Search results for "attenuation"
showing 10 items of 283 documents
A theoretical model for laser and powder particles interaction during laser cladding
2002
Abstract Interactions between the laser and the powder particles lead to attenuation of the laser and make the powder particles temperatures raise. According to given stream spread and speed of the powder particles, their temperature distribution at the surface of the workpiece is calculated. The attenuation of the laser induced by the cloud is also computed. These results are plotted for the case of a Gaussian distribution. Results show that with the increasing of the powder jet incidence angle, both temperature distribution of powder particles and attenuation of the laser have very different profiles. Their effects on the clad should be considered for modelling of laser cladding.
Distillation and stripping pilot plants for the JUNO neutrino detector: Design, operations and reliability
2019
Abstract This paper describes the design, construction principles and operations of the distillation and stripping pilot plants tested at the Daya Bay Neutrino Laboratory, with the perspective to adapt these processes, system cleanliness and leak-tightness standards to the final full scale plants to be used for the purification of the liquid scintillator of the JUNO neutrino detector. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Purification of liquid scintillator will be performed with a system combining alumina oxide, distillation, water extraction and steam (or N 2 gas) stripping. Such a combined…
Evaluation of viscoelastic constants of metallic materials by laser-ultrasonics at elevating temperature
2002
The main objective of this study is the determination of elastic moduli and viscosity coefficients of metals at elevating temperature up to melting point. More specifically, it involves the analysis of the propagation of acoustic waves generated and detected simultaneously by laser-ultrasonic for the measurement of longitudinal and shear velocities. This preliminary work primarily concerns Tin (Sn) metal known for its low melting point and attenuation coefficient.
Laser-ultrasonics: a non-contact method to link the acoustic attenuation to metal damping properties up to the melting point
2004
The objective of this work is to describe the viscoelastic behavior of metals up to their melting temperature by measuring the velocity and the attenuation of ultrasonics waves. For that purpose, a technique called laser-ultrasonics has been optimized for the high temperature domain and the solid to liquid transition. This paper is especially applied to the viscoelastic characterization of tin, from room temperature up to the melting point.
Time-variations of zeroth-order vegetation absorption and scattering at L-band
2021
Abstract Surface soil moisture and vegetation optical depth (VOD), as an indicator of vegetation wet biomass, from passive microwave remote sensing have been increasingly applied in global ecology and climate research. Both soil moisture and VOD are retrieved from satellite brightness temperature measurements assuming a zeroth order radiative transfer model, commonly known as the tau-omega model. In this model the emission of a vegetated surface is dependent on soil moisture, vegetation absorption and vegetation scattering. Vegetation scattering is normally represented by the single scattering albedo, ω, and is commonly assumed to be a time-invariant calibration parameter to achieve high ac…
'Tell Us Only What You Know': Evidentiality in the Discourse of Participants in Spanish Trials
2019
El objetivo de esta propuesta es explorar el uso de la evidencialidad en los juicios españoles y su relación con las convenciones del género y los roles de los participantes en estos eventos discursivos. Para ello, basamos nuestro estudio en un análisis cuantitativo-cualitativo de un corpus transcrito de ensayos orales en español. La evidencialidad es una categoría semántico-funcional que incluye dispositivos lingüísticos que marcan la fuente de información detrás de las declaraciones del hablante. El marcado explícito de la fuente no es obligatorio en español; sin embargo, en géneros específicos (legal, parlamentario y académico), se convierte en una poderosa herramienta argumentativa para…
Diagnostic accuracy of non-invasive tests for advanced fibrosis in patients with NAFLD : an individual patient data meta-analysis
2021
ObjectiveLiver biopsy is still needed for fibrosis staging in many patients with non-alcoholic fatty liver disease. The aims of this study were to evaluate the individual diagnostic performance of liver stiffness measurement by vibration controlled transient elastography (LSM-VCTE), Fibrosis-4 Index (FIB-4) and NAFLD (non-alcoholic fatty liver disease) Fibrosis Score (NFS) and to derive diagnostic strategies that could reduce the need for liver biopsies.DesignIndividual patient data meta-analysis of studies evaluating LSM-VCTE against liver histology was conducted. FIB-4 and NFS were computed where possible. Sensitivity, specificity and area under the receiver operating curve (AUROC) were c…
Prevalence, predictors, and severity of lean nonalcoholic fatty liver disease in patients living with human immunodeficiency virus
2020
Abstract Background The burden of nonalcoholic fatty liver disease (NAFLD) is growing in people living with human immunodeficiency virus (HIV). NAFLD is associated with obesity; however, it can occur in normoweight (lean) patients. We aimed to investigate lean NAFLD in patients living with HIV. Methods We included patients living with HIV mono-infection from 3 prospective cohorts. NAFLD was diagnosed by transient elastography (TE) and defined as controlled attenuation parameter ≥248 dB/m, in absence of alcohol abuse. Lean NAFLD was defined when a body mass index was <25 kg/m2. Significant liver fibrosis was defined as TE ≥7.1 kPa. The presence of diabetes, hypertension, or hyperlipid…
Method to examine macrobending loss in deformed optical fibre loop
2005
This paper presents the method of research and measurement of macrobending attenuation, present during alteration of geometrical system of optical fibre loop. Presentation of a measuring device, which allows to unifying measurements in (under) conditions close to those present in industrial constructions of devices. Annexed exemplary research of macrobending loss in systems deforming optical fibre loops made from various types of optical fibres.
Output-feedback-based H∞ control for vehicle suspension systems with control delay
2014
This paper deals with the problem of output-feedback H∞ control for a class of active quarter-car suspension systems with control delay. The dynamic system of the suspension systems is first formed in terms of the control objectives, i.e., ride comfort, road holding, suspension deflection, and maximum actuator control force. Then, the objective is to the design of the dynamic output-feedback H∞ controller in order to ensure asymptotic stability of the closed-loop system with H∞ disturbance attenuation level and the output constraints. Furthermore, using Lyapunov theory and linear matrix inequality (LMI) approach, the existence of admissible controllers is formulated in terms of LMIs. With t…