SYNTHESIS OF NOVEL BLOCK COPOLYMERS OF POLY(3-HYDROXYBUTYRIC ACID)WITH POLY(ETHYLENE GLYCOL)THROUGH ANIONIC POLYMERISATION

A novel kind of copolymer with ABA-type block structure was synthesized by anionic ring-openingpolymerization of β-butyrolactone (β-BL) in the presence of a PEG-based dicarboxylates as macroinitiators which wereprepared by the esterification of aliphatic cyclic anhydride and poly(ethylene glycol) (PEG) oligomers (M_n=2000, 4000 and6000) and conversion of potassium dicarboxylates. The resultant copolymers as well as the intermediates were characterizedby IR,~1H-NMR and GPC.     

DISTRIBUTION OF VOTAW'S λ_1(vc) CRITERION FOR TESTING COMPOUND SYMMETRY OF A COVARIANCE MATRIX

1IntroductionLetnbeanormalt--variatepopulationandXj,j=1,'',t(t23)bethej--thvariateinn.Letthesetofvariatesxl,''txtbepartitionedintoqmutuanyexclusivesubsetsofwhich.say,esubsetscontainexactlyonevariateandthereasoningk=q--esubsets(k21)containti,''ttkvariatesrespectively,wheref.22(y=1,''tk;e Z:=,t.=f).Nogeneralityislostinassumingthatthetvariatesareorderedsothatthefirst,belongtothe,subsetscontainingoneyaxiateeach,andnexttivariatesbelongto(I 1)--fhsubset,'',thelasttivariatestotheq--thsubset,whe…     

神府煤热解-活化耦合反应产物特性及机制研究

利用两段式固定床反应装置,研究了神府煤热解-活化耦合产物的特性,探讨了热解温度及活化剂(H_2O(g)、CO_2和H_2O(g)/CO_2)对产物性能的影响,揭示了热解-活化耦合反应机制。结果表明,热解温度对半焦的CO_2化学反应性影响较小;采用热解-活化两段耦合工艺,可使神府煤热解的焦油产率明显提高,产率最高为17.8%;不同活化剂对两段耦合过程产生的混合煤气(mixture coal gases,MCG)和焦油产率影响为H_2O(g)H_2O(g)/CO_2CO_2,其焦油组分均以饱和分和芳香分为主;采用H_2O(g)/CO_2(1∶1)活化剂,可有效提高活性炭的比表面积,其BET比表面积为845.37 m~2/g。热解-活化耦合机制主要为活化段产生的合成气(synthesis gases,SG)为热解段煤的加氢热解提供了氢源,丰富的氢自由基促进了煤的加氢热解反应,改变了耦合过程的产物分布和特性。     

棕榈壳酶解-温和酸解木质素的结构及热解特性研究

采用酶解/温和酸解法提取了棕榈壳和麦秆的木质素(EMALs),利用傅里叶红外光谱(FT-IR)、裂解器-气相色谱质谱联用(Py-GC/MS)和热重-红外联用(TG-FTIR)技术,对两种EMALs的化学结构和热解特性进行了对比研究,并采用Ozaw a-Flynn-Wall方法计算了其热解反应的活化能。结果表明,棕榈壳EM AL和麦秆EM AL均为HGS型木质素。500℃下,两种EMALs的热解产物主要包括酚类、酸类和少量的醇类、醛酮类等化合物;棕榈壳EMAL热解酚类产物中H、G、S型单体酚类的比例分别为47.61%、25.64%和17.18%,而麦秆EMAL分别为23.66%、51.90%和15.50%。在热解反应主失重区(200-380℃),棕榈壳EM AL的主失重速率(50.80%/min)低于麦秆EM AL(78.63%/min);但棕榈壳EM AL热解同时存在肩状失重峰(265℃,27.40%/min),这与其较多H结构产物的释放相关。H型结构产物释放的放热效应降低了棕榈壳EMAL热解初期的活化能(20%,127.92 k J/mol),同时使其热解过程(20%-80%)的平均活化能(152.32 k J/mol)低于麦秆EMAL(161.75 k J/mol)。     

不同金属改性对Pt/β-分子筛催化柴油车尾气中HC、CO及SO_2氧化性能的影响

采用共浸渍法制备了Ce、Cr、Mo和Cu改性的Pt/β-分子筛催化剂,运用氮吸附、XRD、H_2-TPR、NH_3-TPD和XPS等手段对该催化剂进行了表征,研究了不同金属改性对催化剂的织构性质、骨架结构、表面酸性以及在模拟柴油车尾气中抑制SO_2氧化性能和催化HC、CO氧化活性的影响。结果表明,金属改性对催化剂织构性能和骨架结构影响较小。Cr、Mo和Cu的添加可以调变催化剂酸强度,进而抑制SO_2的氧化;Cu改性的催化剂具有最好的抑制SO_2氧化的能力,在350和450℃条件下,与未改性Pt/β-分子筛催化剂相比,Cu改性催化剂上SO_2转化率分别下降了70.4%和70.2%。然而,改性金属与Pt物种之间产生的相互作用,会使Pt物种更难还原,导致Pt对HC和CO氧化的催化活性降低。     

VISCOSITY BEHAVIOR OF PS/TOLUENE SOLUTION IN DILUTE AND EXTREMELY DILUTE CONCENTRATION REGION

1.INTRODUCTIONAsearlyas1950sitwasfoundthatsolutionviscosityofasinglepolymerinextremelydiluteconcentrationregionusuallyrevealssomeabnormalities,i.e.,thereducedviscosityconcentration(hsp/c~c)curvesdeviatefromlinearrelationshippredictedasHugginsequationandshoweitheranupwardoradownwardturnasconcentrationisverylow[1].Evenifforthe[()-0.2()]identicalPMMA/toluenesolution,therearetwocontraryresults:onereportedthecurvebendsupward[2],whiletheotherfounditdownward[3].Inordertointerpretthisabnormalphe…     

大白鼠脑中风模型的核磁共振成像(英文)

核磁共振成像现今已经成为临床神经影像的常规工具.在诊断、评估和监测中风从急性到慢性的各个阶段的脑组织的变化过程中,核磁共振成像扮演了一个重要的角色.该综述提供了多种核磁共振成像方法的描述,以及选择性地展示了作者在美国亨利福特医院神经科核磁共振成像实验室所获得的大白鼠栓塞中风模型的核磁共振成像研究成果.     

A New Taxane Diterpenoid from the Seeds of Taxus yunnanensis

Plant from the genus of Taxus are a rich source of biologically active diterpennodsbelonging to the unique structural family of taxoids'. Although more than 300 taxoidswere isolated from yew tree', new taxoids still were isolated. In our continuing studieson the yew tree, we have previously isolated several new taxoids from seeds of theChinese yew, Taxus chinensiS var mairei. T yunnanensiS, and Japanese yew, TCuspidata'-'. Further investigation on the extract of the seeds of T yunnanensis …     

Design and Analysis of Diffractive Axicons for Gaussian Beam Illumination

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