35,578 research outputs found
Theoretical mean colors for RR Lyrae variables
A hydrodynamically pulsating 0.6 solar mass model of a typical RR Lyrae variable was studied with a radiation transport-hydrodynamic computer program to predict theoretical T sub 3 and colors at many phases and to find the proper methods for getting mean colors and the consequent mean effective temperatures. The variable Eddington radiation approximation method was used with gray and with multifrequency absorption coefficients to represent the radiation flow in the outer optically thin layers. Comparison between observed and computed B-V colors indicate that these low Z population 2 models are reasonably accurate using King 1A composition opacities. The well known Oke, Giver, and Searle relation between B-V and T sub e reproduced. Mean colors were found by four different averaging methods. The method that gives a mean color and the mean T sub e closest to the nonpulsating model was the separate intensity means of B and V
Eyes in the sky: Interactions between AGB winds and the interstellar magnetic field
We aim to examine the role of the interstellar magnetic field in shaping the
extended morphologies of slow dusty winds of Asymptotic Giant-branch (AGB)
stars in an effort to pin-point the origin of so-called eye shaped CSE of three
carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary
nebula (PN) shaping can be responsible for asymmetries observed in PNe.
Hydrodynamical simulations are used to study the effect of typical interstellar
magnetic fields on the free-expanding spherical stellar winds as they sweep up
the local interstellar medium (ISM). The simulations show that typical Galactic
interstellar magnetic fields of 5 to 10 muG, are sufficient to alter the
spherical expanding shells of AGB stars to appear as the characteristic eye
shape revealed by far-infrared observations. The typical sizes of the simulated
eyes are in accordance with the observed physical sizes. However, the eye
shapes are of transient nature. Depending on the stellar and interstellar
conditions they develop after 20,000 to 200,000yrs and last for about 50,000 to
500,000 yrs, assuming that the star is at rest relative to the local
interstellar medium. Once formed the eye shape will develop lateral outflows
parallel to the magnetic field. The "explosion" of a PN in the center of the
eye-shaped dust shell gives rise to an asymmetrical nebula with prominent
inward pointing Rayleigh-Taylor instabilities.
Interstellar magnetic fields can clearly affect the shaping of wind-ISM
interaction shells. The occurrence of the eyes is most strongly influenced by
stellar space motion and ISM density. Observability of this transient phase is
favoured for lines-of-sight perpendicular to the interstellar magnetic field
direction. The simulations indicate that shaping of the pre-PN envelope can
strongly affect the shape and size of PNe.Comment: Accepted for publication in A&A. Final version will contain animated
result
Triple mode Cepheid masses
Unconventional composition structures are proposed to explain the periods of the triple mode Cepheid aC And. A strong Cepheid wind appears to enrich helium in the convection zones down to about 60,000 K or 70,000 K. Then some downward partial mixing occurs to the bottom of a layer with about 1-q = .0005 of the stellar mass. It was found that AC And was not unlike anomalous Cepheids. However, masses of betwen one and two solar masses are suggested and the population is more likely a type two
International students' networks: a case study in a UK university
The great influx of international students into UK universities has led to internationalisation becoming an important issue. Previous studies have focused on the integration of home and international students, illustrating a lack of intercultural interaction. Yet there has been a lack of research investigating international students' networks and how these networks evolve over time. The study reported in the current paper sought to fill this gap. The research findings were interpreted through the lens of community of practice (COP) and social networks (SN) theories. Findings confirmed that international students have four distinct types of network. The class did not evolve towards a single cohesive network, rather there were changing clusters of relationship. The findings showed that although co-national factors are important at the beginning of students' learning, they are not always the main influences shaping student networks. The findings are significant for both institutions and teachers
Deep Proteomics of Mouse Skeletal Muscle Enables Quantitation of Protein Isoforms, Metabolic Pathways, and Transcription Factors
Skeletal muscle constitutes 40% of individual body mass and plays vital roles in locomotion and whole-body metabolism. Proteomics of skeletal muscle is challenging because of highly abundant contractile proteins that interfere with detection of regulatory proteins. Using a state-of-the art MS workflow and a strategy to map identifications from the C2C12 cell line model to tissues, we identified a total of 10,218 proteins, including skeletal muscle specific transcription factors like myod1 and myogenin and circadian clock proteins. We obtain absolute abundances for proteins expressed in a muscle cell line and skeletal muscle, which should serve as a valuable resource. Quantitation of protein isoforms of glucose uptake signaling pathways and in glucose and lipid metabolic pathways provides a detailed metabolic map of the cell line compared with tissue. This revealed unexpectedly complex regulation of AMP-activated protein kinase and insulin signaling in muscle tissue at the level of enzyme isoforms
A discussion of Cepheid masses
Masses and compositions of Cepheids are essential to map the places in the Hertzsprung-Russell diagram where various radial pulsation modes occur. Luminosity observations and stellar evolution theory give masses for Cepheids which range from 10 percent to a factor of four more than those given by pulsation theory. Combining the evolution and pulsation theories, a theoretical mass was determined using only the period and an approximate surface effective temperature. The ratio of the theoretical to evolutionary masses averaged 0.99 + or - 0.07 for 16 Cepheids
Solution of the Two-Channel Anderson Impurity Model - Implications for the Heavy Fermion UBe -
We solve the two-channel Anderson impurity model using the Bethe-Ansatz. We
determine the ground state and derive the thermodynamics, obtaining the
impurity entropy and specific heat over the full range of temperature. We show
that the low temperature physics is given by a line of fixed points decribing a
two-channel non Fermi liquid behavior in the integral valence regime associated
with moment formation as well as in the mixed valence regime where no moment
forms. We discuss relevance for the theory of UBe.Comment: 4 pages, 2 figures, (to be published in PRL
The Nikolaevskiy equation with dispersion
The Nikolaevskiy equation was originally proposed as a model for seismic
waves and is also a model for a wide variety of systems incorporating a
neutral, Goldstone mode, including electroconvection and reaction-diffusion
systems. It is known to exhibit chaotic dynamics at the onset of pattern
formation, at least when the dispersive terms in the equation are suppressed,
as is commonly the practice in previous analyses. In this paper, the effects of
reinstating the dispersive terms are examined. It is shown that such terms can
stabilise some of the spatially periodic traveling waves; this allows us to
study the loss of stability and transition to chaos of the waves. The secondary
stability diagram (Busse balloon) for the traveling waves can be remarkably
complicated.Comment: 24 pages; accepted for publication in Phys. Rev.
Pressure-Induced Insulating State in Ba1-xRExIrO3 (RE = Gd, Eu) Single Crystals
BaIrO3 is a novel insulator with coexistent weak ferromagnetism, charge and
spin density wave. Dilute RE doping for Ba induces a metallic state, whereas
application of modest pressure readily restores an insulating state
characterized by a three-order-of-magnitude increase of resistivity. Since
pressure generally increases orbital overlap and broadens energy bands, a
pressure-induced insulating state is not commonplace. The profoundly dissimilar
responses of the ground state to light doping and low hydrostatic pressures
signal an unusual, delicate interplay between structural and electronic degrees
of freedom in BaIrO3
The incidence of mid-infrared excesses in G and K giants
Using photometric data from the 2MASS and GLIMPSE catalogues, I investigate
the incidence of mid-infrared excesses (~10 microns) of G and K stars of
luminosity class III. In order to obtain a large sample size, stars are
selected using a near-IR colour-magnitude diagram. Sources which are candidates
for showing mid-IR excess are carefully examined and modelled to determined
whether they are likely to be G/K giants. It is found that mid-IR excesses are
present at a level of (1.8 +/- 0.4) x 10^-3. While the origin of these excesses
remains uncertain, it is plausible that they arise from debris discs around
these stars. I note that the measured incidence is consistent with a scenario
in which dust lifetimes in debris discs are determined by Poynting-Robertson
drag rather than by collisions.Comment: Accepted for publication in MNRAS. 13 pages, 5 figures, 2 tables (1
landscape table
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