2,111 research outputs found
An exploration of sex-specific linkage disequilibrium on chromosome X in Caucasians from the COGA study
This paper explores the decay of linkage disequilibrium (LD) on the autosomes and chromosome X. The extent of marker-marker LD is important for both linkage and association studies. The analysis of the Caucasian sample from the Collaborative Study on the Genetics of Alcoholism study revealed the expected negative relationship between the magnitude of the marker-marker LD and distance (cM), with the male and female subgroups exhibiting similar patterns of LD. The observed extent of LD in females was less across the pseudoautosomal markers relative to the heterosomal region of chromosome X. Marked differences in LD patterns were also observed between chromosomes X and the 22 autosomes in both males and females
Griffiths phase of the Kondo insulator fixed point
Heavy fermion compounds have long been identified as systems which are
extremely sensitive to the presence of impurities and other imperfections. In
recent years, both experimental and theoretical work has demonstrated that such
disorder can lead to unusual, non-Fermi liquid behavior for most physical
quantities. In this paper, we show that this anomalous sensitivity to disorder,
as well as the resulting Griffiths phase behavior, directly follow from the
proximity of metallic heavy fermion systems to the Kondo insulator fixed point.Comment: 5 pages, 4 figures; Proceedings of the SCES, August 2000, to appear
in the Journal of Magnetism and Magnetic Material
Dynamics of disordered heavy Fermion systems
Dynamics of the disordered heavy Fermion model of Dobrosavljevic et al. are
calculated using an expression for the spectral function of the Anderson model
which is consistent with quantum Monte Carlo results. We compute the
self-energy for three distributions of Kondo scales including the distribution
of Bernal et al. for UCu{5-x}Pd{x}. The corresponding low temperature optical
conductivity shows a low-frequency pseudogap, a negative optical mass
enhancement, and a linear in frequency transport scattering rate, consistent
with results in Y{1-x}U{x}Pd{3} and UCu{5-x}Pd{x}.Comment: 5 pages, LaTeX and 4 PS figure
Ground-State Properties of Extended Two-Channel Kondo Model
Ground-state properties are examined for an extended two-channel Kondo model
where the Hilbert space of the localized states is extended to include a
singlet state in addition to the doublet states. By means of zero-th order
variational wavefunctions with different symmetries, which are associated with
the non-Fermi-liquid and the Fermi-liquid ground states, we demonstrate that
the channel exchange coupling via the localized singlet state stabilizes the
Fermi-liquid wavefunction. The ground-state phase diagrams, which are in
qualitative agreement with the previous study performed by Koga and Shiba, are
obtained. The comparison to the structure of the resultant wavefunctions
suggests that a unique non-Fermi-liquid (Fermi-liquid) fixed point exists,
irrespective of the localized ground state.Comment: 4 pages(3 figures), LaTeX, appear in J. Phys. Soc. Jpn Vol. 67 No.
Crystal Field Triplets: A New Route to Non-Fermi Liquid Physics
A model for crystal field triplet ground states on rare earth or actinide
ions with dipolar and quadrupolar couplings to conduction electrons is studied
for the first time with renormalization group methods. The quadrupolar coupling
leads to a new nontrivial, non-Fermi liquid fixed point, which survives in an
intermediate valence Anderson model. The calculated magnetic susceptibility
displays one parameter scaling, going as ()
at intermediate temperatures, reminiscent of the non-Fermi liquid alloy
UCu_{5-x}Pd_x.Comment: 4 pages, 3 figures, REVTe
Anomalous heavy-fermion and ordered states in the filled skutterudite PrFe4P12
Specific heat and magnetization measurements have been performed on
high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to
study the high-field heavy-fermion state (HFS) and low-field ordered state
(ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields
applied along the direction, the Kondo temperature of ~ 9 K and the
existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear
Schottky contribution, which works as a highly-sensitive on-site probe for the
Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03
\mu_B/Pr-ion. This fact strongly indicates that the primary order parameter in
the ODS is nonmagnetic and most probably of quadrupolar origin, combined with
other experimental facts. Significantly suppressed heavy-fermion behavior in
the ODS suggests a possibility that the quadrupolar degrees of freedom is
essential for the heavy quasiparticle band formation in the HFS. Possible
crystalline-electric-field level schemes estimated from the anisotropy in the
magnetization are consistent with this conjecture.Comment: 7 pages and 7 figures. Accepted for publication in Phys. Rev.
Evidence for a common physical description of non-Fermi-liquid behavior in f-electron systems
The non-Fermi-liquid (NFL) behavior observed in the low temperature specific
heat and magnetic susceptibility of f-electron systems is
analyzed within the context of a recently developed theory based on Griffiths
singularities. Measurements of and in the systems
, , and (M = Pd,
Pt) are found to be consistent with predicted by this model with in the NFL regime.
These results suggest that the NFL properties observed in a wide variety of
f-electron systems can be described within the context of a common physical
picture.Comment: 4 pages, 4 figure
Kondo Effect in Systems with Spin Disorder
We consider the role of static disorder in the spin sector of the one- and
two-channel Kondo models. The distribution functions of the disorder-induced
effective energy splitting between the two levels of the Kondo impurity are
derived to the lowest order in the concentration of static scatterers. It is
demonstrated that the distribution functions are strongly asymmetric, with the
typical splitting being parametrically smaller than the average rms value. We
employ the derived distribution function of splittings to study the temperature
dependence of the low-temperature conductance of a sample containing an
ensemble of two-channel Kondo impurities. The results are used to analyze the
consistency of the two-channel Kondo interpretation of the zero-bias anomalies
observed in Cu/(Si:N)/Cu nanoconstrictions.Comment: 16 pages, 5 figures, REVTe
Assessing the cost of global biodiversity and conservation knowledge
Knowledge products comprise assessments of authoritative information supported by stan-dards, governance, quality control, data, tools, and capacity building mechanisms. Considerable resources are dedicated to developing and maintaining knowledge productsfor biodiversity conservation, and they are widely used to inform policy and advise decisionmakers and practitioners. However, the financial cost of delivering this information is largelyundocumented. We evaluated the costs and funding sources for developing and maintain-ing four global biodiversity and conservation knowledge products: The IUCN Red List ofThreatened Species, the IUCN Red List of Ecosystems, Protected Planet, and the WorldDatabase of Key Biodiversity Areas. These are secondary data sets, built on primary datacollected by extensive networks of expert contributors worldwide. We estimate that US116–204 million), plus 293 person-years of volunteer time (range: 278–308 person-years) valued at US12–16 million), were invested inthese four knowledge products between 1979 and 2013. More than half of this financingwas provided through philanthropy, and nearly three-quarters was spent on personnelcosts. The estimated annual cost of maintaining data and platforms for three of these knowl-edge products (excluding the IUCN Red List of Ecosystems for which annual costs were notpossible to estimate for 2013) is US6.2–6.7 million). We esti-mated that an additional US12 million. These costs are much lower than those tomaintain many other, similarly important, global knowledge products. Ensuring that biodi-versity and conservation knowledge products are sufficiently up to date, comprehensiveand accurate is fundamental to inform decision-making for biodiversity conservation andsustainable development. Thus, the development and implementation of plans for sustain-able long-term financing for them is critical
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