854 research outputs found
Arachidonic acid-induced release of calcium in permeabilized human neutrophils
AbstractThe addition of arachidonic acid to a suspension of digitonin-permeabilized human neutrophils was found to induce, in a dose-dependent manner (ED50 about 15 μM), the release of calcium from internal stores. Arachidic acid was without effect, while linoleic acid and linolenic acid were (on a concentration basis) at least 5-times less active than arachidonic acid. The activity of arachidonic acid appears to be due to the fatty acid itself and not to one of its metabolites. The pool of calcium mobilized by arachidonic acid includes that sensitive to inositol 1,4,5-trisphosphate. These results demonstrate a significant intracellular role for arachidonic acid at the level of the internal mobilization of calcium in human neutrophils
Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies
We use cosmological simulations from the Feedback In Realistic Environments
(FIRE) project, which implement a comprehensive set of stellar feedback
processes, to study ultra-violet (UV) metal line emission from the
circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover
the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of
Lyman break galaxies. Of the transitions we analyze, the low-ionization C III
(977 A) and Si III (1207 A) emission lines are the most luminous, with C IV
(1548 A) and Si IV (1394 A) also showing interesting spatially-extended
structures. The more massive halos are on average more UV-luminous. The UV
metal line emission from galactic halos in our simulations arises primarily
from collisionally ionized gas and is strongly time variable, with
peak-to-trough variations of up to ~2 dex. The peaks of UV metal line
luminosity correspond closely to massive and energetic mass outflow events,
which follow bursts of star formation and inject sufficient energy into
galactic halos to power the metal line emission. The strong time variability
implies that even some relatively low-mass halos may be detectable. Conversely,
flux-limited samples will be biased toward halos whose central galaxy has
recently experienced a strong burst of star formation. Spatially-extended UV
metal line emission around high-redshift galaxies should be detectable by
current and upcoming integral field spectrographs such as the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web
Imager (KCWI).Comment: 16 pages, 8 figures, accepted for publication in MNRA
Magnetic and Thermodynamic Properties of the Collective Paramagnet-Spin Liquid Pyrochlore Tb2Ti2O7
In a recent letter [Phys. Rev. Lett. {\bf 82}, 1012 (1999)] it was found that
the Tb magnetic moments in the TbTiO pyrochlore lattice of
corner-sharing tetrahedra remain in a {\it collective paramagnetic} state down
to 70mK. In this paper we present results from d.c. magnetic susceptibility,
specific heat data, inelastic neutron scattering measurements, and crystal
field calculations that strongly suggest that (1) the Tb ions in
TbTiO possess a moment of approximatively 5, and (2)
the ground state tensor is extremely anisotropic below a temperature of
K, with Ising-like Tb magnetic moments confined to point along
a local cubic direction
dramatically reduces the frustration otherwise present in a Heisenberg
pyrochlore antiferromagnet. The results presented herein underpin the
conceptual difficulty in understanding the microscopic mechanism(s) responsible
for TbTiO failing to develop long-range order at a temperature of
the order of the paramagnetic Curie-Weiss temperature K. We suggest that dipolar interactions and extra perturbative exchange
coupling(s)beyond nearest-neighbors may be responsible for the lack of ordering
of TbTiO.Comment: 8 POSTSCRIPT figures included. Submitted to Physical Review B.
Contact: [email protected]
Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion
We investigate stellar metallicity distribution functions (MDFs), including
Fe and -element abundances, in dwarf galaxies from the Feedback in
Realistic Environments (FIRE) project. We examine both isolated dwarf galaxies
and those that are satellites of a Milky Way-mass galaxy. In particular, we
study the effects of including a sub-grid turbulent model for the diffusion of
metals in gas. Simulations that include diffusion have narrower MDFs and
abundance ratio distributions, because diffusion drives individual gas and star
particles toward the average metallicity. This effect provides significantly
better agreement with observed abundance distributions of dwarf galaxies in the
Local Group, including the small intrinsic scatter in [/Fe] vs.
[Fe/H] (less than 0.1 dex). This small intrinsic scatter arises in our
simulations because the interstellar medium (ISM) in dwarf galaxies is
well-mixed at nearly all cosmic times, such that stars that form at a given
time have similar abundances to within 0.1 dex. Thus, most of the scatter in
abundances at z = 0 arises from redshift evolution and not from instantaneous
scatter in the ISM. We find similar MDF widths and intrinsic scatter for
satellite and isolated dwarf galaxies, which suggests that environmental
effects play a minor role compared with internal chemical evolution in our
simulations. Overall, with the inclusion of metal diffusion, our simulations
reproduce abundance distribution widths of observed low-mass galaxies, enabling
detailed studies of chemical evolution in galaxy formation.Comment: 19 pages, 13 figures, published in MNRA
What Does a habitus of the Soul Do? : The Case of the habitus of Faith in Bonaventure, Peter John Olivi and John Duns Scotus
While a habitus can be described as a disposition towards a certain type of act, such a definition is not sufficient to encompass the diversity of uses the medieval thinkers made of this concept. It is the aim of this paper to examine the habitus of faith in the voluntarist Franciscan tradition in order to illustrate several of its functions and how these varied from author to author. Studying how the habitus of faith works for Bonaventure, Peter John Olivi and John Duns Scotus allows us to examine different takes on these functions and illustrate the variety of possible positions even within a tradition that emphasizes the freedom and agency of the moral subject above all. We will emphasize the capacity a habitus grants to pick out its proper objects, in the present case, the objects of faith; the capacity to elicit certain acts that without it would not have been possible or at least that would not have had the moral value the habitus grants them; the capacity to unite several powers in the accomplishment of a given act.Peer reviewe
High resolution spatial analyses of trace elements in coccoliths reveal new insights into element incorporation in coccolithophore calcite
Femtosecond time resolved CARS spectroscopy of H2-N2 mixtures in the Dicke regime: Experiments and modeling of velocity effects
International audienceIn this paper, we present measurements and modeling of femtosecond time resolved CARS signal in H2-N2 mixtures at low densities. Three approaches have been used to model the CARS response. The first is the usual sum of Voigt profiles. In the second approach, the speed dependent Voigt profile is used. In the last approach, a new model of the CARS signal is developed which takes into account the velocity changes induced by collisions and the speed dependence of the collisional parameters. The velocity changes are modeled using the Keilson and Storer memory function; the radiator speed dependences of the collisional parameters are determined from their temperature dependences. The results show that the changes of the velocity have important effects for the H2/N2 system at the Dicke density regime
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