6,483 research outputs found
Inertia and chiral edge modes of a skyrmion magnetic bubble
The dynamics of a vortex in a thin-film ferromagnet resembles the motion of a
charged massless particle in a uniform magnetic field. Similar dynamics is
expected for other magnetic textures with a nonzero skyrmion number. However,
recent numerical simulations revealed that skyrmion magnetic bubbles show
significant deviations from this model. We show that a skyrmion bubble
possesses inertia and derive its mass from the standard theory of a thin-film
ferromagnet. Besides center-of-mass motion, other low energy modes are waves on
the edge of the bubble traveling with different speeds in opposite directions.Comment: updated simulation detail
Adiabatic radio frequency potentials for the coherent manipulation of matter waves
Adiabatic dressed state potentials are created when magnetic sub-states of
trapped atoms are coupled by a radio frequency field. We discuss their
theoretical foundations and point out fundamental advantages over potentials
purely based on static fields. The enhanced flexibility enables one to
implement numerous novel configurations, including double wells, Mach-Zehnder
and Sagnac interferometers which even allows for internal state-dependent atom
manipulation. These can be realized using simple and highly integrated wire
geometries on atom chips.Comment: 13 pages, 2 figure
Strong plasmonic fluorescence enhancement of individual plant light-harvesting complexes
Plasmonic coupling of metallic nanoparticles and adjacent pigments can
dramatically increase the brightness of the pigments due to the enhanced local
electric field. Here, we demonstrate that the fluorescence brightness of a
single plant light-harvesting complex (LHCII) can be significantly enhanced
when coupled to single gold nanorods (AuNRs). The AuNRs utilized in this study
were prepared via chemical reactions, and the hybrid system was constructed
using a simple and economical spin-assisted layer-by-layer technique.
Enhancement of fluorescence brightness of up to 240-fold was observed,
accompanied by a 109-fold decrease in the average (amplitude-weighted)
fluorescence lifetime from approximately 3.5 ns down to 32 ps, corresponding to
an excitation enhancement of 63-fold and emission enhancement of up to
3.8-fold. This large enhancement is due to the strong spectral overlap of the
longitudinal localized surface plasmon resonance of the utilized AuNRs and the
absorption or emission bands of LHCII. This study provides an inexpensive
strategy to explore the fluorescence dynamics of weakly emitting photosynthetic
light-harvesting complexes at the single molecule level.Comment: 23 pages, 6 figures, 2 supplementary figures, and supplementary
equation
Dynamically controlled toroidal and ring-shaped magnetic traps
We present traps with toroidal and ring-shaped topologies, based on
adiabatic potentials for radio-frequency dressed Zeeman states in a ring-shaped
magnetic quadrupole field. Simple adjustment of the radio-frequency fields
provides versatile possibilities for dynamical parameter tuning, topology
change, and controlled potential perturbation. We show how to induce toroidal
and poloidal rotations, and demonstrate the feasibility of preparing degenerate
quantum gases with reduced dimensionality and periodic boundary conditions. The
great level of dynamical and even state dependent control is useful for atom
interferometry.Comment: 6 pages, 4 figures. Paragraphs on gravity compensation and expected
trap lifetimes adde
The influence of transformational policies on the operational competitiveness of South African businesses
Since the dawn of democracy in South Africa in 1994, transformational policies such as black economic empowerment (BEE) and affirmative action (AA) have increasingly and inextricably become part of the everyday political, economic and social life of its populace. As a result, South African businesses are subject to a whole array of mandatory regulations which ostensibly influence their operational capabilities to effectively and efficiently compete in national and global markets. In a survey of the largest 500 (including the top 100 JSE listed) companies in South Africa, it appears that transformational policies are positively supported and endorsed, although their impact on the operational competitiveness of these companies is largely unclear and unknown. A number of warning signs, however, are now being detected from reports in the popular media and in the academic literature about the possible negative consequences of such policies. BEE malpractices, which basically result in the continuation of past injustices against the majority of poor and unskilled people of the country, are becoming increasingly evident. Even more alarming is the fact that the corruption, nepotism and self-enrichment that accompany most BEE transactions are attributed to the ruling ANC political elite
Self Consistent Random Phase Approximation and the restoration of symmetries within the three-level Lipkin model
We show that it is possible to restore the symmetry associated with the
Goldstone mode within the Self Consistent Random Phase Approximation (SCRPA)
applied to the three-level Lipkin model. We determine one and two-body
densities as very convergent expansions in terms of the generators of the RPA
basis. We show that SCRPA excitations correspond to the heads of some
rotational bands in the exact spectrum. It turns out that the SCRPA eigenmodes
for N=2 coincide with exact solutions, given by the diagonalisation procedure
Modeling near-field radiative heat transfer from sharp objects using a general 3d numerical scattering technique
We examine the non-equilibrium radiative heat transfer between a plate and
finite cylinders and cones, making the first accurate theoretical predictions
for the total heat transfer and the spatial heat flux profile for
three-dimensional compact objects including corners or tips. We find
qualitatively different scaling laws for conical shapes at small separations,
and in contrast to a flat/slightly-curved object, a sharp cone exhibits a local
\emph{minimum} in the spatially resolved heat flux directly below the tip. The
method we develop, in which a scattering-theory formulation of thermal transfer
is combined with a boundary-element method for computing scattering matrices,
can be applied to three-dimensional objects of arbitrary shape.Comment: 5 pages, 4 figures. Corrected background information in the
introduction, results and discussion unchange
Guidelines for initiation of anti-tumour necrosis factor therapy in rheumatoid arthritis: similarities and differences across Europe.
Contains fulltext :
80544.pdf (publisher's version ) (Closed access
Spin Stiffness in the Hubbard model
The spin stiffness of the repulsive Hubbard model that occurs
in the hydrodynamic theory of antiferromagnetic spin waves is shown to be the
same as the thermodynamically defined stiffness involved in twisting the order
parameter. New expressions for are derived, which enable easier
interpretation, and connections with superconducting weight and gauge
invariance are discussed.Comment: 21 Pages LaTeX2e, to be published in Journal of Physics
Superfluid flow past an obstacle in annular BoseâEinstein condensates
We investigate the flow of a one-dimensional nonlinear Schrödinger model with periodic boundary conditions past an obstacle, motivated by recent experiments with BoseâEinstein condensates in ring traps. Above certain rotation velocities, localized solutions with a nontrivial phase profile appear. In striking difference from the infinite domain, in this case there are many critical velocities. At each critical velocity, the steady flow solutions disappear in a saddle-center bifurcation. These interconnected branches of the bifurcation diagram lead to additions of circulation quanta to the phase of the associated solution. This, in turn, relates to the manifestation of persistent current in numerous recent experimental and theoretical works, the connections to which we touch upon. The complex dynamics of the identified waveforms and the instability of unstable solution branches are demonstrated
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