On graphs determining links with maximal number of components via medial construction

Let G be a connected plane graph, D(G) be the corresponding link diagram via medial construction, and μ(D(G)) be the number of components of the link diagram D(G). In this paper, we first provide an elementary proof that μ(D(G))≤n(G)+1, where n(G) is the nullity of G. Then we lay emphasis on the extremal graphs, i.e. the graphs with μ(D(G))=n(G)+1. An algorithm is given firstly to judge whether a graph is extremal or not, then we prove that all extremal graphs can be obtained from K₁ by applying two graph operations repeatedly. We also present a dual characterization of extremal graphs and finally we provide a simple criterion on structures of bridgeless extremal graphs.     

Pressurized hot water extraction of bioactive or marker compounds in botanicals and medicinal plant materials

To reduce the use of organic solvent, pressurized hot water extraction (PHWE) has been shown to be a feasible option for the extraction of bioactive and marker compounds in botanicals and medicinal plants. The parameters that may affect the extraction efficiencies in PHWE include temperature, extraction time and addition of small percentage of organic solvent or surfactants. Currently, applications of PHWE for the extraction of thermally labile compounds in botanicals are still rather limited. PHWE with and without the additional of a small percentage of organic solvent such as ethanol is highly suited for the chemical standardization and quality control of medicinal plants. At the same time, it can be applied at the pilot scale as a manufacturing process for medicinal plants. Surfactant assisted PHWE was found to enhance the extraction of thermally labile and more hydrophobic species in medicinal plants at a lower temperature. The addition of small amount of surfactants in PHWE is highly suited for the determination of bioactive or marker compounds in medicinal plants. With proper optimization, PHWE was observed to have good extraction efficiency and precision when compared to other reference methods of extraction.     

Magnetic properties of neutron irradiated RPV steel

The neutron irradiated reactor pressure vessel (RPV) steels at various dose of 0–10¹⁸ n/cm² have been studied with Mössbauer, x-ray diffraction, and VSM. The Mössbauer data shows that the value of magnetic hyperfine field of Fe atom that exist at martensite is 330 kOe at site 1 and 305 kOe at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 0–10¹⁶ n/cm², while over the dose of 0–10¹⁷ n/cm² the absorption area decreases rapidly. But the doublet area for the dose of 0–10¹⁶ n/cm² is constant, while over the dose of 10¹⁷ n/cm² it increases with increasing the fluence level of neutron. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², compared with that of the as-received sample.     

A metacognitive-based instruction for Primary Four students to approach non-routine mathematical word problems

Many Primary Four students (fourth graders) in Singapore have difficulties initiating or persevering in the problem-solving process even though the curriculum has focused on problem solving since 1992. This study served to examine the role of metacognition in self-regulated problem solving. The study, a quasi-experimental pretest–posttest design involving a convenience sample of 63 students from two intact mixed-ability Primary Four classes, examined the impact of using a metacognitive scheme that focuses on the understanding and planning stages of Pòlya’s four-stage approach on students’ mathematical problem-solving behavior, performance and attitudes. The findings revealed that the metacognitive-based scheme had a positive impact on students’ understanding of the problem posed, solution planning, confidence in and personal control of problem-solving behavior and emotions. It had also helped them to initiate and persevere in the problem-solving process to achieve a higher level of problem-solving success. Limitations and instructional implications are discussed.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

An Efficient Method for the Preparation of Nitriles via the Dehydration of Aldoximes with Phthalic Anhydride

A new and highly efficient method for the conversion of aldoximes to nitriles was established. By fusing with phthalic anhydride, aldoximes were efficiently and smoothly converted into nitriles, in high yields (over 85%) and in a short time (within 5 minutes). The mixture of phthalic anhydride, a cyclic anhydride, and aldoximes in fusing state set up an ideal transition state for a selective [3.3]‐sigmatropic rearrangement of the acylated aldoximes to nitriles.     

Enantioselective luminescence quenching of DNA light-switch [Ru(phen)2dppz]2+ by electron transfer to structural homologue [Ru(phendione)2dppz]2+

The quenching of the luminescence of [Ru(phen)(2)dppz](2+) by structural homologue [Ru(phendione)(2)dppz](2+), when both complexes are bound to DNA, has been studied for all four combinations of Delta and Lambda enantiomers. Flow linear dichroism spectroscopy (LD) indicates similar binding geometries for all the four compounds, with the dppz ligand fully intercalated between the DNA base pairs. A difference in the LD spectrum observed for the lowest-energy MLCT transition suggests that a transition, potentially related to the final localization of the excited electron to the dppz ligand in [Ru(phen)(2)dppz](2+), is overlaid by an orthogonally polarized transition in [Ru(phendione)(2)dppz](2+). This would be consistent with a low-lying LUMO of the phendione moiety of [Ru(phendione)(2)dppz](2+) that can accept the excited electron from [Ru(phen)(2)dppz](2+), thereby quenching the emission of the latter. The lifetime of excited Delta-[Ru(phen)(2)dppz](2+) is decreased moderately, from 664 to 427 ns, when bound simultaneously with the phendione complex to DNA. The 108 ns lifetime of opposite enantiomer, Lambda-[Ru(phen)(2)dppz](2+), is only shortened to 94 ns. These results are consistent with an average rate constant for electron transfer of approximately 1.10(6) s(-1) between the phenanthroline- and phendione-ruthenium complexes. At binding ratios close to saturation of DNA, the total emission of the two enantiomers is lowered equally much, but for the Lambda enantiomer, this is not paralleled by a decrease in luminescence lifetime. A binding isotherm simulation based on a generalized McGhee-von Hippel approach shows that the Delta enantiomer binds approximately 3 times stronger to DNA both for [Ru(phendione)(2)dppz](2+) and [Ru(phen)(2)dppz](2+). This explains the similar decrease in total emission, without the parallel decrease in lifetime for the Lambda enantiomer. The simulation also does not indicate any significant binding cooperativity, in contrast to the case when Delta-[Rh(phi)(2)bipy](3+) is used as quencher. The very slow electron transfer from [Ru(phen)(2)dppz](2+) to [Ru(phendione)(2)dppz](2+), compared to the case when [Rh(phi)(2)phen](3+) is the acceptor, can be explained by a much smaller driving free-energy difference.