43 research outputs found
Metallic ferromagnetism without exchange splitting
In the band theory of ferromagnetism there is a relative shift in the
position of majority and minority spin bands due to the self-consistent field
due to opposite spin electrons. In the simplest realization, the Stoner model,
the majority and minority spin bands are rigidly shifted with respect to each
other. Here we consider models at the opposite extreme, where there is no
overall shift of the energy bands. Instead, upon spin polarization one of the
bands broadens relative to the other. Ferromagnetism is driven by the resulting
gain in kinetic energy. A signature of this class of mechanisms is that a
transfer of spectral weight in optical absorption from high to low frequencies
occurs upon spin polarization. We show that such models arise from generalized
tight binding models that include off-diagonal matrix elements of the Coulomb
interaction. For certain parameter ranges it is also found that reentrant
ferromagnetism occurs. We examine properties of these models at zero and finite
temperatures, and discuss their possible relevance to real materials
Magnetic Reversal on Vicinal Surfaces
We present a theoretical study of in-plane magnetization reversal for vicinal
ultrathin films using a one-dimensional micromagnetic model with
nearest-neighbor exchange, four-fold anisotropy at all sites, and two-fold
anisotropy at step edges. A detailed "phase diagram" is presented that catalogs
the possible shapes of hysteresis loops and reversal mechanisms as a function
of step anisotropy strength and vicinal terrace length. The steps generically
nucleate magnetization reversal and pin the motion of domain walls. No sharp
transition separates the cases of reversal by coherent rotation and reversal by
depinning of a ninety degree domain wall from the steps. Comparison to
experiment is made when appropriate.Comment: 12 pages, 8 figure
The implications of service quality gaps for strategy implementation
This article addresses the problem of service quality strategy implementation and
proposes three interrelated models: a static model of the organisation; a comprehensive
dynamic model of the implementation process, both synthesised from the literature; and
a mixed model, which integrates static and dynamic models. The mixed model is
combined with the service quality gaps (SQGs) model, drawn at a previous congress
paper, to propose a map of the pattern of SQGs occurring at each implementation stage;
the organisational variables that can be manipulated to eliminate SQGs; and several
implications to practising managers
Fotopedologia, espectroscopia e sistema de informação geogråfica na caracterização de solos desenvolvidos do Grupo Barreiras no Amapå
Crossovers in Unitary Fermi Systems
Universality and crossover is described for attractive and repulsive
interactions where, respectively, the BCS-BEC crossover takes place and a
ferromagnetic phase transition is claimed. Crossovers are also described for
optical lattices and multicomponent systems. The crossovers, universal
parameters and phase transitions are described within the Leggett and NSR
models and calculated in detail within the Jastrow-Slater approximation. The
physics of ultracold Fermi atoms is applied to neutron, nuclear and quark
matter, nuclei and electrons in solids whenever possible. Specifically, the
differences between optical lattices and cuprates is discussed w.r.t.
antiferromagnetic, d-wave superfluid phases and phase separation.Comment: 50 pages, 15 figures. Contribution to Lecture Notes in Physics
"BCS-BEC crossover and the Unitary Fermi Gas" edited by W. Zwerge
Resposta espectral de solos em razão do ângulo de visada, da umidade e da rugosidade superficial
Amine Containing Analogs of Sulindac for Cancer Prevention
Background:
Sulindac belongs to the chemically diverse family of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) that effectively prevent adenomatous colorectal polyps and colon cancer, especially in patients with familial adenomatous polyposis. Sulindac sulfide amide (SSA), an amide analog of sulindac sulfide, shows insignificant COX-related activity and toxicity while enhancing anticancer activity in vitro and demonstrating in vivo xenograft activity.
Objective:
Develop structure-activity relationships in the sulindac amine series and identify analogs with promising anticancer activities.
Method:
A series of sulindac amine analogs were designed and synthesized and then further modified in a âlibraries from librariesâ approach to produce amide, sulfonamide and N,N-disubstituted sulindac amine sub-libraries. All analogs were screened against three cancer cell lines (prostate, colon and breast).
Results:
Several active compounds were identified viain vitro cancer cell line screening with the most potent compound (26) in the nanomolar range.
Conclusion:
Compound 26 and analogs showing the most potent inhibitory activity may be considered for further design and optimization efforts as anticancer hit scaffolds
Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases
We analyze the properties of a single impurity immersed in a Fermi sea. At
positive energy and scattering lengths, we show that the system possesses a
well-defined but metastable excitation, the repulsive polaron, and we calculate
its energy, quasiparticle residue and effective mass. From a thermodynamic
argument we obtain the number of particles in the dressing cloud, illustrating
the repulsive character of the polaron. Identifying the important 2- and 3-body
decay channels, we furthermore calculate the lifetime of the repulsive polaron.
The stability conditions for the formation of fully spin polarized
(ferromagnetic) domains are then examined for a binary mixture of atoms with a
general mass ratio. Our results indicate that mass imbalance lowers the
critical interaction strength for phase-separation, but that very short
quasiparticle decay times will complicate the experimental observation of
itinerant ferromagnetism. Finally, we present the spectral function of the
impurity for various coupling strengths and momenta.Comment: Substantial improvements to the section describing quasiparticle
decays (included a discussion of two-body and three-body processes), and to
the criteria for the stability of the itinerant ferromagnetic phas