807 research outputs found
Transmogrifying Fuzzy Vortices
We show that the construction of vortex solitons of the noncommutative
Abelian-Higgs model can be extended to a critically coupled gauged linear sigma
model with Fayet-Illiopolous D-terms. Like its commutative counterpart, this
fuzzy linear sigma model has a rich spectrum of BPS solutions. We offer an
explicit construction of the degree static semilocal vortex and study in
some detail the infinite coupling limit in which it descends to a degree
\C\Pk^{N} instanton. This relation between the fuzzy vortex and
noncommutative lump is used to suggest an interpretation of the noncommutative
sigma model soliton as tilted D-strings stretched between an NS5-brane and a
stack of D3-branes in type IIB superstring theory.Comment: 21 pages, 4 figures, LaTeX(JHEP3
Solar Magnetic Carpet I: Simulation of Synthetic Magnetograms
This paper describes a new 2D model for the photospheric evolution of the
magnetic carpet. It is the first in a series of papers working towards
constructing a realistic 3D non-potential model for the interaction of
small-scale solar magnetic fields. In the model, the basic evolution of the
magnetic elements is governed by a supergranular flow profile. In addition,
magnetic elements may evolve through the processes of emergence, cancellation,
coalescence and fragmentation. Model parameters for the emergence of bipoles
are based upon the results of observational studies. Using this model, several
simulations are considered, where the range of flux with which bipoles may
emerge is varied. In all cases the model quickly reaches a steady state where
the rates of emergence and cancellation balance. Analysis of the resulting
magnetic field shows that we reproduce observed quantities such as the flux
distribution, mean field, cancellation rates, photospheric recycle time and a
magnetic network. As expected, the simulation matches observations more closely
when a larger, and consequently more realistic, range of emerging flux values
is allowed (4e16 - 1e19 Mx). The model best reproduces the current observed
properties of the magnetic carpet when we take the minimum absolute flux for
emerging bipoles to be 4e16 Mx. In future, this 2D model will be used as an
evolving photospheric boundary condition for 3D non-potential modeling.Comment: 33 pages, 16 figures, 5 gif movies included: movies may be viewed at
http://www-solar.mcs.st-and.ac.uk/~karen/movies_paper1
Five-brane Instantons vs Flux-induced Gauging of Isometries
In five-dimensional heterotic M-theory there is necessarily nonzero
background flux, which leads to gauging of an isometry of the universal
hypermultiplet moduli space. This isometry, however, is poised to be broken by
M5-brane instanton effects. We show that, similarly to string theory, the
background flux allows only brane instantons that preserve the above isometry.
The zero-mode counting for the M5 instantons is related to the number of
solutions of the Dirac equation on their worldvolume. We investigate that
equation in the presence of generic background flux and also, in a particular
case, with nonzero worldvolume flux.Comment: 27 pages; reference adde
Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition
Cetacean watching from tour boats has increased in recent years and has been promoted as an ethically
viable alternative to cetacean viewing in captive facilities or directed take. However, short- and longterm
impacts of this industry on the behaviour and energetic expenditure of cetaceans have been
documented. Although multiple studies have investigated the acoustic response of dolphins to marine
tourism, there are several covariates that could also explain some of these results and should be
considered simultaneously. Here, we investigated whether common bottlenose dolphins, Tursiops
truncatus, inhabiting Walvis Bay, Namibia vary their whistle parameters in relation to boat presence,
surface behaviour and/or group composition. We detected an upward shift of up to 1.99 kHz in several
whistle frequency parameters when dolphins were in the presence of one or more tour boats and the
research vessel. No changes were demonstrated in the frequency range, number of inflection points or
duration of whistles. A similar, although less pronounced difference was observed in response to engine
noise generated by the research vessel when idling, suggesting that noise alone plays an important role
in driving this shift in whistle frequency. Additionally, a strong effect of surface behaviour was observed,
with the greatest difference in whistle parameters detected between resting and other behavioural states
that are associated with higher degrees of emotional arousal. Group composition also contributed to the
variation observed, with the impact of boats dependent on whether calves were present or not. Overall
these results demonstrate high natural variation in the frequency parameters of whistles utilized by
dolphins over varying behavioural states and group composition. Anthropogenic impact in the form of
marine tour boats can influence the vocalization parameters of dolphins and such changes could have a
long-term impact if they reduce the communication range of whistles or increase energy expenditure.T.G. was funded during the initial stages of this work by a NERC PhD studentship, a University of St Andrews Russell Trust Award and later the University of Pretoria Vice Chancellor's postdoctoral fellowship. Postdoctoral fellowships from the University of Pretoria and Claude Leon Foundation provided assistance to S.E. Equipment and running costs were provided by Idea Wild Fund, Professor V. Janik and the Nedbank Go Green Fund. International Master of Science in Marine Biodiversity and Conservation Programme.http://www.elsevier.com/locate/anbehav2017-07-31hb2016Mammal Research InstituteZoology and Entomolog
Non BPS noncommutative vortices
We construct exact vortex solutions to the equations of motion of the Abelian
Higgs model defined in non commutative space, analyzing in detail the
properties of these solutions beyond the BPS point. We show that our solutions
behave as smooth deformations of vortices in ordinary space time except for
parity symmetry breaking effects induced by the non commutative parameter
.Comment: 17 pages, 5 figure
Small scale energy release driven by supergranular flows on the quiet Sun
In this article we present data and modelling for the quiet Sun that strongly suggest a ubiquitous small-scale atmospheric heating mechanism that is driven solely by converging supergranular flows.
A possible energy source for such events is the power transfer to the plasma via the work done on the magnetic field by photospheric convective flows, which exert drag of the footpoints of magnetic structures. In this paper we present evidence of small scale energy release events driven directly by the hydrodynamic forces that act on the magnetic elements in the photosphere, as a result of supergranular scale flows. We show strong spatial and temporal correlation between quiet Sun soft X-ray emission (from <i>Yohkoh</i> and <i>SOHO</i> MDI-derived flux removal events driven by deduced photospheric flows.
We also present a simple model of heating generated by flux submergence, based on particle acceleration by converging magnetic mirrors.
In the near future, high resolution soft X-ray images from XRT on the <i>Hinode</i> satellite will allow definitive, quantitative verification of our results
Parameters of the Magnetic Flux inside Coronal Holes
Parameters of magnetic flux distribution inside low-latitude coronal holes
(CHs) were analyzed. A statistical study of 44 CHs based on Solar and
Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284\AA
images showed that the density of the net magnetic flux, , does
not correlate with the associated solar wind speeds, . Both the area and
net flux of CHs correlate with the solar wind speed and the corresponding
spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A
possible explanation for the low correlation between and
is proposed. The observed non-correlation might be rooted in the structural
complexity of the magnetic field. As a measure of complexity of the magnetic
field, the filling factor, , was calculated as a function of spatial
scales. In CHs, was found to be nearly constant at scales above 2 Mm,
which indicates a monofractal structural organization and smooth temporal
evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP
data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller
than 2 Mm, the filling factor decreases rapidly, which means a mutlifractal
structure and highly intermittent, burst-like energy release regime. The
absence of necessary complexity in CH magnetic fields at scales above 2 Mm
seems to be the most plausible reason why the net magnetic flux density does
not seem to be related to the solar wind speed: the energy release dynamics,
needed for solar wind acceleration, appears to occur at small scales below 1
Mm.Comment: 6 figures, approximately 23 pages. Accepted in Solar Physic
Can sexual selection drive female life histories? A comparative study on Galliform birds
Sexual selection is an important driver of many of the most spectacular morphological traits that we find in the animal kingdom (for example see Andersson, 1994). As such, sexual selection is most often emphasized as
The Horizontal Component of Photospheric Plasma Flows During the Emergence of Active Regions on the Sun
The dynamics of horizontal plasma flows during the first hours of the
emergence of active region magnetic flux in the solar photosphere have been
analyzed using SOHO/MDI data. Four active regions emerging near the solar limb
have been considered. It has been found that extended regions of Doppler
velocities with different signs are formed in the first hours of the magnetic
flux emergence in the horizontal velocity field. The flows observed are
directly connected with the emerging magnetic flux; they form at the beginning
of the emergence of active regions and are present for a few hours. The Doppler
velocities of flows observed increase gradually and reach their peak values
4-12 hours after the start of the magnetic flux emergence. The peak values of
the mean (inside the +/-500 m/s isolines) and maximum Doppler velocities are
800-970 m/s and 1410-1700 m/s, respectively. The Doppler velocities observed
substantially exceed the separation velocities of the photospheric magnetic
flux outer boundaries. The asymmetry was detected between velocity structures
of leading and following polarities. Doppler velocity structures located in a
region of leading magnetic polarity are more powerful and exist longer than
those in regions of following polarity. The Doppler velocity asymmetry between
the velocity structures of opposite sign reaches its peak values soon after the
emergence begins and then gradually drops within 7-12 hours. The peak values of
asymmetry for the mean and maximal Doppler velocities reach 240-460 m/s and
710-940 m/s, respectively. An interpretation of the observable flow of
photospheric plasma is given.Comment: 20 pages, 10 figures, 3 tables. The results of article were presented
at the ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102,
P.4.12,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
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