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The relaxor transition in cubic perovskite relaxors (PMN, PSN and PST) and tungsten bronze relaxor (SBN) has been studied by NMR. The observed spectra are composed of a narrow -1/2 « 1/2 central transition superimposed on a broad background due to satellite transitions. The chemical heterogeneity, responsible for relaxor properties, is reflected here in the structure of the central transition part. The latter is composed of two components, one due to ordered and the other due to disordered regions. Despite of the fact that the macroscopic symmetry does not change when relaxor transition occurs, a non-zero quadruple coupling constant determined from NMR clearly demonstrates the broken local symmetry.

Depression is estimated to affect 350 million people worldwide. The World Mental Health Survey conducted in 17 countries found that, on average, about one in 20 people reported having an episode of depression in the previous year. Although depression has been shown to be moderately heritable by studies conducted in the past, the search for its so-called missing heritability has so far been unsuccessful. The difficulty in identifying common genetic variants predisposing to depression could be due to large sample sizes needed to detect small effects on genetic risk and the heterogeneous nature of major depressive disorder (MDD). The aim of our study was to determine whether there was a connection between a family history of depression in MDD patients and the presence of putative risk variants in the well-studied SLC6A4, COMT and PCLO genes. We analyzed 133 patients with MDD (30.0% with a positive family history for MDD and 70.0% sporadic cases) and compared them to 279 healthy controls. When comparing all the depressed patients to controls, no significant differences in genotype and allele distributions were detected. After stratifying patients according to their family history, the PCLO rs2522833 C allele was shown to be significantly less common in patients with a positive family history (p = 0.001), indicating a possible difference in the genetic structure of MDD between familial and sporadic cases and a less important role of the common genetic risk variants for the development of MDD in familial cases.

Materials exhibiting a large caloric effect could lead to the development of a new generation of heat-management technologies that will have better energy efficiency and be potentially more environmentally friendly. The focus of caloric materials investigations has shifted recently from solid-state materials towards soft materials, such as liquid crystals and liquid crystalline elastomers. It has been shown recently that a large electrocaloric effect exceeding 6 K can be observed in smectic liquid crystals. Here, we report on a significant elastocaloric response observed by direct elastocaloric measurements in main-chain liquid crystal elastomers. It is demonstrated that the character of the nematic to paranematic / isotropic transition can be tuned from the supercritical regime towards the first-order regime, by decreasing the density of crosslinkers. In the latter case, the latent heat additionally enhances the elastocaloric response. Our results indicate that a significant elastocaloric response is present in main-chain liquid crystalline elastomers, driven by stress fields much smaller than in solid elastocaloric materials. Therefore, elastocaloric soft materials can potentially play a significant role as active cooling/heating elements in the development of new heat-management devices. [ABSTRACT FROM AUTHOR]

The [sup 207]Pb, [sup 45]Sc, and [sup 93]Nb nuclear magnetic resonance spectra have been measured for the relaxor ferroelectric single crystal Pb(Sc[sub 1/2]Nb[sub 1/2])O[sub 3] both above and below T[sub c]. The [sup 45]Sc spectra suggest that the "disordered" part of the crystal occupies about 60% and the "ordered" cubic part about 40% of the crystal volume. In agreement with the spherical random bond-random field (SRBRF) model the square of the polarization linearly increases with decreasing T below T[sub c] in both the ordered as well as in the disordered regions. The Edwards-Anderson order parameter q similarly increases linearly with decreasing T below T[sub c]. For the disordered region we find J[sub 0]approx. 328 K and Japprox. 227 K whereas Δ/J[sub 0][SUP ARRANGE="STAGGER"]2]approx. 0.006. In the ordered region J[sub 0]approx. 297 K, whereas J and Δ are too small to be determined from this experiment. The results demonstrate that the SRBRF model works not only for pure relaxors but also for relaxor ferroelectrics. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]