31,200 research outputs found
New Measurements of the Radio Photosphere of Mira based on Data from the JVLA and ALMA
We present new measurements of the millimeter wavelength continuum emission
from the long period variable Mira ( Ceti) at frequencies of 46 GHz, 96 GHz,
and 229 GHz (~7 mm, 3 mm, and 1 mm) based on observations obtained
with the Jansky Very Large Array (JVLA) and the Atacama Large
Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities
are consistent with a radio photosphere model derived from previous
observations, where flux density, . The stellar disk
is resolved, and the measurements indicate a decrease in the size of the radio
photosphere at higher frequencies, as expected if the opacity decreases at
shorter wavelengths. The shape of the radio photosphere is found to be slightly
elongated, with a flattening of ~10-20%. The data also reveal evidence for
brightness non-uniformities on the surface of Mira at radio wavelengths. Mira's
hot companion, Mira B was detected at all three observed wavelengths, and we
measure a radius for its radio-emitting surface of
cm. The data presented here highlight the power of the JVLA and ALMA for the
study of the atmospheres of evolved stars.Comment: Accepted to ApJ; 27 pages, 7 figure
Effect of topology on dynamics of knots in polymers under tension
We use computer simulations to compare the dynamical behaviour of torus and
even-twist knots in polymers under tension. The knots diffuse through a
mechanism similar to reptation. Their friction coefficients grow linearly with
average knot length for both knot types. For similar complexity, however, the
torus knots diffuse faster than the even twist knots. The knot-length
auto-correlation function exhibits a slow relaxation time that can be linked to
a breathing mode. Its timescale depends on knot type, being typically longer
for torus than for even-twist knots. These differences in dynamical behaviour
are interpreted in terms of topological features of the knots.Comment: 6 pages, 8 figure
Complex dynamics of knotted filaments in shear flow
Coarse-grained simulations are used to demonstrate that knotted filaments in
shear flow at zero Reynolds number exhibit remarkably rich dynamic behaviour.
For stiff filaments that are weakly deformed by the shear forces, the knotted
filaments rotate like rigid objects in the flow. But away from this regime the
interplay between between shear forces and the flexibility of the filament
leads to intricate regular and chaotic modes of motion that can be divided into
distinct families. The set of accessible mode families depends to first order
on a dimensionless number that relates the filament length, the elastic
modulus, the friction per unit length and the shear rate.Comment: 6 pages, 6 figure
Age-Gapped and Age-Condensed Lineages: Patterns of Intergenerational Age Structure among Canadian Families
This paper examines intergenerational connections within Canadian families. Its focus is on intergenerational age structure, the interval or 'gap' in years that separates one generation from the next. Intergenerational age structure is measured in terms of the age of a mother at the birth of her first child. Using data from the 1995 General Social Survey of Canada, the study examines the socio-demographic characteristics of women (n=404) in three- and four-generation families (lineages) that are age-condensed (small age distances between generations that are the result of early fertility) and those that are age- gapped (with large age distances between generations that are the result of late fertility patterns). Across two generations of women, there is a striking similarity in the distributions of age at first birth with just under one-third of the sample having early fertility, just over one-half falling into a normative or "on-time" category, and one-seventh having delayed fertility. However, when matched pairs of mothers and daughters are compared across generations, age-condensed and age-gapped lineage patterns show considerable variability. Although just under one-half of mother-daughter dyads show lineage consistency in family age structure across three generations (most typically in age-condensed/age-condensed or normative/normative age structures), low percentages of women whose family of origin was age-gapped repeat that age structure pattern in their own families of procreation. Socio-demographic factors such as mother's and daughter's age, family size, age at first marriage, and level of education are associated with lineage continuity and discontinuity in family age structure.intergenerational age structure; GSS
Pulsation models for the roAp star HD 134214
Precise time-series photometry with the MOST satellite has led to
identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp)
star HD 134214. We have fitted the observed frequencies with theoretical
frequencies of axisymmetric modes in a grid of stellar models with dipole
magnetic fields. We find that, among models with a standard composition of
and with suppressed convection, eigenfrequencies of a
model with and a polar
magnetic field strength of 4.1kG agree best with the observed frequencies. We
identify the observed pulsation frequency with the largest amplitude as a
deformed dipole () mode, and the four next-largest-amplitude
frequencies as deformed modes. These modes have a radial quasi-node
in the outermost atmospheric layers (). Although the model
frequencies agree roughly with observed ones, they are all above the acoustic
cut-off frequency for the model atmosphere and hence are predicted to be
damped. The excitation mechanism for the pulsations of HD 134214 is not clear,
but further investigation of these modes may be a probe of the atmospheric
structure in this magnetic chemically peculiar star.Comment: 9 pages, 6 figures; accepted for publication in MNRA
Dusty Plasma Correlation Function Experiment
Dust particles immersed within a plasma environment, such as those in
protostellar clouds, planetary rings or cometary environments, will acquire an
electric charge. If the ratio of the inter-particle potential energy to the
average kinetic energy is high enough the particles will form either a "liquid"
structure with short-range ordering or a crystalline structure with long range
ordering. Many experiments have been conducted over the past several years on
such colloidal plasmas to discover the nature of the crystals formed, but more
work is needed to fully understand these complex colloidal systems. Most
previous experiments have employed monodisperse spheres to form Coulomb
crystals. However, in nature (as well as in most plasma processing
environments) the distribution of particle sizes is more randomized and
disperse. This paper reports experiments which were carried out in a GEC rf
reference cell modified for use as a dusty plasma system, using varying sizes
of particles to determine the manner in which the correlation function depends
upon the overall dust grain size distribution. (The correlation function
determines the overall crystalline structure of the lattice.) Two dimensional
plasma crystals were formed of assorted glass spheres with specific size
distributions in an argon plasma. Using various optical techniques, the pair
correlation function was determined and compared to those calculated
numerically.Comment: 6 pages, Presented at COSPAR '0
The bloodstream differentiation - division of Trypanosoma brucei studied using mitochondrial markers
In the bloodstream of its mammalian host, the African trypanosome Trypanosoma brucei undergoes a life cycle stage differentiation from a long, slender form to a short, stumpy form. This involves three known major events: exit from a proliferative cell cycle, morphological change and mitochondrial biogenesis. Previously, models have been proposed accounting for these events (Matthews & Gull 1994a). Refinement of, and discrimination between, these models has been hindered by a lack of stage-regulated antigens useful as markers at the single-cell level. We have now evaluated a variety of cytological markers and applied them to investigate the coordination of phenotypic differentiation and cell cycle arrest. Our studies have focused on the differential expression of the mitochondrial enzyme dihydrolipoamide dehydrogenase relative to the differentiation-division of bloodstream trypanosomes. The results implicate a temporal order of events: commitment, division, phenotypic differentiation
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