1,785 research outputs found
A note on chromospheric fine structure at active region polarity boundaries
High resolution H-alpha photographs for studying chromospheric fine structure at active region polarity boundarie
Interpreting Rock-Cut Grave Cemeteries: the early medieval necropolis and enclosure of São Gens, Portugal
EXCAVATION AT SÃO GENS (Guarda district) in central Portugal has revealed an early medieval rock-cut grave cemetery and settlement, along with Roman and prehistoric evidence. The site presents an exceptionally rich palimpsest of archaeological monuments. This paper reviews the findings and seeks to address the problem of interpreting rock-cut grave cemeteries, by describing a spatial analytical methodology that draws on comparisons with early medieval cemeteries in England, as a means of enhancing the information deficit of such necropolises. In the light of these analyses, an interpretation of the São Gens site is offered in conclusion
Retrieval of SO2 from thermal infrared satellite measurements: correction procedures for the effects of volcanic ash
The simultaneous presence of SO2 and ash in
a volcanic plume can lead to a significant error in the SO2
column abundance retrieval when multispectral Thermal InfraRed
(TIR) data are used. The ash particles within the
plume with effective radii from 1 to 10μm reduce the Top Of
Atmosphere (TOA) radiance in the entire TIR spectral range,
including the channels used for SO2 retrieval. The net effect
is a significant SO2 overestimation.
In this work the interference of ash is discussed and two
correction procedures for satellite SO2 volcanic plume retrieval
in the TIR spectral range are developed to achieve an
higher computational speed and a better accuracy.
The ash correction can be applied when the sensor spectral
range includes the 7.3 and/or 8.7μm SO2 absorption bands,
and the split window bands centered around 11 and 12μm
required for ash retrieval. This allows the possibility of simultaneous
estimation of both volcanic SO2 and ash in the
same data set. The proposed ash correction procedures have
been applied to the Moderate Resolution Imaging Spectroradiometer
(MODIS) and the Spin Enhanced Visible and Infrared
Imager (SEVIRI) measurements. Data collected during
the 24 November 2006 Mt. Etna eruption have been used
to illustrate the technique. The SO2 and ash estimation is carried
out by using a best weighted least squares fit method and
the Brightness Temperature Difference (BTD) procedures,
respectively. The simulated TOA radiance Look-Up Table
(LUT) needed for the SO2 column abundance and the ash
retrievals have been computed using the MODTRAN 4 Radiative
Transfer Model.
The results show the importance of the ash correction on
SO2 retrievals at 8.7μm, where the corrected SO2 column abundance values are less than 50% of the uncorrected values.
The ash correction on SO2 retrieval at 7.3μm is much
less important and only significant for low SO2 column abundances.
Results also show that the simplified and faster
correction procedure underestimates the ash correction compared
with the more time consuming but more accurate correction
procedure. Such underestimation is greater for instruments
having better ground pixel resolution, i.e. greater for
MODIS than for SEVIRI
On the Integrability of the Bukhvostov-Lipatov Model
The integrability of the Bukhvostov-Lipatov four-fermion model is
investigated. It is shown that the classical model possesses a current of
Lorentz spin 3, conserved both in the bulk and on the half-line for specific
types of boundary actions. It is then established that the conservation law is
spoiled at the quantum level -- a fact that might indicate that the quantum
Bukhvostov-Lipatov model is not integrable, contrary to what was previously
believed.Comment: 11 pages, 1 figure, LaTeX2e, AMS; new references adde
Long range transport and fate of a stratospheric volcanic cloud from Soufrière Hills volcano, Montserrat
International audienceVolcanic eruptions emit gases, ash particles and hydrometeors into the atmosphere, occasionally reaching heights of 20 km or more, to reside in the stratospheric overworld where they affect the radiative balance of the atmosphere and the Earth's climate. Here we use satellite measurements and a Lagrangian particle dispersion model to determine the mass loadings, vertical penetration, horizontal extent, dispersion and transport of volcanic gases and particles in the stratosphere from the volcanic cloud emitted during the 20 May 2006 eruption of Soufrière Hills volcano, Montserrat, West Indies. Infrared, ultraviolet and microwave radiation measurements from two polar orbiters are used to quantify the gases and particles, and track the movement of the cloud for 23 days, over a distance of ~18 000 km. Approximately, 0.1±0.01 Tg(S) was injected into the stratosphere in the form of SO2: the largest single sulphur input to the stratosphere in 2006. Microwave Limb Sounder measurements indicate an enhanced mass of HCl of ~0.003?0.01 Tg. Geosynchronous satellite data reveal the rapid nature of the stratospheric injection and indicate that the eruption cloud contained ~2 Tg of ice, with very little ash reaching the stratosphere. These new satellite measurements of volcanic gases and particles can be used to test the sensitivity of climate to volcanic forcing and assess the impact of stratospheric sulphates on climate cooling
Carrapato e vermes: inimigos do gado e do produtor.
bitstream/item/65290/1/CT-95-Carrapato-e-vermes.pd
Role of Mesenchymal Stem Cells in Counteracting Oxidative Stress\u2014Related Neurodegeneration
Neurodegenerative diseases include a variety of pathologies such as Alzheimer\u2019s
disease, Parkinson\u2019s disease, Huntington\u2019s disease, amyotrophic lateral sclerosis, and so forth,
which share many common characteristics such as oxidative stress, glycation, abnormal protein
deposition, inflammation, and progressive neuronal loss. The last century has witnessed significant
research to identify mechanisms and risk factors contributing to the complex etiopathogenesis of
neurodegenerative diseases, such as genetic, vascular/metabolic, and lifestyle-related factors, which
often co-occur and interact with each other. Apart from several environmental or genetic factors,
in recent years, much evidence hints that impairment in redox homeostasis is a common mechanism
in different neurological diseases. However, from a pharmacological perspective, oxidative stress is a
difficult target, and antioxidants, the only strategy used so far, have been ineffective or even provoked
side effects. In this review, we report an analysis of the recent literature on the role of oxidative stress
in Alzheimer\u2019s and Parkinson\u2019s diseases as well as in amyotrophic lateral sclerosis, retinal ganglion
cells, and ataxia. Moreover, the contribution of stem cells has been widely explored, looking at their
potential in neuronal differentiation and reporting findings on their application in fighting oxidative
stress in different neurodegenerative diseases. In particular, the exposure to mesenchymal stem cells
or their secretome can be considered as a promising therapeutic strategy to enhance antioxidant
capacity and neurotrophin expression while inhibiting pro-inflammatory cytokine secretion, which
are common aspects of neurodegenerative pathologies. Further studies are needed to identify a
tailored approach for each neurodegenerative disease in order to design more effective stem cell
therapeutic strategies to prevent a broad range of neurodegenerative disorder
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