308 research outputs found
Devonian of the Aran Valley Synclinorium, Central Pyrenees, Spain: stratigraphical and paleontological data
In the Aran Valley Synclinorium, situated in the Axial Zone of the Pyrenees, a Devonian succession crops out. This succession has been studied in three localities, two on its southern limb and one on the northern one. These series can be correlated and show the sharp lithological changes occurring in the Devonian of this area, with a predominance of sandstones towards the North and an important development of limestones towards the South. The paleontological study has allowed, on the basis of conodonts, to date several levels in the two sections on the southern limb; in one of them the Middle- Upper Devonian boundary has been traced fairly accurately. Anomalous faunal distributions have been detected in some of the successions and it is suggested that they are related to the existence of thrusts. However, other processes such as folding or sedimentary reworking, cannot be rejected
Tractor Stability for Agricultural Engineering Students: Learning Through a Project-Based Task
Human Cerebral Activation during Steady-State Visual-Evoked Responses
Flicker stimuli of variable frequency (2-90 Hz) elicit a steady-state
visual-evoked response (SSVER) in the electroencephalogram (EEG) with the same
frequency as the stimulus. In humans, the amplitude of this response peaks at
approximately 15 Hz, decreasing at higher stimulation frequencies. It was not
known whether this peak response corresponds to increased synaptic activity in
the visual cortex or to other mechanisms [for instance, the temporal coherence
(phase summation) of evoked responses]. We studied the SSVER in 16 normal
volunteers by means of visual stimulation at 14 different frequencies (from 5 to
60 Hz) while recording the EEG. In nine subjects of the group, we measured
regional cerebral blood flow (rCBF) with positron emission tomography
(PET)-H2(15)O at rest and during visual stimulation at five different
frequencies: 5, 10, 15, 25, and 40 Hz. We confirmed that the amplitude of the
SSVER in occipital regions peaks at 15 Hz stimulation. Applying to the PET rCBF
data a contrast weighted by the amplitude of the SSVER, we determined that the
primary visual cortex rCBF follows an activation pattern similar to the SSVER.
This finding suggests that the amplitude of the SSVER corresponds to increased
synaptic activity, specifically in Brodmann's area 17. Additionally, this study
showed that visual stimulation at 40 Hz causes selective activation of the
macular region of the visual cortex, and that a region in the dorsal aspect of
the Crus I lobule of the left cerebellar hemisphere is activated during
repetitive visual stimulation
Transient Posterior Encephalopathy Induced by Chemotherapy in Children
The cases of three children, 16, 12, and 12 years of age, who suffered sudden confusional state and cortical blindness lasting 12 to 30 minutes while under treatment with high-dose methotrexate, cyclophosphamide, and dactinomycin for a lower limb osteosarcoma are reported. Transient neuropsychologic deficits arose after the acute phase of treatment: left hemispatial neglect and constructive apraxia (Patient 1); constructive apraxia (Patient 2); and constructive apraxia and alexia without aphasia (Patient 3). The three patients recovered completely from all their deficits within the time frame of 3 hours to 2 weeks. Arterial hypertension and hypomagnesemia were found during the acute phase in all patients. In Patients 2 and 3, magnetic resonance imaging revealed increased parieto-occipital T(2) signal involving gray and white matter. In Patients 1 and 2, HmPAO-SPECT revealed parieto-occipital hypoperfusion that resolved a few days later. The alterations detected by neuroimaging were concurrent with the appearance and disappearance of the clinical symptoms. Such transient acute episodes have been named occipital-parietal encephalopathy. On the basis of our clinical, laboratory, and neuroimaging findings, an explanation for the origin of this syndrome, a migrainelike mechanism, triggered by chemotherapy-induced hypomagnesemia, is proposed
Revisión de las aplicaciones de la electroerosión por penetración al mecanizado de cerámicas conductoras
Análisis de la influencia de las condiciones de proceso sobre el acabado superficial de materiales cerámicos fabricados por electroerosión
Evolutionary-based prediction interval estimation by blending solar radiation forecasting models using meteorological weather types
Recent research has shown that the integration or blending of different forecasting models is able to improve the predictions of solar radiation. However, most works perform model blending to improve point forecasts, but the integration of forecasting models to improve probabilistic forecasting has not received much attention. In this work the estimation of prediction intervals for the integration of four Global Horizontal Irradiance (GHI) forecasting models (Smart Persistence, WRF-solar, CIADcast, and Satellite) is addressed. Several short-term forecasting horizons, up to one hour ahead, have been analyzed. Within this context, one of the aims of the article is to study whether knowledge about the synoptic weather conditions, which are related to the stability of weather, might help to reduce the uncertainty represented by prediction intervals. In order to deal with this issue, information about which weather type is present at the time of prediction, has been used by the blending model. Four weather types have been considered. A multi-objective variant of the Lower Upper Bound Estimation approach has been used in this work for prediction interval estimation and compared with two baseline methods: Quantile Regression (QR) and Gradient Boosting (GBR). An exhaustive experimental validation has been carried out, using data registered at Seville in the Southern Iberian Peninsula. Results show that, in general, using weather type information reduces uncertainty of prediction intervals, according to all performance metrics used. More specifically, and with respect to one of the metrics (the ratio between interval coverage and width), for high-coverage (0.90, 0.95) prediction intervals, using weather type enhances the ratio of the multi-objective approach by 2%¿. Also, comparing the multi-objective approach versus the two baselines for high-coverage intervals, the improvement is 11%¿% over QR and 10%¿% over GBR. Improvements for low-coverage intervals (0.85) are smaller.The authors are supported by projects funded by Agencia Estatal de Investigación, Spain (PID2019-107455RB-C21 and PID2019-107455RB-C22/AEI/10.13039/501100011033). Also supported by Spanish Ministry of Economy and Competitiveness, project ENE2014-56126-C2-1-R and ENE2014-56126-C2-2-R (http://prosol.uc3m.es). The University of Jaén team is also supported by FEDER, Spain funds and by the Junta de Andalucía, Spain (Research group TEP-220
11C-Methionine-Positron Emission Tomography as prognostic factor of recurrence in glioblastoma
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