10,748 research outputs found
The Planetary Nebulae Luminosity Function and distances to Virgo, Hydra I and Coma clusters
The luminosity function of planetary nebulae populations in galaxies within
10-15 Mpc distance has a cut-off at bright magnitudes and a functional form
that is observed to be invariant in different galaxy morphological types. Thus
it is used as a secondary distance indicator in both early and late-type
galaxies. Recent deep surveys of planetary nebulae populations in brightest
cluster galaxies (BCGs) seem to indicate that their luminosity functions
deviate from those observed in the nearby galaxies. We discuss the evidence for
such deviations in Virgo, and indicate which physical mechanisms may alter the
evolution of a planetary nebula envelope and its central star in the halo of
BCGs. We then discuss preliminary results for distances for the Virgo, Hydra I
and Coma clusters based on the observed planetary nebulae luminosity functions.Comment: 5 pages, one figure. To appear on the Proceedings of the IAU Symp.
289 "Advancing the physics of cosmic distances
Atomistic study of electronic structure of PbSe nanowires
Lead Selenide (PbSe) is an attractive `IV-VI' semiconductor material to
design optical sensors, lasers and thermoelectric devices. Improved fabrication
of PbSe nanowires (NWs) enables the utilization of low dimensional quantum
effects. The effect of cross-section size (W) and channel orientation on the
bandstructure of PbSe NWs is studied using an 18 band tight-binding
theory. The bandgap increases almost with the inverse of the W for all the
orientations indicating a weak symmetry dependence. [111] and [110] NWs show
higher ballistic conductance for the conduction and valence band compared to
[100] NWs due to the significant splitting of the projected L-valleys in [100]
NWs.Comment: 4 figures, Prepared for AP
Fluctuations of a long, semiflexible polymer in a narrow channel
We consider an inextensible, semiflexible polymer or worm-like chain, with
persistence length and contour length , fluctuating in a cylindrical
channel of diameter . In the regime , corresponding to a long,
tightly confined polymer, the average length of the channel
occupied by the polymer and the mean square deviation from the average vary as
and , respectively, where
and are dimensionless amplitudes. In earlier work
we determined and the analogous amplitude for a
channel with a rectangular cross section from simulations of very long chains.
In this paper we estimate and from the simulations.
The estimates are compared with exact analytical results for a semiflexible
polymer confined in the transverse direction by a parabolic potential instead
of a channel and with a recent experiment. For the parabolic confining
potential we also obtain a simple analytic result for the distribution of
or radial distribution function, which is asymptotically exact
for large and has the skewed shape seen experimentally.Comment: 21 pages, including 4 figure
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