Steady Migration Research Articles

Analysis and prediction for dynamic migration behavior of NEPE propellant/liner interface layer full components

The migration behavior of nitrate ester-plasticized polyether (NEPE) propellant components significantly impacts safety. Experimentally observing the migration process is challenging and time-consuming. This study employed molecular dynamics (MD) methods to simulate a molecular model of the NEPE propellant/liner interface layer, enabling the prediction of component migration behavior. We visualized the migration process of all propellant components and studied the interface layer components' migration patterns, diffusion coefficients, and concentration gradient distributions. The contents of migrated components of the propellant and liner at different accelerated aging times at 70 °C were determined using high-performance liquid chromatography (HPLC), and the simulation patterns were compared with experimental observations. The results indicate that the migrated components in the propellant mainly consist of nitrate esters (Nitroglycerin, abbreviated as NG, and Butanetriol Trinitrate, abbreviated as BTTN), stabilizers (NMethylnitroaniline, abbreviated as MNA, and 2-Nitrodiphenylamine, abbreviated as 2-NDPA), and solid component (Hexahydro-1,3,5-trinitro-1,3,5-triazine, abbreviated as RDX). The migration process is primarily dominated by the substantial migration of nitrate esters, which is a key factor contributing to the degradation of propellant performance during storage. The migration process can be divided into three stages: swift migration, steady slow migration, and migration equilibrium. The diffusion coefficients are ranked from most significant to most minor as NG > BTTN > RDX > MNA > 2-NDPA. Three migration stages consistent with the simulation process were observed using HPLC, and the migration behavior of nitrate esters aligned with simulation patterns. Our designed full-component model can qualitatively predict component migration behavior. Additionally, a faster diffusion coefficient does not necessarily lead to a greater amount of migration. We employed MD simulations combined with density functional theory (DFT) calculations to explain this phenomenon and found that intermolecular interactions may influence the diffusion coefficient. At the same time, the migration amount is highly correlated with molecular polarity. Therefore, increasing the molecular polarity difference between easily migrating components and liner materials is a beneficial strategy for slowing the migration process and enhancing the storage safety of propellants.

Species distribution models to predict the potential niche shift and priority conservation areas for mangroves (Rhizophora apiculata, R. mucronata) in response to climate and sea level fluctuations along coastal India

Mangroves are more than just a tree as they are home to thousands of species, carbon absorbers and a natural coastal fortress against floods and storm surges. Hence, conservation planning and decision making for this valuable ecosystem must involve identification of priority conservation areas (PCAs) at species-specific dimensions. In the present study, we adopted an ensemble modelling approach for the distribution of two mangrove species (Rhizophora apiculata, Rhizophora mucronata) using high-resolution environmental and edaphic datasets, to identify the PCAs for future conservation. We also identified the key environmental variables shaping their distribution and precisely estimated the core distributional shift along the Indian coastline under changing climate scenario. The findings revealed that about 5844 km2 and 7846 km2 areas were identified as extremely suitable areas, which were distributed along Maharashtra coast and Kerala coast for R. mucronata and R. apiculata, respectively, in the current climate scenario. The distribution of R. apiculata was found to be mostly shaped by mean diurnal range and annual mean temperature, whereas the distribution of R. mucronata was primarily shaped by annual mean temperature and altitude. The highest range expansion of mangrove species occurred during middle Holocene due to high precipitation and sea-level rise and this finding is further supported by fossil pollen evidence. The suitable habitat range for R. apiculata is predicted to increase along Kerala coast under RCP2.6 scenario by 6.90% and 6.93% and under RCP8.5 scenario by 9.33% and 9.90% in the year 2050 and 2070, respectively, whereas the range for R. mucronata is getting reduced in the future climate scenario. Overall, our predictions reveal a steady migration of conducive mangrove habitat towards land or higher elevations due to relative sea level rise in future. These results would aid in planning a long-term species-specific conservation and management strategy for mangrove ecosystem along coastal India.

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiation

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiations with uniform and non-uniform fluxes is first analyzed. The creeping flow solutions show that the deformed droplet has a slender or a cardioid shape, which depends on the form of the radiation flux. The deviation from a sphere depends not only on the viscosity and the conductivity ratios of two-phase fluids but also on capillary and thermal radiation numbers. Moreover, in the roles of interfacial rheology on thermocapillary migration of a deformed droplet, only the surface dilatational viscosity and the surface internal energy can reduce the steady migration velocity, but the surface shear viscosity has not any effects on the steady migration velocity. The surface shear and dilatational viscosities affect the deformation of the droplet by increasing the viscosity ratio of two-phase fluids. The surface internal energy directly reduces the deformation of the droplet. However, the deformed droplet still keeps its original shape without the influence of interfacial rheology. Furthermore, it is found that, based on the net force balance condition of the droplet, the normal stress balance at the interface can be used to determine the steady migration velocity, which is not affected by the surface deformation in the creeping flow. From the expressions of the normal/the tangential stress balance, it can be proved that the surface shear viscosity does not affect the steady migration velocity. The results could not only provide a valuable understanding of thermocapillary migration of a deformed droplet with/without the interfacial rheology in a vertical temperature gradient controlled by thermal radiation but also inspire its potential practical applications in microgravity and microfluidic fields.

Approximate analytical solutions for multispecies convection-dispersion transport equation with variable parameters

Multispecies pollutant migration often occurs in polluted groundwater systems. Most of the multispecies problems that have been dealt in the literature assume constant transport parameters, primarily because analytical solutions for varying parameters become a challenge. The present study analytically solves a two-species convection-dispersion transport equation, considering spatially varying dispersion coefficient and seepage velocity, which corresponds to the steady migration in a steady flow domain. Indeed, the methodology can be adopted for other cases, such as the transient migration in a steady flow domain and transient migration in an unsteady flow domain, without any difficulty. Three kinds of homotopy-based methods, namely the homotopy perturbation method (HPM), homotopy analysis method (HAM), and optimal homotopy asymptotic method (OHAM), are used to derive approximate analytical solutions in the form of truncated series. In homotopy analysis method, the convergence-control parameter ℏ plays a key role in the convergence of the series solution. It is observed that for a specific case of this parameter, namely ℏ=−1, the HAM-based solution recovers the HPM-based solution. For the verification of homotopy-based solutions, we utilize the MATLAB routine pdepe, which efficiently solves a class of parabolic PDEs (single/system). An excellent agreement is found between the derived analytical solutions and the numerical solutions for all three methods. Further, a quantitative assessment is carried out for the derived solutions. Also, convergence theorems are proposed for the series solutions obtained using HAM and OHAM.

Inaugural Editorial: Welcome to ASCE OPEN

Much time has passed since Newton wrote to Robert Hooke in a 1675 letter, “If I have seen further, it is by standing on the shoulders of giants”—a metaphor that predates even Newton by more than four centuries. His distinct acknowledgment of others who paved the way for his own revolutionary work is remarkable in both its simplicity and humility. It was clear that others also deserved recognition, but in that statement, he implicitly acknowledged the power of scientific correspondence as well because, without it, he might not have even known there were giants around from whom he could learn. It is thus how science and engineering, including our own—and arguably the most senior of them all—civil engineering, make progress. We, often without personal acquaintance and almost always asynchronously, communicate and learn from each other, with sometimes decades or even centuries separating us. The conduits of these interactions are manifold, but the main one today is our peer-reviewed journals. The moniker implies printed matter, yet that format has all but evolved out of existence. Needless to say, just like our science, our journals do evolve. The latest development we are experiencing in the world of science and engineering communications is a steady migration toward open publishing. Simply put, open publishing is the practice of making information and creative works available to the general public without restrictions or cost. This mode of publishing offers many virtues that benefit both the creators and the consumers of knowledge and information. Open publishing spurs creativity and knowledge development by removing access barriers and bringing more people from diverse backgrounds into collaboration and cocreation. Otherwise, you might be less inclined to access an article from a neighboring discipline, or from the same discipline but a different country, if it required additional subscriptions. Open publishing can also benefit creators by giving them broader exposure and recognition (citations). By the same token, constructive criticism from a wider audience can help authors improve their work. Finally, open publishing reduces the barriers that prevent marginalized groups from accessing knowledge, which is a prerequisite for participating in knowledge production. In all, open publishing should accelerate the pace of inventions and discoveries in our community, and supporting and promoting it will enable a more informed, creative, and just society.

Job satisfaction of selected Filipino teachers working in Philippine public schools and in U.S. public schools: A comparative study

There is a steady migration of Filipino teachers to the US, while teachers that remain in the Philippines face a number of challenges. This study sought to ascertain whether a difference exists between the job satisfaction levels of Filipino teachers based in the Philippines and those based in the US. Through snowball and quota sampling, 30 Filipino teachers working in Philippine public schools and 30 Filipino teachers working in US public schools were invited to participate in this research. The Teacher Job Satisfaction Scale 9-item questionnaire (TJSS-9) was used as the instrument for this study. The results revealed that for the domain of satisfaction with co-workers, Filipino teachers based in the US had higher levels of job satisfaction. But for the domains of student discipline and parental involvement, the Filipino teachers based in the Philippines had higher levels of job satisfaction. However, t-test results indicate that these differences were not statistically significant.

Particle dispersion and deposition in wall-bounded turbulent flow

Particle dispersion and deposition in a fully developed turbulent channel flow at a friction Reynolds number of Reτ=180 for a wide range of Stokes numbers (St = 1-130) are investigated using the direct numerical simulation (DNS). The combined effect of gravity and the Saffman lift force on the particle deposition velocities in upward and downward flows are considered. The results are compared with recent experimental measurements and numerical benchmark solutions. For particle–wall collisions, two scenarios of fully elastic and no-rebound (trap-wall) collisions are considered. Due to the turbophoresis effect and the steady migration of particles toward the walls, a stationary state cannot be reached for particle concentration with the fully elastic assumption. To alleviate this problem, for every particle that impacts the wall a new particle is added to the computational domain with the trap-wall assumption. The stationary particle field is further time-averaged to present the average particle velocities, particle concentrations, and particle velocity fluctuations profiles. It is shown that at lower Stokes numbers, the deposition velocity of downward channel flow is higher than the upward flow, whereas at higher Stokes numbers the upward flow has a higher deposition rate but a lower near-wall particle concentration. This higher deposition rate is attributed to the combined effect of gravity and the positive Saffman lift force that brings the inactive particles trapped in the viscous sublayer to the buffer layer, resulting in an increase of their wall-normal turbulent fluctuations and their wall-collision rates.

One-Step Synthesis of Ultrathin Zeolitic Imidazole Framework-8 (ZIF-8) Membrane on Unmodified Porous Support via Electrophoretic Deposition.

Metal-organic frameworks (MOFs) are regarded as the next-generation, disruptive membrane materials, yet the straightforward fabrication of ultrathin MOF membranes on an unmodified porous support remains a critical challenge. In this work, we proposed a facile, one-step electrophoretic deposition (EPD) method for the growth of ultrathin zeolitic imidazole framework-8 (ZIF-8) membranes on a bare porous support. The crystallinity, morphology and coverage of ZIF-8 particles on support surface can be optimized via regulating EPD parameters, yet it is still difficult to ensure the integrity of a ZIF-8 membrane with the constant voltage mode. In contrast, the constant current mode is more beneficial to the growth of a defect-free ZIF-8 membrane due to the steady migration rate of colloid particles toward the electrode. With a current of 0.65 mA/cm2 and deposition time of 60 min, a 300 nm thick ZIF-8 membrane was obtained, which exhibits a CO2 permeance of 334 GPU and a CO2/CH4 separation factor of 8.8, evidencing the defect-free structure.

Factors of migration growth in modern Russia’s regions

This article provides the analysis of migration situation in Russian regions. It also deals with such issue as uneven flows of migration among the regions. Such quantative methods were used to evaluate the factors of migration processes, as correlation, regression, cluster, factor analysis, analysis of variance and GIS analysis. Basing on the results of statistical analysis it was found that the strongest factors that make an impact on migration situation in regions are region’s public image and social-economical profile. Furthermore, six groups of regions were developed based on their migration attraction. The least favorable in terms of this study are “outsider” regions, in which the migration loss is high due to low value of certain variables (this includes Far Eastern District, Siberian District and North Caucasus District). At the same time, there is a rather small group of favorable districts with steady migration flow. Such Districts’ subjects as North-West and South Federal were found to be the center of attraction. Despite the above, most regions of Central Russia are neutral in terms of migration dynamics. It was concluded that social-economic factors such as standards of life and public image of a region (recreational appeal, climate etc.) make a valuable impact on migration attraction of Russian Federation subjects.

Diurnal Variability in Aeolian Sediment Transport at Gale Crater, Mars

AbstractA suite of high resolution cameras onboard the Mars Science Laboratory (MSL) Curiosity rover have provided an unparalleled look at active aeolian processes on Mars, including within the first active dune field explored on another planet, the Bagnold Dunes. Here we present results from a subset of MSL's repeat imaging (“change detection”) experiments with temporal resolutions sufficient to probe the diurnal variability in winds within Gale crater. Images reveal that saltation is a near‐daily phenomenon during southern summer, with repeatable diurnal circulation patterns producing steady impact ripple migration toward the west/southwest. Nighttime fluxes are inferred to be ∼four times larger than daytime fluxes, consistent with predictions from the MarsWRF model of multiple periods of enhanced wind between sunset and sunrise. Multiple factors are likely facilitating saltation at this time: (a) time‐averaged nighttime winds have a higher degree of variance (i.e., higher peak friction speeds) than daytime winds, (b) interactions between regional Hadley flows and local, thermally driven slope winds cause increased turbulence at night, and (c) relatively higher atmospheric density produces correspondingly higher shear stresses and decreases critical thresholds. Observations of sand transport at a range of spatiotemporal scales (down to scale of individual particles moving on the timescale of seconds) support the idea that bedform migration is driven by intermittent, low‐flux saltation events when winds fluctuate between canonical impact and fluid thresholds. Yet, whereas gustiness may play a role in initiating transport, saltation is found to be highly predictable on diurnal timescales and is only stochastic on the shortest timescales characteristic of turbulent fluctuations in wind.

Thermocapillary droplet migration in a vertical temperature gradient controlled by thermal radiations

Thermocapillary migration of a droplet in a vertical temperature gradient controlled by uniform and non-uniform thermal radiations is theoretically analyzed and numerically investigated. A non-dimensionlized thermal radiation number is proposed to quantitatively depict the intensity ratio of the thermal radiation flux to the uniform temperature gradient. From the momentum and energy equations at zero limits of Reynolds and Marangoni numbers, analytical results for the uniform and non-uniform thermal radiations are determined. The steady migration velocity raises with the increasing of the thermal radiation number. By using the front-tracking method, it is observed that thermocapillary droplet migration under the uniform thermal radiation at moderate Marangoni and moderate thermal radiation numbers reaches a steady process. The steady migration velocity decreases with the increasing of Marangoni number and increases with the increasing of thermal radiation number. Moreover, the intensity of thermal energy transferred from the interface to both fluids depends on the volume heat capacity ratio. For the larger/smaller volume heat capacity ratio, more heat is transferred into the continuous phase fluid/the droplet. Furthermore, when the uniform thermal radiation is replaced by the non-uniform ones, the time evolutions, the structures of temperature fields, and parameter dependencies of thermocapillary droplet migration at moderate Marangoni and moderate thermal radiation numbers remain qualitatively unchanged. This study provides a profound understanding of thermocapillary droplet migration in a vertical temperature gradient controlled by thermal radiations, which is of great significance for practical applications in microgravity and microfluidic fields.

Chitosan nanoparticles encapsulating lemongrass (Cymbopogon commutatus) essential oil: Physicochemical, structural, antimicrobial and in-vitro release properties

This study was aimed to encapsulate lemongrass (Cymbopogon commutatus) essential oil (LGEO) into chitosan nanoparticles (CSNPs) and to investigate their physicochemical, morphological, structural, thermal, antimicrobial and in-vitro release properties. CSNPs exhibited spherical morphology with an average hydrodynamic size of 175–235 nm. Increasing EO loading increased the average size of CSNPs from 174 to 293 nm (at CS:EO ratio from 1:0 to 1:1.25). SEM and AFM confirmed the results obtained by hydrodynamic size indicating that EO loading led to formation of large aggregated NPs. The successful physical entrapment of EO within NPs was shown by fourier-transform infrared spectroscopy. X-ray diffractogram of loaded-CSNPs compared to non-loaded CSNPs exhibited a broad high intensity peak at 2θ = 19–25° implying the entrapment of LGEO within CSNPs. Thermogravimetric analysis (TGA) showed that encapsulated EO was decomposed at a temperature of 252 °C compared to a degradation temperature of 126 °C for pure LGEO, indicating a two-fold enhancement in thermal stability of encapsulated CSNPs. Differential scanning calorimetry also proved the physical entrapment of EO into polymeric matrix of chitosan. In-vitro release study showed a time- and pH-dependent release of EO into release media demonstrating a three-stage release behavior with a rapid initial release of EO, followed by a steady state migration of EO from its surrounding envelope at the later stages. Antimicrobial assay showed strong antimicrobial properties of free form of LGEO against the bacteria (both gram positive and gram negative) and fungi species tested. Moreover, loaded-CSNPs exhibited stronger antibacterial and anti-fungal activities than non-loaded CSNPs.

Moment tensor inversion of microearthquakes along the Santorini-Amorgos zone: Tensile faulting and emerging volcanism in an extensional setting

The Santorini-Amorgos zone is an area rich in microseismicity at the center of the Hellenic volcanic arc. The microseismicity of the zone is distributed along the Santorini-Amorgos ridge and Kolumbo submarine volcano. In this study, we utilized crustal events that were recorded by temporary networks during September 2002 to July 2004 and October 2005 to March 2007, and also by the permanent network from 2011 to 2020. These events were inverted for their moment tensors by using P-wave polarities as well as SV/P and SH/P amplitude ratios, yielding 74 well-constrained moment tensor solutions. Most of these moment tensors have significant CLVD and isotropic components that are positively correlated to each other (R2 = 0.68). Tensile faulting due to high pore pressure is considered as the most likely cause of the observed non-DC components. The positive and negative non-DC components observed in Kolumbo may be generated by the opening and closing of cracks beneath the shallow (6–7 km) magma chamber due to a steady migration of magmatic fluids from the deep reservoir into the chamber. In Anydros, most of the microearthquakes have positive non-DC components associated with the opening of cracks. It is possible that the extensional deformation and high pore fluid pressure in the area opens subvertical cracks that become pathways for upward migrating fluids. The upward migration of magmatic fluids in an extensional regime such as the Santorini-Amorgos zone can also be viewed as an indication of emerging volcanic activity in this area.

Maternal Neutrophil Depletion Fails to Avert Systemic Lipopolysaccharide-Induced Early Pregnancy Defects in Mice.

Maternal infection-induced early pregnancy complications arise from perturbation of the immune environment at the uterine early blastocyst implantation site (EBIS), yet the underlying mechanisms remain unclear. Here, we demonstrated in a mouse model that the progression of normal pregnancy from days 4 to 6 induced steady migration of leukocytes away from the uterine decidual stromal zone (DSZ) that surrounds the implanted blastocyst. Uterine macrophages were found to be CD206+ M2-polarized. While monocytes were nearly absent in the DSZ, DSZ cells were found to express monocyte marker protein Ly6C. Systemic endotoxic lipopolysaccharide (LPS) exposure on day 5 of pregnancy led to: (1) rapid (at 2 h) induction of neutrophil chemoattractants that promoted huge neutrophil infiltrations at the EBISs by 24 h; (2) rapid (at 2 h) elevation of mRNA levels of MyD88, but not Trif, modulated cytokines at the EBISs; and (3) dose-dependent EBIS defects by day 7 of pregnancy. Yet, elimination of maternal neutrophils using anti-Ly6G antibody prior to LPS exposure failed to avert LPS-induced EBIS defects allowing us to suggest that activation of Tlr4-MyD88 dependent inflammatory pathway is involved in LPS-induced defects at EBISs. Thus, blocking the activation of the Tlr4-MyD88 signaling pathway may be an interesting approach to prevent infection-induced pathology at EBISs.

Tectonic and eustatic control of Mesaverde Group (Campanian–Maastrichtian) architecture, Wyoming-Utah-Colorado region, USA

AbstractWe describe and analyze the depositional history and stratigraphic architecture of the Campanian and Maastrichtian succession of the southern greater Green River basin of Wyoming, USA, and surrounding areas to better understand the interplay between tectonic and eustatic drivers that built the stratigraphy. By integrating new measured sections with published outcrop, well-log, and paleogeographic data, two new stratigraphic correlation diagrams, 35 new paleogeographic reconstructions, and six new tectonic diagrams were created for this part of the Western Interior Seaway. From this work, two time-scales of organization are evident: (1) 100–300 k.y.-scale, mainly eustatically driven regressive-transgressive shoreline oscillations that generated repeated sequences of alluvial-coastal plain-shoreline deposits, passing basinward to subaqueous deltas, then capped by transgressive estuarine/barrier lagoon deposits, and (2) 3.0–4.0 m.y.-scale, tectonically driven groups of 10 to 15 of these eustatically driven units stacked in an offset arrangement to form larger clastic units, which are herein referred to as clastic wedges. Four regional clastic wedges are recognized, based on the architectures of these clastic packages. These are the: (1) Adaville, (2) Rock Springs, (3) Iles, and (4) Williams Fork clastic wedges. Pre-Mesaverde deposition in the Wyoming-Utah-Colorado (USA) region during the Middle Cretaceous was characterized by thickening of the clastic wedge close to the thrust-front, driven primarily by retroarc foreland basin (flexural) tectonics. However, a basinward shift in deposition during the Santonian into the early Campanian (Adaville clastic wedge) signaled a change in the dominant stratigraphic drivers in the region. Shoreline advance accelerated in the early to middle Campanian (Rock Springs clastic wedge), as the end of activity in the thrust belt, growing importance of flat-slab subduction, and steady eastward migration of the zone of dynamic subsidence led to loss of the foredeep and forebulge, with the attendant formation of a low-accommodation shelf environment. This “flat-shelf” environment promoted large shoreline advances and retreats during sea-level rise and fall. During the middle to late Campanian (Iles clastic wedge), deep erosion on the crest of the Moxa Arch, thinning on the crests of the Rock Springs and Rawlins uplifts, and subsequent Laramide-driven basin formation occurred as the Laramide blocks began to partition the region. The next clastic package (Williams Fork clastic wedge) pushed the shoreline over 400 km away from the thrust belt during the late Campanian. This was followed by a very large and persistent marine transgression across the region, with the formation of a Laramide-driven deepwater turbidite basin with toe-of-slope fans into the early Maastrichtian. The Mesaverde Group in the Wyoming-Utah-Colorado region is thus characterized by: (1) a succession of four tectonically driven classic wedges, each comprised of a dozen or so eustatically driven packages that preserve large basinward and landward shoreline shifts, (2) broad regional sand and silt dispersal on a low-accommodation marine shelf setting, (3) a progressive, tectonically driven, basinward shift of deposition with offset, basinward stacking of successive clastic wedges, and (4) the gradual formation of various uplifts and sub-basins, the timing and sizes of which were controlled by the movement of deep-seated Laramide blocks. The Mesaverde Group in the Wyoming-Utah-Colorado region provides an outstanding opportunity to study the dynamic interaction among the tectonic control elements of a subducting plate (crustal loading-flexure, dynamic subsidence/uplift, and regional flat-slab basin partitioning), as well as the dynamic interaction of tectonic and eustatic controls.

Steady thermocapillary droplet migration under thermal radiation with a uniform flux

Thermocapillary migration of a droplet under thermal radiation with a uniform flux is numerically investigated and theoretically analyzed. By using the front-tracking method, it is observed that thermocapillary droplet migration at small Reynolds numbers and moderate Marangoni numbers reaches a steady process. The steady migration velocity decreases as Marangoni number increases. The time-evolution behavior of temperature fields in the steady migration process is found to be a quadratic function, in which the linear rise of the steady state temperatures with the relative time is a main characteristics. The quadratic function behavior of the temperature fields is further used to derive the steady energy equations. From the steady momentum and energy equations, an analytical result at small Reynolds number and zero Marangoni number is determined by using the method of matched asymptotic expansions. The steady migration velocity decreases as Reynolds number increases, which is in qualitatively agreement with the numerical result.

Ontological Transparency, (In)visibility, and Hidden Curricula: Critical Pedagogy Amidst Contentious Edtech

The steady migration of higher education online has accelerated in the wake of Covid-19. The implications of this migration on critical praxis—the theory-in-practice of pedagogy—deserve further scrutiny. This paper explores how teacher and student-led educational technology research and development can help rethink online critical praxis. The paper is based on a recent research project at the University of Edinburgh that speculatively explored the potential for automation in teaching, which generated insights into current and future pedagogical practice among both teachers and students. From this project emerged a series of pedagogical positions that were centred around visions of the future of teaching in response to automation: the pedagogical potential of visibility and invisibility online, transparency, and interrogating the hidden curricula of both higher education and educational technology itself. Through the surfacing of these pedagogical positions, this paper explores how critical pedagogy can be built into the broader teacher function and begins to identify the institutional structures that could potentially impede or accelerate that process.

Grain boundary migration and Zener pinning in a nanocrystalline Cu–Ag alloy

Grain boundary (GB) migration and Zener pinning, i.e. retardment of migrating GBs by second-phase particles, in a nanocrystalline Cu–Ag alloy have been investigated via molecular dynamics simulation. Among 86 GBs of different rotation axes and misorientation angles, about half of the GBs either did not move for an obvious distance within limited simulation time or underwent unsteady migration, and the other GBs exhibited steady migration. For the motionless and unsteady-migration GBs, boundary faceting was frequently observed. In particular, as found in experiments, all low angle GBs and several high angle GBs became faceted. For the steady-migration GBs, rotation-axis and misorientation dependences of GB energy, GB mobility and particle pinning effects have been systematically revealed. It is found that both the energy and mobility of low angle GBs were generally lower than those of high angle GBs, GBs of distinct rotation axes differed in mobility by as large as three orders of magnitude, and the maximum pinning force always agreed well with the theoretical prediction proposed by Ashby et al []. Moreover, pinning efficiency obtained via comparisons between boundary migration with and without the pinning indicates that the efficiency is not related to the GB mobility or the maximum pinning force and a nanosized second phase particle seems to have a limited effect on retarding GB motion in very fine nanograins.

The Gondwanan margin in West Antarctica: Insights from Late Triassic magmatism of the Antarctic Peninsula

Triassic orthogneisses of the Antarctic Peninsula provide evidence for the Palaeozoic and Mesozoic geological evolution of southern Gondwana within Pangaea. These rocks are sporadically exposed in southeastern Graham Land and northwestern Palmer Land, although reliable geochronological, geochemical and isotopic data are sparse. We combine new geochronological (LA-ICP-MS zircon UPb), geochemical, and zircon (Hf, O) and whole rock isotopic (Nd, Sr and Pb) data to constrain the age and Triassic – Palaeozoic tectonic setting of these rocks. Zircon cores record Palaeozoic arc magmatism between 253 ± 2 and 528 ± 6 Ma, which was mainly located to the west of the Eastern Palmer Land Shear Zone (Central Domain; Vaughan and Storey, 2000). The arc is considered to be an extension of contemporaneous Palaeozoic arcs that have been identified along the Pacific margin of South America and the Thurston Island Block. Regions to the east of the Palmer Land Shear Zone (Eastern Domain, Vaughan and Storey, 2000) were located distal from the Terra Australis Margin, and possibly resided within Sunsas-aged belts within Pangaea. Triassic continental arc, calc-alkaline magmatism during 223–203 Ma modified the crust of the Antarctic Peninsula on both sides of the Eastern Palmer Land Shear Zone. Magmatic sources included igneous and sedimentary crustal material, which formed by crustal reworking during Sunsas- and Braziliano-aged orogenesis, and Palaeozoic arc magmatism. Arc magmatism accompanied sinistral extension which brought both domains into the arc and resulted in steady oceanward migration of the Triassic arc during the Middle – Late Triassic. We propose that sinistral displacement occurred along the Eastern Palmer Land Shear Zone, and this structure was active as early as the Triassic. Finally, we conclude that both the Eastern and Central Domains are autochthonous to Gondwana.

Thermocapillary migration of a planar droplet at small and large Marangoni numbers: effects of interfacial rheology

In this paper, roles of interfacial rheology on thermocapillary migration of a planar droplet at small and large Marangoni numbers are analyzed. Under quasi-steady-state assumption, the time-independent momentum and energy equations of thermocapillary droplet migration with boundary conditions are determined. An exact solution of the steady thermocapillary migration of the deformed droplet at small Marangoni numbers is obtained. It is found that the deformed droplet has an oblate shape. The deviation from the circular section depends on the Weber number and the migration speed. The surface shear viscosity, the dilatational viscosity and the surface internal energy parameter affect the deformation of the droplet through reducing the migration speed. The validity of the steady thermocapillary droplet migration at small Marangoni numbers is confirmed by determining the conservative overall integral energy equations. At large Marangoni numbers, the non-conservative overall integral energy equations imply that thermocapillary droplet migration is always an unsteady process.