由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Siev...由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Sieve自助法的思想,定义了顾及设计矩阵误差AR模型精度评定的Sieve块自助采样方法。根据不同的分块准则和采样策略,给出了4种方法的重采样步骤。模拟实验结果表明,精度评定的Sieve块自助采样方法能够得到比最小二乘法、经典的AR模型迭代解法更加可靠的自回归系数标准差,具有更强的适用性。同时,北斗卫星精密钟差真实案例表明,所提出的Sieve移动块自助法、Sieve非重叠块自助法、Sieve圆形块自助法以及Sieve静止块自助法的均方根(root mean square,RMS)比总体最小二乘的RMS分别减小了70.25%、78.65%、70.89%和79.24%,进一步验证了所提算法的有效性和可靠性,为时间序列AR模型的精度评定问题提供了一种采样思路。展开更多
Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)ca...Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)capture.It is urgently needed for membrane-based CO_(2)capture to develop the high-performance membrane materials with high permeability,selectivity,and stability.Herein,ultrapermeable carbon molecular sieve(CMS)membranes are fabricated by py roly zing a finely-engineered benzoxazole-containing copolyimide precursor for efficient CO_(2)capture.The microstructure of CMS membrane has been optimized by initially engineering the precursor-chemistry and subsequently tuning the pyrolysis process.Deep insights into the structure-property relationship of CMSs are provided in detail by a combination of experimental characterization and molecular simulations.We demonstrate that the intrinsically high free volume environment of the precursor,coupled with the steric hindrance of thermostable contorted fragments,promotes the formation of loosely packed and ultramicroporous carbon structures within the resultant CMS membrane,thereby enabling efficient CO_(2)discrimination via size sieving and affinity.The membrane achieves an ultrahigh CO_(2)permeability,good selectivity,and excellent stability.After one month of long-term operation,the CO_(2)permeability in the mixed gas is maintained at 11,800 Barrer,with a CO_(2)/N_(2)selectivity exceeding 60.This study provides insights into the relationship between precursor-chemistry and CMS performance,and our ultrapermeable CMS membrane,which is scalable using thin film manufacturing,holds great potential for industrial CO_(2)capture.展开更多
Porous molecular sieve catalysts,including aluminosilicate zeolites and silicoaluminophosphate(SAPO)molecular sieves,have found widespread use in heterogeneous catalysis and are expected to play a key role in advancin...Porous molecular sieve catalysts,including aluminosilicate zeolites and silicoaluminophosphate(SAPO)molecular sieves,have found widespread use in heterogeneous catalysis and are expected to play a key role in advancing carbon neutrality and sustainable development.Given the ubiquitous presence of water during catalyst synthesis,storage,and application,the interactions between water and molecular sieves as well as their consequent effects on frameworks and catalytic reactions have attracted considerable attention.These effects are inherently complex and highly dependent on various factors such as temperature,water phase,and partial pressure.In this review,we provide a comprehensive overview of the current understanding of water-molecular sieve interactions and their roles in catalysis,based on both experimental and theoretical calculation results.Special attention is paid to water-induced reversible and irreversible structural changes in aluminosilicate and SAPO frameworks at the atomic level,underscoring the dynamic and labile nature of these frameworks in water environments.The influence of water on catalytic performance and reaction kinetics in molecular sieve-catalyzed reactions is discussed from two perspectives:(1)its participation in reaction through hydrogen bonding interactions,such as competitive adsorption at active sites,stabilization of ground and transition states,and proton transfer bridge;(2)its role as a direct reactant forming new species via reactions with other vip molecules.Recent advancements in this area provide valuable insights for the rational design and optimization of catalysts for water-involved reactions.展开更多
Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certai...Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certain SAPO materials remains challenging,which limits their catalytic applications.Here,we report the synthesis of a series of SAPO materials using a developed SAPO precursor plus dual template(SPDT)strategy.A variety of SAPO materials characterized by high silica content and enhanced acidity,such as SAPO-34/56 intergrowths,SAPO-56,and SAPO-17,have been synthesized and thoroughly characterized using various techniques including integrated differential phase-contrast scanning transmission electron microscopy,two-dimensional solid-state nuclear magnetic resonance spectroscopy,and continuous rotation electron diffraction.The use of silica-enriched SAPO precursor combined with the flexible selection of the second template enables the crystalline phase regulation and improves the Si atoms incorporation into the framework.Notably,the synthesized SAPO-17 with abundant Si(4Al)species and unprecedentedly high acid density exhibits exceptional DeNO_(x)activity after Cu loading,with NO_(x)conversion exceeding 90%at 175–700℃.This outstanding performance can be attributed to the unique ERI structure and the increased acidity of SAPO-17.This work not only presents an effective method for synthesizing SAPO molecular sieves with enhanced acidity but also offers a new perspective for expanding the active temperature range of the ammonia selective catalytic reduction reaction.展开更多
In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))ha...In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))has emerged as a promising gate dielectric material due to its suitable dielectric constant,wide band gap,ideal valence-band offset,and good thermodynamic stability.However,current deposition methods face compatibility issues with 2D semiconductors,highlighting the need for high-quality dielectrics and interfaces.Here,high-quality 2D m-ZrO_(2)single crystals are successfully prepared using a onestep chemical vapor deposition(CVD)method,aided by 5A molecular sieves for oxygen supply.The prepared ZrO_(2)is utilized as a gate dielectric in the construction of MoS2 field-effect transistors(FETs)to investigate its electrical property.The FETs exhibit a high carrier mobility of up to 5.50 cm^(2)·V^(−1)·s^(−1),and a current switching ratio(Ion/off)of approximately 10^(4),which aligns with the current standards of logic circuits,indicating that ZrO_(2)has application value as a gate dielectric.The successful onestep preparation of single-crystal ZrO_(2)paves the way for the utilization of high-κgate dielectrics and creates favorable conditions for the development of high-performance semiconductor devices,offering new possibilities for transistor miniaturization.展开更多
The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing spe...The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch-like granules separately sheathed with a layer of membrane and usually with mitochondria around. These gnanules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.展开更多
Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples...Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.展开更多
A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe t...A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe the adsorption performance of the adsorbent, the linear driving force (LDF) model is used to describe the mass transfer rate, and the thermal effect during adsorption is considered. The finite difference method is used in simulation and comparison. Numerical results have a reasonable agreement with the experimental research.展开更多
Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not chang...Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not change the equilibrium relation between vapor and bulk liquid phase. A calculation procedure is proposed to predict vapor liquid solid (adsorbent) three phase euquilibria.展开更多
Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desor...Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.展开更多
This paper introduces a method of sieve which can be to calculate the number of residues of the integers 1,2,...,2a sifted by n paiwise coprime numbers.
Samples of methane molecules grade diameter channel CHA-type molecular sieves(Chabazite-K, SAPO-34 and SSZ-13) were investigated using the adsorption separation of CH4/N2 mixtures. The isotherms recorded for CH4 and N...Samples of methane molecules grade diameter channel CHA-type molecular sieves(Chabazite-K, SAPO-34 and SSZ-13) were investigated using the adsorption separation of CH4/N2 mixtures. The isotherms recorded for CH4 and N2 follow a typical type-Ι behavior, which were fitted well with the Sips model(R2>0.999) and the selectivity was calculated using IAST theory. The results reveal that Chabazite-K has the highest selectivity(SCH4/N= 5.5).2 SSZ-13 has the largest capacity, which can adsorb up to a maximum of 30.957 cm3·g-1(STP) of CH4, due to it having the largest pore volume and surface area, but the lowest selectivity(SCH4/N2= 2.5). From the breakthrough test, we can conclude that SSZ-13 may be a suitable candidate for the recovery of CH4 from low concentration methane(CH4<20%) based on its larger pore volume and higher CH4 capacity. Chabazite-K is more suited to the separation of high concentration methane(CH4>50%) due to its higher selectivity.展开更多
Recent decades witnessed the significant progress made in the research field of 2D molecular sieve membranes.In comparison with their 3D counterparts, 2D molecular sieve membranes possessed several unique advantages l...Recent decades witnessed the significant progress made in the research field of 2D molecular sieve membranes.In comparison with their 3D counterparts, 2D molecular sieve membranes possessed several unique advantages like significantly reduced membrane thickness(one atom thick in theory) and diversified molecular sieving mechanisms(in-plane pores within nanosheets & interlayer galleries between nanosheets). M. Tsapatsis first carried out pioneering work on fabrication of lamellar ZSM-5 membrane. Since then, diverse 2D materials typically including graphene oxides(GOs) have been fabricated into membranes showing promising prospects in energy-efficient gas separation, pervaporation, desalination and nanofiltration. In addition to GOs, other emerging 2D materials, including 2D zeolites, 2D metal–organic frameworks(MOFs), 2 D covalent-organic frameworks(COFs), layered double hydroxides(LDHs), transition metal dichalcogenides(TMDCs), MXenes(typically Ti3C2TX), graphitic carbon nitrides(typically g-C3N4), hexagonal boron nitride(h-BN) and montmorillonites(MT) are showing intriguing performance in membrane-based separation process. This article summarized the most recent developments in the field of 2D molecular sieve membranes aside from GOs with particular emphasis on their structure–performance relationship and application prospects in industrial separation.展开更多
Photochemical oxidation of thiophene in n-octane/water extraction system using O2 as oxidant was studied. The reaction mechanism ofthiophene oxidation was proposed. Results obtained here can be used as the reference f...Photochemical oxidation of thiophene in n-octane/water extraction system using O2 as oxidant was studied. The reaction mechanism ofthiophene oxidation was proposed. Results obtained here can be used as the reference for the oxidative desulfurization of gasoline because thiophene is one of the main components containing sulfur in fluid catalytic cracking gasoline. Thiophene dissolved in n-octane was photodecomposed and removed into the water phase at ambient temperature and atmospheric pressure. A 500 W high-pressure mercury lamp （main wave length 365 nm, 0.22 kW/m） was used as light source for irradiation, and air was introduced by a gas pump to supply O2. Thiophene can be photo-oxidized to sulfone, oxalic acid, SO4^2-, and CO2. The desulfurization yield of thiophene in n-octane is 58.9% under photo-irradiation for 5 h under the conditions of air flow at 150 mL/min and V（water）：V（n-octane）=1：1. It can be improved to 92.3% by adding 0.15 g zeoliteartificial into 100 mL reaction system, which is the adsorbent for O2 and thiophene. And under such conditions, the photo-oxidation kinetics of thiophene with O2/zeoliteartificial is first-order with an apparent rate constant of 0.5047 h^-1 and a half-time of 1.37 h. The sulfur content can be depressed from 800 μL/L to less than 62 μL/L.展开更多
Flavonoids play essential roles in human health.Apple(Malus domestica Borkh.),one of the most widely produced and economically important fruit crops in temperate regions,is a significant source of flavonoids in the hu...Flavonoids play essential roles in human health.Apple(Malus domestica Borkh.),one of the most widely produced and economically important fruit crops in temperate regions,is a significant source of flavonoids in the human diet and is among the top nutritionally rated and most widely consumed fruits worldwide.Epidemiological studies have shown that the consumption of apples,which are rich in a variety of free and easily absorbable flavonoids,is associated with a decreased risk of various diseases.However,apple production is challenged by serious inbreeding problems.The narrowing of the hereditary base has resulted in apples with poor nutritional quality and low flavonoid contents.Recently,there have been advances in our understanding of the roles that Malus sieversii(Ledeb.)M.Roem has played in the process of apple domestication and breeding.In this study,we review the origin of cultivated apples and red-fleshed apples,and discuss the genetic diversity and construction of the core collections of M.sieversii.We also discuss current research progress and breeding programs on red-skinned and red-fleshed apples and summarize the exploitation and utilization of M.sieversii in the breeding of high-flavonoid,and red-fleshed apples.This study highlights a valuable pattern of horticultural crop breeding using wild germplasm resources.The future challenges and directions of research on the molecular mechanisms of flavonoid accumulation and high-flavonoid apple breeding are discussed.展开更多
文摘由于传统求解时间序列自回归(auto-regressive,AR)模型的最小二乘方法无法顾及设计矩阵误差,现有的AR模型迭代解法难以应用协方差传播率给出较为精确的精度评定公式。将块自助采样方法引入到AR模型精度评定研究中,并在其基础上借助Sieve自助法的思想,定义了顾及设计矩阵误差AR模型精度评定的Sieve块自助采样方法。根据不同的分块准则和采样策略,给出了4种方法的重采样步骤。模拟实验结果表明,精度评定的Sieve块自助采样方法能够得到比最小二乘法、经典的AR模型迭代解法更加可靠的自回归系数标准差,具有更强的适用性。同时,北斗卫星精密钟差真实案例表明,所提出的Sieve移动块自助法、Sieve非重叠块自助法、Sieve圆形块自助法以及Sieve静止块自助法的均方根(root mean square,RMS)比总体最小二乘的RMS分别减小了70.25%、78.65%、70.89%和79.24%,进一步验证了所提算法的有效性和可靠性,为时间序列AR模型的精度评定问题提供了一种采样思路。
基金financial support from the National Key R&D Program of China(2021YFB3801200)the National Natural Science Foundation of China(22278051,22178044,22308043)CNPC Innovation Found(2022DQ02-0608)。
文摘Carbon capture is an important strategy and is implemented to achieve the goals of CO_(2)reduction and carbon neutrality.As a high energy-efficient technology,membrane-based separation plays a crucial role in CO_(2)capture.It is urgently needed for membrane-based CO_(2)capture to develop the high-performance membrane materials with high permeability,selectivity,and stability.Herein,ultrapermeable carbon molecular sieve(CMS)membranes are fabricated by py roly zing a finely-engineered benzoxazole-containing copolyimide precursor for efficient CO_(2)capture.The microstructure of CMS membrane has been optimized by initially engineering the precursor-chemistry and subsequently tuning the pyrolysis process.Deep insights into the structure-property relationship of CMSs are provided in detail by a combination of experimental characterization and molecular simulations.We demonstrate that the intrinsically high free volume environment of the precursor,coupled with the steric hindrance of thermostable contorted fragments,promotes the formation of loosely packed and ultramicroporous carbon structures within the resultant CMS membrane,thereby enabling efficient CO_(2)discrimination via size sieving and affinity.The membrane achieves an ultrahigh CO_(2)permeability,good selectivity,and excellent stability.After one month of long-term operation,the CO_(2)permeability in the mixed gas is maintained at 11,800 Barrer,with a CO_(2)/N_(2)selectivity exceeding 60.This study provides insights into the relationship between precursor-chemistry and CMS performance,and our ultrapermeable CMS membrane,which is scalable using thin film manufacturing,holds great potential for industrial CO_(2)capture.
文摘Porous molecular sieve catalysts,including aluminosilicate zeolites and silicoaluminophosphate(SAPO)molecular sieves,have found widespread use in heterogeneous catalysis and are expected to play a key role in advancing carbon neutrality and sustainable development.Given the ubiquitous presence of water during catalyst synthesis,storage,and application,the interactions between water and molecular sieves as well as their consequent effects on frameworks and catalytic reactions have attracted considerable attention.These effects are inherently complex and highly dependent on various factors such as temperature,water phase,and partial pressure.In this review,we provide a comprehensive overview of the current understanding of water-molecular sieve interactions and their roles in catalysis,based on both experimental and theoretical calculation results.Special attention is paid to water-induced reversible and irreversible structural changes in aluminosilicate and SAPO frameworks at the atomic level,underscoring the dynamic and labile nature of these frameworks in water environments.The influence of water on catalytic performance and reaction kinetics in molecular sieve-catalyzed reactions is discussed from two perspectives:(1)its participation in reaction through hydrogen bonding interactions,such as competitive adsorption at active sites,stabilization of ground and transition states,and proton transfer bridge;(2)its role as a direct reactant forming new species via reactions with other vip molecules.Recent advancements in this area provide valuable insights for the rational design and optimization of catalysts for water-involved reactions.
文摘Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certain SAPO materials remains challenging,which limits their catalytic applications.Here,we report the synthesis of a series of SAPO materials using a developed SAPO precursor plus dual template(SPDT)strategy.A variety of SAPO materials characterized by high silica content and enhanced acidity,such as SAPO-34/56 intergrowths,SAPO-56,and SAPO-17,have been synthesized and thoroughly characterized using various techniques including integrated differential phase-contrast scanning transmission electron microscopy,two-dimensional solid-state nuclear magnetic resonance spectroscopy,and continuous rotation electron diffraction.The use of silica-enriched SAPO precursor combined with the flexible selection of the second template enables the crystalline phase regulation and improves the Si atoms incorporation into the framework.Notably,the synthesized SAPO-17 with abundant Si(4Al)species and unprecedentedly high acid density exhibits exceptional DeNO_(x)activity after Cu loading,with NO_(x)conversion exceeding 90%at 175–700℃.This outstanding performance can be attributed to the unique ERI structure and the increased acidity of SAPO-17.This work not only presents an effective method for synthesizing SAPO molecular sieves with enhanced acidity but also offers a new perspective for expanding the active temperature range of the ammonia selective catalytic reduction reaction.
基金support from the National Natural Science Foundation of China(No.21975067)Shenzhen Science and Technology Program(No.JCYJ20220530160407016).
文摘In order to address challenges posed by the reduction in transistor size,researchers are concentrating on two-dimensional(2D)materials with high dielectric constants and large band gaps.Monoclinic ZrO_(2)(m-ZrO_(2))has emerged as a promising gate dielectric material due to its suitable dielectric constant,wide band gap,ideal valence-band offset,and good thermodynamic stability.However,current deposition methods face compatibility issues with 2D semiconductors,highlighting the need for high-quality dielectrics and interfaces.Here,high-quality 2D m-ZrO_(2)single crystals are successfully prepared using a onestep chemical vapor deposition(CVD)method,aided by 5A molecular sieves for oxygen supply.The prepared ZrO_(2)is utilized as a gate dielectric in the construction of MoS2 field-effect transistors(FETs)to investigate its electrical property.The FETs exhibit a high carrier mobility of up to 5.50 cm^(2)·V^(−1)·s^(−1),and a current switching ratio(Ion/off)of approximately 10^(4),which aligns with the current standards of logic circuits,indicating that ZrO_(2)has application value as a gate dielectric.The successful onestep preparation of single-crystal ZrO_(2)paves the way for the utilization of high-κgate dielectrics and creates favorable conditions for the development of high-performance semiconductor devices,offering new possibilities for transistor miniaturization.
文摘The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch-like granules separately sheathed with a layer of membrane and usually with mitochondria around. These gnanules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.
文摘Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.
文摘A mathematical model for simulating concentric-bed and other components of molecular sieve oxygen concentrator is established. In the model, the binary Langmuir equilibrium adsorption equation is adopted to describe the adsorption performance of the adsorbent, the linear driving force (LDF) model is used to describe the mass transfer rate, and the thermal effect during adsorption is considered. The finite difference method is used in simulation and comparison. Numerical results have a reasonable agreement with the experimental research.
文摘Vapor liquid solid three phase equilibria of ethanol water 4A molecular sieve system are studied experimentally and theoritically. It is proved that the addition of adsorbent does not change the equilibrium relation between vapor and bulk liquid phase. A calculation procedure is proposed to predict vapor liquid solid (adsorbent) three phase euquilibria.
基金supported by the National Basic Research Program of China(2010CB732300)the National Natural Science Foundation of China(21103048)~~
文摘Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.
文摘This paper introduces a method of sieve which can be to calculate the number of residues of the integers 1,2,...,2a sifted by n paiwise coprime numbers.
基金financial support from the National Natural Science Foundation of China (Nos. 51672186, 21676175)
文摘Samples of methane molecules grade diameter channel CHA-type molecular sieves(Chabazite-K, SAPO-34 and SSZ-13) were investigated using the adsorption separation of CH4/N2 mixtures. The isotherms recorded for CH4 and N2 follow a typical type-Ι behavior, which were fitted well with the Sips model(R2>0.999) and the selectivity was calculated using IAST theory. The results reveal that Chabazite-K has the highest selectivity(SCH4/N= 5.5).2 SSZ-13 has the largest capacity, which can adsorb up to a maximum of 30.957 cm3·g-1(STP) of CH4, due to it having the largest pore volume and surface area, but the lowest selectivity(SCH4/N2= 2.5). From the breakthrough test, we can conclude that SSZ-13 may be a suitable candidate for the recovery of CH4 from low concentration methane(CH4<20%) based on its larger pore volume and higher CH4 capacity. Chabazite-K is more suited to the separation of high concentration methane(CH4>50%) due to its higher selectivity.
基金Supported by the National Natural Science Foundation of China(21176231)the Fundamental Research Funds for the Central Universities(DUT16RC(3)103)Thousand Youth Talents Program
文摘Recent decades witnessed the significant progress made in the research field of 2D molecular sieve membranes.In comparison with their 3D counterparts, 2D molecular sieve membranes possessed several unique advantages like significantly reduced membrane thickness(one atom thick in theory) and diversified molecular sieving mechanisms(in-plane pores within nanosheets & interlayer galleries between nanosheets). M. Tsapatsis first carried out pioneering work on fabrication of lamellar ZSM-5 membrane. Since then, diverse 2D materials typically including graphene oxides(GOs) have been fabricated into membranes showing promising prospects in energy-efficient gas separation, pervaporation, desalination and nanofiltration. In addition to GOs, other emerging 2D materials, including 2D zeolites, 2D metal–organic frameworks(MOFs), 2 D covalent-organic frameworks(COFs), layered double hydroxides(LDHs), transition metal dichalcogenides(TMDCs), MXenes(typically Ti3C2TX), graphitic carbon nitrides(typically g-C3N4), hexagonal boron nitride(h-BN) and montmorillonites(MT) are showing intriguing performance in membrane-based separation process. This article summarized the most recent developments in the field of 2D molecular sieve membranes aside from GOs with particular emphasis on their structure–performance relationship and application prospects in industrial separation.
基金Science and Technology Development Planning Foundation of Jilin Province, China(No.20030405)
文摘Photochemical oxidation of thiophene in n-octane/water extraction system using O2 as oxidant was studied. The reaction mechanism ofthiophene oxidation was proposed. Results obtained here can be used as the reference for the oxidative desulfurization of gasoline because thiophene is one of the main components containing sulfur in fluid catalytic cracking gasoline. Thiophene dissolved in n-octane was photodecomposed and removed into the water phase at ambient temperature and atmospheric pressure. A 500 W high-pressure mercury lamp （main wave length 365 nm, 0.22 kW/m） was used as light source for irradiation, and air was introduced by a gas pump to supply O2. Thiophene can be photo-oxidized to sulfone, oxalic acid, SO4^2-, and CO2. The desulfurization yield of thiophene in n-octane is 58.9% under photo-irradiation for 5 h under the conditions of air flow at 150 mL/min and V（water）：V（n-octane）=1：1. It can be improved to 92.3% by adding 0.15 g zeoliteartificial into 100 mL reaction system, which is the adsorbent for O2 and thiophene. And under such conditions, the photo-oxidation kinetics of thiophene with O2/zeoliteartificial is first-order with an apparent rate constant of 0.5047 h^-1 and a half-time of 1.37 h. The sulfur content can be depressed from 800 μL/L to less than 62 μL/L.
基金This work was supported by the National Key Research Project of China(2016YFC0501505)the National Natural Science Foundation of China(CN)(31572091,31730080).
文摘Flavonoids play essential roles in human health.Apple(Malus domestica Borkh.),one of the most widely produced and economically important fruit crops in temperate regions,is a significant source of flavonoids in the human diet and is among the top nutritionally rated and most widely consumed fruits worldwide.Epidemiological studies have shown that the consumption of apples,which are rich in a variety of free and easily absorbable flavonoids,is associated with a decreased risk of various diseases.However,apple production is challenged by serious inbreeding problems.The narrowing of the hereditary base has resulted in apples with poor nutritional quality and low flavonoid contents.Recently,there have been advances in our understanding of the roles that Malus sieversii(Ledeb.)M.Roem has played in the process of apple domestication and breeding.In this study,we review the origin of cultivated apples and red-fleshed apples,and discuss the genetic diversity and construction of the core collections of M.sieversii.We also discuss current research progress and breeding programs on red-skinned and red-fleshed apples and summarize the exploitation and utilization of M.sieversii in the breeding of high-flavonoid,and red-fleshed apples.This study highlights a valuable pattern of horticultural crop breeding using wild germplasm resources.The future challenges and directions of research on the molecular mechanisms of flavonoid accumulation and high-flavonoid apple breeding are discussed.
