Central Barrier Research Articles

The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña

The frequencies of marine heatwaves and thermal coral bleaching events (CBEs) over the Great Barrier Reef (GBR) continue to increase with five mass CBEs reported since 2016. While changes in the local meteorology, such as reduced wind speeds and decreased cloud cover, are known to heat the shallow reef waters, little consideration has been given to the overriding synoptic meteorology. The 2022 CBE, occurring under La Niña conditions, saw ocean temperatures at Davies Reef increase 1.9 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ \\hbox {C}$$\\end{document} over 19-days and subsequently cool 2.1 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ \\hbox {C}$$\\end{document} back to seasonal norms over eight days. This event was found to be triggered by repeated Rossby wave breaking disrupting the local trade winds, thus inhibiting the latent heat flux. Latent heat fluxes, the primary driver of the event, tripled as the trade winds returned via rapid coastal ridging. These same synoptic features are concurrent with the historic Lismore flooding located hundreds of kilometres south of the GBR.

Who owns reefer vessels? Uncovering the ecosystem of transshipment in fisheries.

A central barrier to effective governance and accountability in fisheries is the limited transparency of corporate ownership. Transshipment-the transfer of catches, fuel, parts, or crew between fishing and cargo vessels known as reefers-is often criticized for its opacity and poor governance. Better insight into the beneficial ownership of vessels involved in transshipment and their operational patterns could lead to more effective management. Our study presents a publicly accessible database of reefers' owners, operators, and flags. We identified 569 individual reefers and found that Russian and Chinese owners control 26 and 20% of the global reefer fleet, respectively. Results also show that 65% of all reefer vessels fly the flags of Russia, Panama, or China. This high level of consolidation suggests considerable leverage for enhancing transparency and governance. Our findings highlight the potential for reforming existing transshipment practices through collaboration among owners, flag states, fishery regulators, and scientists.

Aerodynamic and flutter performance of the bridge deck with various countermeasures using computational fluid dynamics

Aerodynamic layouts of bridge decks considerably affect aerostatic torsional divergence and flutter for bridges. The crucial operation is choosing the optimal bridge deck shape considering the aerodynamic effect. The present study intends to provide a better solution for the flutter control scheme by changing five aspect ratios and four passive aerodynamic countermeasures. The countermeasures are an eccentric wing, inspection rail, down vertical central stabilizer and wind barrier, which have been used for three deck shapes: streamlined, semi-streamline and bluff body sections with large angles of attack. Nowadays, wind barriers are frequently installed on bridges to shield vehicles from the harmful effects of crosswinds, which can influence the flutter characteristics of the bridge. Therefore, the present study contemplates reducing the flutter effect with countermeasures. These countermeasures adversely affect the deck’s dynamic stability, mainly manifested in the different divergence forms of the structure. Finally, the eccentric wing, which runs parallel to the bridge deck, increases the critical flutter speed. However, the flow that passes through the eccentric wing extracts considerable energy from the flow field of the countermeasure. Therefore, the framework and solution of the present investigation are sustainable and safe for bridge design.

Inflammation-Triggered Enlargement of Choroid Plexus in Subacute COVID-19 Patients with Neurological Symptoms.

To investigate whether choroid plexus volumes in subacute coronavirus disease 2019 (COVID-19) patients with neurological symptoms could indicate inflammatory activation or barrier dysfunction and assess their association with clinical data. Choroid plexus volumes were measured in 28 subacute COVID-19 patients via cerebral magnetic resonance imaging (MRI), compared with those in infection-triggered non-COVID-19 encephalopathy patients (n = 25), asymptomatic individuals after COVID-19 (n = 21), and healthy controls (n = 21). Associations with inflammatory serum markers (peak counts of leukocytes, C-reactive protein [CRP], interleukin 6), an MRI-based marker of barrier dysfunction (CSF volume fraction [V-CSF]), and clinical parameters like olfactory performance and cognitive scores (Montreal Cognitive Assessment) were investigated. COVID-19 patients showed significantly larger choroid plexus volumes than control groups (p < 0.001, η2 = 0.172). These volumes correlated significantly with peak leukocyte levels (p = 0.001, Pearson's r = 0.621) and V-CSF (p = 0.009, Spearman's rho = 0.534), but neither with CRP nor interleukin 6. No significant correlations were found with clinical parameters. In patients with subacute COVID-19, choroid plexus volume is a marker of central nervous system inflammation and barrier dysfunction in the presence of neurologic symptoms. The absence of plexus enlargement in infection-triggered non-COVID-19 encephalopathy suggests a specific severe acute respiratory syndrome coronavirus 2 effect. This study also documents an increase in choroid plexus volume for the first time as a parainfectious event. ANN NEUROL 2024.

The Potential for Digital Phenotyping in Understanding Mindfulness App Engagement Patterns: A Pilot Study.

Background: Low app engagement is a central barrier to digital mental health efficacy. With mindfulness-based mental health apps growing in popularity, there is a need for new understanding of factors influencing engagement. This study utilized digital phenotyping to understand real-time patterns of engagement around app-based mindfulness. Different engagement metrics are presented that measure both the total number of app-based activities participants completed each week, as well as the proportion of days that participants engaged with the app each week. Method: Data were derived from two iterations of a four-week study exploring app engagement in college students (n = 169). This secondary analysis investigated the relationships between general and mindfulness-based app engagement with passive data metrics (sleep duration, home time, and screen duration) at a weekly level, as well as the relationship between demographics and engagement. Additional clinically focused analysis was performed on three case studies of participants with high mindfulness activity completion. Results: Demographic variables such as gender, race/ethnicity, and age lacked a significant association with mindfulness app-based engagement. Passive data variables such as sleep and screen duration were significant predictors for different metrics of general and mindfulness-based app engagement at a weekly level. There was a significant interaction effect for screen duration between the number of mindfulness activities completed and whether or not the participant received a mindfulness notification. K-means clusters analyses using passive data features to predict mindfulness activity completion had low performance. Conclusions: While there are no simple solutions to predicting engagement with mindfulness apps, utilizing digital phenotyping approaches at a population and personal level offers new potential. The signal from digital phenotyping warrants more investigation; even small increases in engagement with mindfulness apps may have a tremendous impact given their already high prevalence of engagement, availability, and potential to engage patients across demographics.

The feedback dilemma in medical education: insights from medical residents’ perspectives

BackgroundFeedback is a critical component of the learning process in a clinical setting. This study aims to explore medical residents’ perspectives on feedback delivery and identify potential barriers to feedback-seeking in clinical training.MethodsThis cross-sectional study involved 180 medical residents across seventeen specialties. We employed the validated Residency Education Feedback Level Evaluation in Clinical Training (REFLECT) tool to assess residents’ perspectives on their attitude toward feedback, quality of feedback, perceived importance, and reaction to feedback. Additionally, we explored barriers to feedback-seeking behavior among medical residents.ResultsThe majority of medical residents held positive attitudes toward feedback. They agreed that feedback improves their clinical performance (77.7%), professional behavior (67.2%), and academic motivation (56.7%), while also influencing them to become a better specialist in their future career (72.8%). However, the study revealed critical deficiencies in the feedback process. Only 25.6% of residents reported receiving regular feedback and less than half reported that feedback was consistently delivered at suitable times and locations, was sufficiently clear or included actionable plans for improvement. A minority (32.2%) agreed that faculty had sufficient skills to deliver feedback effectively. Moreover, peer-to-peer feedback appeared to be a primary source of feedback among residents. Negative feedback, though necessary, often triggered feelings of stress, embarrassment, or humiliation. Notably, there were no significant differences in feedback perceptions among different specialties. The absence of a feedback-seeking culture emerged as a central barrier to feedback-seeking behavior in the clinical setting.ConclusionsEstablishing shared expectations and promoting a culture of feedback-seeking could bridge the gap between residents’ perceptions and faculty feedback delivery. Furthermore, recognizing the role of senior and peer residents as valuable feedback sources can contribute to more effective feedback processes in clinical training, ultimately benefiting resident development and patient care.

Controllable-gradient-porous cooling materials driven by multistage solvent displacement method

Passive radiative cooling holds significant potential for efficiently cooling terrestrial objects by simultaneously reflecting sunlight and radiating heat to the cold outer space. Numerous studies have designed high-performance radiative cooling structures using polymethyl methacrylate (PMMA) due to its inherent extinction coefficient.However, obtaining highly favorable spectral characteristics for reflecting sunlight using PMMA, often done through the fabrication of micro/nanoscale structures, remains a central barrier for widespread application. Herein, we report a facile, economical, and scalable multistage solvent displacement-based method for fabricating hierarchically gradient porous PMMA metafilms with highly efficient daytime and nighttime passive radiative cooling performance. Here, the “ouzo effect” works as the driving force for micro/nanopore formation by solvent displacement, which also controls the size of the pores based on different solution ratios. The PMMA metafilm features an ultrahigh solar reflectance of 0.99 and superior mid-infrared thermal emittance of 0.97, which allows for the average and peak subambient temperature drops of 4.6 °C and 8.2 °C, respectively, along with an average radiative cooling power of 90 W/m2 during a 24-h uninterrupted thermal measurement. The hierarchically gradient micro/nanopore distribution of the PMMA metafilm significantly enhances the solar reflectance and thermal emittance within the atmospheric transparency window. Moreover,the multistage solvent displacement method is highly versatile and promising for fabricating porous structures, further offering a cost-efficient, eco-friendly, and sustainable manufacturing path for high-performance radiative cooling application.

Analyzing Various Structural and Temperature Characteristics of Floating Gate Field Effect Transistors Applicable to Fine-Grain Logic-in-Memory Devices.

Although the von Neumann architecture-based computing system has been used for a long time, its limitations in data processing, energy consumption, etc. have led to research on various devices and circuit systems suitable for logic-in-memory (LiM) computing applications. In this paper, we analyze the temperature-dependent device and circuit characteristics of the floating gate field effect transistor (FGFET) source drain barrier (SDB) and FGFET central shallow barrier (CSB) identified in previous papers, and their applicability to LiM applications is specifically confirmed. These FGFETs have the advantage of being much more compatible with existing silicon-based complementary metal oxide semiconductor (CMOS) processes compared to devices using new materials such as ferroelectrics for LiM computing. Utilizing the 32 nm technology node, the leading-edge node where the planar metal oxide semiconductor field effect transistor structure is applied, FGFET devices were analyzed in TCAD, and an environment for analyzing circuits in HSPICE was established. To seamlessly connect FGFET-based devices and circuit analyses, compact models of FGFET-SDB and -CSBs were developed and applied to the design of ternary content-addressable memory (TCAM) and full adder (FA) circuits for LiM. In addition, depression and potential for application of FGFET devices to neural networks were analyzed. The temperature-dependent characteristics of the TCAM and FA circuits with FGFETs were analyzed as an indicator of energy and delay time, and the appropriate number of CSBs should be applied.

Effect of parabolic structure potentials on electron mobility in AlxGa1-xAs quantum well based field effect transistor structure

Here, we theoretically calculate and analyze electron mobility μ in AlxGa1-xAs double parabolic and semi-parabolic quantum well (DPQW and DSPQW) based field effect transistor structures. We compute μ as a function of applied electric field F by considering ionized impurity (II) and alloy disorder (AL) screened scattering potentials (VscrII/AL) and show that μ(DPQW) > μ (DSPQW). The symmetric property of VscrII/AL makes μ to vary symmetrically around F = 0 at which two subbands are occupied. The shape of the DSPQW structure potential, compared to DPQW, causes the subband wave functions ψ0 and ψ1 to lie nearer and also penetrate more into the central barrier. Accordingly, the II-scattering is reduced due to increased distance of the electrons from the ionized donors (lying in the side barriers), while AL-scattering is enhanced through increased scattering in the central barrier. As a result, we obtain for F = 0, μII (DSPQW) > μII (DPQW) and μAL (DSPQW) < μAL (DPQW). Further, we show that μ enhances in DPQW by increasing design parameters such as well width, spacer width, and central barrier width. However, μ reduces with the increase in alloy concentrations inside the well through intersubband interaction. The obtained results reflect the suitability of parabolic potential based quantum well structures in emerging optoelectronic devices to enhance the transport and optical properties.

Sea‐weeding: Manual removal of macroalgae facilitates rapid coral recovery

Abstract Coral reef ecosystems globally are under threat, leading to declining coral cover and macroalgal proliferation. Manually removing macroalgae (i.e. ‘sea‐weeding’) may promote local‐scale coral recovery by reducing a biological barrier, though the impact of removal on community composition of benthic reef organisms has not been quantified. In this three‐year study (2018–2021), fleshy macroalgae (predominantly Sargassum spp.) were periodically removed from 25 m2 experimental plots on two inshore fringing reefs of Yunbenun (Magnetic Island) in the central Great Barrier Reef. By the end of the study, coral cover in removal plots (n = 12 plots) assessed through in‐field transects increased by at least 47% (2019 mean: 25.5%, 2021 mean: 37.4%), and macroalgal cover decreased by more than half. In contrast, in control plots (n = 12 plots), there was no change in macroalgal cover while coral cover remained stable (2019 mean: 16.4%, 2021 mean: 13.6%). Changes in benthic cover were supported by photoquadrat data, with Bayesian probability modelling indicating a 100% likelihood that coral cover more than doubled in removal plots over the study period, compared to only a 29% chance of increased coral cover in control plots. Synthesis and applications. Manual macroalgal removal can provide rapid benefits and enhance inshore coral reef recovery. Through involvement of community groups and citizen scientists, larger scale removal of macroalgae is a low‐tech, high‐impact, and achievable method for local reef management.

Regular reaction dynamics in analytical form in the vicinity of symmetrical transition states. Central barrier crossings in SN2 reactions.

When an activated complex, as defined in transition state theory (TST), has a polyhedral shape, its kinetic energy is found to be diagonal in a system of spherical polar coordinates. If, in addition, the polyhedron is characterized by a high symmetry, then its dynamics considerably simplifies. An application of this approach to the most symmetrical TS known to date, i.e., that which controls the Cl- + CH3Cl → ClCH3 + Cl- SN2 nucleophilic substitution, is presented and an analytical expression of its potential energy surface is provided. In a substantial range around the saddle point, approximate equations of motion for the two components of the reaction coordinate, i.e., the antisymmetrical stretching motion of the ClCCl core and the wagging motion of the hydrogen triad, can be derived in an analytical form. During an extensive period of time, the main component of the reaction coordinate is governed by an unexpectedly simple equation of motion that depends on a single initial condition, irrespective of the other ones and of the internal energy. Reactive trajectories are observed to form a perfectly collimated bundle characterized by undetectable dispersion, thereby giving a spectacular example of regular dynamics in an anharmonic potential. Regularity and collimation are brought about by local symmetry, which is a widespread feature of potential energy surfaces. Anharmonicity is observed to influence the dynamics only at a late stage. As energy increases, trajectories tend to fan out and to deviate from the analytical equation. For the wagging motion, chaos sets in at much lower energies.

Vegetative fragment production as a means of propagule dispersal for tropical seagrass meadows

Background and aimsLong distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species and regions. The goal of this paper is to measure seagrass fragment density and viability in two tropical species, assessing various factors influencing their distribution. MethodsWe measured the density and viability of floating seagrass fragments for two tropical seagrass species (Zostera muelleri and Halodule uninervis) in two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. We assessed the effect of wind speed, wind direction, seagrass growing/senescent season, seagrass meadow density, meadow location and dugong foraging intensity on fragment density. We also measured seagrass fragment structure and fragment viability; i.e., potential to establish into a new plant. Key resultsWe found that seagrass meadow density, season, wind direction and wind speed influenced total fragment density, while season and wind speed influenced the density of viable fragments. Dugong foraging intensity did not influence fragment density. Our results indicate that wave action from winds combined with high seagrass meadow density increases seagrass fragment creation, and that more fragments are produced during the growing than the senescent season. Seagrass fragments classified as viable for Z. muelleri and H. uninervis had significantly more shoots and leaves than non-viable fragments. We collected 0.63 (±0.08 SE) floating viable fragments 100 m−2 in the growing season, and 0.13 (±0.03 SE) viable fragments 100 m−2 in the senescent season. Over a third (38%) of all fragments collected were viable. ConclusionThere is likely to be a large number of viable seagrass fragments available for long distance dispersal. This study's outputs can inform dispersal and connectivity models that are used to direct seagrass ecosystem management and conservation strategies.

Branching coral growth and visual health during bleaching and recovery on the central Great Barrier Reef

Coral reefs are under threat from cumulative impacts such as cyclones, crown-of-thorns starfish (COTS) outbreaks and climate-driven coral bleaching events. Branching corals are more severely impacted by these events than other coral morphologies due to their sensitivity to heat stress and weaker skeletons and COTS preferred prey. The central Great Barrier Reef experienced unprecedented back-to-back bleaching events in 2016 and 2017. This study commenced in 2017 at the peak of heat stress and examined the impact of the heatwave on the survival and recovery of corals by assessing the growth, health (based on the visual health index) and physiological parameters (chlorophyll a, zooxanthellae density, lipid and protein content) of two species, Acropora millepora and Pocillopora acuta (N = 60 colonies for each species). It was conducted across a gradient of turbidity at three reefs, Pandora, Orpheus and Rib, that experienced in April 2017, degree heating weeks (DHW) of 9, 8 and 7, respectively. Orpheus experienced the worst bleaching, based on visual health score, followed by Rib and Pandora. Rib experienced the greatest mortality (78% by Nov 2017); however, this was attributed to the presence of actively feeding crown-of-thorns starfish. Growth rates of A. millepora were almost twice the rate of P. acuta. Both species showed significant seasonal variation with growth of A. millepora and P. acuta 35–40% and 23–33% significantly greater in the summer, respectively. Differences in growth rates were best explained by indicators of energy acquisition. For example, the most important predictor variable in determining higher growth rates and visual health score in A. millepora was chlorophyll a content. For P. acuta, visual health score was the best predictor variable for higher growth rates. This study highlights the important role that chlorophyll a and associated symbionts play in growth and survival in these corals during and after a heat stress event.

Roles of depth, current speed, and benthic cover in shaping gorgonian assemblages at the Palm Islands (Great Barrier Reef)

Gorgonians are a diverse and conspicuous component of coral reef ecosystems, providing habitat structure that supports unique assemblages of fishes and invertebrates. Evaluating their overall importance as ecological engineers requires an understanding of their spatial patterns of distribution, abundance and assemblage composition, and the biophysical factors that drive these patterns. No baseline data are available on the spatial patterns of distribution of gorgonians for the Great Barrier Reef. In this study, we quantified the abundance, genera richness, and composition of gorgonian assemblages using video surveys at three depths (5, 10, and 15 m) at 16 locations at the Palm Islands, an inshore island group in the central Great Barrier Reef. We compared gorgonian abundance and genera richness between depths and assessed the role of benthic habitat in structuring gorgonian communities. We also conducted a preliminary investigation of the potential role of water currents in driving gorgonian spatial patterns in the Palm Islands, using in situ current meters. Gorgonian abundance and genera richness consistently increased with depth, although the magnitude of the depth effect varied among locations. Abundance increased with increasing percent cover of rubble and conversely declined with increasing cover of hard corals. The composition of gorgonian assemblages also varied among depths, with whip (Junceella, Viminella) and fan (Acanthogorgia, Anthogorgia, Annella) growth forms being dominant at depths of 5 and 10 m, and branching (Dichotella, Icilogorgia) and candelabrum (Ctenocella) forms being dominant at 15 m. The shallow gorgonian assemblage was associated with high coral cover, whilst the deeper assemblage was associated with high per cent cover of rubble, turf and/or macroalgae. This study highlighted that the abundance, diversity, and composition of gorgonian assemblages on coral reefs in the Palm Islands are determined by a range of biophysical factors linked to depth. Further work is required to isolate the primary drivers of these depth-related effects and evaluate their relative importance.

A test of adaptive strategy theory using fifteen years of change in coral abundance

Universal Adaptive Strategy Theory aims to predict how taxa and assemblages respond to disturbances on the basis of adaptive strategy group (ASG) membership. Here, we test such predictions using the adaptive strategy scheme for reef-building corals developed by Darling et al. (Ecol Lett 15:1378–1386, 2012) and a long-term dataset of coral assemblage structure from inshore reefs on the central Great Barrier Reef. Several disturbances including mass bleaching and tropical storms were recorded in this 15-year interval from 1998 to 2013. ASG membership did not predict how a given taxon responded to disturbance. In fact, all ASGs were on average equally affected by bleaching and a period of multiple disturbances. Furthermore, there were no consistent winners at these sites in response to the 1998 bleaching in contrast to previous work suggesting clear hierarchies in susceptibility to bleaching. In conclusion, while further efforts to re-evaluate the utility of ASGs for reef corals should be encouraged our results and a re-examination of the literature suggests that direct trait-based approaches might prove more useful when exploring how corals respond to disturbance.

Implication of Central Nervous System Barrier Impairment in Amyotrophic Lateral Sclerosis: Gender-Related Difference in Patients.

Central nervous system (CNS) barrier impairment has been reported in amyotrophic lateral sclerosis (ALS), highlighting its potential significance in the disease. In this context, we aim to shed light on its involvement in the disease, by determining albumin quotient (QAlb) at the time of diagnosis of ALS in a large cohort of patients. Patients from the university hospital of Tours (n = 307) were included in this monocentric, retrospective study. In total, 92 patients (30%) had elevated QAlb levels. This percentage was higher in males (43%) than in females (15%). Interestingly, QAlb was not associated with age of onset, age at sampling or diagnostic delay. However, we found an association with ALS functional rating scale-revised (ALSFRS-r) at diagnosis but this was significant only in males. The QAlb levels were not linked to the presence of a pathogenic mutation. Finally, we performed a multivariate survival analysis and found that QAlb was significantly associated with survival in male patients (HR = 2.3, 95% CI = 1.2-4.3, p = 0.009). A longitudinal evaluation of markers of barrier impairment, in combination with inflammatory biomarkers, could give insight into the involvement of CNS barrier impairment in the pathogenesis of the disease. The gender difference might guide the development of new drugs and help personalise the treatment of ALS.

Disused coal tip management in Wales: environmental regulation under climate change

In view of recent coal tip failures in Wales under pressures of climate change conditions, particularly severe rainfall, the Welsh Government has committed to taking preventive action to address threats associated with disused coal tips, which number more than 2,500. This legislation is currently under development, aided by a report from the Law Commission of England and Wales, which recommended the creation of a coal tips register and the designation of an authority for overseeing inspections, assessing risk levels, and ensuring appropriate management. Whilst the intent of such regulatory action on coal tips is the protection of both public safety and environmental health, paradoxically a central barrier to an effective regime is the body of environmental regulations which constrain development. This article reviews such tensions in areas such as waste management, environmental permitting, habitat protection, ecological assessments, and nature conservation, before considering potential solutions to enable timely implementation of coal tip safety measures whilst safeguarding long-term ecological health and sustainability. The conclusion reflects on how the issue of disused coal tip safety serves as a harbinger of the types of legislative challenges likely to arise under climate change.

Effect of a central barrier potential on asymmetry-induced transport in a coaxial Malmberg–Penning trap

Experiments are presented measuring the radial particle flux produced when a central barrier potential is applied to the central ring of a coaxial Malmberg–Penning trap at the same time as the voltages producing the main asymmetry potential ϕ1(r) cos (kz) cos (lθ−ωt). When a negative DC voltage is applied to the entire central ring, the peak flux produced by the main asymmetry is reduced by a factor e(Veff/1.2), where Veff is the effective applied potential in volts. This barrier potential also increases the frequency of this peak flux. When asymmetric ± voltages are applied to the two azimuthally divided halves of the central ring, DC voltages increase the radial flux while AC voltages decrease it. It is shown that these asymmetric barrier voltages produce their own transport and that the resulting modification of the plasma may be a factor in changing the observed flux.

Improvement of electron mobility mediated by interface roughness scattering in pseudomorphic GaAs/In0.15Ga0.85As asymmetric double quantum well structure

We analyse low temperature multisubband electron mobility mediated by interface roughness (ir-) scattering i.e., µirs as a function of electric field F in a pseudomorphic modulation δ-doped GaAs/In0.15Ga0.85As asymmetry-double-quantum-well (ADQW) structure. The asymmetry is obtained by considering different (I) well widths (w1 = 100 Å and w2 = 150 Å) and (II) doping concentrations (Nd1 = 1.0 × 1018 cm−3 and Nd2 = 1.5 × 1018 cm−3). We adopt random phase approximation and calculated µirs by considering screened ir-scattering potential. The cusp like behaviour of Fermi Energy levels at resonance field Fr makes µirs non-monotonic through intersubband interaction. We show that there is an enhancement of µirs and shifting of the resonance position with increasing central barrier width b in both cases. However, in case I, the increase in Nd enhances µirs but Fr doesn’t change. Whereas, in case II, as w increases, not only µirs but also Fr changes. The effect of the structure parameters on µirs can be utilized to improve the surface roughness effect in new emerging opto-electronic devices.

Ring structural transitions in strongly coupled dusty plasmas.

This paper presents a numerical study of ring structural transitions in strongly coupled dusty plasma confined in a ring-shaped (quartic) potential well with a central barrier, whose axis of symmetry is parallel to the gravitational attraction. It is observed that increasing the amplitude of the potential leads to a transition from a ring monolayer structure (rings of different diameters nested within the same plane) to a cylindrical shell structure (rings of similar diameter aligned in parallel planes). In the cylindrical shell state, the ring's alignment in the vertical plane exhibits hexagonal symmetry. The ring transition is reversible, but exhibits hysteresis in the initial and final particle positions. As the critical conditions for the transitions are approached, the transitional structure states exhibit zigzag instabilities or asymmetries on the ring alignment. Furthermore, for a fixed amplitude of the quartic potential that results in a cylinder-shaped shell structure, we show that additional rings in the cylindrical shell structure can be formed by decreasing the curvature of the parabolic potential well, whose axis of symmetry is perpendicular to the gravitational force, increasing the number density, and lowering the screening parameter. Finally, we discuss the application of these findings to dusty plasma experiments with ring electrodes and weak magnetic fields.