冻融循环过程中混凝土的过冷现象及其原因分析

在研究冻融循环过程中混凝土和砂浆试件湿度和变形随温度变化规律时发现,在降温段混凝土和砂浆试件在0℃时并没有结冰,其冰点为-15℃,即出现了过冷现象.分析了产生过冷现象的原因,认为提供一定数量的凝结核可以消除过冷现象.试验中采取在砂浆试件中掺入水泥质量1％的碘化银和胆固醇来消除过冷现象,结果表明,掺入碘化银或胆固醇可以使砂浆试件的结冰温度提高5℃左右,即碘化银或胆固醇具有消除过冷现象的作用.     

循环荷载下钢渣砂浆的压敏特性研究

为研究钢渣掺量对钢渣砂浆强度特性的影响及钢渣砂浆压敏性在循环荷载下的变化规律,对不同钢渣掺量、不同龄期的钢渣砂浆进行无侧限抗压强度测试,分析了循环荷载下抗压强度范围内电阻率变化率随应力变化的规律.结果表明:钢渣砂浆无侧限抗压强度随钢渣掺量的增加而降低,随龄期的增加而增加;此外,在电阻率测试及压敏性分析时,由于电阻率受电流频率影响较大,建议选用50 kHz作为取值频率;当应力变化在无侧限抗压强度范围内时,电阻率变化率幅度随养护龄期的增加逐渐减小,其变化率可由养护7 d时的-4.83％降至28 d时-3.16％,同时变化幅度随钢渣掺量的增加逐渐增大.     

钢渣砂浆的交流电阻率特性

通过对钢渣砂浆电阻率及无侧限抗压强度的测定,研究了交流电流频率、龄期、钢渣掺量对砂浆试件电阻率的影响,并且对钢渣砂浆无侧限抗压强度与电阻率的关系进行了分析.分析结果表明,在50 Hz～50 kHz范围内时,交流电流频率对钢渣砂浆的电阻率影响较大;在50 kHz～1 MHz范围内时,随着电流频率的增大,试件的电阻率变化趋于平缓.钢渣砂浆试块电阻率随养护龄期的增大而增大,随钢渣掺量的增加总体呈减小趋势.钢渣砂浆的无侧限抗压强度随钢渣掺量的增加而减小,与电阻率之间存在正相关关系.     

冻融循环下混凝土内部结冰及氯离子传输规律的数值研究

北方除冰盐地区和临海地区的混凝土耐久性问题显著。冻融循环作用会粗化孔隙结构,促进氯离子传输;另外,温度的降低会使孔隙溶液结冰,阻碍离子传输。而氯盐浓度的改变也会影响孔隙相变,进而再度作用于离子传输。针对这一复杂的耦合过程,本工作提出了冻融过程中孔隙溶液结冰率计算模型,进而分析溶液结冰对离子传输的影响,并建立经过多组第三方试验验证的冻融–离子传输的多相数值模型。结果表明：混凝土的结冰率及氯离子浓度均随着冻融循环次数的增加而增大;冻融温度及冻融持续时间对氯离子的传输具有重要影响;外界盐溶液浓度的增加虽有利于孔隙结冰温度的降低和结冰率的减小,但总体上仍加速氯离子的传输,加速混凝土耐久性的恶化。     

水泥沥青砂浆力学性能的温度敏感性

研究了不同温度条件下不同沥青含量的水泥沥青砂浆的抗压性能,以揭示该类有机–无机复合材料力学性能的温度敏感性规律。在–40～80℃范围内选择不同环境温度,采用电液伺服控制材料万能试验机测试了水泥沥青砂浆静态单轴抗压荷载下的应力–应变全曲线,获得了峰值应力和弹性模量随温度变化的基本规律。结果表明:随温度的降低,应力–应变曲线的上升段斜率增大,峰后下降段逐渐变陡,力学特性逐渐出现韧–脆转换。一般而言,水泥沥青砂浆的弹性模量和峰值应力随温度的升高和沥青含量的增大而降低,其温度敏感性随沥青含量的增大而增大。沥青含量较大的水泥沥青砂浆,其弹性模量和峰值应力随沥青含量变化幅度不大。建立的经验关系式成功描述了不同沥青含量的水泥沥青砂浆力学性能随温度变化的定量关系,且拟合结果表明以温感因子表征其力学性能对温度的敏感性具有一定的合理性。温感因子随着沥青含量的增大而增大,峰值应力的温感因子大于弹性模量的。     

冻融循环作用下半套筒灌浆连接节点试验研究

通过对φ14 mm与φ20 mm两种规格的半灌浆连接接头试件进行冻融循环及单向拉伸试验,对比常温及冻融循环作用下接头试件力学性能,分析冻融循环条件、冻融循环次数及钢筋直径对半套筒灌浆接头力学性能的影响.结果 表明:与常温下试件相比,经冻融循环作用后试件的极限承载力较常温下试件出现一定程度下降,且随冻融循环次数增加下降幅度增大;经冻融循环作用后试件的破坏位移较常温下试件出现一定程度增加,且位移增加幅度随冻融循环次数增加而增大,破坏位移越大,表明钢筋与灌浆料之间的锚固性能越差;尽管试验用接头试件经冻融循环作用后力学性能出现一定程度下降,但其仍满足规范所需强度要求,可用于寒冷地区冻融循环条件下装配式建筑的施工.     

冻融循环作用下饱水砂浆孔结构的演变规律

为揭示水泥基材料低温冻融孔结构损伤的演变规律,以饱水白水泥砂浆为研究对象,利用低场磁共振技术测试了砂浆试件在连续冻融循环作用下的孔结构。设计了20℃常规养护和80℃高温养护制度以改变砂浆的初始孔隙结构,随后对这两种相同配比、不同孔结构的砂浆进行快速和慢速冻融循环试验。结果表明:80℃高温养护会显著降低砂浆抗冻性,增大凝胶孔并提高粗毛细孔体积分数,但不会显著改变介观毛细孔的分布强度;与高温养护作用相反,冻融循环作用不会改变凝胶孔和粗毛细孔的分布强度,但能显著提高微裂纹的分布强度;80℃高温养护砂浆在冻融作用下的微裂纹体积增长速率显著高于20℃常规养护砂浆;冻融速率不会显著影响砂浆的孔径分布变化规律;砂浆内部微裂纹体积增大和质量损失增加呈双线性关系。砂浆内部冻融破坏和外部剥落均主要源自于微裂纹的产生和发展,与凝胶孔和粗毛细孔无明显相关性。     

多层石墨烯/钢纤维复合砂浆导电性能研究

制备了多层石墨烯(MG)/钢纤维(SF)复合砂浆.利用四电极法测试复合砂浆的电阻率,研究了测试时间、MG和SF掺量、养护龄期和含水量对砂浆电阻率的影响,并通过扫描电镜观察多层石墨烯在砂浆中的微观形貌.结果表明:砂浆外通电流后,内部产生的极化效应导致测试电阻率随导电时间增长而增大,导电填料抗氧化性越强,极化效应越小;砂浆的电阻率随MG和SF掺量的变化出现了渗流现象,运用GEM理论拟合了单掺MG和SF砂浆的电导率与其掺量的关系;MG和SF的协同作用可以增加导电链条、提高导电能力,其中复掺SM比单掺MG电阻率降低21.7％～41.8％;养护龄期越长,砂浆导电能力越差;砂浆干燥状态下的电阻率比湿润状态增加了29％～199％,复掺不同导电填料或增加导电填料含量,都能降低含水量对电阻率的影响.     

降温速率对Ba0.92Ca0.08TiO3 PTCR陶瓷室温电阻率"反常"现象的影响

通过系统研究烧结工艺对BaO92Ca0.08TiO3电阻正温度系数(possitive temperature coefficient resistance，PTCR)陶瓷的影响，在晶粒生长过程中分析液相在晶界中的分布。着重研究降温速率对PTCR室温电阻率的影响。发现在1300～1150℃温区内，当降温速率大于15℃／min时，出现随降温速率增加，室温电阻率增大的“反常”现象。根据液相在晶界区分布随降温速率的变化规律，对这种“反常”进行解释。     

不同温度条件下废弃牛奶盒/聚乙烯复合材料性能的研究

研究了温度对于废弃牛奶盒/聚乙烯复合材料性能的影响。结果表明:(1)废弃牛奶盒/聚乙烯复合材料在52、85、-29、-40℃四种典型的温度环境中处理15 d后,各个方向的尺寸变化率符合热胀冷缩的规律,且各个方向的尺寸变化率呈现出典型的各项异性特征,其中厚度方向的尺寸变化率最大;(2)材料在52、85℃下处理一个月后,弹性模量和弯曲强度都降低了很多,且随着温度的升高,降低的幅度也有所增加,85℃下材料几乎丧失了弯曲强度;在-29、-40℃下处理一个月后,弹性模量和弯曲强度都呈现出了增大的趋势,且随着温度的降低,增大的幅度也在变大;(3)材料经历不同的温度段的冻融循环后,弹性模量和弯曲强度降低的幅度随着温度差的增加而增加;随着循环次数的增加而增加;与经历单纯的高温或者低温的材料的弹性模量和弯曲强度保留率进行对比,冻融循环对材料的弯曲性能影响更大。     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

Sapindaceae,cyanolipids, and bugs

Scentless plant bugs (Heteroptera: Rhopalidae) are so named because adults of the Serinethinae have vestigial metathoracic scent glands. Serinethines are seed predators of Sapindales, especially Sapindaceae that produce toxic cyanolipids. In two serinethine species whose ranges extend into the southern United States,Jadera haematoloma andJ. sanguinolenta, sequestration of host cyanolipids as glucosides renders these gregarious, aposematic insects unpalatable to a variety of predators. The blood glucoside profile and cyanogenesis ofJadera varies depending on the cyanolipid chemistry of hosts, and adults and larvae fed golden rain tree seeds (Koelreuteria paniculata) excrete the volatile lactone, 4-methyl-2(5H)-furanone, to which they are attracted.Jadera fed balloon vine seeds (Cardiospermum spp.) do not excrete the attractive lactone. Loss of the usual heteropteran defensive glands in serinethines may have coevolved with host specificity on toxic plants, and the orientation ofJadera to a volatile excretory product could be an adaptive response to save time.Mention of a commercial product does not consititute an endorsement by the USDA.     

2008～2009年世界塑料工业进展

收集了2008年7月～2009年6月世界塑料工业的相关资料,介绍了2008～2009年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况。按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、环氧树脂、不饱和聚酯树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍。     

ICP-MS法测定地球化学样品中As、Cr、Ge、V等18种微量痕量元素的研究

建立了测定地球化学样品中包括As、Cr、Ge、V等18种微量、痕量元素的ICP-MS方法。地化试样用HF-HNO3混酸分解后,以1 1 HNO3溶解干渣。由于制样不使用盐酸,避免了Cl对As、Cr、Ge、V的质谱干扰。用国家一级地球化学标准物质GBW 07309制备溶液优化仪器工作参数,并用于校准。方法测定限(6s)为:0.007~6.4μg/g,精密度(RSD%,n=12)为:29%~9.4%,经过国家一级地球化学标准物质的分析验证,结果与标准值吻合。方法已应用于国土资源调查的试样分析。     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.