This paper studies the relationship between state feedback policies and disturbance response policies for the standard Linear Quadratic Regulator (LQR). For open-loop stable plants, we establish a ...simple relationship between the optimal state feedback controller ut = K*xt and the optimal disturbance response controller ut = L(H)*;1wt-1 +...+ L(H)*;1wt-H with H-order. Here xt, wt, ut stands for the state, disturbance, control action of the system, respectively. Our result shows that L(H)*,1 is a good approximation of K* and the approximation error ∥K* — L(H)*;1∥ decays exponentially with H. We further extend this result to LQR for open-loop unstable systems, when a pre-stabilizing controller K0 is available.
Carbon monoxide (CO) is a hazardous gas discharged during municipal solid waste incineration (MSWI). Its emission concentration serves as a vital indicator for assessing the stability of the MSWI ...process. Therefore, accurate prediction of CO emissions is crucial. While existing research predominantly relies on historical real data-driven models, it often overlooks the effective utilization of the combustion mechanism. This article introduced a novel approach: a heterogeneous ensemble prediction model that integrates virtual and real data. Firstly, virtual mechanism data was obtained through a multi-condition mechanism model constructed using coupled numerical simulation software of FLIC and Aspen Plus. Secondly, based on this virtual mechanism data, a linear regression decision tree (LRDT) algorithm was employed to establish the mechanism mapping model. Simultaneously, a real historical data-driven model based on a long short-term memory (LSTM) neural network algorithm was developed. In the offline training verification phase, the heterogeneous models were combined using an inequality-constrained random weighted neural network (CIRWNN) after aligning virtual and real samples representing operating conditions based on the k-nearest neighbor (KNN) approach. Subsequently, in the online testing verification stage, CO online prediction was achieved by ensemble the LRDT-based mechanism mapping model and.
the LSTM-based historical data-driven model. The proposed method's effectiveness and rationality were validated through an industrial case study of MSWI process in Beijing.
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•Heterogeneously ensemble model based on mechanism and data driven for CO prediction.•Multi-condition virtual mechanism data generated based on simulation software.•Strategy for balancing mechanism-driven and data-driven model fusion based on KNN.
Internal defects such as porosities are often formed in additively manufactured metal components. The pores nucleate, grow, and coalesce to form cracks under loads, leading to eventual catastrophic ...failure. In this paper, the full-field porosity evolution, including pore growth and coalescence in a wire-arc additively manufactured (WAAM) aluminum alloy cylinder under tension is observed with in-situ X-ray micro-computed tomography (μCT). The pore size distribution, density, and tensile stress are calculated from the volumetric images analyzed by a convolutional neural network (CNN) algorithm, which provides rapid analysis of 12,950 slice images from μCT volumetric images at the reference state and 13 tensile strains. The results show the quantitative evolution of the growth and coalescence of macropores under tension. A strong correlation is found between the local pore volume fraction and the true tensile stress when the tensile strain is larger than 5%.
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This experimental work is the first to investigate the directed energy deposition (DED) process at low temperature. DED is a metal additive manufacturing process commonly used to print or repair ...metal parts. Currently, DED can only be performed under laboratory conditions with the temperatures of 68°F to 77°F (20–25 °C). The manufacturing characteristics of DED make it have great potential in onsite additive manufacturing. However, the onsite DED needs to conducted at the temperature of the field environment, which cannot be changed to the optimal laboratory temperature. When onsite DED is carried out in a low-temperature environment, such as winter or the northern hemisphere, the ambient temperature is usually very cold, often below freezing temperature. The ambient temperature has a great influence on the DED process, such as the temperature gradient and cooling rate. So far, low-temperature DED has not been studied specifically for potential applications in on-site maintenance or remanufacturing. This experimental study fills this gap. In this work, the temperature of DED ambient (including substrate) was −20 °C, in order to simulate the DED process carried out in the field with low temperatures. The authors printed three thin-wall samples with stainless steel 316L powder at the low temperature condition. As comparative test, another thin-wall sample with same dimension and material was printed with same DED processing parameters at room temperature (20 °C). Then, the molten pool morphology, the sample geometry, the sample hardness and tensile mechanical properties were investigated experimentally. The results show that DED process can print SS316L powder smoothly at low temperature. Two interesting findings are that the sample height and molten pool size are larger at −20 °C temperature than the sample printed at 20 °C. In addition, the hardness values of thin-wall specimens printed at −20 °C are larger than those printed at room temperature and the tensile tests of low-temperature DED samples show the better mechanical properties. Comparing to the hardness value (107.5) of the sample printed at regular ambient temperature 20 °C, the hardness values of the low-temp DED printed sample had a trend of obvious increase to more than 120. In addition, the modulus acquired from tensile test was improved from 13,888 MPa to about 20,000 MPa. The Yield strength increased from 366 MPa to 400 MPa, and UTS increased from 602 MPa to about 630 MPa.
Water vapor condensation is a ubiquitous process in nature and industry. Over the past century, methods achieving dropwise condensation using a thin (<1 µm) hydrophobic “promoter” layer have been ...developed, which increases the condensation heat transfer by ten times compared to filmwise condensation. Unfortunately, implementations of dropwise condensation have been limited due to poor durability of the promoter coatings. Here, thin‐film condensation which utilizes a promoter layer not as a condensation surface, but rather to confine the condensate within a porous biphilic nanostructure, nickel inverse opals (NIO) with a thin (<20 nm) hydrophobic top layer of decomposed polyimide is developed. Filmwise condensation confined to thicknesses <10 µm is demonstrated. To test the stability of thin‐film condensation, condensation experiments are performed to show that at higher supersaturations droplets coalescing on top of the hydrophobic layer are absorbed into the superhydrophilic layer through coalescence‐induced transitions. Through detailed thermal‐hydrodynamic modeling, it is shown that thin‐film condensation has the potential to achieve heat transfer coefficients approaching ≈100 kW m−2 while avoiding durability issues by significantly reducing nucleation on the hydrophobic surface. The work presented here develops an approach to potentially ensure durable and high‐performance condensation comparable to dropwise condensation.
Thin‐film condensation on hydrophobic‐coated nickel inverse opal structures enables heat transfer performance approaching that of dropwise condensation while achieving higher robustness by confining the condensate film and reducing nucleation on the hydrophobic layer.
We document a significantly negative association between the nominal price measure of Birru and Wang (2015) and the profit of the stock momentum strategy. The negative relationship is driven by the ...underperformance of loser stocks with high nominal price illusions. Further analysis shows that the previously documented positive correlations between return skewness measures and momentum profit are subsumed by the effect of nominal price on momentum profit.
•A positive relation between nominal price illusion and momentum profit is documented.•It is driven by the underperformance of loser stocks of high nominal price illusions.•The relation subsumes the positive association between skewness and momentum profit.
Wire arc additive manufacturing (WAAM) has received increasing use in 3D printing because of its high deposition rates suitable for components with large and complex geometries. However, the lower ...forming accuracy of WAAM than other metal additive manufacturing methods has imposed limitations on manufacturing components with high precision. To resolve this issue, we herein implemented the hybrid manufacturing (HM) technique, which integrated WAAM and subtractive manufacturing (via a milling process), to attain high forming accuracy while taking advantage of both WAAM and the milling process. We describe in this paper the design of a robot-based HM platform in which the WAAM and CNC milling are integrated using two robotic arms: one for WAAM and the other for milling immediately following WAAM. The HM was demonstrated with a thin-walled aluminum 5356 component, which was inspected by X-ray micro-computed tomography (μCT) for porosity visualization. The temperature and cutting forces in the component under milling were acquired for analysis. The surface roughness of the aluminum component was measured to assess the surface quality. In addition, tensile specimens were cut from the components using wire electrical discharge machining (WEDM) for mechanical testing. Both machining quality and mechanical properties were found satisfactory; thus the robot-based HM platform was shown to be suitable for manufacturing high-quality aluminum parts.
Template-directed assembly has been shown to yield a broad diversity of highly ordered mesostructures
, which in a few cases exhibit symmetries not present in the native material
. However, this ...technique has not yet been applied to eutectic materials, which underpin many modern technologies ranging from high-performance turbine blades to solder alloys. Here we use directional solidification of a simple AgCl-KCl lamellar eutectic material within a pillar template to show that interactions of the material with the template lead to the emergence of a set of microstructures that are distinct from the eutectic's native lamellar structure and the template's hexagonal lattice structure. By modifying the solidification rate of this material-template system, trefoil, quatrefoil, cinquefoil and hexafoil mesostructures with submicrometre-size features are realized. Phase-field simulations suggest that these mesostructures appear owing to constraints imposed on diffusion by the hexagonally arrayed pillar template. We note that the trefoil and hexafoil patterns resemble Archimedean honeycomb and square-hexagonal-dodecagonal lattices
, respectively. We also find that by using monolayer colloidal crystals as templates, a variety of eutectic mesostructures including trefoil and hexafoil are observed, the former resembling the Archimedean kagome lattice. Potential emerging applications for the structures provided by templated eutectics include non-reciprocal metasurfaces
, magnetic spin-ice systems
, and micro- and nano-lattices with enhanced mechanical properties
.
Existing persistent memory file systems usually ignore the problem that persistent memories (PMs) have limited write endurance. Then the underlying PMs can be damaged easily by the unbalanced writes ...of file systems. However, existing wear-leveling-aware space management techniques mainly focus on providing higher-balanced writes to PMs rather than reducing the overhead, which can lead to serious performance degradation of persistent memory file systems. In this paper, we propose an efficient wear-leveling-aware buddy-like memory allocator, called WBAlloc, to achieve a higher-accuracy wear-leveling of PM while improving the performance of persistent memory file systems. Like the buddy memory allocator, WBAlloc adopts a multi-level allocator to manage the unused space of PM, and each allocator represents a range of allocation granularity, which can achieve O(1) time complexity in both allocation and deallocation. We implement the proposed WBAlloc in the Linux kernel based on NOVA, a typical persistent memory file system. Compared with original NOVA, DWARM, and WMAlloc (DWARM and WMAlloc are the state-of-the-art wear-leveling-aware allocators of persistent memory file systems), the experimental results show that the proposed WBAlloc can achieve 26.23%, 80.46%, 15.61% performance improvement while reducing the maximum writes by up to 338.88%, 159.28%, and 29.45% on average, respectively.
•We reveal the high overhead and severe imbalanced wear problem caused by allocator of PM file systems.•We propose WBAlloc which provides O(1) time complexity in both allocation and deallocation while achieving near-balanced writes.•Extensive experiments show that the proposed WBAlloc can outperform existing solutions.
The intestinal barrier has always been the rate-limiting step in the oral administration process. To overcome the intestinal barrier, researchers have widely adopted nanocarriers, especially ...active-targeting nanocarriers strategies. However, most of these strategies focus on the ligand decoration of nanocarriers targeting specific receptors, so their applications are confined to specific receptors or specific cell types. In this study, we tried to investigate more common strategies in the field of transmembrane transport enhancement. Trans-Golgi network (TGN) is the sorting center of biosynthetic route which could achieve polarized localization of proteins in polarized epithelial cells, and the basolateral plasma membrane is where all transcytotic cargos have to pass through. Thus, it is expected that guiding nanocarriers to TGN or basolateral plasma membrane may improve the transcytosis. Hence, we choose sorting signal peptide to modify micelles to guide micelles to TGN (named as BAC decorated micelles, BAC-M) or to basolateral plasma membrane (named as STX decorated micelles, STX-M). By incorporating coumarin-6 (C6) or Cy5-PEG-PCL in the micelles to indicate the behavior of micelles, the effects of these two strategies on the transcytosis were investigated. To our surprise, BAC-M and STX-M behaved quite differently when crossing biological barriers. BAC-M showed significant superiority in colocalization with TGN, transmembrane transport and even in vivo absorption, while STX-M had no significant difference from blank micelles. Further investigation revealed that the strategy of directly guiding nanocarriers to the basolateral plasma membrane (STX-M) only caused the stack of vesicles near the basolateral plasma membrane. So, we concluded that guiding nanocarriers to TGN which related to secretion may contribute to the transmembrane transport. This common strategy based on the physiological function of TGN in polarized epithelial cells will have broad application prospects in overcoming biological barrier.
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