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Singlet exciton fission is the spin-allowed generation of two triplet electronic excited states from a singlet state. Intramolecular singlet fission has been suggested to occur on individual carotenoid molecules within protein complexes, provided the conjugated backbone is twisted out-of-plane. However, this hypothesis has only been forwarded in protein complexes containing multiple carotenoids and bacteriochlorophylls in close contact. To test the hypothesis on twisted carotenoids in a 'minimal' one-carotenoid system, we study the orange carotenoid protein (OCP). OCP exists in two forms: in its orange form (OCPo), the single bound carotenoid is twisted, whereas in its red form (OCPr), the carotenoid is planar. To enable room-temperature spectroscopy on canthaxanthin-binding OCPo and OCPr without laser-induced photoconversion, we trap them in trehalose glass. Using transient absorption spectroscopy, we show that there is no evidence of long-lived triplet generation through intramolecular singlet fission, despite the canthaxanthin twist in OCPo.

The orange carotenoid protein (OCP) is the water-soluble mediator of non-photochemical quenching in cyanobacteria, a crucial photoprotective mechanism in response to excess illumination. OCP converts from a dark-adapted inactive state (OCPo) to an active quenching conformation (OCPr) under high-light conditions, resulting in a concomitant redshift in the absorption of the bound carotenoid. Here, we test whether a long-lived carotenoid singlet excited state (S*) is required for this photoconversion. We measured pump wavelength-dependent transient absorption of OCPo trapped in trehalose-sucrose glass films. We found that initial OCP photoproducts are still formed despite the glass preventing completion to OCPr, and that S* is only apparent for <495 nm pumps. By comparison to the pump wavelength-dependence of the OCPo to OCPr conversion in buffer, we show that S* is not required for photoconversion, and that S* likely arises from ground-state heterogeneity within OCPo.

Singlet fission (SF), the spin-allowed conversion of one singlet exciton into two triplet excitons, offers a promising strategy for enhancing the efficiency of photovoltaic devices. However, realising this potential necessitates materials capable of ultrafast (sub-picosecond) SF and the generation of long-lived (> microsecond) triplet excitons, a synthetic challenge. Some photosynthetic organisms have evolved sophisticated molecular architectures that demonstrate these criteria, but despite 40 years of study, the underlying SF mechanisms and its functional significance in these organisms remain unclear. Here, we use a suite of ultrafast and magneto-optical spectroscopic techniques to understand the mechanism of SF within light-harvesting 1 (LH1) complexes from wild-type and genetically modified photosynthetic bacteria. Our findings reveal a SF process, termed \"heterofission\", wherein singlet excitons are transformed into triplet excitons localised on adjacent carotenoid (Crt) and bacteriochlorophyll (BChl) molecules. We also uncover an unexpected functional role for SF in augmenting Crt-to-BChl photosynthetic energy transfer efficiency. By transiently storing electronic excitation within the SF-generated triplet pair, the system circumvents rapid thermalisation of Crt excitations, thereby enhancing energy transfer efficiency to the BChl Qy state, and enabling the organism to usefully harvest more sunlight.

Enhanced silicate rock weathering (ERW), deployable with croplands, has potential use for atmospheric carbon dioxide (CO 2 ) removal (CDR), which is now necessary to mitigate anthropogenic climate change 1 . ERW also has possible co-benefits for improved food and soil security, and reduced ocean acidification 2 – 4 . Here we use an integrated performance modelling approach to make an initial techno-economic assessment for 2050, quantifying how CDR potential and costs vary among nations in relation to business-as-usual energy policies and policies consistent with limiting future warming to 2 degrees Celsius 5 . China, India, the USA and Brazil have great potential to help achieve average global CDR goals of 0.5 to 2 gigatonnes of carbon dioxide (CO 2 ) per year with extraction costs of approximately US$80–180 per tonne of CO 2 . These goals and costs are robust, regardless of future energy policies. Deployment within existing croplands offers opportunities to align agriculture and climate policy. However, success will depend upon overcoming political and social inertia to develop regulatory and incentive frameworks. We discuss the challenges and opportunities of ERW deployment, including the potential for excess industrial silicate materials (basalt mine overburden, concrete, and iron and steel slag) to obviate the need for new mining, as well as uncertainties in soil weathering rates and land–ocean transfer of weathered products. A detailed assessment of the techno-economic potential of enhanced rock weathering on croplands identifies national CO 2 removal potentials, costs and engineering challenges if it were to be scaled up to help meet ambitious global CO 2 removal targets.

Seagrass ecosystems are recognized for their capacity to sequester and store organic carbon, but there is large variability in soil organic carbon stocks associated with plant traits and environmental conditions, making the quantification and scaling of carbon storage and fluxes needed to contribute to climate change mitigation highly challenging. Here, we provide estimates of carbon stocks associated with seagrass systems (biomass and soil) through analyses of a comprehensive global database including 2700+ seagrass soil cores. The median global soil C org stock estimate is 24.2 (12.4 – 44.9) Mg C org ha −1 in the top 30 cm of soil, 27% lower than estimates from previous global syntheses, refining the IPCC Tier 1 soil C org stock currently used for carbon accounting in places without local data. We estimate that seagrass carbon stocks at risk of degradation could emit 1,154 Tg (665 – 1699) CO 2 with a social cost of $213 billion (2020 US dollars), if no action is taken to conserve these habitats. Johannes Krause et al. synthesized seagrass carbon stock data from 2700+ soil cores to find that they vary by plant functional group and coastal setting, indicating where conservation efforts would most effectively avoid emissions from seagrass loss

Enhanced weathering (EW) with agriculture uses crushed silicate rocks to drive carbon dioxide removal (CDR) 1 , 2 . If widely adopted on farmlands, it could help achieve net-zero emissions by 2050 2 , 3 – 4 . Here we show, with a detailed US state-specific carbon cycle analysis constrained by resource provision, that EW deployed on agricultural land could sequester 0.16–0.30 GtCO 2  yr −1 by 2050, rising to 0.25–0.49 GtCO 2  yr −1 by 2070. Geochemical assessment of rivers and oceans suggests effective transport of dissolved products from EW from soils, offering CDR on intergenerational timescales. Our analysis further indicates that EW may temporarily help lower ground-level ozone and concentrations of secondary aerosols in agricultural regions. Geospatially mapped CDR costs show heterogeneity across the USA, reflecting a combination of cropland distance from basalt source regions, timing of EW deployment and evolving CDR rates. CDR costs are highest in the first two decades before declining to about US$100–150 tCO 2 −1 by 2050, including for states that contribute most to total national CDR. Although EW cannot be a substitute for emission reductions, our assessment strengthens the case for EW as an overlooked practical innovation for helping the USA meet net-zero 2050 goals 5 , 6 . Public awareness of EW and equity impacts of EW deployment across the USA require further exploration 7 , 8 and we note that mobilizing an EW industry at the necessary scale could take decades. A state-level analysis of the impact of enhanced weathering deployment on carbon sequestration on agricultural land suggests that enhanced weathering could help the USA meet net-zero 2050 goals.

Enhanced silicate rock weathering (ERW), deployable with croplands, has potential use for atmospheric carbon dioxide (CO ) removal (CDR), which is now necessary to mitigate anthropogenic climate change . ERW also has possible co-benefits for improved food and soil security, and reduced ocean acidification . Here we use an integrated performance modelling approach to make an initial techno-economic assessment for 2050, quantifying how CDR potential and costs vary among nations in relation to business-as-usual energy policies and policies consistent with limiting future warming to 2 degrees Celsius . China, India, the USA and Brazil have great potential to help achieve average global CDR goals of 0.5 to 2 gigatonnes of carbon dioxide (CO ) per year with extraction costs of approximately US$80-180 per tonne of CO . These goals and costs are robust, regardless of future energy policies. Deployment within existing croplands offers opportunities to align agriculture and climate policy. However, success will depend upon overcoming political and social inertia to develop regulatory and incentive frameworks. We discuss the challenges and opportunities of ERW deployment, including the potential for excess industrial silicate materials (basalt mine overburden, concrete, and iron and steel slag) to obviate the need for new mining, as well as uncertainties in soil weathering rates and land-ocean transfer of weathered products.

Pocket-size, user-friendly roadmap to learning the basic skills of orthopaedic surgery! Surgery requires a combination of knowledge and skill acquired through years of direct observation, mentorship, and practice. The learning curve can be steep, frustrating, and intimidating for many medical students and junior residents. Too often, books and texts that attempt to translate the art of surgery are far too comprehensive for this audience and counterproductive to learning important basic skills to succeed. Outlines in Orthopaedic Surgery by Valentin Antoci and Adam Eltorai is the orthopaedic volume in a series of textbooks that offer a simplified roadmap to surgery. The text serves as starting point for learning orthopaedic surgery techniques, with room for adding notes, details, and pearls collected during the journey. This unique resource outlines key steps for common orthopaedic procedures, laying a solid foundation of basic knowledge from which trainees can easily build and expand. Thirty-five chapters are systematically organized and formatted by subspecialty, starting with an introduction, followed by sections covering surgery of the hand, shoulder and elbow, joint arthroplasty, sports orthopaedics, spine surgery, orthopaedic trauma, foot and ankle, and pediatrics. Each chapter includes symptoms and signs, surgical pathology, diagnostic modalities, differential diagnosis, treatment options, indications for surgical intervention, step-by-step procedures, pitfalls, and prognosis. Key Features * Concise text and bullets provide quick procedural outlines essential for understanding procedural steps * The generously illustrated text encompasses a full spectrum of musculoskeletal disorders related to degenerative changes, injuries, and congenital conditions * Treatment of a variety of fractures including both bones of the forearm, Monteggia and olecranon, lateral malleolus/bimalleolar ankle, and supracondylar humeral and intramedullary fixation of forearm fractures in pediatric patients This is an ideal, easy-to-read resource for medical students and junior residents to utilize during orthopaedic surgery rotations and for quick consultation during the early years of practice. It will also benefit allied health professionals who need a quick guide on core orthopaedic surgery procedures.

Enhanced weathering (EW) is a promising modification to current agricultural practices that uses crushed silicate rocks to drive carbon dioxide removal (CDR). If widely adopted on farmlands, it could help achieve net-zero or negative emissions by 2050. We report detailed state-level analysis indicating EW deployed on agricultural land could sequester 0.23-0.38 Gt CO\\(_2\\) yr\\(^{-1}\\) and meet 36-60 % of U.S. technological CDR goals. Average CDR costs vary between state, being highest in the first decades before declining to a range of $\\sim\\$$100-150 tCO\\(_2{}^{-1}\\) by 2050, including for three states (Iowa, Illinois, and Indiana) that contribute most to total national CDR. We identify multiple electoral swing states as being essential for scaling EW that are also key beneficiaries of the practice, indicating the need for strong bipartisan support of this technology. Assessment the geochemical capacity of rivers and oceans to carry dissolved EW products from soil drainage suggests EW provides secure long-term CO\\(_2\\) removal on intergenerational time scales. We additionally forecast mitigation of ground-level ozone increases expected with future climate change, as an indirect benefit of EW, and consequent avoidance of yield reductions. Our assessment supports EW as a practical innovation for leveraging agriculture to enable positive action on climate change with adherence to federal environmental justice priorities. However, implementing a stage-gating framework as upscaling proceeds to safeguard against environmental and biodiversity concerns will be essential.