230 research outputs found
On the monitoring of surface displacement in connection with volcano reactivation in Tenerife, Canary Islands, using space techniques
Geodetic volcano monitoring in Tenerife has mainly focused on the Las Cañadas Caldera, where a geodetic micronetwork and a levelling profile are located. A sensitivity test of this geodetic network showed that it should be extended to cover the whole island for volcano monitoring purposes. Furthermore, InSAR allowed detecting two unexpected movements that were beyond the scope of the traditional geodetic network. These two facts prompted us to design and observe a GPS network covering the whole of Tenerife that was monitored in August 2000. The results obtained were accurate to one centimetre, and confirm one of the deformations, although they were not definitive enough to confirm the second one. Furthermore, new cases of possible subsidence have been detected in areas where InSAR could not be used to measure deformation due to low coherence. A first modelling attempt has been made using a very simple model and its results seem to indicate that the deformation observed and the groundwater level variation in the island may be related. Future observations will be necessary for further validation and to study the time evolution of the displacements, carry out interpretation work using different types of data (gravity, gases, etc) and develop models that represent the island more closely. The results obtained are important because they might affect the geodetic volcano monitoring on the island, which will only be really useful if it is capable of distinguishing between displacements that might be linked to volcanic activity and those produced by other causes. One important result in this work is that a new geodetic monitoring system based on two complementary techniques, InSAR and GPS, has been set up on Tenerife island. This the first time that the whole surface of any of the volcanic Canary Islands has been covered with a single network for this purpose. This research has displayed the need for further similar studies in the Canary Islands, at least on the islands which pose a greater risk of volcanic reactivation, such as Lanzarote and La Palma, where InSAR techniques have been used already
Development of Type 1 Diabetes Mellitus in Nonobese Diabetic Mice Follows Changes in Thymocyte and Peripheral T Lymphocyte Transcriptional Activity
As early as one month of age, nonobese diabetic (NOD) mice feature pancreatic infiltration of autoreactive T lymphocytes, which destruct insulin-producing beta cells, producing autoimmune diabetes mellitus (T1D) within eight months. Thus, we hypothesized that during the development of T1D, the transcriptional modulation of immune reactivity genes may occur as thymocytes mature into peripheral T lymphocytes. The transcriptome of thymocytes and peripheral CD3+ T lymphocytes from prediabetic or diabetic mice analyzed through microarray hybridizations identified 2,771 differentially expressed genes. Hierarchical clustering grouped mice according to age/T1D onset and genes according to their transcription profiling. The transcriptional activity of thymocytes developing into peripheral T lymphocytes revealed sequential participation of genes involved with CD4+/CD8+ T-cell differentiation (Themis), tolerance induction by Tregs (Foxp3), and apoptosis (Fasl) soon after T-cell activation (IL4), while the emergence of T1D coincided with the expression of cytotoxicity (Crtam) and inflammatory response genes (Tlr) by peripheral T lymphocytes
Synthesis and stereochemical assignment of methyl 3-(3-hydroxyphenoxy) acrylate via cis-trans photoisomerization
Methyl 3-(3-hydroxyphenoxy)acrylate (2), a new and important starting material for several reactions and a potential precursor of the natural product 3-(3-hydroxyphenoxy)-2-propenal (1), was synthesized from resorcinol and methyl propiolate. The trans configuration of the double bond present in 2 was confirmed through a photoisomerization reaction.3-(3-Hidroxi-fenoxi)acrilato de metila (2), um novo e importante material de partida para inĂșmeras reaçÔes e um precursor potencial do produto natural 3-(3-hidroxi-fenoxi)-2-propenal (1), foi sintetizado a partir de resorcinol e propiolato de metila. A configuração trans da dupla ligação presente no composto 2 foi confirmada atravĂ©s de uma reação de fotoisomerização.Fundação de Amparo Ă Pesquisa do Estado de SĂŁo Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientĂfico e TecnolĂłgico (CNPq
A young binary Brown Dwarf in the R-CrA star formation region
We present imaging and spectroscopic observations with HST (WFPC2, ACS/HRC
and STIS), VLT (FORS2) and Keck (HIRES) of the dM8 ultra-cool dwarf DENIS-P
J185950.9-370632, located in the R-CrA region. The presence of lithium
absorption at 670.8 nm and the strong Halpha emission indicate a young age and
a sub-stellar mass. Our diffraction-limited images resolve a companion at the
separation limit of HST/ACS (~0.06"). The 2.1 mJy flux in the LW2 filter
(5.0-8.5 microns) of the Infrared Space Observatory (see 1999A&A...350..883)
likely corresponds to an infrared excess, suggesting the presence of
circumstellar material. Proper motion and photometric measurements, as well as
the Halpha activity, confirm membership in the R-CrA star forming region. If
confirmed by further observations, DENIS-P J185950.9-370632 would be the first
accreting sub-stellar multiple system observed to date.Comment: 18 pages, 11 figures, 3 tables Version with full resolution figures
available on: ftp://ftp.mpe.mpg.de/people/hbouy/publications/DENIS1859.ps.g
Global and decomposition evolutionary support vector machine approaches for time series forecasting
Multi-step ahead Time Series Forecasting (TSF) is a key tool for support- ing tactical decisions (e.g., planning resources). Recently, the support vector machine emerged as a natural solution for TSF due to its nonlinear learning capabilities. This paper presents two novel Evolutionary Support Vector Machine (ESVM) methods for multi-step TSF. Both methods are based on an Estimation Distribution Algorithm (EDA) search engine that automatically performs a simultaneous variable (number of inputs) and model (hyperparameters) selection. The Global ESVM (GESVM) uses all past patterns to fit the support vector machine, while the Decomposition ESVM (DESVM) separates the series into trended and stationary effects, using a distinct ESVM to forecast each effect and then summing both predictions into a sin- gle response. Several experiments were held, using six time series. The proposed approaches were analyzed under two criteria and compared against a recent Evolu- tionary Artificial Neural Network (EANN) and two classical forecasting methods, Holt-Winters and ARIMA. Overall, the DESVM and GESVM obtained competitive and high quality results. Furthermore, both ESVM approaches consume much less computational effort when compared with EANN.The authors wish to thank Ramon Sagarna for introducing the subject of EDA. The work of P. Cortez was supported by FEDER (program COMPETE and FCT) under project FCOMP-01-0124-FEDER-022674
On the circum(sub)stellar environment of brown dwarfs in Taurus
Aims : We want to investigate whether brown dwarfs (BDs) form like stars or
are ejected embryos. We study the presence of disks around BDs in the Taurus
cloud, and discuss implications for substellar formation models. Methods : We
use photometric measurements from the visible to the far infrared to determine
the spectral energy distributions (SEDs) of Taurus BDs. Results: We use Spitzer
color indices, Halpha as an accretion indicator, and models fit to the SEDs in
order to estimate physical parameters of the disks around these BDs. We study
the spatial distribution of BDs with and without disks across the Taurus
aggregates, and we find that BDs with and without disks are not distributed
regularly across the Taurus cloud. Conclusions: We find that 48%+/- 14% of
Taurus BDs have a circumstellar disk signature, a ratio similar to recent
results from previous authors in other regions. We fit the SEDs and find that
none of the disks around BDs in Taurus can be fitted convincingly with a
flaring index beta = 0, indicating that heating by the central object is
efficient and that the disks we observe retain a significant amount of gas. We
find that BDs with disks are proportionally more numerous in the northern
Taurus filament, possibly the youngest filament. We do not find such a clear
segregation for classical T Tauri stars (CTTS) and weak-lined T Tauri stars
(WTTS), suggesting that, in addition to the effects of evolution, any
segregation effects could be related to the mass of the object. A by-product of
our study is to propose a recalibration of the Barrado y Navascues & Martin
(2003) accretion limit in the substellar domain. The global shape of the limit
fits our data points if it is raised by a factor 1.25-1.30.Comment: 11 pages, 5 figures, A&A accepte
On the properties of young multiple stars
Abridged/ We present numerical results on the properties of young binary and
multiple stellar systems. Our analysis is based on a series of SPH + Nbody
simulations of the fragmentation of small molecular clouds, that fully resolve
the opacity limit for fragmentation. We have produced a statistically
significant number of stable multiple systems, with components separations in
the range 1-1000 AU. At the end of the hydrodynamical evolution (0.5 Myr) we
find that ~60% of stars and brown dwarfs are members of multiples systems, with
about a third of these being low mass, weakly bound outliers in wide eccentric
orbits. Our results imply that in the stellar regime most stars are in
multiples (~80%) and that this fraction is an increasing function of primary
mass. After Nbody integration to 10.5 Myr, the percentage of bound objects has
dropped to ~40%, as most very low mass stars and brown dwarfs have been
released to the field. Brown dwarfs are never found to be very close companions
to stars (brown dwarf desert at very small separations), but one case exists of
a brown dwarf companion at intermediate separations (10 AU). Our simulations
can accommodate the existence of brown dwarf companions at large separations,
but only if the primaries of these systems are themselves multiples. We have
compared the outcome of our simulations with the properties of real stellar
systems as deduced from the IR CM diagram of the Praesepe cluster and from
spectroscopic and high-resolution imaging surveys of young clusters and the
field.Comment: 14 pages, 4 figures, 1 table, accepted by MNRA
A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low mass IMF
We present the results of a deep wide-field near-infrared survey of 12 square
degrees of the Pleiades conducted as part of the UKIDSS Deep Infrared Sky
Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high
probability proper motion members down to 0.03 solar masses using a combination
of UKIDSS photometry and proper motion measurements obtained by
cross-correlating the GCS with data from the Two Micron All Sky Survey (2MASS),
the Isaac Newton (INT) and the Canada-France-Hawai'i (CFHT) telescopes.
Additionally, we have unearthed 73 new candidate brown dwarf members on the
basis of five band UKIDSS photometry alone. We have identified 23 substellar
multiple system candidates out of 63 candidate brown dwarfs from the (Y-K,Y)
and (J-K,J) colour-magnitude diagrams, yielding a binary frequency of 28-44% in
the 0.075-0.030 Msun mass range. Our estimate is three times larger than the
binary fractions reported from high-resolution imaging surveys of field
ultracool dwarfs and Pleiades brown dwarfs. However, it is marginally
consistent with our earlier ``peculiar'' photometric binary fraction of
50+/-10% presented in Pinfield et al. (2003), in good agreement with the 32-45%
binary fraction derived from the recent Monte-Carlo simulations of Maxted &
Jeffries (2005) and compatible with the 26+/-10% frequency recently estimated
by Basri & Reiners (2006). A tentative estimate of the mass ratios from
photometry alone seems to support the hypothesis that binary brown dwarfs tend
to reside in near equal-mass ratio systems. (abridged)Comment: 21 pages, 8 figures, 6 tables, 1 electronic table, 6 appendices with
tables, accepted to MNRA
Finding benchmark brown dwarfs to probe the IMF as a function of time
Using a simulated disk brown dwarf (BD) population, we find that new large
area infrared surveys are expected to identify enough BDs covering wide enough
mass--age ranges to potentially measure the mass function down to ~0.03Mo, and
the BD formation history out to 10 Gyr, at a level capable of establishing if
BD formation follows star formation. We suggest these capabilities are best
realised by spectroscopic calibration of BD properties (Teff, g and [M/H])
which, when combined with a measured luminosity and an evolutionary model can
give BD mass and age relatively independent of BD atmosphere models. Such
calibration requires an empirical understanding of how BD spectra are affected
by variations in these properties, and thus the identification and study of
"benchmark BDs" whose age and composition can be established independently. We
identify the best sources of benchmark BDs as young open cluster members,
moving group members, and wide (>1000AU) BD companions to both subgiant stars
and high mass white dwarfs (WDs). We have used 2MASS to measure a wide L dwarf
companion fraction of 2.7(+0.7/-0.5)%, which equates to a BD companion fraction
of 34(+9/-6)% for an alpha~1 companion mass function. Using this value we
simulate populations of wide BD binaries, and estimate that 80(+21/-14)
subgiant--BD binaries, and 50(+13/-10) benchmark WD--BD binaries could be
identified using current and new facilities. The WD--BD binaries should all be
identifiable using the Large Area Survey component of UKIDSS combined with
Sloan. Discovery of the subgiant--BD binaries will require a NIR imaging
campaign around a large (~900) sample of Hipparcos subgiants. If identified,
spectral studies of these benchmark brown dwarfs could reveal the spectral
sensitivities across the Teff, g and [M/H] space probed by new surveys.Comment: 18 pages, 12 figures, accepted for publication in MNRA
A novel method of using accelerometry for upper limb FES control.
This paper reports on a novel approach to using a 3-axis accelerometer to capture body segment angle for upper limb functional electrical stimulation (FES) control. The approach calculates the angle between the accelerometer x -axis and the gravity vector, while avoiding poor sensitivity at certain angles and minimizing errors when true acceleration is relatively large in comparison to gravity. This approach was incorporated into a state-machine controller which is used for the real-time control of FES during up- per limb functional task performance. An experimental approach was used to validate the new method. Two participants with different upper limb impairments resulting from a stroke carried out four different FES-assisted tasks. Comparisons were made between angle calculated from arm-mounted accelerometer data using our algorithm and angle calculated from limb-mounted reflective marker data. After removal of coordinate misalignment error, mean error across tasks and subjects ranged between 1.4 and 2.9 °. The approach shows promise for use in the control of upper limb FES and other human movement applications where true acceleration is relatively small in comparison with gravity
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