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Precambrian supercontinents,glaciations,atmospheric oxygenation,metazoan evolution and an impact that may have changed the second half of Earth history

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Geoscience Frontiers 2013年第3期4卷 247-261页

作者： grant M.Young Department of Earth Sciences Western University1151 Richmond Street NLondonOntarioCanada N6A 5B7

In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian ＂explosion＂ of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth＇s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break- up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic （Huronian） carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off a

关键词： Proterozoic supercontinents Glaciations Impacts Oxygenation Metazoa

Windows of opportunity:a new tree-shrub dynamic at alpine treeline?

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National Science Review 2023年第10期10卷 13-14页

作者： grant P.Elliott Department of Geography University of Missouri

Of increasing importance while the climate is under the influence of chronic environmental change driven by rising levels of CO2,temperature and vapor pressure deficit(VPD),is understanding how vegetation will respond over space and time as we cross critical thresholds [1].This is especially true in mountain regions where amplified rates of warming are expected to affect the elevational zonation of plant communities [2].

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Environmental upheavals of the Ediacaran period and the Cambrian “explosion” of animal life

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Geoscience Frontiers 2015年第4期6卷 523-535页

作者： grant M.Young Department of Earth Sciences University of Western Ontario

The second half of the Ediacaran period began with a large impact - the Acraman impact in South Australia, which was accompanied by a negative δ^13Ccarb anomaly and an extinction-radiation event involving acritarchs. A few million years later （-570 Ma？） there was a second, deeper and longer-lived world-wide δ^13Ccarb anomaly （the Shuram anomaly） which coincides with extinction of the acanthomorphic acritarchs. Wide distribution of the Shuram event is exemplified by stratigraphic sections from South Australia, Oman, southern California and South China. The widespread anomaly has been tentatively attributed to a marine impact. During recovery from the Shuram event the enigmatic Ediacaran biota achieved its zenith, only to be extirpated and replaced by a polyphyletic assemblage of shelly animals in what is known as the Cambrian ＂explosion＂. This extinction-radiation cycle was preceded by glaciation, another δ^13Ccarb excursion and the highest ^87Sr/^86Sr values known from marine carbonates. These high Sr ratios have been linked to weathering of extensive tracts of continental crust that were elevated during amalgamation of the supercontinent Gondwana. Introduction of essential nutrients to the oceans would have promoted biological production of oxygen and provided P and Ca for the important skeletonization that characterizes the Cambrian ＂explosion＂ and caused a quantum leap in the preservation potential of animal remains. Turbulent events of the last 50 million years of Precambrian time include three glaciations, two large impacts and a massive orogenic episode. These dramatic environmental upheavals are held responsible for three consecutive extinction-radiation cycles that culminated in the appearance of a diverse array of shelly fossils. Various lines of evidence suggest that the metazoans have deep roots so that they too may have been subjected to the environmental pressures of the late Ediacaran period clearly illustrated by acritarchs and the Ediacaran biota but

关键词： Ediacaran Sburam Impacts Orogeny Cambrian explosion

Competition for food in 2 populations of a wild-caught fish

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Current Zoology 2018年第5期64卷 615-622页

作者： Pierre J.C. CHUARD grant E. BROWN James W.A. grant Research School of Biology The Australian National University Canberra ACT 0200 Australia Departmentof Biology Concordia University 7141 Sherbrooke Street West Montreal Quebec Canada H4B 1R6

Aggressive behavior when competing for resources is expected to increase as the ratio of competitors-to-resource ratio （CRR） units increases. Females are expected to be more aggressive than males when competing for food when body size is more strongly related to reproductive suc- cess in females than in males, whereas aggression is predicted to decrease under high ambient predation risk by natural selection. Under the risk allocation model, however, individuals under high ambient predation risk are expected to be more aggressive, and forage more in the absence of imminent risk than their low risk counterparts. An interaction between adult sex ratio （i.e., adult males/females）, ambient predation risk （high vs. low）, and sex on intrasexual competition for mates in Trinidadian guppies Poecilia reticulata has been shown. The interaction suggested an increase in aggression rates as CRR increased, except for males from the high predation population. To compare the patterns of competition for food versus mates, we replicated this study by using food patches. We allowed 4 male or 4 female guppies from high and low predation populations to com- pete for 5, 3, or 1 food patches. The foraging rate was higher in a high rather than low ambient pre- dation risk population. Surprisingly, CRR, sex, and population of origin had no effect on aggression rates. Despite other environmental differences between the 2 populations, the effect of ambient predation risk may be a likely explanation for differences in foraging rates. These results highlight the importance for individuals to secure food despite the cost of competition and predation.

关键词： aggression competitor-to-resource ratio foraging Poecifia reticulata population differences predation risk sex

Effects of Mn content on recrystallization resistance of AA6082 aluminum alloys during post-deformation annealing

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Journal of Materials Science & Technology 2020年第17期52卷 189-197页

作者： Xiaoming Qian Nick Parson X.-grant Chen Department of Applied Science University of Quebec at ChicoutimiSaguenay G7H 2B1Canada Arvida Research and Development Centre Rio Tinto AluminumSaguenay G7S 4K8Canada

The microstructural evolutions under as-homogenized and as-deformed conditions and after the postdeformation annealing of AA6082 aluminum alloys with different Mn content(0.05 wt.%-1 wt.%)were studied by optical,scanning electron,and transmission electron *** results showed that the presence of a large amount ofα-Al(Mn,Fe)Si dispersoids induced by Mn addition significantly improved the recrystallization *** the base alloy free of Mn,static recrystallization occurred after 2 h of annealing,and grain growth commenced after 4 h of annealing,whereas in Mn-containing alloys,the recovered grain structure was well-retained after even 8 h of *** alloy with 0.5%Mn exhibited the best recrystallization resistance,and a further increase of the Mn levels to 1%resulted in a gradual reduction of the recrystallization resistance,the reason for which was that recrystallization occurred only in the dispersoid-free zones(DFZs)and the increased DFZ fraction with Mn content led to an increase in the recrystallization *** variation in the dispersoid number density and a coarsening of dispersoids during annealing have a limited influence on the static recrystallization in Mn-containing alloys.

关键词： AA6082 alloys Mn effects Recrystallization resistance Dispersoid precipitation Post-deformation annealing

Improvement of elevated-temperature strength and recrystallization resistance via Mn-containing dispersoid strengthening in Al-Mg-Si 6082 alloys

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Journal of Materials Science & Technology 2020年第4期39卷 135-143页

作者： Chen Li Kun Liu X.-grant Chen Department of Applied Science University of Québec at ChicoutimiChicoutimiQC G7H 2B1Canada

The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents(0,0.5 and 1.0 wt%)during various heat treatments(300–500℃)was *** effects of dispersoids on elevated-temperature strength and recrystallization resistance during hot-rolling and post-rolling annealing were *** results showed that the dispersoids in the Mn-containing alloys(0.5 and 1.0%)began to precipitate at 350℃and reached the optimum conditions after 2–4 h at 400℃.However,the dispersoids coarsened with increasing holding time at temperatures above450℃.After the peak precipitation treatment at 400℃for 2 h,the yield strength at 300℃increased from 28 MPa(base alloy free of Mn)to 55 MPa(alloy with 0.5%Mn)and 70 MPa(alloy with 1%Mn),respectively,demonstrating a significant dispersoid strengthening effect at elevated *** addition,the dispersoids were thermally stable at 300℃for up to 1000 h holding owing to its relative high precipitation temperature(350–400℃),leading to the superior constant mechanical performance at elevated temperature during the long service *** hot rolling and post-rolling annealing,the presence of a large amount of dispersoids results in the higher Zener drag PZcompared with base alloy and then significantly improved the recrystallization *** alloy containing 0.5%Mn exhibited the highest recrystallization resistance among three experimental alloys studied during the post-rolling process,likely resulted from the lower coarsening rate of dispersoids and the lower dispersoids free zone.

关键词： Al-Mg-Si 6082 alloy Mn addition Dispersoid precipitation Elevated-temperature strength Recrystallization resistance

Cystic neoplasms of the pancreas: A diagnostic challenge

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World Journal of Gastroenterology 2009年第1期15卷 48-54页

作者： grant F Hutchins Peter V Draganov Department of Gastroenterology Hepatology and Nutrition University of Florida1600 SW Archer Rd Room HD 602 PO Box 100214 Gainesville Florida 32610 United States

Cystic neoplasms of the pancreas are increasingly recognized due to the expanding use and improved sensitivity of cross-sectional abdominal imaging. Major advances in the last decade have led to an improved understanding of the various types of cystic lesions and their biologic behavior. Despite signifi cant improvements in imaging technology and the advent of endoscopic-ultrasound (EUS)-guided fineneedle aspiration, the diagnosis and management of pancreatic cystic lesions remains a significant clinical challenge. The fi rst diagnostic step is to differentiate between pancreatic pseudocyst and cystic neoplasm. If a pseudocyst has been effectively excluded, the cornerstone issue is then to determine the malignant potential of the pancreatic cystic neoplasm. In the majority of cases, the correct diagnosis and successful management is based not on a single test but on incorporating data from various sources including patient history, radiologic studies, endoscopic evaluation, and cyst fluid analysis. This review will focus on describing the various types of cystic neoplasms of the pancreas, their malignant potential, and will provide the clinician with a comprehensive diagnostic approach.

关键词： Cystic neoplasm Endoscopic ultrasound Pancreas Pancreatic cyst Pancreatitis

Detection and monitoring prostate specific antigen using nanotechnology approaches to biosensing

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Frontiers of Chemical Science and Engineering 2020年第1期14卷 4-18页

作者： grant Perry Fernando Cortezon-Tamarit Sofia I.Pascu Department of Chemistry University of BathClaverton DownBath BA27AYUK

Prostate cancer has a high incidence in men and remains the second cause of mortality due to cancer *** the development of the disease is greatly correlated to age,the identification of novel detection methods reliable,efficient,and cost effective is a matter of significant importance in the ageing population of western *** detection of the prostate specific antigen(PSA)in blood samples has been the preferred method for the detection and monitoring of prostate cancer over the past *** the indications against its use in massive population screening,PSA still remains the best studied biomarker for prostate cancer and the detection of its different forms and incorporation in multiplexed designs with other biomarkers still remains a highly valuable indicator in the theranostics of prostate *** latest developments in the use of nanomaterials towards the construction of PSA biosensors are reviewed *** incorporation of gold nanoparticles,silica nanoparticles and graphene nanostructures to biosensing devices has represented a big leap forward in terms of sensitivity,stability and *** electrochemical and optical detection methods for the detection of PSA will be reviewed herein.

关键词： biosensing immunosensor PSA prostate cancer fluorescence

Impact of COVID-19 on Safety Performance for Motorcycles:Pre- and during-Pandemic Conditions

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