2,903 research outputs found
Quantitative genetics of disease traits
John James authored two key papers on the theory of risk to relatives for binary disease traits and the relationship between parameters on the observed binary scale and an unobserved scale of liability (James Annals of Human Genetics, 1971; 35: 47; Reich, James and Morris Annals of Human Genetics, 1972; 36: 163). These two papers are John James' most cited papers (198 and 328 citations, November 2014). They have been influential in human genetics and have recently gained renewed popularity because of their relevance to the estimation of quantitative genetics parameters for disease traits using SNP data. In this review, we summarize the two early papers and put them into context. We show recent extensions of the theory for ascertained case-control data and review recent applications in human genetics
Emergence of Fermi pockets in an excitonic CDW melted novel superconductor
A superconducting (SC) state (Tc ~ 4.2K) has very recently been observed upon
successful doping of the CDW ordered triangular lattice TiSe, with copper.
Using high resolution photoemission spectroscopy we identify, for the first
time, the momentum space locations of the doped electrons that form the Fermi
sea of the parent superconductor. With doping, we find that the kinematic
nesting volume increases whereas the coherence of the CDW order sharply drops.
In the superconducting doping, we observe the emergence of a large density of
states in the form of a narrow electron pocket near the \textit{L}-point of the
Brillouin Zone with \textit{d}-like character. The \textit{k}-space electron
distributions highlight the unconventional interplay of CDW to SC cross-over
achieved through non-magnetic copper doping.Comment: 4+ pages, 5 figures; Accepted for publication in Phys. Rev. Lett.
(2007
Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2
We utilize fine-tuned polarization selection coupled with excitation-energy
variation of photoelectron signal to image the \textit{complete d}-band
dispersion relation in sodium cobaltates. A hybridization gap anticrossing is
observed along the Brillouin zone corner and the full quasiparticle band is
found to emerge as a many-body entity lacking a pure orbital polarization. At
low dopings, the quasiparticle bandwidth (Fermion scale, many-body
\textit{E} 0.25 eV) is found to be smaller than most known oxide
metals. The low-lying density of states is found to be in agreement with
bulk-sensitive thermodynamic measurements for nonmagnetic dopings where the 2D
Luttinger theorem is also observed to be satisfied.Comment: 4+ pages, 5 Fig
Low-lying quasiparticle states and hidden collective charge instabilities in parent cobaltate superconductors (NaxCoO2)
We report a state-of-the-art photoemission (ARPES) study of high quality
single crystals of the NaxCoO2 series focusing on the fine details of the
low-energy states. The Fermi velocity is found to be small (< 0.5 eV.A) and
only weakly anisotropic over the Fermi surface at all dopings setting the size
of the pair wavefunction to be on the order of 10-20 nanometers. In the low
doping regime the exchange inter-layer splitting vanishes and two dimensional
collective instabilities such as 120-type fluctuations become kinematically
allowed. Our results suggest that the unusually small Fermi velocity and the
unique symmetry of kinematic instabilities distinguish cobaltates from other
unconventional oxide superconductors such as the cuprates or the ruthenates.Comment: Accepted for publication in Phys. Rev. Lett. (2006
Quasiparticle coherence and the nature of the metal-insulator phase transition in NaCoO
Layered cobaltates embody novel realizations of correlated quantum matter on
a spin-1/2 triangular lattice. We report a high-resolution systematic
photoemission study of the insulating cobaltates (Na1/2CoO2 and K1/2CoO2).
Observation of single-particle gap opening and band-folding provides direct
evidence of anisotropic particle-hole instability on the Fermi surface due to
its unique topology. Kinematic overlap of the measured Fermi surface is
observed with the x cobalt charge-order Brillouin zone near
x=1/3 but not at x=1/2 where insulating transition is actually observed. Unlike
conventional density-waves, charge-stripes or band insulators, the on-set of
the gap depends on the quasiparticle's quantum coherence which is found to
occur well below the disorder-order symmetry breaking temperature of the
crystal (the first known example of its kind).Comment: 4+ pages, 5 figure
Numerical MHD Simulations of Solar Magnetoconvection and Oscillations in Inclined Magnetic Field Regions
The sunspot penumbra is a transition zone between the strong vertical
magnetic field area (sunspot umbra) and the quiet Sun. The penumbra has a fine
filamentary structure that is characterized by magnetic field lines inclined
toward the surface. Numerical simulations of solar convection in inclined
magnetic field regions have provided an explanation of the filamentary
structure and the Evershed outflow in the penumbra. In this paper, we use
radiative MHD simulations to investigate the influence of the magnetic field
inclination on the power spectrum of vertical velocity oscillations. The
results reveal a strong shift of the resonance mode peaks to higher frequencies
in the case of a highly inclined magnetic field. The frequency shift for the
inclined field is significantly greater than that in vertical field regions of
similar strength. This is consistent with the behavior of fast MHD waves.Comment: 9 pages, 6 figures, Solar Physics (in press
- …