14,718 research outputs found
X-ray iron-line emission from the SN 185 remnant
Radio and optical research was carried out in order to show that the supernova remnant RCW86 is a remnant of the earliest supernova event ever recorded in history (185 AD). The results are as follows: (1) an iron-line emission was found at 6.7 keV; (2) the temperature measured from HEAO-1 was approximately 6 keV; and (3) the equivalent width was consistent within the uncertainties with a cosmic iron abundance. These results support the identification of the supernova remnant RCW86 (it's X-ray source) with the historic supernova event
Semiflexible polymers under external fields confined to two dimensions
The non-equilibrium structural and dynamical properties of semiflexible
polymers confined to two dimensions are investigated by molecular dynamics
simulations. Three different scenarios are considered: The force-extension
relation of tethered polymers, the relaxation of an initially stretched
semiflexible polymer, and semiflexible polymers under shear flow. We find
quantitative agreement with theoretical predictions for the force-extension
relation and the time dependence of the entropically contracting polymer. The
semiflexible polymers under shear flow exhibit significant conformational
changes at large shear rates, where less stiff polymers are extended by the
flow, whereas rather stiff polymers are contracted. In addition, the polymers
are aligned by the flow, thereby the two-dimensional semiflexible polymers
behave similarly to flexible polymers in three dimensions. The tumbling times
display a power-law dependence at high shear rate rates with an exponent
comparable to the one of flexible polymers in three-dimensional systems.Comment: Accepted for publication in J. Chem. Phy
Periodic orbit theory for the H\'enon-Heiles system in the continuum region
We investigate the resonance spectrum of the H\'enon-Heiles potential up to
twice the barrier energy. The quantum spectrum is obtained by the method of
complex coordinate rotation. We use periodic orbit theory to approximate the
oscillating part of the resonance spectrum semiclassically and Strutinsky
smoothing to obtain its smooth part. Although the system in this energy range
is almost chaotic, it still contains stable periodic orbits. Using Gutzwiller's
trace formula, complemented by a uniform approximation for a codimension-two
bifurcation scenario, we are able to reproduce the coarse-grained
quantum-mechanical density of states very accurately, including only a few
stable and unstable orbits.Comment: LaTeX (v3): 10 pages, 9 figures (new figure 6 added), 1 table; final
version for Phys. Rev. E (in print
Steady state sedimentation of ultrasoft colloids
The structural and dynamical properties of ultra-soft colloids - star
polymers - exposed to a uniform external force field are analyzed applying the
multiparticle collision dynamics approach, a hybrid coarse-grain mesoscale
simulation approach, which captures thermal fluctuations and long-range
hydrodynamic interactions. In the weak field limit, the structure of the star
polymer is nearly unchanged, however in an intermediate regime, the radius of
gyration decreases, in particular transverse to the sedimentation direction. In
the limit of a strong field, the radius of gyration increases with field
strength. Correspondingly, the sedimentation coefficient increases with
increasing field strength, passes through a maximum and decreases again at high
field strengths. The maximum value depends on the functionality of the star
polymer. High field strengths lead to symmetry breaking with trailing, strongly
stretched polymer arms and a compact star polymer body. In the weak field
linear response regime, the sedimentation coefficient follows the scaling
relation of a star polymer in terms of functionality and arm length
A program for calculating optimum dimensions of alpha radioisotope capsules exposed to varying stress and temperature
Method and computer program for calculating creep and optimizing dimensions of capsules filled with alpha-emitting radioisotopes and exposed to varying stress and temperatur
The Proper Motion of the Central Compact Object RX J0822-4300 in the Supernova Remnant Puppis A
Using the High Resolution Camera (HRC) aboard the Chandra X-ray Observatory,
we have re-examined the proper motion of the central compact object RX
J0822-4300 in the supernova remnant Puppis A. New data from 2010 August,
combined with three archival data sets from as early as 1999 December, provide
a baseline of 3886 days (more than 10 1/2 years) to perform the measurement.
Correlating the four positions of RX J0822-4300 measured in each data set
implies a projected proper motion of mu 71 \pm 12 masy. For a distance of 2 kpc
this proper motion is equivalent to a recoil velocity of 672 \pm 115 km/s. The
position angle is found to be 244 \pm 11 degrees. Both the magnitude and
direction of the proper motion are in agreement with RX J0822-4300 originating
near the optical expansion center of the supernova remnant. For a displacement
of 371 \pm 31 arcsec between its birth place and today's position we deduce an
age of (5.2 \pm 1.0) 10^3 yrs for RX J0822-4300. The age inferred from the
neutron star proper motion and filament motions can be considered as two
independent measurements of the same quantity. They average to 4450 \pm 750 yrs
for the age of the supernova remnant Puppis A.Comment: Accepted for publication in the Astrophysical Journa
Level density of the H\'enon-Heiles system above the critical barrier Energy
We discuss the coarse-grained level density of the H\'enon-Heiles system
above the barrier energy, where the system is nearly chaotic. We use periodic
orbit theory to approximate its oscillating part semiclassically via
Gutzwiller's semiclassical trace formula (extended by uniform approximations
for the contributions of bifurcating orbits). Including only a few stable and
unstable orbits, we reproduce the quantum-mechanical density of states very
accurately. We also present a perturbative calculation of the stabilities of
two infinite series of orbits (R and L), emanating from the shortest
librating straight-line orbit (A) in a bifurcation cascade just below the
barrier, which at the barrier have two common asymptotic Lyapunov exponents
and .Comment: LaTeX, style FBS (Few-Body Systems), 6pp. 2 Figures; invited talk at
"Critical stability of few-body quantum systems", MPI-PKS Dresden, Oct.
17-21, 2005; corrected version: passages around eq. (6) and eqs. (12),(13)
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