1,346 research outputs found
Cluster Dynamical Mean Field analysis of the Mott transition
We investigate the Mott transition using a cluster extension of dynamical
mean field theory (DMFT). In the absence of frustration we find no evidence for
a finite temperature Mott transition. Instead, in a frustrated model, we
observe signatures of a finite temperature Mott critical point in agreement
with experimental studies of kappa-organics and with single site DMFT. As the
Mott transition is approached, a clear momentum dependence of the electron
lifetime develops on the Fermi surface with the formation of cold regions along
the diagonal direction of the Brillouin zone. Furthermore the variation of the
effective mass is no longer equal to the inverse of the quasi particle residue,
as in DMFT, and is reduced approaching the Mott transition.Comment: 4 page
Development of a Nursing Care Management Model for Community-Dwelling Individuals with Heart Failure
The aging of the population, with an increasing prevalence of chronic illness, contributes to the need for innovative approaches to delivery of care in the American health care system. Heart failure is the most common chronic illness leading to hospital admission in the United States for persons 65 years of age or older (Knox & Mischke, 1999). Multidisciplinary strategies for management of individuals with heart failure have been shown to reduce hospital readmission rates and mortality (McAlister, Stuart, Ferrua, & McMurray, 2004). My systems change project focused on assisting a group of clinic-based, nurse care managers to develop a new model of care management for high risk, community-dwelling individuals with heart failure who receive care within a large, metropolitan health system. Utilizing a participatory action research process, the care managers were guided to identify needs and opportunities related to the model of care, review best practice evidence from the literature, and come to consensus about implementation of changes to improve the efficiency and effectiveness of their care delivery. Over the course of 11 months, this systems change project contributed to developments that improved systems, workflow, care manager competence, and outcomes for the care management program for individuals with heart failure
On `maximal' poles of zeta functions, roots of b-functions and monodromy Jordan blocks
The main objects of study in this paper are the poles of several local zeta
functions: the Igusa, topological and motivic zeta function associated to a
polynomial or (germ of) holomorphic function in n variables. We are interested
in poles of maximal possible order n. In all known cases (curves,
non-degenerate polynomials) there is at most one pole of maximal order n which
is then given by the log canonical threshold of the function at the
corresponding singular point.
For an isolated singular point we prove that if the log canonical threshold
yields a pole of order n of the corresponding (local) zeta function, then it
induces a root of the Bernstein-Sato polynomial of the given function of
multiplicity n (proving one of the cases of the strongest form of a conjecture
of Igusa-Denef-Loeser). For an arbitrary singular point we show under the same
assumption that the monodromy eigenvalue induced by the pole has a Jordan block
of size n on the (perverse) complex of nearby cycles.Comment: 8 pages, to be published in Journal of Topolog
Ni impurity induced enhancement of the pseudogap in cuprate high T_c superconductors
The influence of magnetic Ni and non-magnetic Zn impurities on the normal
state pseudogap (PG) in the c-axis optical conductivity of NdBa\{Cu(Ni,Zn)O crystals was studied by spectral
ellipsometry. We find that these impurities which strongly suppress
superconductivity have a profoundly different impact on the PG. Zn gives rise
to a gradual and inhomogeneous PG suppression while Ni strongly enhances the
PG. Our results challenge theories that relate the PG either to precursor
superconductivity or to other phases with exotic order parameters, such as flux
phase or d-density wave states, that should be suppressed by potential
scattering. The apparent difference between magnetic and non-magnetic
impurities instead points towards an important role of magnetic correlations in
the PG state.Comment: 11 pages and 2 figure
Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study
Magnetic materials are usually divided into two classes: those with localised
magnetic moments, and those with itinerant charge carriers. We present a
comprehensive experimental (spectroscopic ellipsomerty) and theoretical study
to demonstrate that these two types of magnetism do not only coexist but
complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material
the itinerant charge carriers interact with large localised magnetic moments of
Tb(4f) states, forming complex magnetic lattices at low temperatures, which we
associate with self-organisation of magnetic clusters. The formation of
magnetic clusters results in low-energy optical spectral weight shifts, which
correspond to opening of the pseudogap in the conduction band of the itinerant
charge carriers and development of the low- and high-spin intersite electronic
transitions. This phenomenon, driven by self-trapping of electrons by magnetic
fluctuations, could be common in correlated metals, including besides
Kondo-lattice metals, Fe-based and cuprate superconductors.Comment: 30 pages, 6 Figure
Ageing and the pathogenesis of osteoarthritis
Ageing-associated changes that affect articular tissues promote the development of osteoarthritis (OA). Although ageing and OA are closely linked, they are independent processes. Several potential mechanisms by which ageing contributes to OA have been elucidated. This Review focuses on the contributions of the following factors: age-related inflammation (also referred to as 'inflammaging'); cellular senescence (including the senescence-associated secretory phenotype (SASP)); mitochondrial dysfunction and oxidative stress; dysfunction in energy metabolism due to reduced activity of 5'-AMP-activated protein kinase (AMPK), which is associated with reduced autophagy; and alterations in cell signalling due to age-related changes in the extracellular matrix. These various processes contribute to the development of OA by promoting a proinflammatory, catabolic state accompanied by increased susceptibility to cell death that together lead to increased joint tissue destruction and defective repair of damaged matrix. The majority of studies to date have focused on articular cartilage, and it will be important to determine whether similar mechanisms occur in other joint tissues. Improved understanding of ageing-related mechanisms that promote OA could lead to the discovery of new targets for therapies that aim to slow or stop the progression of this chronic and disabling condition
Photoemission Evidence for a Remnant Fermi Surface and d-Wave-Like Dispersion in Insulating Ca2CuO2Cl2
An angle resolved photoemission study on Ca2CuO2Cl2, a parent compound of
high Tc superconductors is reported. Analysis of the electron occupation
probability, n(k) from the spectra shows a steep drop in spectral intensity
across a contour that is close to the Fermi surface predicted by the band
calculation. This analysis reveals a Fermi surface remnant even though
Ca2CuO2Cl2 is a Mott insulator. The lowest energy peak exhibits a dispersion
with approximately the |cos(kxa)-cos(kya)| form along this remnant Fermi
surface. Together with the data from Dy doped Bi2Sr2CaCu2O(8 + delta) these
results suggest that this d-wave like dispersion of the insulator is the
underlying reason for the pseudo gap in the underdoped regime.Comment: 9 pages, including 7 figures. Published in Science, one figure
correcte
Theory of Quasi-Particles in the Underdoped High Tc Superconducting State
The microscopic theory of superconducting (SC) state in the SU(2) slave-boson
model is developed. We show how the pseudogap and Fermi surface (FS) segments
in the normal state develop into a d-wave gap in the superconducting state.
Even though the superfluid density is of order x (the doping concentration),
the physical properties of the low lying quasiparticles are found to resemble
those in BCS theory. Thus the microscopic theory lay the foundation for our
earlier phenomenological discussion of the unusual SC properties in the
underdoped cuprates.Comment: 4 pages in RevTeX, 1 figure in eps, revised versio
Pseudogap and photoemission spectra in the attractive Hubbard model
Angle-resolved photoemission spectra are calculated microscopically for the
two-dimensional attractive Hubbard model. A system of self-consistent T-matrix
equations are solved numerically in the real-time domain. The single-particle
spectral function has a two-peak structure resulting from the presense of bound
states. The spectral function is suppressed at the chemical potential, leading
to a pseudogap-like behavior. At high temperatures and densities the pseudogap
diminishes and finally disappears; these findings are similar to experimental
observations for the cuprates.Comment: 5 pages, 4 figures, published versio
High-Resolution Photoemission Study of MgB2
We have performed high-resolution photoemission spectroscopy on MgB2 and
observed opening of a superconducting gap with a narrow coherent peak. We found
that the superconducting gap is s-like with the gap value of 4.5 meV at 15 K.
The temperature dependence (15 - 40 K) of gap value follows well the BCS form,
suggesting that 2Delta/kBTc at T=0 is about 3. No pseudogap behavior is
observed in the normal state. The present results strongly suggest that MgB2 is
categorized into a phonon-mediated BCS superconductor in the weak-coupling
regime.Comment: 3 pages, 3 figures, accepted in Physical Review Letter
- …