Search results for " SEM"
showing 10 items of 1467 documents
Bloque detector PET basado en cristales monolíticos y fotomultiplicadores de silicio
2017
La tomografía por emisión de positrones (PET) es una técnica de imagen médica, encuadrada en la medicina nuclear, consistente en la generación de imágenes a partir de la detección de radiación gamma resultante de la aniquilación de positrones, emitidos por un radiotrazador, con los electrones de tejidos circundantes. Las imágenes PET son de tipo funcional, lo que permite la observación y estudio de procesos fisiológicos, sin embargo, se ha probado que la integración de estos escáneres con otros sistemas de imagen médica que proporcionen imágenes de carácter anatómico mejora notablemente las prestaciones clínicas de ambos equipos. Este tipo de equipos multimodales se conocen como sistemas hí…
Problemas multiplicativos relacionados con la división de fracciones : un estudio sobre su enseñanza y aprendizaje
2013
Los estudiantes tienen dificultades para asociar el enunciado de un problema multiplicativo con la operación que permite resolverlo; esta investigación identifica los tipos de problemas multiplicativos que los estudiantes reconocen como de división de fracciones. Mediante el análisis histórico-epistemológico de textos de enseñanza sobre tres épocas históricas y ocho períodos diferentes, se obtiene un listado de variables de enseñanza (algoritmos, sentidos de uso de fracción y de división de fracciones, representaciones, problemas), así como los valores de dichas variables. Se localizan en los textos consultados algunas reglas particulares y seis algoritmos generales, cuyo predominio ha vari…
Response of AGATA segmented HPGe detectors to gamma rays up to 15.1MeV
2013
WOS: 000314826000009
Light-induced transmission nonlinearities in gallium selenide
1999
The intensity of a He–Ne laser (633 nm, 5 mW) transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium–aluminum–garnet laser pulse (532 nm, 7.8 ns, 3 mJ) which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and temperatures. Chantal.Ferrer@uv.es ; Jaqueline.Bouvier@uv.es ; Miguel.Andres@…
Ab Initio Studies of Triplet-State Properties for Organic Semiconductor Molecules
2012
Triplet–triplet annihilation (TTA) leads to a reduced efficiency of organic light-emitting diodes (OLEDs) at high current densities. Spacial confinement of the triplet excitons, which is mainly dependent on triplet energy differences, can reduce the TTA rate. Therefore, a deliberate choice of the organic semiconductor materials with particular attention to their triplet energies can help to considerably increase the device efficiency. Organic solid-state lasers are, on the other hand, efficiently quenched by singlet–triplet annihilation (STA), which is closely related to the triplet–triplet absorption of the organic semiconductors. To establish a useful set of parameters related to the proc…
Semantic structures of timbre emerging from social and acoustic descriptions of music
2011
The perceptual attributes of timbre have inspired a considerable amount of multidisciplinary research, but because of the complexity of the phenomena, the approach has traditionally been confined to laboratory conditions, much to the detriment of its ecological validity. In this study, we present a purely bottom-up approach for mapping the concepts that emerge from sound qualities. A social media ( http://www.last.fm ) is used to obtain a wide sample of verbal descriptions of music (in the form of tags) that go beyond the commonly studied concept of genre, and from this the underlying semantic structure of this sample is extracted. The structure that is thereby obtained is then evaluated th…
Physicochemical characterization of passive films on niobium by admittance and electrochemical impedance spectroscopy studies
2005
An analysis of the electronic properties of amorphous semiconductor-electrolyte junction is reported for thin (D ox < 20 nm) passive film grown on Nb in acidic electrolyte. It will be shown that the theory of amorphous semiconductor-electrolyte junction (a-SC/EI) both in the low band-bending and high band-bending regime is able to explain the admittance data of a-Nb 2 O 5 /El interface in a large range (10 Hz-10 kHz) of frequency and electrode potential values. A modelling of experimental EIS data at different potentials and in the frequency range of 0.1 Hz-100 kHz is presented based on the theory of amorphous semiconductor and compared with the results of the fitting of the admittance data…
Dysarthria in acute ischemic stroke: lesion topography, clinicoradiologic correlation, and etiology.
2001
Background and purpose: Although dysarthria is a frequent symptom in cerebral ischemia, there is little information on its anatomic specificity, spectrum of associated clinical characteristics, and etiologic mechanisms. Methods: An investigation of 68 consecutive patients with sudden onset of dysarthria due to a single infarction confirmed by MRI or CT was conducted. Results: Dysarthria was associated with a classic lacunar stroke syndrome in 52.9% of patients. Isolated dysarthria and dysarthria–central facial and lingual paresis occurred in 2.9% (n = 2) and 10.3% (n = 7), respectively. Dysarthria–clumsy hand syndrome was observed in 11.7% (n = 8) of patients and associated with pure motor …
Identification of a novel LMF1 nonsense mutation responsible for severe hypertriglyceridemia by targeted next-generation sequencing
2016
Background Severe hypertriglyceridemia (HTG) may result from mutations in genes affecting the intravascular lipolysis of triglyceride (TG)-rich lipoproteins. Objective The aim of this study was to develop a targeted next-generation sequencing panel for the molecular diagnosis of disorders characterized by severe HTG. Methods We developed a targeted customized panel for next-generation sequencing Ion Torrent Personal Genome Machine to capture the coding exons and intron/exon boundaries of 18 genes affecting the main pathways of TG synthesis and metabolism. We sequenced 11 samples of patients with severe HTG (TG>885 mg/dL–10 mmol/L): 4 positive controls in whom pathogenic mutations had pre…
A semi-automatic approach for epicardial adipose tissue segmentation and quantification on cardiac CT scans
2019
Abstract Many studies have shown that epicardial fat is associated with a higher risk of heart diseases. Accurate epicardial adipose tissue quantification is still an open research issue. Considering that manual approaches are generally user-dependent and time-consuming, computer-assisted tools can considerably improve the result repeatability as well as reduce the time required for performing an accurate segmentation. Unfortunately, fully automatic strategies might not always identify the Region of Interest (ROI) correctly. Moreover, they could require user interaction for handling unexpected events. This paper proposes a semi-automatic method for Epicardial Fat Volume (EFV) segmentation a…