5,582 research outputs found
Finite time distributions of stochastically modeled chemical systems with absolute concentration robustness
Recent research in both the experimental and mathematical communities has
focused on biochemical interaction systems that satisfy an "absolute
concentration robustness" (ACR) property. The ACR property was first discovered
experimentally when, in a number of different systems, the concentrations of
key system components at equilibrium were observed to be robust to the total
concentration levels of the system. Followup mathematical work focused on
deterministic models of biochemical systems and demonstrated how chemical
reaction network theory can be utilized to explain this robustness. Later
mathematical work focused on the behavior of this same class of reaction
networks, though under the assumption that the dynamics were stochastic. Under
the stochastic assumption, it was proven that the system will undergo an
extinction event with a probability of one so long as the system is
conservative, showing starkly different long-time behavior than in the
deterministic setting. Here we consider a general class of stochastic models
that intersects with the class of ACR systems studied previously. We consider a
specific system scaling over compact time intervals and prove that in a limit
of this scaling the distribution of the abundances of the ACR species converges
to a certain product-form Poisson distribution whose mean is the ACR value of
the deterministic model. This result is in agreement with recent conjectures
pertaining to the behavior of ACR networks endowed with stochastic kinetics,
and helps to resolve the conflicting theoretical results pertaining to
deterministic and stochastic models in this setting
MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214
We report on the analysis of high-precision space-based photometry of the
roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three
stars were observed by the MOST satellite for more than 25 days, allowing
unprecedented views of their pulsation. We find previously unknown candidate
frequencies in all three stars. We establish the rotation period of HD 9289
(8.5 d) for the first time and show that the star is pulsating in two modes
that show different mode geometries. We present a detailed analysis of HD
99563's mode multiplet and find a new candidate frequency which appears
independent of the previously known mode. Finally, we report on 11 detected
pulsation frequencies in HD 134214, 9 of which were never before detected in
photometry, and 3 of which are completely new detections. Thanks to the
unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214
can be seen to have a well-defined large frequency spacing similar to the
well-studied roAp star HD 24712 (HR 1217).Comment: 11 pages, 12 figures, accepted for publication in A&
A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry
Observations of Epsilon UMa obtained with the star tracker on the Wide Field
Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed.
This is one of the most precise photometry of an Ap star. The amplitude
spectrum is used to set an upper limit of 75 parts per million for the
amplitude of stellar pulsations in this star unless it accidentally oscillates
with a single mode at the satellite orbit, its harmonics or their one day
aliases. This is the tightest limit put on the amplitude of oscillations in an
Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it
cannot be argued that the observations were made at a wrong rotational phase.
Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ
Proper Motion of Pulsar B1800-21
We report high angular resolution, multi-epoch radio observations of the
young pulsar PSR B1800-21. Using two pairs of data sets, each pair spanning
approximately a ten year period, we calculate the proper motion of the pulsar.
We obtain a proper motion of mu_alpha=11.6 +- 1.8 mas/yr, mu_delta=14.8 +- 2.3
mas/yr, which clearly indicates a birth position at the extreme edge of the W30
supernova remnant. Although this does not definitively rule out an association
of W30 and PSR B1800-21, it does not support an association.Comment: 13 pages, 1 color figure. Replaced with version accepted for
publication in Astrophysical Journa
Ecología, arquitectura y rehabilitación: necesidad de soluciones integradas
Los edificios son en buena medida responsables de la insostenibilidad del sistema productivo. En España, una importante labor para la disminución del impacto ambiental de la edificación radica en la adaptación del parque edificatorio existente a las nuevas exigencias.
Sin embargo, la profesión del arquitecto tiene arraigados unos cánones de la buena
Arquitectura que no contemplan el criterio de la sostenibilidad y la rehabilitación con criterios ecológicos, representando una minoría los arquitectos que sí se han embarcado en este compromiso. En este trabajo estudiamos los aspectos ecológicos en la normativa española y europea de edificios, que representa las preocupaciones de la sociedad, así como en los premios de Arquitectura, que representan la mirada del arquitecto. Con ello, buscamos demostrar la divergencia entre dos mundos, frente a la que proponemos la necesidad de soluciones integradas de rehabilitación que ponen en valor los aspectos ecológicos y arquitectónicos de la edificación
Triggered massive-star formation on the borders of Galactic HII regions. III. Star formation at the periphery of Sh2-219
Context. Massive-star formation triggered by the expansion of HII regions.
Aims. To understand if sequential star formation is taking place at the
periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line
observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta,
Spain). Results. In the optical, Sh2-219 is spherically symmetric around its
exciting star; furthermore it is surrounded along three quarters of its
periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at
infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies
at the southwestern border of Sh2-219, in the HI gap. Two molecular
condensations, elongated along the ionization front, probably result from the
interaction between the expanding HII region and the molecular cloud. In this
region of interaction there lies a cluster containing many highly reddened
stars, as well as a massive star exciting an ultracompact HII region. More
surprisingly, the brightest parts of the molecular cloud form a `chimney',
perpendicular to the ionization front. This chimney is closed at its south-west
extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5
pc long. A luminous H-alpha emission-line star, lying at one end of the chimney
near the ionization front, may be responsible for this structure. Confrontation
of the observations with models of HII region evolution shows that Sh2-219 is
probably 10^5 yr old. The age and origin of the near-IR cluster observed on the
border of Sh2-219 remain unknown.Comment: 11 pages, 10 figures. To be published in A&
Circumbinary Molecular Rings Around Young Stars in Orion
We present high angular resolution 1.3 mm continuum, methyl cyanide molecular
line, and 7 mm continuum observations made with the Submillimeter Array and the
Very Large Array, toward the most highly obscured and southern part of the
massive star forming region OMC1S located behind the Orion Nebula. We find two
flattened and rotating molecular structures with sizes of a few hundred
astronomical units suggestive of circumbinary molecular rings produced by the
presence of two stars with very compact circumstellar disks with sizes and
separations of about 50 AU, associated with the young stellar objects 139-409
and 134-411. Furthermore, these two circumbinary rotating rings are related to
two compact and bright {\it hot molecular cores}. The dynamic mass of the
binary systems obtained from our data are 4 M for 139-409 and
0.5 M for 134-411. This result supports the idea that
intermediate-mass stars will form through {\it circumstellar disks} and
jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass
stars are in multiple systems they seem to form a circumbinary ring similar to
those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic
The UPC Addresses the Class-Gift and Intestacy Rights of Children of Assisted Reproduction Technologies
Editor\u27s Synopsis: Recent years\u27 advances in assisted reproduction technology have enabled the conception of children in ways in addition to the traditional way. The Uniform Probate Code was amended last year to address the status of children born from assisted reproductive technologies for intestacy and class-gift purposes. This article discusses the relevant UPC provisions and offers several hypothetical cases to show how they operate. The article concludes expressing the hope that states will consider the new UPC approach
- …