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Characterization of a smog chamber for studying formation of gas-phase products and secondary organic aerosol

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Journal of Environmental Sciences 2024年第2期136卷 570-582页

作者： Qi Yuan Zhuozhi Zhang Meng Wang Kin Fai Ho Tao Wang Shuncheng Lee Department of Civil and Environmental Engineering The Hong Kong Polytechnic UniversityKowloonHong KongChina School of Public Health and Primary Care The Chinese University of Hong KongShatinHong KongChina

Smog chambers provide a potent approach to explore the secondary organic aerosol formation under varied *** study describes the construction and characterization of a new smog chamber facility for studying the formation mechanisms of gas-phase products and secondary organic aerosol from the photooxidation of volatile organic *** chamber is a 5.4 m^(3) Fluorinated Ethylene Propylene(FEP)Teflon reactor with the potential to perform photooxidation experiments at controlled temperature and relative *** characterizations were conducted for evaluation of stability of environmental parameters,mixing time,background contamination,light intensity,and wall losses of gases and *** photolysis rate of NO_(2)(J_(NO2))ranged from(1.02-3.32)×10^(-3)sec^(-1),comparable to the average J_(NO2)in ambient *** wall loss rates for NO,NO_(2),and O_(3)were 0.47×10^(-4),0.37×10^(-4),and 1.17×10^(-4)min^(-1),while wall loss of toluene was obsoletely found in a 6 hr *** particle number wall loss rates are(0.01-2.46)×10^(-3)min^(-1)for 40-350 nm with an average lifetime of more than one day.A series of toluene photooxidation experiments were carried out in absence of NO_xunder dry *** results of the simulation experiments demonstrated that the chamber is well designed to simulate photolysis progress in the atmosphere.

关键词： Smog chamber Gas-phase oxidation Chamber characterization Chemical mechanism

Selective nano-buckling improves the performance of graphene logic transistors

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National Science Review 2024年第2期11卷 95-96页

作者： Tong Yang Ming Yang Department of Applied Physics The Hong Kong Polytechnic University Research Centre for Nanoscience and Nanotechnology The Hong Kong Polytechnic University

The massive integration of silicon-based transistors into modern electronic devices greatly increases power consumption and heat generation/dissipation[1]. In this concern, transistors based on atomically-thin graphene that exhibit high electric and thermoelectric conductivities with negligible contact resistance,

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Nanoimprint-induced strain engineering of two-dimensional materials

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Microsystems & Nanoengineering 2024年第2期10卷 323-332页

作者： Chuying Sun Jianwen Zhong Zhuofei Gan Liyang Chen Chuwei Liang hongtao Feng Zhao Sun Zijie Jiang Wen-Di Li The university of hong kong Hong KongChina

The high stretchability of two-dimensional(2D)materials has facilitated the possibility of using external strain to manipulate their ***,strain engineering has emerged as a promising technique for tailoring the performance of 2D materials by controlling the applied elastic strain *** various types of strain engineering methods have been proposed,deterministic and controllable generation of the strain in 2D materials remains a challenging ***,we report a nanoimprint-induced strain engineering(NISE)strategy for introducing controllable periodic strain profiles on 2D materials.A three-dimensional(3D)tunable strain is generated in a molybdenum disulfide(MoS_(2))sheet by pressing and conforming to the topography of an imprint *** strain profiles generated in MoS_(2)are demonstrated and verified by Raman and photoluminescence(PL)*** strain modulation capability of NISE is investigated by changing the imprint pressure and the patterns of the imprint molds,which enables precise control of the strain magnitudes and distributions in MoS_(2).Furthermore,a finite element model is developed to simulate the NISE process and reveal the straining behavior of MoS_(2).This deterministic and effective strain engineering technique can be easily extended to other materials and is also compatible with common semiconductor fabrication processes;therefore,it provides prospects for advances in broad nanoelectronic and optoelectronic devices.

关键词： strain dimensional molybdenum

Interfacial friction induced capillary flow within nanofiber-supported ionic liquid droplets

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Green Energy & Environment 2024年第5期9卷 789-791页

作者： Yuanyuan Zhao Gang Xia Yintung Lam John Haozhong Xin School of Fashion and Textiles The Hong Kong Polytechnic UniversityHong KongChina Shenzhen Research Institute The Hong Kong Polytechnic UniversityShenzhenChina

As global economic growth increases,the demand for energy sources *** fossil fuels have traditionally satisﬁed this demand,their environmental inﬂuence and limited reserves require *** fuel combustion contributes substantially to greenhouse gas emissions,with a pressing need to halve these emissions by 2030 and target net-zero by *** energy sources,contributing currently to 29%of global electricity,are viewed as promising *** wind energy's potential,Zheng's team developed a novel method to harness even low wind speeds using well-aligned nanoﬁbers and an innovative“drop wind generator”.This system,combining moisture-saturated ionic liquid 3-Methyl-1-octylimidazolium chloride with speciﬁc nanoﬁber arrays,exploits wind-inducedﬂows for energy *** study highlights the vast untapped potential of low-speed wind as a sustainable energy source potentially for electronics.

关键词： Wind energy Low-speed wind Ionic liquid Electronic devices

Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys:A study based on in-situ monitoring and image analysis

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Journal of Magnesium and Alloys 2024年第4期12卷 1346-1366页

作者： Weijie Xie Hau-Chung Man Chi-Wai Chan Department of Industrial and Systems Engineering The Hong Kong Polytechnic UniversityHong KongChina School of Mechanical and Aerospace Engineering Queen’s UniversityBelfast BT95AHUK Research Institute for Advanced Manufacturing The Hong Kong Polytechnic UniversityHong KongChina

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)***-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 *** morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore *** laser power led to increased pore coverage,whereas a denser structure was observed at higher laser *** laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the *** increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore *** laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher *** interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

关键词： Selective laser melting(SLM) Magnesium(Mg)alloys Biodegradable implants Porosity In-situ monitoring

Data-driven Static Equivalence with Physics-informed Koopman Operators

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CSEE Journal of Power and Energy Systems 2024年第1期10卷 432-438页

作者： Wei Lin Changhong Zhao Maosheng Gao C.Y.Chung Department of Electrical Engineering The Hong Kong Polytechnic UniversityHong Kong SARChina Department of Information Engineering The Chinese University of Hong KongHong Kong SARChina School of Electrical Engineering Chongqing UniversityChongqing 400044China

With deployment of measurement units,fitting static equivalent models of distribution networks(DNs)by linear regression has been recognized as an effective method in power flow analysis of a transmission *** volatility of measurements caused by variable distributed renewable energy sources makes it more difficult to accurately fit such equivalent *** tackle this challenge,this letter proposes a novel data-driven method to improve equivalency accuracy of DNs with distributed energy *** letter provides a new perspective that an equivalent model can be regarded as a mapping from internal conditions and border voltages to border power *** mapping can be established through 1)Koopman operator theory,and 2)physical features of power flow equations at the root node of a *** of the proposed method is demonstrated on the IEEE 33-bus and IEEE 136-bus test systems connected to a 661-bus utility system.

关键词： Data-driven distribution network Koopman operator theory static equivalent model

Tree‑Inspired Structurally Graded Aerogel with Synergistic Water,Salt,and Thermal Transport for High‑Salinity Solar‑Powered Evaporation

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Nano-Micro Letters 2024年第11期16卷 19-37页

作者： Xiaomeng Zhao Heng Zhang Kit‑Ying Chan Xinyue Huang Yunfei Yang Xi Shen Department of Aeronautical and Aviation Engineering The Hong Kong Polytechnic UniversityHung HomKowloonHong Kong SARPeople’s Republic of China Research Institute for Sports Science and Technology The Hong Kong Polytechnic UniversityHung HomKowloonHong Kong SARPeople’s Republic of China Research Institute for Advanced Manufacturing The Hong Kong Polytechnic UniversityHung HomKowloonHong Kong SARPeople’s Republic of China

Solar-powered interfacial evaporation is an energy-efficient solution for water *** requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient ***,downward salt ion transport is also desired to prevent salt ***,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal ***,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal *** arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat *** structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without *** in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal *** work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.

关键词： Composite aerogel Graded structure Solar-powered evaporation Thermal insulation Salt rejection

Cumulative Exposure to Natural Hazards and Mental Health in China: Are Older People More Vulnerable or More Resilient Than Younger and Middle-Aged Adults?

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International Journal of Disaster Risk Science 2024年第2期15卷 277-289页

作者： Shuai Zhou Crystal Kwan Department of Applied Social Sciences The Hong Kong Polytechnic UniversityHong Kong 999077China

Despite the well-documented impacts of single natural hazards like earthquakes, less is known about the psychological adaptation to multiple natural hazards, particularly in rural areas. This study investigated the associations of multiple natural hazards with depression among Chinese adults. Data were retrieved from the China Family Panel Studies conducted during 2010–2018. With a sample of 11,633 Chinese adults, multilevel logistic regression was employed to examine the relationships between natural hazard exposure and depression in the total sample and different age groups. Overall, experiencing four or more natural hazards was associated with a higher risk of being depressed. Regarding hazard type, the number of hydrometeorological and biological hazards was associated with a higher likelihood of depression, whereas the number of geologic and other hazards was related to a lower risk of depression. Middle-aged adults from villages were more likely to be affected by natural hazard exposure than older and younger adults. The findings of this study show that cumulative exposure to natural hazards can generate lasting effects on depressive symptoms, particularly in middle adulthood. The findings also suggest that older adults from rural areas may have accumulated more resilience to mitigate the adverse well-being effects of hazard events. Policies and interventions should enhance disaster awareness and preparation for aging residents from multi-hazard communities.

关键词： Age differences China Depressive symptoms Multi-hazard communities Natural hazard exposure

The effect of topographic density variations on the geoid and orthometric heights in hong kong

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Geodesy and Geodynamics 2024年第5期15卷 495-503页

作者： Albertini Nsiah Ababio Department of Land Surveying and Geo-Informatics Hong Kong Polytechnic UniversityHong KongChina

Utilizing the adopted average topographic density of 2670 kg/m^(3)in the reduction of gravity anomalies introduces errors attributed to topographic density variations,which consequently affect geoid modeling ***,the mean gravity along the plumbline within the topography in the definition of Helmert orthometric heights is computed approximately by applying the Poincar e-Prey gravity reduction where the topographic density variations are *** Helmert orthometric heights of benchmarks are then affected by *** errors could be random or systematic depending on the specific geological setting of the region where the leveling network is physically established and/or the geoid model is *** example of systematic errors in orthometric heights can be given for large regions characterized by sediment or volcanic deposits,the density of which is substantially lower than the adopted topographic density used in Helmert's definition of *** same applies to geoid modeling *** this study,we investigate these errors in the hong kong territory,where topographic density is about 20%lower than the density of 2670 kg/m^(3).We use the digital rock density model to estimate the effect of topographic density variations on the geoid and orthometric *** results show that this effect on the geoid and Helmert orthometric heights reach maxima of about 2.1 and 0.5 cm,*** results provide clear evidence that rock density models are essential in physical geodesy applications involving gravimetric geoid modeling and orthometric height determination despite some criticism that could be raised regarding the reliability of these density ***,in regions dominated by sedimentary and igneous rocks,the geological information is essential in these applications because topographic densities are substantially lower than the average density of 2670 kg/m^(3),thus introducing large systematic errors in geoid and orthometric

关键词： Rock density Geoid Topography Heights Leveling network