57 research outputs found
Strong-coupling limit of depleted Kondo- and Anderson-lattice models
Fourth-order strong-coupling degenerate perturbation theory is used to derive
an effective low-energy Hamiltonian for the Kondo-lattice model with a depleted
system of localized spins. In the strong-J limit, completely local Kondo
singlets are formed at the spinful sites which bind a fraction of conduction
electrons. The low-energy theory describes the scattering of the excess
conduction electrons at the Kondo singlets as well as their effective
interactions generated by virtual excitations of the singlets. Besides the
Hubbard term, already discussed by Nozieres, we find a ferromagnetic Heisenberg
interaction, an antiferromagnetic isospin interaction, a correlated hopping
and, in more than one dimensions, three- and four-site interactions. The
interaction term can be cast into highly symmetric and formally simple
spin-only form using the spin of the bonding orbital symmetrically centered
around the Kondo singlet. This spin is non-local. We show that, depending on
the geometry of the depleted lattice, spatial overlap of the non-local spins
around different Kondo singlets may cause ferromagnetic order. This is
sustained by a rigorous argument, applicable to the half-filled model, by a
variational analysis of the stability of the fully polarized Fermi sea of
excess conduction electrons as well as by exact diagonalization of the
effective model. A similar fourth-order perturbative analysis is performed for
the depleted Anderson lattice in the limit of strong hybridization. Even in a
parameter regime where the Schrieffer-Wolff transformation does not apply, this
yields the same effective theory albeit with a different coupling constant.Comment: 14 pages, 5 figure
Competition between Kondo screening and indirect magnetic exchange in a quantum box
Nanoscale systems of metal atoms antiferromagnetically exchange coupled to
several magnetic impurities are shown to exhibit an unconventional re-entrant
competition between Kondo screening and indirect magnetic exchange interaction.
Depending on the atomic positions of the magnetic moments, the total
ground-state spin deviates from predictions of standard
Ruderman-Kittel-Kasuya-Yosida perturbation theory. The effect shows up on an
energy scale larger than the level width induced by the coupling to the
environment and is experimentally verifiable by studying magnetic field
dependencies.Comment: 5 pages, 2 figures, v3 with minor change
Dynamical mean-field theory of indirect magnetic exchange
To analyze the physical properties arising from indirect magnetic exchange
between several magnetic adatoms and between complex magnetic nanostructures on
metallic surfaces, the real-space extension of dynamical mean-field theory
(R-DMFT) appears attractive as it can be applied to systems of almost arbitrary
geometry and complexity. While R-DMFT describes the Kondo effect of a single
adatom exactly, indirect magnetic (RKKY) exchange is taken into account on an
approximate level only. Here, we consider a simplified model system consisting
of two magnetic Hubbard sites ("adatoms") hybridizing with a non-interacting
tight-binding chain ("substrate surface"). This two-impurity Anderson model
incorporates the competition between the Kondo effect and indirect exchange but
is amenable to an exact numerical solution via the density-matrix
renormalization group (DMRG). The particle-hole symmetric model at half-filling
and zero temperature is used to benchmark R-DMFT results for the magnetic
coupling between the two adatoms and for the magnetic properties induced in the
substrate. In particular, the dependence of the local adatom and the nonlocal
adatom-adatom static susceptibilities as well as the magnetic response of the
substrate on the distance between the adatoms and on the strength of their
coupling with the substrate is studied. We find both, excellent agreement with
the DMRG data even on subtle details of the competition between RKKY exchange
and the Kondo effect but also complete failure of the R-DMFT, depending on the
parameter regime considered. R-DMFT calculations are performed using the
Lanczos method as impurity solver. With the real-space extension of the
two-site DMFT, we also benchmark a simplified R-DMFT variant.Comment: 14 pages, 8 figure
Анализ, моделирование и поиск способов оптимизации процессов растворения полимерных реагентов для бурения скважин
Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTIC‐HF: baseline characteristics and comparison with contemporary clinical trials
Aims:
The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC‐HF) trial. Here we describe the baseline characteristics of participants in GALACTIC‐HF and how these compare with other contemporary trials.
Methods and Results:
Adults with established HFrEF, New York Heart Association functional class (NYHA) ≥ II, EF ≤35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokinetic‐guided dosing: 25, 37.5 or 50 mg bid). 8256 patients [male (79%), non‐white (22%), mean age 65 years] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NT‐proBNP 1971 pg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTIC‐HF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressure < 100 mmHg (n = 1127), estimated glomerular filtration rate < 30 mL/min/1.73 m2 (n = 528), and treated with sacubitril‐valsartan at baseline (n = 1594).
Conclusions:
GALACTIC‐HF enrolled a well‐treated, high‐risk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation
Patrick Boyle, trumpet; Brian Way, piano; Danette Dickinson, piano; Grant Etchegary, bassoon; Tony Chadwick; Frank Fusari
Gunther Schuller spelled Gunter in the progra
Ferromagnetism of magnetic impurities coupled indirectly via conduction electrons: Insights from various theoretical approaches
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