Electron Excited L X-Ray Spectra of the Elements 24 ≤ Z ≤ 33

A reinvestigation was undertaken in order to obtain reliable data of the relative intensities of the L spectra for the elements 24 ≤ Z ≤ 33. A TAP crystal with a periodicity of 25.757 ? was used as the dispersing element. With this crystal one is able to resolve the lines/bands Ll = L₃M₁, Lη = L₂M₁, Lα_1,2 = L₃M_4,5, Lβ₁ = L₂M₄, and Lβ_3,4 = L₁M_2,3. Among the investigated elements ³³As is the only one for which the energy of the lines Lα_1,2 and Lβ₁ is below the L₃ absorption edge. For all the other elements the lines Ll, Lη, and Lα_1,2 are below the L₃ edge, whereas Lβ₁ and Lβ_3,4 are above this edge. This difference leads to effects of differential absorption, where the absorption is stronger for decreasing line energy. For the net peak height ratio β₁/α we obtained results which are of the same order of magnitude as those given by White and Johnson (W&J) in their popular tables. But for l/α and β_3,4/β₁ our results show an atomic number dependence which is completely different from those given by W&J.     

Measurements of calcium with a fluorescent probe Rhod-5N: Influence of high ionic strength and pH

We describe a new method for the spectroscopic determination of high calcium concentration using a fluorescent probe Rhod-5N. This method was investigated in order to be utilized in high ionic strength solution, such as seawater. The probe is fluorescent when bound to calcium, LM, but not as the free form L. The dissociation constant of the equilibrium (0.14 mM) was determined at several ionic strengths, i.e. in the absence and in the presence of additional ions (0.7 M NaCl). The influence of pH was studied. In order to correctly model the experimental data, we included a new fluorescent compound: LHM (calcium bound protonated probe). The first acidity constant (0.02 μM) and the second dissociation constant (4.5 mM) were calculated. A useful range for the determination of calcium concentration is provided. Such a method is fast and easy to carry out.     

Surface composition of alloys

The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success.     

经济活动中的几个数学模型及其应用

随着市场经济的不断发展，利用数学知识解决实际问题变得越来越重要。本文重点探讨了经济活动中几个非常实用的数学模型的构建与应用问题。     

Single tungsten nanowires as pH sensitive electrodes

The electrochemical potentials of tungsten nanowire samples, covered with their own oxide, were measured in dependence of the pH value. The samples were prepared by selective etching of a directionally solidified eutectic NiAl–W alloy. Directional solidification in a Bridgman-type crystal growth furnace yields nanostructured two-phase materials. Electrochemical processing allows selective etching of the phases exposing the nanoscale structures. In this work, pointed samples with a single wire 200 nm in diameter protruding from the tip were produced. Subsequently the tungsten oxide layer on these single nanowires was electrochemically modified to optimize their pH sensing capabilities. The method has a potential for further downsizing since the wire diameter and exposed length can be controlled by the process parameters during solidification and during electrochemical processing. The advantages of these nanowire pH probes along with possible applications such as the pH measurement in ultra small cavities and other small systems of interest such as corrosion pits and biological cells are discussed.     

Electrochemical Probe of the Reduced Graphene Oxide Modified by Bare Gold Nanoparticles Functionalized Zr(IV)-based Metal-organic Framework for Detecting Nitrite

Widely presented nitrite in drinking water, food and even physiological system endangers human health. Here,bare gold nanoparticles functionalized Zr-based metal-organic framework modified reduced graphene oxide (GNPs/UiO-66-NH₂/rGO) nanocomposites were prepared by hydrothermal method. This experiment studies the morphology, composition, structure and electrochemical behavior of the sensor. The experimental results show that the sensor has a peak potential of 0.9 V, the concentration range of NO₂⁻ is 5.0 μM to 768 μM, the linear regression equation of the calibration curve is I_pa=0.3646+0.00642 C (R²=0.9998), and the LOD is as low as 3.7 μM (S/N=3). Therefore, an electrochemical sensor platform for trace detection of NO₂⁻ was successfully constructed.     

Au@SiO_2单层膜间耦合效应的表面增强拉曼光谱研究

借助水/油两相界面自组装形成致密排列且有序稳定的Au@SiO2单层膜,通过膜层层转移到固相基底的方法制备了具有不同纳米粒子层数的SERS基底,成功在同一硅片上制备了六层Au@SiO2纳米粒子膜,研究了不同膜层数与SERS信号的关系,结合SERS成像技术可测定纳米粒子膜在基底上的层数。通过改变探针分子在多层纳米粒子膜上的位置,研究了纳米粒子膜间的耦合增强效应。研究表明,同一层膜表面探针分子的SERS信号分布均匀,随膜层数的增加,SERS信号明显增强,当膜层达到第五层时探针分子的SERS信号最强,之后几乎保持不变,说明SERS信号主要来源于表层的五层纳米粒子膜,位于五层以下纳米粒子对SERS效应并没有贡献。固定探针分子仅吸附于底层纳米粒子表面,当再覆盖一层裸露纳米粒子膜后,SERS信号达到最大,其主要源于热点的增强作用占主导地位,而覆盖至第三层时,SERS信号反而出现微小减弱,这是由于多层的Au@SiO2纳米粒子膜影响了激发光以及信号的传播,但粒子间产生的耦合效应仍对底层的探针分子起增强作用,当覆盖至五层Au@SiO2膜后,探针分子SERS信号完全消失,由此说明纳米粒子单层膜控制在三层以内可有效检测底层及以上所有纳米粒子上吸附分子的SERS信号,该结果为制备理想SERS基底提供了实验依据。     

Luminescent CuS nanotubes as silver ion probes

CuS nanotubes (NTs) made up of nanoparticles were successfully prepared in large quantities in an O/W microemulsion system under low temperature. Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional copper sulphide (CuS) nanotubes as a fluorescence probe. Under optimal conditions, functional copper sulphide displayed a calibration response for silver ion over a wide concentration range from 1.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ mol L⁻¹. The limit of detection was 0.5 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of eight replicate measurements for the highest concentration (1 × 10⁻⁸ mol L⁻¹) was 3%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.     

Fluorescence study on the nyctinasty of Phyllanthus urinaria L. using novel fluorescence-labeled probe compounds

We report the synthesis of fluorescence-labeled probes based on phyllanthurinolactone 1, which is a leaf-closing substance of Phyllanthus urinaria L. The fluorescence study using biologically active probe 2 and inactive probes (epi-2 and 31) revealed that the target cell for 1 is a motor cell and suggested that some receptors, which recognize the aglycon of 1 exist on the plasma membrane of the motor cell, as with leaf-opening substances. Moreover, binding of probe 2 was specific to the plant motor cell contained in the plants belonging to the genus Phyllanthus. These results showed that the binding of probe 2 with a motor cell is specific to the plant genus and suggested that the genus-specific receptor for the leaf-closing substance would be involved in nyctinasty.