178 research outputs found
The Dielectric Skyrme model
We consider a version of the Skyrme model where both the kinetic term and the
Skyrme term are multiplied by field-dependent coupling functions. For suitable
choices, this "dielectric Skyrme model" has static solutions saturating the
pertinent topological bound in the sector of baryon number (or topological
charge) but not for higher . This implies that higher charge
field configurations are unbound, and loosely bound higher skyrmions can be
achieved by small deformations of this dielectric Skyrme model. We provide a
simple and explicit example for this possibility. Further, we show that the
BPS sector continues to exist for certain generalizations of the model
like, for instance, after its coupling to a specific version of the BPS Skyrme
model, i.e., the addition of the sextic term and a particular potential.Comment: Latex file, 13 pages, no figure
Mechanism of the Verwey transition in magnetite
By combining {\it ab initio} results for the electronic structure and phonon
spectrum with the group theory, we establish the origin of the Verwey
transition in FeO. Two primary order parameters with and
symmetries are identified. They induce the phase transformation from
the high-temperature cubic to the low-temperature monoclinic structure. The
on-site Coulomb interaction between 3d electrons at Fe ions plays a crucial
role in this transition -- it amplifies the coupling of phonons to conduction
electrons and thus opens a gap at the Fermi energy. {\it Published in Phys.
Rev. Lett. {\bf 97}, 156402 (2006).}Comment: 5 pages, 3 figure
The Role of Psychological Capital and the Areas of Worklife Model in Predicting Job Burnout
Job burnout is a widely spread global phenomenon that has been linked to negative work outcomes. Various factors can either contribute to or hinder job burnout development. Previous research established the role of the six areas of worklife model as well as psychological capital on job burnout. However, the relationship among these variables has not been clearly defined. The purpose of the present study was to attempt to understand predictors of job burnout in order to reduce its occurrence. Data was collected with a sample of college students. Four areas of worklife (workload, control, reward, and values) as well as three dimensions of psychological capital (hope, optimism, and resiliency) were predictive of job burnout. In addition, the negative effect of person-job mismatch in areas of worklife on job burnout was weaker when psychological capital was high as opposed to low. Finally, the study examined the mediating role of areas of worklife in relationship between psychological capital and job burnout, but failed to find any effect. Our findings underline the importance of fostering psychological capital in the workplace as well as ensuring congruence between individuals\u27 person-job fit through areas of worklife, and specifically through workload, control, reward and values, in order to decrease job burnout occurrence
Order parameters in the Verwey phase transition
The Verwey phase transition in magnetite is analyzed on the basis of the
Landau theory. The free energy functional is expanded in a series of components
belonging to the primary and secondary order parameters. A low-temperature
phase with the monoclinic P2/c symmetry is a result of condensation of two
order parameters X_3 and \Delta_5 . The temperature dependence of the shear
elastic constant C_44 is derived and the mechanism of its softening is
discussed.Comment: 4 pages, 1 figur
Quantum disorder versus order-out-of-disorder in the Kugel-Khomskii model
The Kugel-Khomskii model, the simplest model for orbital degenerate magnetic
insulators, exhibits a zero temperature degeneracy in the classical limit which
could cause genuine quantum disorder. Khaliullin and Oudovenko [Phys. Rev. B
56, R14 243 (1997)] suggested recently that instead a particular classical
state could be stabilized by quantum fluctuations. Here we compare their
approach with standard random phase approximation and show that it strongly
underestimates the strength of the quantum fluctuations, shedding doubts on the
survival of any classical state.Comment: 4 pages, ReVTeX, 4 figure
Kink-antikink collisions in a weakly interacting model
We study kink-antikink scattering in a one-parameter variant of the
theory where the model parameter controls the static intersoliton force. We
interpolate between the limit of no static force (BPS limit) and the regime
where the static interaction is small (non-BPS). This allows us to study the
impact of the strength of the intersoliton static force on the soliton
dynamics.
In particular, we analyze how the transition of a bound mode through the mass
threshold affects the soliton dynamics in a generic process, i.e., when a
static intersoliton force shows up. We show that the thin, precisely localized
spectral wall which forms in the limit of no static force, broadens in a
well-defined manner when a static force is included, giving rise to what we
will call a thick spectral wall. This phenomenon just requires that a discrete
mode crosses into the continuum at some intermediate stage of the dynamics and,
therefore, should be observable in many soliton-antisoliton collisions.Comment: version accepted in Phys. Rev.
Sphaleron without shape mode and its oscillon
We find that an oscillon can possess a characteristic double oscillation
structure even though it results in a decay of a sphaleron which does not have
any positive energy vibrational mode. We show that dynamics of such an oscillon
can still be captured by collective coordinates provided by the sphaleron.
Namely, its unstable mode and its scaling deformation i.e., Derrick mode.Comment: 10 pages, 12 figure
Collective coordinate model of kink-antikink collisions in theory
The fractal velocity pattern in symmetric kink-antikink collisions in
theory is shown to emerge from a dynamical model with two effective
moduli, the kink-antikink separation and the internal shape mode amplitude. The
shape mode usefully approximates Lorentz contractions of the kink and antikink,
and the previously problematic null-vector in the shape mode amplitude at zero
separation is regularized.Comment: the metric and potential of the effective model are now include
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Riparian Meadow Response to Modern Conservation Grazing Management.
Riparian meadows occupy a small proportion of the public lands in the western United States but they provide numerous ecosystem services, including the production of high-quality forage for livestock grazing. Modern conservation management strategies (e.g., reductions in livestock stocking rates and adoption of new riparian grazing standards) have been implemented to better balance riparian conservation and livestock production objectives on publicly managed lands. We examined potential relationships between long-term changes in plant community, livestock grazing pressure and environmental conditions at two spatial scales in meadows grazed under conservation management strategies. Changes in plant community were not associated with either livestock stocking rate or precipitation at the grazing allotment (i.e., administrative) scale. Alternatively, both grazing pressure and precipitation had significant, albeit modest, associations with changes in plant community at the meadow (i.e., ecological site) scale. These results suggest that reductions in stocking rate have improved the balance between riparian conservation and livestock production goals. However, associations between elevation, site wetness, precipitation, and changes in plant community suggest that changing climate conditions (e.g., reduced snowpack and changes in timing of snowmelt) could trigger shifts in plant communities, potentially impacting both conservation and agricultural services (e.g., livestock and forage production). Therefore, adaptive, site-specific management strategies are required to meet grazing pressure limits and safeguard ecosystem services within individual meadows, especially under more variable climate conditions
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