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A linear actuator controlled by the reversed-phase connection of two piezoelectric bimorphs is proposed in this study to solve the problem of drawback in the existing piezoelectric linear actuators. The actuator is driven by one excitation signal, the two piezoelectric bimorphs will always bend in opposite directions by the reversed-phase connection, so the directions of the force output by the two piezoelectric bimorphs are opposite. Because of the length difference of the clamping blocks, the two forces outputted by each bending is different in magnitude, and always have a resultant force in the same direction to make the actuator move forward two steps in one cycle without drawback. A series of experiments were conducted to evaluate the performance of the actuator provided. The starting voltage is 40 $\text{V}_{\mathrm {p-p}}$ , resolution can reach $1.16~\mu \text{m}$ without load. The load capacity of the actuator is 450 g with a 100 $\text{V}_{\mathrm {p-p}}$ voltage, a 2-Hz frequency, and the average step displacement in this case is $0.725~\mu \text{m}$ . The prototype has high linearity and good repeatability. Experiments have proved that the actuator controlled by reversed-phase connection can eliminate drawback in principle, and can move forward two steps in one cycle. The resolution of the prototype by the reversed-phase connection is much higher than the in-phase connection, and it is a new method to improve the driving performance of piezoelectric actuators.

Closed-loop disturbance rejection without sacrificing overall system performance is a fundamental issue in a wide range of applications from precision motion control, active noise cancellation, to advanced manufacturing. The core of rejecting band-limited disturbances is the shaping of feedback loops to actively and flexibly respond to different disturbance spectra. However, such strong and flexible local loop shaping (LLS) has remained underdeveloped for systems with nonminimum-phase zeros due to challenges to invert the system dynamics. This article proposes an LLS with prescribed performance requirements in systems with nonminimum-phase zeros. Pioneering an integration of the interpolation theory with a model-based parameterization of the closed loop, the proposed solution provides a filter design to match the inverse plant dynamics locally and, as a result, creates a highly effective framework for controlling both narrowband and wideband vibrations. From there, we discuss methods to control the fundamental waterbed limitation, verify the algorithm on a laser beam steering platform in selective laser sintering additive manufacturing, and compare the benefits and tradeoffs over the conventional direct inverse-based loop-shaping method. The results are supported by both simulation and experimentation.

Capable of building high-quality, complex parts directly from digital models, selective laser sintering (SLS) additive manufacture (AM) is a core method of agile manufacturing. Polyamide 12 is the most commonly and successfully used polymer powders to date in SLS due to the conforming thermal behaviors of this thermoplastic polymer. State of the art technology produces a substantial amount of un-sintered powders after the manufacturing process. Failure to recycle and reuse these aged powders not only leads to economic losses but also is environmentally unfriendly. This is particularly problematic for powders close to the heat-affected zones that go through severe thermal degradations during the laser sintering processes. Limited procedures exist for systematically reusing such extremely aged powders. This work proposes a new process control method to maximize reusability of aged and extremely aged polyamide 12 powders. Building on a previously untapped interlayer heating, preprocessing, and mixing of powder materials, we show how reclaimed polyamide 12 powders can be consistently reprinted into functional samples, with mechanical properties even superior to current industrial norms. In particular, the proposed method can yield printed samples with 18.04 % higher tensile strength and 55.29 % larger elongation at break using as much as 30 % of extremely aged powders compared to the benchmark sample.

Two new 3D fluorescence metal–organic frameworks, namely [Zn2(p-bdc)4(dfdp)2]n (1) and [Cd2(p-bdc)4(dfdp)4]n (2) (p-H2bdc = 1,4-benzenedicarboxylic acid; dfdp = 4,4′-(2,5-difluoro-1,4-phenylene)dipyridine) have been synthesized under solvothermal conditions and structurally characterized by elemental analysis, infrared spectra, TG, UV–Vis spectra, fluorescence spectra, single crystal and powder X-ray diffraction. Compound 1 shows a 3D framework constructed by infinite [Zn2(p-bdc)4]n layer as nodes and the dfdp ligands as connected linkers. Compound 2 reveals a different structure from compound 1 which can be mainly attributed to different coordination numbers of dfdp linkers. Compared with compound 2, UV–vis spectrum of compound 1 is 25 nm red-shifted. Both compounds show strong solid-state luminescence at about 400 nm. Of particular interest is that the quantum yield of compound 1 is 11.73. Two novel 3D fluorescence metal–organic frameworks [Zn2(p-bdc)4(dfdp)2]n (1) and [Cd2(p-bdc)4(dfdp)4]n (2) have been synthesized and structurally characterized. Compound 1 show strong solid-state purple luminescence with 11.73 quantum yield (QY).

Environmentally friendly and biodegradable hybrid composites of starch/enteromorpha/nano-clay were developed. Enteromorpha was used as cheaper filler since it is a waste from marine pollution, while nano-clay acted as a reinforcing agent. The microstructures and performance of these composites were investigated by SEM, DMA, XRD, TGA and tensile testing. Enteromorpha has a hollow tubular thallus structure with very weak mechanical properties, so it is not expected to have the ability to reinforce the starch matrix even though they have very a good interface. However, the granulated fine particles of enteromorpha can mix well with the starch matrix and reduce weak points. Furthermore, the delaminated clay by water and ultrasonic treatment reinforced the mechanical properties of the starch-based materials. The results showed that the hybrid composite containing up to 40% enteromorpha reinforced with nano-clay still has similar or even slightly better mechanical properties compared with pure starch-based materials. Since all components are hydrophilic natural materials, the interfaces between them are very good, and the composites are environmentally friendly and biodegradable.

A fundamental problem arises in feedback control when the system is subject to fast disturbances but can only get slowly updated sensor feedback. The problem is particularly challenging when the disturbances have frequency components near or beyond the sensor’s Nyquist sampling frequency. Such difficulties occur to selective laser sintering, an additive manufacturing process that employs galvo scanners to steer high-power laser beams and relies on non-contact, slow sensing such as visual feedback to enhance the product quality. In pursuit of addressing the fundamental challenge in quality control under slow sensor feedback, this paper introduces a multi-rate control scheme to compensate beyond-Nyquist disturbances with application to selective laser sintering. This is achieved by designing a special bandpass filter with tailored frequency response beyond the slow Nyquist frequency of the sensor, along with integrating model-based predictor that reconstructs signals from limited sensor data. Verification of the algorithm is conducted by both simulation and experimentation on a galvo scanner that directs the energy beam in the additive manufacturing process.

Polyamide 12 is one of the most extensively used semi-crystalline polymer materials to date in selective laser sintering (SLS) additive manufacturing, or SLS 3D printing. In this powder-based direct digital manufacturing process, a substantial amount of expensive materials remains un-sintered, recyclable, and reusable. Recently, understanding the mechanisms of degradation and the reusability of reclaimed polyamide 12 powders has attracted increasing industrial and research interests. However, using reclaimed polyamide 12 powder in SLS results in problems with part surface quality such as undesirable part surface finish with poor textures and numerous un-sintered particles. Limited research is available on the improvement of part surface quality. In particular, results barely exist on improving or modifying the surface quality of parts using extremely aged powders – powders that are held close to the heat-affected zones (HAZs) and suffer from severe degradations during the sintering process. To improve the surface quality and to build interrelations between process parameters and surface quality, we propose a novel approach for SLS with (extremely) aged polyamide 12 powders. By combining material preparation, powder and part characterizations, and SLS with customized post-heating, we obtain parts with improved surface quality (e.g., reduced roughness and porosities, and eliminated un-sintered particles). Particularly, parts 3D-printed using the 30%-30%–40% new-aged-extremely-aged powder mixtures exhibit the smoothest and flattest surface with no unmolten particles and nearly zero porosity.

Although laser-based additive manufacturing (AM) has enabled unprecedented fabrication of complex parts directly from digital models, broader adoption of the technology remains challenged by insufficient reliability and in-process variations. In pursuit of assuring quality in the selective laser sintering (SLS) AM, this paper builds a modeling and control framework of the key thermodynamic interactions between the laser source and the materials to be processed. First, we develop a three-dimensional finite element simulation to understand the important features of the melt pool evolution for designing sensing and feedback algorithms. We explore how the temperature field is affected by hatch spacing and thermal properties that are temperature-dependent. Based on high-performance computer simulation and experimentation, we then validate the existence and effect of periodic disturbances induced by the repetitive in- and cross-layer thermomechanical interactions. From there, we identify the system model from the laser power to the melt pool width and build a repetitive control algorithm to greatly attenuate variations of the melt pool geometry.

Prior research has recognized the need to associate affective polarities with events and has produced several techniques and lexical resources for identifying affective events. Our research introduces new classification models to assign affective polarity to event phrases. First, we present a BERT-based model for affective event classification and show that the classifier achieves substantially better performance than a large affective event knowledge base. Second, we present a discourse-enhanced self-training method that iteratively improves the classifier with unlabeled data. The key idea is to exploit event phrases that occur with a coreferent sentiment expression. The discourse-enhanced self-training algorithm iteratively labels new event phrases based on both the classifier's predictions and the polarities of the event's coreferent sentiment expressions. Our results show that discourse-enhanced self-training further improves both recall and precision for affective event classification.

Plug-in or add-on control is integral for high-performance control in modern precision systems. Despite the capability of greatly enhancing the steady-state performance, add-on compensation can introduce output discontinuity and significant transient response. Motivated by the vast application and the practical importance of add-on control designs, this paper identifies and investigates how general nonsmoothness in signals transmits through linear control systems. We explain the jump of system states in the presence of nonsmooth inputs in add-on servo enhancement, and derive formulas to mathematically characterize the transmission of the nonsmoothness. The results are then applied to devise fast transient responses over the traditional choice of add-on design at the input of the plant. Application examples to a manufacturing control system are conducted, with simulation and experimental results that validate the developed theoretical tools.

Modern hard disk drive (HDD) systems are subjected to various external disturbances. One particular category, defined as wide-band disturbances, can generate vibrations with their energy highly concentrated at several frequency bands. Such vibrations are commonly time-varying and strongly environment/product-dependent, and the wide spectral peaks can occur at frequencies above the servo bandwidth. This paper considers the attenuation of such challenging vibrations in the track-following problem of HDDs. Due to the fundamental limitation imposed by the Bode’s integral theorem, the attenuation of such wide-band disturbances may cause unacceptable amplifications at other frequencies. To achieve a good performance and an optimal tradeoff, an add-on adaptive vibration-compensation scheme is proposed in this paper. Through parameter adaptation algorithms that online identify both the center frequencies and the widths of the spectral peaks, the proposed control scheme automatically allocates the control efforts with respect to the real-time disturbance characteristics. The effect is that the position error signal in HDDs can be minimized with effective vibration cancelation. Evaluation of the proposed algorithm is performed by experiments on a voice-coil-driven flexible positioner system.

In this work, we fabricated a miniaturized water quality monitoring system with microfluidic analysis chip to meet the high density and network requirements of wide area water system monitoring. The framework of the system is a layered tower structure, including human-computer interaction module, micro-control module, microfluidic chip and master control module. The miniaturized water quality monitoring system optimizes the integration of microfluidic technology and absorption photometric detection methods, and the design of the micro control system ensures automatic analysis of water quality. Experiments show that the system has excellent detection performance while achieving miniaturization. The detection limit (LOD) of the miniatured analyzer was 3.4 μM, and the reaction time was between 100 s and 300 s. The reagent consumption is only 6 μL per sample.

Surface acoustic wave (SAW) optical sensor based on two-dimensional (2D) sensing layer can always provide extremely high sensitivity. As an attractive option, the application of exfoliated 2D perovskite on acousto-optic coupling optical sensor is investigated. In this work, exfoliated 2D (PEA) 2 PbI 4 sheet was transferred as a sensing layer onto the delay area of a dual-port SAW resonator with resonant frequency ~497 MHz. From the response under 532 nm laser with intensity of 0.9 mW/cm2, a largest frequency shift of ~13.92 MHz was observed. The ultrahigh sensitivity up to 31.6 ppm/(μW/cm2) was calculated by experiment results. We also carried out theoretical analysis and finite element simulation of 3D model to demonstrate the mechanism and validity for optical sensing. The fabricated optical sensor expressed great potential for a variety of optical applications.

A comparison study of the phase transition and structure of waxy cornstarch in DMSO and AMIMCl systems was conducted using a differential scanning calorimeter, an optical microscope, a scanning electron microscope, X-ray diffraction and thermogravimetric analysis. A full disruption and dissolution of starch granules was completed in 10 h at room temperature in pure DMSO, which was faster and more effective than that in ionic liquid 1-allyl-3-methylimidazolium chloride (AMIMCl). When dispersed in DMSO/water and AMIMCl/water at various ratios, respectively, different phase transitions were clearly exhibited, and the appearance and crystal structure of starch granules were significantly damaged with an increase in the concentration. Basing on the study of the decomposition temperature change through TGA measurements, a decreased temperature was observed in both DMSO and AMIMCl system, meaning starch degradation occurred with different levels. The huge temperature change from 357 to 328 °C were found in AMIMCl system, which most likely induced the distinct exothermic phenomenon in the DSC observation due to a significant depolymerization of starch.

A novel bioluminescence probe for mercury(II) was obtained on the basis of the distinct deprotection reaction of dithioacetal to decanal, so as to display suitable sensitivity and selectivity toward mercury(II) over other ions with bacterial bioluminescence signal. These experimental results indicated such a probe was a novel promising method for mercury(II) bioluminescence imaging in environmental and life sciences ex vivo and in vivo.

The transition from the current 4th generation mobile networks (4G) to the next generation, known as 5th generation mobile networks (5G), is expected to occur within the next decade. To provide greater network speed, capacity and better coverage, the wireless broadband technologies need to update traditional antennas for high frequency and millimeter wavelengths. In this study, meander line dipole antennas produced by direct ink-injecting technology have been successfully designed, fabricated and characterized, where the ink-injecting technology may open new routes to the fabrication of wireless antenna applications. An accurate electromagnetic numerical analysis model for the proposed meander line antenna is also developed. The designed dual-band antenna based on graphene flakes and Ag nanowires can operate from 1.2 GHz up to the 1.5 GHz band and from 3.2 GHz up to the 3.8 GHz band with |S11| > 10 dB for wireless communications applications. Different mixtures by mass ratio of aqueous dispersions of CNTs and Ag nanowires (1 : 1, 5 : 1, 10 : 1, 20 : 1) are also prepared to investigate the influence of the network structure on the performance of the meander line antennas.

During the 30th Chinese Antarctic Expedition in 2013/14, the Chinese icebreaker RV Xuelong answered a rescue call from the Russian RV Akademik Shokalskiy. While assisting the repatriation of personnel from the Russian vessel to the Australian RV Aurora Australis, RV Xuelong itself became entrapped within the compacted ice in the Adélie Depression region. Analysis of MODIS and SAR imagery provides a detailed description of the regional sea-ice conditions which led to the 6 day long besetment of RV Xuelong. The remotely sensed imagery revealed four stages of sea-ice characteristics during the entrapment: the gathering, compaction, dispersion and calving stages. Four factors characterizing the local sea-ice conditions during late December 2013 and early January 2014 were identified: surface component of the coastal current; near-surface wind; ocean tides; and surface air temperature. This study demonstrates that shipping activity in ice-invested waters should be underpinned by general knowledge of the ice situation. In addition, during such activity high spatiotemporal resolution remotely sensed data should be acquired regularly to monitor local and regional sea-ice changes with a view to avoiding the besetment of vessels.

The traditional proportional resonant (PR) regulator is sensitive to the frequency fluctuation of the power grid, and the gain is very limited for the non-resonant frequency. Therefore, in this paper, a quasi-PR controller easy to be implemented is proposed. The frequency feedback is introduced in order to increase bandwidth, and the frequency fluctuation of the power grid is controlled by the phase locked loop. The solar grid-connected inverter based on the PR controller had some advantages, such as making use of the controller infinite gain in the resonance frequency and eliminating the steady-state error. The simulation model of the grid-connected inverter is constructed to verify the theoretical analysis. The PR control algorithm can selectively make certain frequency enhancement, so as to achieve the effect of harmonic filtering.

Biodegradable elastomer poly[(1,4-butylene terephthalate)-co-(1,4-butylene adipate)] foam was successfully prepared using supercritical CO2. The elastomer foam has closed and uniform cell structure with density about 90 g/L. Narrow size distribution with average cell diameter 32 μm were obtained. The foamed balls show rubbery properties and can recover well (>90%) to their original shape quickly after releasing press stress. Cell growth needs to take place at melting state where the migration and orientation of polymer chains are permanently kept without remained force of springback. Some unique phenomena were observed during foaming the elastomer: post-expansion (about 40%) was obtained after removing the foamed samples from a cylinder mold, which results in forming a ball rather than a cylinder like the mold. This phenomenon was explained by the lower glass transition temperature of the elastomer, in which residual CO2 foam continuously in the room temperature; and “memory” of internal strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44354.

Add-on control is commonly used in control systems for disturbance rejection and servo enhancements. Despite the capability of greatly enhancing the steady-state performance, even an ideal add-on compensation can introduce significant output discontinuity and transient response. This paper presents an exact formula for computing the output discontinuity during add-on servo, and discusses its influence on transient performance in different control designs. We show that adding the compensation signal as an update of the reference yields much more desirable transient response than the traditional choice of add-on design at the input of the plant. Evaluation of the results is performed on a semiconductor manufacturing system.