ABSTRACT
Quantum systems in contact with a thermal environment experience coherent and incoherent dynamics. These drive the system back toward thermal equilibrium after an initial perturbation. The relaxation process involves the reorganization of spin state populations and the decay of spin state coherences. In general, individual populations and coherences may exhibit different relaxation time constants. Particular spin configurations may exhibit exceptionally long relaxation time constants. Such spin configurations are known as long-lived spin order. The existence of long-lived spin order is a direct consequence of the symmetries of the system. For nuclear spin systems, rotational and permutational symmetries are of fundamental importance. Based on the Schur-Weyl duality theorem, we describe a theoretical framework for the study of rotational and permutational dual-symmetries in the context of long-lived spin order. Making use of the proposed formalism, we derive refined bounds on the number on long-lived spin populations and coherences for systems exhibiting rotational-permutational dual-symmetries.
ABSTRACT
The singlet state of nuclear spin-1/2 pairs is protected against many common relaxation mechanisms. Singlet order, which is defined as the population difference between the nuclear singlet and triplet states, usually decays more slowly than the nuclear magnetization. Nevertheless, some decay mechanisms for nuclear singlet order persist. One such mechanism is called scalar relaxation of the second kind (SR2K) and involves the relaxation of additional nuclei ("third spins") which have scalar couplings to the spin-1/2 pair. This mechanism requires a difference between the couplings of at least one third spin with the two members of the spin-1/2 pair, and depends on the longitudinal relaxation time of the third spin. The SR2K mechanism of nuclear singlet relaxation has previously been examined in the case where the relaxation rate of the additional spins is on the time scale of the nuclear Larmor frequency. In this paper, we consider a different regime, in which the longitudinal relaxation of the third spins is on a similar time scale to the J-coupling between the members of the spin pair. This regime is often encountered when the spin-1/2 pair has scalar couplings to nearby deuterium nuclei. We show that the SR2K mechanism may be suppressed in this regime by applying a radiofrequency field which is resonant either with the members of the spin pair, or with the third spins. These phenomena are analyzed theoretically and by numerical simulations, and demonstrated experimentally on a diester of [13C2, 2H2]-labeled fumarate in solution.
ABSTRACT
OBJECTIVES: Although research has consistently shown a higher prevalence of depression among women compared with men, there is a lack of consensus regarding explanatory factors for these gender-related differences. The aim of this paper was to analyse the scientific quality of different gender-related explanatory models of depression in the medical database PubMed. STUDY DESIGN: Qualitative and quantitative analyses of PubMed articles. METHODS: In a database search in PubMed for 2002, 82 articles on gender and depression were selected and analysed with qualitative and quantitative content analyses. In total, 10 explanatory factors and four explanatory models were found. The ISI Web of Science database was searched in order to obtain the citation number and journal impact factor for each article. RESULTS: The most commonly used gender-related explanatory model for depression was the biomedical model (especially gonadal hormones), followed by the sociocultural and psychological models. Compared with the other models, the biomedical model scored highest on bibliometric measures but lowest on measures of multifactorial dimensions and differences within the group of men/women. CONCLUSION: The biomedical model for explaining gender-related aspects of depression had the highest quality when bibliometric methods were used. However, the sociocultural and psychological models had higher quality than the biomedical model when multifactoriality and intersectionality were analysed. There is a need for the development of new methods in order to evaluate the scientific quality of research.
