nos. 6–10 was in the range of 70–80% w/w, while for sample nos. 11–15 it was higher than 80% w/w. In coal sample nos. 6–15, the oxygen content changed from 8.19% w/w to 1.09% w/w. The lowest oxygen content of sample no. 15 corresponded with the highest carbon content equal to 89.11% w/w. The petrographic analysis of coals showed that coal sample nos. 4, 6, 7, 11, 12, 13, and 15 are characterized by a high content of inertinite maceral in the range from 44 vol % to 58 vol %. The lowest values of inertinite were determined in coal sample nos. 3 and 14 (below 20 vol %).2 and CO at given temperatures.As can be seen in 2/CO can reach high values, in particular for low rank coal, and, as a result of a further thermal runaway this ratio will tend to decrease to a constant value. In previous works [2/CO ratio with the increase of coal temperature was also observed.At the temperature of 323 K and 373 K, the ratio gained high values in the range of 10–23 and 2–16 respectively, because of low carbon monoxide emission. Along with the coal temperature increase to the values of 423 K and 472 K, the ratio decreased to the much narrower range of 1–5 due to a significant increase in the amount of CO generation. By contrast, at the highest temperature of 523 K, the ratio continues to be stable and the value is in the range of 3–4, independently of coal rank used. This implies that at the beginning of the coal spontaneous heating the ratio of COus works , the decBased on the results, it was found that carbon dioxide is released in abundant quantities  already at low temperatures compared to carbon monoxide, which may suggest that this gas is a better indicator of fire risk. However, the use of carbon dioxide as a fire detecting gas has some limitations, making this gas unreliable. The gas can originate from sources other than the self-heating process, i.e., natural content, acid mine water neutralization, machines with diesel-fueled engines working underground or the injection of carbon dioxide into a sealed area as an inert gas ,32. Addi2/CO were observed mostly for samples with the low carbon content. These findings may suggest that the ratio can depend on coal rank, particularly in the initial stage of coal self-heating process. As can be seen in 2 and CO were noted at the temperature of 523 K, these values were in the following ranges of 8.99–11.41 vol % and 3.00–3.23 vol % respectively. For the third group of coal sample nos. 11–15 and at the same temperature of 523 K, the concentration of carbon dioxide changed from 7.20 to 9.64 vol %, while the content of carbon monoxide was in the range of 2.31–3.13 vol %, so the values were even 20–30% lower than for coal sample nos. 6–10. A high amount of carbon oxides produced from low rank coal can be explained by the loosely packed structure of these samples. The condensed homo- or heterocyclic aromatic compounds constitute the basic structural unit of coal; the structures are connected by means of extreme groups consisting of aliphatic and alicyclic chains [3, carboxyls –COOH, or carbonyls =CO) on the coal surface. Thus, the high oxygen content from ultimate analysis may suggest a high number of active oxygen containing functional groups. As the coalification process progresses, the degree of ordering and the share of aromatic compounds increase, whereas the number of side groups decreases [The results presented in c chains . Within ecreases ,37. Aromecreases .2) and hydrogen (ΔH2) emission in the temperature range of 323–373 K, respectively as a function of oxygen content in coal and oxygen depletion in the gaseous mixture at the outlet of the reactor. As can be seen in 2  emitted during the self-ignition process at the temperature of 323 and 373 K, respectively (parameters nos. 10–15). The HCA allows to effectively investigate the similarity between studied coal samples in the parameters space and the similarities between studied parameters in the objects space. The HCA dendrograms were developed with the use of Ward’s linkage method and the Euclidean distance. The studied dendrograms are presented in The analysis of the complex effect of the physical and chemical parameters on the self-heating of coal was performed with the application of hierarchical clustering analysis (HCA) ,48,49,50Dendrograms presented in The dendrogram presented in —Subcluster B1 composed of coal sample nos. 2 and 4, and—Subcluster B2 collecting the coal sample nos. 3 and 5, respectively.The dendrogram constructed for studied parameters in the objects space see b allows 2 emitted at the temperature of 323 K),—Cass A containing parameters nos. 10 and 12 ,—Class C collecting parameters nos. 4, 7, and 8 , 2 emitted at the temperature 373 K), and—Class D grouping parameters nos. 1, 9, and 15 .—Class E containing parameters nos. 11 and 14  among all studied coal samples. Sub-cluster A1 collects coal samples which are characterized by a relatively higher carbon content in the sample (parameter no. 1) among all studied coal samples. Moreover, coal sample no. 13 is unique due to the highest inertinite content in the sample (parameter no. 9) and the lowest vitrinite content in the sample (parameter no. 8), whereas the coal sample no. 15 is characterized by the highest content of carbon and the lowest content of oxygen in the sample (parameters nos. 1 and 2). By contrast, coal sample no. 14 is characterized by the high amount of H2 emitted at the temperature of 373 K (parameter no. 15) and the highest vitrinite content in the sample (parameter no. 8).In order to explain the reason of grouping the studied samples into two main clusters as well as to explain the uniqueness of coal sample no.1, the dendrogram of objects in the space of studied parameters with the color map of studied standardized data see c sorted 2 emitted at the temperature of 373 K and 323 K . Moreover, coal sample nos. 6 and 7 are characterized by the highest volatile and mineral matter contents in the coal samples (parameter nos. 6 and 7), respectively, whereas object no. 12 is unique due to the highest amount of H2 emitted at the temperature of 373 K (parameter no. 15).The objects belonging to sub-cluster A2 are described by a relatively higher inertinite content in the sample as well as a higher amount of CO and HNon-clustered coal sample no. 1 is unique due to the lowest volatile matter content (parameter no. 6) and the highest ash and mineral matter content in the sample (parameters nos. 4 and 7).2 emitted at the temperature of 373 K . The sub-cluster B1, collecting coal sample nos. 2 and 4, is additionally unique due to the higher amount of CO and CO2 emitted at the temperature of 323 K (parameter nos. 10 and 12). Moreover, coal sample no. 2 is characterized by the highest sulfur content in the sample and the highest amount of CO and CO2 emitted at the temperature of 323 K  among all studied coal samples, whereas coal sample no. 2 is characterized by the highest amount of CO2 emitted at the temperature of 373 K (parameter no. 13). Cluster B collecting the remaining coal samples with low carbon content  is characterized by higher content of oxygen, sulfur, moisture, and the amount of COSub-cluster B2 is unique due to the highest moisture content in the coal sample (parameter no. 5). Additionally, coal sample no. 3 is characterized by the highest oxygen content in the sample (parameter no. 2).2/CO ratio was above 10 and then it showed a decreasing tendency to the level of constant value when a controlled rise of temperature occurred. Based on the measurements, it can be concluded that coals even of the same rank may exhibit significant differences in the amounts of gaseous products generated during the thermal oxidation process due to their various physical and chemical properties. The differences in the tendency to the spontaneous heating of coals were mainly caused by the different carbon, oxygen, sulfur, and ash as well as inertinite contents in the studied coal samples. The lignite oxidation process was characterized by a higher total amount of carbon oxides generated in comparison to the values obtained for the bituminous samples. High sulfur content in lignite and high inertinite content in bituminous contributed to a significantly higher emission of carbon dioxide and carbon monoxide. The chemometric method such as HCA enabled to effectively explore the relationship between the amounts of carbon monoxide, carbon dioxide, and hydrogen generated during the oxidation process and the properties of coal. In the research, no correlation between coal parameters and the production of hydrogen was observed. In the case of the low temperature oxidation process, hydrogen reached concentration values at the level of a few parts per million. This means that the high concentration of hydrogen in underground mine atmosphere could result in an advanced heating phase.The results presented in this work provide evidence that carbon dioxide, carbon monoxide and hydrogen are sensitive to coal heating temperature and their concentration increases regularly with the temperature of coal. The emission of carbon dioxide is much higher than that of carbon monoxide probably as a result of the lower value of activation energy. It was noted that at the beginning of the test, the CO