21 research outputs found
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
C9ORF72-derived poly-GA DPRs undergo endocytic uptake in iAstrocytes and spread to motor neurons
Dipeptide repeat (DPR) proteins are aggregation-prone polypeptides encoded by the pathogenic GGGGCC repeat expansion in the C9ORF72 gene, the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. In this study, we focus on the role of poly-GA DPRs in disease spread. We demonstrate that recombinant poly-GA oligomers can directly convert into solid-like aggregates and form characteristic ÎČ-sheet fibrils in vitro. To dissect the process of cell-to-cell DPR transmission, we closely follow the fate of poly-GA DPRs in either their oligomeric or fibrillized form after administration in the cell culture medium. We observe that poly-GA DPRs are taken up via dynamin-dependent and -independent endocytosis, eventually converging at the lysosomal compartment and leading to axonal swellings in neurons. We then use a co-culture system to demonstrate astrocyte-to-motor neuron DPR propagation, showing that astrocytes may internalise and release aberrant peptides in disease pathogenesis. Overall, our results shed light on the mechanisms of poly-GA cellular uptake and propagation, suggesting lysosomal impairment as a possible feature underlying the cellular pathogenicity of these DPR species
A collision in 2009 as the origin of the debris trail of asteroid P/2010 A2
The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth
asteroid survey in January 2010 and given a cometary designation due to the
presence of a trail of material, although there was no central condensation or
coma. The appearance of this object, in an asteroidal orbit (small eccentricity
and inclination) in the inner main asteroid belt attracted attention as a
potential new member of the recently recognized class of 'Main Belt Comets'
(MBCs). If confirmed, this new object would greatly expand the range in
heliocentric distance over which MBCs are found. Here we present observations
taken from the unique viewing geometry provided by ESA's Rosetta spacecraft,
far from the Earth, that demonstrate that the trail is due to a single event
rather than a period of cometary activity, in agreement with independent
results from the Hubble Space Telescope (HST). The trail is made up of
relatively large particles of millimetre to centimetre size that remain close
to the parent asteroid. The shape of the trail can be explained by an initial
impact ejecting large clumps of debris that disintegrated and dispersed almost
immediately. We determine that this was an asteroid collision that occurred
around February 10, 2009.Comment: Published in Nature on 14/10/2010. 25 pages, includes supplementary
materia
Vitamin C and total phenols quantification in calli of native passion fruit induced by combinations of Picloram and Kinetin
Nota sobre abelhas Lestrimelitta rufipes (Freise) (Hymenoptera, Meliponina), atraĂdas por armadilhas com iscas odorĂferas, na regiĂŁo Sul Fluminense do Estado do Rio de Janeiro
Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past
The Rosetta spacecraft spent ~2 years orbiting comet 67P/Churyumov-Gerasimenko, most of it at distances that allowed surface characterization and monitoring at submeter scales. From December 2014 to June 2016, numerous localized changes were observed, which we attribute to cometary-specific weathering, erosion, and transient events driven by exposure to sunlight and other processes. While the localized changes suggest compositional or physical heterogeneity, their scale has not resulted in substantial alterations to the cometâs landscape. This suggests that most of the major landforms were created early in the cometâs current orbital configuration. They may even date from earlier if the comet had a larger volatile inventory, particularly of CO or CO2 ices, or contained amorphous ice, which could have triggered activity at greater distances from the Sun
Tensile strength of 67P/ChuryumovâGerasimenko nucleus material from overhangs
We directly measured twenty overhanging cliffs on the surface of comet 67P/ChuryumovâGerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the cometâs gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features andthe implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the ~10â100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)
Technical and clinical feasibility of contrast-enhanced ultrasound evaluation of long bone non-infected nonunion healing
Purpose: To assess the technical feasibility of contrast-enhanced ultrasound (CEUS) in the monitoring of non-infected long bone nonunion healing. Methods: Twenty-five patients (16 males; mean age: 40.4 \ub1 11.7) with long bone nonunion were treated using surgery and mesenchymal stem cells and platelet-rich plasma. They performed CEUS up to 15 days before, 7 days, 4 and 8 weeks after treatment. To categorize the angiogenesis around the fracture site, the microvascular blood flow from CEUS was classified into four categories, depending on the portion of the investigated area that was involved in the neovascularization process: grade 0 = 0%; grade 1 = 0\u201330%; grade 2 = 30\u201370%; grade 3 = 70\u2013100%. Nonparametric Friedman and Wilcoxon statistics were used. Results: Before treatment, neovascularization was graded as 0 in 15/25 patients, as 1 in 10/25. Vascularity significantly increased over time (P < 0.001), namely: 1 (25th\u201375th percentile = 1\u20132) at 7 days; 2 (1\u20132) at 4 weeks; 3 (0\u20132) at 8 weeks. All patients but one showed early progressive increase in neovascularization well identified with CEUS at the fracture site. Conclusion: CEUS is a feasible method to monitor healing in patients with long bone nonunion