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It is crucial to understand the genetic mechanisms and biological pathways underlying the relationship between obesity and serum lipid levels. Structural equation models (SEMs) were constructed to calculate heritability for body mass index (BMI), total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and the genetic connections between BMI and the four classes of lipids using 1197 pairs of twins from the Chinese National Twin Registry (CNTR). Bivariate genomewide association studies (GWAS) were performed to identify genetic variants associated with BMI and lipids using the records of 457 individuals, and the results were further validated in 289 individuals. The genetic background affecting BMI may differ by gender, and the heritability of males and females was 71% (95% CI [.66, .75]) and 39% (95% CI [.15, .71]) respectively. BMI was positively correlated with TC, TG and LDL-C in phenotypic and genetic correlation, while negatively correlated with HDL-C. There were gender differences in the correlation between BMI and lipids. Bivariate GWAS analysis and validation stage found 7 genes (LOC105378740, LINC02506, CSMD1, MELK, FAM81A, ERAL1 and MIR144) that were possibly related to BMI and lipid levels. The significant biological pathways were the regulation of cholesterol reverse transport and the regulation of high-density lipoprotein particle clearance (p < .001). BMI and blood lipid levels were affected by genetic factors, and they were genetically correlated. There might be gender differences in their genetic correlation. Bivariate GWAS analysis found MIR144 gene and its related biological pathways may influence obesity and lipid levels.
According to Hamilton's rule, matrilineal-biased investment restrains men in matrilineal societies from maximising their inclusive fitness (the ‘matrilineal puzzle'). A recent hypothesis argues that when women breed communally and share household resources, a man should help his sisters' household, rather than his wife's household, as investment to the later but not the former would be diluted by other unrelated members (Wu et al., 2013). According to this hypothesis, a man is less likely to help on his wife's farm when there are more women reproducing in the wife's household, because on average he would be less related to his wife's household. We used a farm-work observational dataset, that we collected in the matrilineal Mosuo in southwest China, to test this hypothesis. As predicted, high levels of communal breeding by women in his wife's households do predict less effort spent by men on their wife's farm, and communal breeding in men's natal households do not affect whether men help on their natal farms. Thus, communal breeding by women dilutes the inclusive fitness benefits men receive from investment to their wife and children, and may drive the evolution of matrilineal-biased investment by men. These results can help solve the ‘matrilineal puzzle'.
Chapter 6 studies the Josephson tunneling effect in a superconductor-insulator-superconductor junction. The d-wave energy gap gives rise to a geometry dependent phase factor in the tunneling current. This leads to a unique phase-sensitive tool for experimentally detecting the d-wave pairing symmetry through a corner-sharing or tri-crystal junction. It is this kind of measurement that yields the strongest evidence for identifying the pairing symmetry in cuprate superconductors. The paramagnetic Meissner effect is discussed at the end of the chapter.
Chapter 3 derives the gap equation and determines the critical transition temperature as well as the zero-temperature energy gap as a function of coupling constant for d-wave superconductors. The energy dependence of the density of states and its effects on the temperature dependence of the gap function, entropy and other thermodynamic quantities are also discussed. Low energy nodal excitations lead to characteristic power-law behaviors in the specific heat or other thermodynamic response functions of d-wave superconductors at low temperatures, in contrast to the activated behaviors in s-wave superconductors. The probability density current and charge density current operators of d-wave quasiparticles, together with the gap operators in the continuum limit, are derived and discussed with the BdG framework.
Starting from a brief introduction to the Meissner effect and other defining properties of superconductivity, Chapter 1 recapitulates the phenomenological theories, including the two-fluid model and the Ginzburg-Landau theory, and the groundbreaking microscopic theory of Bardeen-Cooper-Schrieffer for describing this macroscopic quantum phenomenon. The Cooper pairing and other basic concepts of superconductivity, such as the gap function, off-diagonal long-range order, quasiparticle excitations, coherence length, penetration depth, type-I and type-II superconductors, and phase fluctuations are also introduced, followed by a summary on the classification and experimental identification for the pairing symmetry of high-Tc superconductors.
Chapter 14 introduces the theory of d-wave superconductors in the mixed state. It starts with a detailed derivation for the Caroli-de Gennes-Matricon vortex core states and then discusses the properties of low-lying excitations under the semi-classical approximation. The universal scaling laws for several different thermodynamic quantities are derived and compared with experimental observations for high-Tc cuprates.
Chapter 13 studies the dynamic spin response function measured by neutron scattering experiments. In particular, the magnetic resonance states revealed by the neutron scattering measurements for high-Tc cuprates in the superconducting state are discussed. It is argued that this spin resonance mode may arise either from a spin exciton excitation induced by an attractive residual spin interaction in the particle-hole channel or from a collective ?-resonance mode in the particle-particle channel which emerges in the neutron scattering spectrum thanks to the particle-hole mixing in the superconducting state.
Chapter 12 studies the property of magnetic response functions of electrons probed by nuclear magnetic resonance (NMR) experiments. The Knight shift is shown to be proportional to the real part of the local magnetic susceptibility. The spin-lattice relaxation, on the other hand, provides an effective measure of the imaginary part of the susceptibility averaged by the interaction form factor over the whole Brillouin zone. The effect of impurity scattering, particularly the impurity induced resonance states, on the NMR spectra is discussed and compared with experimental results.
Chapter 8 studies the many-impurity scattering effects in d-wave superconductors, particularly in the unitary or Born scattering limit. The impurity corrections to self-energy, density of states, superconducting critical temperature, entropy and specific heat are derived and compared with measurement data for high-Tc superconductors.
Chapter 2 starts with a brief review on the phase diagram of high-Tc cuprates, particularly on the phases of Mott insulators and pseudogaps. A number of microscopic models of high-Tc superconductors, including the three-band Hubbard model and its effective low-energy models in the strong coupling limit, namely the t-J model or its equivalent single-band Hubbard model, are then introduced. The models for describing the interlayer hopping and the system with Zn or Ni impurities in the copper oxides are also discussed. The Friedel sum rule is shown to be severely modified in the strong coupling limit, which reveals the perplexing but inherent nature of Zn as a unitary scattering potential of non-magnetic impurity.
Chapter 7 studies the single-impurity scattering effect on the density of states and other physical quantities. A low-energy resonance state induced by a unitary scattering potential is shown to exist in a d-wave superconductor, but is absent in an s-wave superconductor. The tunneling spectrum associated with a Zn impurity and the phenomenological theory of quasiparticle interference are discussed and compared with the experimental results. The in-gap resonance or bound states induced by a magnetic impurity and the Kondo effect in a d-wave superconductor are also discussed.