45,386 research outputs found
Common Bulkhead Joint Development and Evaluation Final Report
Optimized composite welded joint design for Saturn booster common bulkhea
Can Long-Range Nuclear Properties Be Influenced By Short Range Interactions? A chiral dynamics estimate
Recent experiments and many-body calculations indicate that approximately
20\% of the nucleons in medium and heavy nuclei () are part of
short-range correlated (SRC) primarily neutron-proton () pairs. We find
that using chiral dynamics to account for the formation of pairs due to
the effects of iterated and irreducible two-pion exchange leads to values
consistent with the 20\% level. We further apply chiral dynamics to study how
these correlations influence the calculations of nuclear charge radii, that
traditionally truncate their effect, to find that they are capable of
introducing non-negligible effects.Comment: 6 pages, 0 figures. This version includes many improvement
The magnetic field of M31 from multi-wavelength radio polarization observations
The configuration of the regular magnetic field in M31 is deduced from radio
polarization observations at the wavelengths 6, 11 and 20 cm. By fitting the
observed azimuthal distribution of polarization angles, we find that the
regular magnetic field, averaged over scales 1--3 kpc, is almost perfectly
axisymmetric in the radial range 8 to 14 kpc, and follows a spiral pattern with
pitch angles of p\simeq -19\degr to p\simeq -8\degr. In the ring between 6
and 8 kpc a perturbation of the dominant axisymmetric mode may be present,
having the azimuthal wave number m=2. A systematic analysis of the observed
depolarization allows us to identify the main mechanism for wavelength
dependent depolarization -- Faraday rotation measure gradients arising in a
magneto-ionic screen above the synchrotron disk. Modelling of the
depolarization leads to constraints on the relative scale heights of the
thermal and synchrotron emitting layers in M31; the thermal layer is found to
be up to three times thicker than the synchrotron disk. The regular magnetic
field must be coherent over a vertical scale at least similar to the scale
height of the thermal layer, estimated to be h\therm\simeq 1 kpc. Faraday
effects offer a powerful method to detect thick magneto-ionic disks or halos
around spiral galaxies.Comment: 17 pages, 16 figures, accepted for publication in A&
Resilience Capacity and Strategic Agility: Prerequisites for Thriving in a Dynamic Environment
organizational resilience, strategic agility, competitive dynamics
Magnetic fields and spiral arms in the galaxy M51
(Abridged) We use new multi-wavelength radio observations, made with the VLA
and Effelsberg telescopes, to study the magnetic field of the nearby galaxy M51
on scales from 200\pc to several \kpc. Interferometric and single dish data
are combined to obtain new maps at \wwav{3}{6} in total and polarized emission,
and earlier \wav{20} data are re-reduced. We compare the spatial distribution
of the radio emission with observations of the neutral gas, derive radio
spectral index and Faraday depolarization maps, and model the large-scale
variation in Faraday rotation in order to deduce the structure of the regular
magnetic field. We find that the \wav{20} emission from the disc is severely
depolarized and that a dominating fraction of the observed polarized emission
at \wav{6} must be due to anisotropic small-scale magnetic fields. Taking this
into account, we derive two components for the regular magnetic field in this
galaxy: the disc is dominated by a combination of azimuthal modes, , but
in the halo only an mode is required to fit the observations. We disuss
how the observed arm-interarm contrast in radio intensities can be reconciled
with evidence for strong gas compression in the spiral shocks. The average
arm--interam contrast, representative of the radii r>2\kpc where the spiral
arms are broader, is not compatible with straightforward compression: lower
arm--interarm contrasts than expected may be due to resolution effects and
\emph{decompression} of the magnetic field as it leaves the arms. We suggest a
simple method to estimate the turbulent scale in the magneto-ionic medium from
the dependence of the standard deviation of the observed Faraday rotation
measure on resolution. We thus obtain an estimate of 50\pc for the size of
the turbulent eddies.Comment: 21 pages, 18 figures (some at lower resolution than submitted
version), accepted for publication in MNRA
Magnetic fields near the peripheries of galactic discs
Magnetic fields are observed beyond the peripheries of optically detected
galactic discs, while numerical models of their origin and the typical
magnitudes are still absent. Previously, studies of galactic dynamo have
avoided considering the peripheries of galactic discs because of the very
limited (though gradually growing) knowledge about the local properties of the
interstellar medium. Here we investigate the possibility that magnetic fields
can be generated in the outskirts of discs, taking the Milky Way as an example.
We consider a simple evolving galactic dynamo model in the "no-z" formulation,
applicable to peripheral regions of galaxies, for various assumptions about the
radial and vertical profiles of the ionized gas disc. The magnetic field may
grow as galaxies evolve, even in the more remote parts of the galactic disc,
out to radii of 15 to 30 kpc, becoming substantial after times of about 10 Gyr.
This result depends weakly on the adopted distributions of the half thickness
and surface density of the ionized gas component. The model is robust to
changes in the amplitude of the initial field and the position of its maximum
strength. The magnetic field in the remote parts of the galactic disc could be
generated in situ from a seed field by local dynamo action. Another possibility
is field production in the central regions of a galaxy, followed by transport
to the disc's periphery by the joint action of the dynamo and turbulent
diffusivity. Our results demonstrate the possibilities for the appearance and
strengthening of magnetic fields at the peripheries of disc galaxies and
emphasize the need for observational tests with new and anticipated radio
telescopes (LOFAR, MWA, and SKA).Comment: 8 pages, 5 figure
Tsallis' q index and Mori's q phase transitions at edge of chaos
We uncover the basis for the validity of the Tsallis statistics at the onset
of chaos in logistic maps. The dynamics within the critical attractor is found
to consist of an infinite family of Mori's -phase transitions of rapidly
decreasing strength, each associated to a discontinuity in Feigenbaum's
trajectory scaling function . The value of at each transition
corresponds to the same special value for the entropic index , such that the
resultant sets of -Lyapunov coefficients are equal to the Tsallis rates of
entropy evolution.Comment: Significantly enlarged version, additional figures and references. To
be published in Physical Review
Study of ambiguities in scattering amplitudes
Amplitudes for the reaction are reconstructed from
data on the differential cross section , the recoil
polarization , and on the spin rotation parameter . At low energies,
no data on exist, resulting in ambiguities. An approximation using
and waves leads only to a fair description of the data on
and ; in this case, there are two sets of amplitudes. Including waves,
the data on and are well reproduced by the fit but now,
there are several distinct solutions which describe the data with identical
precision. In the range where the spin rotation parameter was measured,
a full and unambiguous reconstruction of the partial wave amplitudes is
possible. The energy-independent amplitudes are compared to the energy
dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to
a large data set including both pion and photo-induced reactions. Significant
deviations are observed. Consistency between energy dependent and energy
independent solutions by choosing the energy independent solution which is
closest to the energy dependent solution. In a second step, the {\it known}
energy dependent solution for low (or high) partial waves is imposed and only
the high (or low) partial waves are fitted leading to smaller uncertainties
Recommended from our members
The economics of health
This report presents results from the Economics of Health project funded by the East Midlands Development Agency. The work was undertaken between November 2007 and February 2008. The main aim of the project was to examine the relationship between mental and physical health and employability, labour market participation and economic performance, with specific attention given to the direction of causal relationships
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