10,749 research outputs found
Solar gravitational energy and luminosity variations
Due to non-homogeneous mass distribution and non-uniform velocity rate inside
the Sun, the solar outer shape is distorted in latitude. In this paper, we
analyze the consequences of a temporal change in this figure on the luminosity.
To do so, we use the Total Solar Irradiance (TSI) as an indicator of
luminosity. Considering that most of the authors have explained the largest
part of the TSI modulation with magnetic network (spots and faculae) but not
the whole, we could set constraints on radius and effective temperature
variations (dR, dT). However computations show that the amplitude of solar
irradiance modulation is very sensitive to photospheric temperature variations.
In order to understand discrepancies between our best fit and recent
observations of Livingston et al. (2005), showing no effective surface
temperature variation during the solar cycle, we investigated small effective
temperature variation in irradiance modeling. We emphasized a phase-shift
(correlated or anticorrelated radius and irradiance variations) in the (dR,
dT)-parameter plane. We further obtained an upper limit on the amplitude of
cyclic solar radius variations, deduced from the gravitational energy
variations. Our estimate is consistent with both observations of the
helioseismic radius through the analysis of f-mode frequencies and observations
of the basal photospheric temperature at Kitt Peak. Finally, we suggest a
mechanism to explain faint changes in the solar shape due to variation of
magnetic pressure which modifies the granules size. This mechanism is supported
by our estimate of the asphericity-luminosity parameter, which implies an
effectiveness of convective heat transfer only in very outer layers of the Sun.Comment: 17 pages, 2 figure, 1 table, published in New Astronom
High-quality ion beams by irradiating a nano-structured target with a petawatt laser pulse
We present a novel laser based ion acceleration scheme, where a petawatt
circularly polarized laser pulse is shot on an ultra-thin (nano-scale)
double-layer target. Our scheme allows the production of high-quality light ion
beams with both energy and angular dispersion controllable by the target
properties. We show that extraction of all electrons from the target by
radiation pressure can lead to a very effective two step acceleration process
for light ions if the target is designed correctly. Relativistic protons should
be obtainable with pulse powers of a few petawatt. Careful analytical modeling
yields estimates for characteristic beam parameters and requirements on the
laser pulse quality, in excellent agreement with one and two-dimensional
Particle-in Cell simulations.Comment: 18 pages, 7 figures, accepted in New. J. Phy
Repetition and difference: Lefebvre, Le Corbusier and modernity's (im)moral landscape: a commentary
This article engages with the relationship between social theory, architectural theory and material culture. The article is a reply to an article in a previous volume of the journal in question (Smith, M. (2001) ‘Repetition and difference: Lefebvre, Le Corbusier and modernity’s (im)moral landscape’, Ethics, Place and Environment, 4(1), 31-34) and, consequently, is also a direct engagement with another academic's scholarship. It represents a critique of their work as well as a recasting of their ideas, arguing that the matter in question went beyond interpretative issues to a direct critique of another author's scholarship on both Le Corbusier and Lefebvre. A reply to my article from the author of the original article was carried in a later issue of the journal (Smith, M. (2002) ‘Ethical Difference(s): a Response to Maycroft on Le Corbusier and Lefebvre’, Ethics, Place and Environment, 5(3), 260-269)
Modulation of NK Cell Autocrine-Induced Eosinophil Chemotaxis by Interleukin-15 and Vitamin D3: A Possible NK-Eosinophil Crosstalk via IL-8 in the Pathophysiology of Allergic Rhinitis
Natural killer cells (NK) secrete eosinophilotactic cytokines, however, whether they contribute to eosinophil chemotaxis by secreting IL-8 is not known. We investigated the ability of CD56+CD3-ve (NK cells) to induce chemotaxis of peripheral blood eosinophils from allergic rhinitis (AR) patients, through IL-8 secretion, and the effects of IL-15, the NK cell proactivating cytokine, and calcitriol: 1α, 25-dihydroxy Vitamin D3 (vitamin D3), the immunomodulator agent, in this scenario. Herein, it is shown that supernatants from unstimulated NK cells exhibited chemotactic activity against eosinophil. This effect was significantly augmented by IL-15 (1 ng/mL) treatment, resulting in an increase in the chemotactic index of approximately 3 folds and was abrogated by neutralizing antibody (Ab) to IL-8 in a dose-dependent fashion. The amount of IL-8 secreted by NK cells was increased by IL-15 treatment from levels of 88.64 ± 21.5 to 178.9 ± 23.6 Pg/mL and was significantly reduced by 10−6 M vitamin D3 to levels of 59.2 ± 16.3 Pg/mL. Our results indicate a novel inflammatory crosstalk between NK cells and eosinophils via IL-15/IL-8 axis that can be modulated by vitamin D3
Spin-Exchange Interaction in ZnO-based Quantum Wells
Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit
unprecedented tunability of the short-range spin exchange interaction. In the
context of large exciton binding energies and electron-hole exchange
interaction in ZnO, this tunability results from the competition between
quantum confinement and giant quantum confined Stark effect. By using
time-resolved photoluminescence we identify, for well widths under 3 nm, the
redistribution of oscillator strengths between the A and B excitonic
transitions, due to the enhancement of the exchange interaction. Conversely,
for wider wells, the redistribution is cancelled by the dominant effect of
internal electric fields, which dramatically reduce the exchange energy.Comment: 14 pages, 3 figure
The Collaborative Development of New CFD Methods Adapted for Tilt Rotor Aircraft in the HiPerTilt Project
No abstract available
Observation of Feshbach resonances in an ultracold gas of Cr
We have observed Feshbach resonances in elastic collisions between ultracold
Cr atoms. This is the first observation of collisional Feshbach
resonances in an atomic species with more than one valence electron. The zero
nuclear spin of Cr and thus the absence of a Fermi-contact interaction
leads to regularly-spaced resonance sequences. By comparing resonance positions
with multi-channel scattering calculations we determine the s-wave scattering
length of the lowest potentials to be
\unit[112(14)]{a_0}, \unit[58(6)]{a_0} and -\unit[7(20)]{a_0} for S=6, 4,
and 2, respectively, where a_{0}=\unit[0.0529]{nm}.Comment: 4 pages, 2 figures, 1 tabl
Breakup of diminutive Rayleigh jets
Discharging a liquid from a nozzle at sufficient large velocity leads to a
continuous jet that due to capillary forces breaks up into droplets. Here we
investigate the formation of microdroplets from the breakup of micron-sized
jets with ultra high-speed imaging. The diminutive size of the jet implies a
fast breakup time scale of the
order of 100\,ns{}, and requires imaging at 14 million frames per second. We
directly compare these experiments with a numerical lubrication approximation
model that incorporates inertia, surface tension, and viscosity [Eggers and
Dupont, J. Fluid Mech. 262, 205 (1994); Shi, Brenner, and Nagel, Science 265,
219 (1994)]. The lubrication model allows to efficiently explore the parameter
space to investigate the effect of jet velocity and liquid viscosity on the
formation of satellite droplets. In the phase diagram we identify regions where
the formation of satellite droplets is suppressed. We compare the shape of the
droplet at pinch-off between the lubrication approximation model and a boundary
integral (BI) calculation, showing deviations at the final moment of the
pinch-off. Inspite of this discrepancy, the results on pinch-off times and
droplet and satellite droplet velocity obtained from the lubrication
approximation agree with the high-speed imaging results
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