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The following article presents and corroborates an outcome space branch-and-bound algorithm for solving the general linear multiplicative programming problem (GLMPP). In this new algorithm, GLMPP is transformed into its equivalent problem by introducing auxiliary variables. To compute the tight upper bound for the optimal value of GLMPP, the linear relaxation programming problem is assembled by using bound and hull linear approximations. Furthermore, the global convergence and computational complexity of the algorithm are demonstrated. Finally, the soundness and advantage of the proposed algorithm are validated by solving a demonstrative linear multiplicative problem. [ABSTRACT FROM AUTHOR]

To assess the diagnostic accuracy of noninvasive prenatal screening (NIPS) in screening for copy number variations (CNVs). We conducted a systematic review and meta-analysis by combining our study results with those reported in other articles. We retrospectively collected the data of pregnant women with NIPS testing in the Hangzhou Women's Hospital from December 2019 to February 2022. Simultaneously, a systematic search of PubMed, EMBASE, and Web of Science was carried out to identify all relevant peer-reviewed publications. Statistical analysis was performed based on the random-effects model to determine a pooled estimate of the positive predictive value (PPV). A total of 29 studies involving 2,667 women were included for analysis. The pooled PPV of NIPS in the detection of CNVs was 32.86% (95% confidence interval [24.61–41.64]). Statistical heterogeneity was high, while no significant publication bias was found in this meta-analysis. There were insufficient data to accurately determine sensitivity and specificity, as most studies only performed confirmatory tests on high-risk women. The PPV of NIPS in screening for CNVs was approximately 33%. Cautions should be kept in mind for the pretest guidance and subsequent after-test counseling when offering such genome-wide NIPS tests. [ABSTRACT FROM AUTHOR]

In this paper, by using the special structure of the real representation of quaternion matrices, the properties of the Moore–Penrose inverse of quaternion matrices and the Kronecker product of matrices, we study least-squares bihermitian and skew bihermitian solutions of the quaternion matrix equation AXB = C, respectively. First we study the special structures of quaternion bihermitian and skew bihermitian matrices. Then the problem of solving the least-squares bihermitian and skew bihermitian solutions of the quaternion matrix equation AXB = C can be transformed into particular real linear system using these special structures. We deduce the form of all least-squares bihermitian and skew bihermitian solutions of the quaternion matrix equation AXB = C and propose real structure-preserving algorithms to compute the minimal norm least-squares bihermitian and skew bihermitian solution. All the computation process only involve real arithmetic. Numerical examples are provided to verify the effectiveness of our algorithms. Particularly, we also propose the conditions and computation method of bihermitian and skew bihermitian solutions of quaternion matrix equation AXB = C. [ABSTRACT FROM AUTHOR]

Compound machining (CM) compounded by arc machining and electrical discharge machining (EDM) milling is a new and fast processing method used to machine so-called “difficult-to-machine” materials. This method has an exciting maximum material removal rate that reaches 11,218 mm3/min with the relative electrode wear rate (REWR) of 1.54% when machining Inconel718. The electrode material is an important factor that affects the processing cost and quality of CM. Traditionally used electrode materials in arc machining and EDM, including pure tungsten (W), cerium tungsten (WCe20), copper (Cu), tungsten copper alloy (W80), and graphite (C), were used as electrode materials to process Inconel718. Experimental results show that tubular C is the best electrode material for CM. When tubular C is unavailable, WCe20 is the suitable electrode material for rough machining and W is a better choice in finish machining. Cu electrode is unsuitable for CM because of its low melting point. Results of this work provide guidance for selecting electrode materials for the industry application of efficient CM. [ABSTRACT FROM AUTHOR]

The bouncing motion of aqueous drops between two oppositely charged electrodes has been observed. However, the forward and backward velocities of the drops are nonuniform in some cases because of unknown reasons. In this study, the velocity difference was mainly caused by the distribution of ions that altered the electric field strength between the electrodes. This result yielded accurate control of the drops in the electric field and opened opportunities for industrial applications. [ABSTRACT FROM PUBLISHER]

In this study, the dehydration of water-in-oil emulsion subjected to an electric field was investigated both experimentally and via computer simulation. The time evolution of the droplets subjected to an electric field was investigated using optical microscopy. We also implemented a computer simulation of the dynamic behavior of the droplets resulting from the balance of forces applied on them. The probability of coalescence between droplets as well as coalescence between droplets and the water/oil interface was also investigated. Thus, the behavior of the droplets could be observed more directly, and the problem could be solved stochastically and mathematically. Through adjustment of the values of the two coalescence probabilities, the simulated results could accurately represent the actual process. [ABSTRACT FROM AUTHOR]

This article proposes a high current density electrical discharge milling for machining Inconel 718. The proposed power supply comprises a pulse generator with high voltage and a DC power source with high current. The pip graphite electrode and the workpiece are connected to the negative and positive poles of the power supply, respectively. Benefiting from efficient flushing and high current density, the maximum material removal rate (MRR) achieved 15,062 mm3/min with a relative electrode wear ratio (REWR) of 1.73%. The effects of peak current and injection flushing pressure on the MRR and REWR were investigated. Experiments showed little differences between the thickness of recast layer with the peak currents of 150 A and 920 A, and the thickness was less than 50 µm. It is also evident that the microcracks within the recast layer penetrated into the base material and propagated along the grain boundar. [ABSTRACT FROM AUTHOR]

Micro-electric discharge machining (micro-EDM) has become an important issue in the fabrication of microcomponents, especially after the development of the wire electro discharge grinding (WEDG) technology. However, the fabrication of microelectrodes through the WEDG technology is very complicated and time consuming, which limits the extensive industrial application of micro-EDM. This article reports the feasibility of utilizing carbon fiber as the electrode in micro-EDM. A novel chucking method and device are developed to chunk the extremely slender carbon fiber. The experiment results show that carbon fiber is a promising material in micro-EDM. [ABSTRACT FROM AUTHOR]

Electrical discharge machining (EDM) has been wildly used in the modern manufacture industry due to its advantage over the traditional manufacture method of some hard-to-cut materials. However, compared with the traditional manufacture method, the EDM process was inefficient and environmentally hazardous due to the decomposition of the dielectrics, especially in the case of sinking EDM which used oil-based dielectric. In order to improve the EDM performance, and for the other hand, alleviate the environmental impact of the process, a new type of dielectric, water in oil (W/O) emulsion was proposed as the working fluid. This work presents a systematical study on the performance of this new type dielectric based on the orthogonal and additional single factor experiments. Statistical analysis of the results show that discharge current (I) and water content of the emulsion significantly influence the machining performance of sinking EDM. The study also analyzed the influence of the emulsion temperature and flushing condition on its EDM performance. It was observed that both MRR and EWR decrease with increasing temperature of the emulsion. Experiments results indicated that W/O emulsion can be used as the working fluid of sinking EDM and alleviated the environmental impact of the process. [ABSTRACT FROM PUBLISHER]

Adsorption of surfactants at water-oil interfaces is of great importance in the coalescence of drops and stability of emulsions. In this work, we have studied the adsorption of nonionic surfactants Span 80 at water-oil interfaces and its influence on the drop rest phenomenon and W/O emulsion stability in a pulsed DC electrical field. The variation of interfacial tension with the concentration of surfactant was studied and the data were fitted using a surface equation of state derived from the Langmuir adsorption isotherm. A stochastic model for coalescence was used to fit the coalescence time distributions. The significance of the model parameters was discussed. The stability of the emulsion was evaluated by conductivity methods. The researches in this article indicated that both of the rest time distribution of the drops at the interface and stability of the emulsion in the electrical field was significantly affected by surfactant concentration. [ABSTRACT FROM AUTHOR]

The influence of several factors on the electrostatic dehydration process of water-in-model oil emulsions in high-frequency electrical field has been studied using conductivity technique. The ascending and the descending periods of the observed conductivity versus time curves were fit to sigmoid and power function, respectively, which revealed the model parameters that were used to quantify anew dehydration efficiency (DE) index. Experiments results shown that not only water content, surfactant concentration, salt concentration in the aqueous phase and temperature but also homogenization were all found to play a non-negligible role in the electrostatic dehydration process. [ABSTRACT FROM AUTHOR]

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is able to effectively machine insulating ceramics. To further explore the process characteristics, the single pulse discharge experiments have been carried out in kerosene. The effects of polarity, capacitance, peak voltage, and current-limiting resistance on the process performance such as the crater volume, crater depth, tool wear ratio (TWR), and assisting electrode wear ratio (AEWR) have been investigated. The microstructure of the discharge crater has been examined with a scanning electron microscope (SEM). The results show that the insulating Al2O3 ceramic materials are mostly removed by spalling, at the center region of the discharge some materials are removed by melting and evaporation. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramic has been widely used in modern industry for its excellent physical and mechanical properties. However, SiC ceramic is difficult to machine owing to its high hardness and brittleness. This article presents a novel compound process that integrates end electric discharge (ED) milling and mechanical grinding to machine SiC ceramic. The process is able to effectively machine a large surface area on SiC ceramic with a good surface quality. The effect of tool polarity on the machining characteristics such as the material removal rate (MRR), tool wear ratio (TWR), and surface roughness (SR) has been explored. The effects of pulse on-time, pulse off-time, discharge current and open voltage on MRR, TWR, and SR have been investigated with Taguchi experimental design. The experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the machining characteristics are obtained. The confirmation experiment results confirm the validity of the used Taguchi method for enhancing the machining performance and optimizing the machining parameters. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramics have found a variety of engineering applications due to their superior properties. However, the manufacture of SiC ceramics is not an efficient process. A new process of machining SiC ceramics using end electrical discharge (ED) milling is presented in this research. End ED milling employs a turntable with several small cylindrical rods as the tool electrode, and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on SiC ceramic. The machining principle and characteristics of the technique are introduced. The effects of tool polarity, pulse on-time, pulse off-time, peak voltage, and peak current on the process performance such as the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR) have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope and an energy dispersive spectrometer. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramics have been widely used in modern industry. However, the manufacture of SiC ceramics is not an efficient process. This paper proposes a new technology of machining SiC ceramics with electrical discharge milling and mechanical grinding compound method. The compound process employs the pulse generator used in electrical discharge machining, and uses a water-based emulsion as the machining fluid. It is able to effectively machine a large surface area on SiC ceramics with a good surface quality. In this paper, the effects of pulse duration, pulse interval, peak voltage, peak current and feed rate of the workpiece on the process performance parameters, such as material removal rate, relative electrode wear ratio and surface roughness, have been investigated. A L25 orthogonal array based on Taguchi method is adopted, and the experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the process performance are obtained. In addition, the workpiece surface microstructure is examined with a scanning electron microscope and an energy dispersive spectrometer. [ABSTRACT FROM AUTHOR]