Stages Of Spreading Research Articles

Wetting and pressureless infiltration of Cu-xTi/SiC system at 1373 K

In order to clarify more clearly the action mechanism of Ti at the interface between Cu–Ti alloy and SiC during wetting, the monocrystal, polycrystalline, and porous α-SiC substrates were selected for study by modified sessile drop method under high vacuum at 1373 K. The results show that there is no significant difference in wettability and spreading dynamics between monocrystal and polycrystalline α-SiC substrates. The critical titanium concentration causing wettability transformation is between 5 wt% and 7.5 wt%. The transformation of wettability mainly depends on the precipitation of continuous Ti3SiC2 layer with metalloid properties. Multilayer precipitation layers were observed in the interface structure, corresponding to three spreading stages: rapid spreading stage, which may be caused by TiC precipitation; At the stage of spreading stagnation, the corresponding interface failed to produce enough TiC; Slowly spreading to the equilibrium stage corresponds to the precipitation of Ti3SiC2. Cu-xTi on porous-SiC substrate failed to achieve complete pressureless infiltration during wetting, mainly because the volume of SiC and TiC consumed by the reaction is much smaller than the volume of the precipitated phase Ti3SiC2, which closed the pores and hindered the infiltration process. The results can provide theoretical basis for regulating the wettability, optimizing the interface structure between titanium-containing active alloys and carbide ceramics.

Dynamic behavior of droplet impacting on a moving surface

The research specifically analyzes the characteristics of the impacting droplet and its behavior on the moving surface. The experimental results demonstrate that the droplet impact can be divided into two stages: spreading and stretching. The surface shear force is found to play a decisive role in the droplet's dynamic behaviors. Specifically, the surface shear force inhibits liquid fingers at the front edge of the liquid film during the spreading stage, but promotes the extension of liquid fingers at the trailing edge of the droplet during the stretching stage. The surface shear force has a significant influence on the longitudinal spreading factor of the droplet during the spreading stage. The transverse maximum spreading time decreases with the increase of shear weber number. The wake flow of the droplet is mainly divided into four types: wetting deposition, fracture separation, single finger, and multi-fingers. Additionally, the ratio of the horizontal maximum spreading factor to the longitudinal spreading factor in the same time is found to be positively correlated with the ratio of the two weber numbers. The research findings contribute to the fundamental understanding of droplet dynamics on moving surfaces and highlights the importance of considering surface shear force in understanding droplet dynamics and provides a basis for further research in this field.

Laboratory benchmark of low-cost portable gas and particle analysers at the source of smouldering wildfires

Background Smouldering wildfires emit large amounts of carbon, toxic gases and particulate matter (PM), posing health and environmental hazards. It is challenging to conduct field measurements on wildfire emissions, and available instruments are limited by high cost and low mobility. Aim Here, we contribute to solving this challenge by studying three commercial low-cost and portable air quality analysers (KANE101, SDS011 and FLOW) and comparing them with research-grade instruments (FTIR, PM Cascade Impactor and DustTrak). Methods A series of laboratory experiments on peat smouldering were conducted including the stages of ignition, spread and burnout to provide conditions of emission measurements near the source. Key results The gas analyser KANE101 accurately measured CO2 and allowed calculation of modified combustion efficiency (MCE). The FLOW air pollution sensor was found unsuitable for PM measurements near fire sources because of its narrow range. FLOW captured the variation of volatile organic compounds (VOCs), but measurements did not correlate well with NO2 measurements. The SDS011 PM sensor responded well in measuring PM10 in this study. Conclusions KANE101 and SDS011 can be used in the field after calibration to measure CO2/CO and PM. Implications This work provides a better understanding of how low-cost and portable emission sensors can be of use for wildfire measurements in the field.

Seismic structures of Zhenbei and Huangyan seamounts and their postspreading volcanic evolution

The Zhenbei and Huangyan seamounts located close to the extinct spreading ridge (ESR) in the South China Sea (SCS) have provided fundamental insight into postspreading magmatism. Long debates on the source and evolutional process of the postspreading seamounts are due to the lack of detailed structural crustal constraints. Here, we present three-dimensional (3D) crustal thickness and the Moho geometry of the Zhenbei and Huangyan seamounts and their surrounding area by forwarding and interpolating P-wave forward velocity structures along 14 seismic refraction and wide-angle profiles. We analyzed the variation in crustal velocity and thickness from the waning stage of seafloor spreading to the postspreading magmatism stage. Results show that the original oceanic crust, with an average thickness of 4.5 ± 0.7 km, is characterized by thin lower crust, thick upper crust, and low crustal velocity, compared with Atlantic oceanic crust, reflecting reduced magma supply and intense tectonic fracturing. Both the Zhenbei and Huangyan seamounts show high extrusion to intrusion ratio (2.6 and 2.7) and low P-wave velocities in the upper crust, indicating that extrusive processes are dominant during the postspreading volcanism in the SCS. The total magma volumes for building Zhenbei and Huangyan seamounts are estimated to be 4995 km3 and 3674 km3, respectively, with a related volume flux of ∼0.032 m3/s and ∼ 0.023 m3/s. These values are larger than those of Longnan seamount (2884 km3, 0.018 m3/s) but smaller than those of plume-derived seamounts. The relationship between average lower crustal velocity and crustal thickness also indicates that the postspreading magma may not be caused by the higher degree of mantle melting driven by elevated temperature, but by multiple lower degree of melting caused partly by the enriched mantle.

ApoE4 and Connectivity-Mediated Spreading of Tau Pathology at Lower Amyloid Levels

For the Alzheimer disease (AD) therapies to effectively attenuate clinical progression, it may be critical to intervene before the onset of amyloid-associated tau spreading, which drives neurodegeneration and cognitive decline. Time points at which amyloid-associated tau spreading accelerates may depend on individual risk factors, such as apolipoprotein E ε4 (ApoE4) carriership, which is linked to faster disease progression; however, the association of ApoE4 with amyloid-related tau spreading is unclear. To assess if ApoE4 carriers show accelerated amyloid-related tau spreading and propose amyloid positron emission tomography (PET) thresholds at which tau spreading accelerates in ApoE4 carriers vs noncarriers. This cohort study including combined ApoE genotyping, amyloid PET, and longitudinal tau PET from 2 independent samples: the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 237; collected from April 2015 to August 2022) and Avid-A05 (n = 130; collected from December 2013 to July 2017) with a mean (SD) tau PET follow-up time of 1.9 (0.96) years in ADNI and 1.4 (0.23) years in Avid-A05. ADNI is an observational multicenter Alzheimer disease neuroimaging initiative and Avid-A05 an observational clinical trial. Participants classified as cognitively normal (152 in ADNI and 77 in Avid-A05) or mildly cognitively impaired (107 in ADNI and 53 in Avid-A05) were selected based on ApoE genotyping, amyloid-PET, and longitudinal tau PET data availability. Participants with ApoE ε2/ε4 genotype or classified as having dementia were excluded. Resting-state functional magnetic resonance imaging connectivity templates were based on 42 healthy participants in ADNI. Mediation of amyloid PET on the association between ApoE4 status and subsequent tau PET increase through Braak stage regions and interaction between ApoE4 status and amyloid PET with annual tau PET increase through Braak stage regions and connectivity-based spreading stages (tau epicenter connectivity ranked regions). The mean (SD) age was 73.9 (7.35) years among the 237 ADNI participants and 70.2 (9.7) years among the 130 Avid-A05 participants. A total of 107 individuals in ADNI (45.1%) and 45 in Avid-A05 (34.6%) were ApoE4 carriers. Across both samples, we found that higher amyloid PET-mediated ApoE4-related tau PET increased globally (ADNI b, 0.15; 95% CI, 0.05-0.28; P = .001 and Avid-A05 b, 0.33; 95% CI, 0.14-0.54; P < .001) and in earlier Braak regions. Further, we found a significant association between ApoE4 status by amyloid PET interaction and annual tau PET increases consistently through early Braak- and connectivity-based stages where amyloid-related tau accumulation was accelerated in ApoE4carriers vs noncarriers at lower centiloid thresholds, corrected for age and sex. The findings in this study indicate that amyloid-related tau accumulation was accelerated in ApoE4 carriers at lower amyloid levels, suggesting that ApoE4 may facilitate earlier amyloid-driven tau spreading across connected brain regions. Possible therapeutic implications might be further investigated to determine when best to prevent tau spreading and thus cognitive decline depending on ApoE4 status.

Slab Pull Drives IBM Trench Advance Despite the Weakened Philippine Sea Plate

AbstractThe mechanism behind the significant Izu‐Bonin‐Mariana (IBM) trench advance is still controversial. We conduct slab subduction numerical models that reproduce the spatio‐temporal tectonic evolution of the Philippine Sea region to investigate whether slab pull from the Ryukyu subduction zone can cross the weakened Philippine Sea Plate and act on the IBM trench. Model results show that the lithospheric strengthening and weakening effects cancel out each other during the rift stage so that the slab pull from the Ryukyu Trench can transmit through the weak fossil spreading centers and intra‐arc rifts and drive the Izu‐Bonin Trench's advance. In contrast, lithospheric weakening overwhelms lithospheric strengthening and impedes stress transfer in the back‐arc spreading stage, suggesting that the slab pull cannot directly pull the Mariana Trench to advance at present. Our study indicates that extreme rheological parameters are not needed for the IBM trench advance, despite the Philippine Sea Plate is weakened.

Wetting and spreading of AgCuTi on Fe substrate at high temperatures: A molecular dynamics study

In this study, the wetting and spreading behavior of AgCuTi ternary alloys on Fe substrate was investigate using a molecular dynamics (MD) modeling method. Modeling indicates that precursor films consisted of single-layer atoms are formed and that the wetting and spreading morphologies of the molten droplets on various crystal surfaces are distinct. Diffusive processes play a key role in the formation of the precursor film, and the droplet spreading morphology is correlated critically with the atomic arrangement of the substrate. The droplet spreading process can be divided into two stages of rapid and slow spreading, and there is an obvious interdiffusion phenomenon close to the solid-liquid contact line. The rate at which droplets spread quickens as the temperature rises. Furthermore, the spreading and diffusion capacities of various elements vary, and these properties are closely related to their chemical reactivity.

Directional Rebound of Microdroplets on a Magneto-Responsive Micropillar Array Surface.

The manipulation of droplet movement behavior is of scientific importance and has practical applications in many fields, such as biological analysis, water collection, oil-water separation, deicing, antifrosting, and so on. Using the magneto-responsive surface to dynamically change the surface morphology is an effective method to realize droplet manipulation. A replica molding technique was used to fabricate the surface with the magneto-responsive micropillar array, and the direction of the micropillar array could be changed dynamically with the magnetic induction intensity. The mechanism of the droplet directional rebound on the magneto-responsive surface and the implementation of the controllability of droplet movement were investigated. On the magneto-responsive surface, it was achievable to realize the directional rebound of droplets on the micrometer scale. The critical condition for the droplet directional rebound was identified. The force and energy of the droplet during the spreading and retraction stages were analyzed, which lay a theoretical foundation for the precise control of droplet directional rebound.

Rolling and Sliding Modes of Nanodroplet Spreading: Molecular Simulations and a Continuum Approach.

Molecular simulations discover a new mode of dynamic wetting that manifests itself in the very earliest stages of spreading, after a droplet contacts a solid. The observed mode is a "rolling" type of motion, characterized by a contact angle lower than the classically assumed value of 180°, and precedes the conventional "sliding" mode of spreading. This motivates the development of a novel continuum framework that captures all modes of motion, allows the dominant physical mechanisms to be understood, and permits the study of larger droplets.

Jet or wet? Droplet post-impact regimes on concave contours.

Droplet collision and subsequent spreading or wetting interactions with the solid substrate exhibit rich and interesting physics and are also important for various utilities. The fluid dynamics becomes more interesting and insightful when the wettability and geometry of the surface are tuned and altered. This study investigates the post-impact regimes of droplet impact on hydrophilic and superhydrophobic concave profile grooves (having dimensions comparable to that of the droplet). The post-collision hydrodynamics for such substrate-droplet system is three-dimensional, as in addition to droplet dynamics in the azimuthal direction, liquid jets may also be generated in the axial direction of the groove. Thereby the system may either lead to wetting or jetting, depending on the impact conditions. The effect of the impact Weber number (We) on the jet velocity, non-dimensional spreading width (γ) and non-dimensional south-pole film thickness (h*) has been probed and quantified. The observations reveal that the role of the wettability of the substrate is more profound in the recoiling stage than in the spreading stage, because inertial forces dominate in the latter. It is also noted that the spreading width increases and south-pole height decreases with increasing the impact Weber number. The opposite trend is noted upon increasing the groove concavity by altering just one dimension of the groove. The jet velocity is found to be the highest immediately after the impact and eventually decreases in a nonlinear fashion. Further, it has been found that the jet velocity increases with increasing the impact Weber number and that this effect is more prominent for superhydrophobic surfaces. A semi-analytical framework has been proposed to predict the jet velocity evolution in terms of governing Weber (We) and capillary (Ca) numbers. The predictions of the proposed model are in good agreement with the experimental observations.

Dynamics of droplet generation in a wedge-shaped step-emulsification microchannel

The droplet generation in a wedge-shaped step-emulsification microchannel is investigated experimentally and the generation dynamics of dripping flow as a main applicable flow regime is primarily studied. The sodium alginate aqueous solution and liquid paraffin are used as dispersed phase and continuous phase respectively. The droplet generation process is divided into four stages: two-dimensional retracting stage, two-dimensional spreading stage, three-dimensional necking stage, and three-dimensional pinch-off stage. The head of the dispersed phase retracts and spreads faster under higher dispersed phase flow rate or viscosity. The critical neck width between the necking and the pinch-off stages is independent of the dispersed phase flow rate and viscosity. With the increase of dispersed phase flow rate, the droplet size increases while its formation period decreases. The droplet size and formation period increase with the increase in the dispersed phase viscosity. The flow regime of droplet generation relies primarily on the flow rate ratio and viscosities. A correlation is proposed for predicting the droplet size.

The impact of multiple population-wide testing and social distancing on the transmission of an infectious disease

Under the background that asymptomatic virus carriers are contagious and the virus in the infected individuals has mild pathogenicity and enhanced transmissivity for an infectious disease, the phenomenon appears that the majority of infected people do not show any symptoms, but can infect others. Multiple population-wide testing can screen out asymptomatic virus carriers in time. Thus, we develop an infectious disease transmission dynamics model that includes three stages: non-testing period, testing period and testing interval, with multiple population-wide testing and social distancing to study the effects of the first testing time, total testing number, and testing interval time on the transmission of infectious diseases in this paper. The existence, uniqueness, boundedness and positivity of the solution, as well as the formulas of the basic reproduction number and the control reproduction number of the established model are established The numerical results show that the earlier the population-wide testing measure is implemented, the fewer the final size and necessary testing frequency. In the initial stage of the larger-scale spread of infectious disease, the existing virus carriers are not the most. But if population-wide testing measure is implemented during this period, the strongest testing force is required to contain the spread of the epidemic. Besides, population-wide testing combined with restrictive social distancing will significantly reduce the final size, necessary testing frequency, and duration of the epidemic. The testing interval time should be no longer than the incubation period of the virus to prevent and control the epidemic accurately. Therefore, the paper provides a theoretic basis for developing and implementing scientific testing strategies.

Development of e-commerce in the context of digitalisation of social life

The subject of the study is the organisational, economic and marketing aspects of the development of the electronic (digital) economy and e-commerce as the most promising segment of modern markets in the context of restrictions on direct contacts and movement of people due to measures to combat the COVID-19 pandemic and personal safety. The purpose of the article is to study the organisational, economic and marketing aspects of the development of the electronic (digital) economy and e-commerce as the most promising segment of modern markets in the context of restrictions on direct contacts and movement of people due to measures to combat the COVID-19 pandemic and personal security. The methodological basis of the article is based on the following methods: system-structural analysis and synthesis (in determining the set of factors of influence and its level on the electronic economy and commerce; determining the composition and structure of the digital economy and e-commerce); historical and monographic (in identifying the stages of development and territorial spread of e-commerce); statistical and economic (for establishing and analysing quantitative indicators of the status, trends and prospects of e-commerce development). Results of the article. As a result of the research, it was found that the following are of the greatest importance in the modern digital economy: digitalisation of business processes and organisational structure of enterprises with a view to their optimisation; digitalisation of document flow; and e-commerce. The latter is an independent and most progressive segment of the consumer market. The author identifies the main factors influencing the development of the electronic economy and, in particular, e-commerce; its main components and features of work in the online network; identifies the benefits and problems for organisations, employees and consumers. The scale, trends and prospects for the development of e-commerce are determined on the basis of analysis and synthesis, evaluation and diagnostics of quantitative indicators. Field of application of results. The results of the article can be used by representatives of small businesses that carry out e-commerce or plan to develop it; scientists, teachers and students of higher education institutions. Conclusions. Prospects for the development of e-commerce are associated with the promotion of the following areas and the use of the following tools: improving the institutional support for e-commerce and security (especially personal data) of its participants; involvement of marketing strategies based on their specificity in the online environment; establishing comprehensive aspects of behavioural economics and behavioural finance to monitor and predict and increase demand and form product offers; promotion of mobile commerce through the global.

Assessment of the early detection of anosmia-ageusia symptoms in COVID-19 on Twitter: A retrospective study.

During the unprecedented COVID-19 pandemic, social media has been extensively used to amplify the spread of information and to express personal health-related experiences regarding symptoms, including anosmia and ageusia, two symptoms that have been reported later than other symptoms. Our objective is to investigate to what extent Twitter users reported anosmia and ageusia symptoms in their tweets and if they connected them to COVID-19, to evaluate whether these symptoms could have been identified as COVID-19 symptoms earlier using Twitter rather than the official notice. We collected French tweets posted between January 1, 2020 and March 31, 2020 containing anosmia or ageusia related keywords. Symptoms were detected using fuzzy matching. The analysis consisted of three parts. First, we compared the coverage of anosmia-ageusia symptoms in Twitter and in traditional media to determine if the association between COVID-19 and anosmia-ageusia could have been identified earlier through Twitter. Second, we conducted a manual analysis of anosmia-ageusia related tweets to obtain quantitative and qualitative insights regarding their nature and to assess when the first associations between COVID-19 and these symptoms were established. We randomly annotated tweets from two periods: the early stage and the rapid spread stage of the epidemic. Each symptom/tweet was annotated regarding three modalities: symptom (yes/no), associated with COVID-19 (yes/no/unknown), and whether it was experienced by someone (yes/no/unknown). Third, to evaluate if there was a global increase of tweets mentioning anosmia-ageusia in early 2020, corresponding to the beginning of the COVID-19 epidemic, we compared the tweets reporting experienced anosmia or ageusia between the first periods of 2019 and 2020. 832 (resp. 12,544) tweets containing anosmia (resp. ageusia) related keywords were extracted over the analysis period in 2020. The comparison to traditional media showed a strong correlation without any lag, which suggests an important reactivity of Twitter but no earlier detection on Twitter. The annotation of tweets from 2020 showed that tweets correlating anosmia-ageusia with COVID-19 could be found a few days before the official announcement. However, no association could be found during the first stage of the pandemic. Information about the temporality of symptoms and the psychological impact of these symptoms could be found in the tweets. The comparison between early 2020 and early 2019 showed no difference regarding the volumes of tweets. Based on our analysis of French tweets, associations between COVID-19 and anosmia-ageusia by web users could have been found on Twitter just a few days before the official announcement but not during the early stage of the pandemic. Patients share qualitative information on Twitter regarding anosmia-ageusia symptoms that could be of interest for future analyses.

Early wetting and interfacial behavior of Sn-based solder on copper substrates with different roughness

Purpose This paper aims to investigate the effect of solder composition and roughness on early wetting behavior and interfacial reaction under atmospheric conditions. Design/methodology/approach High-speed photography is used to observe the early wetting and spreading process of the solder on the substrate in real time. The morphology of intermetallic compounds (IMCs) was observed by scanning electron microscopy, and the composition of IMCs micro bumps was determined by energy dispersive spectroscopy. Findings With a roughness range of 0.320–0.539 µm, the solder is distributed in an elliptical trilinear pattern along the grinding direction. With a roughness range of 0.029–0.031 µm, the solder spreads in the direction of grinding and perpendicular, forming a perfect circle (except in the case of Sn63Pb37 solder). The effect of three types of solder on early wettability is Sn63Pb37 &gt; Sn96.5Ag3Cu0.5 &gt; Sn. The wetting behavior is consistent with the Rn∼t model. The rapid spreading stage (Stage I) is controlled by the interfacial reaction with n1 values between 2.4 and 4. The slow spreading stage (stage II) is controlled by diffusion with n2 values between 4 and 6.7. The size of Cu6Sn5 formed on a rough substrate is greater than that produced on a smooth substrate. Originality/value Investigating the effect of solder composition and roughness on early wettability. This will provide a powerful guide in the field of soft brazing.

Experimental study on flame length and pulsation behavior of n-heptane continuous spill fires on water

Continuous spill fires pose significant risks to the storage and transportation industries of liquid fuels. To investigate the flame length and pulsation behavior of continuous spill fires, large-scale spill fire experiments were conducted on water to simulate the burning fuel on a water surface that could occur during firefighting of tank fires or due to leaked fuels on water during transportation, with varying discharge rates (3, 6, 9, 14 mL/s) and ignition delays (0, 10, 20, 30 s). The results suggest that the flame length increased initially with the spread area and reached the maximum at the end of the spreading stage, then followed by a decrease at the shrinking stage and kept nearly constant at the steady stage. For the steady flame length, a new correlation (Ls/D=3.1(Q˙*)0.42) was established based on dimensionless analysis, which was higher than that for pool fires, highlighting the important differences between spill and pool fires. This developed model was also used to predict the maximum flame length with a maximum deviation of 19.2%, as the heat transfer mechanism and air entrainment are expected to be similar at the shrinking and steady stages. The flame pulsation frequency was determined through the fast Fourier transform (FFT) method, which shows a gradual decrease during the spreading stage while remaining higher than that of pool fires at the steady stage. Subsequently, two new correlations (fi=0.525g/D and fs=0.724g/D) were derived from experimental data to predict the pulsation frequency at both spreading and steady stages. The higher frequencies during the steady stage can have a significant influence on the radiation impact to adjacent equipment or personnel. This study not only provides insights into the flame and pulsation behaviors of spill fires but lays a solid foundation for the thermal hazard and risk assessment analysis in the liquid fuel storage and transportation industries.

Liquid-Liquid Phase Separation Induced by Vapor Transfer in Evaporative Binary Sessile Droplets.

Drying of binary sessile droplets consisting of ethanol and octamethyltrisiloxane on a high-energy surface is investigated. During the process of evaporation, the droplets undergo liquid-liquid phase separation, resulting in the appearance of microdroplets at the liquid-air interface, which subsequently violently burst. This phase separation is attributed to water vapor transfer into the droplet, which modifies the solubility and leads to the formation of a ternary mixture. The newly formed ternary mixture may undergo nucleation and growth or spinodal decomposition, depending on the droplet composition path. By control of the relative humidity of air, phase separation can be mitigated or even eliminated. The droplets also display high mobility and complex wetting behavior due to phase separation, with two contracting and two spreading stages. The mass loss experiments reveal that the droplets undergo three distinct drying stages with an enhanced evaporation rate observed during the phase separation stage. A modified diffusion-limited model was employed to predict the evaporation rate, accounting for the physiochemical changes during evaporation and proved to be consistent with experimental observations. The findings of this work enhance our understanding of a coupled fundamental process involving the evaporation of multicomponent mixtures, wetting, and phase separation.

A novel method for ball forming by cross wedge rolling

In this paper, a novel method for ball forming by cross wedge rolling (CWR) was proposed, and the finite element (FE) simulation and experimental verification were carried out with the 26 mm diameter steel ball as an example. First of all, the die parameters including spreading angle β and forming angle α were selected and the 3D models of the die and guide plate were designed. Then, the FE model was established and preliminary simulation was carried out using the Simufact 16.0 software. The preliminary simulation results showed that the pushing empty defect occurred in the process due to lack of transition from spreading stage to sizing stage and conical die section. Modifying the die design by adopting the method of adding transition spreading angle θ and forming angle α´ increasing with the increase of rolling depth to, the defect could be eliminated and the full filling can be obtained. In addition, the simulation analysis after modified also included effective strain and stress distribution, the kinematic analysis of metal flow, the damage distribution based on the Cockcroft-Latham criterion, the temperature evolution and force parameters in the CWR process. Finally, the rolling experiments and radial rolling force testing experiments were carried out to verify the numerical results. The results indicated that the FE simulation results were consistent with the experimental results through quantitative analysis, which proved that the novel method for ball forming by CWR was feasible simultaneously.

Spatial scale plasticity of urban residential areas: Lessons from Shanghai’s model in response to COVID-19

Shanghai&amp;rsquo;s measures to address the COVID-19 pandemic since March 2022 have attracted world-wide attention. The response to public emergency and pandemic in built environment has prompted a profound reflection in residential planning. This case study investigated an under-developed site located in Shanghai&amp;rsquo;s Huangpu River waterfront. Based on a site survey, interviews, the phased lockdown policies of different urban areas, and published data on the spatial distribution of infection cases, this paper analyzes the effectiveness of strategies for coping with different stages of epidemic spread at different spatial scales. In addition to ensuring the privacy of living quarters, our residential planning ensures the flow and social communication of people in different neighborhoods, achieving the resilience of local lockdown and flow. This study redefines the openness and reasonable scale of residential areas based on analysis of the advantages and disadvantages of gated and block residential areas facing pandemic. This paper analyzes the feasibility of a residential site plan based on the above conception, which has spatial scale composable features for the basic residential building groups. This study emphasizes that design should be considered to achieve the flexibility of spatial scale through the different assembling pattern of basic-living-space-unit.

Origins of magmatism in the Okinawa Trough: Fe–Sr–Nd–Pb–Hf isotopic constraints

ABSTRACT The Okinawa Trough is an incipient back-arc basin formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate and is a natural laboratory for studying basin evolution, magmatism, and crust-mantle interactions during the early stages of back-arc spreading. Back-arc spreading and recent magmatism are occurring mainly in the Middle Okinawa Trough (MOT) and Southern Okinawa Trough (SOT). In order to investigate the magmatism in the Okinawa Trough, volcanic rock samples from the MOT and SOT were analysed for Fe – Sr – Nd – Pb – Hf isotopic compositions. The Fe isotopic compositions of basaltic andesite samples from the SOT are similar to or lower than MORBs. The fluid/melt derived from the subducted slab, especially the fluid dehydrated from slab serpentinites and sediment-derived melts, entered the overlying depleted mantle wedge and participated in magma generation, which resulted in the low δ56Fe values of the SOT basaltic magmas. The δ56Fe values of volcanic rocks from the MOT increase with increasing SiO2 contents, suggesting a gradual enrichment of heavy Fe isotopes during the evolution of the magma as it ascended to the surface. While the Sr – Nd – Pb – Hf isotopic compositions do not vary significantly, suggesting that the different samples are the products of different degrees of crystal fractionation of comagma. The fractional crystallization of olivine, pyroxene, and ilmenite minerals, which enrich in light Fe isotopes, resulted in the gradual increase in Fe isotopic values of magma during its evolution. The dacites and rhyolites from the southernmost Okinawa Trough have the similar δ56Fe values with the basaltic andesite and the basalt from the SOT and MOT, accompanied by significantly lower Nd and Hf isotope ratios relative to basalts, reflecting that the contamination of crustal materials would not change the magma in Fe isotope compositions evidently. Compared with the MOT, the volcanic rocks from the SOT was more affected by subduction components on their underlying mantle, and those from the southernmost experienced more contamination by crustal materials in the evolving magma.