Tibial plateau fractures with significant joint depression and metaphyseal comminution pose a challenge. In order to prevent the collapse of the articular surface, some authors propose filling the ...subchondral void created during reduction with bone graft/substitute, which can add further complications. We present two cases of tibial plateau fractures with severe joint depression of the lateral condyle; both treated with a periarticular rafting construct, in one caseadditional bone substitute was used and in the other case no bone graft/substitute was used; their final outcomes were reported. The treatment of joint depression in tibial plateau fractures using periarticular rafting constructs without bone graft, may be also a valid option, to achieve good final results without the morbidity associated with the use of bone graft/substitutes.
Marine anthropogenic debris was sampled from two beaches on the remote South Pacific island Rapa Nui (Easter Island). Abundance, composition, and the attached fouling assemblages on stranded litter ...were analysed. Most litter (n = 172 items found) was composed of plastic material, and 34% of all litter items were fouled. The main fouling species was the encrusting bryozoan Jellyella eburnea. Transporting vectors were exclusively made from plastics and were mainly small items and fragments, probably stemming from the South Pacific Subtropical Gyre. We present the first report of Planes major, Halobates sericeus, and Pocillopora sp. on anthropogenic litter in the South Pacific.
•Anthropogenic marine litter from the South Pacific Subtropical Gyre strands on Rapa Nui.•34% of all stranded items carried attached biota.•Rafts were exclusively made from plastics (mainly small items and fragments).•The main fouling species was the encrusting bryozoan Jellyella eburnea.•Anthropogenic marine litter transports non-native biota to Rapa Nui.
The Holocene temperature discrepancy between paleoclimate reconstructions and climate model simulations—known as the Holocene temperature conundrum—calls for new high‐quality Holocene temperature ...records at high elevations. Here, we present a quantitative Holocene mean annual air temperature record based on a site‐specific branched glycerol dialkyl glycerol tetraethers calibration from a small remote alpine lake on the southeastern Tibetan Plateau. The record reveals a temperature history comprising a relatively cool early Holocene (before 7 ka) followed by a warmer mid‐ to late‐Holocene (after 7 ka), which was likely linked to increasing local annual insolation and greenhouse gases. Three cold events punctuated the general warming trend ca. 10.4 ka, 3.7 ka, and 1.7 ka BP, and correspond closely in time to ice rafting events in the North Atlantic, and to episodes of volcanism and/or unusual solar activity. The entire Holocene temperatures are cooler than the previously identified anthropogenic warming from 1990–2015 AD.
Plain Language Summary
The scarcity of high‐quality, quantitative Holocene temperature records from terrestrial archives, especially at high elevations, such as the Tibetan Plateau, limits our understanding of the temperature history of the Holocene. Here, we present a molecular fossil‐based mean annual air temperature record for the last 12,000 years from sediments preserved in a small remote alpine lake. The new record shows that the early Holocene was relatively cool and was followed by a warmer mid‐ to late‐ Holocene, which is consistent with results from climate modeling studies. This Holocene warming trend was probably due to increases in regional annual solar radiation and additional radiative forcing of greenhouse gases. The reconstruction captures the anthropogenic warming of the past 25 years (1990–2015 AD) and shows it to be unusual during the past 12,000 years.
Key Points
An unreported cooler early Holocene (before 7 ka BP) temperature record was presented at high elevations on the southeastern Tibetan Plateau
The entire Holocene mean annual temperatures are cooler than the previously identified anthropogenic warming at this site from 1990 to 2015 AD
Three multi‐centennial cold events centered on 10.4, 3.7, and 1.7 ka BP are observed in the record
Tsunami-driven rafting Carlton, James T.; Chapman, John W.; Geller, Jonathan B. ...
Science (American Association for the Advancement of Science),
09/2017, Letnik:
357, Številka:
6358
Journal Article
Recenzirano
Odprti dostop
The 2011 East Japan earthquake generated a massive tsunami that launched an extraordinary transoceanic biological rafting event with no known historical precedent. We document 289 living Japanese ...coastal marine species from 16 phyla transported over 6 years on objects that traveled thousands of kilometers across the Pacific Ocean to the shores of North America and Hawai‘i. Most of this dispersal occurred on nonbiodegradable objects, resulting in the longest documented transoceanic survival and dispersal of coastal species by rafting. Expanding shoreline infrastructure has increased global sources of plastic materials available for biotic colonization and also interacts with climate change–induced storms of increasing severity to eject debris into the oceans. In turn, increased ocean rafting may intensify species invasions.
Cobalt-based alloys with γ/γ′ microstructures have the potential to become the next generation of superalloys, but alloy compositions and processing steps must be optimized to improve coarsening, ...creep, and rafting behavior. While these behaviors are different than in nickel-based superalloys, alloy development can be accelerated by understanding the thermodynamic factors influencing microstructure evolution. In this work, we develop a phase field model informed by first-principles density functional theory and experimental data to predict the equilibrium shapes of Co-Al-W γ′ precipitates. Three-dimensional simulations of single and multiple precipitates are performed to understand the effect of elastic and interfacial energy on coarsened and rafted microstructures; the elastic energy is dependent on the elastic stiffnesses, misfit strain, precipitate size, applied stress, and precipitate spatial distribution. We observe characteristic microstructures dependent on the type of applied stress that have the same γ′ morphology and orientation seen in experiments, indicating that the elastic stresses arising from coherent γ/γ′ interfaces are important for morphological evolution during creep. The results also indicate that the narrow γ channels between γ′ precipitates are energetically favored, and provide an explanation for the experimentally observed directional coarsening that occurs without any applied stress.
Display omitted
The teleconnection between the Asian monsoon system and North Atlantic forcing is an enduring prospect of the Earth’s climate. During the Holocene interstadial, the Indian summer monsoon showed ...asynchronous weakening links to ice rafting events documented in the North Atlantic region. However, the sensitivity of the Indian Winter Monsoon in response to North Atlantic cold spells is unclear due to a lack of compelling evidence. This study aims to extract the deglacial Indian Winter Monsoon signals using lithogenic tracers in coastal sediments and explore its association with the North Atlantic cooling episodes. A 5.1 m sediment core was retrieved from Pottuvil Lagoon in the southeastern coast of Sri Lanka, and the concentrations of K, Rb, Mg, Al, and Ti in 101 sub-sections were analysed using ICP-MS. The core- chronology was established by Bacon 2.2 age-depth modelling based on calibrated AMS 14C dates. The monsoon signal was reconstructed using element proxies and compared with the drift ice indices from the North Atlantic deep-sea sediments. Results revealed distinct phases of intense monsoon activity at 2553–2984 years BP, 3899–5021 years BP, and 5244–5507 years BP intervals with intermittent weak phases during 2253–2553, 2984–3899, and 5021–5244 years BP. The episodes of the intensified Indian Winter Monsoon coincided with Bond Events 2, 3, and 4, showing a strong coherence with the North Atlantic’s deglacial climate. Thus, on a millennial scale, North-Atlantic cooling has triggered intense winter monsoon conditions over the tropical Indian Ocean region from the mid to late Holocene. In comparison with regional monsoon archives, the Pottuvil winter monsoon record exhibits an anti-phase association with the Indian Summer Monsoon during Holocene ice-rafted debris events. The geochemical approach executed in this study could provide new insight into the millennial-scale pacing of the winter counterpart of the Indian monsoon links to climate extremes of high northern latitudes.
Nickel-based single crystal superalloys (Ni-SXs) are of great interests in aircraft industry due to their excellent high temperature creep strength deriving from the rigid gamma/gamma prime (γ/γ′) ...microstructure and the single crystal nature. The creep properties of Ni-SXs depend strongly on the degradation rate of the original rigid γ/γ′ microstructure with the dislocation movements in the microstructure. Since the applied temperature and stress strongly affect the dislocation movements, the different creep mechanisms are displayed to Ni-SXs during low temperature (∼750 °C), mid-temperature (∼950 °C) and high temperature (∼1100 °C) creep. The creep deformation during low temperature creep is mainly caused by the shearing of γ′ phase by a limited number of dislocations, while high temperature creep mainly occurs to the accumulation of creep strains with the increased dislocation activities in γ phase. To enhance the creep properties of alloy, a variety of strategies of the microstructural optimization need to be considered. One is to increase the volume fraction of γ′ phase to enhance the precipitation strengthening effects. But excessive amounts of γ′ phase are disadvantageous to low temperature strength of alloy. The coarsening of γ′ phase and the rafting process strongly correlates to dislocation movements. It is of importance to discuss the specific mechanisms of coarsening and rafting as well as their influence to the creep properties of alloy. The lattice misfit between the γ and γ′ phase plays an important role in influencing the coarsening of γ′ phase and the creep properties of alloy. A proper lattice misfit helps to form the cubic γ′ phase which is advantageous to alloy. But a too large lattice misfit can promote the coarsening of γ′ phase that damages the structural stability of alloy at high temperatures. The increased additions of refractory elements in alloy promote the formation of topologically close-packed (TCP) phase. TCP phase facilitates the nucleation and propagation of micro-cracks around it that damages the creep properties of alloy. This review aims to summarize some aspects of microstructural evolution during creep of alloy with considering their effects to creep properties. To guide the design of Ni-SXs in future, some perspectives about the microstructural optimization are properly provided.
•The creep properties of Nickel-based superalloys are greatly decided by the microstructural evolution during creep.•The creep mechanisms are determined by the intrinsic dislocation activities occurred in the microstructure.•The coarsening of γ′ phase is emphasized, especially the rafting process.•Lattice misfit strongly affects the formation of dislocation networks and coarsening of γ′ phase.•The formation of TCP phase which is detrimental to creep properties need to be strictly restricted in superalloy design.
The history and driving forces of aeolian activity in western Mongolia remain poorly understood due to the scarcity of geological archives. Here, we obtained a record of sediment grain size from ...Tolbo Lake in western Mongolia to reconstruct changes in aeolian activity since ∼14 ka. The results suggest that intensified aeolian activity in the late Holocene may mainly have been a response to stronger surface winds resulting from an increase in spring insolation and mountain snow. The stable weak aeolian activity appears to coincide with ice‐rafting events in the North Atlantic during the middle Holocene and may be a response to warming at northern high latitudes, increased humidity and vegetation coverage in western Mongolia, indicating that dust from western Mongolia would possibly contribute minimally to dust deposition in Greenland during this period. This study will help understand the atmospheric dust emissions and transport processes in the earth system.
Plain Language Summary
Mongolia is one of the main dust source regions in East Asia and has significant effects on ecosystems and human activities in both source and downwind regions. However, the history of aeolian activity and its possible driving forces remain unclear because of the lack of well‐dated and continuous records in western Mongolia. With high‐resolution grain‐size data from Tolbo Lake, it is possible to better understand the history and driving forces of aeolian activity in western Mongolia over the last ∼14,000 years. Our findings suggest that stronger surface winds due to an increase in spring insolation in the Northern Hemisphere and greater snow cover in the Altai Mountains are important factors in strengthened aeolian activity during the late Holocene in this study area. Our new evidence of the aeolian activity history also provides important insight into dust emission and transport linkages between Asian dust source regions and Greenland, indicating that dust from western Mongolia likely had limited delivery to Greenland in the middle Holocene.
Key Points
A ∼14 ka aeolian activity record from a high‐altitude lake in the dust source region of western Mongolia
Enhanced aeolian activity in the late Holocene may be related to stronger surface winds due to increasing spring insolation and mountain snow
Dust from western Mongolia had a minor contribution to non‐sea salt ions in Greenland during the middle Holocene
PDF
