11,813 research outputs found
M82 - A radio continuum and polarisation study II. Polarisation and rotation measures
The composition and morphology of the interstellar medium in starburst
galaxies has been well investigated, but the magnetic field properties are
still uncertain. The nearby starburst galaxy M82 provides a unique opportunity
to investigate the mechanisms leading to the amplification and reduction of
turbulent and regular magnetic fields. Possible scenarios of the contribution
of the magnetic field to the star-formation rate are evaluated. Archival data
from the VLA and WSRT were combined and re-reduced to cover the wavelength
regime between 3cm and 22cm. All observations revealed polarised emission in
the inner part of the galaxy, while extended polarised emission up to a
distance of 2kpc from the disk was only detected at 18cm and 22cm. The
observations hint at a magnetised bar in the inner part of the galaxy. We
calculate the mass inflow rate due to magnetic stress of the bar to 7.1 solar
masses per year, which can be a significant contribution to the star-formation
rate of M82 of approximately 13 solar masses per year. The halo shows polarised
emission, which might be the remnant of a regular disk field. Indications for a
helical field in the inner part of the outflow cone are provided. The coherence
length of the magnetic field in the centre is similar to the size of giant
molecular clouds. Using polarisation spectra more evidence for a close coupling
of the ionised gas and the magnetic field as well as a two-phase magnetic field
topology were found. Electron densities in the halo are similar to the ones
found in the Milky Way. The magnetic field morphology is similar to the one in
other nearby starburst galaxies with possible large-scale magnetic loops in the
halo and a helical magnetic field inside the outflow cones. The special
combination of a magnetic bar and a circumnuclear ring are able to
significantly raise the star-formation rate in this galaxy by magnetic braking
M82 - A radio continuum and polarisation study I. Data reduction and cosmic ray propagation
The potential role of magnetic fields and cosmic ray propagation for feedback
processes in the early Universe can be probed by studies of local starburst
counterparts with an equivalent star-formation rate. Archival data from the
WSRT was reduced and a new calibration technique introduced to reach the high
dynamic ranges needed for the complex source morphology of M82. This data was
combined with archival VLA data, yielding total power maps at 3cm, 6cm, 22cm
and 92cm. The data shows a confinement of the emission at wavelengths of 3/6cm
to the core region and a largely extended halo reaching up to 4kpc away from
the galaxy midplane at wavelengths of 22/92cm up to a sensitivity limit of
90muJy and 1.8mJy respectively. The results are used to calculate the magnetic
field strength in the core region to 98muG and to 24muG in the halo regions.
From the observation of free-free losses the filling factor of the ionised
medium could be estimated to 2%. We find that the radio emission from the core
region is dominated by very dense HII-regions and supernova remnants, while the
surrounding medium is filled with hot X-ray and neutral gas. Cosmic rays
radiating at frequencies higher than 1.4 GHz are suffering from high
synchrotron and inverse Compton losses in the core region and are not able to
reach the halo. Even the cosmic rays radiating at longer wavelengths are only
able to build up the observed kpc sized halo, when several starbursting periods
are assumed where the photon field density varies by an order of magnitude.
These findings together with the strong correlation between Halpha, PAH+, and
our radio continuum data suggests a magnetic field which is frozen into the
ionised medium and driven out of the galaxy kinematically.Comment: 17 pages, 17 figures, to be published in A&
Remote measurement utilizing NASA's scanning laser Doppler systems. Volume 2: Laser Doppler dust devil velocity profile measurement program
The first detailed velocity profile data on thermally induced dust vortices are presented. These dust devils will be analyzed and studied to determine their flow fields and origin in an effort to correlate this phenomena with the generation and characteristics of tornadoes. A continuing effort to increase mankind's knowledge of vortex and other meteorological phenomena will hopefully allow the prediction of tornado occurrence, their path, and perhaps eventually even lead to some technique for their destruction
Remote measurement utilizing NASA's scanning laser Doppler systems. Volume 1. Laser Doppler wake vortex tracking at Kennedy Airport
Test operations of the Scanning Laser Doppler System (SLDS) at Kennedy International Airport (KIA) during August 1974 through June 1975 are reported. A total of 1,619 data runs was recorded with a totally operational system during normal landing operations at KIA. In addition, 53 data runs were made during cooperative flybys with the C880 for a grand total of 1672 recorded vortex tracks. Test crews were in attendance at KIA for 31 weeks, of which 25 weeks were considered operational and the other six were packing, unpacking, setup and check out. Although average activity equates to 67 recorded landing operations per week, two periods of complete runway inactivity spanned 20 days and 13 days, respectively. The operation frequency therefore averaged about 88 operations per week
Novel thin film polymer foaming technique for low and ultra low-k dielectrics
The results presented show a novel route for the preparation of thin ultra-low-k polymer films based on commercial and "non-exotic" (non-expensive) polyimide by a foaming technique. Dependent on the glass transition temperature of the polyimide mechanically and thermally stable (> 300 °C) films having porosities of ca. 40 % and k-values below 2.0 are formed. A further reduction into the ultra low k region may be accomplished by tailoring the shape of the pores from spherical into disc-like void
Анализ поляризационных состояний умеренно релятивистских позитронов при регистрации аннигиляционных фотонов
Предложен и обоснован новый метод анализа поляризационных состояний умеренно релятивистских позитронных пучков. В отличие от известных методов предлагается измерить продольную поляризацию позитронов по выходу аннигиляционных квантов из намагниченной железной мишени, через которую проходит позитронный пучок. На базе библиотек GEANT4 построена математическая модель эксперимента. Проведены сравнения с существующей моделью
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Choline PET and PET/CT in Primary Diagnosis and Staging of Prostate Cancer
PET and PET/CT using [11C]- and [18F]-labelled choline derivates is increasingly being used for imaging of primary and recurrent prostate cancer. While PET and PET/CT with [11C]- and [18F]-labelled choline derivates in patients suffering from biochemical recurrence of prostate cancer has been examined in many studies that demonstrate an increasing importance, its role in the primary staging of prostate cancer is still a matter of debate
Measurement of the Casimir force between dissimilar metals
The first precise measurement of the Casimir force between dissimilar metals
is reported. The attractive force, between a Cu layer evaporated on a
microelectromechanical torsional oscillator, and an Au layer deposited on an
AlO sphere, was measured dynamically with a noise level of 6
fN/. Measurements were performed for separations in the 0.2-2
m range. The results agree to better than 1% in the 0.2-0.5 m range
with a theoretical model that takes into account the finite conductivity and
roughness of the two metals. The observed discrepancies, which are much larger
than the experimental precision, can be attributed to a lack of a complete
characterization of the optical properties of the specific samples used in the
experiment.Comment: 6 pages, 4 figure
When planning fails: Individual differences and error-related brain activity in problem solving.
The neuronal processes underlying correct and erroneous problem solving were studied in strong and weak problem-solvers using functional magnetic resonance imaging (fMRI). During planning, the right dorsolateral prefrontal cortex was activated, and showed a linear relationship with the participants' performance level. A similar pattern emerged in right inferior parietal regions for all trials, and in anterior cingulate cortex for erroneously solved trials only. In the performance phase, when the pre-planned moves had to be executed by means of an fMRI-compatible computer mouse, the right dorsolateral prefrontal cortex was again activated jointly with right parahippocampal cortex, and displayed a similar positive relationship with the participants' performance level. Incorrectly solved problems elicited stronger bilateral prefrontal and left inferior parietal activations than correctly solved trials. For both individual ability and trial-specific performance, our results thus demonstrate the crucial involvement of right prefrontal cortex in efficient visuospatial planning
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