3,564 research outputs found
The timing and location of dust formation in the remnant of SN 1987A
The discovery with the {\it Herschel Space Observatory} of bright far
infrared and submm emission from the ejecta of the core collapse supernova
SN\,1987A has been interpreted as indicating the presence of some
0.4--0.7\,M of dust. We have constructed radiative transfer models of
the ejecta to fit optical to far-infrared observations from the literature at
epochs between 615 days and 24 years after the explosion, to determine when and
where this unexpectedly large amount of dust formed.
We find that the observations by day 1153 are consistent with the presence of
310M of dust. Although this is a larger amount than has
previously been considered possible at this epoch, it is still very small
compared to the amount present in the remnant after 24 years, and significantly
higher dust masses at the earlier epochs are firmly ruled out by the
observations, indicating that the majority of the dust must have formed at very
late times. By 8515-9200 days after the explosion, 0.6--0.8\,M of dust
is present, and dust grains with radii greater than 2\,m are required to
obtain a fit to the observed SED. This suggests that the dust mass increase at
late times was caused by accretion onto and coagulation of the dust grains
formed at earlier epochs.
These findings provide further confirmation that core collapse supernovae can
create large quantities of dust, and indicate that the reason for small dust
masses being estimated in many cases is that the vast majority of the dust
forms long after most supernovae have been detectable at mid-infrared
wavelengths.Comment: 13 pages, 16 figures. Accepted for publication in MNRA
A Microscopic Mechanism for Muscle's Motion
The SIRM (Stochastic Inclined Rods Model) proposed by H. Matsuura and M.
Nakano can explain the muscle's motion perfectly, but the intermolecular
potential between myosin head and G-actin is too simple and only repulsive
potential is considered. In this paper we study the SIRM with different complex
potential and discuss the effect of the spring on the system. The calculation
results show that the spring, the effective radius of the G-actin and the
intermolecular potential play key roles in the motion. The sliding speed is
about calculated from the model which well agrees with
the experimental data.Comment: 9 pages, 6 figure
Experimental validation of equilibria in fuel cells with dead-ended anodes
This paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. Surprisingly the dynamic evolution of nitrogen and water accumulation in the dead-ended anode (DEA) of a PEM fuel cell arrives to a steady-state suggesting the existence of equilibrium behavior. We use a multi-component model of the two-phase one-dimensional (along-the-channel) system behavior to analyze and exploit this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized for showing the evolution towards equilibrium. The full order model is reduced to a second-order ordinary differential equation (ODE) with one state, which can be used to predict and amalyse the surprising but experimentally observed steady state DEA behavior
A "Firework" of H2 Knots in the Planetary Nebula NGC 7293 (the Helix Nebula)
We present a deep and wide field-of-view (4' × 7') image of the planetary nebula (PN) NGC 7293 (the Helix Nebula) in the 2.12 μm H2 v = 1 → 0 S(1) line. The excellent seeing (0farcs4) at the Subaru Telescope, allows the details of cometary knots to be examined. The knots are found at distances of 2farcm2-6farcm4 from the central star (CS). At the inner edge and in the inner ring (up to 4farcm5 from the CS), the knot often show a "tadpole" shape, an elliptical head with a bright crescent inside and a long tail opposite to the CS. In detail, there are variations in the tadpole shapes, such as narrowing tails, widening tails, meandering tails, or multipeaks within a tail. In the outer ring (4farcm5-6farcm4 from the CS), the shapes are more fractured, and the tails do not collimate into a single direction. The transition in knot morphology from the inner edge to the outer ring is clearly seen. The number density of knots governs the H2 surface brightness in the inner ring: H2 exists only within the knots. Possible mechanisms which contribute to the shaping of the knots are discussed, including photoionization and streaming motions. A plausible interpretation of our images is that inner knots are being overrun by a faster wind, but that this has not (yet) reached the outer knots. Based on H2 formation and destruction rates, H2 gas can survive in knots from formation during the late asymptotic giant branch phase throughout the PN phase. These observations provide new constraints on the formation and evolution of knots, and on the physics of molecular gas embedded within ionized gas. Based on data taken with the Subaru Telescope, National Astronomical Observatory of Japan (proposal ID S07B-054).Peer reviewe
Anomalous phase of MnP at very low field
Manganese phosphide MnP has been investigated for decades because of its rich
magnetic phase diagram. It is well known that the MnP exhibits the
ferromagnetic phase transition at \Tc=292 K and the helical magnetic phase
below \TN=47 K at zero field. Recently, a novel magnetic phase transition was
observed at K when the magnetic field is lower than 5 Oe. However,
the nature of the new phase has not been illuminated yet. In order to reveal
it, we performed the AC and the DC magnetization measurements for a single
crystal MnP at very low field. A divergent behavior of the real and the
imaginary part of the AC susceptibility and a sharp increase of the DC
magnetization was observed at , indicating the magnetic phase transition
at . Furthermore a peculiar temperature hysteresis was observed: namely,
the magnetization depends on whether cooling sample to the temperature lower
than \TN or not before the measurements. This hysteresis phenomenon suggests
the complicated nature of the new phase and a strong relation between the
magnetic state of the new phase and the helical structure.Comment: 4 pages, 2 figure
Temperature independent diffuse scattering and elastic lattice deformations in relaxor PbMg1/3Nb2/3O3
The results of diffuse neutron scattering experiment on PbMg1/3Nb2/3O3 single
crystal above the Burns temperature are reported. It is shown that the high
temperature elastic diffuse component is highly anisotropic in low-symmetry
Brillouin zones and this anisotropy can be described using Huang scattering
formalism assuming that the scattering originates from mesoscopic lattice
deformations due to elastic defects. The qualitative agreement between this
model and the experimental data is achieved with simple isotropic defects. It
is demonstrated that weak satellite maxima near the Bragg reflections can be
interpreted as the finite resolution effect.Comment: 7 pages, 7 figure
The mass-loss return from evolved stars to the Large Magellanic Cloud III. Dust properties for carbon-rich asymptotic giant branch stars
We present a 2Dust model for the dust shell around a LMC long-period variable
(LPV) previously studied as part of the OGLE survey. OGLE LMC LPV 28579 (SAGE
J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for
which we have photometry and spectra from the Spitzer SAGE and SAGE-Spec
programs along with UBVIJHK_s photometry. By modeling this source, we obtain a
baseline set of dust properties to be used in the construction of a grid of
models for carbon stars. We reproduce its spectral energy distribution using a
mixture of AmC and SiC (15% by mass). The grain sizes are distributed according
to the KMH model. The best-fit model has an optical depth of 0.28 for the shell
at the peak of the SiC feature, with R_in~1430 R_sun or 4.4 R_star. The
temperature at this inner radius is 1310 K. Assuming an expansion velocity of
10 km s^-1, we obtain a dust mass-loss rate of 2.5x10^-9 M_sun yr-1. We
calculate a 15% variation in this rate by testing the fit sensitivity against
variation in input parameters. We also present a simple model for the molecular
gas in the extended atmosphere that could give rise to the 13.7 \mu m feature
seen in the spectrum. We find that a combination of CO and C_2H_2 gas at an
excitation temperature of about 1000 K and column densities of 3x10^21 cm^-2
and 10^19 cm^-2 respectively are able to reproduce the observations. Given that
the excitation temperature is close to T_dust(R_in), most of the molecular
contribution probably arises from the inner shell region. The luminosity
corresponding to the first epoch of SAGE observations is 6580 L_sun. For an
effective temperature of about 3000 K, this implies a stellar mass of 1.5-2
M_sun and an age of 1-2.5 Gyr. For a gas:dust ratio of 200, we obtain a gas
mass-loss rate of 5.0x10^-7 M_sun yr^-1, consistent with the gas mass-loss
rates estimated from the period, color and 8 \mu m flux of the source.Comment: 14 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Determination of W-boson Properties at Hadron Colliders
Methods for measuring the W-boson properties at hadron colliders are
discussed. It is demonstrated that the ratio between the W- and Z-boson
observables can be reliably calculated using perturbative QCD, even when the
individual W- and Z-boson observables are not. Hence, by using a measured
Z-boson observable and the perturbative calculation of the ratio of the W- over
Z-boson observable, we can accurately predict the W-boson observable. The use
of the ratio reduces both the experimental and theoretical systematic
uncertainties substantially. Compared to the currently used methods it might,
at high luminosity, result in a smaller overall uncertainty on the measured
W-boson mass and width.Comment: 11 pages, 10 ps file
Search for Radiative Decays of Cosmic Background Neutrino using Cosmic Infrared Background Energy Spectrum
We propose to search for the neutrino radiative decay by fitting a photon
energy spectrum of the cosmic infrared background to a sum of the photon energy
spectrum from the neutrino radiative decay and a continuum. By comparing the
present cosmic infrared background energy spectrum observed by AKARI and
Spitzer to the photon energy spectrum expected from neutrino radiative decay
with a maximum likelihood method, we obatined a lifetime lower limit of to years at 95% confidence level for the
third generation neutrino in the mass range between 50 \mmev
and 150 \mmev under the present constraints by the neutrino oscillation
measurements. In the left-right symmetric model, the minimum lifetime of
is predicted to be years for of 50 \mmev. We
studied the feasibility of the observation of the neutrino radiative decay with
a lifetime of years, by measuring a continuous energy
spectrum of the cosmic infrared background
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