5,128 research outputs found
Hinode Observations of Magnetic Elements in Internetwork Areas
We use sequences of images and magnetograms from Hinode to study magnetic
elements in internetwork parts of the quiet solar photosphere. Visual
inspection shows the existence of many long-lived (several hours) structures
that interact frequently, and may migrate over distances ~7 Mm over a period of
a few hours. About a fifth of the elements have an associated bright point in
G-band or Ca II H intensity. We apply a hysteresis-based algorithm to identify
elements. The algorithm is able to track elements for about 10 min on average.
Elements intermittently drop below the detection limit, though the associated
flux apparently persists and often reappears some time later. We infer proper
motions of elements from their successive positions, and find that they obey a
Gaussian distribution with an rms of 1.57+-0.08 km/s. The apparent flows
indicate a bias of about 0.2 km/s toward the network boundary. Elements of
negative polarity show a higher bias than elements of positive polarity,
perhaps as a result of to the dominant positive polarity of the network in the
field of view, or because of increased mobility due to their smaller size. A
preference for motions in X is likely explained by higher supergranular flow in
that direction. We search for emerging bipoles by grouping elements of opposite
polarity that appear close together in space and time. We find no evidence
supporting Joy's law at arcsecond scales.Comment: 22 pages, 12 figure
Parton Distributions Working Group
The main focus of this working group was to investigate the different issues
associated with the development of quantitative tools to estimate parton
distribution functions uncertainties. In the conclusion, we introduce a
"Manifesto" that describes an optimal method for reporting data.Comment: Report of the Parton Distributions Working Group of the 'QCD and Weak
Boson Physics workshop in preparation for Run II at the Fermilab Tevatron'.
Co-Conveners: L. de Barbaro, S.A. Keller, S. Kuhlmann, H. Schellman, and
W.-K. Tun
Statistics of convective collapse events in the photosphere and chromosphere observed with the Hinode SOT
Aims. Convective collapse, a theoretically predicted process that intensifies
existing weak magnetic fields in the solar atmosphere, was first directly
observed in a single event by Nagata et al. (2008) using the high resolution
Solar Optical Telescope (SOT) of the Hinode satellite. Using the same space
telescope, we performed a statistical analysis of convective collapse events.
Methods. Our data sets consist of high resolution time series of polarimetric
spectral scans of two iron lines formed in the lower photosphere and filter
images in Mg I b2 and Ca II H, spectral lines that are formed in the high
photosphere and the lower chromosphere, respectively. We were thus able to
study the implication of convective collapse events on the high photospheric
and the chromospheric layers. The physical parameters from the full Stokes
profiles were obtained with the MERLIN Milne-Eddington inversion code.
Results. We found that in all cases, the event was accompanied by a continuum
bright point and nearly always by a brightening in the Ca II H images. The
magnesium dopplergram exhibits a strong downflow in about three quarters of the
events that took place within the field of view of the magnesium dopplergram.
For each of the 49 events we determined the duration, maximum photospheric
downflow, field strength increase and size. We found event durations of about
10 minutes, magnetic element radii of about 0.43 arcsec and 0.35 arcsec, before
and after the event, respectively, and field strengths of up to 1.65 kG.Comment: 7 pages,11 figures,1 tabl
Super AutoDipole
The publicly available package for an automated dipole subtraction,
AutoDipole, is extended to include the SUSY dipoles in the MSSM. All fields in
the SM and the MSSM are available. The code is checked against the analytical
expressions for a simple process. The extended package makes it possible to
compute the QCD NLO corrections to SUSY multi-parton processes like the stop
pair production plus jets at the LHC.Comment: 16 pages, 1 figure, v2: a few typos to match the published version in
Eur. Phys. J.
Small-scale solar magnetic fields
As we resolve ever smaller structures in the solar atmosphere, it has become
clear that magnetism is an important component of those small structures.
Small-scale magnetism holds the key to many poorly understood facets of solar
magnetism on all scales, such as the existence of a local dynamo, chromospheric
heating, and flux emergence, to name a few. Here, we review our knowledge of
small-scale photospheric fields, with particular emphasis on quiet-sun field,
and discuss the implications of several results obtained recently using new
instruments, as well as future prospects in this field of research.Comment: 43 pages, 18 figure
Electroweak Radiative Corrections to W Boson Production in Hadronic Collisions
The O(\alpha) electroweak radiative corrections to the process pp, ppbar\to W
\to\ell^\pm\nu (\ell=e,\mu) are calculated. The O(\alpha) corrections can be
decomposed into separately gauge invariant contributions to the W boson
production and decay processes. Factorizing the collinear singularity
associated with initial state photon radiation into the parton distribution
functions, we find that initial state corrections have a significantly smaller
effect than final state radiative corrections. We study in detail the effect of
electroweak radiative corrections on a number of interesting observables: the W
transverse mass distribution, the W to Z transverse mass ratio, the charge
asymmetry of leptons in W\to\ell\nu decays, as well as the W production cross
section and the W to Z cross section ratio. We also investigate how
experimental lepton identification requirements change the effect of the
electroweak corrections.Comment: 38 pages, Revtex, 13 embedded postscript figure
Membrane transport proteins in human melanoma: associations with tumour aggressiveness and metastasis
BACKGROUND: Malignant melanoma, generally described as incurable, is notoriously refractory to chemotherapy. The mechanisms contributing to this have not yet been defined and the contributions of drug efflux pumps, implicated in chemo-resistance of many other cancer types, have not been extensively investigated in melanoma.
METHODS: In this study, expression of multi-drug resistant (MDR1/P-gp and MRP-1) proteins was examined, by immunohistochemistry, in archival specimens from 134 melanoma patients. This included 92 primary tumours and 42 metastases.
RESULTS: On assessing all specimens, MRP-1 and MDR1/P-gp expression was found to be common, with the majority (81%) of melanomas expressing at least one of these efflux pumps. Although there is significant association between expression of these pumps (P=0.007), MRP-1 was found to be the predominant (67% of cases) form detected. chi(2) analysis showed significant associations between expression of MRP-1 and/or MDR1/P-gp and the aggressive nature of this disease specifically increased Breslow's depth, Clark's level and spread to lymph nodes. This association with aggressiveness and spread is further supported by the observation that a significantly higher percentage of metastases, than primary tumours, express MRP-1 (91% vs 57%; P<0.0001) and MDR1/P-gp (74% vs 50%; P=0.010).
CONCLUSION: The predominant expression of these pumps and, in particular, MRP-1 suggests that they may be important contributors to the inherent aggressive and resistant nature of malignant melanoma
Magnetic Coupling in the Quiet Solar Atmosphere
Three kinds of magnetic couplings in the quiet solar atmosphere are
highlighted and discussed, all fundamentally connected to the Lorentz force.
First the coupling of the convecting and overshooting fluid in the surface
layers of the Sun with the magnetic field. Here, the plasma motion provides the
dominant force, which shapes the magnetic field and drives the surface dynamo.
Progress in the understanding of the horizontal magnetic field is summarized
and discussed. Second, the coupling between acoustic waves and the magnetic
field, in particular the phenomenon of wave conversion and wave refraction. It
is described how measurements of wave travel times in the atmosphere can
provide information about the topography of the wave conversion zone, i.e., the
surface of equal Alfv\'en and sound speed. In quiet regions, this surface
separates a highly dynamic magnetic field with fast moving magnetosonic waves
and shocks around and above it from the more slowly evolving field of high-beta
plasma below it. Third, the magnetic field also couples to the radiation field,
which leads to radiative flux channeling and increased anisotropy in the
radiation field. It is shown how faculae can be understood in terms of this
effect. The article starts with an introduction to the magnetic field of the
quiet Sun in the light of new results from the Hinode space observatory and
with a brief survey of measurements of the turbulent magnetic field with the
help of the Hanle effect.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Graphene Photonics and Optoelectronics
The richness of optical and electronic properties of graphene attracts
enormous interest. Graphene has high mobility and optical transparency, in
addition to flexibility, robustness and environmental stability. So far, the
main focus has been on fundamental physics and electronic devices. However, we
believe its true potential to be in photonics and optoelectronics, where the
combination of its unique optical and electronic properties can be fully
exploited, even in the absence of a bandgap, and the linear dispersion of the
Dirac electrons enables ultra-wide-band tunability. The rise of graphene in
photonics and optoelectronics is shown by several recent results, ranging from
solar cells and light emitting devices, to touch screens, photodetectors and
ultrafast lasers. Here we review the state of the art in this emerging field.Comment: Review Nature Photonics, in pres
Measurements of Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Measurements of transverse energy flow are presented for neutral current
deep-inelastic scattering events produced in positron-proton collisions at
HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to
2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the
hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in
the hadronic centre of mass frame and is studied as a function of Q^2, x, W and
pseudorapidity. A comparison is made with QCD based models. The behaviour of
the mean transverse energy in the central pseudorapidity region and an interval
corresponding to the photon fragmentation region are analysed as a function of
Q^2 and W.Comment: 26 pages, 8 figures, submitted to Eur. Phys.
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