3,475 research outputs found
О некоторых тенденциях, осложнивших в начале ХХI века перспективы курортно-рекреационного развития Крыма
Целью работы явился анализ взаимовлияния различных факторов, сужающих потенциал туристско-рекреационной привлекательности Крыма, для уточнения возможностей объективного прогнозирования его перспективного развития
An integrating factor matrix method to find first integrals
In this paper we developed an integrating factor matrix method to derive
conditions for the existence of first integrals. We use this novel method to
obtain first integrals, along with the conditions for their existence, for two
and three dimensional Lotka-Volterra systems with constant terms. The results
are compared to previous results obtained by other methods
Formation of Structure in Snowfields: Penitentes, Suncups, and Dirt Cones
Penitentes and suncups are structures formed as snow melts, typically high in
the mountains. When the snow is dirty, dirt cones and other structures can form
instead. Building on previous field observations and experiments, this work
presents a theory of ablation morphologies, and the role of surface dirt in
determining the structures formed. The glaciological literature indicates that
sunlight, heating from air, and dirt all play a role in the formation of
structure on an ablating snow surface. The present work formulates a
mathematical model for the formation of ablation morphologies as a function of
measurable parameters. The dependence of ablation morphologies on weather
conditions and initial dirt thickness are studied, focusing on the initial
growth of perturbations away from a flat surface. We derive a single-parameter
expression for the melting rate as a function of dirt thickness, which agrees
well with a set of measurements by Driedger. An interesting result is the
prediction of a dirt-induced travelling instability for a range of parameters.Comment: 28 pages, 13 figure
The Anomalous Infrared Emission of Abell 58
We present a new model to explain the excess in mid and near infrared
emission of the central, hydrogen poor dust knot in the planetary nebula (PN)
Abell 58. Current models disagree with ISO measurement because they apply an
average grain size and equilibrium conditions only. We investigate grain size
distributions and temperature fluctuations affecting infrared emission using a
new radiative transfer code and discuss in detail the conditions requiring an
extension of the classical description. The peculiar infrared emission of V605
Aql, the central dust knot in Abell 58, has been modeled with our code. V605
Aql is of special interest as it is one of only three stars ever observed to
move from the evolutionary track of a central PN star back to the post-AGB
state.Comment: 17 pages, 4 figures; accepted and to be published in Ap
Pulsations and Long-Term Light Variability of Three Candidates to Protoplanetary Nebulae
We present new photometric data and analysis of the long-duration UBV
photoelectric observations for three candidates to protoplanetary objects -
F-supergiants with IR-excesses located at large galactic latitudes, IRAS
18095+2704, IRAS 19386+0155, and IRAS 19500-1709. All three stars have revealed
quasiperiodic low-amplitude variabilities caused by pulsations observed against
the long-term trends of brightnesses. For IRAS 18095+2704=V887 Her we have
found a pulsation period of 109 days and a linear trend of brightness under the
constant colours if being averaged over the year timescale. The light curve of
IRAS 19386+0155=V1648 Aql over 2000-2008 can be approximated by a wave with a
main period of 102 days which is modulated by close frequency, with a period of
98 days, that results in brightness oscillations with a variable amplitude.
V1648 Aql has also shown synchronous reddening together with a persistent rise
of brightness in the V-band. IRAS 19500-1709=V5112 Sgr experiences irregular
pulsations with the periods of 39 and 47 days. The long-term component of the
variability of V5112 Sgr may be related to the binary character of this star.Comment: 11 pages, 6 figures, accepted for publication in Pis'ma Astron. Z
Generating Functions for Coherent Intertwiners
We study generating functions for the scalar products of SU(2) coherent
intertwiners, which can be interpreted as coherent spin network evaluations on
a 2-vertex graph. We show that these generating functions are exactly summable
for different choices of combinatorial weights. Moreover, we identify one
choice of weight distinguished thanks to its geometric interpretation. As an
example of dynamics, we consider the simple case of SU(2) flatness and describe
the corresponding Hamiltonian constraint whose quantization on coherent
intertwiners leads to partial differential equations that we solve.
Furthermore, we generalize explicitly these Wheeler-DeWitt equations for SU(2)
flatness on coherent spin networks for arbitrary graphs.Comment: 31 page
An HST Snapshot Survey of Proto-Planetary Nebulae Candidates: Two Types of Axisymmetric Reflection Nebulosities
We report the results from an optical imaging survey of proto-planetary
nebula candidates using the HST. We exploited the high resolving power and wide
dynamic range of HST and detected nebulosities in 21 of 27 sources. All
detected reflection nebulosities show elongation, and the nebula morphology
bifurcates depending on the degree of the central star obscuration. The
Star-Obvious Low-level-Elongated (SOLE) nebulae show a bright central star
embedded in a faint, extended nebulosity, whereas the DUst-Prominent
Longitudinally-EXtended (DUPLEX) nebulae have remarkable bipolar structure with
a completely or partially obscured central star. The intrinsic axisymmetry of
these proto-planetary nebula reflection nebulosities demonstrates that the
axisymmetry frequently found in planetary nebulae predates the proto-planetary
nebula phase, confirming previous independent results. We suggest that
axisymmetry in proto-planetary nebulae is created by an equatorially enhanced
superwind at the end of the asymptotic giant branch phase. We discuss that the
apparent morphological dichotomy is caused by a difference in the optical
thickness of the circumstellar dust/gas shell with a differing equator-to-pole
density contrast. Moreover, we show that SOLE and DUPLEX nebulae are physically
distinct types of proto-planetary nebulae, with a suggestion that higher mass
progenitor AGB stars are more likely to become DUPLEX proto-planetary nebulae.Comment: 27 pages (w/ aaspp4.sty), 6 e/ps figures, 4 tables (w/ apjpt4.sty).
Data images are available via ADIL
(http://imagelib.ncsa.uiuc.edu/document/99.TU.01) To be published in Ap
Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"
We present high-angular resolution images of the post-AGB nebula
IRAS18276-1431 (also known as OH17.7-2.0) obtained with the Keck II Adaptive
Optics (AO) system in its Natural Guide Star (NGS) mode in the Kp, Lp, and Ms
near-infrared bands. We also present supporting optical F606W and F814W HST
images as well as interferometric observations of the 12CO(J=1-0), 13CO(J=1-0),
and 2.6mm continuum emission with OVRO. The envelope of IRAS18276-1431 displays
a clear bipolar morphology in our optical and NIR images with two lobes
separated by a dark waist and surrounded by a faint 4.5"x3.4" halo. Our Kp-band
image reveals two pairs of radial ``searchlight beams'' emerging from the
nebula center and several intersecting, arc-like features. From our CO data we
derive a mass of M>0.38[D/3kpc]^2 Msun and an expansion velocity v_exp=17km/s
for the molecular envelope. The density in the halo follows a radial power-law
proportional to r^-3, which is consistent with a mass-loss rate increasing with
time. Analysis of the NIR colors indicates the presence of a compact central
source of ~300-500K dust illuminating the nebula in addition to the central
star. Modeling of the thermal IR suggests a two-shell structure in the dust
envelope: 1) an outer shell with inner and outer radius R_in~1.6E16cm and
R_out>~1.25E17cm, dust temperature T_d~105-50K, and a mean mass-loss rate of
Mdot~1E-3Msun/yr; and 2) an inner shell with R_in~6.3E14cm, T_dust~500-105K,
and Mdot~3E-5Msun/yr. An additional population of big dust grains (radius
a>~0.4mm) with T_dust=150-20K and mass M_dust=(0.16-1.6)E-3 [D/3kpc]^2 Msun can
account for the observed sub-mm and mm flux excess. The mass of the envelope
enclosed within R_out=1.25E17cm derived from SED modeling is ~1[D/3kpc]^2 Msun.Comment: 46 pages, 14 figures, 3 tables, accepted for publication in ApJ.
Figures 12 & 13 in low resolution. Full resolution versions are available
upon request to the first autho
Near-Infrared Photometric Survey of Proto-Planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consisting of
proto-planetary nebula candidates. Photometric magnitudes are determined by
means of imaging and aperture photometry. Unlike the observations with a
photometer with a fixed-sized beam, the method of imaging photometry permits
accurate derivation of photometric values because the target sources can be
correctly identified and confusion with neighboring sources can be easily
avoided. Of the 78 sources observed, we report 10 cases in which the source
seems to have been misidentified or confused by nearby bright sources. We also
present nearly two dozen cases in which the source seems to have indicated a
variability which prompts a follow-up monitoring. There are also a few sources
that show previously unreported extendedness. In addition, we present H band
finding charts of the target sources.Comment: 3 tables, 1 figur
High-latitude supergiants: anomalies in the spectrum of LN Hya in 2010
High-resolution echelle spectra taken with the 6-m telescope in 2003-2011 are
used to study features of the optical spectrum and the velocity field in the
atmosphere of the semiregular variable LN Hya in detail. The weak symmetric
photospheric absorptions indicate radial velocity variations from night to
night (by as much as 3 km/s), resulting from small pulsations. Peculiarities
and profile variations were found for strong lines of FeI, FeII, BaII, SiII,
etc. The profiles of these lines were asymmetric: their short-wave wings were
extended and their cores were either split or distorted by emission. During the
2010 observing season, the position and depth of the Halpha absorption
component, the intensities of the short and long-wave emission components, and
the intensity ratio of the latter components varied from spectrum to spectrum.
Weak emissions of neutral atoms (VI, MnI, CoI, NiI, FeI) appeared in the
spectrum of June 1, 2010. All these spectral peculiarities, recorded for the
first time, suggest that we have detected rapid changes in the physical
conditions in the upper atmospheric layers of LN Hya in 2010.Comment: 17 pages, 5 figures, 3 table
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