排序方式: 共有49条查询结果,搜索用时 15 毫秒
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实验研究了硅胶在293、303和313 K下,从水溶液中对丙酸和丁酸的吸附.发现该吸附服从液 固吸附中的计量置换吸附模型(SDM A).根据吸附模型的线性参数研究了吸附热力学和吸附机理.该吸附是一个自发的、放热的熵减少过程.丁酸的标准吸附自由能比丙酸大,而标准吸附焓比丙酸小.推导出了实验条件下吸附自由能变化的计算公式. 相似文献
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利用荧光光谱法,研究了1,4,7,10-四氮杂环十二烷合钴(Cyclen-Co(Ⅱ))配合物与牛血清白蛋白(BSA)的相互作用,用Stern-Volmer和Lineweaver Burk方程确定了其荧光猝灭机理为静态猝灭,计算得到了在不同温度和pH值条件下以及在聚氧乙烯(23)月桂醇醚(Brij35)、十六烷基三甲基溴化铵(CTAB)、十二烷基硫酸钠(SDS)3种表面活性剂胶束溶液中,Cyclen-Co(Ⅱ)和BSA作用的结合点位数、结合常数和热力学参数,研究结果表明,其作用力主要为氢键和范德华力。 相似文献
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绿锈与As(V)可共存于土壤、沉积物和地下水等缺氧环境,但As(V)如何影响绿锈转化过程和机制了解甚少.本工作通过溶液化学和光谱学方法,系统研究了As(V)浓度、pH、温度和空气流速对硫酸盐绿锈(GR)转化的影响.GR转化过程中通过吸附和共沉淀作用对As(V)有极强的去除能力,同时As(V)增强了GR的稳定性,显著影响转化产物的结晶度、矿物类型和生成机制.随As(V)浓度增加,GR氧化转化由溶解-氧化-沉淀机制向固态氧化机制过渡,产物由针铁矿和纤铁矿混合相向纯纤铁矿向纤铁矿、水铁矿和高铁绿锈混合相转变;高As(V)浓度时形成无定形FeAsO4表面沉淀.Fe/As=24时,pH 6.5~9、温度(5~45℃)和空气流速(0~0.05 m3/h)条件下纤铁矿均为主要产物,随pH和空气流速增加或温度减小纤铁矿结晶度逐渐减弱;高pH或高空气流速或低温有利于高铁绿锈和水铁矿形成,高温有利于针铁矿形成.上述结果对深入理解环境中各种铁氧化物的形成转化机制和As(V)的环境行为有重要意义. 相似文献
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A novel structure is proposed for doubling the vertical breakdown voltage of silicon-on-insulator(SOI) devices. In this new structure, the conventional buried oxide(BOX) in an SOI device is split into two sections: the source-section BOX and the drain-section BOX. A highly-doped Si layer, referred to as a non-depletion potential-clamped layer(NPCL), is positioned under and close to the two BOX sections. In the split BOXes and the Si region above the BOXes, the blocking voltage(BV) is divided into two parts by the NPCL. The voltage in the NPCL is clamped to be nearly half of the drain voltage. When the drain voltage approaches a breakdown value, the voltage sustained by the source-section BOX and the Si region under the source are nearly the same as the voltage sustained by the drain-section BOX and the Si region under the drain. The vertical BV is therefore almost doubled. The effectiveness of this new structure was verified for a P-channel SOI lateral double-diffused metal-oxide semiconductor(LDMOS) and can be applied to other high-voltage SOI devices. The simulation results show that the BV in an NPCL P-channel SOI LDMOS is improved by 55% and the specific on-resistance(Ron,sp) is reduced by 69% in comparison to the conventional structure. 相似文献
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High-level theoretical study of the evolution of abundances and interconversion of glycine conformers 下载免费PDF全文
The relative conformer energies of glycine are evaluated by using a focal point analysis expressed as(HF→MP2→MP3→CCSD→CCSD(T)).The conformer abundances at various temperatures(298–500 K) are calculated based on the relative energies and Boltzmann statistical thermostatistical analysis with and without considering internal hindered rotations.A comparison between the available Raman spectrum and the electron momentum spectrum confirms that the influence of rigid-rotor hindered rotation on the conformational proportions of glycine is considerable,especially for the IIIp structure.The conformational interconversions are discussed.It is found that with increasing temperature,the mole fraction of IIn keeps constant and Ip structure can convert into IVn and IIIp,leading to the decrease in the weight of Ip and the increase in the weights of IVn and IIIp conformers,which is in accordance with experimental observations. 相似文献
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为了准确地测量轴锥透镜锥角值,根据无衍射光同心圆环间距不随距离改变的特点和莫尔条纹放大的特性,提出了一种基于无衍射光莫尔条纹的轴锥透镜锥角的测量方法。当无衍射光束经分束器分光合束后形成莫尔条纹,平移其中一束光在图像传感器上的位置,实现莫尔条纹数量的变化,通过记录不同莫尔条纹下的中心距离计算出轴锥透镜锥角。实验以锥角为0.5°的轴锥透镜作为被测对象,与CMM测量结果进行比较,该文提出的方法相对测量误差近似为0.54%,重复性为0.86″,验证了该文方法测量轴锥透镜锥角的可行性。 相似文献