2,146 research outputs found
Variable features in the Valles Marineris region of Mars
Transient phenomena on Mars have long been recognized in Mariner and Viking images as well as in decades of Earth based telescopic observations. These events are of interest because of the information they present on currently active meteorological and geological processes. Changes in surface albedo patterns and atmospheric conditions can also affect the analysis and interpretation of data based on spectral or morphological properties of geologic units on the surface. The mechanism responsible for albedo pattern change is currently under investigation. Generation and subsequent transportation and deposition of dark sands has been interpreted in the Valles. However, the removal of a bright dust layer is more consistent with the rapid time period of the change (about two months) and with preliminary multispectral mapping results which suggest that the dark streak south of Eos and Coprates Chasmata is spectrally distinguishable from the dark saltating materials found elsewhere in the canyon system. If a layer of bright dust was removed to affect the albedo change, questions concerning how such micron-sized particles are mobilized by the winds during a normally quiescent season (Southern Hemisphere Autumn) should be addressed
A different glance to the site testing above Dome C
Due to the recent interest shown by astronomers towards the Antarctic Plateau
as a potential site for large astronomical facilities, we assisted in the last
years to a strengthening of site testing activities in this region,
particularly at Dome C. Most of the results collected so far concern
meteorologic parameters and optical turbulence measurements based on different
principles using different instruments. At present we have several elements
indicating that, above the first 20-30 meters, the quality of the optical
turbulence above Dome C is better than above whatever other site in the world.
The challenging question, crucial to know which kind of facilities to build on,
is to establish how much better the Dome C is than a mid-latitude site. In this
contribution we will provide some complementary elements and strategies of
analysis aiming to answer to this question. We will try to concentrate the
attention on critical points, i.e. open questions that still require
explanation/attention.Comment: 3 figures, EAS Publications Series, Volume 25, 2007, pp.5
Near-optimal protocols in complex nonequilibrium transformations
The development of sophisticated experimental means to control nanoscale
systems has motivated efforts to design driving protocols which minimize the
energy dissipated to the environment. Computational models are a crucial tool
in this practical challenge. We describe a general method for sampling an
ensemble of finite-time, nonequilibrium protocols biased towards a low average
dissipation. We show that this scheme can be carried out very efficiently in
several limiting cases. As an application, we sample the ensemble of
low-dissipation protocols that invert the magnetization of a 2D Ising model and
explore how the diversity of the protocols varies in response to constraints on
the average dissipation. In this example, we find that there is a large set of
protocols with average dissipation close to the optimal value, which we argue
is a general phenomenon.Comment: 6 pages and 3 figures plus 4 pages and 5 figures of supplemental
materia
Aerodynamics research at MSFC
Aerodynamics research in rarefied gas dynamics, base heating, and turbulent fluctuation
The limits of filopodium stability
Filopodia are long, finger-like membrane tubes supported by cytoskeletal
filaments. Their shape is determined by the stiffness of the actin filament
bundles found inside them and by the interplay between the surface tension and
bending rigidity of the membrane. Although one might expect the Euler buckling
instability to limit the length of filopodia, we show through simple energetic
considerations that this is in general not the case. By further analyzing the
statics of filaments inside membrane tubes, and through computer simulations
that capture membrane and filament fluctuations, we show under which conditions
filopodia of arbitrary lengths are stable. We discuss several in vitro
experiments where this kind of stability has already been observed.
Furthermore, we predict that the filaments in long, stable filopodia adopt a
helical shape
Force-induced unfolding of a homopolymer on fractal lattice: exact results vs. mean field predictions
We study the force-induced unfolding of a homopolymer on the three
dimensional Sierpinski gasket. The polymer is subject to a contact energy
between nearest neighbour sites not consecutive along the chain and to a
stretching force. The hierarchical nature of the lattice we consider allows for
an exact treatment which yields the phase diagram and the critical behaviour.
We show that for this model mean field predictions are not correct, in
particular in the exact phase diagram there is {\em not} a low temperature
reentrance and we find that the force induced unfolding transition below the
theta temperature is second order.Comment: 15 pages, 5 eps figure
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Interleukin-17A upregulates receptor activator of NF-kappaB on osteoclast precursors.
IntroductionThe interaction between the immune and skeletal systems is evidenced by the bone loss observed in autoimmune diseases such as rheumatoid arthritis. In this paper we describe a new mechanism by which the immune cytokine IL-17A directly affects osteoclastogenesis.MethodsHuman CD14+ cells were isolated from healthy donors, cultured on dentine slices and coverslips and stimulated with IL-17A and/or receptor activator of NF-kappaB ligand (RANKL). Osteoclast differentiation was evaluated by gene expression, flow cytometry, tartrate-resistant acid phosphatase staining, fluorescence and electron microscopy. Physiologic bone remodelling was studied in wild-type (Wt) and IL-17A-/- mice using micro-computer tomography and serum RANKL/osteoprotegerin concentration. Functional osteoclastogenesis assays were performed using bone marrow macrophages isolated from IL-17A-/- and Wt mice.ResultsIL-17A upregulates the receptor activator for NF-kappaB receptor on human osteoclast precursors in vitro, leading to increased sensitivity to RANKL signalling, osteoclast differentiation and bone loss. IL-17A-/- mice have physiological bone homeostasis indistinguishable from Wt mice, and bone marrow macrophages isolated from these mice develop fully functional normal osteoclasts.ConclusionsCollectively our data demonstrate anti-IL-17A treatment as a selective therapeutic target for bone loss associated with autoimmune diseases
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