Search results for "homogeneity"
showing 10 items of 111 documents
Barrier inhomogeneity in vertical Schottky diodes on free standing gallium nitride
2019
Abstract In this paper, the electrical behavior of a Ni/Au Schottky barrier on free standing GaN has been studied employing a variety of techniques and correlated with the material and interface quality. The temperature dependence of the ideality factor (n) and of the Schottky barrier height (ΦB) revealed a spatial inhomogeneity of the barrier. This behavior has been described by means of the Tung's model on inhomogeneous Schottky barriers. The origin of the barrier inhomogeneity can be likely associated to the surface quality of the GaN epilayer or to microstructure of the Ni/GaN interface.
Hydrodynamic characterization of a new small-scale reactor mixed by a magnetic bar
2015
International audience; The purpose of this study was to evaluate the mixing characteristics of a new milliliter-scale (mL-scale) reactor developed for studying enzymatic activity or physiological cell response. The mL-scale reactor was designed to enable the integration of several sensors to carry out dynamic measurements in a controlled environment. Rapid homogeneity of the entire system is essential to ensure reproducible and reliable results, consequently the reactor was stirred to optimize both mass and heat transfers. A comparative study using three different techniques was undertaken to study mixing performances in the system. Firstly, mixing time (4,) was estimated in the reactor us…
Nonlinear network dynamics for interconnected micro-grids
2018
Abstract This paper deals with transient stability in interconnected micro-grids. The main challenge is to understand the impact of the connectivity of the graph and model nonlinearities on transient and steady-state behavior of the system as a whole. The contribution of this paper is three-fold. First, we provide a robust classification of transient dynamics for different intervals of the parameters for a single micro-grid. We prove that underdamped dynamics and oscillations arise when the damping coefficient is below a certain threshold which we calculate explicitly as function of the product between the inertia coefficient and the synchronization parameter. Second, for interconnected mic…
Physical activity and aerobic fitness in relation to local and interhemispheric functional connectivity in adolescents' brains
2021
Abstract Introduction Adolescents have experienced decreased aerobic fitness levels and insufficient physical activity levels over the past decades. While both physical activity and aerobic fitness are related to physical and mental health, little is known concerning how they manifest in the brain during this stage of development, characterized by significant physical and psychosocial changes. The aim of the study is to examine the associations between both physical activity and aerobic fitness with brains’ functional connectivity. Methods Here, we examined how physical activity and aerobic fitness are associated with local and interhemispheric functional connectivity of the adolescent brai…
Hyperechogenicity of the substantia nigra in healthy controls is related to MRI changes and to neuronal loss as determined by F-Dopa PET
2009
Abstract Transcranial ultrasound (TCS) has been shown to reveal hyperechogenicity of the substantia nigra (SN) in Parkinsonian patients and in about 10% of healthy controls. It is hypothesized that SN hyperechogenicity in healthy subjects is a vulnerability marker for idiopathic Parkinson's disease (IPD). Although there is strong evidence that the echomarker results from increased local iron content, the exact pathophysiological mechanisms remain incompletely understood. Thus, prognostic impact can only be estimated. We examined 14 subjects with SN hyperechogenicity (SN+) (7 IPD patients and 7 controls) and 7 healthy controls without the echomarker (SN−) by a magnetic resonance imaging meth…
Demographic and behavioural profiles of patients with common oral mucosal lesions by a homogeneity analysis
2012
Objective: The aim of this study is to assess the main oral mucosal lesions (OMLs) within a hospital base and to provide an anamnestic, diagnostic model based on homogeneity analysis of some variables. Methods: The demographic and behavioural data (i.e. gender, age, smoking status, alcohol consumption and therapeutic drug usage) of 1753 patients with at least one OML were considered. Multiple correspondence analysis (MCA) and multivariate tests of the simultaneous marginal homogeneity hypothesis (SMH) were used to analyse the evidence of any differences between the demographic and behavioural profiles relating to OMLs diagnoses. Statistical significance of P<0.05 was chosen. Results: With r…
Fuzzy C-Means Segmentation on Brain MR Slices Corrupted by RF-Inhomogeneity
2007
Brain MR Images corrupted by RF-Inhomogeneity exhibit brightness variations in such a way that a standard Fuzzy C-Means (fcm) segmentation algorithm fails. As a consequence, modified versions of the algorithm can be found in literature, which take into account the artifact. In this work we show that the application of a suitable pre-processing algorithm, already presented by the authors, followed by a standard fcm segmentation achieves good results also. The experimental results ones are compared with those obtained using SPM5, which can be considered the state of the art algorithm oriented to brain segmentation and bias removal.
Illumination Correction on MR Images
2006
Objective. An important artifact corrupting Magnetic Resonance Images is the rf inhomogeneity, also called bias artifact. This anomaly produces an abnormal illumination fluctuation on the image, due to variations of the device magnetic field. This artifact is particularly strong on images acquired with a device specialized on upper and lower limbs due to their coil configuration. A method based on homomorphic filtering aimed to suppress this artifact was proposed by Guillemaud. This filter has two faults: it doesnt provide an indication about the cutoff frequency (cf) and introduces another illumination artifact on the edges of the foreground. This work is an improvement to this method because i…
Volumetric Bias Correction
2007
This paper presents a method to suppress the bias artifact, also known as RF-inhomogeneity, in Magnetic Resonance Imaging (MRI). This artifact produces illumination variations due to magnetic field fluctuations of the device. In the latest years many works have been devoted to face this problem. In this work we present the 3D version of a new approach to bias correction, which is called Exponential Entropy Driven Homomorphic Unsharp Masking (E2D-HUM). This technique has been already presented by some of the authors for the 2D case only. The description of the whole method is detailed, and some experimental results are reported.
Overview of Prognostic Systems for Hepatocellular Carcinoma and ITA.LI.CA External Validation of MESH and CNLC Classifications
2021
Simple Summary This review proposes a comprehensive overview of the main prognostic systems for HCC classified as prognostic scores, staging systems, or combined systems. Prognostic systems for HCC are usually compared in terms of homogeneity, monotonicity of gradients, and discrimination ability. However, despite the great number of published studies comparing HCC prognostic systems, it is rather difficult to identify a system that could be universally accepted as the best prognostic scheme for all HCC patients encountered in clinical practice. In order to give a contribute in this topic, we conducted a study aimed at externally validate the MESH score and the CNLC classification using the…