A role of constraint in self-organization

In this paper we introduce a neural network model of self-organization. This model uses a variation of Hebb rule for updating its synaptic weights, and surely converges to the equilibrium status. The key point of the convergence is the update rule that constrains the total synaptic weight and this seems to make the model stable. We investigate the role of the constraint and show that it is the constraint that makes the model stable. For analyzing this setting, we propose a simple probabilistic game that models the neural network and the self-organization process. Then, we investigate the characteristics of this game, namely, the probability that the game becomes stable and the number of the steps it takes.Comment: To appear in the Proc. RANDOM'98, Oct. 199

Establishment and calibration of consensus process model for nitrous oxide dynamics in water quality engineering

Forskning i biologisk kvælstoffjernelse på spildevandsrensningsanlæg har historisk fokuseret på at opnå en god udledningskvalitet, mens opmærksom-heden de seneste år er blevet rettet mod energibesparelser og CO2-udslip. Nye processer og driftsforhold, der nedsætter omkostninger og øger energieffekti-viteten for biologisk kvælstoffjernelse implementeres samtidig med at udled-ningskvaliteten fastholdes. Senest er der kommet øget opmærksomhed på di-rekte emissioner af dinitrogenoxid (N2O), også kaldt lattergas, som er et bi-produkt af biologisk kvælstoffjernelse. Lattergas er en drivhusgas med et højt drivhusgaspotentiale og en ozonnedbrydende kemisk forbindelse. Flere bakterielle processer for lattergasproduktion er blevet identificeret ved hjælp af studier af rene kulturer, mens mekanismerne bag lattergasproduktio-nen stadig undersøges. Både heterotrofe denitrificerende bakterier og ammo-niak-oxiderende bakterier producerer lattergas. Men man ved endnu meget lidt om hvilke faktorer, der regulerer lattergasproduktionen. Igangværende forskning inden for procesmodellering forsøger at reproducere eksperimentel-le data med matematiske ligninger og derved strukturere vores forståelse af systemet. Forskellige mekanistiske modeller med forskellige strukturer der beskriver lattergasproduktion har tidligere været foreslået, men der er ingen konsensus imellem forskere. Derfor mangler de eksisterende drivhusgas-emissionsmodeller for hele renseanlægget stadig en komplet biologisk pro-cesmodel, som kan integreres på en måde der giver mulighed for at vurdere lattergasemissioner og indvirkningen af disse på den samlede anlægspræstati-on. Her foreslås en matematisk modelstruktur, der beskriver lattergasproduktio-nen under biologisk kvælstoffjernelse. To autotrofe og en heterotrof biologisk reaktionsvej er koblet sammen med abiotiske processer. Modellens støkiome-tri og reaktionsrater udspringer fra et omfattende litteraturstudie i de mikro-organismers metabolisme, der er involveret i fjernelse af nitrogen. Modellen kan beskrive alle relevante kvælstofoxid- og lattergas-produktionsveje med færre parametre end i tidligere publicerede modeller. I afhandlingen introduceres også et nyt eksperimentelt design baseret på den udviklede model og på eksisterende respirometriske teknikker. Målinger af opløst oxygen og lattergas gjorde det muligt at isolere individuelle processer og estimering af parametre forbundet med iltforbrug (endogen aktivitet, nitrit- og ammonium-oxidation) og lattergasproduktion (bidrag fra NN-, ND- og HD-productionsveje). For at estimere parametre i lattergas modellerne, fremlægges en stringent procedure som et case study. Den kalibrerede model forudsiger dynamikken af kvæfstofoxid- og lattergas-akkumulering ved forskellige niveauer af am-monium-, nitrit- og opløst oxygen i to uafhængige systemer: (a) en beriget ammoniak-oxiderende biomasse og (b) aktiveret slam biomasse. I alt blev ti (a) og sytten (b) parametre identificeret med høj nøjagtighed (variationskoef-ficienter <25%). Den kritiske validering af modeludkastet og de estimerede parameterværdier repræsenterer et nyt og stringent redskab til lattergas mo-delleringsstudier. For første gang rapporteres usikkerheden i forbindelse med parametervurdering fra lattergas-modeller. Det anbefales at tilføje denne fremgangsmetode til best-fit simuleringsprocedurer. Derudover undersøges modellering af konkurrencen om elektroner imellem de heterotrofe processer analogt til strøm-intensiteten gennem modstande i elektriske kredsløb. Mens yderligere validering af modellen er påkrævet, fan-gede fremgangsmåden den elektronkonkurrence, der forekommer når denitri-ficerende bakterier oxiderer fire forskellige kulstofkilder. Samlet set blev en kombination af modellering og forsøg med formålet at stu-dere N2O-dynamik succesfuldt gennemført. Resultaterne er et skridt fremad i udviklingen af en konsensus procesmodel for lattergasemissioner i ingeni-ørmæssige vandkvalitets-processer.Research on biological nitrogen removal (BNR) in wastewater treatment plants (WWTP) has historically focused on achieving good effluent quality, with more recent attention to energy savings and carbon dioxide (CO2) foot-prints. Novel processes and operating conditions are being implemented that enhance cost and energy efficiency in BNR, while maintaining effluent quali-ty. Now, increasing attention is placed on direct emissions of nitrous oxide (N2O) as by-product of BNR; N2O is a greenhouse gas (GHG) with a high warming potential and also an ozone depleting chemical compound. Several N2O production pathways have been identified from pure culture studies, while mechanisms are still being unravelled. Heterotrophic bacteria (HB) and ammonium oxidizing bacteria (AOB) are well known to produce N2O. However, the effect of environmental factors on N2O production is not yet well understood. Current process modelling efforts aim to reproduce ex-perimental data with mathematical equations, structuring our understanding of the system. Various mechanistic models with different structures describ-ing N2O production have been proposed, but no consensus exists between researchers. Hence, the existing plant-wide GHG models still lack a complete biological process model that can be integrated in a methodology that assess-es N2O emissions and their impact on overall plant performance. A mathematical model structure that describes N2O production during biological nitrogen removal is proposed. Two autotrophic and one heterotrophic biological pathways are coupled with abiotic processes. The model stoichiometry and process rates synthesize a comprehensive literature review on the metabolism of microbes involved in nitrogen removal. The proposed model can describe all relevant NO and N2O production pathways with fewer parameters than present in other proposed models. A novel experimental design based on the developed model and on extant respirometric techniques is introduced. Monitoring dissolved oxygen and N2O allowed the isolation of individual processes and the estimation of parameters associated to oxygen consumption (endogenous activity, nitrite and ammonium oxidation) and N2O production (NN, ND and HD pathway contributions). To estimate parameters of the N2O model a rigorous procedure is presented as a case study. The calibrated model predicts the NO and N2O dynamics at varying ammonium, nitrite and dissolved oxygen levels in two independent systems: (a) an AOB-enriched biomass and (b) activated sludge (AS) mixed liquor biomass. A total of ten (a) and seventeen (b) parameters are identified with high accuracy (coefficients of variation < 25%). The critical validation of the model response and the estimated parameter values represent a novel and rigorous tool for N2O modelling studies. For the first time, uncertainty associated with parameter estimation from N2O models is reported, this procedure is recommended to be included with best-fit simulations. Additionally, modelling electron competition in heterotrophic processes is explored via an analogy to current intensity through resistors in electric circuits. While further model validation is required, this approach captured the electron competition during denitrification for four different carbon sources. Overall, a combination of modelling and experimental efforts to study N2O dynamics was successfully implemented. Results represent a step forward in the development of consensus process model for N2O emissions in WQE processes

Dense Wide-Baseline Stereo with Varying Illumination and its Application to Face Recognition

We study the problem of dense wide baseline stereo with varying illumination. We are motivated by the problem of face recognition across pose. Stereo matching allows us to compare face images based on physically valid, dense correspondences. We show that the stereo matching cost provides a very robust measure of the similarity of faces that is insensitive to pose variations. We build on the observation that most illumination insensitive local comparisons require the use of relatively large windows. The size of these windows is affected by foreshortening. If we do not account for this effect, we incur misalignments that are systematic and significant and are exacerbated by wide baseline conditions. We present a general formulation of dense wide baseline stereo with varying illumination and provide two methods to solve them. The first method is based on dynamic programming (DP) and fully accounts for the effect of slant. The second method is based on graph cuts (GC) and fully accounts for the effect of both slant and tilt. The GC method finds a global solution using the unary function from the general formulation and a novel smoothness term that encodes surface orientation. Our experiments show that DP dense wide baseline stereo achieves superior performance compared to existing methods in face recognition across pose. The experiments with the GC method show that accounting for both slant and tilt can improve performance in situations with wide baselines and lighting variation. Our formulation can be applied to other more sophisticated window based image comparison methods for stereo

Patrón de dieta en la población púnica de Can Marines (Ibiza) a través del análisis de isótopos estables (C y N) en colágeno óseo

En este trabajo se presentan los resultados de análisis de isótopos estables del carbono y del nitrógeno en colágeno óseo de humanos del yacimiento Púnico de Can Marines (ss. V-IV aC) de la isla de Ibiza (España). Hasta la fecha hay pocos estudios isotópicos para estas cronologías en el Mediterráneo, presentando este artículo nuevos datos isotópicos al respecto, en concreto de un yacimiento púnico rural del Mediterráneo Occidental. Los resultados muestran una dieta basada en recursos terrestres sin evidencia isotópica del consumo proteico ni de recursos marinos ni de recursos lacustre-fluviales, y además sugieren la presencia de alimentos C4 en la dieta. We report here on the results of carbon and nitrogen stable isotope analysis on bone collagen of humans from the Punic site of Can Marines (V-IVth BC) from the island of Ibiza (Spain). To date, there are few isotopic studies for this period from the Mediterranean. This article reports new isotopic data from a Western Mediterranean Punic rural settlement. The results show a terrestrial based diet with no isotopic evidence of marine or freshwater protein input, and suggest the presence of C4 resources in it

Estudio de la dieta en poblaciones mesolíticas y neolíticas del sur del País Valenciano. Resultados preliminares de análisis de isótopos estables del C y del N

La reconstrucción de la dieta en momentos prehistóricos es siempre una tarea compleja, especialmente cuando se trata de momentos de cambio como lo es la "transición" entre el Mesolítico y el Neolítico. Sin dejar de lado el uso de evidencias indirectas para su reconstrucción cualitativa, actualmente el estudio de la dieta en la Prehistoria encuentra en las técnicas biogeoquímicas, como lo es el análisis de isótopos estables del carbono y del nitrógeno, una herramienta de gran utilidad. La combinación del análisis de estos dos tipos de isótopos estables permite valorar a nivel proteico el peso relativo en la dieta de los alimentos de origen marino o terrestre, y de las plantas C3 o C4, así como el nivel que ocupa un organismo en la cadena trólica. En este estudio preliminar se obtienen e interpretan los valores d13C y d15N de restos óseos humanos y animales de dos yacimientos del sur del País Valenciano: Santa Maira (Castell de Castells, Alacant) y Cova de la Sarsa (Bocairent, Valencia)

Caracterización de materiales del olivo: Cuquillos (Lechín, Lechín de Granada)

Denominación confusa y, sin duda, muy diversificada, con numerosas sinonimias que pueden inducir a errores o a agrupar en esta denominación materiales vegetales muy distintos, unos de aceituna redonda y otros de aceitunas alargadas, todas ellas de pequeñas a muy pequeñas y aptas para aderezo en negro, siendo muy apreciadas como aceitunas de mesa y también para aceite, que es de altísima calidad

Bulk Mediated Surface Diffusion: The Infinite System Case

An analytical soluble model based on a Continuous Time Random Walk (CTRW) scheme for the adsorption-desorption processes at interfaces, called bulk-mediated surface diffusion, is presented. The time evolution of the effective probability distribution width on the surface is calculated and analyzed within an anomalous diffusion framework. The asymptotic behavior for large times shows a sub-diffusive regime for the effective surface diffusion but, depending on the observed range of time, other regimes may be obtained. Montecarlo simulations show excellent agreement with analytical results. As an important byproduct of the indicated approach, we present the evaluation of the time for the first visit to the surface.Comment: 15 pages, 7 figure

Repaso a la evidencia isotópica sobre alimentación en la prehistoria valenciana durante el Mesolítico y el Neolítico

Los análisis de isótopos estables son una herramienta fundamental a la hora de reconstruir la alimentación de poblaciones prehistóricas. Hasta hace poco este tipo de análisis no se había aplicado en nuestra tierra. Sin embargo, desde hace unos años el Este de la Península Ibérica se está convirtiendo en uno de los lugares del Mediterráneo donde se está realizando un mayor número de este tipo de estudios. Este artículo explica el potencial de los análisis isotópicos de carbono y nitrógeno sobre colágeno óseo para reconstruir las pautas alimentarias de poblaciones pasadas. También repasa todos los estudios publicados en tierras valencianas de cronología prehistórica publicados hasta la fecha, y discute el aporte que los yacimientos valencianos hacen a la cuestión sobre el tipo de alimentación existente en el Mesolítico y el Neolítico europeos a nivel isotópico