36,568 research outputs found
Scalar Casimir-Polder forces for uniaxial corrugations
We investigate the Dirichlet-scalar equivalent of Casimir-Polder forces
between an atom and a surface with arbitrary uniaxial corrugations. The
complexity of the problem can be reduced to a one-dimensional Green's function
equation along the corrugation which can be solved numerically. Our technique
is fully nonperturbative in the height profile of the corrugation. We present
explicit results for experimentally relevant sinusoidal and sawtooth
corrugations. Parameterizing the deviations from the planar limit in terms of
an anomalous dimension which measures the power-law deviation from the planar
case, we observe up to order-one anomalous dimensions at small and intermediate
scales and a universal regime at larger distances. This large-distance
universality can be understood from the fact that the relevant fluctuations
average over corrugation structures smaller than the atom-wall distance.Comment: 25 pages, 7 figure
Continuum EoS for QCD with Nf=2+1 flavors
We report on a continuum extrapolated result [arXiv:1309.5258] for the
equation of state (EoS) of QCD with dynamical quark flavors. In this
study, all systematics are controlled, quark masses are set to their physical
values, and the continuum limit is taken using at least three lattice spacings
corresponding to temporal extents up to . A Symanzik improved gauge and
stout-link improved staggered fermion action is used. Our results are available
online [ancillary file to arXiv:1309.5258].Comment: Conference proceedings, 7 pages, 4 figures. Talk presented at 31st
International Symposium on Lattice Field Theory (LATTICE 2013), July 29 -
August 3, 2013, Mainz, German
The magnetic field topology associated to two M flares
On 27 October, 2003, two GOES M-class flares occurred in the lapse of three
hours in active region NOAA 10486. The two flares were confined and their
associated brightenings appeared at the same location, displaying a very
similar shape both at the chromospheric and coronal levels. We focus on the
analysis of magnetic field (SOHO/MDI), chromospheric (HASTA, Kanzelhoehe Solar
Observatory, TRACE) and coronal (TRACE) observations. By combining our data
analysis with a model of the coronal magnetic field, we compute the magnetic
field topology associated to the two M flares. We find that both events can be
explained in terms of a localized magnetic reconnection process occurring at a
coronal magnetic null point. This null point is also present at the same
location one day later, on 28 October, 2003. Magnetic energy release at this
null point was proposed as the origin of a localized event that occurred
independently with a large X17 flare on 28 October, 2003, at 11:01 UT. The
three events, those on 27 October and the one on 28 October, are homologous.
Our results show that coronal null points can be stable topological structures
where energy release via magnetic reconnection can happen, as proposed by
classical magnetic reconnection models.Comment: 14 pages, 7 figure
Hooked flare ribbons and flux-rope related QSL footprints
We studied the magnetic topology of active region 12158 on 2014 September 10
and compared it with the observations before and early in the flare which
begins at 17:21 UT (SOL2014-09-10T17:45:00). Our results show that the
sigmoidal structure and flare ribbons of this active region observed by SDO/AIA
can be well reproduced from a Grad-Rubin non linear force free field
extrapolation method. Various inverse-S and -J shaped magnetic field lines,
that surround a coronal flux rope, coincide with the sigmoid as observed in
different extreme ultraviolet wavelengths, including its multi-threaded curved
ends. Also, the observed distribution of surface currents in the magnetic
polarity where it was not prescribed is well reproduced. This validates our
numerical implementation and set-up of the Grad-Rubin method. The modeled
double inverse-J shaped Quasi-Separatrix Layer (QSL) footprints match the
observed flare ribbons during the rising phase of the flare, including their
hooked parts. The spiral-like shape of the latter may be related to a complex
pre-eruptive flux rope with more than one turn of twist, as obtained in the
model. These ribbon-associated flux-rope QSL-footprints are consistent with the
new standard flare model in 3D, with the presence of a hyperbolic flux tube
located below an inverse tear drop shaped coronal QSL. This is a new step
forward forecasting the locations of reconnection and ribbons in solar flares,
and the geometrical properties of eruptive flux ropes.Comment: Accepted for publication in Ap
Segmentation of Loops from Coronal EUV Images
We present a procedure which extracts bright loop features from solar EUV
images. In terms of image intensities, these features are elongated ridge-like
intensity maxima. To discriminate the maxima, we need information about the
spatial derivatives of the image intensity. Commonly, the derivative estimates
are strongly affected by image noise. We therefore use a regularized estimation
of the derivative which is then used to interpolate a discrete vector field of
ridge points ``ridgels'' which are positioned on the ridge center and have the
intrinsic orientation of the local ridge direction. A scheme is proposed to
connect ridgels to smooth, spline-represented curves which fit the observed
loops. Finally, a half-automated user interface allows one to merge or split,
eliminate or select loop fits obtained form the above procedure. In this paper
we apply our tool to one of the first EUV images observed by the SECCHI
instrument onboard the recently launched STEREO spacecraft. We compare the
extracted loops with projected field lines computed from
almost-simultaneously-taken magnetograms measured by the SOHO/MDI Doppler
imager. The field lines were calculated using a linear force-free field model.
This comparison allows one to verify faint and spurious loop connections
produced by our segmentation tool and it also helps to prove the quality of the
magnetic-field model where well-identified loop structures comply with
field-line projections. We also discuss further potential applications of our
tool such as loop oscillations and stereoscopy.Comment: 13 pages, 9 figures, Solar Physics, online firs
Behavior of a sandy clay under vertical impact of geometric shapes
Sandy clay response under vertical impact of cone, plate, and plane geometric shape
- …