Epoxy resins of DGEBA type were thermally cured with diaminodiphenylmethane as crosslinking agent, and then analysed by Differential Scanning calorimetry (DSC) at various heating rates in order to determine the glass transition temperatureTg of the final networks. First it was shown that during cyclingTg is shifted towards higher values up to a maximum or
. Such a change is attributed to an increasing extent of cure which develops during the thermal analysis, and also to relaxation processes thermally activated inside the polymeric matrix. Then the dependence of
on the heating rateq imposed by the DSC apparatus was presented forq changing from 0.1 to10‡C min−1. At heating rates exceeding 3‡C min−1 only the classical temperatureTg was detected, but at smallerq values, an additional endothermic transition was revealed, located at higher temperature and linked to a physical aging-like phenomenon, which takes place at low heating rates. The plot of
against logq is divided into two quasi-linear parts on each side ofq=3‡C min−1. In conclusions, an equation was given to describe the
vs. logq function.
The article discusses the existence and outlook of an evolved desire to have children. Twin studies have found a genetic basis for conscious attempts to get pregnant. This heritable disposition increasingly affects societies of wide female reproductive choice (Kohler et al 1999). Based on 106 stories written by Finnish women in 2006, I analyse the symptoms, triggers and behaviour related to longing for babies. I suggest that a strong longing for first or subsequent children is an affective incentive of growing importance in low-fertility societies. Female desire for babies appears in two main forms: as part of a generally care-oriented personality and as a sudden, surprising and largely physical longing. The first type conforms to previous research on nurturing (Miller 1986; Foster 2000) while the second type has not been much studied yet. For both types, a desire to have children is often related to physical age, falling in love, previous pregnancies and to exposure to babies of kin and peers. I discuss evolutionary explanations and suggest that longing for babies may have evolved not only as a by-product of finding care pleasurable, but also as part of mate selection and as a consequence of hormonal changes induced by couple formation and ageing.
Isomalt, a commercial sugar alcohol widely used as a sweetener, is approximately a 1:1 mixture of two diastereomers, -D-glucopyranosyl-1-6-mannitol (GPM) and -D-glucopyranosyl-1-6-sorbitol (GPS). A calorimetric investigation has been carried out on mixtures of isomalt with GPS, in the (molar) composition range 0.45<xGPS<1, for both crystalline and amorphous states.The GPS-rich portion of the solid-liquid GPM/GPS phase diagram was established and discussed in light of the existing literature. New evidence was given for the non-ideality of GPM/GPS mixtures, by indicating excess interactions in the melt and/or in the solid state. The commonly accepted hypothesis of a simple GPM/GPS eutectic forming isomalt was refuted in favour of more complicated mixture behaviour with possible formation of a complex.Glass transition and physical ageing of isomalt and GPS were re-visited, with peculiar attention given to the measurement conditions. Standard thermal histories were adapted to each sample and the fictive temperature was used for the characterisation of the structural glass states. A linear increase of the fictive temperature was found upon passing from pure GPS to xGPS=0.45. GPS showed a slightly higher enthalpy relaxation rate than isomalt.
Authors:Mulayam Singh Gaur, Reeta Singh, Pramod Kumar Singh, Ajay Pal Indolia, and Ranjit Singh
active for the prolonged period [ 8 – 11 ]. The technique further makes it possible to investigate the effect of physicalaging (annealing) of the charged polymer on the charge storage, its distribution and transport in the material [ 12 – 15
Authors:Xing Wen, Xiuping Lu, Quan Peng, Fuyan Zhu, and Ning Zheng
) melting, recrystallization and remelting (mrr) during heating, (2) presence of more than one crystal modifications (polymorphism), (3) different crystalline morphology (lamellar thickness, distribution, perfection, or stability), (4) physicalaging and