Geostatistics of extreme values makes it possible to model the asymptotic behavior of random phenomena that depend on time or space. In this paper, we propose new models of the extremal coefficient of a stationary ran...Geostatistics of extreme values makes it possible to model the asymptotic behavior of random phenomena that depend on time or space. In this paper, we propose new models of the extremal coefficient of a stationary random field where the cumulative distribution is associated with a multivariate copula. More precisely, some models of extensions of the extremogram and these derivatives are built in a spatial framework. Moreover, both these two geostatistical tools are modeled using the extremal variogram which characterizes the asymptotic stochastic behavior of the phenomena.展开更多
A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the develo...A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database.In this work,we show that two new featurization methods,volume occupation spatial matrix and heat contribution spatial matrix,can improve the accuracy in predicting energetic materials' crystal density(ρ_(crystal)) and solid phase enthalpy of formation(H_(f,solid)) using a database containing 451 energetic molecules.Their mean absolute errors are reduced from 0.048 g/cm~3 and 24.67 kcal/mol to 0.035 g/cm~3 and 9.66 kcal/mol,respectively.By leave-one-out-cross-validation,the newly developed ML models can be used to determine the performance of most kinds of energetic materials except cubanes.Our ML models are applied to predict ρ_(crystal) and H_(f,solid) of CHON-based molecules of the 150 million sized PubChem database,and screened out 56 candidates with competitive detonation performance and reasonable chemical structures.With further improvement in future,spatial matrices have the potential of becoming multifunctional ML simulation tools that could provide even better predictions in wider fields of materials science.展开更多
Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the pr...Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the practical use of nanothermites. In this work, combustion characteristic and aging behavior of aluminum/iron oxide(Al/Fe2O3) nanothermite mixtures were investigated in the presence of micron-scale nickel aimed to produce bimetal thermite powders. The results showed that the alumina content in the combustion residue increased from 88.3% for Al/Fe2O3 nanothermite to 96.5% for the nanothermite mixture containing 20 wt% nickel. Finer particle sizes of combustion residue were obtained for the nanothermite mixtures containing nickel, indicative of the reduced agglomeration. Both results suggested a more complete combustion in the bimetal thermite powders. Aging behavior of the nanothermite mixture was also assessed by measuring the heat of combustion of the mixture before and after aging process. The reduction in heat of combustion of nanothermite mixtures containing nickel was less severe as compared to a significant decrease for the nanothermite mixture without nickel, indicating better aging resistance of the bimetal thermite powders.展开更多
本文讨论了曲苞芋属(Gonatanthus)的研究历史、属的范围。该属在天南星科的自然系统中归属于芋亚科下的泉七族和泉七亚族。曲苞芋属与同一亚族的岩芋属Remusatia的区别在于植株开花时有叶同在,子房具基底胎座。曲苞芋属现含两种,即曲苞...本文讨论了曲苞芋属(Gonatanthus)的研究历史、属的范围。该属在天南星科的自然系统中归属于芋亚科下的泉七族和泉七亚族。曲苞芋属与同一亚族的岩芋属Remusatia的区别在于植株开花时有叶同在,子房具基底胎座。曲苞芋属现含两种,即曲苞芋G.pumilus(D.Don)Engl.et Krause和本文描述的云南曲苞芋G.yunnanensis H.Li et A Hay。展开更多
New data and ideas are changing our view of conditions during the Cretaceous.Paleotopography of the continents was lower than originally thought,eliminating the'cold continental interior paradox'of fossils of ...New data and ideas are changing our view of conditions during the Cretaceous.Paleotopography of the continents was lower than originally thought,eliminating the'cold continental interior paradox'of fossils of plants that could not tolerate freezing occurring in regions indicated by climate models to be well below freezing in winter.The controversy over the height of Cretaceous sea levels has been resolved by knowledge of the effects of passage of the subducted slab of the Farallon Plate beneath the North American crust.The cause of shorter term sea level changes of the order of 30 to 50 meters is not because of growth and decay of ice sheets,but more likely the filling and release of water from groundwater reservoirs and lakes although there may have been some ice in the Early and latest Cretaceous.Carbon dioxide was not the only significant greenhouse gas;methane contributed significantly to the warmer climate.Suggestions of very warm tropical ocean temperatures(>40℃)have implications for the nature of plant life on land limited by Rubisco activase.The land surfaces were much wetter than has been thought,with meandering rivers and many oxbow lakes providing habitat for large dinosaurs.A major rethinking of the nature of conditions on a warmer Earth is underway,and a new suite of paleoclimate simulations for the Cretaceous is needed.展开更多
Solventless mechanochemical synthesis by manual grinding was applied to grow organic proton conducting salts,imidazole-succinic acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(2)COOH)and imidazole-glutaric acid(C_(3)H_(4)N_(2)-HOO...Solventless mechanochemical synthesis by manual grinding was applied to grow organic proton conducting salts,imidazole-succinic acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(2)COOH)and imidazole-glutaric acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(3)COOH).This synthesis method induces crystallization and provides the phase-pure compounds.The compounds exhibit different electric conducting behavior and activation energies Ea compared with the reported single crystals obtained from the solution method.The difference in conducting property can be related to intrinsic defects and structural disorder introduced by mechanochemical grinding,indicating that the mechanochemical method bears strong capability for tuning conductivities.Moreover,complete deuteration of the organic salts is achieved by the method.The mechanochemical synthesis of organic salts also holds high potential for the actual industrialized large-scale production.展开更多
This paper examines dependencies of voice and video contents on human perception of group (or inter-destination) synchronization error in remote learning by Quality of Experience (QoE) assessment. In our assessment, w...This paper examines dependencies of voice and video contents on human perception of group (or inter-destination) synchronization error in remote learning by Quality of Experience (QoE) assessment. In our assessment, we use two videos and three voices (two voices for one video and one voice for the other video). We also investigate influences of silence periods in the voices and temporal relations between the voices and videos (called the tightly-coupled and loosely-coupled contents here). The voices are spoken by a teacher according to the videos. Each subject as a student assesses the group synchronization quality by watching each lecture video and the corresponding explanation voice, and then the subject answers whether he/she perceives the group synchronization error or not. As a result, assessment results illustrate that silence periods mitigate the perception rate of the error, and we can also find that we can more easily perceive the error for tightly-coupled contents than loosely-coupled ones.展开更多
Additives are chemical compounds that are added to concrete during its manufacture to modify one or more of its properties. The first additive used in modern concrete was the accelerator, intended to shorten the time ...Additives are chemical compounds that are added to concrete during its manufacture to modify one or more of its properties. The first additive used in modern concrete was the accelerator, intended to shorten the time during which the material is not capable of supporting stress. Traditionally, accelerators have been made from calcium chloride, but today the trend is to use chloride-free additives to prevent reinforcing steel from corroding and thereby make constructions durable. The objective of this study was to evaluate the effects on the concrete of two types of accelerating admixture, using limestone aggregates, under warm sub-humid climate conditions. The applied methodology consisted of the measurement in the laboratory of some of the main properties of concrete in fresh and hardened states, in samples manufactured both with and without accelerators. The results showed that the accelerator without chloride was less effective than the one based on calcium chloride and that without doses of the accelerator, the effectiveness documented by the manufacturers was achieved.展开更多
There are several previous studies on the association of vitamin E with prevention of stroke but the findings remain controversial.We have conducted a systematic review,meta-analysis together with trial sequential ana...There are several previous studies on the association of vitamin E with prevention of stroke but the findings remain controversial.We have conducted a systematic review,meta-analysis together with trial sequential analysis of randomised controlled trials to evaluate the effect of vitamin E supplementation versus placebo/no vitamin E on the risk reduction of total,fatal,non-fatal,haemorrhagic and ischaemic stroke.Relevant studies were identified by searching online databases through Medline,PubMed and Cochrane Central Register of Controlled Trials.A total of 18 studies with 148016 participants were included in the analysis.There was no significant difference in the prevention of total stroke(RR(relative risk)=0.98,95% CI 0.92-1.04,p=0.57),fatal stroke(RR=0.96,95% CI 0.77-1.20,p=0.73)and non-fatal stroke(RR=0.96,95% CI 0.88-1.05,p=0.35).Subgroup analyses were performed under each category(total stroke,fatal stroke and non-fatal stroke)and included the following subgroups(types of prevention,source and dosage of vitamin E and vitamin E alone vs control).The findings in all subgroup analyses were statistically insignificant.In stroke subtypes analysis,vitamin E showed significant risk reduction in ischaemic stroke(RR=0.92,95% CI 0.85-0.99,p=0.04)but not in haemorrhagic stroke(RR=1.17,95%CI 0.98-1.39,p=0.08).However,the trial sequential analysis demonstrated that more studies were needed to control random errors.Limitations of this study include the following:trials design may not have provided sufficient power to detect a change in stroke outcomes,participants may have had different lifestyles or health issues,there were a limited number of studies available for subgroup analysis,studies were mostly done in developed countries,and the total sample size for all included studies was insufficient to obtain a meaningful result from meta-analysis.In conclusion,there is still a lack of statistically significant evidence of the effects of vitamin E on the risk reduction of stroke.Nevertheless,vitamin E may offer some benefi展开更多
Human stem cells are scalable cell populations capable of cellular differentiation.This makes them a very attractive in vitro cellular resource and in theory provides unlimited amounts of primary cells.Such an approac...Human stem cells are scalable cell populations capable of cellular differentiation.This makes them a very attractive in vitro cellular resource and in theory provides unlimited amounts of primary cells.Such an approach has the potential to improve our understanding of human biology and treating disease.In the future it may be possible to deploy novel stem cell-based approaches to treat human liver diseases.In recent years,eff icient hepatic differentiation from human stem cells has been achieved by several research groups including our own.In this review we provide an overview of the f ield and discuss the future potential and limitations of stem cell technology.展开更多
In a recent study in Nature,Kadosh et al.1 established a landmark relationship between the gut microbiome and host epigenetics in intestinal oncogenesis.They demonstrated the substantial plasticity of mutant p53 in WN...In a recent study in Nature,Kadosh et al.1 established a landmark relationship between the gut microbiome and host epigenetics in intestinal oncogenesis.They demonstrated the substantial plasticity of mutant p53 in WNT-driven tumorigenesis,and the crucial involvement of gut microbiome in modulating this plasticity.展开更多
Objective： Focused Abdominal Sono graphy for Trauma （FAST） is widely used for the detection of intraperitoneal free fluids in patients suffering from blunt abdominal trauma （BAT）. This study aimed at assessing th...Objective： Focused Abdominal Sono graphy for Trauma （FAST） is widely used for the detection of intraperitoneal free fluids in patients suffering from blunt abdominal trauma （BAT）. This study aimed at assessing the diagnostic accuracy of this investigation in a designated trauma centre. Methods： This was a retrospective study of BAT pa tients over a 6 year period seen in a trauma centre in Hong Kong. FAST findings were compared with laparotomy, ab dominal computed tomography or autopsy findings, which served as the gold standard for presence of intraperi toneal free fluids. The patients who did not have FAST or gold standard confirmatory test performed, had preexisting peritoneal fluid, died at resuscitation or had imcomplete docu mentation of FAST findings were excluded. The performance of FAST was expressed as sensitivity, specificity, predictive values （PV）, likelihood ratios （LR） and accuracy. Results： FAST was performed in 302 patients and 153 of them were included in this analysis. The sensitivity, specificity, positive PV, negative PV, positive LR, negative LR and accuracy for FAST were respectively 50.0%, 97.3%, 87.0%, 84.6%, 18.8, 0.5 and 85.0%. FAST was found to be more sensitive in less severely injured patients and more specific in more severely injured patients. Conclusion： FAST is a reliable investigation in the initial assessment of BAT patients. The diagnostic values of FAST could be affected by the severity of injury and staff training is needed to further enhance its effective use.展开更多
文摘Geostatistics of extreme values makes it possible to model the asymptotic behavior of random phenomena that depend on time or space. In this paper, we propose new models of the extremal coefficient of a stationary random field where the cumulative distribution is associated with a multivariate copula. More precisely, some models of extensions of the extremogram and these derivatives are built in a spatial framework. Moreover, both these two geostatistical tools are modeled using the extremal variogram which characterizes the asymptotic stochastic behavior of the phenomena.
基金support from the Ministry of Education(MOE) Singapore Tier 1 (RG8/20)。
文摘A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database.In this work,we show that two new featurization methods,volume occupation spatial matrix and heat contribution spatial matrix,can improve the accuracy in predicting energetic materials' crystal density(ρ_(crystal)) and solid phase enthalpy of formation(H_(f,solid)) using a database containing 451 energetic molecules.Their mean absolute errors are reduced from 0.048 g/cm~3 and 24.67 kcal/mol to 0.035 g/cm~3 and 9.66 kcal/mol,respectively.By leave-one-out-cross-validation,the newly developed ML models can be used to determine the performance of most kinds of energetic materials except cubanes.Our ML models are applied to predict ρ_(crystal) and H_(f,solid) of CHON-based molecules of the 150 million sized PubChem database,and screened out 56 candidates with competitive detonation performance and reasonable chemical structures.With further improvement in future,spatial matrices have the potential of becoming multifunctional ML simulation tools that could provide even better predictions in wider fields of materials science.
文摘Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the practical use of nanothermites. In this work, combustion characteristic and aging behavior of aluminum/iron oxide(Al/Fe2O3) nanothermite mixtures were investigated in the presence of micron-scale nickel aimed to produce bimetal thermite powders. The results showed that the alumina content in the combustion residue increased from 88.3% for Al/Fe2O3 nanothermite to 96.5% for the nanothermite mixture containing 20 wt% nickel. Finer particle sizes of combustion residue were obtained for the nanothermite mixtures containing nickel, indicative of the reduced agglomeration. Both results suggested a more complete combustion in the bimetal thermite powders. Aging behavior of the nanothermite mixture was also assessed by measuring the heat of combustion of the mixture before and after aging process. The reduction in heat of combustion of nanothermite mixtures containing nickel was less severe as compared to a significant decrease for the nanothermite mixture without nickel, indicating better aging resistance of the bimetal thermite powders.
文摘本文讨论了曲苞芋属(Gonatanthus)的研究历史、属的范围。该属在天南星科的自然系统中归属于芋亚科下的泉七族和泉七亚族。曲苞芋属与同一亚族的岩芋属Remusatia的区别在于植株开花时有叶同在,子房具基底胎座。曲苞芋属现含两种,即曲苞芋G.pumilus(D.Don)Engl.et Krause和本文描述的云南曲苞芋G.yunnanensis H.Li et A Hay。
基金a contribution in the frame of UNESCO IGCP Project 609 "Climate-environmental deteriorations during greenhouse phases:Causes and consequences of short-term Cretaceous sea-level changes "
文摘New data and ideas are changing our view of conditions during the Cretaceous.Paleotopography of the continents was lower than originally thought,eliminating the'cold continental interior paradox'of fossils of plants that could not tolerate freezing occurring in regions indicated by climate models to be well below freezing in winter.The controversy over the height of Cretaceous sea levels has been resolved by knowledge of the effects of passage of the subducted slab of the Farallon Plate beneath the North American crust.The cause of shorter term sea level changes of the order of 30 to 50 meters is not because of growth and decay of ice sheets,but more likely the filling and release of water from groundwater reservoirs and lakes although there may have been some ice in the Early and latest Cretaceous.Carbon dioxide was not the only significant greenhouse gas;methane contributed significantly to the warmer climate.Suggestions of very warm tropical ocean temperatures(>40℃)have implications for the nature of plant life on land limited by Rubisco activase.The land surfaces were much wetter than has been thought,with meandering rivers and many oxbow lakes providing habitat for large dinosaurs.A major rethinking of the nature of conditions on a warmer Earth is underway,and a new suite of paleoclimate simulations for the Cretaceous is needed.
基金support of the National Natural Science Foundation of China(No.12005243,22205239,U1930102 and 11805034)Guangdong Basic and Applied Basic Research Foundation(No.2022B1515120014 and 2022A1515110210)+1 种基金China Postdoctoral Science Foundation(No.2022M721906 and 2022M721909)The neutron diffraction experiments were carried out under the fast-track proposal at Australian Nuclear Science and Technology Organisation(ANSTO)and the general user program(No.P1622061700003)at China Spallation Neutron Source(CSNS).
文摘Solventless mechanochemical synthesis by manual grinding was applied to grow organic proton conducting salts,imidazole-succinic acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(2)COOH)and imidazole-glutaric acid(C_(3)H_(4)N_(2)-HOOC(CH_(2))_(3)COOH).This synthesis method induces crystallization and provides the phase-pure compounds.The compounds exhibit different electric conducting behavior and activation energies Ea compared with the reported single crystals obtained from the solution method.The difference in conducting property can be related to intrinsic defects and structural disorder introduced by mechanochemical grinding,indicating that the mechanochemical method bears strong capability for tuning conductivities.Moreover,complete deuteration of the organic salts is achieved by the method.The mechanochemical synthesis of organic salts also holds high potential for the actual industrialized large-scale production.
文摘This paper examines dependencies of voice and video contents on human perception of group (or inter-destination) synchronization error in remote learning by Quality of Experience (QoE) assessment. In our assessment, we use two videos and three voices (two voices for one video and one voice for the other video). We also investigate influences of silence periods in the voices and temporal relations between the voices and videos (called the tightly-coupled and loosely-coupled contents here). The voices are spoken by a teacher according to the videos. Each subject as a student assesses the group synchronization quality by watching each lecture video and the corresponding explanation voice, and then the subject answers whether he/she perceives the group synchronization error or not. As a result, assessment results illustrate that silence periods mitigate the perception rate of the error, and we can also find that we can more easily perceive the error for tightly-coupled contents than loosely-coupled ones.
文摘Additives are chemical compounds that are added to concrete during its manufacture to modify one or more of its properties. The first additive used in modern concrete was the accelerator, intended to shorten the time during which the material is not capable of supporting stress. Traditionally, accelerators have been made from calcium chloride, but today the trend is to use chloride-free additives to prevent reinforcing steel from corroding and thereby make constructions durable. The objective of this study was to evaluate the effects on the concrete of two types of accelerating admixture, using limestone aggregates, under warm sub-humid climate conditions. The applied methodology consisted of the measurement in the laboratory of some of the main properties of concrete in fresh and hardened states, in samples manufactured both with and without accelerators. The results showed that the accelerator without chloride was less effective than the one based on calcium chloride and that without doses of the accelerator, the effectiveness documented by the manufacturers was achieved.
文摘There are several previous studies on the association of vitamin E with prevention of stroke but the findings remain controversial.We have conducted a systematic review,meta-analysis together with trial sequential analysis of randomised controlled trials to evaluate the effect of vitamin E supplementation versus placebo/no vitamin E on the risk reduction of total,fatal,non-fatal,haemorrhagic and ischaemic stroke.Relevant studies were identified by searching online databases through Medline,PubMed and Cochrane Central Register of Controlled Trials.A total of 18 studies with 148016 participants were included in the analysis.There was no significant difference in the prevention of total stroke(RR(relative risk)=0.98,95% CI 0.92-1.04,p=0.57),fatal stroke(RR=0.96,95% CI 0.77-1.20,p=0.73)and non-fatal stroke(RR=0.96,95% CI 0.88-1.05,p=0.35).Subgroup analyses were performed under each category(total stroke,fatal stroke and non-fatal stroke)and included the following subgroups(types of prevention,source and dosage of vitamin E and vitamin E alone vs control).The findings in all subgroup analyses were statistically insignificant.In stroke subtypes analysis,vitamin E showed significant risk reduction in ischaemic stroke(RR=0.92,95% CI 0.85-0.99,p=0.04)but not in haemorrhagic stroke(RR=1.17,95%CI 0.98-1.39,p=0.08).However,the trial sequential analysis demonstrated that more studies were needed to control random errors.Limitations of this study include the following:trials design may not have provided sufficient power to detect a change in stroke outcomes,participants may have had different lifestyles or health issues,there were a limited number of studies available for subgroup analysis,studies were mostly done in developed countries,and the total sample size for all included studies was insufficient to obtain a meaningful result from meta-analysis.In conclusion,there is still a lack of statistically significant evidence of the effects of vitamin E on the risk reduction of stroke.Nevertheless,vitamin E may offer some benefi
基金Supported by A RCUK fellowship,EP/E500145/1,to Hay DCA grant from the Edinburgh Bioquarter,to Medine CNChina Scholarship Council,No.2010658022,to Zhou WL
文摘Human stem cells are scalable cell populations capable of cellular differentiation.This makes them a very attractive in vitro cellular resource and in theory provides unlimited amounts of primary cells.Such an approach has the potential to improve our understanding of human biology and treating disease.In the future it may be possible to deploy novel stem cell-based approaches to treat human liver diseases.In recent years,eff icient hepatic differentiation from human stem cells has been achieved by several research groups including our own.In this review we provide an overview of the f ield and discuss the future potential and limitations of stem cell technology.
基金supported by National Key R&D Program of China(No.2018YFC1315000/2018YFC1315004)RGC-CRF Hong Kong(C4039-19G)and RGCGRF Hong Kong(14163817).
文摘In a recent study in Nature,Kadosh et al.1 established a landmark relationship between the gut microbiome and host epigenetics in intestinal oncogenesis.They demonstrated the substantial plasticity of mutant p53 in WNT-driven tumorigenesis,and the crucial involvement of gut microbiome in modulating this plasticity.
文摘Objective： Focused Abdominal Sono graphy for Trauma （FAST） is widely used for the detection of intraperitoneal free fluids in patients suffering from blunt abdominal trauma （BAT）. This study aimed at assessing the diagnostic accuracy of this investigation in a designated trauma centre. Methods： This was a retrospective study of BAT pa tients over a 6 year period seen in a trauma centre in Hong Kong. FAST findings were compared with laparotomy, ab dominal computed tomography or autopsy findings, which served as the gold standard for presence of intraperi toneal free fluids. The patients who did not have FAST or gold standard confirmatory test performed, had preexisting peritoneal fluid, died at resuscitation or had imcomplete docu mentation of FAST findings were excluded. The performance of FAST was expressed as sensitivity, specificity, predictive values （PV）, likelihood ratios （LR） and accuracy. Results： FAST was performed in 302 patients and 153 of them were included in this analysis. The sensitivity, specificity, positive PV, negative PV, positive LR, negative LR and accuracy for FAST were respectively 50.0%, 97.3%, 87.0%, 84.6%, 18.8, 0.5 and 85.0%. FAST was found to be more sensitive in less severely injured patients and more specific in more severely injured patients. Conclusion： FAST is a reliable investigation in the initial assessment of BAT patients. The diagnostic values of FAST could be affected by the severity of injury and staff training is needed to further enhance its effective use.
