Volatile organic compound emissions from markers used in preschools,schools, and homes

There is little published research examining volatile organic compound (VOC) emissions from art markers. In this study, we characterised VOC emission rates from markers commonly used by children at home and in school, and by teachers in their classrooms. We developed a method to measure standardised emission rates under controlled laboratory conditions, focusing on four major marker types: permanent, dry erase, highlighter, and washable. Emission rates for other less common marker types were also measured. We conducted additional experiments determining changes in emission profiles over short and long time periods (several hours up to daily use over about 2 months), as well as during periods of active drawing. We tested a total of 101 markers and report emission rates for 60 chemicals. Permanent and dry erase markers had average total VOC emissions more than 400 times higher than highlighters and washable markers. Alcohols were the most highly emitted class of VOCs from permanent and dry erase markers. Some chemicals associated with potentially serious health concerns were also identified. Future studies that employ full-scale chamber experiments and personal monitoring in classrooms to measure children’s actual exposures are recommended.     

Pervaporation by a continuous membrane column

The possibility and applicability of the continuous membrane column concept to the membrane separation process of pervaporation has been demonstrated. It shows that a mixture of two or more liquids can be separated to a high degree without cascading several stages of individual pervaporation units. The degree of enrichment is unlimited in a continuous membrane column while a maximum limit exists in a conventional pervaporator. This new concept of membrane operation has been shown previously to give enhanced separations in gaseous systems without the expense and complexity of a multi-staged cascade.

The permeabilities of silicone rubber to ethanol—water and isopropanol—water mixtures were determined at 25 and 40°C as a function of concentration. Separation experiments were carried out in small membrane columns. Included were instances in which feed mixtures just below the azeotrope (because of the small size of the experimental column) were enriched beyond the normal azeotropic composition (0.89 mole fraction ethanol) on a continuous basis. Feed compositions at other levels were also investigated; for example, a feed at 0.50 mole fraction ethanol was continuously separated into two streams at 0.69 and 0.12 mole fraction ethanol Finally, a mathematical analysis has been developed which adequately describes capillary membrane pervaporation within a continuous membrane column configuration.     

Allgemeine Apparate

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联苯胺分光光度法测定食盐中碘含量

基于在盐酸介质中,碘酸钾氧化联苯胺使其显色,提出了光度法测定食盐中微量碘的方法。在40℃的水浴中,当2 mol.L-1盐酸溶液用量为1.00 mL0、.42 g.L-1联苯胺溶液用量为0.80 mL时,方法的线性范围为100~1 400μg.L-1,最大吸收波长在425 nm处,表观摩尔吸光率为1.4×105L.mol-1.cm-1。用于测定加碘食盐中碘含量的测定,回收率在97.5%~101.2%之间,相对标准偏差(n=7)在0.9%~1.9%之间。     

Time-reversible continuum mechanics

Levesque and Verlet developed a time-reversible and bit-reversible computational leapfrog algorithm. Their algorithm uses integer arithmetic and is exactly time reversible to the last computational bit describing the particle coordinates. We generalize their idea, developed for atomistic molecular dynamics, to smoothed-particle continuum mechanics. In the special case of a two-dimensional isentropic ideal gas, these two approaches, one microscopic and the other macroscopic, are isomorphic. In the more general nonadiabatic case, but still without dissipative terms, our continuum extension of the leapfrog scheme remains stable and also exhibits the exact time and bit reversibility associated with Levesque and Verlet's atomistic approach.     

Monoreduced 1,2‐dihydrocorannulene versus the parent corannulene

The monoanion of dihydrogenated corannulene isolated in the form of its potassium salt, namely tris(diglyme‐κ³O,O′,O′′)potassium hexacyclo[11.5.2.0^4,17.0^7,16.0^10,15.0^14,18]icosa‐1,3,5,7(16),8,10(15),11,13,17‐nonaenide, [K(C₆H₁₄O₃)₃](C₂₀H₁₂), has been structurally characterized for the first time. The X‐ray study confirms the previous NMR spectroscopic prediction that the two H atoms are attached to the same six‐membered ring to form 1,2‐dihydrocorannulene, thus destroying the aromaticity of only one arene ring of the corannulene core. The direct comparison of (C₂₀H₁₂)⁻ with the parent corannulene anion, (C₂₀H₁₀)⁻, is provided to illustrate the geometry perturbations caused by rim hydrogenation.     

To change or not to change: adapting mathematical knowledge for teaching (MKT) measures for use in Korea

This paper examines challenges in adapting mathematical knowledge for teaching (MKT) measures developed in the United States for use in Korea. After an initial analysis of candidate issues regarding the “fit” of items to the Korean context—whether items were familiar, authentic, and realistic as characterized by Delaney et al. (J Math Teach Educ 11:171–197, 2008)—we adapted and administered an instrument developed by the Learning Mathematics for Teaching project with 93 Korean teachers and conducted follow-up interviews with nine teachers. Based on analysis of this data, we conducted a second round of revision and then administered the revised test to 101 Korean teachers. Results showed that small modifications that were made to increase fit often increased teachers’ performance on the items as expected, but the impact of changes was at times difficult to interpret. For several items, modifications introduced unanticipated validity issues. The paper discusses dynamics that arise in making changes to MKT items—in particular, the tension in modifying items to increase the fit to specific educational contexts while maintaining validity.