174 research outputs found
The Hercules-Lyra Association revisited New age estimation and multiplicity study
The Her-Lyr assoc., a nearby young MG, contains a few tens of ZAMS stars of
SpT F to M. The existence and the properties of the Her-Lyr assoc. are
controversial and discussed in the literature. The present work reassesses
properties and the member list of Her-Lyr assoc., based on kinematics and age.
Many objects form multiple systems or have low-mass companions and so we need
to account for multiplicity. We use our own new imaging obs. and archival data
to identify multiple systems. The colors and magnitudes of kinematic candidates
are compared to isochrones. We derive further information on the age based on
Li depletion, rotation, and coronal and chromospheric activity. A set of
canonical members is identified to infer mean properties. Membership criteria
are derived from the mean properties and used to discard non-members. The
candidates selected from the literature belong to 35 stellar systems, 42.9% of
which are multiple. Four multiple systems are confirmed in this work by common
proper motion. An orbital solution is presented for the binary system HH Leo B
and C. Indeed, a group of candidates displays signatures of youth. 7 canonical
members are identified. The distribution of EWLi of canonical Her-Lyr members
is spread widely and is similar to that of the Pleiades and the UMa group.
Gyrochronology gives an age of 257+-46 Myr which is in between the ages of the
Pleiades and the Ursa Major group. The measures of chromospheric and coronal
activity support the young age. Four membership criteria are presented based on
kinematics, EWLi, chromospheric activity, and gyro. age. In total, 11 stars are
identified as certain members including co-moving objects plus additional 23
possible members while 14 candidates are doubtful or can be rejected. A
comparison to the mass function, however, indicates the presence of a large
number of additional unidentified low-mass members.Comment: 19 pages 16 figure
Turbulent structure inside and above shallow to deep canopies
Multi-plane PIV measurements were performed in an open-channel flume filled with elongated prisms of height k and width to investigate the effect of the deepening of the canopy on the flow structure. Velocity measurements were performed both inside the canopy and above it. Analysis of the spatial convergence for the double-averaged quantities shows that for canopy flow investigations (z k). Three canopy aspect ratios, k/ℓ = [1, 3, 6] were investigated for a fixed modified-submergence ratio β = (h − k)/ℓ = 3 where h is the water depth. As the canopy deepens, the hydraulic roughness decreases and the velocity near the bottom of the canopy becomes gradually constant, as expected for deep canopies. We show how the highly converged (both in space and time) profiles of double-averaged longitudinal velocity and total shear stress can be used to calculate the vertical distribution of drag in the canopy. With this methodology, values of the drag coefficient CD(z) can be calculated, and are found to be always close to unity, even in the upper part of the canopy
Applied environmental stresses to enhance the levels of polyphenolics in leaves of hawthorn plants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72331/1/j.1399-3054.2004.00332.x.pd
Search for associations containing young stars (SACY):II. Chemical abundances of stars in 11 young Associations in the Solar neighborhood
The recently discovered coeval, moving groups of young stellar objects in the
solar neighborhood represent invaluable laboratories to study recent star
formation and to search for high metallicity stars which can be included in
future exo-planet surveys. In this study we derived through an uniform and
homogeneous method stellar atmospheric parameters and abundances for iron,
silicium and nickel in 63 Post T-Tauri Stars from 11 nearby young associations.
We further compare the results with two different pre-main sequence (PMS) and
main sequence (MS) star populations. The stellar atmospheric parameters and the
abundances presented here were derived using the equivalent width of individual
lines in the stellar spectra through the excitation/ionization equilibrium of
iron. Moreover, we compared the observed Balmer lines with synthetic profiles
calculated for model atmospheres with a different line formation code. We found
that the synthetic profiles agree reasonably well with the observed profiles,
although the Balmer lines of many stars are substantially filled-in, probably
by chromospheric emission. Solar metallicity is found to be a common trend on
all the nearby young associations studied. The low abundance dispersion within
each association strengthens the idea that the origin of these nearby young
associations is related to the nearby Star Forming regions (SFR). Abundances of
elements other than iron are consistent with previous results on Main Sequence
stars in the solar neighborhood. The chemical characterization of the members
of the newly found nearby young associations, performed in this study and
intended to proceed in subsequent works, is essential for understanding and
testing the context of local star formation and the evolutionary history of the
galaxy.Comment: 13 pages, 7 figures, 6 tables, accepted for publication in A&A on
26/03/200
Shallow flow over a bed with a lateral change of roughness
River beds frequently exhibit a lateral variation of roughness. For example, in the case of an overflowing river, the main channel has a smoother topography compared to the adjacent floodplains where vegetation and land occupation yield an important hydraulic roughness. The lateral difference in roughness can induce a high lateral velocity gradient within the river crosssection that gives birth to a mixing layer. This mixing layer leads to fluid and momentum transfers between the two adjacent beds. To understand such mixing processes in rivers is important for predicting stage-discharge relationships and the velocity distribution within the cross-section. In order to address these issues in the context of a shallow water flow with a water depth h of the same order as the roughness elements of the bed, experiments were undertaken in a 26 m long and 1.1 m wide glass-walled open-channel flume. One half-side of the bed was covered with an array of cubes of height k arranged in a square configuration, the other side with smooth glass. Three different levels of cube submergence h/k were examined (h/k = 0.8, 1.5 and 2). The experiments and measurements were designed to yield the flow in the complete volume of the interstices across the cube array. To achieve this, 2C-3D linear-scanning PIV measurements with zero-parallax optics were developed and set up. The measurements revealed the complexity of the flow structure around the interface between the rough and smooth beds. The results show that the ability of the mixing layer to exchange momentum is highly dependent on the level of the cube submergence h/k
Surface Incompressibility from Semiclassical Relativistic Mean Field Calculations
By using the scaling method and the Thomas-Fermi and Extended Thomas-Fermi
approaches to Relativistic Mean Field Theory the surface contribution to the
leptodermous expansion of the finite nuclei incompressibility has been
self-consistently computed. The validity of the simplest expansion, which
contains volume, volume-symmetry, surface and Coulomb terms, is examined by
comparing it with self-consistent results of the finite nuclei
incompressibility for some currently used non-linear sigma-omega parameter
sets. A numerical estimate of higher-order contributions to the leptodermous
expansion, namely the curvature and surface-symmetry terms, is made.Comment: 18 pages, REVTeX, 3 eps figures, changed conten
Accurate fundamental parameters for 23 bright solar-type stars
We combine results from interferometry, asteroseismology and spectroscopy to
determine accurate fundamental parameters of 23 bright solar-type stars, from
spectral type F5 to K2 and luminosity classes III to V. For some stars we can
use direct techniques to determine the mass, radius, luminosity and effective
temperature, and we compare with indirect methods that rely on photometric
calibrations or spectroscopic analyses. We use the asteroseismic information
available in the literature to infer an indirect mass with an accuracy of 4-15
percent. From indirect methods we determine luminosity and radius to 3 percent.
For Teff we find a slight offset of -40+-20 K between the spectroscopic method
and the direct method, meaning the spectroscopic temperatures are too high.
From the spectroscopic analysis we determine the detailed chemical
composition for 13 elements, including Li, C and O. We find no significant
offset between the spectroscopic surface gravity and the value from combining
asteroseismology with radius estimates. From the spectroscopy we also determine
vsini and we present a new calibration of macro- and microturbulence. From the
comparison between the results from the direct and spectroscopic methods we
claim that we can determine Teff, log g, and [Fe/H] with absolute accuracies of
80 K, 0.08 dex, and 0.07 dex. The indirect methods are important to obtain
reliable estimates of the fundamental parameters of relatively faint stars when
interferometry cannot be used. Our study is the first to compare direct and
indirect methods for a large sample of stars, and we conclude that indirect
methods are valid, although slight corrections may be needed.Comment: Accepted by MNRAS. Abstract abridge
Defining the roughness sublayer and its turbulent statistics
The roughness sublayer in a turbulent openchannel flow over a very rough wall is investigated experimentally both within the canopy and above using particle image velocimetry by gaining complete optical access with new methodologies without disturbing the flow. This enabled reliable estimates of the double-averaged mean and turbulence profiles to be obtained by minimizing and quantifying the usual errors introduced by limited temporal and spatial sampling. It is shown, for example, that poor spatial sampling can lead to erroneous vertical profiles in the roughness sublayer. Then, in order to better define and determine the roughness sublayer height, a methodology based on the measured spatial dispersion is proposed which takes into account temporal sampling errors. The results reveal values well below the usual more ad hoc estimates for all statistics. Finally, the doubleaveraged mean and turbulence statistics in the roughness sublayer are discussed
Differential responses of osteoblasts and macrophages upon Staphylococcus aureus infection
Background
Staphylococcus aureus (S. aureus) is one of the primary causes of bone infections which are often chronic and difficult to eradicate. Bacteria like S. aureus may survive upon internalization in cells and may be responsible for chronic and recurrent infections. In this study, we compared the responses of a phagocytic cell (i.e. macrophage) to a non-phagocytic cell (i.e. osteoblast) upon S. aureus internalization. Results
We found that upon internalization, S. aureus could survive for up to 5 and 7 days within macrophages and osteoblasts, respectively. Significantly more S. aureus was internalized in macrophages compared to osteoblasts and a significantly higher (100 fold) level of live intracellular S. aureus was detected in macrophages compared to osteoblasts. However, the percentage of S. aureus survival after infection was significantly lower in macrophages compared to osteoblasts at post-infection days 1–6. Interestingly, macrophages had relatively lower viability in shorter infection time periods (i.e. 0.5-4 h; significant at 2 h) but higher viability in longer infection time periods (i.e. 6–8 h; significant at 8 h) compared to osteoblasts. In addition, S. aureusinfection led to significant changes in reactive oxygen species production in both macrophages and osteoblasts. Moreover, infected osteoblasts had significantly lower alkaline phosphatase activity at post-infection day 7 and infected macrophages had higher phagocytosis activity compared to non-infected cells. Conclusions
S. aureus was found to internalize and survive within osteoblasts and macrophages and led to differential responses between osteoblasts and macrophages. These findings may assist in evaluation of the pathogenesis of chronic and recurrent infections which may be related to the intracellular persistence of bacteria within host cells
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