80 research outputs found
Dynamir: optical manipulations using dynamic mirror brushes
Mirror surfaces are part of our everyday life. Among them, curved mirrors are used to enhance our perception of the physical space, e.g., convex mirrors are used to increase our field of view in the street, and concave mirrors are used to zoom in on parts our face in the bathroom. In this paper, we investigate the opportunities opened when these mirrors are made dynamic, so that their effects can be modulated to adapt to the environment or to a user's actions. We introduce the concept of dynamic mirror brushes that can be moved around a mirror surface. We describe how these brushes can be used for various optical manipulations of the physical space. We also present an implementation using a flexible mirror sheet and three scenarios that demonstrate some of the interaction opportunities
Evidence of Explosive Evaporation in a Microflare Observed by Hinode/EIS
We present a detailed study of explosive chromospheric evaporation during a
microflare which occurred on 2007 December 7 as observed with the EUV Imaging
Spectrometer (EIS) onboard Hinode. We find temperature-dependent upflows for
lines formed from 1.0 to 2.5 MK and downflows for lines formed from 0.05 to
0.63 MK in the impulsive phase of the flare. Both the line intensity and the
nonthermal line width appear enhanced in most of the lines and are temporally
correlated with the time when significant evaporation was observed. Our results
are consistent with the numerical simulations of flare models, which take into
account a strong nonthermal electron beam in producing the explosive
chromospheric evaporation. The explosive evaporation observed in this
microflare implies that the same dynamic processes may exist in events with
very different magnitudes.Comment: 14 pages, 8 figures. Accepted for publication in the Astrophysical
Journa
Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line
and G-band image sequences and their relation to simultaneous and co-spatial
magnetic field measurements. We explore the G-band and H-line intensity
oscillation spectra both separately and comparatively via their relative phase
differences, time delays and cross-coherences. In the non-magnetic situations,
both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band
centered at 4.5 mHz, but this is suppressed as magnetic field increases. A
relative phase analysis gives a time delay of H-line after G-band of 20\pm1 s
in non-magnetic situations implying a mean effective height difference of 140
km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the
measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A
second coherence maximum appears between 7.5 - 10 mHz. Investigation of the
locations of this doubled-frequency coherence locates it in diffuse rings
outside photospheric magnetic structures. Some possible interpretations of
these results are offered.Comment: 19 pages, 6 figure
MHD waves in sunspots
The review addresses the spatial frequency morphology of sources of sunspot
oscillations and waves, including their localization, size, oscillation
periods, height localization with the mechanism of cut-off frequency that forms
the observed emission variability. Dynamic of sunspot wave processes, provides
the information about the structure of wave fronts and their time variations,
investigates the oscillation frequency transformation depending on the wave
energy is shown. The initializing solar flares caused by trigger agents like
magnetoacoustic waves, accelerated particle beams, and shocks are discussed.
Special attention is paid to the relation between the flare reconnection
periodic initialization and the dynamics of sunspot slow magnetoacoustic waves.
A short review of theoretical models of sunspot oscillations is provided.Comment: 20 pages, 6 figures, Chapter in AGU Monograph (in press), Review
articl
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
An investigation of a genomewide supported psychosis variant in ZNF804A and white matter integrity in the human brain
ZNF804A, a genomewide supported susceptibility gene for schizophrenia and bipolar disorder, has been associated with task-independent functional connectivity between the left and right dorsolateral prefrontal cortices. Several lines of evidence have converged on the hypothesis that this effect may be mediated by structural connectivity. We tested this hypothesis using diffusion tensor magnetic resonance imaging in three samples: one German sample of 50 healthy individuals, one Scottish sample of 83 healthy individuals and one Scottish sample of 84 unaffected relatives of bipolar patients. Voxel-based analysis and tract-based spatial statistics did not detect any fractional anisotropy (FA) differences between minor allele carriers and individuals homozygous for the major allele at rs1344706. Similarly, region-of-interest analyses and quantitative tractography of the genu of the corpus callosum revealed no significant FA differences between the genotype groups. Examination of effect sizes and confidence intervals indicated that this negative finding is very unlikely to be due to a lack of statistical power. In summary, despite using various analysis techniques in three different samples, our results were strikingly and consistently negative. These data therefore suggest that it is unlikely that the effects of genetic variation at rs1344706 on functional connectivity are mediated by structural integrity differences in large, long-range white matter fiber connections
Varying driver velocity fields in photospheric MHD wave simulations
Torsional motions are ubiquitous in the solar atmosphere. In this work, we perform 3D numerical simulations which mimic a vortex-type photospheric driver with a Gaussian spatial profile. This driver is implemented to excite MHD waves in an axially symmetric, 3D magnetic flux tube embedded in a realistic solar atmosphere. The Gaussian width of the driver is varied and the resulting perturbations are compared. Velocity vectors were decomposed into parallel, perpendicular and azimuthal components with respect to pre-defined magnetic flux surfaces. These components correspond broadly to the fast, slow and Alfvén modes, respectively. From these velocities the corresponding wave energy fluxes are calculated, allowing us to estimate the contribution of each mode to the energy flux. For the narrowest driver (0.15 Mm) the parallel component accounts for ∼55 − 65% of the flux. This contribution increases smoothly with driver width up to nearly 90% for the widest driver (0.35 Mm). The relative importance of the perpendicular and azimuthal components decrease at similar rates. The azimuthal energy flux varied between ∼35% for the narrowest driver and <10% for the widest one. Similarly, the perpendicular flux was ∼25 − 10%. We also demonstrate that the fast mode corresponds to the sausage wave in our simulations. Our results therefore show that the fast sausage wave is easily excited by this driver and that it carries the majority of the energy transported. For this vortex-type driver the Alfvén wave does not contribute a significant amount of energy
Pulse-driven nonlinear Alfv\'en waves and their role in the spectral line broadening
We study the impulsively generated non-linear Alfv\'en waves in the solar
atmosphere, and describe their most likely role in the observed non-thermal
broadening of some spectral lines in solar coronal holes. We solve numerically
the time-dependent magnetohydrodynamic equations to find temporal signatures of
large-amplitude Alfv\'en waves in the model atmosphere of open and expanding
magnetic field configuration, with a realistic temperature distribution. We
calculate the temporally and spatially averaged, instantaneous transversal
velocity of non-linear Alfv\'en waves at different heights of the model
atmosphere, and estimate its contribution to the unresolved non-thermal motions
caused by the waves. We find that the pulse-driven nonlinear Alfv\'en waves
with the amplitude =50 km s are the most likely candidates
for the non-thermal broadening of Si VIII 1445.75 \AA\ line profiles
in the polar coronal hole as reported by Banerjee et al. (1998). We also
demonstrate that the Alfv\'en waves driven by comparatively smaller velocity
pulse with its amplitude =25 km s may contribute to the
spectral line width of the same line at various heights in coronal hole without
any significant broadening. The main conclusion of this paper is that
non-linear Alfv\'en waves excited impulsively in the lower solar atmosphere are
responsible for the observed spectral line broadening in polar coronal holes.
This is an important result as it allows us to conclude that such large
amplitude and pulse-driven Alfv\'en waves do indeed exist in solar coronal
holes. The existence of these waves and their undamped growth may impart the
required momentum to accelerate the solar wind
- …