Deep Transition Research Articles

Evaluating the Formation Pressure of Diamond‐Hosted Majoritic Garnets: A Machine Learning Majorite Barometer

AbstractDiamond‐hosted majoritic garnet inclusions provide unique insights into the Earth's deep, and otherwise inaccessible, mantle. Compared with other types of mineral inclusions found in sub‐lithospheric diamonds, majoritic garnets can provide the most accurate estimates of diamond formation pressures because laboratory experiments have shown that garnet chemistry varies strongly as a function of pressure. However, evaluation using a compilation of experimental data demonstrates that none of the available empirical barometers are reliable for predicting the formation pressure of many experimental majoritic garnets and cannot be applied with confidence to diamond‐hosted garnet inclusions. On the basis of the full experimental data set, we develop a novel type of majorite barometer using machine learning algorithms. Cross validation demonstrates that Random Forest Regression allows accurate prediction of the formation pressure across the full range of experimental majoritic garnet compositions found in the literature. Applying this new barometer to the global database of diamond‐hosted inclusions reveals that their formation occurs in specific pressure modes. However, exsolved clinopyroxene components that are often observed within garnet inclusions are not included in this analysis. Reconstruction of inclusions, in the 8 cases where this is currently possible, reveals that ignoring small exsolved components can lead to underestimating inclusion pressures by up to 7 GPa (∼210 km). The predicted formation pressures of majoritic garnet inclusions are consistent with crystallization of carbon‐rich slab‐derived melts in Earth's deep upper mantle and transition zone.

Impact of middle atmospheric humidity on boundary layer turbulence and clouds

An attempt is made to connect the moisture present above the boundary layer and its association with the cloud development and boundary layer turbulence using Large Eddy Simulation (LES) and aircraft observations. The dry boundary layer (BL) with shallow clouds observed during Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the arid Indian peninsula is investigated in this study. The constant altitude aircraft observations at different elevations are used to verify LES derived fluxes and variances. LES simulations with the drier conditions above BL resulted in deeper, warmer and drier BL with an enhanced boundary layer turbulent kinetic energy. A dynamic feedback from dry air intrusion into the BL resulted in energetic BL eddies in the dry conditions and a doubling of moisture exchange coefficients. The liquid water content in cloud updrafts rather than in downdrafts were depleted significantly in dry conditions. LES sensitivity indicates that the middle atmospheric water vapor alone could influence the shallow to deep cumulus cloud transitions in the monsoon regime in a dramatic way, by changing the population of cumulus, congestus or deep cumulus clouds. A 30% drying above the BL could drastically reduce the liquid water path and cloud albedo by 10–15%.

Reversible optical control of the metal-insulator transition across the epitaxial heterointerface of a VO2/Nb:TiO2 junction

Optical control of exotic properties in strongly correlated electron materials is very attractive owing to their potential applications in optical and electronic devices. Herein, we demonstrate a vertical heterojunction made of a correlated electron oxide thin film VO2 and a conductive 0.05 wt% Nb-doped TiO2 single crystal, whose metal-insulator transition (MIT) across the nanoscale heterointerface can be efficiently modulated by visible light irradiation. The magnitude of the MIT decreases from ~350 in the dark state to ~7 in the illuminated state, obeying a power law with respect to the light power density. The junction resistance is switched in a reversible and synchronous manner by turning light on and off. The optical tunability of it is also exponentially proportional to the light power density, and a 320-fold on/off ratio is achieved with an irradiance of 65.6 mW cm−2 below the MIT temperature. While the VO2 thin film is metallic above the MIT temperature, the optical tunability is remarkably weakened, with a one-fold change remaining under light illumination. These results are co-attributed to a net reduction (~15 meV) in the apparent barrier height and the photo-carrier-injection-induced metallization of the VO2 heterointerface through a photovoltaic effect, which is induced by deep defect level transition upon the visible light irradiance at low temperature. Additionally, the optical tunability is minimal, resulting from the quite weak modulation of the already metallic band structure in the Schottky-type junction above the MIT temperature. This work enables a remotely optical scheme to manipulate the MIT, implying potential uncooled photodetection and photoswitch applications.

Diverging pathways to port sustainability: How social processes shape and direct transition work

To counter climate change, societies are under pressure to transform energy and transport sectors. Considering the crucial node position of ports in the intersection between energy and transport systems and their connecting of numerous sectors, markets, and values chains, they have hitherto received surprisingly little attention as potential sites for whole system thinking and deep transition. Their heterogeneity suggests that ports are likely to follow different transition pathways. This study explores two Norwegian frontrunner ports to demonstrate how social processes are part of the fabric that constitutes transition pathways in ports. The transition pathways in the two ports diverge according to how they are shaped by deep learning, resource capacity and the collective action of their wider networks, as well as the specificity of expectations. The study complements existing research on transition pathways by focusing on social processes beyond the niche level and by suggesting inter-process and inter-level dynamics to be decisive for the direction of transition work. Contrary to earlier findings, the paper demonstrates how broad and diversified networks may also represent a challenge to the directionality of transitions work. Ports can, however, promote transition work by aligning expectations to port sustainability with expectations in specific value chains.

Geothermal Convection and Double Diffusion Based on Profiling Floats in the Black Sea

AbstractHere, we revisit the existing concepts of the vertical structure of deep layers in the Black Sea using data from sensors deployed on profiling floats. The deep transition layer (DTL) between 700 and 1,700 m acts as an interface between the baroclinic layer and the largest bottom convective layer (BCL) of the world oceans. On top of DTL are the warm intermediate layer and deep cold intermediate layer. They both showed strong trends in the last 15 years due to warmer climate and intensification of warmer intrusions from Bosporus. A “salinity wave” was detected in 2005–2009 below ∼1,700 m, which evidenced for the first time the penetration of gravity flow from Bosporus down to the bottom. The layering of water masses was explained as resulting from the different distribution of sources of heat and salt, double diffusion, and balances between the geothermal and salinity flows in the BCL.

Exploring the Intrinsic Point Defects in Cesium Copper Halides

Cesium copper halides Cs3Cu2X5 (X = Cl, Br, and I) have attracted much attention for optoelectronic applications because of their self-trap excitons and high photoluminescence quantum yield. Intrinsic point defects play a critical role in the optoelectronic performance of these materials by affecting fundamental properties, such as carrier mobility, lifetime, and recombination rate. In this work, we have calculated, by means of quantum mechanical calculations, formation energies and transition levels of all possible intrinsic point defects in Cs3Cu2X5. We have found that only Xi and XCs defects show simultaneously, deep transition energy levels and negative formation energies. Interestingly, the dominant defect under halide-rich growth conditions exhibits much higher concentration than that under halide-poor conditions. Thus, avoiding the halide-rich conditions could help in reducing the defect concentration. (Less)

1967/1969: The End, or (Just) a Pause of the Catholic Liberal Dream?

The aim of this paper is to explore the strong connections between the topics of this special volume of Religions: the current crisis of political Catholicism and religious Catholicism; the new questions posed about the relationship between Catholicism and advanced modernization; the relationship between Catholicism and European institutions; and the importance of the North Atlantic relationships within Catholicism. The paper sheds light on these questions through an analysis of a particular but indicative case study, namely, the “Catholic 68” in Italy. Deconstructing the predominant narrative about the relationship between Vatican II and the events of 1968 (or, better, those of the 2-year period 1967–1969) helps to clarify the connections between the topics of this volume in important ways. In fact, the predominant narrative about the “Catholic 68” still pays undue tribute to both an oversimplified reconstruction of the “parties” who fought one another during the Second Vatican Council and an oversimplified reading of the late 1960s. In this perspective, the Italian case is particularly relevant and yields important sociological insight. The starting point of the paper is the abundant literature on the “long 60s”. This scholarship has clarified the presence of an important religious dimension to the social and cultural processes of this period as well as a (generally accepted) link between the Council-issued renewal and “1968”. At the same time that literature has also clarified that the “long 60s” paved the way for a deep social transition which has also marked the first two decades of the 21st century. The nature of this religious renewal and social change has often been described as the triumph of liberal parties over conservative parties. This paper instead proposes a “three parties scheme” (conservative, progressive and liberal) to better understand the confrontation that occurred at the Council and that at the end of the same decade and its consequences for Catholicism and European politics today.

Deep decoupling in subduction zones: Observations and temperature limits

AbstractThe plate interface undergoes two transitions between seismogenic depths and subarc depths. A brittle-ductile transition at 20–50 km depth is followed by a transition to full viscous coupling to the overlying mantle wedge at ∼80 km depth. We review evidence for both transitions, focusing on heat-flow and seismic-attenuation constraints on the deeper transition. The intervening ductile shear zone likely weakens considerably as temperature increases, such that its rheology exerts a stronger control on subduction-zone thermal structure than does frictional shear heating. We evaluate its role through analytic approximations and two-dimensional finite-element models for both idealized subduction geometries and those resembling real subduction zones. We show that a temperature-buffering process exists in the shear zone that results in temperatures being tightly controlled by the rheological strength of that shear zone’s material for a wide range of shear-heating behaviors of the shallower brittle region. Higher temperatures result in weaker shear zones and hence less heat generation, so temperatures stop increasing and shear zones stop weakening. The net result for many rheologies are temperatures limited to ≤350–420 °C along the plate interface below the cold forearc of most subduction zones until the hot coupled mantle is approached. Very young incoming plates are the exception. This rheological buffering desensitizes subduction-zone thermal structure to many parameters and may help explain the global constancy of the 80 km coupling limit. We recalculate water fluxes to the forearc wedge and deep mantle and find that shear heating has little effect on global water circulation.

Experimental and First-Principles Spectroscopy of Cu2SrSnS4 and Cu2BaSnS4 Photoabsorbers.

Cu2BaSnS4 (CBTS) and Cu2SrSnS4 (CSTS) semiconductors have been recently proposed as potential wide band gap photovoltaic absorbers. Although several measurements indicate that they are less affected by band tailing than their parent compound Cu2ZnSnS4, their photovoltaic efficiencies are still low. To identify possible issues, we characterize CBTS and CSTS in parallel by a variety of spectroscopic methods complemented by first-principles calculations. Two main problems are identified in both materials. The first is the existence of deep defect transitions in low-temperature photoluminescence, pointing to a high density of bulk recombination centers. The second is their low electron affinity, which emphasizes the need for an alternative heterojunction partner and electron contact. We also find a tendency for downward band bending at the surface of both materials. In CBTS, this effect is sufficiently large to cause carrier-type inversion, which may enhance carrier separation and mitigate interface recombination. Optical absorption at room temperature is exciton-enhanced in both CBTS and CSTS. Deconvolution of excitonic effects yields band gaps that are about 100 meV higher than previous estimates based on Tauc plots. Although the two investigated materials are remarkably similar in an idealized, defect-free picture, the present work points to CBTS as a more promising absorber than CSTS for tandem photovoltaics.

A systematic comparison of polar and semipolar Si-doped AlGaN alloys with high AlN content

With a view to supporting the development of ultra-violet light-emitting diodes and related devices, the compositional, emission and morphology properties of Si-doped n-type Al x Ga1-x N alloys are extensively compared. This study has been designed to determine how the different Al x Ga1-x N crystal orientations (polar (0001) and semipolar (11–22)) affect group-III composition and Si incorporation. Wavelength dispersive x-ray (WDX) spectroscopy was used to determine the AlN mole fraction (x ≈ 0.57–0.85) and dopant concentration (3 × 1018–1 × 1019 cm−3) in various series of Al x Ga1-x N layers grown on (0001) and (11–22) AlN/sapphire templates by metalorganic chemical vapor deposition. The polar samples exhibit hexagonal surface features with Ga-rich boundaries confirmed by WDX mapping. Surface morphology was examined by atomic force microscopy for samples grown with different disilane flow rates and the semipolar samples were shown to have smoother surfaces than their polar counterparts, with an approximate 15% reduction in roughness. Optical characterization using cathodoluminescence (CL) spectroscopy allowed analysis of near-band edge emission in the range 4.0–5.4 eV as well as various deep impurity transition peaks in the range 2.7–4.8 eV. The combination of spatially-resolved characterization techniques, including CL and WDX, has provided detailed information on how the crystal growth direction affects the alloy and dopant concentrations.

Geophysical mapping of gypsum for exploration of reserves in the Nong Bua area of Thailand

The increasing demand for gypsum as a raw material for construction projects motivates exploration for additional reserves. Electrical resistivity tomography (ERT) and seismic refraction geophysical methods, augmented with borehole and laboratory measurements on core samples, are used here to delineate the top, bottom and lateral boundaries of an important gypsum ore deposit in Thailand, an economically developing region. The gypsum-bearing formation is found throughout the study area to have an irregular upper boundary on account of karstic dissolution processes. The deeper transition from gypsum to anhydrite, however, is not constrained by the measurements. The P-wave velocity measured in the field is consistent with the core specimen measurements. The electrical resistivity of the core specimens, however, is substantially higher than the values measured in the field. The specimen measurements may depend on the presence of micro cracks, whereas electrical resistivity in the field may be affected by the enclosing clay-rich materials.

Governing the second deep transition towards a circular economy: How rules emerge, align and diffuse

The recently developed Deep Transitions framework has so far been mainly used to explore the first deep transition towards industrial modernity. This paper looks at a potential second deep transition towards a circular economy, which is hoped to lead to a more sustainable global economic system. Our focus is on exploring the role of the EU in developing and diffusing this emerging set of rules. We draw on ideas from the international relations literature to explain why and how the EU adopted the idea of a circular economy, helped formulate it into a set of rules and how it promoted its international diffusion. The paper concludes with lessons about the case and critical reflections about the Deep Transitions framework. In particular, we argue for taking a more actor-based approach when researching the unfolding second deep transition.

Emergence, consolidation and dominance of meta-regimes: Exploring the historical evolution of mass production (1765–1972) from the Deep Transitions perspective

Grand environmental and societal challenges have drawn increasing attention to system innovation and socio-technical transitions. A recent Deep Transitions framework has provided a comprehensive theory of the co-evolutionary patterns of multiple socio-technical systems over the last 250 years. However, so far the framework has not been subjected to systematic empirical exploration. In this paper we address this gap by exploring the co-evolutionary model linking niche-level dynamics, transitions in single systems and ‘great surges of development’, as conceptualized by Schot and Kanger (2018) [1]. For this purpose, we conduct a case study on the historical evolution of mass production in the Transatlantic region from 1765 to 1972. Instead of focusing on dominant technologies or common practices the development of mass production is understood as the emergence of a meta-regime, i.e. a set of mutually aligned rules guiding production activities in multiple socio-technical systems. The results broadly confirm the overall model but also enable to extend the Deep Transitions framework by uncovering new mechanisms and patterns in the variation, diffusion and contestation of meta-regimes.

World wars and the age of oil: Exploring directionality in deep energy transitions

This paper explores the role of the world wars in 20th century energy transitions, focusing on the growth of oil as a major energy source which accelerated after the Second World War in North America and Europe. We utilise the recently developed Deep Transitions framework which combines Techno-Economic Paradigms and sociotechnical transitions approaches. The first deep transition entails the long running emergence of industrial modernity since the late 18th century which culminated in the post-Second World War economic ‘golden age’ underpinned by rapid and stable growth and prosperity in North America and Western Europe. The Deep Transitions framework draws attention to the increasing role of fossil fuels over this long period, and how fossil fuel consumption accelerated in the 20th century taking on a particular direction where energy, mobility, and food systems became increasingly reliant on oil while the share of coal as a proportion of the energy mix decreased. This paper integrates sociotechnical, historical and geopolitical literatures to examine how the development of the age of oil was shaped by wartime demand pressures and logistical challenges and the search for new solutions to these challenges in the United States of America and the United Kingdom.

Review: The Sociology of Identity: The Dialectics of Consciousness, Deconstruction and Reconstruction, by Abdulghani Imad

Review: The Sociology of Identity: The Dialectics of Consciousness, Deconstruction and Reconstruction, by Abdulghani Imad

Interpreting COVID-19 through the lens of the second Deep Transition

Is COVID-19 a stepping stone towards a more sustainable future, or it is just a stone in the pond of which the effects will wither away as soon as we are back to normal? A look at the opportunities arising from the crisis.

How Did We Do That? Histories and Political Economies of Rapid and Just Transitions

ABSTRACT It is becoming increasingly clear that deep and rapid transitions in technologies, infrastructures and ways of organising the economy are imperative if we are to live safely within planetary boundaries. But what historical precedents are there for such profound shifts within short spaces of time, and what were the enabling conditions? When have transitions in sectors such as energy, food, finance and transport come about before, and how would they be brought about again? Do these episodes shed any analogous light on our current collective predicament? This paper develops an account of the politics and prospects of deeper transitions towards sustainability based on a critical empirical, but theoretically informed, reading of previous socio-technical transitions. The scale and urgency of our current ecological predicament is daunting and can be disempowering in the absence of strategic thinking about when analogous challenges have been encountered before and how societies have sought to overcome them. Providing a combination of concrete empirical examples drawn both from academic literature and a series of public workshops reflecting on these themes, this paper seeks to provide a basis for understanding as well as engaging with the scope for accelerated transitions within and beyond capitalism.

Luminescence line shapes of band to deep centre and donor–acceptor transitions in AlN

Energy structure and electron coupling with local lattice vibrations have been investigated for deep centres in AlN using hybrid functional density functional theory. Local phonon energies and Huang–Rhys parameters have been calculated for defects and defect complexes containing most common unintentional impurities of carbon, oxygen and silicon, and for intrinsic vacancies, nitrogen split-interstitial defect, and complexes of Al and N vacancies in AlN. Luminescence line shapes of band to deep centre transitions in AlN have been calculated in dependence on temperature for most abundant defects in AlN. Donor–acceptor luminescence line shapes for shallow donor to deep acceptor and deep donor to deep acceptor transitions have been considered theoretically. Configuration diagrams of oxygen and silicon DX centres have been calculated by density functional theory with hybrid functional, and peak energies of optical transitions of an electron from the DX-centres to deep acceptors have been estimated. Possible assignments of the experimental luminescence bands in AlN based on the calculations have been discussed.

Band gap engineering, quantum confinement, defect mediated broadband visible photoluminescence and associated quantum States of size tuned zinc oxide nanostructures

A simple wet chemical method has been used to synthesize ZnO nanostructures. The ZnO nanocrystals exhibit hexagonal unit cell structure as revealed from the XRD pattern. The intensity difference of various diffraction peaks indicates that the growth of the ZnO nanostructure is anisotropic. Various lattice parameters, dislocation density, strain, particle size, and Zn-O bond length were also calculated. The band gap of the synthesized ZnO nanostructures was determined from the UV–vis absorption spectra using Tauc equation and the band gap of the synthesized ZnO varies from 3.34 eV to 3.57 eV by varying the growth duration. Crystallite sizes also decreased with increased growth duration. This variation of size leads to the change in band gap of the nanostructures. Thus, it is possible to tune the band gap of the nanostructures by varying the growth duration. The synthesized ZnO nanostructures exhibit visible photoluminescence due to deep level transitions. A simple weak quantum confinement model has been used to designate the observed photoluminescence emission peak associated with such transitions.

Photo- and electro-luminescence studies of semipolar (112¯2) InxAl1−xN

InxAl1−xN (0.15 < x < 0.4) single layers (thickness = 300 nm) and light emitting diodes (LEDs) with InxAl1−xN (x = 0.24 or 0.28) quantum wells (QWs) were grown on (112¯2) free-standing GaN substrates by metal organic chemical vapor deposition. The emission characteristics of InxAl1−xN films and QWs were then investigated by photoluminescence (PL), cathodoluminescence (CL), and electroluminescence (EL). PL emission down at 1.87 eV (∼660 nm) was observed from In0.37Al0.63N at room temperature. However, its emission wavelength and spectral width showed almost no temperature-dependence, strongly suggesting the radiative recombination process in In0.37Al0.63N is heavily affected by the potential fluctuations associated with the defect levels such as deep donor–acceptor pairs (DAPs). For In0.23Al0.77N, the emission peaks at 3.24 and 2.4 eV were observed at 300 K but CL showed no evidence of compositional fluctuations. Given the wide spectral width and weak In clustering, PL at 3.24 eV is likely from a shallow DAP transition involving an impurity-related shallow donor and valence band. PL emission at 2.4 eV, on the other hand, behaved more like In0.37Al0.63N, suggesting significant deep DAP transitions. Both LEDs with In0.24Al0.76N and In0.28Al0.72N QWs showed a discrete blueshift of the emission peak with increasing injection current, which is very different from the gradual shift observed in InGaN LEDs. The high-energy peak was much narrower than the low-energy peak, suggesting it could be the near-band edge emission. Si doping of In0.24Al0.76N QWs lowered the injection current level at which the high-energy peak appears.