Wide bandgap perovskite solar cells(PSCs)have attracted significant attention because they can be applied to the top cells of tandem solar cells.However,high open-circuit voltage(V_(OC))deficit(>0.4 V)result from p...Wide bandgap perovskite solar cells(PSCs)have attracted significant attention because they can be applied to the top cells of tandem solar cells.However,high open-circuit voltage(V_(OC))deficit(>0.4 V)result from poor crystallization and high non-radiative recombination losses become a serious limitation in the pursuit of high performance.Here,the relevance between different Pbl_(2)proportions and performance parameters are revealed through analysis of surface morphology,residual stress,and photostability.The increase of Pbl_(2)proportion promotes crystal growth and reduces the work function of the perovskite film surface and promotes the energy level alignment with the carrier transport layer,which decreased the V_(OC)deficit.However,residual PbI_(2)exacerbated the stress level of perovskite film,and the resulting lattice disorder deteriorated the photostability of the device.Ultimately,after the synergistic passivation of residual PbI_(2)and PEAI,the V_(OC)achieves 1.266 V and V_(OC)deficit is less than 0.4 V,the record value in wide bandgap PSCs.展开更多
To improve the productivity of oil wells,perforation technology is usually used to improve the productivity of horizontal wells in oilfield exploitation.After the perforation operation,the perforation channel around t...To improve the productivity of oil wells,perforation technology is usually used to improve the productivity of horizontal wells in oilfield exploitation.After the perforation operation,the perforation channel around the wellbore will form a near-well high-permeability reservoir area with the penetration depth as the radius,that is,the formation has different permeability characteristics with the perforation depth as the dividing line.Generally,the permeability is measured by the permeability tester,but this approach has a high workload and limited application.In this paper,according to the reservoir characteristics of perforated horizontal wells,the reservoir is divided into two areas:the original reservoir area and the near-well high permeability reservoir area.Based on the theory of seepage mechanics and the formula of open hole productivity,the permeability calculation formula of near-well high permeability reservoir area with perforation parameters is deduced.According to the principle of seepage continuity,the seepage is regarded as the synthesis of two directions:the horizontal plane elliptic seepage field and the vertical plane radial seepage field,and the oil well productivity prediction model of the perforated horizontal well is established by partition.The model comparison demonstrates that the model is reasonable and feasible.To calculate and analyze the effect of oil well production and the law of influencing factors,actual production data of the oilfield are substituted into the oil well productivity formula.It can effectively guide the technical process design and effect prediction of perforated horizontal wells.展开更多
Leopard coral groupers(Plectropomus leopardus),commercially bred in South China,are a significant economical fish species.In this study,by means of quantitative real-time PCR(qRT-PCR)technology,we assessed the stabili...Leopard coral groupers(Plectropomus leopardus),commercially bred in South China,are a significant economical fish species.In this study,by means of quantitative real-time PCR(qRT-PCR)technology,we assessed the stability of six common reference genes expression and selected the appropriate reference genes in leopard coral groupers with or without Vibrio harveyi stimulation at different time points.These data produced by qRT-PCR was handled via the geNorm,NormFinder,and BestKeeper software.The results revealed all the examined reference genes had manifest tissue-specific expression in different tissues.Prior to V.harveyi stimulation,RPL13 gene was the appropriate reference gene among eleven tissue types(blood,spleen,hepatopancreas,kidney,stomach,gill,heart,skin,muscle,intestine,brain)in leopard coral groupers.Under V.harveyi stimulation,the most reliable reference genes varied from tissue to tissue and were closely hinged upon different time points.At 6-h post-bacterial injection,the appropriate reference genes in hepatopancreas,spleen,kidney,and gill were Actin,B2M,UBCE,and Actin,respectively.At 9-and 12-h post-bacterial injection,the appropriate reference genes in hepatopancreas,spleen,kidney,and gill were RPL13,Actin,Actin,and Actin,respectively.If one reference gene was preferable,RPL13,Actin,Actin,and Actin could be selected as the reference gene in hepatopancreas,spleen,kidney,and gill of leopard coral groupers after V.harveyi infection,respectively.Expression profiles of two target genes(IL-6 and NK-lysin)were used to further validate reliability of these selected appropriate candidates.This study will lay a solid foundation for the future research on qRTPCR analysis of gene expression in leopard coral groupers.展开更多
In order to overcome the typical limitations of numerical simulation methods used to estimate the production of low-permeability reservoirs,in this study,a new data-driven approach is proposed for the case of water-dr...In order to overcome the typical limitations of numerical simulation methods used to estimate the production of low-permeability reservoirs,in this study,a new data-driven approach is proposed for the case of water-driven hypo-permeable reservoirs.In particular,given the bottlenecks of traditional recurrent neural networks in handling time series data,a neural network with long and short-term memory is used for such a purpose.This method can reduce the time required to solve a large number of partial differential equations.As such,it can therefore significantly improve the efficiency in predicting the needed production performances.Practical examples about water-driven hypotonic reservoirs are provided to demonstrate the correctness of the method and its ability to meet the requirements for practical reservoir applications.展开更多
The development of socialist economy and market in China is rapid,which raises people’s demand for energy in daily life.The development of energy industry has,to a large extent,boosted the development of national eco...The development of socialist economy and market in China is rapid,which raises people’s demand for energy in daily life.The development of energy industry has,to a large extent,boosted the development of national economy.In the current society,in order to increase GDP in an all-round way,China should take full advantage of clean energy and economical energy in the development of energy.This thesis will analyze the energy situation and energy policies in China,in the hope of promoting the sustainable development in China.展开更多
With the increasing integration level of modern electronics,thermal management becomes an urgent issue for guaranteeing the work efficiency and lifespan of electronics.On the basis of intrinsic high thermal conductivi...With the increasing integration level of modern electronics,thermal management becomes an urgent issue for guaranteeing the work efficiency and lifespan of electronics.On the basis of intrinsic high thermal conductivity nature,highly ordered graphite and copper stripes are densely aligned in the silicone gel pads in vertical(VCuGr)and oblique(@15°CuGr)directions to couple the high thermal conductivity and mechanical softness.The wetting nature of liquid metal(LM)on the chemically treated Cu surface is utilized to form a LM layer on the two surfaces of thermal pads.The obtained LM-pad TIMs possessed ultrahigh through-plane thermal conductivity(VCuGr:71.4 W/(m K),@15°CuGr:62.5 W/(m K))under the normal packaging pressure.The thermal resistance decreased from 0.69 cm^(2) K/W to 0.25 cm^(2) K/W with the surface modification with LM.Theoretical simulation and practical thermal dissipation test results further demonstrate the excellent thermal management capability of these composites in high-power electronics.展开更多
Heat shock protein 90(Hsp90) is an appealing anticancer drug target that provoked a tremendous wave of investigations. Geldanamycin(GA) is the first identified Hsp90 inhibitor that exhibited potent anticancer activity...Heat shock protein 90(Hsp90) is an appealing anticancer drug target that provoked a tremendous wave of investigations. Geldanamycin(GA) is the first identified Hsp90 inhibitor that exhibited potent anticancer activity, but the off-target toxicity associated with the benzoquinone moiety hampered its clinical application. Until now, structure optimization of GA is still in need to fully exploit the therapeutic value of Hsp90. Due to the structural complexity and synthetic challenge of this compound family, conventional optimization is bound to be costly but high efficiency is expected to be reachable by combining the art of rational design and total synthesis. Described in this paper is our first attempt at this approach aiming at rational modification of the C6-position of GA. The binding affinities towards Hsp90 of compound 1(C6-ethyl) and 2(C6-methyl) were designed and predicted by using Discovery Studio. These compounds were synthesized and further subjected to a thorough in vitro biological evaluation. We found that compounds1 and 2 bind to Hsp90 protein with the IC_(50) of 34.26 nmol/L and 163.7 nmol/L, respectively. Both compounds showed broad-spectrum antitumor effects. Replacing by ethyl, compound 1 exhibited more potent bioactivity than positive control GA, such as in G2/M cell cycle arrest, cell apoptosis and client proteins degradations. The results firstly indicated that the docking study is able to provide a precise prediction of Hsp90 affinities of GA analogues, and the C6 substituent of GA is not erasable without affecting its biological activity.展开更多
Oxazolones are structural subunits in numerous natural products and designed molecules with substantial pharmacological properties.Here,a palladium-catalyzed chemodivergent regio-and enantioselective allylic alkylatio...Oxazolones are structural subunits in numerous natural products and designed molecules with substantial pharmacological properties.Here,a palladium-catalyzed chemodivergent regio-and enantioselective allylic alkylation of 4-or 5-substituted oxazol-2(3H)-ones with Morita-Baylis-Hillman(MBH)adducts has been developed using a spiroketal-based diphosphine as the ligand(50 examples).Interestingly,4-substituted oxazol-2(3H)-ones acted as a C-nucleophiles in the reaction to afford a range of chiral 4,5-substituted oxazol-2(3H)-ones in high yields(72-99%)with good to excellent chemo-,regio-,and enantioselectivities(C/N 95:5->99:1,b/l 91:9->99:1,85-98%ee).When a N-nucleophile was used under otherwise identical conditions,5-substituted oxazol-2(3H)-ones delivered a range of chiral 3,5-substituted oxazol-2(3H)-ones in high yields(68-98%)with good regio-and enantioselectivities(b/l 71:29-91:9,66-94%ee).The synthesis can be readily performed on gram scale under fairly low catalyst loadings,and the utility of the protocol was showcased in the facile transformation of the products into more elaborate chiral molecules.展开更多
Background:To investigate the prognosis and predictors for seizure control in epileptic patients in China.Methods:Eight hundred and twenty patients with epilepsy who visited Xuanwu Hospital from October 2017 to Januar...Background:To investigate the prognosis and predictors for seizure control in epileptic patients in China.Methods:Eight hundred and twenty patients with epilepsy who visited Xuanwu Hospital from October 2017 to January 2020,were enrolled.The clinical information of the patients was obtained by retrospectively reviewing medical records.Prognostic measures of seizure control included remission,relapse and occurrence of drug resistance.The relationship of prognosis of seizure control with factors such as demographics,clinical characteristics and initial electroencephalography(EEG)features was investigated.Results:A total of 503(61.3%)patients experienced a 1-year remission and 330(49.3%of 669)had a 2-year remission.Idiopathic type of epilepsy(P<0.001),normal EEG(P<0.05),number of antiepileptic drugs(P<0.05)and seizure frequency of<1/month(P<0.001)at the first arrival predicted a remission independently.Of the 503 patients who achieved a 1-year remission,184(36.6%)experienced a relapse,due to external reversible causes(58 patients)or with unknown reversible triggers(126 patients).No factors were found to be associated with a relapse(P>0.05).At the end of the study,322 patients(39.3%)developed drug resistance.The development of drug resistance was associated with the following factors:symptomatic aetiology of epilepsy,epileptiform abnormality in EEG,number of antiepileptic drugs and seizure frequency of≥1/month at first arrival(P<0.001).For symptomatic epilepsy,patients with meningitis/encephalitis(P=0.007)were more likely to develop drug-resistant epilepsy than these with other causes.Conclusions:Remission is a common process.The type of epilepsy(idiopathic or symptomatic),EEG features,seizure frequency and treatment history at first arrival are related to both remission and terminal drug resistance.Among various causes of symptomatic epilepsy,meningitis/encephalitis is associated with the worst prognosis of epilepsy.展开更多
Fire-induced pollutant dispersion under the influence of buoyancy in urban street canyons has attracted wide attention given its adverse impact on human health.This study analyzes the influences of fire source locatio...Fire-induced pollutant dispersion under the influence of buoyancy in urban street canyons has attracted wide attention given its adverse impact on human health.This study analyzes the influences of fire source location and crossflowing wind(perpendicular to the canyon centerline)on indoor and outdoor air pollutant dispersion in an idealized urban street canyon by employing large eddy simulation.Three fire scenarios are defined according to the transverse location of the fire source:near the windward building(scenario 1),in the middle of the canyon(scenario 2),and near the leeward building(scenario 3).Results show that a re-entrainment phenomenon appears when the wind velocity reaches a critical value in scenarios 1 and 2,but it doesn't occur in scenario 3.Fire source location significantly influences the critical re-entrainment velocity.The critical velocity in scenario 1 is approximate 1.2-1.5 m/s larger than that in scenario 2.When the heat release rate is large,the critical Fr numbers are less sensitive to changes in HRR,and remain approximately constant with values of 0.47(scenario 1)and 0.37(scenario 2).When the wind velocity is large,more compartments are expected to be affected in the upper floors in all of the three scenarios,and smoke is distributed in an inverted triangle within the buildings.The indoor/outdoor temperature and pollutant concentrations are also analyzed.Our findings can provide valuable information for both human and property safety in relation to urban street canyons and their surrounding buildings.展开更多
High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process,including the synthesis of boron/nickel containing precursors by precipitation reactions and subseq...High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process,including the synthesis of boron/nickel containing precursors by precipitation reactions and subsequent thermally catalytic chemical vapor deposition reactions.The influence of catalyst content and annealing temperature on the phase composition and microstructure of the products were investigated.The results show that it is difficult to exert the catalytic effect of nickel-based catalyst at low temperatures(<1400℃).At appropriate temperatures(1400-1500℃),highly crystalline boron nitride nanotubes with a length of more than 50 mm and a diameter of 50 nm are formed.The content of catalyst in the precursor mainly affects the morphology of the boron nitride product.If the content is too low,it is easy to form boron nitride particles;while high catalyst content can easily lead to catalyst aggregation and form a submicron one-dimensional boron nitride with unregular structure.Based on microstructural evolutions,phase changes,and thermodynamic analysis,the vapor-liquid-solid(V-L-S)growth mechanism of the tip growth mode dominates the formation of boron nitride nanotubes has also been verified.展开更多
基金the supports from the National Natural Science Foundation of China(Nos.62264012,62164009)Inner Mongolia Higher Education Research Project(No.NJZZ22343)+1 种基金Inner Mongolia University Research Foundation for Advanced Talents in 2021(No.10000-21311201/005)the Inner Mongolia Autonomous Region for Advanced Talents in 2020(No.12000-12102628)。
文摘Wide bandgap perovskite solar cells(PSCs)have attracted significant attention because they can be applied to the top cells of tandem solar cells.However,high open-circuit voltage(V_(OC))deficit(>0.4 V)result from poor crystallization and high non-radiative recombination losses become a serious limitation in the pursuit of high performance.Here,the relevance between different Pbl_(2)proportions and performance parameters are revealed through analysis of surface morphology,residual stress,and photostability.The increase of Pbl_(2)proportion promotes crystal growth and reduces the work function of the perovskite film surface and promotes the energy level alignment with the carrier transport layer,which decreased the V_(OC)deficit.However,residual PbI_(2)exacerbated the stress level of perovskite film,and the resulting lattice disorder deteriorated the photostability of the device.Ultimately,after the synergistic passivation of residual PbI_(2)and PEAI,the V_(OC)achieves 1.266 V and V_(OC)deficit is less than 0.4 V,the record value in wide bandgap PSCs.
文摘To improve the productivity of oil wells,perforation technology is usually used to improve the productivity of horizontal wells in oilfield exploitation.After the perforation operation,the perforation channel around the wellbore will form a near-well high-permeability reservoir area with the penetration depth as the radius,that is,the formation has different permeability characteristics with the perforation depth as the dividing line.Generally,the permeability is measured by the permeability tester,but this approach has a high workload and limited application.In this paper,according to the reservoir characteristics of perforated horizontal wells,the reservoir is divided into two areas:the original reservoir area and the near-well high permeability reservoir area.Based on the theory of seepage mechanics and the formula of open hole productivity,the permeability calculation formula of near-well high permeability reservoir area with perforation parameters is deduced.According to the principle of seepage continuity,the seepage is regarded as the synthesis of two directions:the horizontal plane elliptic seepage field and the vertical plane radial seepage field,and the oil well productivity prediction model of the perforated horizontal well is established by partition.The model comparison demonstrates that the model is reasonable and feasible.To calculate and analyze the effect of oil well production and the law of influencing factors,actual production data of the oilfield are substituted into the oil well productivity formula.It can effectively guide the technical process design and effect prediction of perforated horizontal wells.
基金Supported by the Natural Science Foundation of Hainan Province (Nos. 320QN212, 2019RC078)the Key Research Project of Hainan Province (No. ZDKJ2019011)
文摘Leopard coral groupers(Plectropomus leopardus),commercially bred in South China,are a significant economical fish species.In this study,by means of quantitative real-time PCR(qRT-PCR)technology,we assessed the stability of six common reference genes expression and selected the appropriate reference genes in leopard coral groupers with or without Vibrio harveyi stimulation at different time points.These data produced by qRT-PCR was handled via the geNorm,NormFinder,and BestKeeper software.The results revealed all the examined reference genes had manifest tissue-specific expression in different tissues.Prior to V.harveyi stimulation,RPL13 gene was the appropriate reference gene among eleven tissue types(blood,spleen,hepatopancreas,kidney,stomach,gill,heart,skin,muscle,intestine,brain)in leopard coral groupers.Under V.harveyi stimulation,the most reliable reference genes varied from tissue to tissue and were closely hinged upon different time points.At 6-h post-bacterial injection,the appropriate reference genes in hepatopancreas,spleen,kidney,and gill were Actin,B2M,UBCE,and Actin,respectively.At 9-and 12-h post-bacterial injection,the appropriate reference genes in hepatopancreas,spleen,kidney,and gill were RPL13,Actin,Actin,and Actin,respectively.If one reference gene was preferable,RPL13,Actin,Actin,and Actin could be selected as the reference gene in hepatopancreas,spleen,kidney,and gill of leopard coral groupers after V.harveyi infection,respectively.Expression profiles of two target genes(IL-6 and NK-lysin)were used to further validate reliability of these selected appropriate candidates.This study will lay a solid foundation for the future research on qRTPCR analysis of gene expression in leopard coral groupers.
文摘In order to overcome the typical limitations of numerical simulation methods used to estimate the production of low-permeability reservoirs,in this study,a new data-driven approach is proposed for the case of water-driven hypo-permeable reservoirs.In particular,given the bottlenecks of traditional recurrent neural networks in handling time series data,a neural network with long and short-term memory is used for such a purpose.This method can reduce the time required to solve a large number of partial differential equations.As such,it can therefore significantly improve the efficiency in predicting the needed production performances.Practical examples about water-driven hypotonic reservoirs are provided to demonstrate the correctness of the method and its ability to meet the requirements for practical reservoir applications.
文摘The development of socialist economy and market in China is rapid,which raises people’s demand for energy in daily life.The development of energy industry has,to a large extent,boosted the development of national economy.In the current society,in order to increase GDP in an all-round way,China should take full advantage of clean energy and economical energy in the development of energy.This thesis will analyze the energy situation and energy policies in China,in the hope of promoting the sustainable development in China.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.11204097 and U1530120).
文摘With the increasing integration level of modern electronics,thermal management becomes an urgent issue for guaranteeing the work efficiency and lifespan of electronics.On the basis of intrinsic high thermal conductivity nature,highly ordered graphite and copper stripes are densely aligned in the silicone gel pads in vertical(VCuGr)and oblique(@15°CuGr)directions to couple the high thermal conductivity and mechanical softness.The wetting nature of liquid metal(LM)on the chemically treated Cu surface is utilized to form a LM layer on the two surfaces of thermal pads.The obtained LM-pad TIMs possessed ultrahigh through-plane thermal conductivity(VCuGr:71.4 W/(m K),@15°CuGr:62.5 W/(m K))under the normal packaging pressure.The thermal resistance decreased from 0.69 cm^(2) K/W to 0.25 cm^(2) K/W with the surface modification with LM.Theoretical simulation and practical thermal dissipation test results further demonstrate the excellent thermal management capability of these composites in high-power electronics.
基金supported by the CAMS Innovation Fund for Medical Sciences (Nos. CIFMS 2016-I2M-3–009 and CIFMS 2017I2M-3–011)the National Natural Science Foundation of China (No. 21272279)。
文摘Heat shock protein 90(Hsp90) is an appealing anticancer drug target that provoked a tremendous wave of investigations. Geldanamycin(GA) is the first identified Hsp90 inhibitor that exhibited potent anticancer activity, but the off-target toxicity associated with the benzoquinone moiety hampered its clinical application. Until now, structure optimization of GA is still in need to fully exploit the therapeutic value of Hsp90. Due to the structural complexity and synthetic challenge of this compound family, conventional optimization is bound to be costly but high efficiency is expected to be reachable by combining the art of rational design and total synthesis. Described in this paper is our first attempt at this approach aiming at rational modification of the C6-position of GA. The binding affinities towards Hsp90 of compound 1(C6-ethyl) and 2(C6-methyl) were designed and predicted by using Discovery Studio. These compounds were synthesized and further subjected to a thorough in vitro biological evaluation. We found that compounds1 and 2 bind to Hsp90 protein with the IC_(50) of 34.26 nmol/L and 163.7 nmol/L, respectively. Both compounds showed broad-spectrum antitumor effects. Replacing by ethyl, compound 1 exhibited more potent bioactivity than positive control GA, such as in G2/M cell cycle arrest, cell apoptosis and client proteins degradations. The results firstly indicated that the docking study is able to provide a precise prediction of Hsp90 affinities of GA analogues, and the C6 substituent of GA is not erasable without affecting its biological activity.
基金financial supports from the National Key R&D Program of China(grant nos.2022YFA1503702 and 2021YFF0701602)NSFC(grant nos.22231011 and 22271303).
文摘Oxazolones are structural subunits in numerous natural products and designed molecules with substantial pharmacological properties.Here,a palladium-catalyzed chemodivergent regio-and enantioselective allylic alkylation of 4-or 5-substituted oxazol-2(3H)-ones with Morita-Baylis-Hillman(MBH)adducts has been developed using a spiroketal-based diphosphine as the ligand(50 examples).Interestingly,4-substituted oxazol-2(3H)-ones acted as a C-nucleophiles in the reaction to afford a range of chiral 4,5-substituted oxazol-2(3H)-ones in high yields(72-99%)with good to excellent chemo-,regio-,and enantioselectivities(C/N 95:5->99:1,b/l 91:9->99:1,85-98%ee).When a N-nucleophile was used under otherwise identical conditions,5-substituted oxazol-2(3H)-ones delivered a range of chiral 3,5-substituted oxazol-2(3H)-ones in high yields(68-98%)with good regio-and enantioselectivities(b/l 71:29-91:9,66-94%ee).The synthesis can be readily performed on gram scale under fairly low catalyst loadings,and the utility of the protocol was showcased in the facile transformation of the products into more elaborate chiral molecules.
基金This work was supported by the National Natural Science Foundation of China(81571267).
文摘Background:To investigate the prognosis and predictors for seizure control in epileptic patients in China.Methods:Eight hundred and twenty patients with epilepsy who visited Xuanwu Hospital from October 2017 to January 2020,were enrolled.The clinical information of the patients was obtained by retrospectively reviewing medical records.Prognostic measures of seizure control included remission,relapse and occurrence of drug resistance.The relationship of prognosis of seizure control with factors such as demographics,clinical characteristics and initial electroencephalography(EEG)features was investigated.Results:A total of 503(61.3%)patients experienced a 1-year remission and 330(49.3%of 669)had a 2-year remission.Idiopathic type of epilepsy(P<0.001),normal EEG(P<0.05),number of antiepileptic drugs(P<0.05)and seizure frequency of<1/month(P<0.001)at the first arrival predicted a remission independently.Of the 503 patients who achieved a 1-year remission,184(36.6%)experienced a relapse,due to external reversible causes(58 patients)or with unknown reversible triggers(126 patients).No factors were found to be associated with a relapse(P>0.05).At the end of the study,322 patients(39.3%)developed drug resistance.The development of drug resistance was associated with the following factors:symptomatic aetiology of epilepsy,epileptiform abnormality in EEG,number of antiepileptic drugs and seizure frequency of≥1/month at first arrival(P<0.001).For symptomatic epilepsy,patients with meningitis/encephalitis(P=0.007)were more likely to develop drug-resistant epilepsy than these with other causes.Conclusions:Remission is a common process.The type of epilepsy(idiopathic or symptomatic),EEG features,seizure frequency and treatment history at first arrival are related to both remission and terminal drug resistance.Among various causes of symptomatic epilepsy,meningitis/encephalitis is associated with the worst prognosis of epilepsy.
基金This work was sponsored by the National Natural Science Foundation of Shandong Province(No.ZR2020QE279)Shandong Jianzhu University Doctoral Fund(No.X19055Z)Plan of Guidance and Cultivation for Young Innovative Talents of Shandong Province.
文摘Fire-induced pollutant dispersion under the influence of buoyancy in urban street canyons has attracted wide attention given its adverse impact on human health.This study analyzes the influences of fire source location and crossflowing wind(perpendicular to the canyon centerline)on indoor and outdoor air pollutant dispersion in an idealized urban street canyon by employing large eddy simulation.Three fire scenarios are defined according to the transverse location of the fire source:near the windward building(scenario 1),in the middle of the canyon(scenario 2),and near the leeward building(scenario 3).Results show that a re-entrainment phenomenon appears when the wind velocity reaches a critical value in scenarios 1 and 2,but it doesn't occur in scenario 3.Fire source location significantly influences the critical re-entrainment velocity.The critical velocity in scenario 1 is approximate 1.2-1.5 m/s larger than that in scenario 2.When the heat release rate is large,the critical Fr numbers are less sensitive to changes in HRR,and remain approximately constant with values of 0.47(scenario 1)and 0.37(scenario 2).When the wind velocity is large,more compartments are expected to be affected in the upper floors in all of the three scenarios,and smoke is distributed in an inverted triangle within the buildings.The indoor/outdoor temperature and pollutant concentrations are also analyzed.Our findings can provide valuable information for both human and property safety in relation to urban street canyons and their surrounding buildings.
基金supported by the National Natural Science Foundation of China,China(52002293)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology,China(2021QNRC001,YESS20210230)+3 种基金the Open Project of State Key Laboratory of Advanced Technology for Materials Synthesis and Processing of Wuhan University of Technology,China(21-KF-25)the Innovative Project of Key Laboratory of Green Chemical Engineering Process of Ministry of Education(GCX202106)Science Research Fund(K202029)College Students Innovation and Entrepreneurship Training Program(S202110490021)of Wuhan Institute of Technology,China.
文摘High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process,including the synthesis of boron/nickel containing precursors by precipitation reactions and subsequent thermally catalytic chemical vapor deposition reactions.The influence of catalyst content and annealing temperature on the phase composition and microstructure of the products were investigated.The results show that it is difficult to exert the catalytic effect of nickel-based catalyst at low temperatures(<1400℃).At appropriate temperatures(1400-1500℃),highly crystalline boron nitride nanotubes with a length of more than 50 mm and a diameter of 50 nm are formed.The content of catalyst in the precursor mainly affects the morphology of the boron nitride product.If the content is too low,it is easy to form boron nitride particles;while high catalyst content can easily lead to catalyst aggregation and form a submicron one-dimensional boron nitride with unregular structure.Based on microstructural evolutions,phase changes,and thermodynamic analysis,the vapor-liquid-solid(V-L-S)growth mechanism of the tip growth mode dominates the formation of boron nitride nanotubes has also been verified.
