Melt treatment is well known to have an important influence on the properties of metallic glasses(MGs).However,for the MGs quenched from different melt temperatures with a quartz tube,the underlying physical origin re...Melt treatment is well known to have an important influence on the properties of metallic glasses(MGs).However,for the MGs quenched from different melt temperatures with a quartz tube,the underlying physical origin responsible for the variation of properties remains poorly understood.In the present work,we systematically studied the influence of melt treatment on the thermal properties of a Zr50Cu36Al14 glass-forming alloy and unveiled the microscopic origins.Specifically,we quenched the melt at different temperatures ranging from 1.1Tl to 1.5Tl(Tl is the liquidus temperature)to obtain melt-spun MG ribbons and investigated the variation of thermal properties of the MGs upon heating.We found that glass transition temperature,Tg,increases by as much as 36 K,and the supercooled liquid region disappears in the curve of differential scanning calorimetry when the melt is quenched at a high temperature up to 1.5Tl.The careful chemical analyses indicate that the change in glass transition behavior originates from the incorporation of oxygen and silicon in the molten alloys.The incorporated oxygen and silicon can both enhance the interactions between atoms,which renders the cooperative rearrangements of atoms difficult,and thus enhances the kinetic stability of the MGs.展开更多
Objective:In B-cell acute lymphoblastic leukemia(B-ALL),current intensive chemotherapies for adult patients fail to achieve durable responses in more than 50%of cases,underscoring the urgent need for new therapeutic r...Objective:In B-cell acute lymphoblastic leukemia(B-ALL),current intensive chemotherapies for adult patients fail to achieve durable responses in more than 50%of cases,underscoring the urgent need for new therapeutic regimens for this patient population.The present study aimed to determine whether HZX-02-059,a novel dual-target inhibitor targeting both phosphatidylinositol-3-phosphate 5-kinase(PIKfyve)and tubulin,is lethal to B-ALL cells and is a potential therapeutic for B-ALL patients.Methods:Cell proliferation,vacuolization,apoptosis,cell cycle,and in-vivo tumor growth were evaluated.In addition,Genome-wide RNA-sequencing studies were conducted to elucidate the mechanisms of action underlying the anti-leukemia activity of HZX-02-059 in B-ALL.Results:HZX-02-059 was found to inhibit cell proliferation,induce vacuolization,promote apoptosis,block the cell cycle,and reduce in-vivo tumor growth.Downregulation of the p53 pathway and suppression of the phosphoinositide 3-kinase(PI3K)/AKT pathway and the downstream transcription factors c-Myc and NF-κB were responsible for these observations.Conclusion:Overall,these findings suggest that HZX-02-059 is a promising agent for the treatment of B-ALL patients resistant to conventional therapies.展开更多
Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years.Among them is the Crx Tey family...Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years.Among them is the Crx Tey family,the magnetism of which can persist above room temperature,thus providing an ideal system for potential spintronic applications.Here we report the synthesis of a new compound,Cr_(0.82)Te,which demonstrates a record-high topological Hall effect at room temperature in this family.Cr_(0.82)Te displays soft ferromagnetism below the Curie temperature of 340 K.The magnetic measurement shows an obvious magneto-crystalline anisotropy with the easy axis located in the ab plane.The anomalous Hall effect can be well explained by a dominating skew scattering mechanism.Intriguing,after removing the normal Hall effect and anomalous Hall effect,a topological Hall effect can be observed up to 300 K and reaches up to 1.14μΩ·cm at 10 K,which is superior to most topological magnetic structural materials.This giant topological Hall effect possibly originates from the noncoplanar spin configuration during the spin flop process.Our work extends a new Cr_(x)Te_(y) system with topological non-trivial magnetic structure and broad prospects for spintronics applications in the future.展开更多
BACKGROUND Hepatocellular carcinoma(HCC)is the most common type of liver cancer and has a high risk of invasion and metastasis along with a poor prognosis.AIM To investigate the independent predictive markers for dise...BACKGROUND Hepatocellular carcinoma(HCC)is the most common type of liver cancer and has a high risk of invasion and metastasis along with a poor prognosis.AIM To investigate the independent predictive markers for disease-free survival(DFS)in patients with HCC and establish a trustworthy nomogram.METHODS In this study,445 patients who were hospitalized in The First Affiliated Hospital of Anhui Medical College between December 2009 and December 2014 were retrospectively examined.The survival curve was plotted using the Kaplan–Meier method and survival was determined using the log-rank test.To identify the prognostic variables,multivariate Cox regression analyses were carried out.To predict the DFS in patients with HCC,a nomogram was created.C-indices and receiver operator characteristic curves were used to evaluate the nomogram’s performance.Decision curve analysis(DCA)was used to evaluate the clinical application value of the nomogram.RESULTS Longer DFS was observed in patients with the following characteristics:elderly,I–II stage,and no history of hepatitis B.The calibration curve showed that this nomogram was reliable and had a higher area under the curve value than the tumor node metastasis(TNM)stage.Moreover,the DCA curve revealed that the nomogram had good clinical applicability in predicting 3-and 5-year DFS in HCC patients after surgery.CONCLUSION Age,TNM stage,and history of hepatitis B infection were independent factors for DFS in HCC patients,and a novel nomogram for DFS of HCC patients was created and validated.展开更多
Zirconium-based metallic glasses(Zr-MGs)are demonstrated to exhibit high mechanical strength,low elastic modulus and excellent biocompatibility,making them promising materials for endosseous implants.Meanwhile,tantalu...Zirconium-based metallic glasses(Zr-MGs)are demonstrated to exhibit high mechanical strength,low elastic modulus and excellent biocompatibility,making them promising materials for endosseous implants.Meanwhile,tantalum(Ta)is also well known for its ideal corrosion resistance and biological effects.However,the metal has an elastic modulus as high as 186 GPa which is not comparable to the natural bone(10–30 GPa),and it also has a relative high cost.Here,to fully exploit the advantages of Ta as endosseous implants,a small amount of Ta(as low as 3 at.%)was successfully added into a Zr-MG to generate an advanced functional endosseous implant,Zr58Cu25Al14Ta3 MG,with superior comprehensive properties.Upon carefully dissecting the atomic structure and surface chemistry,the results show that amorphization of Ta enables the uniform distribution in material surface,leading to a significantly improved chemical stability and extensive material-cell contact regulation.Systematical analyses on the immunological,angiogenesis and osteogenesis capability of the material are carried out utilizing the next-generation sequencing,revealing that Zr_(58)Cu_(25)Al_(14)Ta_(3)MG can regulate angiogenesis through VEGF signaling pathway and osteogenesis via BMP signaling pathway.Animal experiment further confirms a sound osseointegration of Zr_(58)Cu_(25)Al_(14)Ta_(3)MG in achieving better bone-implant-contact and inducing faster periimplant bone formation.展开更多
采用机械共混法,以导电炭黑(CCB)、天然橡胶(NR)、环氧化天然橡胶(ENR)以及甲基丙烯酸甲酯接枝天然橡胶(MGNR)为原料,制备了复合材料NR/CCB、ENR/CCB、MGNR/CCB、NR/ENR/CCB、NR/MGNR/CCB。研究结果表明,CCB粒子网络在MGNR中比在ENR中...采用机械共混法,以导电炭黑(CCB)、天然橡胶(NR)、环氧化天然橡胶(ENR)以及甲基丙烯酸甲酯接枝天然橡胶(MGNR)为原料,制备了复合材料NR/CCB、ENR/CCB、MGNR/CCB、NR/ENR/CCB、NR/MGNR/CCB。研究结果表明,CCB粒子网络在MGNR中比在ENR中的分散性好,三元共混改性可以进一步提高CCB网络的完整性。在5种复合材料中,NR/ENR/CCB复合材料的有效吸收频宽最宽(3.20 GHz),NR/MGNR/CCB的吸收性能最好(-42.8 d B)。与天然橡胶相比,环氧化改性具有拓宽复合材料有效吸收带宽的作用(拓频),甲基丙烯酸甲酯接枝改性可以增强吸波效能(增效)。结合电磁参数,讨论了复合材料可能的吸波机理。展开更多
近年来,邮轮行业发展突飞猛进,但随之而来的航运污染问题也不容小觑。国际海事组织设立了排放控制区(Emission Control Area,简称ECA)以限制船舶硫排放,包括邮轮在内的所有船舶在ECA内均需使用昂贵的低硫油,这就使得船舶航行方案需要进...近年来,邮轮行业发展突飞猛进,但随之而来的航运污染问题也不容小觑。国际海事组织设立了排放控制区(Emission Control Area,简称ECA)以限制船舶硫排放,包括邮轮在内的所有船舶在ECA内均需使用昂贵的低硫油,这就使得船舶航行方案需要进行重新规划。本文提出了一个有到港时间限制的邮轮航线和速度优化模型,优化船舶在ECA内外的航线及速度,以最小化总燃油成本。同时引用西北大西洋沿岸一条代表性的邮轮航线,通过计算决策出合理的航行方案,并评估ECA对航运的影响,证明模型的有效性和实用性。展开更多
BACKGROUND: Airway management in intensive care unit(ICU) patients is challenging. The aim of this study was to compare the rate of successful first-pass intubation in the ICU by using the direct laryngoscopy(DL) and ...BACKGROUND: Airway management in intensive care unit(ICU) patients is challenging. The aim of this study was to compare the rate of successful first-pass intubation in the ICU by using the direct laryngoscopy(DL) and that by using the video laryngoscopy(VL).METHODS: A randomized, non-blinded trial comparing first-pass success rate of intubation between VL and DL was performed. Patients were recruited in the period from August 2014 to August 2016. All physicians working at ICU received hands-on training in the use of the video and direct laryngoscope. The primary outcome measure was the first-pass intubation success. RESULTS: A total of 163 ICU patients underwent intubation during the study period(81 patients in VL group and 82 in DL group). The rate of successful first-pass intubation was not significantly different between the VL and the DL group(67.9% vs. 69.5%, P=0.824). Moreover, the overall intubation success and total number of attempts to achieve intubation success did not differ between the two groups. In patients with successful first-pass intubation, the median duration of the intubation procedure did not differ between the two groups. The Cormack-Lehane grades and the percentage of glottic opening score were similar, and no significant differences were found between the two groups. There were no statistical differences between the VL and the DL group in intubation complications(all P>0.05). CONCLUSION: Among ICU patients requiring intubation, there was no significant difference in the rate of successful first-pass intubation between VL and DL.展开更多
The cycloaddition between CO_(2)and epoxides to produce cyclic carbonate is an attractive and efficiency pathway for the utilization of CO_(2)as C1 source.The development of catalyst to mediate cycloaddition between C...The cycloaddition between CO_(2)and epoxides to produce cyclic carbonate is an attractive and efficiency pathway for the utilization of CO_(2)as C1 source.The development of catalyst to mediate cycloaddition between CO_(2)and epoxides at low temperature and pressure is still a challenge.Herein,a series of polypyrazoles with glass transition temperature(T_(g))in the range of 42.3-52.5℃ were synthesized and served as catalyst to mediate the cycloaddition of CO_(2)and epoxides by the assistant of tetrabutylammonium bromide.The catalytic behaviors of polypyrazole on the model cycloaddition of CO_(2)to epichlorohydrin,including the reaction parameters optimization and versatility were investigated in detail,and excellent yield(99.9%)and selectivity(99%)were obtained under the optimized reaction conditions of70℃ and 1.0 MPa for 6.0 h.Noteworthily,the polypyrazole acts as homogeneous catalyst during reaction(higher than T_(g)).And under room temperature,polypyrazoles can be easily separated and recovered,which is a promising feature of a heterogeneous catalyst.Furthermore,the reaction mechanism was proposed.The DFT calculation suggested that the formation of hydrogen bond between pyrazole and epoxide greatly reduced the energy barrier,which play an important role in promoting CO_(2)cycloaddition.展开更多
To support and serve engineering design, creative design based on knowledge management is proposed. The key knowledge factors of creative design are analyzed and discussed, and knowledge extraction tools are utilized ...To support and serve engineering design, creative design based on knowledge management is proposed. The key knowledge factors of creative design are analyzed and discussed, and knowledge extraction tools are utilized to distill the important knowledge to serve for knowledge resource of creative design. The implementation of creative design mode is described and executed, which can promote the intelligent asset of the enterprise and shorten the period of creative design. With this study, design afflatus and conceptual design can be achieved expediently and effectively.展开更多
This paper describes a Least Squares (LS) channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error (MSE) of the LS channel estimation, and ...This paper describes a Least Squares (LS) channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error (MSE) of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio (SNR). To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.展开更多
基金The work was financially supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0703600,2021YFA0716302,and 2021YFA0718703)the National Natural Science Foundation of China(Grant Nos.51825104 and 52192602)China Postdoctoral Science Foundation(Grant No.2022T150691).
文摘Melt treatment is well known to have an important influence on the properties of metallic glasses(MGs).However,for the MGs quenched from different melt temperatures with a quartz tube,the underlying physical origin responsible for the variation of properties remains poorly understood.In the present work,we systematically studied the influence of melt treatment on the thermal properties of a Zr50Cu36Al14 glass-forming alloy and unveiled the microscopic origins.Specifically,we quenched the melt at different temperatures ranging from 1.1Tl to 1.5Tl(Tl is the liquidus temperature)to obtain melt-spun MG ribbons and investigated the variation of thermal properties of the MGs upon heating.We found that glass transition temperature,Tg,increases by as much as 36 K,and the supercooled liquid region disappears in the curve of differential scanning calorimetry when the melt is quenched at a high temperature up to 1.5Tl.The careful chemical analyses indicate that the change in glass transition behavior originates from the incorporation of oxygen and silicon in the molten alloys.The incorporated oxygen and silicon can both enhance the interactions between atoms,which renders the cooperative rearrangements of atoms difficult,and thus enhances the kinetic stability of the MGs.
基金funded by the National Natural Science Foundation of China(No.81770126,No.81900160,No.81800163,No.22025702,and No.91853203)the Fujian Natural Science Foundation of China(No.2020J011246 and No.2021J011359)+2 种基金the Foundation of Health and Family Planning Commission of Fujian Province of China(No.2020GGB054)the Xiamen Municipal Bureau of Science and Technology(No.3502Z20209003)the Fundamental Research Funds for the Central Universities of China(No.20720190101).
文摘Objective:In B-cell acute lymphoblastic leukemia(B-ALL),current intensive chemotherapies for adult patients fail to achieve durable responses in more than 50%of cases,underscoring the urgent need for new therapeutic regimens for this patient population.The present study aimed to determine whether HZX-02-059,a novel dual-target inhibitor targeting both phosphatidylinositol-3-phosphate 5-kinase(PIKfyve)and tubulin,is lethal to B-ALL cells and is a potential therapeutic for B-ALL patients.Methods:Cell proliferation,vacuolization,apoptosis,cell cycle,and in-vivo tumor growth were evaluated.In addition,Genome-wide RNA-sequencing studies were conducted to elucidate the mechanisms of action underlying the anti-leukemia activity of HZX-02-059 in B-ALL.Results:HZX-02-059 was found to inhibit cell proliferation,induce vacuolization,promote apoptosis,block the cell cycle,and reduce in-vivo tumor growth.Downregulation of the p53 pathway and suppression of the phosphoinositide 3-kinase(PI3K)/AKT pathway and the downstream transcription factors c-Myc and NF-κB were responsible for these observations.Conclusion:Overall,these findings suggest that HZX-02-059 is a promising agent for the treatment of B-ALL patients resistant to conventional therapies.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1602603)the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)+1 种基金the National Natural Science Foundation of China(Grant No.12104459)the Excellent Program of Hefei Science Center CAS(Grant No.2021HSC-CIP016)。
文摘Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years.Among them is the Crx Tey family,the magnetism of which can persist above room temperature,thus providing an ideal system for potential spintronic applications.Here we report the synthesis of a new compound,Cr_(0.82)Te,which demonstrates a record-high topological Hall effect at room temperature in this family.Cr_(0.82)Te displays soft ferromagnetism below the Curie temperature of 340 K.The magnetic measurement shows an obvious magneto-crystalline anisotropy with the easy axis located in the ab plane.The anomalous Hall effect can be well explained by a dominating skew scattering mechanism.Intriguing,after removing the normal Hall effect and anomalous Hall effect,a topological Hall effect can be observed up to 300 K and reaches up to 1.14μΩ·cm at 10 K,which is superior to most topological magnetic structural materials.This giant topological Hall effect possibly originates from the noncoplanar spin configuration during the spin flop process.Our work extends a new Cr_(x)Te_(y) system with topological non-trivial magnetic structure and broad prospects for spintronics applications in the future.
基金Supported by Research Fund Project of Anhui Institute of Translational Medicine,No.2021zhyx-C54Foundation of Anhui Medical University,No.2019xkj146National and Provincial Key Specialty Construction Plan,No.Z155080000004。
文摘BACKGROUND Hepatocellular carcinoma(HCC)is the most common type of liver cancer and has a high risk of invasion and metastasis along with a poor prognosis.AIM To investigate the independent predictive markers for disease-free survival(DFS)in patients with HCC and establish a trustworthy nomogram.METHODS In this study,445 patients who were hospitalized in The First Affiliated Hospital of Anhui Medical College between December 2009 and December 2014 were retrospectively examined.The survival curve was plotted using the Kaplan–Meier method and survival was determined using the log-rank test.To identify the prognostic variables,multivariate Cox regression analyses were carried out.To predict the DFS in patients with HCC,a nomogram was created.C-indices and receiver operator characteristic curves were used to evaluate the nomogram’s performance.Decision curve analysis(DCA)was used to evaluate the clinical application value of the nomogram.RESULTS Longer DFS was observed in patients with the following characteristics:elderly,I–II stage,and no history of hepatitis B.The calibration curve showed that this nomogram was reliable and had a higher area under the curve value than the tumor node metastasis(TNM)stage.Moreover,the DCA curve revealed that the nomogram had good clinical applicability in predicting 3-and 5-year DFS in HCC patients after surgery.CONCLUSION Age,TNM stage,and history of hepatitis B infection were independent factors for DFS in HCC patients,and a novel nomogram for DFS of HCC patients was created and validated.
基金supported by the National Natural Science Foundation of China(52035001)National Key R&D Program of China(2019YFB1706904)+3 种基金Beijing Training Project for the Leading Talents in S&T(Z191100006119022)National Key Research and Development Plan(2018YFA0703603)National Science 535 Foundation of China(52192602)Youth Fund of the National Natural Science Foundation of China(82201125).
文摘Zirconium-based metallic glasses(Zr-MGs)are demonstrated to exhibit high mechanical strength,low elastic modulus and excellent biocompatibility,making them promising materials for endosseous implants.Meanwhile,tantalum(Ta)is also well known for its ideal corrosion resistance and biological effects.However,the metal has an elastic modulus as high as 186 GPa which is not comparable to the natural bone(10–30 GPa),and it also has a relative high cost.Here,to fully exploit the advantages of Ta as endosseous implants,a small amount of Ta(as low as 3 at.%)was successfully added into a Zr-MG to generate an advanced functional endosseous implant,Zr58Cu25Al14Ta3 MG,with superior comprehensive properties.Upon carefully dissecting the atomic structure and surface chemistry,the results show that amorphization of Ta enables the uniform distribution in material surface,leading to a significantly improved chemical stability and extensive material-cell contact regulation.Systematical analyses on the immunological,angiogenesis and osteogenesis capability of the material are carried out utilizing the next-generation sequencing,revealing that Zr_(58)Cu_(25)Al_(14)Ta_(3)MG can regulate angiogenesis through VEGF signaling pathway and osteogenesis via BMP signaling pathway.Animal experiment further confirms a sound osseointegration of Zr_(58)Cu_(25)Al_(14)Ta_(3)MG in achieving better bone-implant-contact and inducing faster periimplant bone formation.
文摘采用机械共混法,以导电炭黑(CCB)、天然橡胶(NR)、环氧化天然橡胶(ENR)以及甲基丙烯酸甲酯接枝天然橡胶(MGNR)为原料,制备了复合材料NR/CCB、ENR/CCB、MGNR/CCB、NR/ENR/CCB、NR/MGNR/CCB。研究结果表明,CCB粒子网络在MGNR中比在ENR中的分散性好,三元共混改性可以进一步提高CCB网络的完整性。在5种复合材料中,NR/ENR/CCB复合材料的有效吸收频宽最宽(3.20 GHz),NR/MGNR/CCB的吸收性能最好(-42.8 d B)。与天然橡胶相比,环氧化改性具有拓宽复合材料有效吸收带宽的作用(拓频),甲基丙烯酸甲酯接枝改性可以增强吸波效能(增效)。结合电磁参数,讨论了复合材料可能的吸波机理。
文摘近年来,邮轮行业发展突飞猛进,但随之而来的航运污染问题也不容小觑。国际海事组织设立了排放控制区(Emission Control Area,简称ECA)以限制船舶硫排放,包括邮轮在内的所有船舶在ECA内均需使用昂贵的低硫油,这就使得船舶航行方案需要进行重新规划。本文提出了一个有到港时间限制的邮轮航线和速度优化模型,优化船舶在ECA内外的航线及速度,以最小化总燃油成本。同时引用西北大西洋沿岸一条代表性的邮轮航线,通过计算决策出合理的航行方案,并评估ECA对航运的影响,证明模型的有效性和实用性。
文摘BACKGROUND: Airway management in intensive care unit(ICU) patients is challenging. The aim of this study was to compare the rate of successful first-pass intubation in the ICU by using the direct laryngoscopy(DL) and that by using the video laryngoscopy(VL).METHODS: A randomized, non-blinded trial comparing first-pass success rate of intubation between VL and DL was performed. Patients were recruited in the period from August 2014 to August 2016. All physicians working at ICU received hands-on training in the use of the video and direct laryngoscope. The primary outcome measure was the first-pass intubation success. RESULTS: A total of 163 ICU patients underwent intubation during the study period(81 patients in VL group and 82 in DL group). The rate of successful first-pass intubation was not significantly different between the VL and the DL group(67.9% vs. 69.5%, P=0.824). Moreover, the overall intubation success and total number of attempts to achieve intubation success did not differ between the two groups. In patients with successful first-pass intubation, the median duration of the intubation procedure did not differ between the two groups. The Cormack-Lehane grades and the percentage of glottic opening score were similar, and no significant differences were found between the two groups. There were no statistical differences between the VL and the DL group in intubation complications(all P>0.05). CONCLUSION: Among ICU patients requiring intubation, there was no significant difference in the rate of successful first-pass intubation between VL and DL.
基金financially supported by the National Natural Science Foundation of China(21504025)the Natural Science Foundation of Fujian Province(2019J05040)+4 种基金Fujian Provincial Department of Education(JT180038)Key Program of Qingyuan Innovation Laboratory(00221003)Fuzhou University Testing Fund of precious apparatus(2021T022)Talent Program(GXRC18041)Higher Education Disciplinary Innovation Program(‘111’Program)of Fuzhou University。
文摘The cycloaddition between CO_(2)and epoxides to produce cyclic carbonate is an attractive and efficiency pathway for the utilization of CO_(2)as C1 source.The development of catalyst to mediate cycloaddition between CO_(2)and epoxides at low temperature and pressure is still a challenge.Herein,a series of polypyrazoles with glass transition temperature(T_(g))in the range of 42.3-52.5℃ were synthesized and served as catalyst to mediate the cycloaddition of CO_(2)and epoxides by the assistant of tetrabutylammonium bromide.The catalytic behaviors of polypyrazole on the model cycloaddition of CO_(2)to epichlorohydrin,including the reaction parameters optimization and versatility were investigated in detail,and excellent yield(99.9%)and selectivity(99%)were obtained under the optimized reaction conditions of70℃ and 1.0 MPa for 6.0 h.Noteworthily,the polypyrazole acts as homogeneous catalyst during reaction(higher than T_(g)).And under room temperature,polypyrazoles can be easily separated and recovered,which is a promising feature of a heterogeneous catalyst.Furthermore,the reaction mechanism was proposed.The DFT calculation suggested that the formation of hydrogen bond between pyrazole and epoxide greatly reduced the energy barrier,which play an important role in promoting CO_(2)cycloaddition.
基金This project is supported by National Basic Research Program of China(973Program,No.2003CB317005)Shuguang Program of Shanghai City Educational Conunittee China(No.05SG15).
文摘To support and serve engineering design, creative design based on knowledge management is proposed. The key knowledge factors of creative design are analyzed and discussed, and knowledge extraction tools are utilized to distill the important knowledge to serve for knowledge resource of creative design. The implementation of creative design mode is described and executed, which can promote the intelligent asset of the enterprise and shorten the period of creative design. With this study, design afflatus and conceptual design can be achieved expediently and effectively.
基金Project (Nos. 60332030 and 60496316) supported by the NationalNatural Science Foundation of China
文摘This paper describes a Least Squares (LS) channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error (MSE) of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio (SNR). To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.
