BACKGROUND: The incorporation of silica within the plant cell wall has been well documented by botanists and materials scientists; however, the means by which plants are able to transport silicon and ...control its polymerization, together with the roles of silica in situ, are not fully understood. RECENT PROGRESS: Recent studies into the mechanisms by which silicification proceeds have identified the following: an energy-dependent Si transporter; Si as a biologically active element triggering natural defence mechanisms; and the means by which abiotic toxicities are alleviated by silica. A full understanding of silica formation in vivo still requires an elucidation of the role played by the environment in which silica formation occurs. Results from in-vitro studies of the effects of cell-wall components associated with polymerized silica on mineral formation illustrate the interactions occurring between the biomolecules and silica, and the effects their presence has on the mineralized structures so formed. SCOPE: This Botanical Briefing describes the uptake, storage and function of Si, and discusses the role biomolecules play when incorporated into model systems of silica polymerization as well as future directions for research in this field.
Many orogens, including the Central Andes and Himalayas, are characterized by wide areas that have undergone upper crustal shortening and surface uplift. The behaviour of the deep lithosphere is ...poorly constrained, and in some mountain belts, lower crust and mantle lithosphere appear to have been removed through delamination during orogen development. Thermal–mechanical numerical models demonstrate that as crust thickens during shortening, the lowermost crust may undergo metamorphic eclogitization, which increases its density. Even a small density increase (7% or more) causes shortening to localize above the eclogitic crustal root, promoting the development of thick lithosphere in this area which is then prone to gravitational removal. Complete removal of orogen mantle lithosphere occurs if the eclogitized lower crust is weak enough to allow full detachment of negatively buoyant mantle lithosphere; this can occur even if the lower crust is less dense than the mantle. The onset of delamination may be determined by the hydration state of the lower crust, as the presence of water promotes eclogitization and significantly reduces rock strength. Two distinct styles of delamination are observed: (1) retreating delamination in which weak mantle lithosphere rolls back and peels away from the crust, producing a contemporaneous migration of crustal thickening, surface uplift and magmatism, and (2) stationary delamination in which strong lithosphere separates from the weak lower crust and slides into the deep mantle at a stationary detachment point, followed by widespread crustal deformation and magmatism.
► Many orogens have experienced lithosphere removal during shortening. ► Numerical models examine lower crustal eclogization during orogen evolution. ► A small density increase for eclogitized crust causes localized shortening. ► Delamination of orogen mantle lithosphere occurs if the lower crust is weak. ► Two styles of delamination are observed in the models.
The outward growth of many orogens occurs through pulsed migration of the strain front. During Cenozoic shortening of the central Andes, the strain front abruptly migrated ∼400 km eastward across the ...Altiplano, isolating the plateau interior from major deformation. In contrast to the traditional critical wedge model that focuses on shallow crust deformation, our lithosphere‐scale numerical models show the ductile lower crust plays a key role in the dynamics of the orogen. As the orogen grows upward, the lower crust flows outward and causes stepwise expansion of the orogen through landward‐migrating deformation. The step length of the strain‐front migration increases with decreasing lower crustal strength. Topographically, a weaker crust promotes the formation of a smooth plateau and underthrusting of stronger foreland lithosphere. Our results indicate that the seemly unrelated physiography, deep‐lithosphere structure, and plateau‐wide strain migration in the Altiplano may all be the result of a weak lower crust.
Plain Language Summary
The formation of large mountain belts is typically considered using the analogy of the growth of a wedge of snow or soil in front of a bulldozer, and it is expected that the mountain belt widens continually. However, observations show that many mountain belts expand laterally in abrupt pulses, where shortening is punctuated by periods during which the deformation front rapidly migrates inland by 100's of kilometers. This includes the Tibetan plateau in Asia, central Andes in South America, and Sevier orogen in North America. Here, we show that mountain belt growth significantly modified when the lower crust is weak. In this case, initially localized crustal shortening causes the lower crust to flow outward from the elevated mountain to the adjacent low‐elevation region. The subsurface flow redistributes crustal mass and changes the mountain landscape. Crustal flow causes compressional stresses associated with mountain growth to expand into the continental interior, leading to the formation of a new deformation front several hundred kilometers inland. This causes the mountain belt to widen in a stepwise fashion and creates a smooth, high plateau interior. In contrast, if the crust is stronger, pulses of deformation are shorter, resulting in more rugged and steep topography.
Key Points
Lower crustal strength strongly affects the kinematics of the retroarc orogenic strain front
Weak lower crust (≤1020 Pa s) promotes the formation of new strain loci several hundred kilometers landward from the original strain front
A weak lower crust in the Altiplano (central Andes) can explain the ∼400 km eastward jump in deformation in the Eocene
It is difficult to estimate how much distributed generation (DG) capacity will be connected to distribution systems in the coming years; however, it is certain that increasing penetration levels ...require robust tools that help assess the capabilities and requirements of the networks in order to produce the best planning and control strategies. The work of this Task Force is focused on the numerous strategies and methods that have been developed in recent years to address DG integration and planning. This paper contains a critical review of the work in this field. Although there have been numerous publications in this area, widespread implementation of the methods has not taken place. The barriers to implementation of the advanced techniques are outlined, highlighting why network operators have been slow to pick up on the research to date. Furthermore, key challenges ahead which remain to be tackled are also described, many of which have come into clear focus with the current drive towards smarter distribution networks.
Background
Muscle depletion is characterized by reduced muscle mass (myopenia), and increased infiltration by intermuscular and intramuscular fat (myosteatosis). This study examined the role of ...particular body composition profiles as prognostic markers for patients with colorectal cancer undergoing curative resection.
Methods
Patients with colorectal cancer undergoing elective surgical resection between 2006 and 2011 were included. Lumbar skeletal muscle index (LSMI), visceral adipose tissue (VAT) surface area and mean muscle attenuation (MA) were calculated by analysis of CT images. Reduced LSMI (myopenia), increased VAT (visceral obesity) and low MA (myosteatosis) were identified using predefined sex‐specific skeletal muscle index values. Univariable and multivariable Cox regression models were used to determine the role of different body composition profiles on outcomes.
Results
Some 805 patients were identified, with a median follow‐up of 47 (i.q.r. 24·9–65·6) months. Multivariable analysis identified myopenia as an independent prognostic factor for disease‐free survival (hazard ratio (HR) 1·53, 95 per cent c.i. 1·06 to 2·39; P = 0·041) and overall survival (HR 1·70, 1·25 to 2·31; P < 0·001). The presence of myosteatosis was associated with prolonged primary hospital stay (P = 0·034), and myopenic obesity was related to higher 30‐day morbidity (P = 0·019) and mortality (P < 0·001) rates.
Conclusion
Myopenia may have an independent prognostic effect on cancer survival for patients with colorectal cancer. Muscle depletion may represent a modifiable risk factor in patients with colorectal cancer and needs to be targeted as a relevant endpoint of health recommendations.
Myopenia affects survival
Continental rifts are important sources of mantle carbon dioxide (CO
) emission into Earth's atmosphere
. Because deep carbon is stored for long periods in the lithospheric mantle
, rift CO
flux ...depends on lithospheric processes that control melt and volatile transport
. The influence of compositional and thickness differences between Archaean and Proterozoic lithosphere on deep-carbon fluxes remains untested. Here we propose that displacement of carbon-enriched Tanzanian cratonic mantle concentrates deep carbon below parts of the East African Rift System. Sources and fluxes of CO
and helium are examined over a 350-kilometre-long transect crossing the boundary between orogenic (Natron and Magadi basins) and cratonic (Balangida and Manyara basins) lithosphere from north to south. Areas of diffuse CO
degassing exhibit increasing mantle CO
flux and
He/
He ratios as the rift transitions from Archaean (cratonic) to Proterozoic (orogenic) lithosphere. Active carbonatite magmatism also occurs near the craton edge. These data indicate that advection of the root of thick Archaean lithosphere laterally to the base of the much thinner adjacent Proterozoic lithosphere creates a zone of highly concentrated deep carbon. This mode of deep-carbon extraction may increase CO
fluxes in some continental rifts, helping to control the production and location of carbonate-rich magmas.
It is well recognized that active arc volcanism at nearly all subduction zones requires temperatures greater than 1200°C in the subarc mantle, despite the underthrusting cool subducting plate. In ...this study, we document evidence that high upper mantle temperatures are not restricted to the arc but usually extend for several hundred kilometers across the back arc, even in areas that have not undergone extension. For 10 circum‐Pacific back arcs where there has been no significant recent extension, we have compiled observational constraints on the thermal structure using a number of independent indicators of mantle temperature, including surface heat flow, seismic velocity, and xenolith thermobarometry. The observations indicate uniformly high temperatures in the shallow mantle and a thin lithosphere (1200°C at ∼60 km depth) over back‐arc widths of 250 to >900 km. Similar high temperatures are inferred for extensional back arcs of the western Pacific and southern Europe, but the thermal structures are complicated by extension and spreading. A broad hot back arc may be a fundamental characteristic of a subduction zone that places important constraints on back‐arc mantle dynamics. In particular, the thermal structure predicted for slab‐driven corner flow is inconsistent with the observed uniformly high back‐arc temperatures. We favor the alternate model that heat is rapidly carried upward from depth by vigorous thermal convection in the back‐arc upper mantle. Such convection may be promoted by low viscosities, resulting from hydration by fluids from the subducting plate. Following subduction termination, we find that the high temperatures decay over a timescale of about 300 Myr.
Histone H3 lysine 9 methylation (H3K9me) mediates heterochromatic gene silencing and is important for genome stability and the regulation of gene expression
. The establishment and epigenetic ...maintenance of heterochromatin involve the recruitment of H3K9 methyltransferases to specific sites on DNA, followed by the recognition of pre-existing H3K9me by the methyltransferase and methylation of proximal histone H3
. This positive feedback loop must be tightly regulated to prevent deleterious epigenetic gene silencing. Extrinsic anti-silencing mechanisms involving histone demethylation or boundary elements help to limit the spread of inappropriate H3K9me
. However, how H3K9 methyltransferase activity is locally restricted or prevented from initiating random H3K9me-which would lead to aberrant gene silencing and epigenetic instability-is not fully understood. Here we reveal an autoinhibited conformation in the conserved H3K9 methyltransferase Clr4 (also known as Suv39h) of the fission yeast Schizosaccharomyces pombe that has a critical role in preventing aberrant heterochromatin formation. Biochemical and X-ray crystallographic data show that an internal loop in Clr4 inhibits the catalytic activity of this enzyme by blocking the histone H3K9 substrate-binding pocket, and that automethylation of specific lysines in this loop promotes a conformational switch that enhances the H3K9me activity of Clr4. Mutations that are predicted to disrupt this regulation lead to aberrant H3K9me, loss of heterochromatin domains and inhibition of growth, demonstrating the importance of the intrinsic inhibition and auto-activation of Clr4 in regulating the deposition of H3K9me and in preventing epigenetic instability. Conservation of the Clr4 autoregulatory loop in other H3K9 methyltransferases and the automethylation of a corresponding lysine in the human SUV39H2 homologue
suggest that the mechanism described here is broadly conserved.
Enhanced weathering, in comparison to other geoengineering measures, creates the possibility of a reduced cost, reduced impact way of decreasing atmospheric carbon, with positive knock-on effects ...such as decreased oceanic acidity. We argue that ethical concerns have a place alongside empirical, political and social factors as we consider how to best respond to the critical challenge that anthropogenic climate change poses. We review these concerns, considering the ethical issues that arise (or would arise) in the large-scale deployment of enhanced weathering. We discuss post-implementation scenarios, failures of collective action, the distribution of risk and externalities and redress for damage. We also discuss issues surrounding ‘dirty hands’ (taking conventionally immoral action to avoid having to take action that is even worse), whether enhanced weathering research might present a moral hazard, the importance of international governance and the notion that the implementation of large-scale enhanced weathering would reveal problematic hubris. Ethics and scientific research interrelate in complex ways: some ethical considerations caution against research and implementation, while others encourage them. Indeed, the ethical perspective encourages us to think more carefully about how, and what types of, geoengineering should be researched and implemented.
Diamond-bearing Cretaceous kimberlites of western North America were emplaced 1000–1500
km inboard of the Farallon plate subduction margin and overlap with the development of the Western Interior ...Seaway, shut-down of the Sierra Nevada arc, and the Laramide orogeny. These events are consistent with a decrease in subduction angle along much of the margin, which placed the subducted Farallon plate in close proximity to the continental interior at the time of kimberlite magmatism. Our numerical models demonstrate that low-angle subduction can result from high plate convergence velocities and enhanced westward motion of North America. Further, rapid subduction allows hydrous minerals to remain stable within the cool interior of the subducting plate to more than 1200
km from the trench. Destabilization of these minerals provides a fluid source that can infiltrate the overlying material, potentially triggering partial melting and kimberlite/lamproite magmatism.
► Cretaceous–Eocene kimberlites were emplaced in the western North America craton ► Kimberlite magmatism coincides with low-angle subduction of the Farallon plate. ► Numerical models show that hydrous minerals may be subducted below the craton. ► Slab dehydration may trigger melting of the craton lithosphere, producing kimberlites.
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