Chemical characteristics of aerosols at coastal station in Hong Kong.Ⅱ. Environmental behavior of trace elements during the April 1995 to April 1996

An one-year of sampling aerosol program was carried out during the period of April 1995 to April 1996 at coastal region, Cape D′Aguilar, in Hong Kong. The trace element composition of aerosol particles(TSP and PM 10 ) were measured and analyzed by using the Instrumental Neutron Activation Analysis(INAA) and Inductive Couple Plasma-Mass Spectrometry(ICP-MS) techniques. The results showed that the polluted elements such as: V, Zn, As, Pb, Cd, Sb, I, Se, Bi, with high enrichment factor(E.F) values, are derived from anthropogenic sources, while Sc, Al, Fe, Mn, Sm, La, Sr are less than 10 in E.F, these elements are related the crust and soil. The concentration of the trace elements are present seasonal variation i.e. summer low and winter high, whereas the V or noncrustal V(V *) present summer high and winter low, this phenomenon might be explained by local or regional oil combustion sources. Use three type of elemental ratio, e.g. La/Sm, Mn */V * and Bi/Al indicate that both TSP and PM 10 of La/Sm ratios are mainly related to soil and dust, Mn */V * are probably represent fossil combustion and Bi/Al are possibly associated with refuse incineration, ferromanganese alloys and aluminum production. The varimax rotation factor analysis for trace elements was performed. By means of the absolute principal component analysis(APCA) and multiple regression, the contribution of trace elements to possible sources and overall means of trace elements were estimated. The results showed that the present station is impacted by the anthropogenic species, although the quantities are different during the summertime and wintertime.

Investigation on the Consumption Values of Hong Kong People on Tie Products

This study aims at investigating the consumption values of Hong Kong people on necktie. Based on the Sheth-Newman-Gross Model of consumption values on consumers’ choice decision as conceptual framework, results from the focus group interview, a questionnaire was designed and adopted for conducting the survey. Data collected from 245 respondents were analysed using the Factor Analysis to review the important elements of consumers’ decision of purchasing tie products. Implications on the results on the Functional value were reviewed and discussed in details. Interesting elements such as fabric hand-feel were also identified as influential associated in Hong Kong consumers’ selection of necktie. Since, both fibre content and fabric handle were also found as major selection criteria for fabric materials, the study was focused on the analysis of functional value of the product and further extended to study the handle preference for Hong Kong customers, in which a subjective handle assessment of a wide range of tie fabrics being newly developed and introduced in the market was conducted and objective fabric physical and mechanical properties were measured. Important fabric handle attributes that influence the consumers’ preference on tie fabrics were identified and their objective translation by fabric physical and mechanical properties were also obtained. The investigation provides decision support to necktie manufacturers and retailers through scientific and quantitative recommendations for product development of tie products and material selection.

Development of a Fuzzy Fire Risk Evaluation Model for Building Construction Sites in Hong Kong

Earlier research works on fire risk evaluation indicated that an objective,reliable,comprehensive,and practical fire risk evaluation model is essential for mitigating fire occurrence in building construction sites.Nevertheless,real empirical studies in this research area are quite limited.This journal paper gives an account of the second stage of a research study aiming at developing a fuzzy fire risk evaluation model for building construction sites in Hong Kong.The empirical research findings showed that the overall fire risk level of building construction sites is 3.6427,which can be interpreted as“moderate risk”.Also,the survey respondents perceived that“Restrictions for On-Site Personnel”is the most vital fire risk factor;with“Storage of Flammable Liquids or Dangerous Goods”being the second;and“Attitude of Main Contractor”the third.The proposed fuzzy fire risk evaluation model for building construction sites can be used to assess the overall fire risk level for a building construction site,and to identify improvement areas needed.Although the fuzzy fire risk evaluation model was developed domestically in Hong Kong,the research could be reproduced in other nations to develop similar models for international comparisons.Such an extension would provide a deeper understanding of the fire risk management on building construction sites.

Personal Thermal Management by Radiative Cooling and Heating

Maintaining thermal comfort within the human body is crucial for optimal health and overall well-being.By merely broadening the setpoint of indoor temperatures,we could significantly slash energy usage in building heating,ventilation,and air-conditioning systems.In recent years,there has been a surge in advancements in personal thermal management(PTM),aiming to regulate heat and moisture transfer within our immediate surroundings,clothing,and skin.The advent of PTM is driven by the rapid development in nano/micro-materials and energy science and engineering.An emerging research area in PTM is personal radiative thermal management(PRTM),which demonstrates immense potential with its high radiative heat transfer efficiency and ease of regulation.However,it is less taken into account in traditional textiles,and there currently lies a gap in our knowledge and understanding of PRTM.In this review,we aim to present a thorough analysis of advanced textile materials and technologies for PRTM.Specifically,we will introduce and discuss the underlying radiation heat transfer mechanisms,fabrication methods of textiles,and various indoor/outdoor applications in light of their different regulation functionalities,including radiative cooling,radiative heating,and dual-mode thermoregulation.Furthermore,we will shine a light on the current hurdles,propose potential strategies,and delve into future technology trends for PRTM with an emphasis on functionalities and applications.

路堑过渡段对高速列车气动荷载的影响:基于IDDES方法

当高速列车在横风条件下通过路堑过渡段时,列车的气动荷载将发生显著变化。本文基于改进的延迟分离涡湍流模型建立了列车-路基-风的三维空气动力学耦合模型,重点探讨了路堑深度对列车气动载荷变化和气动性能恶化的影响,揭示了相应的列车周围流场的演化机制。结果表明:当路堑深度为6 m时,头车所受的气动冲击能量最高。在列车完全驶入下一运行场景后,随着路堑深度的增大,来流对列车气动荷载的影响减弱,相应的波动幅度降低。头车气动载荷的突变幅值与风速近似满足线性正相关关系。

DYNAMICS FOR A CHEMOTAXIS MODEL WITH GENERAL LOGISTIC DAMPING AND SIGNAL DEPENDENT MOTILITY

In this paper,we consider the fully parabolic Chemotaxis system with the general logistic source{ut=Δ(γ(v)u)+λu-μu^(k),x∈Ω,t>0,vt=△v+wz,x∈Ω,t>0,wt=-wz,x∈Ω,t>0,zt=△z-z+u,x∈Ω,t>0 whereΩ⊂ℝn(n≥1)is a smooth and bounded domain,λ≥0,μ≥0,κ>1,and the motility function satisfies thatγ(v)∈C3([0,∞)),γ(v)>0,γ′(v)≤0 for all v≥0.Considering the Neumann boundary condition,we obtain the global boundedness of solutions if one of the following conditions holds:(i)λ=μ=0,1≤nλ3;(ii)λ>0,μ>0,combined withκ>1,1≤n≤3 or k>n+2/4,,n>3.Moreover,we prove that the solution (u, v, w, z) exponentially converges to the constant steady state ((λ/μ)1/k-1,∫Ωv0dx+∫Ωw0dx/|Ω|,0,(λ/μ)1/k-1).

Tailoring the microstructure of Mg-Al-Sn-RE alloy via friction stir processing and the impact on its electrochemical discharge behaviour as the anode for Mg-air battery

Constructing the magnesium alloy with fine grains,low density of dislocations,and weak crystal orientation is of crucial importance to enhance its comprehensive performance as the anode for Mg-air battery.However,this unique microstructure can hardly be achieved with conventional plastic deformation such as rolling or extrusion.Herein,we tailor the microstructure of Mg-Al-Sn-RE alloy by using the friction stir processing,which obviously refines the grains without increasing dislocation density or strengthening crystal orientation.The Mg-air battery with the processed Mg-Al-Sn-RE alloy as the anode exhibits higher discharge voltages and capacities than that employing the untreated anode.Furthermore,the impact of friction stir processing on the electrochemical discharge behaviour of Mg-Al-Sn-RE anode and the corresponding mechanism are also analysed according to microstructure characterization and electrochemical response.

Comparison study on measurement of rail weld joint between inertial reference method and multi-point chord reference method

Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.

From VIB‑to VB‑Group Transition Metal Disulfides:Structure Engineering Modulation for Superior Electromagnetic Wave Absorption

The laminated transition metal disulfides(TMDs),which are well known as typical two-dimensional(2D)semiconductive materials,possess a unique layered structure,leading to their wide-spread applications in various fields,such as catalysis,energy storage,sensing,etc.In recent years,a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption(EMA)has been carried out.Therefore,it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application.In this review,recent advances in the development of electromagnetic wave(EMW)absorbers based on TMDs,ranging from the VIB group to the VB group are summarized.Their compositions,microstructures,electronic properties,and synthesis methods are presented in detail.Particularly,the modulation of structure engineering from the aspects of heterostructures,defects,morphologies and phases are systematically summarized,focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance.Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

Strain‑Induced Surface Interface Dual Polarization Constructs PML‑Cu/Bi_(12)O_(17)Br_(2) High‑Density Active Sites for CO_(2) Photoreduction

The insufficient active sites and slow interfacial charge trans-fer of photocatalysts restrict the efficiency of CO_(2) photoreduction.The synchronized modulation of the above key issues is demanding and chal-lenging.Herein,strain-induced strategy is developed to construct the Bi–O-bonded interface in Cu porphyrin-based monoatomic layer(PML-Cu)and Bi_(12)O_(17)Br_(2)(BOB),which triggers the surface interface dual polarization of PML-Cu/BOB(PBOB).In this multi-step polarization,the built-in electric field formed between the interfaces induces the electron transfer from con-duction band(CB)of BOB to CB of PML-Cu and suppresses its reverse migration.Moreover,the surface polarization of PML-Cu further promotes the electron converge in Cu atoms.The introduction of PML-Cu endows a high density of dispersed Cu active sites on the surface of PBOB,significantly promoting the adsorption and activation of CO_(2) and CO desorption.The conversion rate of CO_(2) photoreduction to CO for PBOB can reach 584.3μmol g-1,which is 7.83 times higher than BOB and 20.01 times than PML-Cu.This work offers valuable insights into multi-step polarization regulation and active site design for catalysts.

基于随机场理论的下穿盾构隧道施工变形条件下列车动态响应

在以往的路基段铁路行车安全研究中,地基土的物理力学参数常被考虑为确定性的参数。为探究下穿地铁盾构隧道周围土层的随机场特征对地表既有铁路行车安全的影响规律,建立列车-轨道-盾构隧道-地基土耦合系统分析模型。基于随机场理论对地基土的物理力学参数进行随机赋值,并获得轮重减载率和车体加速度等车体动态响应指标的概率密度演化信息。基于概率密度演化理论开展下穿盾构隧道施工变形条件下地表运行列车动态响应分析。结果表明:盾构施工段范围内的地表沉降分布近似呈正态分布,地表沉降均值与标准差的最大值出现在盾构隧道中心线位置,而轮重减载率最大值出现在地表沉降最大值两侧曲线的下降段。随着车速的提高,车体垂向加速度概率密度等高线的分布宽度逐渐增大,当加速度上限曲线取最大值时对应的概率密度分布仍近似呈正态分布。当车速达到300 km/h时,轮重减载率的分布范围超过0.8的限值要求,而在300 km/h以下的行车速度条件下,车体加速度均满足规范要求的1.3 m/s^(2)的要求。为满足三倍标准差的99.74%的行车安全保证率,建议该区域的行车速度不应超过250 km/h。

Emerging catalytic materials for practical lithium-sulfur batteries

High-energy lithium-sulfur batteries(LSBs)have experienced relentless development over the past decade with discernible improvements in electrochemical performance.However,a scrutinization of the cell operation conditions reveals a huge gap between the demands for practical batteries and those in the literature.Low sulfur loading,a high electrolyte/sulfur(E/S)ratio and excess anodes for lab-scale LSBs significantly offset their high-energy merit.To approach practical LSBs,high loading and lean electrolyte parameters are needed,which involve budding challenges of slow charge transfer,polysulfide precipitation and severe shuttle effects.To track these obstacles,the exploration of electrocatalysts to immobilize polysulfides and accelerate Li-S redox kinetics has been widely reported.Herein,this review aims to survey state-of-the-art catalytic materials for practical LSBs with emphasis on elucidating the correlation among catalyst design strategies,material structures and electrochemical performance.We also statistically evaluate the state-of-the-art catalyst-modified LSBs to identify the remaining discrepancy between the current advancements and the real-world requirements.In closing,we put forward our proposal for a catalytic material study to help realize practical LSBs.

Review on Chemical Stability of Lead Halide Perovskite Solar Cells

Lead halide perovskite solar cells(PSCs) have become a promising next-generation photovoltaic technology due to their skyrocketed power conversion efficiency. However, the device stability issues may restrict their commercial applications, which are dominated by various chemical reactions of perovskite layers. Hence, a comprehensive illustration on the stability of perovskite films in PSCs is urgently needed. In this review article, chemical reactions of perovskite films under different environmental conditions(e.g., moisture,oxygen, light) and with charge transfer materials and metal electrodes are systematically elucidated. Effective strategies for suppressing the degradation reactions of perovskites, such as buffer layer introduction and additives engineering,are specified. Finally, conclusions and outlooks for this field are proposed. The comprehensive review will provide a guideline on the material engineering and device design for PSCs.

In situ formed ultrafine metallic Ni from nickel(Ⅱ) acetylacetonate precursor to realize an exceptional hydrogen storage performance of MgH_(2)-Ni-EG nanocomposite

It has been well known that doping nano-scale catalysts can significantly improve both the kinetics and reversible hydrogen storage capacity of MgH_(2) . However, so far it is still a challenge to directly synthesize ultrafine catalysts(e.g., < 5 nm), mainly because of the complicated chemical reaction processes. Here, a facile one-step high-energy ball milling process is developed to in situ form ultrafine Ni nanoparticles from the nickel acetylacetonate precursor in the MgH_(2) matrix. With the combined action of ultrafine metallic Ni and expanded graphite(EG), the formed MgH_(2)-Ni-EG nanocomposite with the optimized doping amounts of Ni and EG can still release 7.03 wt.% H_(2) within 8.5 min at 300 ℃ after 10 cycles. At a temperature close to room temperature(50 ℃), it can also absorb 2.42 wt.% H_(2) within 1 h. It can be confirmed from the microstructural characterization analysis that the in situ formed ultrafine metallic Ni is transformed into Mg_(2)Ni/Mg_(2)NiH_4 in the subsequent hydrogen absorption and desorption cycles. It is calculated that the dehydrogenation activation energy of the MgH_(2)-Ni-EG nanocomposite is also reduced obviously in comparison with the pure MgH_(2) . Our work provides a methodology to significantly improve the hydrogen storage performance of MgH_(2) by combining the in situ formed and uniformly dispersed ultrafine metallic catalyst from the precursor and EG.

Simultaneously mastering operando strain and reconstruction effects via phase-segregation strategy for enhanced oxygen-evolving electrocatalysis

Material strain and reconstruction effects are critical for catalysis reactions,but current insights into operando strain effects during reaction and means to master catalyst reconstruction are still lacking.Here,we propose a facile thermal-induced phase-segregation strategy to simultaneously master material operando strain and reconstruction effects for enhanced oxygen-evolving reaction(OER).Specifically,self-assembled and controllable layered LiCoO_(2)phase and Co_(3)O_(4)spinel can be generated from pristine Li2Co_(2)O_(4)spinel via Li and O volatilization under different temperatures,realizing controllable proportions of two phases by calcination temperature.Combined operando and ex-situ characterizations reveal that obvious tensile strain along(003)plane appears on layered LixCoO_(2)phase during OER,while low-valence Co_(3)O_(4)phase transforms into high-valence CoOOHx,realizing simultaneous operando strain and reconstruction effects.Further experimental and computational investigations demonstrate that both strained LixCoO_(2)phase and reconstructed CoOOHxcompound contribute to the beneficial adsorption of important OH-reactants,while respective roles in activity and stability are uncovered by exploring their latticeoxygen participation mechanism.This work not only reveals material operando strain effects during OER,but also inaugurates a new thermal-induced phase-segregation strategy to artificially master material operando strain and reconstruction effects,which will enlighten rational material design for many potential reactions and applications.

Microcurvature landscapes induce neural stem cell polarity and enhance neural differentiation

Tissue curvature has long been recognized as an important anatomical parameter that affects intracellular behaviors,and there is emerging interest in applying cell-scale curvature as a designer property to drive cell fates for tissue engineering purposes.Although neural cells are known to undergo dramatic and terminal morphological changes during development and curvature-limiting behaviors have been demonstrated in neurite outgrowth studies,there are still crucial gaps in understanding neural cell behaviors,particularly in the context of a three-dimensional(3D)curvature landscape similar to an actual tissue engineering scaffold.In this study,we fabricated two substrates of microcurvature(curvature-substrates)that present a smooth and repeating landscape with focuses of either a concave or a convex pattern.Using these curvature-substrates,we studied the properties of morphological differentiation in N2a neuroblastoma cells.In contrast to other studies where two-dimensional(2D)curvature was demonstrated to limit neurite outgrowth,we found that both the concave and convex substrates acted as continuous and uniform mechanical protrusions that significantly enhanced neural polarity and differentiation with few morphological changes in the main cell body.This enhanced differentiation was manifested in various properties,including increased neurite length,increased nuclear displacement,and upregulation of various neural markers.By demonstrating how the micron-scale curvature landscape induces neuronal polarity,we provide further insights into the design of biomaterials utilizing the influence of surface curvature in neural tissue engineering.

Thermal integrity profiling of cast-in-situ piles in sand using fiber-optic distributed temperature sensing

Defects in cast-in-situ piles have an adverse impact on load transfer at the pile‒soil interface and pile bearing capacity. In recent years, thermal integrity profiling (TIP) has been developed to measure temperature profiles of cast-in-situ piles, enabling the detection of structural defects or anomalies at the early stage of construction. However, using this integrity testing method to evaluate potential defects in cast-in-situ piles requires a comprehensive understanding of the mechanism of hydration heat transfer from piles to surrounding soils. In this study, small-scale model tests were conducted in laboratory to investigate the performance of TIP in detecting pile integrity. Fiber-optic distributed temperature sensing (DTS) technology was used to monitor detailed temperature variations along model piles in sand. Additionally, sensors were installed in sand to measure water content and matric suction. An interpretation method against available DTS-based thermal profiles was proposed to reveal the potential defective regions. It shows that the temperature difference between normal and defective piles is more obvious in wet sand. In addition, there is a critical zone of water migration in sand due to the water absorption behavior of cement and temperature transfer-induced water migration in the early-age concrete setting. These findings could provide important insight into the improvement of the TIP testing method for field applications.

Standard Dual Quaternion Optimization and Its Applications in Hand-Eye Calibration and SLAM

Several common dual quaternion functions,such as the power function,the magnitude function,the 2-norm function,and the kth largest eigenvalue of a dual quaternion Hermitian matrix,are standard dual quaternion functions,i.e.,the standard parts of their function values depend upon only the standard parts of their dual quaternion variables.Furthermore,the sum,product,minimum,maximum,and composite functions of two standard dual functions,the logarithm and the exponential of standard unit dual quaternion functions,are still standard dual quaternion functions.On the other hand,the dual quaternion optimization problem,where objective and constraint function values are dual numbers but variables are dual quaternions,naturally arises from applications.We show that to solve an equality constrained dual quaternion optimization(EQDQO)problem,we only need to solve two quaternion optimization problems.If the involved dual quaternion functions are all standard,the optimization problem is called a standard dual quaternion optimization problem,and some better results hold.Then,we show that the dual quaternion optimization problems arising from the hand-eye calibration problem and the simultaneous localization and mapping(SLAM)problem are equality constrained standard dual quaternion optimization problems.