Search

As perovskite-based photovoltaics near commercialization, it is imperative to develop industrial-scale defect-passivation techniques. Vapor deposition is a solvent-free fabrication technique that is widely implemented in industry and can be used to fabricate metal-halide perovskite thin films. We demonstrate markably improved growth and optoelectronic properties for vapor-deposited [CH(NH2)2]0.83Cs0.17PbI3 perovskite solar cells by partially substituting PbI2 for PbCl2 as the inorganic precursor. We find the partial substitution of PbI2 for PbCl2 enhances photoluminescence lifetimes from 5.6 ns to over 100 ns, photoluminescence quantum yields by more than an order of magnitude, and charge-carrier mobility from 46 cm2/(V s) to 56 cm2/(V s). This results in improved solar-cell power conversion efficiency, from 16.4% to 19.3% for the devices employing perovskite films deposited with 20% substitution of PbI2 for PbCl2. Our method presents a scalable, dry, and solvent-free route to reducing nonradiative recombination centers and hence improving the performance of vapor-deposited metal-halide perovskite solar cells.

Stress in active subduction forearcs is controlled primarily by friction along the megathrust and the gravitational force. The competing deviatoric compressive and tensional stresses generated by megathrust friction and gravity, respectively, are of the same order of magnitude and result in very low deviatoric stress in the forearc. The near neutral stress state in subduction forearcs is supported by observations of stress reversal, that is a change from deviatoric compression to deviatoric tension, caused by very small megathrust shear stress drops (

Earthquake stress drop values estimated from ground-motion spectra commonly vary by several orders of magnitude, particularly for small earthquakes (~M < 3). Stress-drop values have been found to vary with faulting style, faulting type (intraplate, interplate), depth, and to exhibit differences between natural and induced earthquakes. Nevertheless, distinguishing uncertainties from real trends across data sets is challenging, in part due to the variation in methodological approaches and observational constraints. However, the proliferation of high-quality, dense seismic data in recent years has shown that at least some of the variability in stress drop values almost certainly reflects diversity in fault strength and geological conditions. Coupling well-constrained observations to a variety of modeling approaches will help uncover what controls earthquake rupture processes, but deconvolving observational constraints from real variation in rupture behavior is key.We present our stress drop estimates from data sets representing a wide range of fault loading conditions and geological environments, from interplate, intraslab and forearc subduction faults, to volcanic, intraplate, and human induced events. Stress-drop values range primarily between 1 – 100 MPa for events that meet the criteria for spectral-ratio analysis. We present correlations of low relative stress drop values in areas of high seismic attenuation indicative of lower rock strength, and a slight correlation with depth that corresponds to modeled deviatoric stress values. We also show one notable subset of induced events near active injection wells that exhibit stress drop values of ~0.1 MPa and have distinctive low-frequency content. Their spatial distribution, waveform, and source spectral characteristics suggest either slower rupture, lower stress drop values, or a combination of both, and may represent part of the transition between aseismic and seismic slip. We show using a Large-n array that while stress drop values are roughly constant (within 2 orders of magnitude), estimates can vary by roughly 25% when station coverage is limited to 15 stations or less with a maximum azimuthal gap of 90°. Our findings highlight the importance of using modeling approaches to explore relative influence of fault strength and methodological approaches in stress drop variation. In particular, models that incorporate both frictional and thermoelastic approaches may provide clues to the variability of conditions that can activate faults, both within stable sliding and seismic rupture conditions.

We investigate the effects of site response on source parameters using earthquakes recorded by a dense nodal array in Oklahoma. While it is well-known that near-surface unconsolidated sediments can cause an apparent breakdown of earthquake self-similarity, the influence of laterally varying site conditions remains unclear. We analyze site conditions across a 1825-station array on a river plain within an area of 40 km by 51 km, using vertical ground motions from regional earthquakes. While the source radiation pattern controls P-wave ground motions below 8 Hz, the surface geology correlates with P-wave ground motions above 8 Hz and S-wave ground motions at 2–21 Hz. Sites on alluvial sediments can have vertical ground motions that exceed three times the array median. We use ground motions of regional earthquakes as a proxy for site effects. The corner frequencies (fc) and stress drops (Δσ) of local earthquakes (ML0.01–3) estimated using a standard single-spectra approach show negative correlations with the site-effect proxy, while the seismic moments (M0) show positive correlations. In contrast, the spectral-ratio approach effectively removes the site effects. The site-effect biases are consistent but small as expected for this relatively homogeneous structure; they contribute to standard deviations

Vacuumdepositionis a solvent-free method suitable for growing thin films of metal halideperovskite(MHP) semiconductors. However, most reports of high-efficiencysolarcellsbased on suchvacuum-deposited MHP films incorporate solution-processed hole transport layers (HTLs), thereby complicating prospects of industrial upscaling and potentially affecting the overall devicestability. In this work, we investigate organometallic copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc) as alternative, low-cost, and durable HTLs in all-vacuum-deposited solvent-free formamidinium-cesium lead triodide [CH(NH2)2]0.83Cs0.17PbI3(FACsPbI3)perovskitesolarcells. We elucidate that the CuPc HTL, when employed in an “inverted” p–i–nsolarcell configuration, attains asolar-to-electrical power conversion efficiency of up to 13.9%. Importantly, unencapsulated devices as large as 1 cm2exhibited excellent long-termstability, demonstrating no observable degradation in efficiency after more than 5000 h in storage and 3700 h under 85 °C thermal stressing in N2atmosphere.

EErdbeben setzen Spannungen frei, welche sich durch die Bewegung der Erdplatten angesammelt haben. Meine Dissertation zielt darauf ab, die Herdparameter für den statischen Spannungsabfall von kleinen Erdbeben (M < 3) zu bestimmen. Die Bestimmung dieser Herdparameter bringt eine Reihe von Herausforderungen mit sich, und ich skizziere die Vor- und Nachteile verschiedener Ansätze. Die in meiner Dissertation ermittelten Werte für den Spannungsabfall weichen über verschiedene Magnituden und Regionen gemittelt nicht signifikant vom Bereich von 5 bis 10 MPa ab, was die Hypothese der selbstähnlichen Skalierung des Spannungsabfalls bei Erdbeben unterstützt. Außerdem diskutiere ich die weitere Anwendbarkeit dieses Herdparameters in Erdbebensequenzen und Ansätze zur Detektion von kleinen Erdbeben. Meine Arbeit verdeutlicht die Signifikanz kleiner Erdbeben für unser Verständnis der Erdbebenphysik und zeigt deren analytischen Herausforderungen.

Solid cancers exhibit a dynamic balance between cell death and proliferation ensuring continuous tumour maintenance and growth(1,2). Increasing evidence links enhanced cancer cell apoptosis to paracrine activation of cells in the tumour microenvironment initiating tissue repair programs that support tumour growth(3,4), yet the direct effects of dying cancer cells on neighbouring tumour epithelia and how this paracrine effect potentially contributes to therapy resistance are unclear. Here we demonstrate that chemotherapy-induced tumour cell death in patient-derived colorectal tumour organoids causes ATP release triggering P2X4 (also known as P2RX4) to mediate an mTOR-dependent pro-survival program in neighbouring cancer cells, which renders surviving tumour epithelia sensitiveto mTOR inhibition. The induced mTOR addiction in persisting epithelial cells is due to elevated production of reactive oxygen species and subsequent increased DNA damage in response to the death of neighbouring cells. Accordingly, inhibition of the P2X4 receptor or direct mTOR blockade prevents induction of S6 phosphorylation and synergizes with chemotherapy to cause massive cell death induced by reactive oxygen species and marked tumour regression that is not seen when individually applied. Conversely, scavenging of reactive oxygen species prevents cancer cells from becoming reliant on mTOR activation. Collectively, our findings show that dying cancer cells establish a new dependency on anti-apoptotic programs in their surviving neighbours, thereby creating an opportunity for combination therapy in P2X4-expressing epithelial tumours.

The Adapting Agriculture to Climate Change Project set out to improve the diversity, quantity, and accessibility of germplasm collections of crop wild relatives (CWR). Between 2013 and 2018, partners in 25 countries, heirs to the globetrotting legacy of Nikolai Vavilov, undertook seed collecting expeditions targeting CWR of 28 crops of global significance for agriculture. Here, we describe the implementation of the 25 national collecting programs and present the key results. A total of 4587 unique seed samples from at least 355 CWR taxa were collected, conserved ex situ, safety duplicated in national and international genebanks, and made available through the Multilateral System (MLS) of the International Treaty on Plant Genetic Resources for Food and Agriculture (Plant Treaty). Collections of CWR were made for all 28 targeted crops. Potato and eggplant were the most collected genepools, although the greatest number of primary genepool collections were made for rice. Overall, alfalfa, Bambara groundnut, grass pea and wheat were the genepools for which targets were best achieved. Several of the newly collected samples have already been used in pre-breeding programs to adapt crops to future challenges.

The clustering behavior of injection-induced earthquakes is examined using one month of data recorded by the LArge-n Seismic Survey in Oklahoma (LASSO) array. The 1829-node seismic array was deployed in a 25 km×32 km area of active saltwater disposal in northern Oklahoma between 14 April and 10 May 2016. Injection rates in the study area are nearly constant around the time of the deployment. We develop a local magnitude (ML) equation for the region and estimate magnitudes for 1104 earthquakes recorded by the deployment. The determined earthquake magnitudes range from ML 0.01 to 3.0. The majority of earthquakes occurred between 1.5 and 5.5 km depth, and the shallowest earthquake depths overlap with the base of injection wells at depths between 1.5 and 2.5 km. We compute focal mechanisms of the largest events (ML>2.0), and find a mix of normal- and strike-slip-faulting types. Earthquakes occur regularly in time during the deployment, but are not evenly distributed in space across the study area, that is, they are spatially clustered. Analysis of the nearest-neighbor distances in the space–time–magnitude domain shows the seismicity is dominated by single-event clusters (i.e., independent events). This high proportion of single-event clusters compared with multievent clusters has been previously noted for induced events at geothermal sites. When clustering occurs, the number of events in a cluster is typically small. We observe only four clusters with 10 or more events. For these larger clusters, we find equivalent numbers of foreshocks and aftershocks; however, the foreshock sequences are significantly longer in duration lasting days to tens of days, while aftershock sequences are observed only on the order of one day. The minimal clustering observed for events in the LASSO array suggests that the majority of events are being directly driven by stress changes due to local saltwater disposal.

Lead halide perovskites are leading candidates for photovoltaic and light-emitting devices, owing to their excellent and widely tunable optoelectronic properties. Nanostructure control has been central to their development, allowing for improvements in efficiency and stability, and changes in electronic dimensionality. Recently, formamidinium lead triiodide (FAPbI3) has been shown to exhibit intrinsic quantum confinement effects in nominally bulk thin films, apparent through above-bandgap absorption peaks. Here, we show that such nanoscale electronic effects can be controlled through partial replacement of the FA cation with Cs. We find that Cs-cation exchange causes a weakening of quantum confinement in the perovskite, arising from changes in the bandstructure, the length scale of confinement, or the presence of δH-phase electronic barriers. We further observe photon emission from quantum-confined regions, highlighting their potential usefulness to light-emitting devices and single-photon sources. Overall, controlling this intriguing quantum phenomenon will allow for its suppression or enhancement according to need.

The extensive development over the last decade of low-permeability tight shale formations in the Western Canada Sedimentary Basin (WCSB) using hydraulic fracturing (HF) techniques for oil and gas exploration has been associated with an increasing number of M3+ earthquakes (e.g., ML 4.5 on 30 November 2018 near Dawson Creek, and a Mw 4.6 on 17 August 2016 near Fort St. John). Avoiding economic losses due to operational shutdowns and mitigating damage caused by ground shaking requires developing quantitative relationships between operational parameters and the rate of fault activation in areas of low historical seismicity rates such as the WCSB.Here we present the first results of a detailed study of the relationship between earthquake occurrence and operational parameters using dense seismic array and the British Columbia Oil and Gas Commission operational database to quantitatively assess the relative influence of operational parameters and geological conditions on earthquake generation. We first enhance a local, automatically generated seismic catalog of > 8000 events in the Kiskatinaw (Montney Formation) in the time period between July 2017 - December 2020 area using a multi-station matched-filter approach. We then use a machine learning picker as an independent detection algorithm for the same time period and retain events with the best initial locations detected by both the matched-filter and machine-learning approaches. The combined approach leads to > 30,000 additional earthquakes, which we relocate using a double-difference technique, lowering the magnitude of completeness Mc from ~1.3 to ~0.2.As shown by several previous studies, while most earthquakes show a clear spatio-temporal correlation with HF operations, the majority of HF operations are not associated with felt earthquakes (e.g., M3+). To investigate the correlation between individual HF stage stimulation and earthquake occurrence, we correlate operational and geological characteristics with > 13000 HF stages. Geological data consists of the target formation for injection, which consists of either the Lower or Upper Montney Formations for the majority of stages. We then use a gradient-boosted decision tree machine learning algorithm combined with an approach to explain the model predictions to assess whether a specific stage is seismogenic. The decision-tree-algorithm allows us to estimate the importance of each injection parameter for the generation of seismicity. First results show that the target formation is the most influential parameter, where the Lower Montney Formation is more prone to higher rates of seismicity. In addition, the total pumped fluid volume and the maximum treating pressure are the important injection parameters that are positively correlated with seismicity. In contrast, the average injection rate and breakdown pressure may be relatively less influencial. We will present the results for specific stages and discuss the importance of their injection parameters in relation to seismicity. Our results could help to determine why only some HF wells are seismogenic.

The Western Canada Sedimentary Basin (WCSB) has experienced an increase in hydraulic fracturing (HF) operations in the last decade, accompanied by an increase in the number of felt earthquakes, including a Mw 4.6 on 17 August 2015 near Fort St. John and a ML 4.5 (Mw 4.2) on 30 November 2018 near Dawson Creek. While only a small percentage of HF operations induce seismicity, the majority of moderate-sized earthquakes occur in close spatial proximity to HF wells and temporal proximity to individual HF injection stages within the tight shale play of the Montney Formation. Whereas statistical analysis of an enhanced seismicity catalog suggests that the majority of seismicity occurs following HF operations in the relatively older and deeper compartments of the Montney Formation (Lower Montney; LM) and a low number of events are associated with the relatively younger and shallower layers (Upper Montney; UM), the detailed association and triggering mechanism(s) remains unclear.In this study, we investigate induced earthquake source parameter variations resulting from spatial and/or temporal alteration of injection parameters, including injection time, depth, and volume, at three well pads operating between 2018 and 2020 in the Kiskatinaw area. We use dense local station coverage to create an enhanced seismicity catalog with double-difference relative hypocenter relocations to highlight potential fault orientations, confirmed by focal mechanism solutions. We estimate static stress drop values at the individual well pads and their variation over time as well as variation with the choice of empirical Greens function. We also investigate the temporal changes of the VP/VS-ratio in localized areas following HF operations as a proxy for increased fracture density and/or compliance.The case study at three specific sites targeting both the UM and LM layers investigates the relative influence of a number of factors on the spatial and temporal distribution of source properties. Factors include the scale of HF injection parameters, the target formation layer, and site-specific factors, such as localized fluid accumulation. Preliminary results show that injection in the UM generally leads to significantly fewer earthquakes than injection in the LM, and that lateral variations in compartment properties may significantly influence the seismic response. Moreover, we investigate if repetitive injection at the same wellhead may repeatedly (re)activate sets of faults/fractures and lead to increased hydraulic connectivity between the target sedimentary layers and deeper, pre-existing basement faults. An increase in connectivity would imply an increased potential for triggering large mainshocks.

The community-led stress drop validation study initiated in early 2021 aims at understanding and resolving differences in stress drop measurements using a consistent dataset of the 2019 Ridgecrest earthquake sequence. The dataset consists of 13,000 earthquakes with phase arrivals at up to 107 stations in the week following the M7.1 mainshock on 2019-07-04. Stress drop values are commonly estimated by fitting theoretical source models to direct phase (P- or S-wave) or coda wave spectra. In this work, we contribute to the community-led study using different approaches based on earthquake spectra and an alternative approach based on stopping phases to estimate fault dimension and rupture velocity (the main parameters modulating stress drop). The Ridgecrest dataset offers a unique opportunity to explore the applicability, potential benefits, and limitations of each method due to a wide range of earthquake magnitudes, variety of seismic instruments, and extensive body of supporting research related to the sequence. Furthermore, the sequence enables the comparison between different methods to identify consistencies and differences between estimates using different methodologies. We will present stress drop estimates using commonly used frequency-based methods, such as single-spectrum and spectral-ratio fitting. We also further examine the validity of the theoretical assumptions made for each method using anstopping-phase based estimates of rupture velocity. First results show clear detections of stopping phases for a subset of earthquakes that imply stress drop values ranging between 0.1 - 10 MPa. The range agrees with the results from the frequency-based methods, and estimates from different methods show similar patterns. The first results also suggest significant deviation of specific individual earthquake estimates, which will also be explored by a detailed comparison of methods.

This work presents a high resolution source property study of hydraulic fracturing induced earthquakes in the Montney Formation, a low-permeability tight shale reservoir in the Kiskatinaw area, northeast British Columbia, Canada. We estimate source parameters, including focal mechanism solutions (FMSs), seismic moment, spectral corner frequency, and static stress drop values of earthquakes recorded between July 2017 and July 2020. Waveform-similarity-based event classification of 8,283 earthquakes yields 52 event families (clusters) and 1,014 isolated events (individuals). We calculate a total of 64 FMSs of events \(M_{L}\) > 2.5 with high-quality waveforms. Of the 64 solutions, 54 come from events within families, and are used to infer an additional 3,500 focal mechanisms of smaller-magnitude events with similar waveforms. The other 10 are isolated events. The dominant faulting style inferred from FMSs highlights multiple cascading, shallow, strike-slip events and generally isolated, larger-magnitude reverse-style events in close proximity to the Fort St. John Graben system. Inferred nodal planes of strike-slip events are at low-angles to regional \(S_{Hmax}\), suggesting optimally oriented, left-lateral faults. Reverse faulting nodal planes are roughly perpendicular to \(S_{Hmax}\) and have an orientation consistent with the reactivation of pre-existing normal basement faults. Source spectral analysis using three approaches, including spectral-ratio fitting, suggests a constant stress drop of 1–10 MPa and self-similarity for induced events. Constant stress drop scaling breaks down at magnitudes smaller than ~\(M_{L}\) 2.0, likely due to observational bandwidth limitations.

ObjectiveInvestigating the effect of ferroptosis in the tumour microenvironment to identify combinatory therapy for liver cancer treatment.DesignGlutathione peroxidase 4 (GPx4), which is considered the master regulator of ferroptosis, was genetically altered in murine models for hepatocellular carcinoma (HCC) and colorectal cancer (CRC) to analyse the effect of ferroptosis on tumour cells and the immune tumour microenvironment. The findings served as foundation for the identification of additional targets for combine therapy with ferroptotic inducer in the treatment of HCC and liver metastasis.ResultsSurprisingly, hepatocyte-restricted GPx4 loss does not suppress hepatocellular tumourigenesis. Instead, GPx4-associated ferroptotic hepatocyte death causes a tumour suppressive immune response characterised by a CXCL10-dependent infiltration of cytotoxic CD8+T cells that is counterbalanced by PD-L1 upregulation on tumour cells as well as by a marked HMGB1-mediated myeloid derived suppressor cell (MDSC) infiltration. Blocking PD-1 or HMGB1 unleashes T cell activation and prolongs survival of mice withGpx4-deficient liver tumours. A triple combination of the ferroptosis inducing natural compound withaferin A, the CXCR2 inhibitor SB225002 and α-PD-1 greatly improves survival of wild-type mice with liver tumours. In contrast, the same combination does not affect tumour growth of subcutaneously grown CRC organoids, while it decreases their metastatic growth in liver.ConclusionOur data highlight a context-specific ferroptosis-induced immune response that could be therapeutically exploited for the treatment of primary liver tumours and liver metastases.