Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number ...of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a "perfect" NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.
Negative thermal expansion is an intriguing property of functional materials, which will give new phenomena and mechanisms for future studies.
Biological heme–copper oxidases (HCOs) play a critical role in the four-electron, four-proton reduction of O 2 to H 2 O in biosystems. HCOs exhibit high enzymatic activity due to their natural ...structure with heme–non-heme metal active sites, and the non-heme metal plays a role in conferring and fine-tuning the O 2 reduction activity of the HCOs. Inspired by this binuclear active enzyme, herein, we designed an efficient electrocatalyst (Fe, Mn–N/C) for the oxygen reduction reaction, which contains two types of metal–N x active site incorporated within the graphene framework of porous carbon. The catalyst displayed remarkable ORR performance with a half-potential of 0.904 V and kinetic current density of 33.33 mA cm −2 , which is 4.9 times that of 20% Pt/C (6.76 mA cm −2 ). When the Fe, Mn–N/C catalyst was applied as an air electrode in a Zn–air battery, it exhibited a superior performance compared to commercial Pt/C. Its discharge curve showed that the change in output voltage was negligible at 20 mA cm −2 for 23 000 seconds (6.4 h). First principles calculations revealed that Fe, Mn–N/C needs less energy for the protonation of O* to OH* in ORR procedures compared with Fe–N/C. This catalyst, with its bimetal reactive center mimicking a metal enzyme, will pave a new way to design efficient electrocatalysts for the ORR in fuel cells.
In recent years, with the progress and development of social science and technology, remote monitoring of Internet of Things systems has attracted more and more attention. The remote monitoring ...system is mainly a network system with convenient layout, simple maintenance, and high security performance built on the basis of the wireless network, which can realize real-time monitoring, and collects transmit information. It is mostly used in remote monitoring of room temperature, remote monitoring of intelligent furniture, engineering construction, and teaching. Communication technology dominates the operation of remote monitoring systems. With the introduction of 5G technology, mobile Internet technology has been pushed to the top of technology again. Using 5G mobile communication technology in the monitoring system, people can observe or operate the monitored things at any time. The sensor is an indispensable component of the remote monitoring system, and a new type of optical fiber is added to the sensor to make the system function more complete. However, the related technology is not very mature, and the research on remote monitoring system is relatively backward in China. Relevant studies have found that when the remaining energy of the information node in the remote monitoring system reaches 10%, the information node will die and the speed of information transmission will decrease. Therefore, adding new technologies is conducive to improving the performance of remote monitoring systems.
In this paper, combining B-spline function and Tikhonov regularization, we propose an online identification approach for reconstructing a smooth function and its derivative from scattered data with ...heteroscedasticity. Our methodology offers the unique advantage of enabling real-time updates based on new input data, eliminating the reliance on historical information. First, to address the challenge of heteroscedasticity and computation cost, we employ weight coefficients along with a judiciously chosen set of knots for interpolation. Second, a reasonable approach is provided to select weight coefficients and the regularization parameter in objective functional. Finally, We substantiate the efficacy of our approach through a numerical example and demonstrate its applicability in solving inverse problems. It is worth mentioning that the algorithm not only ensures the calculation efficiency, but also trades the data accuracy through the data volume.
In this paper, we consider a portfolio optimization problem where the wealth consists of investing into a risky asset with a slow mean-reverting volatility and receiving an uncontrollable stochastic ...cash flow under the exponential utility. The Hamilton–Jacobi–Bellman equation formulated from the optimal investment problem is a high-dimensional nonlinear partial differential equation and difficult to find its analytical or numerical solutions. The paper provides a tractable asymptotic approach which treats the initial problem as a perturbation around the constant volatility problem. In this paper, we present a formal derivation of asymptotic approximation and prove the accuracy of the value function. Moreover, an illustrative example is provided to assess our approximate strategy and value function.
Abstract We present an algorithm to derive difference images for data taken with JWST with matched point-spread functions (PSFs). It is based on the saccadic fast Fourier transform method but with ...revisions to accommodate the rotations and spatial variations of the PSFs. It allows for spatially varying kernels in B-spline form with separately controlled photometric scaling and Tikhonov kernel regularization for harnessing the ultimate fitting flexibility. We present this method using the JWST/NIRCam images of galaxy cluster Abell 2744 acquired in JWST Cycle 1 as the test data. The algorithm can be useful for time-domain source detection and differential photometry with JWST. It can also coadd images of multiple exposures taken at different field orientations. The coadded images preserve the sharpness of the central cores of the PSFs, and the positions and shapes of the objects are matched precisely with B-splines across the field.
Image Subtraction in Fourier Space Hu, Lei; Wang, Lifan; Chen, Xingzhuo ...
The Astrophysical journal,
09/2022, Letnik:
936, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Image subtraction is essential for transient detection in time-domain astronomy. The point-spread function (PSF), photometric scaling, and sky background generally vary with time and across ...the field of view for imaging data taken with ground-based optical telescopes. Image subtraction algorithms need to match these variations for the detection of flux variability. An algorithm that can be fully parallelized is highly desirable for future time-domain surveys. Here we introduce the saccadic fast Fourier transform (SFFT) algorithm we developed for image differencing. SFFT uses a
δ
-function basis for kernel decomposition, and the image subtraction is performed in Fourier space. This brings about a remarkable improvement in computational performance of about an order of magnitude compared to other published image subtraction codes. SFFT can accommodate the spatial variations in wide-field imaging data, including PSF, photometric scaling, and sky background. However, the flexibility of the
δ
-function basis may also make it more prone to overfitting. The algorithm has been tested extensively on real astronomical data taken by a variety of telescopes. Moreover, the SFFT code allows for the spatial variations of the PSF and sky background to be fitted by spline functions.
With the increasing power density of electronic chips, large radar, laser diode array and other equipments, the conventional heat dissipation methods are difficult to achieve the desired thermal ...control requirements increasingly. Spray cooling has attracted widespread attention due to its advantages in high heat flux removal such as less flow rate demand, high heat dissipation capacity, low superheat degree, no temperature overshoot and no contact thermal resistance with the heating surface. As of today, lots of researchers engage in this field and numerous achievements of spray cooling are obtained theoretically and experimentally. In this paper, an overview with spray cooling was completed. The current research progresses of heat transfer mechanisms of spray cooling in the three stages (single-phase regime, two-phase regime and critical heat flux regime) were summarized, and the influence factors, spray characteristics, heating surface characteristics, fluid characteristics and external environment characteristics, were analyzed in detail. The flash evaporation cooling, a special form of spray cooling, was also explored by a number of studies due to its irreplaceable advantage in low pressure environment or in space. Film flash evaporation and droplet flash evaporation significantly improve the cooling capacity of system and utilization of working fluid. In fact, the application of flash evaporation cooling is profound for development and expansion of spray cooling. Additionally, spray cooling system and nozzle were also elaborated in the paper.
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•Struvite recovery from produced water was investigated for the first time.•Calcium pretreatment by Na2CO3 achieved low Mg2+ loss and high Ca2+ removal.•High-purity struvite was ...obtained under Mg/N/P molar ratio = 1.5:1:1.5 & pH = 9.5.•Struvite precipitate was free of heavy metals and organic contaminants.•High toxicity reduction towards Vibrio fischeri (60%) was observed.
Unconventional oil and gas industries generate huge amounts of produced water (PW) containing high concentrations of potentially hazardous organic and inorganic contaminants. This study demonstrated the feasibility of simultaneously recovering NH4+, K+ and Mg2+ from PW by struvite precipitation after calcium pretreatment with Na2CO3 addition or CO2 stripping. Without pretreatment, calcium exhibited strong competition for phosphate through the formation of Ca3(PO4)2 precipitate. The pretreatment with a Ca2+:CO32− molar ratio of 1:1.2 achieved a relatively low loss rate of Mg2+ (31.3%) and high Ca2+ removal efficiency (95.9%). The results also revealed that the Mg/N/P molar ratio and solution pH had a remarkable effect on the struvite precipitation, while the seeding dosage and Na+ slightly influenced struvite formation. The combination of pH = 9.5 & Mg/N/P molar ratio = 1.5:1:1.5 was ideal for struvite recovery from PW, resulting in NH4+, K+ and Mg2+ recovery efficiencies of 85.9%, 24.8% and 96.8%, respectively. The results of X-ray diffraction and scanning electron microscopy further confirmed that the precipitates generated at this optimal condition were orthorhombic struvite. Moreover, along with the struvite recovery, no accumulation of heavy metals and organic contaminants was observed, indicating that the struvite quality was sufficient for field application. Furthermore, struvite recovery process was able to reduce the Microtox toxicity of PW towards Vibrio fischeri by 60%. Considering the low cost and relatively simple technology, struvite precipitation process has the potential to be used for large-scale applications for produced water treatment and resource recovery.
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