1,095 research outputs found
Orbital motion of the young brown dwarf companion TWA 5 B
With more adaptive optics images available, we aim at detecting orbital
motion for the first time in the system TWA 5 A+B. We measured separation and
position angle between TWA 5 A and B in each high-resolution image available
and followed their change in time, because B should orbit around A. The
astrometric measurement precision is about one milli arc sec. With ten year
difference in epoch, we can clearly detect orbital motion of B around A, a
decrease in separation by ~ 0.0054 arc sec per year and a decrease in position
angle by ~ 0.26 degrees per year. TWA 5 B is a brown dwarf with ~ 25 Jupiter
masses (Neuh\"auser et al. 2000), but having large error bars (4 to 145 Jupiter
masses, Neuh\"auser et al. 2009). Given its large projected separation from the
primary star, ~ 86 AU, and its young age ~ 10 Myrs), it has probably formed
star-like, and would then be a brown dwarf companion. Given the relatively
large changes in separation and position angle between TWA 5 A and B, we can
conclude that they orbit around each other on an eccentric orbit. Some evidence
is found for a curvature in the orbital motion of B around A - most consistent
with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are
detected and show a small-amplitude (~ 18 mas) periodic sinusoid with ~ 5.7 yr
period, i.e., fully consistent with the orbit of the inner close pair TWA 5
Aa+b. Measuring these residuals caused by the photocenter wobble - even in
unresolved images - can yield the total mass of the inner pair, so can test
theoretical pre-main sequence models.Comment: 6 pages, 4 figures, accepted for publication in A&A; corrected typo
in amplitude below Fig.
Pre- and Perinatal Ischemia-Hypoxia, the Ischemia-Hypoxia Response Pathway, and ADHD Risk
This review focuses on how measured pre- and perinatal environmental and (epi)genetic risk factors are interrelated and potentially influence one, of many, common developmental pathway towards ADHD. Consistent with the Developmental Origins of Health and Disease hypothesis, lower birth weight is associated with increased ADHD risk. Prenatal ischemia-hypoxia (insufficient blood and oxygen supply in utero) is a primary pathway to lower birth weight and produces neurodevelopmental risk for ADHD. To promote tissue survival in the context of ischemia-hypoxia, ischemia-hypoxia response (IHR) pathway gene expression is altered in the developing brain and peripheral tissues. Although altered IHR gene expression is adaptive in the context of ischemia-hypoxia, lasting IHR epigenetic modifications may lead to increased ADHD risk. Taken together, IHR genetic vulnerability to ischemia-hypoxia and IHR epigenetic alterations following prenatal ischemia-hypoxia may result in neurodevelopmental vulnerability for ADHD. Limitations of the extant literature and future directions for genetically-informed research are discussed
Symmetries of microcanonical entropy surfaces
Symmetry properties of the microcanonical entropy surface as a function of
the energy and the order parameter are deduced from the invariance group of the
Hamiltonian of the physical system. The consequences of these symmetries for
the microcanonical order parameter in the high energy and in the low energy
phases are investigated. In particular the breaking of the symmetry of the
microcanonical entropy in the low energy regime is considered. The general
statements are corroborated by investigations of various examples of classical
spin systems.Comment: 15 pages, 5 figures include
V4332 Sagittarii: A circumstellar disc obscuring the main object
V4332 Sgr experienced an outburst in 1994 whose observational characteristics
in many respects resemble those of the eruption of V838 Mon in 2002. It has
been proposed that these objects erupted because of a stellar-merger event. Our
aim is to derive, from observational data, information on the present (10-15
yrs after the outburst) nature and structure of the object. We present and
analyse a high-resolution (R = 21 000) spectrum of V4332 Sgr obtained with the
Subaru Telescope in June 2009. Various components (stellar-like continuum,
atomic emission lines, molecular bands in emission) in the spectrum are
analysed and discussed. We also investigate a global spectral energy
distribution (SED) of the object mostly derived from broadband optical and
infrared photometry. The observed continuum resembles that of an M6 giant. The
emission features (atomic and molecular) are most probably produced by
radiative pumping. The observed strengths of the emission features strongly
suggest that we only observe a small part of the radiation of the main object
responsible for pumping the emission features. An infrared component seen in
the observed SED, which can be roughly approximated by two blackbodies of 950
and 200 K, is 50 times brighter than the M6 stellar component seen in the
optical. This further supports the idea that the main object is mostly obscured
for us. The main object in V4332 Sgr, an M6 (super)giant, is surrounded by a
circumstellar disc, which is seen almost edge-on so the central star is
obscured. The observed M6 spectrum probably results from scattering the central
star spectrum on dust grains at the outer edge of the disc.Comment: 12 pages, 8 figures, accepted in Astronomy & Astrophysic
Fano Resonances in Electronic Transport through a Single Electron Transistor
We have observed asymmetric Fano resonances in the conductance of a single
electron transistor resulting from interference between a resonant and a
nonresonant path through the system. The resonant component shows all the
features typical of quantum dots, but the origin of the non-resonant path is
unclear. A unique feature of this experimental system, compared to others that
show Fano line shapes, is that changing the voltages on various gates allows
one to alter the interference between the two paths.Comment: 8 pages, 6 figures. Submitted to PR
Effect of sintering temperature on properties of transparent YSZ-ceramics prepared by spark plasma sintering
Transparent yttria-stabilized zirconia (YSZ) ceramics were sintered with the spark plasma sintering (SPS) method at different temperatures. The influence of sintering temperature (1200-1400°С) on the ceramics microstructure and mechanical properties was investigated and discussed
Transient backbending behavior in the Ising model with fixed magnetization
The physical origin of the backbendings in the equations of state of finite
but not necessarily small systems is studied in the Ising model with fixed
magnetization (IMFM) by means of the topological properties of the observable
distributions and the analysis of the largest cluster with increasing lattice
size. Looking at the convexity anomalies of the IMFM thermodynamic potential,
it is shown that the order of the transition at the thermodynamic limit can be
recognized in finite systems independently of the lattice size. General
statistical mechanics arguments and analytical calculations suggest that the
backbending in the caloric curve is a transient behaviour which should not
converge to a plateau in the thermodynamic limit, while the first order
transition is signalled by a discontinuity in other observables.Comment: 24 pages, 11 figure
Systematic Microcanonical Analyses of Polymer Adsorption Transitions
In detailed microcanonical analyses of densities of states obtained by
extensive multicanonical Monte Carlo computer simulations, we investigate the
caloric properties of conformational transitions adsorbing polymers experience
near attractive substrates. For short chains and strong surface attraction, the
microcanonical entropy turns out to be a convex function of energy in the
transition regime, indicating that surface-entropic effects are relevant.
Albeit known to be a continuous transition in the thermodynamic limit of
infinitely long chains, the adsorption transition of nongrafted finite-length
polymers thus exhibits a clear signature of a first-order-like transition, with
coexisting phases of adsorbed and desorbed conformations. Another remarkable
consequence of the convexity of the microcanonical entropy is that the
transition is accompanied by a decrease of the microcanonical temperature with
increasing energy. Since this is a characteristic physical effect it might not
be ignored in analyses of cooperative macrostate transitions in finite systems.Comment: 8 pages, 6 figure
- …