162 research outputs found
Contemporaneous Broad-Band Photometry and H alpha Observations of T Tau Stars
The study of contemporaneous variations of the continuum flux and emission lines is of great importance to understand the different astrophysical processes at work in T Tauri stars. In this paper we present the results of a simultaneous BV RI and Hα photometric monitoring, contemporaneous to medium-resolution spectroscopy of six T Tauri stars in the Taurus-Auriga star forming region. We have characterized the Hα photometric system using synthetic templates and the contemporaneous spectra of the targets. We show that we can achieve a precision corresponding to 2â3 Ă
in the Hα equivalent width, in typical observing conditions. The spectral analysis has allowed us to determine the basic stellar parameters and the values of quantities related to the accretion. In particular, we have measured a significant veiling only for the three targets with the strongest Hα emission (T Tau, FM Tau, and DG Tau). The broad-band photometric variations are found to be in the range 0.05â0.70 mag and are often paired to variations in the Hα intensity, which becomes stronger when the stellar continuum is weaker. In addition, we have mostly observed a redder V â I and a bluer B âV color as the stars become fainter. For most of the targets, the timescales of these variations seem to be longer than the rotation period. One exception is T Tau, for which the broad-band photometry varies with the rotation period. The most plausible interpretation of these photometric and Hα variations is that they are due to non-stationary mass accretion onto the stars, but rotational modulation can play a major role in some cases
Diffusion model to describe osteogenesis within a porous titanium scaffold.
In this study, we develop a two-dimensional finite element model, which is derived from an animal experiment and allows simulating osteogenesis within a porous titanium scaffold implanted in ewe's hemi-mandible during 12 weeks. The cell activity is described through diffusion equations and regulated by the stress state of the structure. We compare our model to (i) histological observations and (ii) experimental data obtained from a mechanical test done on sacrificed animal. We show that our mechano-biological approach provides consistent numerical results and constitutes a useful tool to predict osteogenesis pattern
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We review the infrared properties of the pure Yang-Mills correlators and
discuss recent results concerning the two classes of low-momentum solutions for
them reported in literature; i.e. decoupling and scaling solutions. We will
mainly focuss on the Landau gauge and pay special attention to the results
inferred from the analysis of the Dyson-Schwinger equations of the theory and
from "{\it quenched}" lattice QCD. The results obtained from properly
interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs
An Xâshooter survey of star forming regions: Lowâmass stars and subâstellar objects*
We present preliminary results of our Xâshooter survey in star forming regions. In this contribution we focus on subsamples of young stellar and subâstellar objects (YSOs) in the Lupus star forming region and in the TW Hya association. We show that the Xâshooter spectra are suitable for conducting several parallel studies such as YSO + disk fundamental parameters, accretion and outflow activity in the very lowâmass (VLM) and subâstellar regimes, as well as magnetic activity in young VLM YSOs, and Li abundance determinations. The capabilities of Xâshooter in terms of wide spectral coverage, resolution and limiting magnitudes, allow us to assess simultaneously the accretion/outflow, magnetic activity, and disk diagnostics, from the UV and optical to the nearâIR, avoiding ambiguities due to possible YSO variability
Location of crossings in the Floquet spectrum of a driven two-level system
Calculation of the Floquet quasi-energies of a system driven by a
time-periodic field is an efficient way to understand its dynamics. In
particular, the phenomenon of dynamical localization can be related to the
presence of close approaches between quasi-energies (either crossings or
avoided crossings). We consider here a driven two-level system, and study how
the locations of crossings in the quasi-energy spectrum alter as the field
parameters are changed. A perturbational scheme provides a direct connection
between the form of the driving field and the quasi-energies which is exact in
the limit of high frequencies. We firstly obtain relations for the
quasi-energies for some common types of applied field in the high-frequency
limit. We then show how the locations of the crossings drift as the frequency
is reduced, and find a simple empirical formula which describes this drift
extremely well in general, and appears to be exact for the specific case of
square-wave driving.Comment: 6 pages, 6 figures. Minor changes to text, this version to be
published in Physical Review
Cytological changes related to Brucella canis variants uptake in vitro
In this study, evidence for in vitro uptake, invasion, and cytopathogonomic effects of normal and variant strains of B. canis on tissue culture, is presented. B. canis L-phase were penicillin-induced and these microorganisms produced revertants on penicillin-free media. Tissue culture (LLC-MK 2 ) cells were divided into different normal and variant-infected groups (IâIV), including controls. Bright-field and electron microscopic observations indicated uptake of all the strains and recognizable host cell damage (CPE) to varying degrees. At 72 h after infection, the extent of damage by L-phase was the least (55.5% CPE). The L-phase-derived revertants resulted in 80% damage; this approximates the adverse effect of normal B. canis (85%). In addition to these gross changes, various structural abnormalities, including pyknosis, nuclear disorganization, vacuolation, and karyorrhexis, were apparent. The implications of these findings and the indirect role of the L-phase in brucellosis due to B. canis are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47529/1/430_2005_Article_BF02123560.pd
Search for non-Gaussian events in the data of the VIRGO E4 engineering run
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