Increasing the reliability of high-temperature electric heaters of the radiant tube type based on graph theory methods

Investigation of the machinability of commercially pure titanium in ultrasonic machining using graph theory and matrix method

Several computer models exist to explain the observation of terrestrial gamma‐ray flashes (TGFs). Some of these models estimate the electric field ahead of lightning leaders and its effects on electron acceleration and multiplication. In this paper, we derive a new set of constraints to do more realistic modeling. We determine initial conditions based on in situ measurements of electric field and vertical separation between the main charge layers of thunderclouds. A maximum electric field strength of 50 kV/cm at sea level is introduced as the upper constraint for the leader electric field. The threshold for electron avalanches to develop of 2.86 kV/cm at sea level is introduced as the lower value. With these constraints, we determine a region where acceleration and multiplication of electrons occur. The maximum potential difference in this region is found to be ∼52 MV, and the corresponding number of avalanche multiplication lengths is ∼3.5. We then quantify the effect of the ambient electric field compared to the leader field at the upper altitude of the negative tip. Finally, we argue that only leaders with the highest potential difference between its tips (∼600 MV) can be candidates for the production of TGFs. However, with the assumptions we have used, these cannot explain the observed maximum energies of at least 40 MeV. Open questions with regard to the temporal development of the streamer zone and its effect on the shape of the electric field remain.

In response to the requirement, the manufacturing processes have evolved from mass production technique, through its implementation on reconfigurable systems. The most difficult part of reconfigurable manufacturing systems (RMSs) is an understanding of the barriers related to their relative interdependencies. This article presents a conceptual framework of various barriers associated with RMSs along with their interdependencies. Using graph theory and matrix methods, the barriers of RMSs presented in the form of a single numerical index. The proposed model is quite versatile from the point of view that it provides an opportunity to integrate new barriers which could impact on manufacturing processes. In the present work, an attempt has been made to develop a mathematical model of these barriers using graph theory and matrix methods. An index of barriers in RMS is proposed which evaluates the inhibiting power of these barriers.

The work is devoted to the consideration of applications of mathematics, in particular, graph theory and group theory in chemistry and physics. Chemistry was one of the first to adopt the ideas of graph theory. Mathematical chemistry is a section of theoretical chemistry that studies the application of mathematics to chemical problems. The possibility of formalizing molecules in the language of structural chemistry using graphs allows one to determine the number of different isomers using graph theory methods. The main tool in mathematical chemistry is mathematical modeling using computer technology. The methods of graph theory are actively used in three areas of chemistry: structural chemistry, chemical kinetics, and chemical physics of polymers. Group theory has found application in many areas of physics. Group theory serves to explain the most important characteristics of atomic spectra. Group theory provides an opportunity for a uniform approach to a large number of problems in solid state physics. Matrix groups and unitary group representations are actively used in these studies. Irreducible group representations are used to classify vibrational and electronic states of a crystal. Methods of group theory are applied to models of problems of classifying electronic states of a crystal. In crystallography, much attention is paid to applications of group theory methods to the study of vibrations of atoms that make up a molecule relative to their equilibrium positions. The results can be useful in encoding information in space communications sessions.

Aging is the fundamental of neurodegeneration and dementia, affecting every organ in the body. With the aggravation of global aging, more and more research is focusing on how brain changes in older adults. This study aimed to uncover the differences in brain functional networks from the perspective of graph theory between young individuals and older individuals. Here, 61 individuals in their 20s and 94 cognitively healthy old individuals in their 70s underwent a resting-state functional magnetic resonance imaging scan. Based on the graph theory method, a functional network was constructed for each participant. Our results revealed that brain functional networks in older adults maintained small-world properties. However other nodal parameters including degree centrality, betweenness centrality, shortest path lengths, local efficiency, nodal efficiency, and cluster coefficients showed significant differences in many nodes (brain regions) between the 2 groups. Moreover, we correlated these nodal parameters with age, exploring 8 brain regions significantly affected with age. 7 out of 8 brain regions including the bilateral superior parietal lobule, bilateral precuneus, right middle cingulate, right inferior parietal lobule and right transverse temporal gyri were distributed in the default mode network. Our findings, based on graph theory, provided evidence for the alteration of the default mode network in older adults from the perspective of the functional network.

Classification of sedimentary and igneous rocks by laser induced breakdown spectroscopy and nanoparticle-enhanced laser induced breakdown spectroscopy combined with principal component analysis and graph theory

Graph theoretical studies have been designed to investigate network topologies during life. Network science and graph theory methods may contribute to a better understanding of brain function, both normal and abnormal, throughout developmental stages. The degree to which childhood epilepsies exert a significant effect on brain network organisation and cognition remains unclear. The hypothesis suggests that the formation of abnormal networks associated with epileptogenesis early in life causes a disruption in normal brain network development and cognition, reflecting abnormalities in later life. Neurological diseases with onset during critical stages of brain maturation, including childhood epilepsy, may threaten this orderly neurodevelopmental process. According to the hypothesis that the formation of abnormal networks associated with epileptogenesis in early life causes a disruption in normal brain network development, it is then mandatory to perform a proper examination of children with new-onset epilepsy early in the disease course and a deep study of their brain network organisation over time. In regards, graph theoretical analysis could add more information. In order to facilitate further development of graph theory in childhood, we performed a systematic review to describe its application in functional dynamic connectivity using electroencephalographic (EEG) analysis, focussing on paediatric epilepsy.

With the exponential growth of electricity generation using intermittent renewable power sources, there is a need for affordable energy storage. For grid level storage in past years, redox flow batteries (RFB) have drawn considerable attention. Most successful RFBs till now are all-vanadium RFB and all-iron RFB. But these RFBs have a few drawbacks associated with them like; First RFB developed by NASA[1], Iron-chromium RFB, had problems of ions crossing over; all-iron RFB [2] have a problem of hydrogen evolution reaction (HER) at the negative electrode which causes capacity decay; and the commercialized all-vanadium RFB's [3] is expensive and has limited vanadium reserves.In an effort to address these problems, we present here the initial development of an all-tungsten RFB. Its key advantage is no capacity fading with cycles due to ions crossing over. The tungsten salt used was phosphotungstic acid (PTA). As shown in cyclic voltammograms (CV) of PTA in Figure 1(a), it is clear that PTA ions exist in four different oxidation states (PTA3-, PTA4-, PTA5- and PTA6-). For all-PTA redox flow battery experiments, we used the same PTA5- active species for both negative as well as positive electrolyte. Prior to the all-PTA RFB tests, PTA3- was reduced to PTA5-. Since PTA3- is the only salt available, it was reduced to PTA5- by using it as a negative electrolyte for the iron-tungsten RFB using a procedure developed earlier [4].As shown in reaction 1, during charging on the negative side, PTA5- gains 2 electrons and reduces to PTA6- oxidation state. Simultaneously, on the positive side PTA5- loses 2 electrons and gets oxidized to PTA3-. Moreover, the maximum potential difference that can be achieved by using the highest reduced form of phosphotungstic acid as a single cell is +0.611 V vs. RHE (Eq. 4). Although we are getting half the potential when compared to an all-vanadium or an all-iron battery. But due to its extremely fast kinetics and large discharge currents makes all-PTA RFB a promising alternative. For the large capacity of the battery, one of the deciding factors is the solubility of its active species salts and the maximum solubility of PTA3- is 0.7 M.Flow cell experiments were conducted using an in-house constructed standard fuel cell setup [4]. Meanwhile, CV experiments were conducted in 3 electrode setup using glassy carbon as working electrode, platinum mesh as counter electrode and mercury/mercurous sulphate (Hg/Hg2SO4) as reference electrode. Hg/Hg2SO4 was calibrated in 0.5 M H2SO4 using an in house RHE. Also, all the potentials mentioned here are with respect to RHE. A CV (see Figure 1(a)) for phosphotungstic acid was obtained which showed 3 distinct peaks corresponding to the 3 reactions. Reactions 2 and 3 involve transfer of 1 electron each, while reaction 1 requires 2 electrons as proven from the current peaks of the CVs as well as limiting currents obtained from their RDEs [5]. The involvement of parasitic HER is clear from the 3rd reduction peak. Kinetic parameters such as rate constant (k0), Tafel slope, diffusion coefficients (Do) and transfer coefficient (α) were determined using RDE studies. From RDE analysis at different RPM, rate constant for PTA3- was found to be 4.49 x 10-3 cm s-1.Meanwhile, for the flow cell experiments we have taken electrolyte solution concentrations similar to that for the CVs. The flow rate (120 mL min-1) and volume (40 mL) for both the electrolyte were kept same. As shown in Figure 1(b), the all-PTA battery was charged and discharged using chronopotentiometry at a current density of 50 mA cm-2. Furthermore, to obtain the i-V performance curve the cell was discharged from 2 mA to 1000 mA for 10s. The potential at the end of 10th second was reported to eliminate the pseudo steady state [6]. i-V and power density performance curve was plotted from these current and potential values (see Figure 1(c)).From just 40mM concentration of PTA5- the maximum volumetric capacity we got is around 200 mAh L-1, the maximum power density obtained was 10 mW cm-2 and the maximum current that can be drawn was 85 mA cm-2. The above results strongly suggest that the all-PTA RFB could indeed be a promising alternative. Figure 1

Abstract. In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007), and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward) convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum) potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South) Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the other intensifies and merges with the opposite main cell of the same polarity to form the large "round-shaped" convection cell when approaching a well-known IMFBy-dominated configuration. Opposite scenarios with interchanged roles of the respective cells occur for the opposite turning of the clock angle and at the Southern Hemisphere. The high-latitude dayside cells become more pronounced with increasing magnitude of the IMF vector.

The effect of the electric field impact on gaseous fuels combustion was extensively studied for several decades. According to the studies results, it is possible to achieve high CO reduction rates with relatively small increase of NO x concentration in flue gases. Despite the fact of a high number of the similar researches, experimental units involved conventional layout of the DC or AC source connection to the electrodes. In framework of the current research was proposed new DC source connection layout to the electrodes, which allowed to rise the electric field intensity to 1150kV/m keeping the maximum potential difference between electrodes at 2.3kV level. The maximum registered CO emissions reduction in application of electric field, which was produced internally in burner, achieved 41% comparing with electric field free conditions. In addition to emissions reduction, FFT analysis of acoustic signal showed significant amplitude rise at high electric field intensity levels.

An experimental study of potential difference between metals of bcc, hcp, fcc and thbcc crystal structure when placed in water and irradiated by a high intensity pulsed ultrasonic field are reported for metal-water interface. A comparison of the work function, threshold transducer voltage and potential difference at these threshold voltages as well as the maximum potential difference as a function of melting point temperatures of platinum, silver, nickel, copper, lead, tin, cadmium, iron and zinc is reported. The present work is useful for providing fruitful information about the effect of the acoustic cavitation.

In this paper the bag-of-words model is applied to image classification and improves the existing problems of the traditional bag-of-words method. We propose a method of combination of corner detection and graph theory for ROI region extraction and fuzzy membership degree. First using corner detection for images, then the ROI region is defined by the method of graph theory. Then the SIFT features of the ROI region are extracted and the visual dictionary is generated. The visual dictionary can be more accurate to describe the image features, which can reduce the influence of background information and other interference information. Secondly, the concept of fuzzy membership function and information of feature space is introduced to improve the image of the visual histogram. Finally, support vector machine classifier is used to classify. Through the experiment of the Caltech 100 database, the result shows that the method improves the accuracy of classification compared with the traditional method.KeywordsBag-of-wordsCorner extractionGraph theoryFuzzy membership degree

The article discusses the use of a specialized software package for analyzing the structural organization of complex control systems for technological objects using graph theory methods. The main attention is paid to verifying the correctness of information links between functional control tasks through the formalization of the concepts of "information field" and "information environment". The developed tools allow one to perform structural analysis of interdependencies, identify topological violations in the communication system and optimize the control architecture. Of particular importance is the adaptation of graph methods for diagnostics of process control systems, which expands the possibilities of modeling and researching of complex industrial objects. The proposed approach demonstrates the effectiveness of using the mathematical apparatus of graph theory to solve practical problems of designing and modernizing automated process control systems.

The rapid growth of cities significantly impacts the development of transport and logistics infrastructure (TLI), creating substantial challenges for the transport network and quality of life. To enhance the efficiency and sustainability of TLI, various approaches, planning methods, and management strategies are employed at the city or agglomeration level. The objective of this study was to investigate, using graph theory and correlation analysis, the relationship between the polarity and logistic flow of the city’s meso-districts. Based on these findings, recommendations for the development of the city’s transport and logistics infrastructure were proposed. The logistic flow, influenced by social, economic, institutional, and environmental factors, plays a critical role in the planning and operation of transport and logistics infrastructure within each meso-district of the city. The determination of the polarity of meso-districts was conducted based on expert assessments by specialists, while the indicators of logistic flow were derived from the average values of statistical data for the period 2021–2023. The results demonstrated that a reduction in the polarity of meso-districts—characterized by multilateral connections between meso-districts and key indicators of logistic flows—can positively influence the quality and accessibility of the city’s transport and logistic infrastructure. This approach enables the identification of the most problematic meso-districts within the city, the mapping of logistic flow directions, and the determination of strategic development pathways for the city’s transport and logistics infrastructure (TLI). Furthermore, it was established that the polarity of the meso-district graph reflects the state of traffic congestion within the districts and its environmental impact. This correlation provides valuable insights into refining the planning and development of the city’s TLI, ensuring a more sustainable and efficient urban transport system. This study contributed to the development of the city’s transport and logistics infrastructure by proposing a comprehensive model that enhances the understanding and strengthens the interconnections between meso-districts and urban logistics. The findings hold significant implications for urban planning, as they highlight the necessity of a detailed consideration of the role of meso-districts, as well as targeted investments in transport and logistics infrastructure to ensure its sustainable development in the future.

To enhance the accuracy of computer-aided diagnosis of adolescent depression based on electroencephalogram signals, this study collected signals of 32 female adolescents (16 depressed and 16 healthy, age: 16.3 ± 1.3) with eyes colsed for 4 min in a resting state. First, based on the phase synchronization between the signals, the phase-locked value (PLV) method was used to calculate brain functional connectivity in the θ and α frequency bands, respectively. Then based on the graph theory method, the network parameters, such as strength of the weighted network, average characteristic path length, and average clustering coefficient, were calculated separately ( P < 0.05). Next, using the relationship between multiple thresholds and network parameters, the area under the curve (AUC) of each network parameter was extracted as new features ( P < 0.05). Finally, support vector machine (SVM) was used to classify the two groups with the network parameters and their AUC as features. The study results show that with strength, average characteristic path length, and average clustering coefficient as features, the classification accuracy in the θ band is increased from 69% to 71%, 66% to 77%, and 50% to 68%, respectively. In the α band, the accuracy is increased from 72% to 79%, 69% to 82%, and 65% to 75%, respectively. And from overall view, when AUC of network parameters was used as a feature in the α band, the classification accuracy is improved compared to the network parameter feature. In the θ band, only the AUC of average clustering coefficient was applied to classification, and the accuracy is improved by 17.6%. The study proved that based on graph theory, the method of feature optimization of brain function network could provide some theoretical support for the computer-aided diagnosis of adolescent depression.