Measurements of low-molecular-mass carboxylic acids in atmospheric aerosols by capillary electrophoresis

Capillary electrophoresis (CE) methods for the determination of low-molecular-mass (LMM) carboxylic acids in airborne particular matter have been developed. The separations of 22 LMM carboxylic acids, including acids derived from the oxidation of biogenic hydrocarbons, are performed using a background electrolyte consisting of 3.0mM 2,6-naphthalenedicarboxylic acid and 18.0mM 2,2-bis (hydroxymethyl)-2,2',2"-nitrilotriethanol (Bis-tris) in 16% (v/v) 1-propanol within 10 min. Using a combination of a buffer mixed with an organic solvent and electroosmotic flow modifier, a minimum of peak overlaps is achieved with migration time variation of less than 1% and peak area ratio (relative to an internal standard) variation of less than 5% within 1 day. The detection limits for the aliphatic LMM acids that can be determined by this method are in the range of 30-140 micro g/L. Furthermore, a simple method for efficient extraction of LMM organic acids from particulate atmospheric matter collected on quartz fiber filters using high-volume samplers is developed. Combining the extraction procedure with a reduction of the extract to approximately 0.2 mL allows for the measurement of LLM in atmospheric particulate organic matter at concentrations well below 1 ng.m(-3). Repeat analysis of filters collected in tunnels, urban, suburban, and forested areas demonstrate that the procedure allows for measurements of aliphatic and aromatic LMM acids within a variability of 10-25%.     

On the alpha --> beta transition of carbon-coated highly oriented PVDF ultrathin film induced by melt recrystallization

Poly(vinylidene fluoride) (PVDF) is one of the polymers which exhibit pronounced polymorphic crystalline forms, depending on crystallization conditions. Four different crystalline modifications, i.e., alpha, beta, gamma, and delta, have been reported so far. Among them, even though the alpha-form is the most common one, the beta-phase is the one that has attracted the widest interest due to its extensive piezo- and pyroelectric applications. During the past few decades, a substantial amount of work has been done in attempts to characterize these crystal modifications and transformations among them. It was well documented that the alpha-form PVDF can be easily obtained through melt crystallization of the PVDF at atmospheric pressure. Its beta-counterpart can, however, only be directly obtained by growth from solution, molecular epitaxy on the surface of potassium bromide, melt crystallization at high pressures, or by applying with a strong electric field. Transformation from its alpha-phase to beta-phase has been achieved by mechanical deformation, while the retransformation could be conducted through melt recrystallization at atmospheric pressure. In the present work, the recrystallization behavior of carbon-coated melt-drawn oriented PVDF ultrathin films at atmospheric pressure was studied by means of transmission electron microscopy and electron diffraction. The results indicate that through vacuum evaporating a thin carbon layer on the surface of highly oriented alpha-PVDF ultrathin film, not only has its high orientation been preserved after a complete melting and recrystallization process, but an alpha --> beta transition of PVDF has also been achieved through melt recrystallization at atmospheric pressure. This technique can be successfully used for preparing highly oriented beta-PVDF ultrathin films, especially patterned microstructures of PVDF with its highly oriented polar beta-phase and nonoriented nonpolar alpha-phase.     

义务教育化学课程标准中"活动与探究建议"的价值、类型和特点分析

在义务教育化学课程内容标准中，每个二级主题都从“标准”和“活动与探究建议”两个维度，对化学学习内容进行了说明。“活动与探究建议”作为化学课程内容的一部分，第一次写进“标准”中，成为化学学习内容的一个新“栏目”。对于这一新的设置，迫切需要进行较为系统的分析和研究。     

人发的光谱分析进展

评述了用分光光度、荧光（原子荧光）、原子吸收、原子发射光谱方法进行人发中我种元素测定的分析（包括发样采集、洗涤、消化），引用文献９６篇。     

Hyperpolarizabilities for the one-dimensional infinite single-electron periodic systems. I. Analytical solutions under dipole-dipole correlations

The analytical solutions for the general-four-wave-mixing hyperpolarizabilities chi(3)[-(omega1 + omega2 + omega3);omega1,omega2,omega3] on infinite chains under both Su-Shrieffer-Heeger and Takayama-Lin-Liu-Maki models of trans-polyacetylene are obtained through the scheme of dipole-dipole correlation. Analytical expressions of dc Kerr effect chi(3)(-omega;0,0,omega), dc-induced second-harmonic generation chi(3)(-2omega;0,omega,omega), optical Kerr effect chi(3)(-omega;omega,-omega,omega), and dc electric-field-induced optical rectification chi(3)(0;omega,-omega,0) are derived. By including or excluding nabla(k) terms in the calculations, comparisons show that the intraband contributions dominate the hyperpolarizabilities if they are included. nabla(k) term or intraband transition leads to the break of the overall permutation symmetry in chi(3) even for the low-frequency and nonresonant regions. Hence it breaks the Kleinman [Phys. Rev. 126, 1977 (1962)] symmetry that is directly based on the overall permutation symmetry. Our calculations provide a clear understanding of the Kleinman symmetry breaks that are widely observed in many experiments. We also suggest a feasible experiment on chi(3) to test the validity of overall permutation symmetry and our theoretical prediction. Finally, our calculations show the following trends for the various third-order nonlinear optical processes in the low-frequency and nonresonant region: chi(nonres)(3)(-3omega;omega,omega,omega)>chi(nonres)(3)(-2omega;0,omega,omega)>chi(nonres)(3)(-omega;omega,-omega,omega)>chi(nonres)(3)(-omega;0,0,omega) > or = chi(nonres)(3)(0;omega,-omega,0), and in the resonant region: chi(res)(3)(-omega;0,0,omega)>chi(res)(3)(-omega;omega,-omega,omega)>chi(res)(3)(-2omega;0,omega,omega)>chi(res)(3)(0;omega,-omega,0)>chi(res)(3)(-3omega;omega,omega,omega).     

129Xeq+轰击N型和P型Si表面时的电子发射产额研究

在兰州重离子加速器国家实验室测量了1.8 MeV Xeq+离子分别轰击N型和P型Si两种靶材表面时的电子发射产额。实验中,通过改变入射离子的电荷态,研究了入射离子势能沉积对两种靶材表面电子发射产额的贡献。结果发现同一离子入射时,N型Si表面的电子发射产额高出P型Si表面的电子发射产额约12.5%;对于具有相同入射动能的Xeq+离子,两种靶材表面的电子发射产额均随着入射离子势能的增加而线性增加。此外,还测量了3.4 MeV Xeq+离子分别轰击以上两种靶材时的电子发射产额,得到了类似的结果。本文利用功函数分别从动能电子发射和势能电子发射两个角度对实验结果进行了分析讨论。The electron emissions from N-type Si and P-type Si induced by 1.8 MeV 129Xeq+are measured in the National Laboratory of Heavy Ion Research Facility in Lanzhou,The contribution to electron emission yield from potential energy of incident ions is studied through changing the charge state of incident ions.The results show that for the same incident ion,electron emission yield of N type Si surface is higher than that of P-type Si surface about 12.5%.For incident ions with the same kinetic energy,both electron emission yields of two targets increase linearly with incident ion energy.In addition,the electron emissions induced by 3.4 MeV 129Xeq+from N-type Si and P-type Si mentioned above are measured,which give similar results.The experimental results are analyzed and discussed using work function from two angles of the kinetic electron emission and the potential energy electron emission.     

Helicity and electron-correlation effects on transport properties of double-walled carbon nanotubes

Starting from selection rules for intershell tunneling in double-walled nanotubes with commensurate (c-DWNTs) and incommensurate (i-DWNTs) shells, we show that for i-DWNTs the coupling is negligible between lowest energy subbands, but it becomes important as the higher subbands become populated. In turn the elastic mean-free path of i-DWNTs is reduced for increasing energy, with additional suppression at subband onsets and crossings. At low energies, a Luttinger liquid theory for DWNTs with metallic shells is derived. Interaction effects are more pronounced in i-DWNTs than in c-DWNTs.     

Cellulose nanosheets induced by mechanical impacts under hydrophobic environment

The nanoscale structural changes of crystalline cellulose by mechanical milling was studied by high-resolution microscopy (AFM, SEM, TEM). We examined influence of environment [dry, water, silicone oil (PDMS)] on cellulose milling, finding their characteristic effects on microscopic morphology of the products. Dry milling of cellulose gave aggregated globular particles with fast decrystallization. Milling with water or PDMS caused partial dispersion of nanofibers. Milling with PDMS formed micro-platelets <1 µm thick with slight decrystallization. Remarkably, nanoscale particles isolated from PDMS-milled cellulose by sonication in ethanol contained cellulose nanosheets, typically 0.1–10 µm wide and 4.2 nm thick, apparently formed by monolayer association of elementary fibrils. TEM and electron diffraction revealed crystalline nature of nanosheets, with specific orientation of (110) plane or (200) plane perpendicular to the sheet plane. A possible mechanism of the nanosheets formation is proposed, in which the elementary fibrils are aligned parallel by mechanical impacts.     

Formation mechanisms and crystallographic characteristics of metastable VO2(A) nanofiber hydrothermally synthesised in V2O5–H2C2O4–H2O system

There are many similarities between VO₂(B) and VO₂(A) from crystallographic view. However, missing of VO₂(A) during the preparation of VO₂ polymorph confused many researchers. Here, the preparation of VO₂(A) was studied systemically via a hydrothermal method in V₂O₅–H₂C₂O₄–H₂O system. As a metastable phase, it can be transferred from VO₂(B) by assembling process. Usually, poly-crystal VO₂(A) nano-fibers are formed by this process. On contrast, owing to the small energy gap between meta-stable VO₂(A) and stable VO₂(R), single crystal VO₂(A) with regular shape can also be obtained by exfoliating some parts of VO₂(R) during non-equilibrium cooling process. VO₂(A) has higher phase transition temperature than stable VO₂(R). The hysteresis in this phase transition can be observed by DSC measurement and the phase transition temperature of VO₂(A) can be tuned down by tungsten doping.     

与科学探究相匹配的化学教学内容选择研究

培养学生的科学探究能力,已经成为当代化学课程与教学改革的核心要求。围绕科学探究进行化学教学内容的选择、创设一个有利于进行科学探究的情景是当前迫切需要解决的问题。本文从增强学生对化学学科内容的理解能力、有助于理解科学家是如何研究自然界的、培养调查能力和科学思维等方面讨论了选择化学教学内容的原则。