Abstract: With the rapid development of anti-stealth technology and the iterative renewal of firepower destruction weapons, the battlefield survivability of modern weapons and equipment has been severely tested. In the modern warfare of over-the-horizon, radar detection technology is currently the most widely used method; therefore, reducing the radar echo signal is the most important factor to improve the stealth ability of weapon equipment. Generally, stealth technology is divided into structural stealth and material stealth. Reasonable shape structure design can reduce the radar cross section (RCS) value of a weapon equipment. However, due to the high cost of shape structure and the easy reduction of the comprehensive performance of equipment, there are many limitations in application. Because the stealth technology of materials is relatively simple and the design difficulty is relatively low, the research and application of stealth materials are popular and have been well explored. Although the traditional absorbing materials have the advantages of low cost, good flexibility, and easy processing, they also have the defects of high density, narrow working frequency band, and limited strength. Core-shell microwave absorber is a composite multiphase structure with a spherical particle as the core and one or more layers of heterogeneous materials coated on the outer surface. Because of its unique structure and excellent performance, it is a promising material to solve the existing problems. On the basis of reviewing the working principle of microwave absorbing materials, the advantages of core-shell structure materials in the field of microwave absorbing were discussed. This paper mainly introduced the research progress of different types of core-shell structure microwave absorbing materials explored in recent years as well as summarized and commented on their preparation methods, structure, and microwave absorbing properties; these materials are mainly based on ferrite, magnetic metal powder and its oxide, ceramic, conductive polymer, and carbon series materials. Finally, the development trend of core-shell structure mircrowave absorbing materials was predicted, including multi-layer core-shell structure, yolk-shell stucture and special structure combined with other structures, whisch can provide reference for futher study of core-shell shtucture composite absorbing materials.
Abstract: Medium manganese steels with the 3%-12% manganese content have outstanding tensile strength and elongation and low production cost. Thus, they are considered as third-generation advanced high-strength steels for automobiles. The research and development prospects and application potential of medium manganese steel in automotive parts have attracted wide attention both in China and overseas. After the medium manganese is deformed by forging or rolling, heat treatments such as quenching, tempering, and intercritical annealing is performed to obtain metastable austenite and ultra-fine ferrite/martensite microstructures. Metastable austenite transforms to martensite under flow stress, resulting in transformation-induced plasticity (TRIP) effect, which may be accompanied by twinning-induced plasticity (TWIP); the steel consequently exhibits good plasticity without sacrificing strength and thus meets the processing requirement of automobile parts with complex structures. The product of tensile strength and elongation of hot-rolled medium manganese steel, with chemical composition of Fe-0.2C-10Mn-4Al, under quenching and tempering can be larger than 70 GPa·%, which is higher than the current literature value. This paper summarized the current research status of medium manganese steel in China and abroad and analyzed the mechanical properties data of medium manganese steel with different chemical compositions, deformation process, and heat treatment process in the literature. The influence of the chemical composition, deformation process, and heat treatment process on the microstructure and mechanical properties was discussed. The influences of special properties of medium manganese steels, such as lüders band and PLC band, on work hardening rate and hydrogen-induced delayed cracking properties were comprehensively discussed. Moreover, based on deformation control and prediction via the stacking fault energy of the second-generation advanced high-strength steel with pure austenite microstructure, the paper presented a deformation prediction model of the austenite phase in the medium manganese steel. Finally, the paper discussed the problems and prospects of the medium manganese steel.
Abstract: Strengthening the embankments on soft foundations is generally capable of improving stability. Based on this understanding, for soil foundations whose stability does not meet specification requirements, embankments are strengthened during design to improve the overall stability of the foundation. However, the actual increase is limited. In particular, for soft foundations, increase in the strength of the embankment is high will damage the foundation. Thus, the use of high-strength geotextiles is common in this situation. This study considers that the safety factor, which is usually determined using the overall stability analysis method, may feature a high level of risk. When the strength of the embankment differs considerably from the strength of the soft foundation, the safety factor of soft foundation embankment may be less than the overall stability safety factor. Therefore, to calculate the stability of soft soil foundation embankment, in addition to the overall stability calculation, the stability of the soft foundation should be reviewed. This study illustrates the correctness of this point of view. A method for calculating the stability of soft foundation is proposed. Based on this method, a calculation method for the overall stability of the embankment under scouring condition is proposed. Based on the original foundation bearing capacity model, the method considers the difference between the dike foundation and rigid foundation. Variable elasticity width fully reflects the most likely point of foundation failure occurrence when the dike is damaged. The stability of the foundation is increased by increasing the accuracy of the slip zone. Based on this method, this study also discusses the stability of the foundation under the scouring of the embankment. This method can provide a more reasonable and reliable design calculation for the safety of embankments on soft foundations.
Abstract: Deep-hole directional cumulative-blasting cracking technology has unique advantages for improving coal seam permeability. This paper was concerned with the range of the effective fracture zone under cumulative blasting using a linear-shaped charge in a coal seam. Based on the analysis of the mechanism of the directional cumulative-blasting in coal seams, the response characteristics of the coal under the coupled effects of the blasting-induced shock wave, stress wave, detonation gas and the energy-cumulative effect, and the partition characteristics of the crack in the cumulative-blasting-affected area were studied by theoretical analysis; moreover, a numerical analysis model of cumulative blasting was established, and the propagation distribution characteristics and range of coal seam fracture under cumulative blasting were investigated through numerical simulation. The results of the theoretical analysis and simulation show that the cumulative-blasting-affected area can be divided into crushed, crack, and elastic-deformation zones; further, the crack zone can be divided into crack-intensive and main crack-propagation zones according to the type and number of cracks. Additionally, a partition model for the influence of deep-hole cumulative blasting with linear-shaped charge in coal seams was constructed. Meanwhile, under the influence of the shaped-charge structure, the crushed zone has an oval-like shape with a small radius in the direction of the shaped-charge jet, while the crack-intensive and main crack-propagation zones have oval-like shapes with a larger radius in the direction of the shaped-charge jet. In addition, field experiments of deep-hole cumulative blasting with linear-shaped charge in coal seams were carried out and the experimental results show that the influence of the cumulative blasting on the increase of the coal-seam-gas volume fraction in each observation hole weakened in a step-wise manner (strong-medium-weak) with increasing distance from the blasting borehole; this is consistent with the partition model of the constructed cumulative blasting, i.e., the cumulative-blasting-affected area has certain zoning characteristics, and the crushed, crack-intensive, and main crack-propagation zones are the main components of the effective fracture zone.
Abstract: Biohydrometallurgy is an increasingly popular ore extraction technology and is especially applicable for low-grade ores. In particular, Acidithiobacillus ferrooxidans (A. ferrooxidans) is by far the most widely used bioleaching microorganism for leaching ores, including for sulfide ores and manganese dioxide ores. At present, many works are focused on the vital facilitating role of A. ferrooxidans in the cycles of sulfur and iron for sulfide ores bioleaching. However, research on the effect of A. ferrooxidans on manganese dioxide ores leaching is limited. The effects of A. ferrooxidans on the electrochemistry behavior of pyrolusite in simulated solutions (9K basic medium, A. ferrooxidans, Fe(Ⅲ), A. ferrooxidans+Fe(Ⅲ)) were investigated using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. Mott-Schottky curves were utilized to determine the passive film formed on the surface of pyrolusite ore in the presence or absence of bacteria bath solutions. The results show that A. ferrooxidans promotes the redox of MnO2/Mn2+ and triggers the reaction of MnO2/Mn(OH)2. A. ferrooxidans accelerates electron exchange between pyrolusite and solution; in the A. ferrooxidans-simulated solution, the charge-transfer reaction resistance of manganese dioxide is 34% lower than that of the control (9K) and 11% lower than that of the Fe(Ⅲ) solution. Germs cause polarization of pyrolusite, leading to an increase in oxidative activity of manganese dioxide. Bacteria facilitate the transformation of MnO2 to MnO·OH and is beneficial to its diffusion. The indirect action mechanism is adopted to explain the interaction between A. ferrooxidans and pyrolusite. The passive films formed in simulated solutions exhibit p-n-p-n type semiconductor properties at the polarization potential of 0.2 V when pH is 2.0, and the depletion layer of pyrolusite appears between 0.2 and 0.4 V. Introducing A.ferrooxidans to the Fe(Ⅲ)-free solution decreases the donor density and the acceptor density because bacteria contain a variety of groups involved in electron transfer, which accept free electrons or fill holes, prompting the exchange of species between manganese oxide and solution. Admixing A. ferrooxidans to Fe(Ⅲ)-containing solution increases carrier density, reducing the corrosion resistance of membrane. The corrosion rate of pyrolusite increases with the addition of A. ferrooxidans.
Abstract: Heterogeneous Fenton-like method has attracted considerable attention because of its potential effectiveness in mineralization of organic contaminants in a wide range of reaction medium pH. Spinel ferrites MFe2O4 (M=Fe, Zn, Cu, Ni, Mn, Co) as heterogeneous Fenton-like catalysts have been studied extensively due to their good catalytic activity, prominent physical and chemical stability, and excellent magnetic properties, which allow their easy separation from the reaction medium by magnetic field for further circular utilization. Considering the group of ferrites, limited research focused on the utilization of MgFe2O4 as heterogeneous Fenton catalytic agent, whereas most of the catalysts are synthesized by pure chemical reagents. In this study, magnetic multi-metal co-doped MgFe2O4 heterogeneous Fenton-like catalyst was synthesized from saprolite laterite by acid leaching-hydrothermal calcination method. The effect of calcination temperature on the phase, morphology, specific surface area, and pore size distribution of samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared, Brunauer-Emmett-Teller/Barrett-Joyner-Halenda analysis. The catalytic activity of the as-prepared products as heterogeneous Fenton catalysts for the degradation of Rhodamine B (RhB) solution was also investigated. The results show that the layered double (multi) hydroxides coupled with a portion of magnesium ferrite are synthesized by hydrothermal method, and the cubic crystal MgFe2O4 is obtained by decomposition of the layered double (multi) hydroxides after calcination above 300℃. With the increase in calcining temperature, the crystallinity of the products increases, and the particle size becomes larger. The morphology gradually grows to near spheroidal particles, and the dispersion degree gradually increases. Meanwhile, the pore size becomes larger, and the specific surface area is reduced. Calcination of sample H-C500 exhibits the best catalytic activity for the degradation of RhB after 500℃, achieving 97.8% degradation efficiency of 10 mg·L-1 RhB after 300 min at the reaction conditions of 45℃, pH 6.44, 0.625 g·L-1 catalyst dosage, and 1.0% (volume fraction) H2O2. The total organic carbon (TOC) removal could reach 77.8%. The reused catalyst can still maintain high activity, and after three consecutive degradation cycles, the reduction of degradation efficiency and TOC removal efficiency are less than 3.0% and 5.0%, respectively.
Abstract: The influences of the normalization parameters and nitriding parameters on the microstructure of normalized samples, the primary recrystallization microstructure, and inhibitors were analyzed by electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) techniques. The effects of normalizing cooling rates, nitriding temperatures and nitrogen content on the primary recrystallization and secondary recrystallization microstructure, textures, and properties were studied. The results show that grain sizes decrease with the increasing normalizing cooling rate; when the rate is slow, the grain size of high-temperature nitriding sample increases with the slow normalizing cooling rate, reducing the driving force for secondary recrystallization and increasing secondary recrystallization temperature. The acquired inhibitor is insufficient, which leads to unsuccessful secondary recrystallization. High-temperature nitriding and low-temperature nitriding lead to different sizes of inhibitors in the decarburized sheets; however, inhibitors in the surface and subsurface regions of high-temperature nitriding samples are primarily of the same size, while the inhibitors in the surface region of low-temperature nitriding samples are larger than those of the subsurface inhibitors. The lower-temperature nitriding sample with low nitrogen content exhibits a poor magnetic property. As the grain size remains small at a low normalizing temperature and high normalizing cooling rate, the second recrystallization starts at a slightly lower temperature and Brass-type oriented grains are present. The secondary recrystallization of high-temperature nitriding and low-temperature nitriding samples with high nitrogen content could be basically completed; however, the magnetic properties of samples are different, and more grains with deviated {210} < 001> orientation lead to a reduction in magnetic properties.
Abstract: Tubes in deep wells are subjected to the mixed effects of the environment and stress and thus suffer many failures. Therefore, studying the corrosion of materials under stress deformation is necessary. This paper aims to investigate the effect of applied tensile stress on the dissolution of passive film and the repair mechanism of L80-13Cr martensitic stainless steel in solution of 80 g·L-1 sodium chloride. Electrochemical tests were employed for measurements, where the main test measurements include open circuit potential (OCP), electrochemical impedance spectra (EIS), and potentiodynamic polarization tests. Contact angle measurement was combined with microscopic morphology analysis (Zoom stereo microscope) to investigate the surface activity. The test results show that there is the positive relation between applied tensile stress and the passivation characteristic of L80-13Cr martensitic stainless steel. Increase in the applied tensile stress negatively shifts the OCP value of L80-13Cr martensitic stainless steel, decreases the electron transfer resistance (Rt) and polarization resistance (Rp), and increases the rate of reaction; however, the passivation region significantly reduces, the passivation current density (Ecorr) increases, and the self-corrosion current density decreases, which forms at a high potential. The results of contact angle test and microscopic morphology analysis show that the applied tensile stress reduces the surface contact angle and promotes the pitting of L80-13Cr martensitic stainless steel. Applied tensile stress can increase the surface energy of L80-13Cr martensitic stainless steel, promote the dissolution of the passivation film, and inhibit the regeneration of the passivation film; thus, it can deteriorate the corrosion resistance of materials.
Abstract: Recently, the use of bromine completion fluids in the oil and gas industry has caused numerous severe corrosion problems of the oil well casing and tubing, particularly the localized corrosion failure. Bromine completion fluids, such as KBr solution, are highly corrosive to steels. Even if the stainless steel is subjected to a high concentration of bromate under high temperature and pressure, it can still experience severe corrosion failure risks. In this study, the influence of KBr concentrations on corrosion behaviors of plain and super 13Cr steels under high temperature and pressure was investigated by corrosion simulation, scanning electron microscopy (SEM) observation, and electrochemical measurements. The results show that both plain and super 13Cr steels exhibit good corrosion resistance in KBr solutions with various concentrations regarding average corrosion rate, which is either mild or moderate. However, the local corrosion rates of plain and super 13Cr steels are serious or extremely serious. With the increase of bromide concentration, the free corrosion and pitting potentials of plain 13Cr steel significantly decrease. Both the average and local corrosion rates increase significantly. For super 13Cr steel, the pitting potential decreases, whereas the free potential remains relatively stable. The average corrosion rate of super 13Cr steel shows a lower scope of change than the local corrosion rate, which increases significantly and indicates that super 13Cr steel is much more corrosion resistant than plain 13Cr steel, but its local corrosion sensitivity is still high. Laser scanning confocal microscopy (LSCM) results show that both plain and super 13Cr steels exhibit serious pitting corrosion in a KBr solution with a concentration of 1.40 g·cm-3, and this is related to the aggressiveness of Br-. Compared with plain 13Cr steel, super 13Cr steel shows a lower pitting sensitivity; however, its pitting corrosion risk cannot be ignored.
Abstract: Silver clad aluminum composite wire, which combines the high electrical conductivity of silver-coated metal, good welding performance, and low density, has wide application prospects in aerospace and other fields. The preparation of silver clad aluminum bars with high surface quality and good combination of interfaces is an important step in the preparation of silver clad aluminum wire with excellent performance. Continuous casting composite forming is a short, high-efficiency material-forming process, which provides methods for the preparation of silver clad aluminum. The boundary conditions of the vertical continuous casting process of silver clad aluminum composite rod that has a diameter of 20 mm and cladding ratio of 50% were established through finite element numerical simulation using the ProCAST software and corresponding experiments. The effect of each process parameter on continuous composite casting was analyzed, based on which the optimized control method was obtained. A silver clad aluminum composite rod with high surface quality and excellent bonding interface was prepared on the basis of the simulation results. The length of the core tube and the speed of continuous casting are considered to be the most important factors affecting the formation process. The length of the core tube is assumed to affect the contact temperature and time of the aluminum liquid and silver tube at the end of the core tube, and result in the variation of the relative position of the solid-liquid interface of the aluminum. The interface reaction is severe when the core tube is too short. Conversely, significant cold separation occurs in aluminum because of the high cooling intensity when length of the core tube is too large. The actual casting temperature increases with the high continuous casting speed, which can be attributed to the reduction in the distance between solid-liquid interface and the outlet of the core tube for silver and the increase for aluminum. The increase in aluminum casting temperature and reduction in the flow rate of cooling water are found to have a similar effect to that of the increase in continuous casting speed. A series of optimized casting parameters was obtained in this study, i.e., length of the core tube 30 mm, the casting speed is 37-67 mm·min-1, the casting temperature of silver is in the range between 1225℃ and 1325℃, casting temperature of aluminum is 800℃, and the flow rate of cooling water is 300 L·h-1.
Abstract: Supercapacitors, also called electrochemical capacitors or ultracapacitors, have attracted increasing attention owing to their high specific capacitance, high power density, long lifecycle, fast charge-discharge ability, wide working temperature range, and environmental friendliness for mobile electronics, power grids, and hybrid electric vehicles. The electrode is the most important part of supercapacitors; therefore, the electrode material is the chief factor that determines the properties of supercapacitors. To enhance the performance of a supercapacitor, particularly its specific energy while retaining its intrinsic high specific power, several researchers have focused mainly on improving the properties of electrode materials. The major classes of materials applied for supercapacitors include various forms of carbon, transition metal oxides, and conductive polymers. Compared to the carbon materials and conducting polymer materials, transition metal oxides can achieve a much higher specific capacitance because of their high theoretical capacitance, well-defined electrochemical redox activity, low cost, and abundant resources. In particular, binary metal oxides, such as NiMoO4, MnMoO4, and CoMoO4, have been extensively studied as pseudocapacitor electrode materials because of their good electronic conductivity and rich redox reactions. In this study, pinecone-like NiMoO4/MnO2 composite materials were successfully synthesized using a facile hydrothermal method. Na2MoO4·2H2O, NiSO4·6H2O, and MnO2 were used as raw materials. The as-products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results show that when the optimal content of MnO2 reaches 10%, the obtained NiMoO4/MnO2 composite materials exhibits a pinecone-like porous morphology, with the particle size ranging from 200 to 600 nm. The results show that NiMoO4/MnO2 composite materials have excellent electrochemical properties. The discharge specific capacitance of NM0, NM5, NM10, NM15, and NM20 composites with corresponding MnO2 contents of 0%, 5%, 10%, 15%, and 20% are 260, 248, 650, 420, and 305 F·g-1, respectively, at a current density of 1 A·g-1. When the current density is up to 10 A·g-1, the initial discharge specific capacitance is 102 F·g-1. After 100-week cycles, the discharge specific capacitance of the NM10 sample is still 147 F·g-1. The improvements can be mainly attributed to the introduction of MnO2 in the NiMoO4/MnO2 composite materials to overcome the shortcomings of single NiMoO4.
Abstract: The existing fused deposition modeling (FDM) technique faces disadvantages of low resolution and limited printable materials; meanwhile the E-jet-based fused deposition method confronts limitations associated with the formation height, material type, conductivity, and flatness of the substrate, and the 3D forming ability. Herein, a new technology called electric-field-driven fused-jet deposition 3D printing was proposed. In the proposed technology, a dual-heated integrated nozzle connected to a single positive-pulse high voltage (single potential) was used to eject and precisely deposit a small amount of molten material to form a high-resolution structure based on the drive of the electric field force. Two novel printing modes, the continuous-cone and pulse-cone jet modes, were developed to broaden the range of printable materials using the proposed technique. The mechanism and rules of formation for the proposed process were systematically investigated via theoretical analysis, numerical simulation, and experimental verification. Using optimized process parameters and the proposed electric-field-driven fused-jet deposition 3D printing method, three typical cases, including a large micro-scale mold, a high-aspect-ratio micros-scale structure, a macro-micro-scale tissue scaffold, and a three-dimensional grid structure were fabricated. Outstanding results were obtained, including the printing of a wire grid structure with a minimum line width of 4 μm and a thin-walled ring microstructure with an aspect ratio of 25:1 using a nozzle with an inner diameter of 250 μm. The experimental results demonstrate that the proposed electric-field-driven fused-jet-deposition 3D printing method is a promising and effective method that meets the requirements of the high-resolution FDM process at low cost. The new technolgy proposed in this paper offers a novel solution for realizing high-resolution and macro/micro-scale fused-jet deposition 3D printing at low cost with good material universality.
Abstract: Due to the narrow roadway and poor working environment, underground mines pose a threat to the safety of vehicle drivers. The realization of automatic driving of underground mine vehicles can improve mining automation and intelligence and ensure safety of workers, and it can significantly increase mining and exploitation efficiency. Automatic driving of underground mining vehicles requires the technologies of location, communication, navigation, and path following control. Automatic driving of mining vehicles is the ultimate approach of autonomous navigation and auto driving, while path following control system is one of the core technologies of the autopilot system. The path following control system is a multi-variable, multi-constraint system. There are optimization problems under multiple constraints as well as challenges such as actuator saturation during the control process. To solve the above problems, a model predictive control method was introduced in this paper. By considering the relationship between the position and situation of the vehicle, the objective function of the predictive control was optimized by minimizing the lateral deviation of the following path and the heading angle deviation of the vehicle. Therefore, the optimal controls of vehicle speed and articulation angle were obtained, and the problem of multi-variable and multi-constraint system was solved. For the tracking overshoot problem caused by the inability of determining sudden changes of road curvature in the model predictive control strategy, a control method based on preview distance was proposed; thus, the vehicle path following control accuracy and stability was improved through the advance judgment of road mutation information. Matlab/Adams simulation software was used to perform a comparison simulation test. The results show that the model predictive following controller is capable of solving the control problem in multi-variable, multi-constrained system and effectively prevent the actuator saturation. Moreover, the model predictive following control strategy based on the preview distance keeps the horizontal deviation of the vehicle within ±0.04 m and the heading angle deviation within ±1.8°. Compared with the controller before improvement, the lateral position deviation is reduced by 80.9%, and the heading angle deviation is reduced by 59.1%; this proves that the improved controller has better lateral stability and accuracy.
Abstract: Storage and transportation are one of the primary restrictions on the approach involving hydrogen energy. The traditional hydrogen storage methods, including high-pressure gas cylinder and cryogenic liquid tank show unfavorable economy, thus hindering their further industrial application and development. Metal hydrides can reversibly react with hydrogen and accomplish the hydriding/dehydriding process under mild operation conditions, which feature advantages such as large hydrogen storage amount, low operation pressure and energy consumption. This process is expected to replace the conventional hydrogen storage and transportation. Meanwhile, considering the strong endothermal/exothermic effect during hydrogenation/dehydrogenation, the prompt heat removal/support inside the metal hydride reactor is a key parameter for H2 absorption/desorption rate and H2 storage efficiency. To improve the heat transfer and absorption/desorption rates of metal hydride reactor, comprehensive analysis and evaluation were conducted. Based on the heat and mass transfer intensification, a new elliptical spiral mini-tube bundle reactor (ESMBR) with high efficiency was designed and proposed; the reactor possesses numerous features, such as high heat transfer speed, compact structure, high reaction rate, and convenient operation. All the hydrogen storage reactor models were established, and both the model accuracy and effectiveness were experimentally validated. Numerical simulations of ESMBR, spiral mini-tube bundle reactor, and mini-tube bundle reactor were calculated and compared by COMSOL. ESMBR was proven to exhibit favorable heat and mass transfer performance during the H2 storage. Results of further analysis indicate that the sensitivity order of elliptical spiral structure parameters as follows: Dc > A > B > Pt > α. A multi-element valued model was used to evaluate the reactor schemes systematically, and the calculation results show the integrated superiority of ESMBR could achieve a value of 0.845. The comparison results indicate that the ESMBR presents an outstanding performance compared with other reactors and features a broad application prospect in the field of hydrogen energy.
Abstract: Clustering is a main task of data mining, and its purpose is to identify natural structures in a dataset. The results of cluster analysis are not only related to the nature of the data itself but also to some priori conditions, such as clustering algorithms, similarity/dissimilarity, and parameters. For data without a clustering structure, clustering results need to be evaluated. For data with a clustering structure, different results obtained under different algorithms and parameters also need to be further optimized by clustering validation. Moreover, clustering validation is vital to clustering applications, especially when external information is not available. It is applied in algorithm selection, parameter determination, number of clusters determination. Most traditional internal clustering validation indices for numerical data fail to measure the categorical data. Categorical data is a popular data type, and its attribute value is discrete and cannot be ordered. For categorical data, the existing measures have their limitations in different application circumstances. In this paper, a new similarity based on the concentration ratio of every attribute value, called CONC, which can evaluate the similarity of objects in a cluster, was defined. Similarly, a new dissimilarity based on the discrepancy of characteristic attribute values, called DCRP, which can evaluate the dissimilarity between two clusters, was defined. A new internal clustering validation index, called CVC, which is based on CONC and DCRP, was proposed. Compared to other indices, CVC has three characteristics: (1) it evaluates the compactness of a cluster based on the information of the whole dataset and not only that of a cluster; (2) it evaluates the separation between two clusters by several characteristic attributes values so that the clustering information is not lost and the negative effects caused by noise are eliminated; (3) it evaluates the compactness and separation without influence from the number of objects. Furthermore, UCI benchmark datasets were used to compare the proposed index with other internal clustering validation indices (CU, CDCS, and IE). An external index (NMI) was used to evaluate the effect of these internal indices. According to the experiment results, CVC is more effective than the other internal clustering validation indices. In addition, CVC, as an internal index, is more applicable than the NMI external index, because it can evaluate the clustering results without external information.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
