1,898 research outputs found
Bi2Te_xSe_y series studied by resistivity and thermopower
We study the detailed temperature and composition dependence of the
resistivity, , and thermopower, , for a series of layered
bismuth chalcogenides BiTeSe, and report the stoichiometry
dependence of the optical band gap. In the resistivity of the most compensated
member, BiTeSe, we find a low-temperature plateau whose
onset temperature correlates with the high-temperature activation energy. For
the whole series can be described by a simple model for an extrinsic
semiconductor. By substituting Se for Te, the Fermi level is tuned from the
valence band into the conduction band. The maximum values of , bulk band
gap as well the activation energy in the resistivity are found for
Aplicación de tecnologías de valuación de empresas : Caso Agrometal SAI
El trabajo tiene como objetivo determinar el valor de la Firma AGROMETAL SAI a través de la aplicación de dos metodologías: a) el descuento de los flujos de fondos libres, y b) Múltiplos comparables. En el desarrollo del trabajo se efectuó primeramente una descripción de la empresa objetivo para luego analizar en detalle el sector de la maquinaria agrícola. Posteriormente se presentaron los cálculos propiamente dichos para efectuar la valuación por el primero de los métodos seleccionados, que es a través del descuento de los flujos de fondos libres. Este método persigue la búsqueda de un valor intrínseco de una empresa a través de tomar en consideración: i) la generación de flujos de caja futuros, ii) un valor terminal, iii) una tasa de descuento apropiada y iv) un horizonte de planificación determinado.
Por último, se desarrolló una metodología de valuación alternativa para la firma, como es la utilización de los múltiplos de empresas comparables.Facultad de Ciencias Económica
Optical properties of Bi2Te2Se at ambient and high pressure
The temperature dependence of the complex optical properties of the
three-dimensional topological insulator Bi2Te2Se is reported for light
polarized in the a-b planes at ambient pressure, as well as the effects of
pressure at room temperature. This material displays a semiconducting character
with a bulk optical gap of 300 meV at 295 K. In addition to the two expected
infrared-active vibrations observed in the planes, there is additional fine
structure that is attributed to either the removal of degeneracy or the
activation of Raman modes due to disorder. A strong impurity band located at
200 cm^{-1} is also observed. At and just above the optical gap, several
interband absorptions are found to show a strong temperature and pressure
dependence. As the temperature is lowered these features increase in strength
and harden. The application of pressure leads to a very abrupt closing of the
gap above 8 GPa, and strongly modifies the interband absorptions in the
mid-infrared spectral range. While ab initio calculations fail to predict the
collapse of the gap, they do successfully describe the size of the band gap at
ambient pressure, and the magnitude and shape of the optical conductivity.Comment: 8 pages, 7 figure
Indirect-to-direct band-gap crossover in few-layer MoTe
We study the evolution of the band-gap structure in few-layer MoTe
crystals, by means of low-temperature micro-reflectance (MR) and
temperature-dependent photoluminescence (PL) measurements. The analysis of the
measurements indicate that, in complete analogy with other semiconducting
transition metal dichalchogenides (TMDs), the dominant PL emission peaks
originate from direct transitions associated to recombination of excitons and
trions. When we follow the evolution of the PL intensity as a function of layer
thickness, however, we observe that MoTe behaves differently from other
semiconducting TMDs investigated earlier. Specifically, the exciton PL yield
(integrated PL intensity) is identical for mono and bilayer and it starts
decreasing for trilayers. A quantitative analysis of this behavior and of all
our experimental observations is fully consistent with mono and bilayer
MoTe being direct band-gap semiconductors, with tetralayer MoTe being
an indirect gap semiconductor, and with trilayers having nearly identical
direct and indirect gaps.This conclusion is different from the one reached for
other recently investigated semiconducting transition metal dichalcogenides,
for which only monolayers are found to be direct band-gap semiconductors, with
thicker layers having indirect band gaps that are significantly smaller, by
hundreds of meV, than the direct gap. We discuss the relevance of our findings
for experiments of fundamental interest and possible future device
applications.Comment: 20 pages, 4 Figure
Method and system for the automatic recognition of lesions in a set of breast magnetic resonance images
A method of identification of potential lesions of a breast from tomographic image datasets of a chest region of a patient, the- datasets comprising a plurality of voxels (2) each having an intensity value, the images including a region of interest (10) which comprises at least one breast (6). The method comprises the steps of: acquiring a set of images after the administration of a contrast agent to the patient; normalizing (254) the intensity of voxels (2) belonging to the region of interest (10) of the acquired images according to at least one normalization factor; classifying (255) each of the normalized voxels (2) on the basis of a classification criterion, in such a way as to identify regions (40) representing potential lesions. The method is characterized in that the normalization factor is based on normalization voxels (2) corresponding to an anatomical structure (34), the normalization voxels (2) having intensity values enhanced due to the administration of the contrast agent
Validation of the angular measurements of a new inertial-measurement-unit based rehabilitation system: comparison with state-of-the-art gait analysis
Background: Several rehabilitation systems based on inertial measurement units (IMU) are entering the market for the control of exercises and to measure performance progression, particularly for recovery after lower limb orthopaedic treatments. IMU are easy to wear also by the patient alone, but the extent to which IMU's malpositioning in routine use can affect the accuracy of the measurements is not known. A new such system (Riablo™, CoRehab, Trento, Italy), using audio-visual biofeedback based on videogames, was assessed against state-of-the-art gait analysis as the gold standard.Methods. The sensitivity of the system to errors in the IMU's position and orientation was measured in 5 healthy subjects performing two hip joint motion exercises. Root mean square deviation was used to assess differences in the system's kinematic output between the erroneous and correct IMU position and orientation.In order to estimate the system's accuracy, thorax and knee joint motion of 17 healthy subjects were tracked during the execution of standard rehabilitation tasks and compared with the corresponding measurements obtained with an established gait protocol using stereophotogrammetry.Results: A maximum mean error of 3.1 ± 1.8 deg and 1.9 ± 0.8 deg from the angle trajectory with correct IMU position was recorded respectively in the medio-lateral malposition and frontal-plane misalignment tests. Across the standard rehabilitation tasks, the mean distance between the IMU and gait analysis systems was on average smaller than 5°.Conclusions: These findings showed that the tested IMU based system has the necessary accuracy to be safely utilized in rehabilitation programs after orthopaedic treatments of the lower limb
Categorical Foundations of Explainable AI
Explainable AI (XAI) aims to address the human need for safe and reliable AI
systems. However, numerous surveys emphasize the absence of a sound
mathematical formalization of key XAI notions -- remarkably including the term
``\textit{explanation}'' which still lacks a precise definition. To bridge this
gap, this paper presents the first mathematically rigorous definitions of key
XAI notions and processes, using the well-funded formalism of Category theory.
We show that our categorical framework allows to: (i) model existing learning
schemes and architectures, (ii) formally define the term ``explanation'', (iii)
establish a theoretical basis for XAI taxonomies, and (iv) analyze commonly
overlooked aspects of explaining methods. As a consequence, our categorical
framework promotes the ethical and secure deployment of AI technologies as it
represents a significant step towards a sound theoretical foundation of
explainable AI
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