In the last decade,intraductal papillary mucinous neoplasms(IPMNs) have become commonly diagnosed.From a morphological standpoint,they are classified in main-duct IPMNs(MD-IPMNs) and branch-duct IPMNs(BD-IPMNs),depend...In the last decade,intraductal papillary mucinous neoplasms(IPMNs) have become commonly diagnosed.From a morphological standpoint,they are classified in main-duct IPMNs(MD-IPMNs) and branch-duct IPMNs(BD-IPMNs),depending on the type of involvement of the pancreatic ductal system by the neoplasm.Despite the fact that our understanding of their natural history is still incomplete,recent data indicate that MD-IPMNs and BD-IPMNs show significant differences in terms of biological behaviour with MD-IPMNs at higher risk of malignant degeneration.In the present paper,clinical and epidemiological characteristics,rates of malignancy and the natural history of MD-IPMNs and BD-IPMNs are analyzed.The profile of IPMNs involving both the main pancreatic duct and its side branches(combined-IPMNs) are also discussed.Finally,general recommendations for management based on these differences are given.展开更多
AIM:To compare characteristics and outcomes of resected and nonresected main-duct and mixed intraductal papillary mucinous neoplasms of the pancreas(IPMN).METHODS:Over a 14-year period,50 patients who did not undergo ...AIM:To compare characteristics and outcomes of resected and nonresected main-duct and mixed intraductal papillary mucinous neoplasms of the pancreas(IPMN).METHODS:Over a 14-year period,50 patients who did not undergo surgery for resectable main-duct or mixed IPMN,for reasons of precluding comorbidities,age and/or refusal,were compared with 74 patients who underwent resection to assess differences in rates of survival,recurrence/occurrence of malignancy,and prognostic factors.All study participants had dilatation of the main pancreatic duct by ≥ 5 mm,with or without dilatation of the branch ducts.Some of the nonsurgical patients showed evidence of mucus upon perendoscopic retrograde cholangiopancreatography or endoscopic ultrasound and/or after fine needle aspiration.For the surgical patients,pathologic analysis of resected specimens confirmed a diagnosis of IPMN with involvement of the main pancreatic duct or of both branch ducts as well as the main pancreatic duct.Clinical and biologic follow-ups were conducted for all patients at least annually,through hospitalization or consultation every six months during the first year of follow-up,together with abdominal imaging analysis(magnetic resonance cholangiopancreatography or computed tomography) and,if necessary,endoscopic ultrasound with or without fine needle aspiration.RESULTS:The overall five-year survival rate of patients who underwent resection was significantly greater than that for the nonsurgical patients(74% vs 58%; P =0.019).The parameters of age(< 70 years) and absence of a nodule were associated with better survival(P < 0.05); however,the parameters of main pancreatic duct diameter > 10 mm,branch ductdiameter > 30 mm,or presence of extra pancreatic cancers did not significantly influence the prognosis.In the nonsurgical patients,pancreatic malignancy occurred in 36% of cases within a mean time of 33 mo(median:29 mo; range:8-141 mo).Comparison of the nonsurgical patients who experienced disease progression with those who did not progress showed no significant differences in age,sex,symptoms,subtype of IPMN,or follow-up period; only the size of the main pancreatic duct was significantly different between these two sub-groups,with the nonsurgical patients who experienced progression showing a greater diameter at the time of diagnosis(> 10 mm).CONCLUSION:Patients unfit for surgery have a 36% greater risk of developing pancreatic malignancy of the main-duct or mixed IPMN within a median of 2.5 years.展开更多
Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not r...Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio （SNR）, which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.展开更多
The synthesis of a new azobenzene(azo)-containing main-chain crystalline polymer with reactive secondary amino groups in its backbone and photodeformation behaviors of its supramolecular hydrogen-bonded fibers are des...The synthesis of a new azobenzene(azo)-containing main-chain crystalline polymer with reactive secondary amino groups in its backbone and photodeformation behaviors of its supramolecular hydrogen-bonded fibers are described. This main-chain azo polymer(namely Azo-MP6) was prepared via first the synthesis of a diacrylate-type azo monomer and its subsequent Michael addition copolymerization with trans-1,4-cyclohexanediamine under a mild reaction condition. Azo-MP6 was found to have a linear main-chain chemical structure instead of a branched one, as verified by comparing its ~1H-NMR spectrum with that of the azo polymer prepared via the polymer analogous reaction of AzoMP6 with acetic anhydride. The thermal stability, phase transition behavior, and photoresponsivity of Azo-MP6 were characterized with TGA,DSC, POM, XRD, and UV-Vis spectroscopy. The experimental results revealed that it had good thermal stability, low glass transition temperature,broad crystalline phase temperature range, and highly reversible photoresponsivity. Physically crosslinked supramolecular hydrogen-bonded fibers with good mechanical properties and a high alignment order of azo mesogens were readily fabricated from Azo-MP6 by using the simple melt spinning method, and they could show "reversible" photoinduced bending under the same UV light irradiation and good anti-fatigue properties.展开更多
A main-chain liquid crystalline ionomer（MLCI） containing sulfonic group was synthesized by an interfacial condensation reaction.The MLCI was blended with polybutylene terephthalate（PBT） and polypropylene（PP）.MLC...A main-chain liquid crystalline ionomer（MLCI） containing sulfonic group was synthesized by an interfacial condensation reaction.The MLCI was blended with polybutylene terephthalate（PBT） and polypropylene（PP）.MLCI interacted with both the dispersed（PP） phase and the matrix（PBT） phase to modify the interfacial interaction of PBT and PP.Differential scanning calorimetry（DSC）,scanning electron microscopy（SEM） and FTIR imaging system analysis demonstrated the significance of interfacial interaction in the polymer blends.MLCI brought about good adhesion at the interfacial,which reduced the disperse phase size and enabled a fine PP phase at matrix.The mechanical properties of the ternary blends were improved when a proper amount of MLCI was added.This was attributed to enhanced adhesion at the interface,which invoked better mechanical properties in the blends.展开更多
The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been deter...The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.展开更多
Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （...Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （RLOF）. The RLOF can be divided into two cases： dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056 yr^- 1 or 0.045 yr^-1 depending on different assumptions; in the stable RLOF case, it is 0.002 yr^-1 or 0.005yr^-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution （ ≤ 8%） to the whole population of symbiotic stars in the Galaxy.展开更多
Based on the measured discharge,sediment load,and cross-sectional data from 1986 to 2015 for the lower Yellow River,changes in the morphological parameters(width,depth,and cross-sectional geomorphic coefficient)of the...Based on the measured discharge,sediment load,and cross-sectional data from 1986 to 2015 for the lower Yellow River,changes in the morphological parameters(width,depth,and cross-sectional geomorphic coefficient)of the main channel are analyzed in this paper.The results show that before the operation of the Xiaolangdi Reservoir(XLDR)from 1986 to 1999,the main channel shrunk continually,with decreasing width and depth.The rate of reduction in its width decreased along the river whereas that of depth increased in the downstream direction.Because the rate of decrease in the width of the main channel was greater than that in channel depth,the cross-sectional geomorphic coefficient decreased in the sub-reach above Gaocun.By contrast,for the sub-reach below Gaocun,the rate of decrease in channel width was smaller than that in channel depth,and the cross-sectional geomorphic coefficient increased.Once the XLDR had begun operation,the main channel eroded continually,and both its width and depth increased from 2000 to 2015.The rate of increase in channel width decreased in the longitudinal direction,and the depth of the main channel in all sub-reaches increased by more than 2 m.Because the rate of increase in the depth of the main channel was clearly larger than that of its width,the cross-sectional geomorphic coefficient decreased in all sub-reaches.The cross-sectional geometry of the main-channel of the lower Yellow River exhibited different adjustment patterns before and after the XLDR began operation.Before its operation,the main channel mainly narrowed in the transverse direction and silted in the vertical direction in the sub-reach above Aishan;in the sub-reach below Aishan,it primarily silted in the vertical direction.After the XLDR began operation,the main channel adjusted by widening in the transverse direction and deepening in the vertical direction in the sub-reach above Aishan;in the sub-reach below it,the main channel adjusted mainly by deepening in the vertical direction.Compared with the rates of decrease in the width and depth of the main channel during the siltation period,the rate of increase in channel width during the scouring period was clearly smaller while the rate of increase in channel depth was larger.After continual siltation and scouring from 1986 to 2015,the cross-sectional geometry of the main-channel changed from wide and shallow to relatively narrow and deep.The pattern of adjustment in the main channel was closely related to the water and sediment conditions.For the braided reach,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with suspended sediment concentration(SSC)during the siltation period.By contrast,the cross-sectional geomorphic coefficient was positively correlated with discharge and negatively correlated with SSC during the scouring period.For the transitional and meandering reaches,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with SSC.展开更多
Recent studies have addressed that the cache be havior is important in the design of main memory index structures. Cache-conscious indices such as the CSB^＋-tree are shown to outperform conventional main memory indic...Recent studies have addressed that the cache be havior is important in the design of main memory index structures. Cache-conscious indices such as the CSB^＋-tree are shown to outperform conventional main memory indices such as the AVL-tree and the T-tree. This paper proposes a cacheconscious version of the T-tree, CST-tree, defined according to the cache-conscious definition. To separate the keys within a node into two parts, the CST-tree can gain higher cache hit ratio.展开更多
加快建设沙戈荒源网荷储一体化基地有力推动了电力系统低碳转型,但基地内缺乏常规电源,呈现出电网弱、低惯量、弱阻尼等特征。高压大功率变流器是主力电源型新能源场站的关键电气装备,起到自主构建电压/频率,提供阻尼和惯量支撑等作用...加快建设沙戈荒源网荷储一体化基地有力推动了电力系统低碳转型,但基地内缺乏常规电源,呈现出电网弱、低惯量、弱阻尼等特征。高压大功率变流器是主力电源型新能源场站的关键电气装备,起到自主构建电压/频率,提供阻尼和惯量支撑等作用。在此背景下,首先介绍了源网荷储一体化基地变流拓扑及汇集方式,对“多机并联-多级升压”汇集拓扑所引发的宽频振荡、协同构网控制困难以及过载能力弱等问题进行了分析。其次,分别对光伏发电系统、蓄电池储能系统(battery energy storage system,BESS)以及光储一体化系统的高压大功率变流拓扑特点进行了梳理和分析。最后,探索了高压大功率变流器亟待解决的关键问题。展开更多
文摘In the last decade,intraductal papillary mucinous neoplasms(IPMNs) have become commonly diagnosed.From a morphological standpoint,they are classified in main-duct IPMNs(MD-IPMNs) and branch-duct IPMNs(BD-IPMNs),depending on the type of involvement of the pancreatic ductal system by the neoplasm.Despite the fact that our understanding of their natural history is still incomplete,recent data indicate that MD-IPMNs and BD-IPMNs show significant differences in terms of biological behaviour with MD-IPMNs at higher risk of malignant degeneration.In the present paper,clinical and epidemiological characteristics,rates of malignancy and the natural history of MD-IPMNs and BD-IPMNs are analyzed.The profile of IPMNs involving both the main pancreatic duct and its side branches(combined-IPMNs) are also discussed.Finally,general recommendations for management based on these differences are given.
文摘AIM:To compare characteristics and outcomes of resected and nonresected main-duct and mixed intraductal papillary mucinous neoplasms of the pancreas(IPMN).METHODS:Over a 14-year period,50 patients who did not undergo surgery for resectable main-duct or mixed IPMN,for reasons of precluding comorbidities,age and/or refusal,were compared with 74 patients who underwent resection to assess differences in rates of survival,recurrence/occurrence of malignancy,and prognostic factors.All study participants had dilatation of the main pancreatic duct by ≥ 5 mm,with or without dilatation of the branch ducts.Some of the nonsurgical patients showed evidence of mucus upon perendoscopic retrograde cholangiopancreatography or endoscopic ultrasound and/or after fine needle aspiration.For the surgical patients,pathologic analysis of resected specimens confirmed a diagnosis of IPMN with involvement of the main pancreatic duct or of both branch ducts as well as the main pancreatic duct.Clinical and biologic follow-ups were conducted for all patients at least annually,through hospitalization or consultation every six months during the first year of follow-up,together with abdominal imaging analysis(magnetic resonance cholangiopancreatography or computed tomography) and,if necessary,endoscopic ultrasound with or without fine needle aspiration.RESULTS:The overall five-year survival rate of patients who underwent resection was significantly greater than that for the nonsurgical patients(74% vs 58%; P =0.019).The parameters of age(< 70 years) and absence of a nodule were associated with better survival(P < 0.05); however,the parameters of main pancreatic duct diameter > 10 mm,branch ductdiameter > 30 mm,or presence of extra pancreatic cancers did not significantly influence the prognosis.In the nonsurgical patients,pancreatic malignancy occurred in 36% of cases within a mean time of 33 mo(median:29 mo; range:8-141 mo).Comparison of the nonsurgical patients who experienced disease progression with those who did not progress showed no significant differences in age,sex,symptoms,subtype of IPMN,or follow-up period; only the size of the main pancreatic duct was significantly different between these two sub-groups,with the nonsurgical patients who experienced progression showing a greater diameter at the time of diagnosis(> 10 mm).CONCLUSION:Patients unfit for surgery have a 36% greater risk of developing pancreatic malignancy of the main-duct or mixed IPMN within a median of 2.5 years.
基金National Natural Science Foundation of China Under Grant No.40374017
文摘Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio （SNR）, which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.
基金financially supported by the National Natural Science Foundation of China (Nos. 21574070 and 21774063)Natural Science Foundation of Tianjin (No. 16JCZDJC36800)
文摘The synthesis of a new azobenzene(azo)-containing main-chain crystalline polymer with reactive secondary amino groups in its backbone and photodeformation behaviors of its supramolecular hydrogen-bonded fibers are described. This main-chain azo polymer(namely Azo-MP6) was prepared via first the synthesis of a diacrylate-type azo monomer and its subsequent Michael addition copolymerization with trans-1,4-cyclohexanediamine under a mild reaction condition. Azo-MP6 was found to have a linear main-chain chemical structure instead of a branched one, as verified by comparing its ~1H-NMR spectrum with that of the azo polymer prepared via the polymer analogous reaction of AzoMP6 with acetic anhydride. The thermal stability, phase transition behavior, and photoresponsivity of Azo-MP6 were characterized with TGA,DSC, POM, XRD, and UV-Vis spectroscopy. The experimental results revealed that it had good thermal stability, low glass transition temperature,broad crystalline phase temperature range, and highly reversible photoresponsivity. Physically crosslinked supramolecular hydrogen-bonded fibers with good mechanical properties and a high alignment order of azo mesogens were readily fabricated from Azo-MP6 by using the simple melt spinning method, and they could show "reversible" photoinduced bending under the same UV light irradiation and good anti-fatigue properties.
基金Supported by the High-Tech Research and Development Program of China(No.2006AA02Z291)the National Natural Science Foundation of China(No.50673105)
文摘A main-chain liquid crystalline ionomer（MLCI） containing sulfonic group was synthesized by an interfacial condensation reaction.The MLCI was blended with polybutylene terephthalate（PBT） and polypropylene（PP）.MLCI interacted with both the dispersed（PP） phase and the matrix（PBT） phase to modify the interfacial interaction of PBT and PP.Differential scanning calorimetry（DSC）,scanning electron microscopy（SEM） and FTIR imaging system analysis demonstrated the significance of interfacial interaction in the polymer blends.MLCI brought about good adhesion at the interfacial,which reduced the disperse phase size and enabled a fine PP phase at matrix.The mechanical properties of the ternary blends were improved when a proper amount of MLCI was added.This was attributed to enhanced adhesion at the interface,which invoked better mechanical properties in the blends.
文摘The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.
基金Supported by the National Natural Science Foundation of China.
文摘Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （RLOF）. The RLOF can be divided into two cases： dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056 yr^- 1 or 0.045 yr^-1 depending on different assumptions; in the stable RLOF case, it is 0.002 yr^-1 or 0.005yr^-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution （ ≤ 8%） to the whole population of symbiotic stars in the Galaxy.
基金Key Program of National Natural Science Foundation of China,No.51639005National Key R&D Program of China,No.2017YFC0405202,No.2016YFC0402406。
文摘Based on the measured discharge,sediment load,and cross-sectional data from 1986 to 2015 for the lower Yellow River,changes in the morphological parameters(width,depth,and cross-sectional geomorphic coefficient)of the main channel are analyzed in this paper.The results show that before the operation of the Xiaolangdi Reservoir(XLDR)from 1986 to 1999,the main channel shrunk continually,with decreasing width and depth.The rate of reduction in its width decreased along the river whereas that of depth increased in the downstream direction.Because the rate of decrease in the width of the main channel was greater than that in channel depth,the cross-sectional geomorphic coefficient decreased in the sub-reach above Gaocun.By contrast,for the sub-reach below Gaocun,the rate of decrease in channel width was smaller than that in channel depth,and the cross-sectional geomorphic coefficient increased.Once the XLDR had begun operation,the main channel eroded continually,and both its width and depth increased from 2000 to 2015.The rate of increase in channel width decreased in the longitudinal direction,and the depth of the main channel in all sub-reaches increased by more than 2 m.Because the rate of increase in the depth of the main channel was clearly larger than that of its width,the cross-sectional geomorphic coefficient decreased in all sub-reaches.The cross-sectional geometry of the main-channel of the lower Yellow River exhibited different adjustment patterns before and after the XLDR began operation.Before its operation,the main channel mainly narrowed in the transverse direction and silted in the vertical direction in the sub-reach above Aishan;in the sub-reach below Aishan,it primarily silted in the vertical direction.After the XLDR began operation,the main channel adjusted by widening in the transverse direction and deepening in the vertical direction in the sub-reach above Aishan;in the sub-reach below it,the main channel adjusted mainly by deepening in the vertical direction.Compared with the rates of decrease in the width and depth of the main channel during the siltation period,the rate of increase in channel width during the scouring period was clearly smaller while the rate of increase in channel depth was larger.After continual siltation and scouring from 1986 to 2015,the cross-sectional geometry of the main-channel changed from wide and shallow to relatively narrow and deep.The pattern of adjustment in the main channel was closely related to the water and sediment conditions.For the braided reach,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with suspended sediment concentration(SSC)during the siltation period.By contrast,the cross-sectional geomorphic coefficient was positively correlated with discharge and negatively correlated with SSC during the scouring period.For the transitional and meandering reaches,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with SSC.
基金Supported bythe National High Technology of 863Project (2002AA1Z2308 ,2002AA118030)
文摘Recent studies have addressed that the cache be havior is important in the design of main memory index structures. Cache-conscious indices such as the CSB^＋-tree are shown to outperform conventional main memory indices such as the AVL-tree and the T-tree. This paper proposes a cacheconscious version of the T-tree, CST-tree, defined according to the cache-conscious definition. To separate the keys within a node into two parts, the CST-tree can gain higher cache hit ratio.
文摘加快建设沙戈荒源网荷储一体化基地有力推动了电力系统低碳转型,但基地内缺乏常规电源,呈现出电网弱、低惯量、弱阻尼等特征。高压大功率变流器是主力电源型新能源场站的关键电气装备,起到自主构建电压/频率,提供阻尼和惯量支撑等作用。在此背景下,首先介绍了源网荷储一体化基地变流拓扑及汇集方式,对“多机并联-多级升压”汇集拓扑所引发的宽频振荡、协同构网控制困难以及过载能力弱等问题进行了分析。其次,分别对光伏发电系统、蓄电池储能系统(battery energy storage system,BESS)以及光储一体化系统的高压大功率变流拓扑特点进行了梳理和分析。最后,探索了高压大功率变流器亟待解决的关键问题。
