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Single- and double-chain models of three stereoregular polymers, iso- and syndiotactic poly(methyl methacrylate) and isotactic poly(vinyl chloride), were extensively simulated using systematic coarse-grained (CG) potentials. It was found that, in vacuum, all of these long chains collapse in a two-stage process from their fully extended configurations into coils, and the two chains in each double-chain model ultimately become intertwined. Strong intermolecular interactions were found to occur between two chains of the same polymer (“like pairs”), which helps to explain the high densities of single-component melts. However, the intermolecular interactions between two chains of different polymers (“unlike pairs”) were stronger than those in like pairs. The enthalpy of mixing for unlike pairs—obtained from their intermolecular interaction energies—was negative, indicating that the two binary blends considered here are homogeneous systems. Moreover, a more negative enthalpy of mixing is suggested to correlate with better miscibility. These results agree well with corresponding experimental and simulated results, once again validating the accuracy of CG potentials when they are used to explore structural and energetic properties. The local structure captured by the isolated long chains dictates the ability to elucidate melt-phase behavior. A scheme involving the preparation of bulk models with initially collapsed chains was proposed; such CG models could be widely used to rapidly screen pairs of polymers for specific applications.
Graphical Abstract Melt phase behaviors dictated by isolated chains
龙须草对镉的耐受性和富集特征   总被引:2,自引:0,他引:2  
Liu AZ  Zou DS  Liu F 《应用生态学报》2011,22(2):473-480
利用盆栽试验,研究了龙须草对Cd的耐受能力和富集特征.结果表明:低浓度Cd处理(5 mg·kg-1)能促进龙须草的生长,增强其生理活性,生物量、净光合速率等12个指标比对照提高1.0%~15.5%;高浓度Cd处理(>5 mg.kg-1)对龙须草的生长产生抑制作用,但当Cd浓度达到100 mg.kg-1时,龙须草仍能完成正常的生理周期,生物量、净光合速率仅比对照分别下降27.0%和25.6%.龙须草各器官的Cd含量随Cd污染程度的上升而大幅度增加,根的Cd含量为350~500 mg.kg-1,茎叶为15~35 mg·kg-1.在Cd浓度<50 mg·kg-1时,吸Cd量随添加浓度的增大而增大,茎叶吸Cd量占总吸Cd量的15.7%~38.4%,茎叶与根的吸Cd量比值最高可达0.62.龙须草对Cd污染的耐受性、富集和转运能力均较强,是一种潜在的Cd超富集植物.  相似文献   
《Reproductive biology》2022,22(3):100682
This study compares three different mating techniques in Sprague-Dawley rats, using the pregnancy rate as the main indicator of success. It provides recommendations for timed-pregnancy experiments to achieve an appropriate sample size for the study of human pregnancy disorders. The implementation of a preconditioning phase, determination of the estrous cycle, the use of two mating strategies (Lee-Boot and Whitten effect), female: male mating ratios, and cohabitation duration should be considered as they improve the mating success rate.  相似文献   
《Reproductive biology》2022,22(3):100674
We examined the consequences of high-fat diet (HFD) on prostate histophysiology in two periods along sexual maturation of rats and the impact on the gland in adulthood. After weaning, male Wistar rats were fed a balanced diet (4 % fat-C3, C6, C9) or a HFD (20 % fat- HF3, HF6, HF9) for 3, 6 or 9 weeks. Fat deposit weights, blood glucose and levels of serum testosterone and estrogen were measured. Prostate was evaluated for histology, proliferative and apoptotic cell index, and for the expression of androgen (AR), estrogen receptors type α (ERα) and aromatase. HFD did not affect estrogen levels and elevated serum testosterone only in HF9. HFD reduced prostate weight in HF6 and increased it in adulthood (HF9) but relative prostate weight was unchanged among groups. Cell proliferation, height and density were higher in epithelium of all HFD-groups, compared to controls, featuring the epithelial hyperplasia. Epithelial apoptosis was lower in HF9. HF3 and HF9 exhibited higher expressions of ERα, indicating that HFD triggers a new activation of ERα expression in the acinar epithelium. The content of prostatic aromatase was also elevated in HF9. Increased numbers of AR-positive cells were observed in all HFD groups, and western blotting analysis showed an increase in the truncated form of 45 kDa (AR45) and a reduction in the expression of 110 kDa-AR for HF3 and HF9. In conclusion, excessive dietary fats during sexual maturation of rats led to developmental programming of the prostate, inducing a hyperplastic status with perturbations in AR isoforms expression and reactivation of ERα in adulthood, whose implications for posterior prostatic health could be detrimental.  相似文献   
《Reproductive biology》2022,22(3):100673
The abnormal spindle-like, microcephaly-associated (ASPM) gene is a causative gene of autosomal recessive primary microcephaly (MCPH) 5 in humans, which is characterized by a reduction in brain volume. It was previously reported that truncated Aspm proteins in transgenic mice caused major defects in the germline, a severe reduction in ovary weight and the number of follicles accompanied by reduced fertility. However; it remains unknown whether a loss of Aspm induces abnormal ovarian function, resulting in female infertility. In order to assess the ovary function, we examined vaginal smear cytology from the age of 7 weeks to 100 weeks in CAG-mediated Cre-loxP conditional Aspm-/- knockout mice and control female mice. In addition, we evaluated the ovarian size, fibrosis ratio and the number of follicles (primordial, primary, secondary, antral and atretic follicles) in mice from 15 weeks to 100 weeks old by image analyses. Mann-Whitney U-test was used for statistical analysis. The size of the ovary was significantly reduced in Aspm knockout mice at 15–20 weeks, 40–50 weeks and 70–80 weeks old compared with the control mice. Furthermore, at all stages, we found a severe decrease in the number of developing follicles at 10–15 weeks, 40–50 weeks and 70–80 weeks old, accompanied by disrupted cyclic changes of vaginal cytology and an aberrant upregulation of Foxo3, Kitl, and Lhcgr in Aspm knockout female. These results suggested that Aspm might play an important role in the folliculogenesis and estrous cyclicity of the postnatal ovary during maturation and aging.  相似文献   
以‘深两优5814’水稻种子为试验材料,用2.5%吡·咪、3%恶·咪、锐胜和适乐时分别包衣种子,测定水稻幼苗抗氧化酶活性、MDA含量、GSH含量、叶绿素含量和叶绿素荧光参数,探讨种衣剂对幼苗的胁迫机理,为种衣剂的安全高效应用提供理论依据。结果表明:(1)种衣剂能提高水稻幼苗的抗氧化酶活性,播种后14d,2.5%吡·咪和锐胜处理组叶片的SOD活性上升,3%恶·咪处理组叶片的POD活性上升;播种后22d,2.5%吡·咪和3%恶·咪处理组叶片的CAT活性上升;播种后26d,锐胜和适乐时处理组叶片的CAT活性上升;2.5%吡·咪和3%恶·咪显著提高了播种后22d叶片的MDA含量。4种种衣剂均能提升幼苗叶片GSH含量,并以3%恶·咪的提升效果最为明显。(2)4种种衣剂均能降低叶绿素含量,但随培养时间的延长叶片内叶绿素含量逐渐恢复到正常水平。(3)4种种衣剂对水稻叶片最大光化学效率φPo无显著影响,吸光性能指数PIABS值也未呈下降趋势,比活性参数ABS/CSM值随培养时间的延长出现下降趋势,其中以3%恶·咪处理组下降最为明显;同时,3%恶·咪处理组叶片的热耗散DIo/CSM值也显著高于对照。研究认为,各种衣剂对水稻幼苗生长造成了一定的胁迫,但水稻自身防御体系能有效缓解农药胁迫作用,种衣剂的使用处于安全水平,但3%恶·咪的胁迫较严重,使用效果较差。  相似文献   
[目的] 了解洞庭湖区入侵植物分布规律及其危害,对洞庭湖区入侵植物区系、种类组成、类型、生活型和原产地进行较为深入的研究。[方法] 通过实地调查、采集标本、查阅资料进行统计分析。[结果] 洞庭湖区外来入侵植物共有86种,隶属于24科64属,原产于美洲的有51种,占总数的58.6%,双子叶植物有21科53属73种,单子叶植物仅有5科12属13种,草本植物共84种,占97.6%,洞庭湖区入侵植物科的区系类型主要为世界广布;入侵植物属的区系类型以泛热带分布和世界广布为主。[结论] 洞庭湖区入侵植物种类较多、适应性强、繁殖速度快、繁殖能力强、传播途径多样、区系成分复杂且危害严重,应根据入侵现状对洞庭湖区外来入侵植物采取相应的的防治措施。  相似文献   
以13种苎麻属植物为试验材料,于植物工艺成熟期取样测定经济性状并用显微镜观察横截面及离析纤维细胞形态,研究苎麻属植物纤维细胞形态结构与其经济性状和物理性能的相关性。结果显示:(1)苎麻属野生种质的纤维细胞外观形态表现与栽培种苎麻基本一致,多呈圆形、多边形、椭圆形和肾形等,形态各异,大小不一。(2)茎秆横截面纤维细胞直径、腔径和纤维胞总数都明显少于对照栽培种,与其原麻产量存在不同程度的正相关性。(3)离析纤维细胞长度、宽度、壁厚和结节数与纤维细度存在不显著负相关,且野生苎麻属种质的细胞长度、宽度明显小于栽培种苎麻。研究表明,野生苎麻属种质在提高栽培种产量上无太大效应,但其在优良纤维基因选育方面和改良栽培种苎麻纤维品质上具有重要应用价值。  相似文献   
为了研究细胞骨架蛋白FtsZ在螺旋藻形态建成中的作用,通过PCR克隆了ftsZ基因并进行原核表达,对表达的融合蛋白进行了纯化。通过免疫小鼠制备了FtsZ的多克隆抗体。分别用Western blot和免疫荧光技术检测螺旋藻不同形态藻丝体中ftsZ的表达和定位。结果表明,在两株不同螺旋藻Spirulina platensisFACHB869和FACHB882中,ftsZ在直线形藻丝体中的表达量都高于螺旋形藻丝体。免疫荧光定位结果显示,FtsZ蛋白在藻细胞中呈环状分布于细胞膜上,且这种环状结构在直线形藻丝体中排列较密而在螺旋形藻丝体中排列疏松。ftsZ在不同形态藻丝体中的表达量和细胞定位差异说明,细胞骨架蛋白FtsZ可能通过改变细胞刚性而参与螺旋藻形态建成。  相似文献   
A novel series of hedgehog signaling pathway inhibitors has been designed based on the 4-(2-pyrimidinylamino) benzamides scaffold. The synthesis and SAR of these compounds are described. Optimization leads to the identification of compound 3c, a potent and orally available agent with improved physicochemical and pharmacokinetic properties.  相似文献   
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