Initial Structure Parameters Research Articles

Integrated thermal error modeling of machine tool spindle using a chicken swarm optimization algorithm-based radial basic function neural network

Thermal errors are one of the main error sources affecting the machining accuracy of the machine tool. Thermal error modeling is a prerequisite for thermal error compensation to reduce the thermal error and improve machining accuracy. In this paper, a chicken swarm optimization algorithm-based radial basic function (CSO-RBF) neural network is applied to integrated thermal error modeling. At first, correlation analysis-based K-Means clustering and radial basis function neural network (KC-RBF) approach is proposed to screen optimal temperature-sensitive point combination. The correlation analysis-based K-Means clustering is used to obtain temperature-sensitive point combinations corresponding to different K values. The mean value of residual and root mean square error are established to evaluate the results of RBF model to filter the optimal temperature-sensitive point combination. Secondly, one CSO-RBF neural network is proposed to handle the nonlinear relationship between temperature variables and thermal errors. RBF model-based fitness function is proposed for CSO to obtain the optimal initial structure parameters of RBF. The optimal thermal error model is established by training RBF with the optimal initial structure parameters and the measured data. At last, different experiments are carried out on VMC850 machining center: training and testing of thermal error models at a fixed speed for Y-direction thermal drift error; verification of thermal error models for different speeds of different error parameters. It is worth mentioning that the model trained with one thermal error parameter measured at a certain speed is also applied for different thermal error parameters at different speeds. Results show that the proposed CSO-RBF model has high accuracy and strong robustness.

White Light Transmitting Antenna for Four-spectrum Mobile WDM-VLC

In this paper, we propose a mixing white light antenna with a homogenizer and an amplification system, and demonstrated its utilization in a four-spectrum mobile VLC. The central element is the homogenizer, which is a square integrating rod that mixes four-spectrum light into white light. Behind it, there are two Fresnel lenses to amplify the light-mixing area. The system is compact with a length of 80 mm and maximal diameter of 58.5 mm. We determined the initial structural parameters of the antenna by theoretical analysis, and then we determine the best parameters by simulation. Simulation results indicate that a 0.75 m×0.75 m area can be illuminated at 1.7 m distance. The detection surface has a high uniformity (76.27%), which can meet illumination and mobile communication requirements simultaneously.

Research on Superconducting Magnet in a Superconducting Synchronous Generator

Design and test of superconducting magnet (SM) for a superconducting synchronous generator (SSG) are studied in this paper. First, a suitable superconducting material is selected to make SM by analyzing the characteristics and application background of the five practical superconducting materials, and the applicability and feasibility of the selected superconducting materials are demonstrated. Second, the initial structural parameters of the SM are obtained by finite element method (FEM). In addition, the influence of structural parameters of SM on the performance of SSG is analyzed by simulation. Then, an optimal algorithm combining response surface methodology (RSM) and particle swarm optimization (PSO) is proposed to optimize the structure of SM in order to give full play to the advantages of SM. The simulated results verify that the proposed optimal algorithm is feasible and effective. Finally, the prototype of SM is made by the optimized size, and the SM is tested at a low temperature to obtain the critical temperature and critical current of the SM; the experimental results verify that the designed SM can meet the requirements of SSG.

Novel Wideband Microstrip Filtering Power Divider Using Multiple Resistors for Port Isolation

In this paper, a novel wideband filtering power divider with third-order quasi-Elliptic bandpass response is proposed. Its physical mechanism is revealed by the lumped-element equivalent circuit, such as how its transmission poles and zeros are formed. The design of the proposed filtering power divider can be simplified as its even-mode model can be synthesized by conventional filter synthesis technique, and then the initial structure parameters can be analytically determined. Owing to the fact that as many as three resistors are joined, high isolation can be achieved between two output ports. To demonstrate its good performance, an example was designed, fabricated, and measured, whose center frequency is 1.99 GHz and 3-dB fractional bandwidth is 43.7%. Moreover, as great as 34 and 28 dB out-of-band suppression can be achieved in the lower and upper stopbands, respectively. The isolation between two output ports is better than 20 dB for a wide frequency range.

Compact third‐order microstrip bandpass filter designed by the distributed‐ to lumped‐element equivalence

SummaryIn reality, it is not easy to design microstrip filters for the sake of distributed‐element effect. It is an effective approach to approximate distributed‐element structures through appropriate lumped‐element circuits. In this paper, some basic microstrip structures are discussed, whose equivalent lumped‐element circuits are derived. Then, a novel microstrip filter is obtained by connecting these microstrip structures, according to the similar topology of the third‐order lumped‐element bandpass filter. The equivalent lumped‐element counterpart of the proposed microstrip filter clearly reveals its physical mechanism, ie, how the resonances are created and coupled and how the transmission zeros are created. Furthermore, a set of the design formulas are presented, which can be used to calculate initial structure parameters and then facilitate design process. The proposed microstrip bandpass filter can realize a third‐order elliptic bandpass response with one transmission zero at each side of the passband. In addition, two short‐circuited stubs are added to input/output ports to create the third transmission zero. The filter is featured by good frequency selectivity and out‐of‐band suppression. For demonstration, an actual example was designed, fabricated, and measured.

Design of optical system of miniature spectrometer for ultrahigh-resolution

Because of the size limit of the spectrometer, the resolution of the micro-spectrometer is usually difficultly less than 0.1 nm when it meets certain spectral range. While some special applications require that the spectrometer not only has small size, but also requires extremely high spectral resolution. We used Zemax (optical design software) to choose the initial structure parameters and evaluation function to automatically optimize angle and distance of focus lens, cylindrical lens and CCD to design an optical system of spectrometer of Czerny-Turner structure. Its resolution is better than 0.05 nm, and the volume of the system is 90 mm×130 mm×40 mm. On this basis, eight grating slanting angles were optimized, and the spectral resolution of the micro-spectrometer is better than 0.05 nm, while the band range reaches 820 nm~980 nm. So the spectrometer has the characteristics of high resolution, wide spectrum and small volume.

The distributed‐element to lumped‐element equivalence for transmission‐line filter synthesis

SummaryFilters play an important role in frequency selection. However, to design transmission‐line filters such as microstrip filters is a very challenging task because of their distributed‐element effect. In this paper, the concept of the distributed‐element to lumped‐element equivalence is applied in the design of microstrip filters. The lumped‐element equivalent networks of some basic microstrip structures are presented and are applied to derive the whole lumped‐element equivalent networks of microstrip filters constituted by them. Then, the physical mechanism of microstrip filters is revealed, ie, how the resonances are created and coupled and how the transmission zeros are formed. The distributed‐element to lumped‐element equivalence relations between the electrical parameters of microstrip filters and the element values of their lumped‐element equivalent networks are derived. Through comparison between the lumped‐element equivalent networks of microstrip filters and those obtained by direct synthesis technique we recently proposed, initial structural parameters of microstrip filters can be calculated, which greatly simplifies their design. To verify it, several microstrip filter examples are presented for demonstration.

Optimal design of third‐order microstrip bandpass filters by direct synthesis technique (DST)

SummaryTo design microstrip filters is not easy for the sake of their distributed‐element effect. Undoubtedly, to understand their physical mechanism is very important to their design. In this paper, one effective approach to design some third‐order microstrip bandpass filters with each of 2 transmission zeros at each side of the passband is discussed. Lumped‐element equivalent circuits are used to represent these microstrip filters. Then, these lumped‐element equivalent circuits can be synthesized by direct synthesis technique we recently proposed, so that it is likely to calculate initial structural parameters of these microstrip filters and then facilitate their design. Verified by the measured results of the filter designed through the approach in this paper, the performance of the filters is close to ideal frequency responses. Furthermore, another third‐order microstrip bandpass filter is presented, in which open‐circuited stubs at input/output ports are introduced to suppress one specified harmonic to improve out‐of‐band attenuation.

A Stochastic Model of Cascading Failure Dynamics in Communication Networks

In this brief, we propose a stochastic model based on state transition theory to investigate the dynamics of cascading failures in communication networks. We describe the failure events of the nodes in the network as node state transitions. Taking a probabilistic perspective, we focus on two uncertain conditions in the failure propagation process: which node in the network will fail next and how long it will last before the next node state transition takes place. The stochastic model gives each overloaded element a probability of failing, and the failure rate is relevant to the degree of overloading. Moreover, the time dimension is considered in the stochastic process, by removing a node after a time delay when its traffic load exceeds its capacity. We employ this proposed model to study the dynamics of cascading failure evolution in a Barabasi–Albert scale-free network and an Internet AS-level network. Simulation results reveal the effects of the initial failure pattern, community structure and network design parameters on the dynamic propagation of cascading failures.

Compact Microstrip Filter With Third-Order Quasi-Elliptic Bandpass Response

In this paper, a novel microstrip filter is proposed, which can realize a third-order quasi-elliptic bandpass response. In order to reveal the physical mechanism of the microstrip filter, a lumped-element equivalent circuit is set up and the equivalence relations between its circuit elements and the electrical parameters of the microstrip filter are presented. According to filter specifications, the initial structural parameters of the microstrip filter can be easily calculated through these equivalence relations. As demonstration, an actual microstrip filter was designed, fabricated and measured, whose center frequency is at 2.50 GHz and fractional bandwidth is 36%. There are two transmission zeros near to the passband to improve the frequency selectivity, which makes the roll-off rate at each side of the passband as high as 125 and 50 dB/GHz, respectively. The out-of-band suppression from 3.6 to 6.1 GHz is greater than 40 dB. The size of the fabricated filter is $0.21\lambda \text {g} \times 0.18\lambda \text{g}$ , which is very compact.

Adsorption and Desulfurization Mechanism of Thiophene on Layered FeS(001), (011), and (111) Surfaces: A Dispersion-Corrected Density Functional Theory Study.

Layered transition-metal chalcogenides have emerged as a fascinating new class of materials for catalysis. Here, we present periodic density functional theory (DFT) calculations of the adsorption of thiophene and the direct desulfurization reaction pathways on the (001), (011), and (111) surfaces of layered FeS. The fundamental aspects of the thiophene adsorption, including the initial adsorption geometries, adsorption energies, structural parameters, and electronic properties, are presented. From the calculated adsorption energies, we show that the flat adsorption geometries, wherein the thiophene molecule forms multiple π-bonds with the FeS surfaces, are energetically more favorable than the upright adsorption geometries, with the strength of adsorption decreasing in the order FeS(111) > FeS(011) > FeS(001). The adsorption of the thiophene onto the reactive (011) and (111) surfaces is shown to be characterized by charge transfer from the interacting Fe d-band to the π-system of the thiophene molecule, which causes changes of the intramolecular structure including loss of aromaticity and elongation of the C–S bonds. The thermodynamic and kinetic analysis of the elementary steps involved in the direct desulfurization of thiophene on the reactive FeS surfaces is also presented. Direct desulfurization of thiophene occurs preferentially on the (111) surface, as reflected by the overall exothermic reaction energy calculated for the process (ER = −0.15 eV), with an activation energy of 1.58 eV.

Unidirectional coupler optimization of surface plasmon polaritons based on co-simulation of genetic algorithm and COMSOL

The unidirectional excitation of surface plasmon polaritons has been an important subject for the development of plasmonic devices and systems. This study presents the use of co-simulation method of genetic algorithm and COMSOL in MATLAB environment to optimize quasi-periodic and aperiodic surface plasmon polaritons slit unidirectional coupler. The extinction ratio of all the surface plasmon polaritons slit unidirectional couplers is greater than 60dB under arbitrary initial structure parameters with genetic algorithm options of population size of 20 and generations of 20. Therefore, the co-simulation method of genetic algorithm with COMSOL not only greatly speeds up the process to find the optimal parameters, but also does not depend on the initial structure parameters. Moreover, this method can also be applied to optimization of other photonic devices, such as the perfect mirror, the anti-reflective film of photovoltaic cell surface. Even with little knowledge of optimization, photonic devices with good performance can be obtained with this method.

Phase fraction evolution in hot working of a two-phase titanium alloy: experiment and modeling

In the present work, the coupled effects of initial structure and processing parameters on microstructure of a two-phase titanium alloy were investigated to predict the microstructural evolution in multiple hot working. It is found that microstructure with different constituent phases can be obtained by regulating the initial structure and hot working conditions. The variation of deformation degree and cooling rate can change the morphology of the constituent phases, but do not alter the phase fraction. The phase transformation during heating and holding determines the phase fraction for a certain initial structure. β–α–β transformation occurs during heating and holding. β to α transformation leads to a significant increase in content and size of lamellar α. The α to β transformation occurs simultaneously in equiaxed α and lamellar α. The thickness of lamellar α increases with temperature, which is caused by the vanishing of fine α lamellae due to phase transformation and coarsening by termination migration. By assuming a quasi-equilibrium phase transformation in heating and holding, a modeling approach is proposed for predicting microstructural evolution. The three stages of phase transformation are modeled separately and combined to predict the variation of phase fraction with temperature. Model predictions agree well with the experimental results.

Factors influencing the structure build-up of fresh cement asphalt emulsion paste

Fresh cement asphalt emulsion mortar (CA mortar) is required to be highly flowable for grouting when it is employed in slab track structure. Segregation and bleeding easily occur after placement. In essence, it is because fresh CA paste has a low rate of structure build-up. However, limited information is reported about the thixotropy of CA paste. A thixotropy model based on structure parameter, which is deduced from constant shear rate test, is proposed to study the structure build-up of CA paste. In the model, the initial structure parameter and the rate of structure build-up are used to describe the evolution law of the structure parameter with resting time, which can be employed to quantitatively evaluate the structure build-up process of CA paste. The thixotropy model is used to study the influence of every constituent on the structural build-up process of CA paste. Results show that asphalt emulsion and superplasticizer dosage are two main factors influencing the structure build-up of CA paste, but water-to-cement ratio and viscosity-modified agent dosage have little effect on the structure build-up of CA paste.

The thixotropic behavior of fresh cement asphalt emulsion paste

The workability of grouting cement asphalt emulsion (CA) mortar is governed by the intrinsic thixotropic behavior of CA paste, but limited information is reported about the thixotropic behavior of CA paste. A new thixotropy method of constant shear rate test is proposed to study the thixotropic behavior of CA paste with different asphalt emulsion to cement ratios (AE/C). In the model, the initial structure parameter and the structure rebuilding rate are used to quantitatively describe the structure rebuilding process, the characteristic time of de-flocculation is used to evaluate the de-flocculation process, and the equilibrium shear stress is used to study the irreversible change of CA paste in the thixotropy test. Results show that CA pastes have significantly different thixotropic behavior compared to cement paste. The initial structure parameter and structure rebuilding rate of CA pastes are much smaller than cement paste, and the structure rebuilding rate decreases significantly with AE/C. The characteristic time of de-flocculation of cement paste changes little at different resting time, however, it increases significantly at the first 5min resting time and then keep stable for CA pastes. The equilibrium shear stress of cement paste does not change in 20min, but it increases with time for CA pastes due to the demulsification of asphalt emulsion.

X-ray focusing optics and its application in X-ray communication system

X-ray communication, which was first introduced by Keith Gendreau in 2007, is potential to compete with conventional communication methods, such as microware and laser communication, against space surroundings. Researchers have spent much time and effort on the mission making the initial idea into reality in recent years. Eventually, the X-ray communication demonstration system based on the grid-controlled X-ray source and single-photon detection technique can deliver both audio and video information in a 6-meter vacuum tunnel, and the bit-error-rate performance of the communication system is analyzed. But it is difficult to implement applications in industries. The point is to find a way to reduce the signal divergence geometrical attenuation and increase the distance of the communication which can be regarded as an important foundation of future deep-space X-ray communication applications. Therefore, it is urgent to study the X-ray communication system. By using a nested X-ray focusing optics as transmitting and receiving antennas of the communication system, the signal gain and the distance of X-ray communication can be greatly improved. Specifically, the nested X-ray focusing optics is similar to the Wolter type I telescope, which is widely used in the field of X-ray astronomy. The difference between them is that the Wolter type I optics is originally proposed based on a paraboloid mirror and a hyperboloid mirror, but X-ray focusing optics, the simplified Wolter type I optics, provides a single reflection by a conical approximation mirror, and it is more suitable for X-ray communication. In this paper, aiming at the future demand of X-ray communication, the optimization and analysis of the nested X-ray focusing optics are carried out, and the recurrence relations between the layers of mirrors are derived. Reasonable initial structural parameters and structure of the optics are designed. In addition, the theoretical effective collection area is calculated. Feasibility of using the X-ray focusing optics as transmitting and receiving antennas is analyzed, and the theory and structural design of the X-ray focusing optical are discussed. Signal divergence of transmitting antenna, effective area of receiving antenna, the focal spot size, and the signal gain properties are preliminary studied. The results show that the signal divergence is about 3 mrad, and the transmit gain is 23 dB; the effective area of receiving antenna is 5700 mm2 at 1.5 keV. Moreover, the focal spot diameter and the receive gain are 4.5 mm and 25 dB, respectively, and the total gain of this communication system can reach up to 48 dB.

基于传递矩阵的宽视场离轴三反光学系统设计

To the problem that off-axis three-mirror optical system has narrow field and complicating initial structure solving process, a method by using optical transfer matrix to solve initial structure was proposed, the focus length and rear cut-off distance of three-mirror system was deduced, then an initial structure parameter of three-mirror system with aperture stop on secondary mirror was given. High order aspheric surface was used to increase system design variance, and making off-axial optimization design to coaxial system based on optical design software ZEMAX, finally got an off-axis three-mirror optical system with wide rectangle field of view 172, focus length of 1 440 mm, F number of 4.8. The system has three high order aspheric optical elements, it can satisfy the requirement of high resolution and large field, the MTF is more than 0.6 at 50 lp/mm, approaches to the diffraction limitation. The designed result shows that the system can be used in space of imaging system with Timed Delay and Integrated Charge-couple Device(TDI-CCD), can expand the ground coverage of system obviously, and achieves high information retrieval efficiency.

A novel method for finding the initial structure parameters of optical systems via a genetic algorithm

A novel method for finding the initial structure parameters of an optical system via the genetic algorithm (GA) is proposed in this research. Usually, optical designers start their designs from the commonly used structures from a patent database; however, it is time consuming to modify the patented structures to meet the specification. A high-performance design result largely depends on the choice of the starting point. Accordingly, it would be highly desirable to be able to calculate the initial structure parameters automatically. In this paper, a method that combines a genetic algorithm and aberration analysis is used to determine an appropriate initial structure of an optical system. We use a three-mirror system as an example to demonstrate the validity and reliability of this method. On-axis and off-axis telecentric three-mirror systems are obtained based on this method.

Theory and design of two-dimensional high-contrast-grating phased arrays.

Optical properties of two-dimensional (2D) high-contrast gratings are investigated. We analyze the mechanisms for high-contrast gratings to function as various high-performance optical components. Our top-down design procedure allows us to efficiently obtain initial structural parameters and engineer them for a wide range of applications, such as reflectors, filters, resonators, waveplates, and even 2D phase plates. Simulation results of our designed structures show ultra-high power efficiency, and excellent agreement with our predicted functionalities.

Crystal structures and enhancement of photoluminescence intensities by effective doping for lithium tantalate phosphors

Crystal structures of (Li0.925Eu3+0.025)TaO3, (Li0.968Eu3+0.032)(Ta0.81Ti0.19)O2.937, (Li0.967Sm3+0.033)(Ta0.89Ti0.11)O2.978, and (Li0.950Sm3+0.033Mg0.017)(Ta0.89Ti0.11)O2.987were investigated by X-ray powder diffraction. The initial structural parameters, taken from those of the isomorphous compound (Li0.977Eu3+0.023)(Ta0.89Ti0.11)O2.968(space groupR3candZ= 6), were refined by the Rietveld method. A pattern-fitting method based on the maximum-entropy method was subsequently used to determine the three-dimensional electron-density distributions (EDDs) that are free from the structural bias. We confirmed that the EDDs are in accord with the resulting structural models, each of which was composed of the [(Ta, Ti)O6] octahedron and [(Li, Eu, Sm, Mg)O12] polyhedron. We compared these polyhedra and found that the prominent difference among these compounds was the centroid-to-(Li, Eu, Sm, Mg) distance (eccentricity) of [(Li, Eu, Sm, Mg)O12]. The high correlation was demonstrated between the magnitude of eccentricity and photoluminescence intensity under near ultraviolet excitation.