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Статті в журналах з теми "Modèle de filtration":
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Vásquez Bedoya, Fredy, and Sergio Restrepo Ochoa. "Efectos de las técnicas de filtrado en la evaluación de un modelo de ciclos económicos reales." Lecturas de Economía, no. 71 (February 23, 2010): 43–76. http://dx.doi.org/10.17533/udea.le.n71a4814.
Анотація:
Este trabajo emplea el filtro de Hodrick y Prescott (HP), el filtro Paso de Banda (PB) y una descomposición teórica (DT), para mostrar cómo las regularidades cíclicas caracterizadas por el modelo de crecimiento exógeno de King, Plosser y Rebelo (1988) dependen de la técnica de filtrado empleada. Este artículo exhibe diferencias estadísticamente significativas entre propiedades de los componentes cíclicos aislados con los filtros HP, PB y DT; en particular entre los filtros HP y PB, lo cual difiere de los resultados de Canova (1998). También se evidencia que el método de filtrado DT no es consistente con la definición del cíclico económico dada por la National Bureau of Economic Research (NBER). Palabras Clave: Modelo de crecimiento neoclásico básico, técnicas de filtrado, contrastes estadísticos, análisis en el dominio de la frecuencia. Clasificación JEL: C14, C15, E32 Abstract: This work uses the Hodrick and Prescott filter (HP), the Band-Pass filter (BP), and a theoretical decomposition (TD), to show how the cyclical regularities characterized by the model of exogenous growth of King, Plosser and Rebelo (1988) depend on the filter technique used. This article exhibits statistically significant differences between properties of the cyclical components isolated with the HP, BP and TD filters; in particular between the HP and BP filters, which differs from the results of Canova (1998). It also shows that the TD filter technique is not consistent with the definition of economic cycle given by the National Bureau of Economic Research (NBER). Key words: Basic Neoclassical Growth Model, Detrending Methods, Statistical Tests, Frequencydomain Analysis. JEL Classification: C14, C15, E32. Résumé: Ce travail utilise le filtre Hodrick-Prescott (CV), le filtre passe bande (PB) et une décomposition théorique (DT) pour montrer comment les régularités cycliques du modèle de croissance exogène de King, Plosser et Rebelle (1988) dépendent de la technique de filtration employée. Cet article montre les différences statistiquement significatives existantes dans les propriétés de composantes cycliques isolées avec les filtres CV, PB et DT. Tout particulièrementnous soulignons les différences entre les filtres CV et PB, dont les résultats diffèrent de ceux présentés par Canova (1998). On démontre également que la méthode de filtration DT n'est pas consistante avec la définition de cyclique économique proposée par le National Bureau of Economic Research (NBER). Mots Clé: Modèle néo-classique de croissance, techniques de filtration, contrastes statistiques, dominance de la fréquence. Classification JEL : C14, C15, E32
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Kübel, Johannes. "From Jantzen to Andersen filtration via tilting equivalence." MATHEMATICA SCANDINAVICA 110, no. 2 (June 1, 2012): 161. http://dx.doi.org/10.7146/math.scand.a-15202.
Анотація:
The space of homomorphisms between a projective object and a Verma module in category $\mathcal O$ inherits an induced filtration from the Jantzen filtration on the Verma module. On the other hand there is the Andersen filtration on the space of homomorphisms between a Verma module and a tilting module. Arkhipov's tilting functor, a contravariant self-equivalence of a certain subcategory of $\mathcal O$, which maps projective to tilting modules induces an isomorphism of these kinds of Hom-spaces. We show that this equivalence identifies both filtrations.
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JENSEN, BERNT TORE, DAG OSKAR MADSEN, and XIUPING SU. "FILTRATIONS IN ABELIAN CATEGORIES WITH A TILTING OBJECT OF HOMOLOGICAL DIMENSION TWO." Journal of Algebra and Its Applications 12, no. 02 (December 16, 2012): 1250149. http://dx.doi.org/10.1142/s0219498812501496.
Анотація:
We consider filtrations of objects in an abelian category [Formula: see text] induced by a tilting object T of homological dimension at most two. We define three extension closed subcategories [Formula: see text] and [Formula: see text] with [Formula: see text] for j > i, such that each object in [Formula: see text] has a unique filtration with factors in these categories. In dimension one, this filtration coincides with the classical two-step filtration induced by the torsion pair. We also give a refined filtration, using the derived equivalence between the derived categories of [Formula: see text] and the module category of [Formula: see text].
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Gruber, Jonathan. "Coxeter combinatorics for sum formulas in the representation theory of algebraic groups." Representation Theory of the American Mathematical Society 26, no. 3 (March 2, 2022): 68–93. http://dx.doi.org/10.1090/ert/599.
Анотація:
Let G G be a simple algebraic group over an algebraically closed field F \mathbb {F} of characteristic p ≥ h p \geq h , the Coxeter number of G G . We observe an easy ‘recursion formula’ for computing the Jantzen sum formula of a Weyl module with p p -regular highest weight. We also discuss a ‘duality formula’ that relates the Jantzen sum formula to Andersen’s sum formula for tilting filtrations and we give two different representation theoretic explanations of the recursion formula. As a corollary, we also obtain an upper bound on the length of the Jantzen filtration of a Weyl module with p p -regular highest weight in terms of the length of the Jantzen filtration of a Weyl module with highest weight in an adjacent alcove.
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Foster, Sylvia M., and Johnny A. Johnson. "The asymptotic and integral closure operations in multiplicative lattice modules." Tamkang Journal of Mathematics 36, no. 4 (December 31, 2005): 345–58. http://dx.doi.org/10.5556/j.tkjm.36.2005.107.
Анотація:
This paper is primarily concerned with the integral and asymptotic closure operations on a multiplicative lattice relative to the greatest element of a lattice module having the ascending chain condition. We show that a cancellation law holds for the asymptotic closure of elements of the multiplicative lattice and we ultimately show, by means of multiplicative filtrations and filtration transforms, that the asymptotic closure of an element in a multiplicative lattice relative to the greatest element of a lattice module, coincides with its integral closure relative to this element in the lattice module.
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Baudu, Michel, Gilles Guibaud, David Raveau, and Pierre Lafrance. "Prévision de l'adsorption de molécules organiques en solution aqueuse en fonctions de quelques caractéristiques physico-chimiques de charbons actifs." Water Quality Research Journal 36, no. 4 (November 1, 2001): 631–57. http://dx.doi.org/10.2166/wqrj.2001.034.
Анотація:
Abstract La production d'eau potable nécessite parfois une filtration sur charbon actif en vue d'éliminer des micropolluants organiques. Afin de développer un modèle prévisionnel de la durée de vie de ces filtres, il est nécessaire de bien connaître les caractéristiques des charbons influençant l'adsorption. Des caractéristiques de la structure physique (porosité et surface) et chimiques (fonction de surface), le potentiel zêta et les constantes thermodynamiques de neuf charbons actifs ont été déterminées et des essais de corrélation ont indiqué une certaine ligne de conduite pour l'utilisation de charbons de différentes origines. Des cinétiques et des isothermes d'adsorption de l'atrazine et du phénol ont été réalisées, ceci afin de mieux comprendre l'influence de la structure et des caractéristiques physico-chimiques des charbons sur les mécanismes d'adsorption. L'étude a mis en évidence les points suivants : (i) le nombre de sites primaires polaires d'adsorption augmente lorsque le nombre de fonctions acides augmente et lorsque le nombre de fonctions basiques diminue ; (ii) la capacité maximale d'eau adsorbée augmente avec la surface spécifique et diminue avec le nombre de fonctions acides du charbon ; (iii) l'adsorption de l'atrazine (molécule peu polaire) est en partie contrôlée par des paramètres physiques comme la surface spécifique ; (iv) les groupements polaires facilitent l'adsorption du phénol (molécule très polaire), et : (v) les valeurs du potentiel zêta sont difficiles à interpréter : la présence de groupements fonctionnels non déterminés pourrait intervenir sur les mécanismes d'adsorption.
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Edelsbrunner, Herbert, and Georg Osang. "The Multi-Cover Persistence of Euclidean Balls." Discrete & Computational Geometry 65, no. 4 (March 31, 2021): 1296–313. http://dx.doi.org/10.1007/s00454-021-00281-9.
Анотація:
AbstractGiven a locally finite $$X \subseteq {{{\mathbb {R}}}}^d$$ X ⊆ R d and a radius $$r \ge 0$$ r ≥ 0 , the k-fold cover of X and r consists of all points in $${{{\mathbb {R}}}}^d$$ R d that have k or more points of X within distance r. We consider two filtrations—one in scale obtained by fixing k and increasing r, and the other in depth obtained by fixing r and decreasing k—and we compute the persistence diagrams of both. While standard methods suffice for the filtration in scale, we need novel geometric and topological concepts for the filtration in depth. In particular, we introduce a rhomboid tiling in $${{{\mathbb {R}}}}^{d+1}$$ R d + 1 whose horizontal integer slices are the order-k Delaunay mosaics of X, and construct a zigzag module of Delaunay mosaics that is isomorphic to the persistence module of the multi-covers.
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BACKHAUS, TEODOR, XIN FANG, and GHISLAIN FOURIER. "DEGREE CONES AND MONOMIAL BASES OF LIE ALGEBRAS AND QUANTUM GROUPS." Glasgow Mathematical Journal 59, no. 3 (March 20, 2017): 595–621. http://dx.doi.org/10.1017/s0017089516000422.
Анотація:
AbstractWe provide ℕ-filtrations on the negative part Uq($\mathfrak{n}$−) of the quantum group associated to a finite-dimensional simple Lie algebra $\mathfrak{g}$, such that the associated graded algebra is a skew-polynomial algebra on $\mathfrak{n}$−. The filtration is obtained by assigning degrees to Lusztig's quantum PBW root vectors. The possible degrees can be described as lattice points in certain polyhedral cones. In the classical limit, such a degree induces an ℕ-filtration on any finite-dimensional simple $\mathfrak{g}$-module. We prove for type An, Cn, B3, D4 and G2 that a degree can be chosen such that the associated graded modules are defined by monomial ideals, and conjecture that this is true for any $\mathfrak{g}$.
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Stäbler, Axel. "The associated graded module of the test module filtration." Communications in Algebra 49, no. 7 (February 16, 2021): 2775–803. http://dx.doi.org/10.1080/00927872.2021.1882475.
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Vostokov, S., I. Nekrasov, and R. Vostokova. "Lutz filtration as a Galois module." Lobachevskii Journal of Mathematics 37, no. 2 (March 2016): 214–21. http://dx.doi.org/10.1134/s1995080216020153.
Дисертації з теми "Modèle de filtration":
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Massoud, Chadi. "Evaluation de la filtration glomérulaire par IRM." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20037.
Анотація:
Cette étude cherche à évaluer le Débit de la Filtration Glomérulaire (DFG) dans le rein humain par IRM. L'estimation de ce paramètre quantitatif nécessite le suivi de la cinétique intrarénale de Gd après son injection en bolus. Pour atteindre cet objectif, nous avons développé sous IDEA Siemens une séquence SR-FLASH strictement pondérée en T1 capable de suivre en dynamique l'évolution du signal RMN après l'injection d'un bolus de produit de contraste. Cette séquence possède un codage de phase centré permettant de déterminer le contraste au début de la période d'acquisition de l'image. Nous avons également mis en oeuvre une séquence d'inversion IR-FLASH (avec codage de phase centré) permettant la mesure de la relaxation longitudinale en l'absence de produit de contraste, ce paramètre étant indispensable à la conversion de l'intensité du signal en concentration. Sachant que la relation entre l'intensité du signal RMN et la concentration de Gd n'est pas linéaire, nous avons proposé deux méthodes originales et malgré tout rapides et robustes pour convertir le signal RMN en concentration locale de Gd. Ceci nous a permis d'évaluer l'évolution de la concentration dans les deux reins et dans l'aorte au cours des premiers passages du produit. L'ajustement des ces mesures de concentration sur les équations décrivant une modélisation bicompartimentale de la fonction rénale a permis de calculer le DFG de chaque rein dans une population de cinq sujets possédant un fonctionnement rénal normalThis study seeks to assess the Glomerular Filtration Rate (GFR) in the human kidney by MRI. To quantitatively estimate this parameter requires monitoring of the intrarenal kinetics of Gd after its bolus injection. To achieve this goal, we have developed under IDEA Siemens a SR-FLASH T1-weighted MRI sequence which can follow dynamic NMR signal changes after a bolus injection of Gd. This sequence has a centric phase-encoding scheme, and thus the image contrast was determined at the beginning of the acquisition period. Subsequently, we have implemented an IR-FLASH (with centric phase-encoding scheme) sequence to measure the longitudinal relaxation time in the absence of any injection of Gd ; this parameter is required to convert NMR signal intensities into Gd concentrations. knowing that the relation between the NMR signal intensities and the Gd concentrations is not linear, we have proposed two novel methods and yet fast and robust for conversion of the NMR signal intensities into local Gd concentration. This allowed us to estimate the temporal evolution of Gd concentrations in both kidneys and aorta. The fit of these concentrations measurements by a two-compartments model describing the function of the kidney allowed us to calculate the GFR of each kidney in a population of five subjects with normal renal function
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Lefebvre, Xavier. "Etude des modèles de transfert en nanofiltration : application du modèle hybride basé sur les équations de Nernst-Planck étendues par le développement du logiciel de simulation "nanoflux"." Montpellier 2, 2003. http://www.theses.fr/2003MON20082.
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Bornaz, Saloua. "Modèle de variation de la texture du beurre et effet de modifications physiques et chimiques de la composition." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL031N.
Анотація:
Après avoir mis au point une méthode d'identification et de quantification des triglycérides du beurre, un modèle de variation naturelle (saison et terroir) reliant la texture du produit à sa composition a pu être établi. Quatre groupes de triglycérides ont été identifiés comme étant des éléments déterminants de la variation naturelle de la fermeté du beurre. En tenant compte des résultats obtenus, deux procédés de modification de la texture ont été étudiés, procédés compatibles avec la conservation de l'image légale et traditionnelle du beurre: tout d'abord, une technique classique, fondée sur l'application de traitements thermiques à la crème avant barattage a été testée. Un phénomène d'inversion de la réponse au traitement a été mis en évidence, montrant l'existence d'une étroite liaison entre la composition triglycéridique et l'effet relatif d'un traitement thermique sur la texture du produit fini. Le second procédé fait appel à une technique de modification de la composition par la mise en œuvre d'une séparation membranaire. Cette étude constitue une première approche du phénomène de partition sur membrane hydrophobe de particules elles-mêmes hydrophobes. Sur un dispositif à percolation, les résultats montrent l'existence de seuils de coupure différents en fonction du taux de saturation des molécules triglycéridiques. En filtration tangentielle, les essais font apparaitre la superposition d'un phénomène d'adsorption préférentielle et d'un phénomène de filtration. Dans tous les cas, une différenciation des taux de matières grasses solides a été observée entre le perméat et le rétentat
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Labbez, Christophe. "Etude du transport et de la rétention de solutés neutres et ioniques par le modèle DSPM : membranes de nano- et d'ultra-filtration fine." Besançon, 2002. http://www.theses.fr/2002BESA2044.
Анотація:
La modélisation du transport de matière à travers une structure microporeuse chargée constitue une étape indispensable à la compréhension de la sélectivité d'une membrane de nanofiltration. Dans ce travail, un modèle reposant sur l'équation étendue de Nernst-Planck pour décrire le transport et l'équation de Donnan modifiée pour décrire l'exclusion électrique-stérique des espèces est développé. Outre l'analyse théorique des phénomènes de transport, le modèle permet de relier les propriétés électriques et structurales d'une membrane au taux de rejet de solutés. Le rayon de pore (rp) et la charge volumique (X) de membranes ont pu être déduits de la modélisation des taux de rejets de solutés neutres et ioniques. La confrontation des valeurs de X et de rp à celles déduites de mesures indépendantes ne permet pas de conclure définitivement quant à la validité du modèle. Les résultats mettent en évidence un phénomène de régulation de charge intervenant à l'intérieur des pores de la membraneModeling of the matter transport through a charged microporous medium is a necessary step to understand and control the selectivity of a nanofiltration membrane. In this work, a model based on the application of the extended Nernst-Planck equation and the assumption of a modified Donnan equilibrium at both membrane/solution interfaces is developed. Besides the analysis of transport mechanisms, the model allows to relate a membrane's microscopic structural and charge properties to the solute retentions. The effective pore radius (rp) and effective volume charge (X) of nanofiltration membranes could be then determined by fitting the experimental retention of neutral and charged solutes. The comparison of the predicted values of the membrane X and rp with those determined from independent measurements does not allow to conclude definitively on the validity of the model. Results show that a charge regulation phenomenon occurs inside the membrane pores
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Boucquemont, Julie. "Modèles statistiques pour l'étude de la progression de la maladie rénale chronique." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0411/document.
Анотація:
Cette thèse avait pour but d'illustrer l'intérêt de méthodes statistiques avancées lorsqu'on s'in téresse aux associations entre différents facteurs et la progression de la maladie rénale chronique (MRC). Dans un premier temps, une revue de la littérature a été effectuée alin d'identifier les méthodes classiquement utilisées pour étudier les facteurs de progression de la MRC ; leurs limites et des méthodes permettant de mieux prendre en compte ces limites ont été discutées. Notre second travail s'est concentré sur les analyses de données de survie et la prise en compte de la censure par intervalle, qui survient lorsque l'évènement d'intérêt est la progression vers un stade spécifique de la MRC, et le risque compétitif avec le décès. Une comparaison entre des modèles de survie standards et le modêle illness-death pour données censurées par intervalle nous a permis d'illustrer l'impact de la modélisation choisie sur les estimations à la fois des effets des facteurs de risque et des probabilités d'évènements, à partir des données de la cohorte NephroTest. Les autres travaux ont porté sur les analyses de données longitudinales de la fonction rénale. Nous avons illustré l'intérêt du modèle linéaire mixte dans ce contexte et présenté son extension pour la prise en compte de sous-populations de trajectoires de la fonction rénale différentes. Nous avons ainsi identifier cinq classes, dont une avec un déclin très rapide et une autre avec une amélioration de la fonction rénale au cours du temps. Des perspectives de travaux liés à la prédiction permettent enfin de lier les deux types d'analyses présentées dans la thèseThe objective of this thesis was to illustrate the benefit of using advanced statistical methods to study associations between risk factors and chrouic kidney disease (CKD) progression. In a first time, we conducted a literature review of statistical methods used to investigate risk factors of CKD progression, identified important methodological issues, and discussed solutions. In our sec ond work, we focused on survival analyses and issues with interval-censoring, which occurs when the event of interest is the progression to a specifie CKD stage, and competing risk with death. A comparison between standard survival models and the illness-death mode! for interval-censored data allowed us to illustrate the impact of modeling on the estimates of both the effects of risk factors and the probabilities of events, using data from the NephroTest cohort. Other works fo cused on analysis of longitudinal data on renal function. We illustrated the interest of linear mixed mode! in this context and presented its extension to account for sub-populations with different trajectories of renal function. We identified five classes, including one with a strong decline and one with an improvement of renal function over time. Severa! perspectives on predictions bind the two types of analyses presented in this thesis
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Herterich, James George. "Mathematical models in water filtration." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:73036408-fbc5-497a-a99f-b8da3dbca0a5.
Анотація:
Membrane filtration is a simple concept for water purification: water containing particulate contaminants is forced through a semi-permeable membrane that rejects the particulates leaving clean water to flow out. Nevertheless, there are many complex features of membrane filtration, the most important of which is the accumulation of the particulates at the membrane surface. This leads ultimately to fouling of the membrane and a reduction in the efficiency of the process. Concentration polarization is the precursor of fouling, that is, a high concentration of contaminants develops in front of the membrane without the contaminants attaching to each other or the membrane surface. However, several types of acute membrane fouling develop from the layer formed in concentration polarization, including internal fouling, pore blocking and caking. Addressing these and related problems has been at the forefront of membrane research since the process' inception. In this thesis we develop mathematical models of aspects of crossflow and directflow filtration operating at constant flux. We begin by addressing questions related to the initial stages of concentration polarization in crossflow systems. In particular, we study the influence of particulates on the viscosity of the filtrate, and show how the filtration efficiency may be improved by tailoring the wall permeability to reduce the effects of osmosis. We then address the development of membrane fouling and caking in directflow systems: the transmembrane pressure difference, the possibility of elastic deformations during filtration, and the influence of these on the development of fouling and caking are all considered. We show that even small elastic effects can worsen fouling and suggest how the process can be operated to avoid this. We then discuss further opportunities for mathematical modelling in this area.
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Barbounaki, Stavroula. "Modélisation et traitement numérique des impulsions électriques générées par le passage des globules rouges à travers des micropores." Paris 5, 1997. http://www.theses.fr/1997PA05S030.
Анотація:
Pour évaluer la déformabilité érythrocytaire qui est un facteur important du comportement rhéologique du sang au niveau de la microcirculation, il existe plusieurs techniques. Parmi ces techniques, on distingue celle de mesure du temps de transit des globules rouges a travers des micropores. Cette technique de filtration permet d'étudier la variation de la conductance électrique du filtre à travers lequel passent les globules rouges considérés comme particules non conductrices. Afin de pouvoir mieux comprendre ce phénomène, un modèle théorique approprié à été mis au point pour valider la méthode utilisée et interpréter qualitativement et quantitativement les résultats expérimentaux obtenus. Par ailleurs, un nouveau système l'analyseur des impulsions électriques générées par le passage des cellules à travers des micropores a été développé. Ce système, rapide et convivial à l'utilisateur, présente plusieurs possibilités de réglages des paramètres expérimentaux. L'analyse du signal acquis permet l'étude de la forme des impulsions électriques qui portent une information intéressante sur le passage des globules rouges et sur les phénomènes d'entrée et de sortie du pore. De plus, le système offre la possibilité d'étudier par analyse statistique la distribution des cellules vis à vis des paramètres mesures et de détecter les éventuelles sous populations globulaires dont la présence est très importante surtout dans les cas pathologiques. La modélisation théorique aide à définir certains paramètres indispensables à la détection et à l'interprétation de la forme des impulsions obtenues par le nouveau système. Les différentes expériences réalisées permettent d'illustrer les possibilités offertes par le nouveau système et aussi de confronter les valeurs théoriques avec les résultats expérimentaux.
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Aksamit, Anna Natalia. "Temps aléatoires, grossissement de filtration et arbitrages." Thesis, Evry-Val d'Essonne, 2014. http://www.theses.fr/2014EVRY0007/document.
Анотація:
Cette thèse traite des problèmes associés à la théorie de grossissement de filtration. Elle est divisée en deux parties.La première partie est consacrée aux temps aléatoires. On étudie les propriétés des différentes classes de temps aléatoires du point de vue du grossissement de la filtration.La deuxième partie concerne l'étude de la stabilité de condition d'arbitrage sur le grossissement de la filtration. On se concentre sur la condition no unbounded profit with bounded risk. Dans un premier temps, on étudie l'absence d'arbitrage dans le cas de grossissement progressif avec un temps aléatoire. Puis on regarde le grossissement initial avec une variable aléatoire qui vérifie l'hypothèse de JacodThis thesis treats the problems settled in elargement of filtration theory. It consists of two parts.The first part is devoted to random times. We study the properties of different classes of random times from enlargement of filtration point of view.The second part concerns the study of the stability of the non-arbitrage condition under anlargement of filtration. We are mainly interested in no bounded profit with bounded risk condition. We study absence of arbitrage in the case progressive enlargement up to random time. Then we look at the case of initial enlargement with random variable satisfying Jacod's hypothesis
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Frappart, Matthieu. "Traitement d'effluents modèles de l'industrie laitière par filtration dynamique." Compiègne, 2006. http://www.theses.fr/2006COMP1651.
Анотація:
Dans un contexte environnemental, l'industrie laitière se doit de trouver de nouvelles solutions pour traiter ces eaux de procédés qui, bien que non toxiques, ont un fort pouvoir polluant du fait des pertes en matière première (lactose, protéines du lait). Les procédés membranaires sont bien adaptés à ce type d'application. Nous avons effectué des études en nanofiltration et osmose inverse afin de produire une eau réutilisable au sein même de l'usine ou qui puisse être rejetée dans le milieu naturel suivant des normes de rejets strictes. Ces études, réalisées sur des systèmes vibrants et rotatifs évitant le colmatage des membranes et donc maintenant leurs performances en termes de flux et de rétentions, ont permis, en nanofiltration, d'obtenir une eau rejetable, alors que les systèmes classiques de filtration tangentielle ne le permettent pas, et d'atteindre, en osmose inverse, des caractéristiques spécifiques de réutilisation (eau de chaudière par exemple)Ln an environmental context, the dairy industry must find new solutions to treat this process waters which, although not toxic, have a strong polluting capacity because of the raw material losses (lactose, milk proteins). The membrane processes are weIl adapted to this type of application. Studies were carried out in nanofiltration and reverse osmosis in order to produce a reusable water or water which can be rejected into the natural environment according to rejection standards. These studies, carried out on vibrating and rotating systems avoiding the fouling of membranes and thus maintaining their performances in terms of fluxes and retentions, have permitted, in nanofiltration, to obtain a rejectable water, whereas the classical crossflow systems do not allow it, and to reach, in reverse osmosis, specific characteristics of reuse (boiler feed water for example)
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Mahnic̆-Kalamiza, Samo. "Effects of electrical and thermal pre-treatment on mass transport in biological tissue." Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2247/document.
Анотація:
Le champ électrique d'une puissance suffisante peut provoquer une augmentation de conductivité et perméabilité de la membrane cellulaire. L'effet est connu comme l'électroporation, attribuée à la création de voies aqueuses dans la membrane. Quantifier le transport de la matière dans le cadre d'électroporation est un objectif important. Comprendre ces processus a des ramifications dans l’extraction du jus ou l’extraction sélective des composés de cellules végétales, l'amélioration de l'administration de médicaments, et des solutions aux défis environnementaux. Il y a un manque de modèles qui pourraient être utilisés pour modéliser le transport de la matière dans les structures complexes (tissus biologiques) par rapport à l'électroporation. Cette thèse présente une description mathématique théorique (un modèle) pour étudier le transport de la matière et le transfert de la chaleur dans tissu traité par l’électroporation. Le modèle a été développé en utilisant les lois de conservation et de transport et permet le couplage des effets de l'électroporation sur la membrane des cellules individuelles au transport de la matière ou la chaleur dans le tissu. Une solution analytique a été trouvée par une simplification, mais le modèle peut être étendu avec des dépendances fonctionnelles supplémentaires et résolu numériquement. La thèse comprend cinq articles sur l'électroporation dans l'industrie alimentaire, la création de modèle pour le problème de diffusion, la traduction du modèle au problème lié à l’expression de jus, validation du modèle, ainsi que des suggestions pour une élaboration future du modèle. Un chapitre supplémentaire est dédié au transfert de la chaleur dans tissuAn electric field of sufficient strength can cause an increase of conductivity and permeability of cell membrane. Effect is known as electroporation and is attributed to creation of aqueous pathways in the membrane. Quantifying mass transport in connection with electroporation of biological tissues is an important goal. The ability to fully comprehend transport processes has ramifications in improved juice extraction and improved selective extraction of compounds from plant cells, improved drug delivery, and solutions to environmental challenges. While electroporation is intensively investigated, there is a lack of models that can be used to model mass transport in complex structures such as biological tissues with relation to electroporation. This thesis presents an attempt at constructing a theoretical mathematical description – a model, for studying mass (and heat) transfer in electroporated tissue. The model was developed employing conservation and transport laws and enables coupling effects of electroporation to the membrane of individual cells with the resulting mass transport or heat transfer in tissue. An analytical solution has been found though the model can be extended with additional dependencies to account for the phenomenon of electroporation, and solved numerically. Thesis comprises five peer-reviewed papers describing electroporation in the food industry, model creation for the problem of diffusion, translation of the model to the mathematically-related case of juice expression, model validation, as well as suggestions for possible future development, extension, and generalization. An additional chapter is dedicated to transfer of heat in tissue
Книги з теми "Modèle de filtration":
1
Huishi, Li. Zariskian filtrations. Dordrecht: Kluwer Academic Publishers, 1996.
2
Konovalov, A. N. Problems of multiphase fluid filtration. Singapore: World Scientific, 1994.
3
Mazo, Aleksandr, and Konstantin Potashev. The superelements. Modeling of oil fields development. ru: INFRA-M Academic Publishing LLC., 2020. http://dx.doi.org/10.12737/1043236.
Анотація:
This monograph presents the basics of super-element modeling method of two-phase fluid flows occurring during the development of oil reservoir. The simulation is performed in two stages to reduce the spatial and temporal scales of the studied processes. In the first stage of modeling of development of oil deposits built long-term (for decades) the model of the global dynamics of the flooding on the super-element computational grid with a step equal to the average distance between wells (200-500 m). Local filtration flow, caused by the action of geological and technical methods of stimulation, are modeled in the second stage using a special mathematical models using computational grids with high resolution detail for the space of from 0.1 to 10 m and time — from 102 to 105 C.
The results of application of the presented models to the solution of practical tasks of development of oil reservoir. Special attention is paid to the issue of value transfer in filtration-capacitive properties of the reservoir, with a detailed grid of the geological model on the larger grid reservoir models.
Designed for professionals in the field of mathematical and numerical modeling of fluid flows occurring during the development of oil fields and using traditional commercial software packages, as well as developing their own software. May be of interest to undergraduate and graduate students studying in areas such as "Mechanics and mathematical modeling", "Applied mathematics", "Oil and gas".
4
Oja, Marja. Pressure filtration of mineral slurries: Modelling and particle shape characterization. Lappeenranta, Finland: Lappeenranta University of Technology, 1996.
5
Wojciechowska, Krystyna. Analiza, modelowanie i symulacja procesu filtracji wody dla celów projektowania i eksploatacji filtrów. Gliwice: Wydawn. Politechniki Śląskiej, 1999.
6
N, Monakhov V., ред. Matematicheskie modeli filʹtrat͡s︡ionnykh prot͡s︡essov: Sbornik nauchnykh trudov. Novosibirsk: Akademii͡a︡ nauk SSSR, Sibirskoe otd-nie, In-t gidrodinamiki im. M.A. Lavrentʹeva, 1991.
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Nikiforov, A. I., та S. F. Korotkov. Voprosy matematicheskogo modelirovanii︠a︡ prot︠s︡essov filʹtrat︠s︡ii i rat︠s︡ionalʹnoĭ razrabotki nefti︠a︡nykh mestorozhdeniĭ. Kazanʹ: Akademii︠a︡ nauk SSSR, Kazanskiĭ filial, Kazanskiĭ fiziko-tekhnicheskiĭ in-t, 1989.
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Molokovich, I︠U︡ M. Neravnovesnai︠a︡ filʹtrat︠s︡ii︠a︡ i eë primenenie v neftepromyslovoĭ praktike. Moskva: Institut kompʹi︠u︡ternykh issledovaniĭ, 2006.
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Majda, Andrew. Filtering complex turbulent systems. Cambridge: Cambridge University Press, 2012.
10
Beli͡aev, A. I͡U. Usrednenie v zadachakh teorii filʹtrat͡sii. Moskva: Nauka, 2004.
Частини книг з теми "Modèle de filtration":
1
Logan, J. David. "Filtration Models." In Interdisciplinary Applied Mathematics, 113–34. New York, NY: Springer New York, 2001. http://dx.doi.org/10.1007/978-1-4757-3518-5_4.
2
Fuchs, László, and Luigi Salce. "Topology and filtration." In Modules over Non-Noetherian Domains, 273–303. Providence, Rhode Island: American Mathematical Society, 2000. http://dx.doi.org/10.1090/surv/084/08.
3
Spitzenberger, Andy, Katrin Bauer, and Rüdiger Schwarze. "Reactive Cleaning and Active Filtration in Continuous Steel Casting." In Multifunctional Ceramic Filter Systems for Metal Melt Filtration, 427–52. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-40930-1_17.
Анотація:
AbstractBasic fluid dynamic processes of melt filtration have been investigated in order to increase the performance and efficiency of filtration systems in steelmaking, especially for continuous steel casting. Numerical simulations have been performed to investigate the interactions between filter structures and the mean melt flow, the development of endogenous non-metallic inclusion (NMI) populations in the flow, and inclusion removal from the melt. For this purpose, Euler–Lagrange models of the particle-laden flow have been developed. As a major finding, the reactive cleaning process of the melt has been proven to be a very efficient cleaning method. Here, inclusion removal is strongly improved by the lifting action of reactively generated gas bubbles at the NMI surfaces. Details of the reactive cleaning process and the combination of reactive cleaning and active filtration have been investigated, too. The prediction quality of the numerical models with regard to fluid flow and the efficiency of the employed filtration systems have been successfully examined by comparing numerical simulations with the results from experimental investigations in different water model experiments and the steel casting simulator.
4
Werzner, Eric, Miguel A. A. Mendes, Cornelius Demuth, Dimosthenis Trimis, and Subhashis Ray. "Simulation of Fluid Flow, Heat Transfer and Particle Transport Inside Open-Cell Foam Filters for Metal Melt Filtration." In Multifunctional Ceramic Filter Systems for Metal Melt Filtration, 301–33. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-40930-1_13.
Анотація:
AbstractIn order to develop improved filters for metal melt filtration, different physical phenomena that take place during depth filtration of liquid metals need to be well understood. Due to the difficult accessibility of the process, the harsh process conditions and the randomness of the typically employed ceramic foam filters, representative experimental investigations are extremely difficult to perform and often provide only integral quantities or selective information. This chapter presents a numerical model for simulating the depth filtration of liquid metal at the pore-scale, i.e., fully resolving the complex filter geometry, which can also accurately handle the curved filter walls. In the model, the velocity and pressure distribution of the melt flow is obtained by the lattice-Boltzmann method and the temperature field is calculated using the finite volume method, while the transport and filtration of the inclusions are predicted by solving the equation of motion for particles in a Lagrangian reference frame. In order to obtain a consistent representation of the curved filter walls for both particle transport and fluid flow, the Euclidean distance field of the filter structures is employed. By comprehensive parametric studies, the sensitivity of the filtration process with respect to various geometric parameters and process conditions is investigated. Therefore, geometries of conventionally manufactured filters, acquired from 3D μCT scanning, as well as computer-generated filter structures are considered. Their performance is assessed by evaluating various effective properties, such as the viscous and inertial permeability and the filtration coefficient. The numerical predictions allow to draw conclusions with respect to the dominant physical mechanisms and are compared with those from simplified physical models, which are shown to be sufficiently accurate for the pre-screening of filters. On the basis of the detailed results, suggestions for improved filter geometries are made, depending on the considered filtration process. Further, simplified models for the prediction of the effective thermal conductivity of open-cell foams in presence and absence of radiation are presented and validated using the detailed numerical predictions.
5
Daus, Sarah, Lisa Ditscherlein, Daniel Hoppach, and Urs A. Peuker. "Metal Melt Filtration in a Water-Based Model System Using a Semi-automated Pilot Plant: Experimental Methods, Influencing Factors, Models." In Multifunctional Ceramic Filter Systems for Metal Melt Filtration, 275–99. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-40930-1_12.
Анотація:
AbstractEven though ceramic foam filters for metal melt filtration have been used in the casting industry for many decades, the filtration mechanisms have not yet been satisfactorily determined. Due to the opaqueness of the melt and the need for high operating temperatures as well as the complexity of the aluminum casting process, filtration experiments are expensive and a detailed insight into the filtration process is hardly achievable. However, the analysis by means of a model system contributes to an essential understanding of the processes taking place. Metal melt systems are characterized by their high surface tension resulting in poor wettability of the solid surfaces in contact with the liquid melt. Therefore, the model system needs to exhibit both similar flow characteristics and wetting properties as the melt system to obtain reliable results. In this study, water was used as the model liquid and the wetting properties of the solid surfaces have been modified to mimic the characteristic wetting behavior of the melt-filter interface. The influence of filter and particle properties as well as process parameters on the filtration efficiency of ceramic foam filters have been investigated. In order to minimize possible overlapping effects in the determination of individual parameters influencing the separation efficiency, care was taken to vary only one parameter, so that the filtration is only dependent on one variable. Besides water-based filtration experiments, it is also possible to have a closer look on interaction forces between inclusion particles and the filter wall and how a higher filtration efficiency can be achieved. Here, too, a water-based model system is beneficial due to the same issues of available devices and costs.
6
Mochizuki, Takuro. "Preliminary for Relative Monodromy Filtrations." In Mixed Twistor D-modules, 143–67. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-10088-3_6.
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Halle, Lars Halvard, and Johannes Nicaise. "The Base Change Conductor and Edixhoven’s Filtration." In Néron Models and Base Change, 89–105. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-26638-1_6.
8
Rõõm, Rein, and Aarne Männik. "Acoustic Filtration in Pressure-Coordinate Models." In IUTAM Symposium on Advances in Mathematical Modelling of Atmosphere and Ocean Dynamics, 221–26. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0792-4_29.
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Bruguieres, Alain. "Filtration de Harder-Narasimhan et Stratification de Shatz." In Module Des Fibrés Stables Sur Les Courbes Algébriques, 81–104. Boston, MA: Birkhäuser Boston, 1985. http://dx.doi.org/10.1007/978-1-4684-7603-3_4.
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Dobrovidov, Alexander V. "Stable Nonparametric Signal Filtration in Nonlinear Models." In Springer Proceedings in Mathematics & Statistics, 61–74. New York, NY: Springer New York, 2014. http://dx.doi.org/10.1007/978-1-4939-0569-0_7.
Тези доповідей конференцій з теми "Modèle de filtration":
1
Sztandera, Adrian, and Roman Kaszynski. "Multitasking Filtration Network." In 2018 23rd International Conference on Methods & Models in Automation & Robotics (MMAR). IEEE, 2018. http://dx.doi.org/10.1109/mmar.2018.8486106.
2
Smith, Karl J. P., Joshua Winans, and James McGrath. "Ultrathin Membrane Fouling Mechanism Transitions in Dead-End Filtration of Protein." In ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icnmm2016-7989.
Анотація:
Ultrathin membranes will likely see great utility in future membrane-based separations, but key aspects of the performance of these membranes, especially when they are used to filter protein, remain poorly understood. In this work we perform protein filtrations using new nanoporous silicon nitride (NPN) membranes. Several concentrations of protein are filtered using dead end filtration in a benchtop centrifuge, and we track fouling based on the amount of filtrate passed over time. A modification of the classic fouling model that includes the effects of using a centrifuge and allow for the visualization of a transition between pore constriction and cake filtration demonstrate that for a range of protein concentrations, cake filtration supersedes pore constriction after ∼30 seconds at 690 g.
3
Jie, Wang, Zahng Yan, and He Yu-qian. "Effects of Module Configuration on Hollow Fiber Filtration Performance." In 2009 International Conference on Energy and Environment Technology. IEEE, 2009. http://dx.doi.org/10.1109/iceet.2009.538.
4
Shen, C., H. T. M. Pham, and P. M. Sarro. "Nano particle filtration module for lab-on-a-chip devices." In 2010 IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS). IEEE, 2010. http://dx.doi.org/10.1109/memsys.2010.5442394.
5
Kang, T. G., K. T. Park, and S. U. Kim. "A Tubular Cross-Flow Filtration Module Based on Chaotic Advection." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-24471.
Анотація:
We propose a tubular membrane module with embedded three-dimensional structures which is efficient in a wide range of operating conditions (covering both laminar and turbulent flows). Thin plates with barriers are inserted periodically in the circular channel geometry, leading to chaotic advection in a spatially periodic channel flow. Using a numerical scheme combining a particle-tracking and the finite element method, the insert geometry is optimized. The performance of the newly proposed membrane module is assessed by experiments. The membrane module with embedded inserts is found to be better in performance than an ordinary tubular membrane module.
6
Dekyvere, Nicolas. "Solutions for Energy Saving Applied on Oil Filtration Modules." In SAE World Congress & Exhibition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2009. http://dx.doi.org/10.4271/2009-01-0347.
7
Nevmerzhitskiy, Yan. "Development of Models for Filtration Simulation in Nonlinear Media." In SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, 2018. http://dx.doi.org/10.2118/194047-stu.
8
Nupehewa, Jinali, Jason Palmer, Piia Suvio, Vesa Koponen, and D. Safonov. "Developing predictive empirical filtration models for advanced tailings handling." In Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings. University of Alberta and Australian Centre for Geomechanics, Edmonton and Perth, 2023. http://dx.doi.org/10.36487/acg_repo/2355_25.
9
Gong, Jian, and Christopher J. Rutland. "Filtration Characteristics of Fuel Neutral Particulates Using a Heterogeneous Multi-Scale Filtration Model." In ASME 2014 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icef2014-5590.
Анотація:
Filtration characteristics of fuel neutral soot particulate were studied using a recently developed heterogeneous multi-scale filtration (HMF) model. In the HMF model, a PDF based pore size distribution and a porosity distribution across the filter wall are introduced to represent the heterogeneous multi-scale porous structure. The HMF model was validated by an exhaust filtration analysis (EFA) system, which was designed for fundamental experimental filtration studies. Various sources of particulates from combustion engines were used in the filtration studies. Some particulates were sampled from a spark ignited direct injection (SIDI) engine fueled with gasoline and ethanol blends. Particulates from a compression ignition engine fueled with diesel for conventional and advanced combustion regimes were investigated as well. The micro-structure of the porous wall was found to be more critical and necessary to simulate filtration of particulates from gasoline and advanced diesel combustion engines than those from conventional diesel combustion engines. The interactions between the porous wall and trapped particulates were investigated. The dynamic filtration characteristics including filtration efficiency, pressure drop and particulate distribution inside the wall are strongly dependent on total particulate volume rather than total particulate number concentration. The change of the filter structure as well as the shape of the particulate size distribution play important roles on particulate penetration.
10
Kohatsu-Higa, Arturo. "Enlargement of Filtrations and Models for Insider Trading." In Proceedings of the Ritsumeikan International Symposium. WORLD SCIENTIFIC, 2004. http://dx.doi.org/10.1142/9789812702852_0008.
Звіти організацій з теми "Modèle de filtration":
1
Beckman, Ivan. Development of alternative air filtration materials and methods of analysis. Engineer Research and Development Center (U.S.), June 2023. http://dx.doi.org/10.21079/11681/47188.
Анотація:
Development of high efficiency particulate air (HEPA) filters demonstrate an effort to mitigate dangerous aerosol hazards at the point of production. The nuclear power industry installs HEPA filters as a final line of containment of hazardous particles. An exploration of analytical, experimental, computational, and machine learning models is presented in this dissertation to advance the science of air filtration technology. This dissertation studies, develops, and analyzes alternative air filtration materials and methods of analysis that optimize filtration efficiency and reduce resistance to air flow. Alternative nonwoven filter materials are considered for use in HEPA filtration. A detailed review of natural and synthetic fibers is presented to compare mechanical, thermal, and chemical properties of fibers to desirable characteristics for air filtration media. Digital replication of air filtration media enables coordination among experimental, analytical, machine learning, and computational air filtration models. The value of using synthetic data to train and evaluate computational and machine learning models is demonstrated through prediction of air filtration performance, and comparison to analytical results. This dissertation concludes with discussion on potential opportunities and future work needed in the continued effort to advance clean air technologies for the mitigation of a global health and safety challenge.
2
Daniel, Richard C., Justin M. Billing, Carolyn A. Burns, Reid A. Peterson, Renee L. Russell, Philip P. Schonewill, and Rick W. Shimskey. Filtration Understanding: FY10 Testing Results and Filtration Model Update. Office of Scientific and Technical Information (OSTI), April 2011. http://dx.doi.org/10.2172/1064600.
3
Lawson. L51597 Feasibility Study of New Technology for Intake Air Filtration. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), June 1989. http://dx.doi.org/10.55274/r0010105.
Анотація:
Inlet air filters are widely used to remove solids and liquid droplets from the ambient air before it enters the compressor of a gas turbine. Clean inlet air provides many advantages: Less corrosion of the compressor and of gas-path hot parts, such as the turbine, decreased compressor fouling, less erosion of the compressor bladeThese in turn prevent deterioration of output and heat rate, and reduce maintenance costs. Compressor fouling is caused by the ingestion of substances that deposit and adhere to blade surfaces, resulting in reduced aerodynamic efficiency and decreased available output. Air contamination could be significantly reduced by the use of more efficient air filtration systems, especially through the reduction of the quantity of smaller particles ingested. The consequent lower loss of output power and decreased cleaning efforts provide lower costs of operation and increased shaft power. This work was composed of three major efforts: 1) A literature search was performed to establish the state of the art for particle removal from gases, particularly by electrostatic precipitation, and to identify the leading vendors of the equipment-considering both experience and technical expertise. 2) Two chosen companies were visited to determine their technical capabilities as they apply to gas turbine inlet air filtration. 3) A representative gas turbine was specified by PRCI as being the equivalent of a GE Model 3002J turbine, with airflow of 91,200 acfm. A specification based upon that airflow was prepared and submitted to the two vendors. Each vendor prepared a proposal for a filter system compliant with the specification. The proposed air filtration equipment is sufficiently different from existing products that it was judged not beneficial to visit manufacturing facilities. Both vendors are reputable suppliers of air filtration equipment. This study is intended to provide definitive information relative to the use of new technology for air inlet filtration on gas turbines in gas pipeline pumping applications.
4
Torres, Modesto. A Novel Predictive Model for Determining Filtration Volume vs. Time for Nano Compounds with Multi-modal Particle Size Distribution. Fort Belvoir, VA: Defense Technical Information Center, November 2013. http://dx.doi.org/10.21236/ada594774.
5
Letellier, Bruce C. Parametric Model of Debris Penetration Through Sump Strainers with Concurrent Filtration and Shedding. Office of Scientific and Technical Information (OSTI), January 2013. http://dx.doi.org/10.2172/1059404.
6
Rahai, Hamid, and Jeremy Bonifacio. Virus Control Aboard a Commuter Bus. Mineta Transporation Institute, October 2023. http://dx.doi.org/10.31979/mti.2023.2248.
Анотація:
A major health concern for public transit users is exposure to viruses from other passengers. This numerical study examines virus containment aboard a public bus with changes to the bus ventilation system. The virus was modeled as a 2.5 µm round solid particle released from the mouth of the infectious passenger at a rate of 21 particles per second at a mouth velocity of 0.278 m/sec. The air delivery to the cabin was two linear ceiling slots spanning the length of the bus delivering 59.38 m3/min (2,097 CFM) of air at a mean velocity of 1 m/sec. Two different axial and vertical linear exhaust slots placed on the side walls were investigated to examine how they affected virus containment and spread to the other parts of the cabin. Simulations were performed for both cases of the bus in transit and at the bus stop when the drop-off door was opened. Results indicate during transit that virus spread was contained to passengers sitting immediately in front of and behind the infectious passenger and the level of virus concentration could merit an increased risk of infection with increased virus residence time. However, augmented air mixing was observed between inside and outside air during the passenger drop-off with viruses spread to the front and back of the bus with reduced concentration and risk of infection. Analytical analyses of the risk of infection using the Wells-Riley equation were performed for the bus ventilation using 100% recirculating air without filtration, and 50% and 100% fresh air ventilation. Results indicate a high risk of infection when recirculating air is used, but the risk is reduced significantly with 50% and 100% fresh air ventilation. These results are critical to informing bus manufacturers, transit agencies, planners, and public transportation users about the potential of virus containment using a new ventilation system.
7
Tipton, Kelley, Brian F. Leas, Emilia Flores, Christopher Jepson, Jaya Aysola, Jordana Cohen, Michael Harhay, et al. Impact of Healthcare Algorithms on Racial and Ethnic Disparities in Health and Healthcare. Agency for Healthcare Research and Quality (AHRQ), December 2023. http://dx.doi.org/10.23970/ahrqepccer268.
Анотація:
Objectives. To examine the evidence on whether and how healthcare algorithms (including algorithm-informed decision tools) exacerbate, perpetuate, or reduce racial and ethnic disparities in access to healthcare, quality of care, and health outcomes, and examine strategies that mitigate racial and ethnic bias in the development and use of algorithms. Data sources. We searched published and grey literature for relevant studies published between January 2011 and February 2023. Based on expert guidance, we determined that earlier articles are unlikely to reflect current algorithms. We also hand-searched reference lists of relevant studies and reviewed suggestions from experts and stakeholders. Review methods. Searches identified 11,500 unique records. Using predefined criteria and dual review, we screened and selected studies to assess one or both Key Questions (KQs): (1) the effect of algorithms on racial and ethnic disparities in health and healthcare outcomes and (2) the effect of strategies or approaches to mitigate racial and ethnic bias in the development, validation, dissemination, and implementation of algorithms. Outcomes of interest included access to healthcare, quality of care, and health outcomes. We assessed studies’ methodologic risk of bias (ROB) using the ROBINS-I tool and piloted an appraisal supplement to assess racial and ethnic equity-related ROB. We completed a narrative synthesis and cataloged study characteristics and outcome data. We also examined four Contextual Questions (CQs) designed to explore the context and capture insights on practical aspects of potential algorithmic bias. CQ 1 examines the problem’s scope within healthcare. CQ 2 describes recently emerging standards and guidance on how racial and ethnic bias can be prevented or mitigated during algorithm development and deployment. CQ 3 explores stakeholder awareness and perspectives about the interaction of algorithms and racial and ethnic disparities in health and healthcare. We addressed these CQs through supplemental literature reviews and conversations with experts and key stakeholders. For CQ 4, we conducted an in-depth analysis of a sample of six algorithms that have not been widely evaluated before in the published literature to better understand how their design and implementation might contribute to disparities. Results. Fifty-eight studies met inclusion criteria, of which three were included for both KQs. One study was a randomized controlled trial, and all others used cohort, pre-post, or modeling approaches. The studies included numerous types of clinical assessments: need for intensive care or high-risk care management; measurement of kidney or lung function; suitability for kidney or lung transplant; risk of cardiovascular disease, stroke, lung cancer, prostate cancer, postpartum depression, or opioid misuse; and warfarin dosing. We found evidence suggesting that algorithms may: (a) reduce disparities (i.e., revised Kidney Allocation System, prostate cancer screening tools); (b) perpetuate or exacerbate disparities (e.g., estimated glomerular filtration rate [eGFR] for kidney function measurement, cardiovascular disease risk assessments); and/or (c) have no effect on racial or ethnic disparities. Algorithms for which mitigation strategies were identified are included in KQ 2. We identified six types of strategies often used to mitigate the potential of algorithms to contribute to disparities: removing an input variable; replacing a variable; adding one or more variables; changing or diversifying the racial and ethnic composition of the patient population used to train or validate a model; creating separate algorithms or thresholds for different populations; and modifying the statistical or analytic techniques used by an algorithm. Most mitigation efforts improved proximal outcomes (e.g., algorithmic calibration) for targeted populations, but it is more challenging to infer or extrapolate effects on longer term outcomes, such as racial and ethnic disparities. The scope of racial and ethnic bias related to algorithms and their application is difficult to quantify, but it clearly extends across the spectrum of medicine. Regulatory, professional, and corporate stakeholders are undertaking numerous efforts to develop standards for algorithms, often emphasizing the need for transparency, accountability, and representativeness. Conclusions. Algorithms have been shown to potentially perpetuate, exacerbate, and sometimes reduce racial and ethnic disparities. Disparities were reduced when race and ethnicity were incorporated into an algorithm to intentionally tackle known racial and ethnic disparities in resource allocation (e.g., kidney transplant allocation) or disparities in care (e.g., prostate cancer screening that historically led to Black men receiving more low-yield biopsies). It is important to note that in such cases the rationale for using race and ethnicity was clearly delineated and did not conflate race and ethnicity with ancestry and/or genetic predisposition. However, when algorithms include race and ethnicity without clear rationale, they may perpetuate the incorrect notion that race is a biologic construct and contribute to disparities. Finally, some algorithms may reduce or perpetuate disparities without containing race and ethnicity as an input. Several modeling studies showed that applying algorithms out of context of original development (e.g., illness severity scores used for crisis standards of care) could perpetuate or exacerbate disparities. On the other hand, algorithms may also reduce disparities by standardizing care and reducing opportunities for implicit bias (e.g., Lung Allocation Score for lung transplantation). Several mitigation strategies have been shown to potentially reduce the contribution of algorithms to racial and ethnic disparities. Results of mitigation efforts are highly context specific, relating to unique combinations of algorithm, clinical condition, population, setting, and outcomes. Important future steps include increasing transparency in algorithm development and implementation, increasing diversity of research and leadership teams, engaging diverse patient and community groups in the development to implementation lifecycle, promoting stakeholder awareness (including patients) of potential algorithmic risk, and investing in further research to assess the real-world effect of algorithms on racial and ethnic disparities before widespread implementation.
8
Yaron, Zvi, Abigail Elizur, Martin Schreibman, and Yonathan Zohar. Advancing Puberty in the Black Carp (Mylopharyngodon piceus) and the Striped Bass (Morone saxatilis). United States Department of Agriculture, January 2000. http://dx.doi.org/10.32747/2000.7695841.bard.
Анотація:
Both the genes and cDNA sequences encoding the b-subunits of black carp LH and FSH were isolated, cloned and sequenced. Sequence analysis of the bcFSHb and LHb5'flanking regions revealed that the promoter region of both genes contains canonical TATA sequences, 30 bp and 17 bp upstream of the transcription start site of FSHb and LHb genes, respectively. In addition, they include several sequences of cis-acting motifs, required for inducible and tissue-specific transcriptional regulation: the gonadotropin-specific element (GSE), GnRH responsive element (GRE), half sites of estrogen and androgen response elements, cAMP response element, and AP1. Several methods have been employed by the Israeli team to purify the recombinant b subunits (EtOH precipitation, gel filtration and lentil lectin). While the final objective to produce pure recombinantGtH subunits has not yet been achieved, we have covered much ground towards this goal. The black carp ovary showed a gradual increase in both mass and oocyte diameter. First postvitellogenic oocytes were found in 5 yr old fish. At this age, the testes already contained spermatozoa. The circulating LH levels increased from 0.5 ng/ml in 4 yr old fish to >5ng/ml in 5 yr old fish. In vivo challenge experiments in black carp showed the initial LH response of the pituitary to GnRH in 4 yr old fish. The response was further augmented in 5 yr old fish. The increase in estradiol level in response to gonadotropic stimulation was first noted in 4 yr old fish but this response was much stronger in the following year. In vivo experiments on the FSHb and LHb mRNA levels in response to GnRH were carried out on common carp as a model for synchronom spawning cyprinids. These experiments showed the prevalence of FSHP in maturing fish while LHP mRNA was prevalent in mature fish, especially in females. The gonadal fat-pad was found to originate from the retroperitoneal mesoderm and not from the genital ridge, thus differing from that reported in certain amphibians This tissue possibly serves as the major source of sex steroids in the immature black carp. However, such a function is taken over by the developing gonads in 4 yr old fish. In the striped bass, we described the ontogeny of the neuro-endocrine parameters along the brain-pituitary-gonadal axis during the first four years of life, throughout gonadal development and the onset of puberty. We also described the responsiveness of the reproductive axis to long-term hormonal manipulations at various stages of gonadal development. Most males reached complete sexual maturity during the first year of life. Puberty was initiated during the third year of life in most females, but this first reproductive cycle did not lead to the acquisition of full sexual maturity. This finding indicates that more than one reproductive cycle may be required before adulthood is reached. Out of the three native GnRHs present in striped bass, only sbGnRH and cGnRH II increased concomitantly with the progress of gonadal development and the onset of puberty. This finding, together with data on GtH synthesis and release, suggests that while sbGnRH and cGnRH II may be involved in the regulation of puberty in striped bass, these neuropeptides are not limiting factors to the onset of puberty. Plasma LH levels remained low in all fish, suggesting that LH plays only a minor role in early gonadal development. This hypothesis was further supported by the finding that experimentally elevated plasma LH levels did not result in the induction of complete ovarian and testicular development. The acquisition of complete puberty in 4 yr old females was associated with a rise in the mRNA levels of all GtH subunit genes, including a 218-fold increase in the mRNA levels of bFSH. mRNA levels of the a and PLH subunits increased only 11- and 8-fold, respectively. Although data on plasma FSH levels are unavailable, the dramatic increase in bFSH mRNA suggests a pivotal role for this hormone in regulating the onset and completion of puberty in striped bass. The hormonal regulation of the onset of puberty and of GtH synthesis and release was studied by chronic administration of testosterone (T) and/or an analog of gonadotropin-releasing hormone (G). Sustained administration of T+G increased the mRNA levels of the PLH subunit to the values characteristic of sexually mature fish, and also increased the plasma levels of LH. However, these changes did not result in the acceleration of sexual maturation. The mRNA levels of the bFSH subunit were slightly stimulated, but remained about 1/10 of the values characteristic of sexually mature fish. It is concluded that the stimulation of FSH gene expression and release does not lead to the acceleration of sexual maturity, and that the failure to sufficiently stimulate the bFSH subunit gene expression may underlie the inability of the treatments to advance sexual maturity. Consequently, FSH is suggested to be the key hormone to the initiation and completion of puberty in striped bass. Future efforts to induce precocious puberty in striped bass should focus on understanding the regulation of FSH synthesis and release and on developing technologies to induce these processes. Definite formulation of hormonal manipulation to advance puberty in the striped bass and the black carp seems to be premature at this stage. However, the project has already yielded a great number of experimental tools of DNA technology, slow-release systems and endocrine information on the process of puberty. These systems and certain protocols have been already utilized successfully to advance maturation in other fish (e.g. grey mullet) and will form a base for further study on fish puberty.