Towards Near-Field Communications for 6G:Challenges and Opportunities

Extremely large-scale multiple-input multiple-output(XL-MIMO)and terahertz(THz)communications are pivotal candidate technologies for supporting the development of 6G mobile networks.However,these techniques invalidate the common assumptions of far-field plane waves and introduce many new properties.To accurately understand the performance of these new techniques,spherical wave modeling of near-field communications needs to be applied for future research.Hence,the investigation of near-field communication holds significant importance for the advancement of 6G,which brings many new and open research challenges in contrast to conventional far-field communication.In this paper,we first formulate a general model of the near-field channel and discuss the influence of spatial nonstationary properties on the near-field channel modeling.Subsequently,we discuss the challenges encountered in the near field in terms of beam training,localization,and transmission scheme design,respectively.Finally,we point out some promising research directions for near-field communications.

Convergent Data-Driven Regularizations for CT Reconstruction

The reconstruction of images from their corresponding noisy Radon transform is a typical example of an ill-posed linear inverse problem as arising in the application of computerized tomography(CT).As the(naive)solution does not depend on the measured data continuously,regularization is needed to reestablish a continuous dependence.In this work,we investigate simple,but yet still provably convergent approaches to learning linear regularization methods from data.More specifically,we analyze two approaches:one generic linear regularization that learns how to manipulate the singular values of the linear operator in an extension of our previous work,and one tailored approach in the Fourier domain that is specific to CT-reconstruction.We prove that such approaches become convergent regularization methods as well as the fact that the reconstructions they provide are typically much smoother than the training data they were trained on.Finally,we compare the spectral as well as the Fourier-based approaches for CT-reconstruction numerically,discuss their advantages and disadvantages and investigate the effect of discretization errors at differentresolutions.

Optimizing Connections:Applied Shortest Path Algorithms for MANETs

This study is trying to address the critical need for efficient routing in Mobile Ad Hoc Networks(MANETs)from dynamic topologies that pose great challenges because of the mobility of nodes.Themain objective was to delve into and refine the application of the Dijkstra’s algorithm in this context,a method conventionally esteemed for its efficiency in static networks.Thus,this paper has carried out a comparative theoretical analysis with the Bellman-Ford algorithm,considering adaptation to the dynamic network conditions that are typical for MANETs.This paper has shown through detailed algorithmic analysis that Dijkstra’s algorithm,when adapted for dynamic updates,yields a very workable solution to the problem of real-time routing in MANETs.The results indicate that with these changes,Dijkstra’s algorithm performs much better computationally and 30%better in routing optimization than Bellman-Ford when working with configurations of sparse networks.The theoretical framework adapted,with the adaptation of the Dijkstra’s algorithm for dynamically changing network topologies,is novel in this work and quite different from any traditional application.The adaptation should offer more efficient routing and less computational overhead,most apt in the limited resource environment of MANETs.Thus,from these findings,one may derive a conclusion that the proposed version of Dijkstra’s algorithm is the best and most feasible choice of the routing protocol for MANETs given all pertinent key performance and resource consumption indicators and further that the proposed method offers a marked improvement over traditional methods.This paper,therefore,operationalizes the theoretical model into practical scenarios and also further research with empirical simulations to understand more about its operational effectiveness.

Exploration of Problems and Solutions in Psychological Health Education for Preschool Children

The preschool period is a crucial stage for children’s physical and mental development,and the mental health status during this period directly affects children’s personality shaping and lifelong development.In recent years,China’s preschool education has flourished,with a continuous increase in the enrollment rate of children and an increasing emphasis on mental health education.However,there are still many problems in the current mental health education for preschool children,which urgently requires attention from all sectors of society.This article analyzes the main problems in mental health education for preschool children and proposes corresponding solutions,hoping to provide references for related research.

Institutions as Tools of Public Policy： A Comparative Evaluation of South East Asian-Sub-Saharan African Post War Development

In general, it can be argued that institutional framework a country or region designs plays a significant role in crafting, applying or even success of public policy. Drawing lessons from how Asia exploited the developmental state＇s concept by designing institutions which targeted key public policy areas such as education, health, domestic savings, and rural development, or aligned infrastructures such as roads, transport and ports, to drive economic development. The paper explores how this approach can be applied in sub-Saharan Africa （or individual countries）. The objective is to extricate constant factors impacting development both in ahistorical and atemporal terms. The investigation is guided by the key question： whether quality of institutions and institutional analysis can help explain development failures in Africa？ Hence, on one part, it probes institutions, institution-making, public policy making and what uniquely the Asian developmental state did that can help illuminate institutional role in policymaking and application. In pursuing this objective, the paper is cognisant of the question by Brousseau et al. asked, regarding generalizability of institutional capabilities, ＂If growth-enhancing institutions are identified in a specific country, can other countries learn from and transplant these＂. The investigation concludes that in public policy and development strategy-making institutions do matter as they delimit or even help create possibilities necessary for development and its sustenance, and to a certain extent, they are the vital constant （factors） that explains development differentiations in different geographic spaces or time periods.

Negative thermal expansion and phase transition of low-temperature Mg_(2)NiH_(4)

The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.

移动紧圆盘上Bernstein-Durrmeyer型算子的逼近

为了逼近移动圆盘上的解析函数,构造了一种新的Bernstein-Durrmeyer型算子,并给出其在移动圆盘上同时逼近的一致逼近速度估计.

Performance and potential of porous carbons derived of electrospun metal-organic frameworks for supercapacitor applications

Supercapacitors(SCs) are energy storage devices with the ability to charge and discharge at very high rates. The fast accumulation and release of charges occurs either electrostatically or electrochemically. There are two types of capacitors: electric double layer capacitors(EDLCs) and pseudocapacitors. EDLCs are the most commercially available.

Field measurement of strain response for typical asphalt pavement

In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.

Dual bound states in the continuum enhanced second harmonic generation with Transition Metal Dichalcogenides monolayer

This file includes:Section 1:Simulation methods Section 2:Field distribution of FW and SHW with homogeneous WS2 monolayer Section 3:Field distribution of FW and SHW with patterned WS2 monolayer Section 4:Asymmetric outcoupling rate of TE-type BIC Section 5:Quality factor of quasi-BIC for a finite size grating Section 6:A flow chart for designing the dual BICs scheme Section 7:TMDs monolayer orientation-dependent polarization-resolved SHG efficiency Section 8:SHG efficiency of homogeneous bulk GaP Section 9:Prospectives for experimental realizations Supplementary information for this paper is available at https://doi.org/10.29026/oea.2022.200097.

Real-Time Four-Dimensional Trajectory Generation Based on Gain-Scheduling Control and a High-Fidelity Aircraft Model

Aircraft ground movement plays a key role in improving airport efficiency,as it acts as a link to all other ground operations.Finding novel approaches to coordinate the movements of a fleet of aircraft at an airport in order to improve system resilience to disruptions with increasing autonomy is at the center of many key studies for airport airside operations.Moreover,autonomous taxiing is envisioned as a key component in future digitalized airports.However,state-of-the-art routing and scheduling algorithms for airport ground movements do not consider high-fidelity aircraft models at both the proactive and reactive planning phases.The majority of such algorithms do not actively seek to optimize fuel efficiency and reduce harmful greenhouse gas emissions.This paper proposes a new approach for generating efficient four-dimensional trajectories(4DTs)on the basis of a high-fidelity aircraft model and gainscheduling control strategy.Working in conjunction with a routing and scheduling algorithm that determines the taxi route,waypoints,and time deadlines,the proposed approach generates fuel-efficient 4DTs in real time,while respecting operational constraints.The proposed approach can be used in two contexts:①as a reactive decision support tool to generate new trajectories that can resolve unprecedented events;and②as an autopilot system for both partial and fully autonomous taxiing.The proposed methodology is realistic and simple to implement.Moreover,simulation studies show that the proposed approach is capable of providing an up to 11%reduction in the fuel consumed during the taxiing of a large Boeing 747-100 jumbo jet.

Dual bound states in the continuum enhanced second harmonic generation with transition metal dichalcogenides monolayer

The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.

Indoor Location Sensing Systems Based on Radio Channel Fingerprinting

This paper reviews and analyses various simplified-RFID (Radio Frequency Identification) indoor location systems, and proposes an improved implementation based on the propagation channel "fingerprinting" principle. The focus of the design aims to provide accurate location estimation, while minimising infrastructural requirements. The proposed approach is based on the LANDMARC (Indoor Location Sensing Using Active RFID) with Virtual Reference tags (VIRE) and implemented with dynamic linear interpolation and lagrange interpolation schemes. According to the simulation results, the proposed dynamic linear interpolation ensures much better performance on location-estimation error.

Genomic consequences of apple improvement

The apple(Malus domestica)is one of the world's most commercially important perennial crops and its improvement has been the focus of human effort for thousands of years.Here,we genetically characterise over 1000 apple accessions from the United States Department of Agriculture(USDA)germplasm collection using over 30,000 singlenucleotide polymorphisms(SNPs).We con fi rm the close genetic relationship between modern apple cultivars and their primary progenitor species,Malus sieversii from Central Asia,and fi nd that cider apples derive more of their ancestry from the European crabapple,Malus sylvestris,than do dessert apples.We determine that most of the USDA collection is a large complex pedigree:over half of the collection is interconnected by a series of fi rst-degree relationships.In addition,15%of the accessions have a fi rst-degree relationship with one of the top 8 cultivars produced in the USA.With the exception of‘Honeycrisp',the top 8 cultivars are interconnected to each other via pedigree relationships.The cultivars‘Golden Delicious'and‘Red Delicious'were found to have over 60 fi rst-degree relatives,consistent with their repeated use by apple breeders.We detected a signature of intense selection for red skin and provide evidence that breeders also selected for increased fi rmness.Our results suggest that Americans are eating apples largely from a single family tree and that the apple's future improvement will bene fi t from increased exploitation of its tremendous natural genetic diversity.

Highly converting syngas to lower olefins over a dual-bed catalyst

Light olefins (C2–C4olefins) are the most important basic carbon-based building blocks, which are mainly produced from the catalytic cracking of naphtha [1–3]. With the rapid depletion of oil reserves and the growing demand for lower olefins, there is an urgent need to develop an alternative technique for producing them from non-petroleum resources such as coal, natural gas, or biomass. Currently, coal has been successfully transformed to olefins in China via the combination of the processes of coal-tosyngas, syngas-to-methanol and methanol-to-olefins [4–6]. In order to further improve efficiency and reduce investment, the direct conversion of syngas to olefins has received extensive attention in recent years [7].

Highly sensitive microfiber ultrasound sensor for photoacoustic imaging

An ultrasound wave is a kind of acoustic signal with a frequency greater than 20 kHz,which is widely used in diverse fields such as medical imaging diagnosis,nondestructive testing and resource exploration.A variety of ultrasound sensors have been developed for ultrasound detection.Particularly for photoacoustic imaging,specialized ultrasound sensors with high sensitivity,small size,and broad bandwidth are needed.However,achieving such sensor perform-ance still poses a great challenge to the current state-of-the-art in ultrasound sensor technology.A recent work pub-lished in Opto-Electronic Advances(DOI:10.29026/oea.2022.200076)proposes a microfiber-based ultrasound sensor that breaks the limitations of existing ultrasound sensors.Benefiting from the large evanescent field characteristic of mi-crofiber,combined with the coherent detection technology,the proposed sensor realized highly sensitive ultrasound de-tection and demonstrated excellent performance in high-resolution photoacoustic imaging.The highly sensitive and mini-aturized microfiber ultrasound sensor provides a competitive alternative for various applications,such as endoscopic photoacoustic imaging of the intestinal tract and blood vessels in animals.

A Permanent Magnet Linear Synchronous Motor Drive for HTS Maglev Transportation Systems

A permanent magnet linear synchronous motor （PMLSM） for a high temperature superconducting （HTS） maglev system has been studied, including the motor structure, control strategy, and analysis techniques. Finite element analysis （FEA） of magnetic field is conducted to accurately calculate major motor parameters. Equivalent electrical circuit is used to predict the drive＇s steady-state characteristics, and a phase variable model is applied to predict the dynamic performance. Preliminary experiment with a prototype has been made to verify the theoretical analysis and the HTS-PM synchronous driving technology.

Analysis of Heat Transfer of a Flat Plate Oscillating Heat Pipe, for Different Surfaces

Recent and constant demands for greater power densities and smaller sizes of electronic systems have stimulated the growth of new designs of different passive heat transfer methods such as heat pipes. Particularly, OHPs （Oscillating Heat Pipes） are relatively novel devices, capable of removing high heat rates over long and short distances with not much temperature drop. This study concentrates on the design, building and assembling a test rig in order to analyse the flow pattern ofdeionised water through a 5 turns flat plate oscillating heat pipe under different heat inputs, which was made in the school of engineering and materials science of the Queen Mary University of London by two energy M.Sc. students. The filling ratio of the water is 40%. Furthermore an experimental study on the OHP thermal performance is carried out in order to examine the effects of different surface wet conditions： super hydrophilic, hydrophilic and cleaned brass. It is demonstrated the formation of liquid slugs and vapour plugs of the water along the channels. The experimental results showed that the hydrophilic surface tends to be more energy efficient. The heat transfer performance of the super-hydrophilic and hydrophilic is higher than brass by 5-12% and 15-20% respectively.

Sustainable Construction --An International Comparison of Civil Engineering Students

Sustainable construction in the future will be influenced significantly by the beliefs and actions of civil engineering students studying at university today. A comparative investigation of the appreciation and attitudes regarding sustainable construction of civil engineering students at The NUCE （National University of Civil Engineering） in Vietnam, and the Universities of Loughborough and Liverpool in the UK were therefore conducted. Results indicate that students at all three universities appreciate the importance of the development of sustainable construction and have positive attitudes with regards to sustainability. Construction design and appropriate use of materials were two issues generally considered the most important with regards to sustainability, but were also thought to be adequately covered on the courses in all three institutions.

Solidification microstructural constituent and its crystallographic morphology of permanent-mould-cast Mg-Zn-Al alloys

The microstructural constituents and the crystallographic morphology of the primary intermetallic phases in permanent-mould-cast Mg-Zn-Al alloys with typical compositions within high zinc castable domain were investigated. Three kinds of primary compounds with distinct morphology were identified as Mg32(Al,Zn)49(τ), MgZn(ε), and a ternary icosahedral quasi-crystalline compound (denoted with Q). The constituent is found to change with Zn and Al content and their concentration ratio. Alloys with middle mass ratio of Zn to Al and Al content, consist of α-Mg and τ phase, while alloys with high mass ratio of Zn to Al and low Al are composed of α-Mg, ε and a small amount of τ, those with low ratio of Zn to Al and high Al consist of α-Mg with Q. Solidification characteristics and process were proposed. The solidification ranges and liquidus temperature decrease with increasing Zn and Al content for τ-and Q-type alloys, whereas ε-type alloy shows reverse tendency. The second phase transformation moves to higher temperature range when Al content increases and ratio of Zn to Al decreases.