Lightness constancy: ratio invariance and luminance profile

The term simultaneous lightness constancy describes the capacity of the visual system to perceive equal reflecting surfaces as having the same lightness despite lying in different illumination fields. In some cases, however, a lightness constancy failure occurs; that is, equal reflecting surfaces appear different in lightness when differently illuminated. An open question is whether the luminance profile of the illumination edges affects simultaneous lightness constancy even when the ratio invariance property of the illumination edges is preserved. To explore this issue, we ran two experiments by using bipartite illumination displays. Both the luminance profile of an illumination edge and the luminance ratio amplitude between the illumination fields were manipulated. Results revealed that the simultaneous lightness constancy increases when the luminance profile of the illumination edge is gradual (rather than sharp) and homogeneous (rather than inhomogeneous), whereas it decreases when the luminance ratio between the illumination fields is enlarged. The results are interpreted according to the layer decomposition schema, stating that the visual system splits the luminance into perceived lightness and apparent illumination components. We suggest that illumination edges having gradual and homogeneous luminance profiles facilitate the luminance decomposition process, whereas wide luminance ratios impede it

Photometric, geometric and perceptual factors in illumination-independent lightness constancy

It has been shown that lightness constancy depends on the articulation of the visual field (Agostini & Galmonte, 1999). However, among researchers there is little agreement about the meaning of “articulation.” Beyond the terminological heterogeneity, an important issue remains: What factors are relevant for the stability of surface color perception? Using stimuli with two fields of illumination, we explore this issue in three experiments. In Experiment 1, we manipulated the number of luminances, the number of reflectances, and the number of surfaces and their spatial relationships; in Experiment 2, we manipulated the luminance range; finally, in Experiment 3 we varied the number of surfaces crossed by the illumination edge. We found that there are two relevant factors in optimizing lightness constancy: (1) the lowest luminance in shadow and (2) the co-presence of patches of equal reflectance in both fields of illumination. The latter effect is larger if these patches strongly belong to each other. We interpret these findings within the albedo hypothesis

Supramolecular and heterosupramolecar chemistry in controlled release and molecular recognition processes

La presente tesis doctoral titulada ¿Supramolecular and heterosupramolecular chemistry in controlled release and molecular recognition processes¿ está centrada en los dos aspectos principales de la química supramolecular que han experimentado un gran auge en los últimos años: el reconocimiento molecular y los procesos de liberación controlada. En particular la primera parte de la tesis se focaliza en el diseño y síntesis de moléculas orgánicas que pueden ser empleados cómo sensores para especies aniónicas y neutras. El paradigma seleccionado para los procesos de reconocimiento molecular fue la aproximación del dosimetro químico. Esta aproximación presenta ventajas con respecto a los otros dos métodos de determinación de aniones (desplazamiento y unidad coordinanteunidad indicadora), cómo, por ejemplo, la posibilidad de determinar los analitos en disolución acuosa. Así se sintetizaron dos sensores selectivos, uno para el anión fluoruro (F-) y el otro para glutatión (GSH). El sensor selectivo para la determinación de F- está basado en un colorante azoico funcionalizado, en su ¿OH fenólico, cómo silileter. Esta molécula presenta una banda de absroción muy intensa centrada a 350 nm que, después de la adición de F- , sufre un efecto hipocrómico significativo y un desplazamiento batocromico ligero (de ca. 10 nm), mientras aparece una nueva banda a 470 nm, determinando un cambio de incoloro a amarillorojo. Para obtener un sensor selectivo para GSH se sintetizó una sonda químico basado en una sal de 2,6-difenilpirilio. Sucesivamente se preparó una disolución de este compuesto en agua/CTAB, que se caracterizaba por un intenso color azul. En este caso, la adición de GSH produce una disminución significativa de la banda del visible, acompañada por la consecuente decoloración. Además la adicón de GSH induce la aparición de Resumen vi una intensa banda de emisión centrada a 485 nm (después de la irradiación a 350 nm). La segunda parte de esta tesis doctoral se basa en el diseño y síntesis de nuevos sistemas híbridos orgánicos-inorgánicos para procesos de liberación controlada en ambiente celular. Estos materiales híbridos se componen en general, de dos unidades: una matriz inorgánica mesoporosa de base silícea, capaz de almacenar moléculas orgánicas (colorantes, farmacos...) y un compuesto orgánico anclado covalentemente a la superficie externa del soporte inorgánico mesoporoso, que actúa cómo puerta molecular. La aplicación de un estímulo externo puede modificar la conformación de la puerta molecular permitiendo o bien impidiendo la difusión de la carga almacenada en los mesoporos hacía el exterior (disolución o citoplasma). El primer sistema sintetizado y estudiado se compone de una matriz inorgánica mesoporosa (MCM-41), cargada con el colorante Ru(bipy)3 2+ y funcionalizada en la superficie con un oligoetilen glicol mediante un grupo ester. La adición de la enzima esterasa determinaba la hidrólisis del grupo ester y la consecuente reducción del tamaño de la puerta molecular, acompañada por la liberación del colorante previamente cargado. Otro sistema de liberación preparado consiste en el uso de la misma matriz MCM-41 nanoscópica y el mismo colorante Ru(bipy)3 2+, pero se funcionalizó la superficie con una puerta molecular fotolabil. La irradiación en el maximo de absorción de la puerta molecular inducía la fotodegradación de la misma y la consecuente liberación del colorante. Un tercer ejemplo de sistema de liberación consiste en una puerta molecular caracterizada por la presencia de dos grupos funcionales hidrolizables con enzimas diferentes: grupos urea y amida. vii El material final, caracterizado por la presencia del mismo esqueleto inorgánico, y cargado con Ru(bipy)3 2+, era capaz de liberar selectivamente cantidades distintas de colorante, dependiendo del enzima empleado. Así se podían conseguir dos tipos de perfiles de liberación: uno muy rápido y poco intenso y otro más lento pero mucho mas intenso. Finalmente se sintetizó un material híbrido siempre basado en la misma matriz de MCM- 41, cargado con rodamina-B y funcionalizado en la superficie con galactooligosacáridos. Con este material se podía conseguir una liberación controlada del colorante selectivamente en células senescentes, debido a que estas sobreexpresan el enzima ß-galactosidasa que es capaz de hidrolizar los galactooligosacáridos.Agostini, A. (2013). Supramolecular and heterosupramolecar chemistry in controlled release and molecular recognition processes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29397TESI

Implementazione di un software CMMS presso Laviosa Chimica Mineraria S.p.A

La presente tesi è focalizzata sullo studio delle necessarie fasi per realizzare una corretta implementazione del software CMMS denominato MIG5®, la creazione di una scomposizione funzionale per l’impianto e la realizzazione di una codifica equipaggiamenti e parti di ricambio. La tesi è stata svolta presso Laviosa Chimica Mineraria S.p.A, azienda leader in Europa nella ricerca e trasformazione di bentonite ed altri minerali di origine argillosa. Nella prima parte sono stati analizzati i processi produttivi e l’organizzazione della manutenzione, nonché le filosofie manutentive TPM ed RCM in modo da effettuare un confronto per rilevare le problematiche che allontanano l’azienda da una corretta gestione. La seconda parte ha riguardato la scomposizione funzionale dell’impianto e la creazione delle codifiche. Successivamente sono state testate le potenzialità del software per comprenderne le reali capacità gestionali. Lo studio si è concluso con la compilazione del database per verificare l’effettiva fruibilità dei dati creati

The perceptual contrast of impossible shadow edges

Luminance ratios along shadow edges remain the same even when they cross reflectance borders. According to Gilchrist (1988, Perception & Psychophysics 43 415 ^ 424) this so-called ratio-invariance property is a crucial factor in the perception of shadows. However, Soranzo and Agostini (2004, Perception 33 1359 ^ 1368) suggested that in some conditions (named `impossible shadows'), a luminance pattern might still be perceived as a shadow even if the ratio-invariance property along its edge is violated. This can occur when an edge is collinear with another edge (contextual edge) which incorporates it, shares the same polarity, and generates a larger ratio. The hypothesis that impossible shadows are actually perceived as shadows is here tested by comparing the perceptual contrast of a luminance edge in the absence of a contextual edge (control condition) to that of both possible shadow edges (where the contextual and mediating edge share the same ratio) and impossible shadow edges (where the ratio of the contextual edge is larger rather than that at the mediating edge). We found that the perceived contrast of luminance edges shrinks in both possible and impossible shadow conditions rather than in the control condition. This evidence supports the hypothesis that a luminance pattern might be perceived as a shadow even when the ratio-invariance property is violated

Photoprotective mechanisms in chlorophyll-binding proteins studied by means of electron paramagnetic spectroscopies

Light is essential for photosynthesis, and hence in supporting life on earth, but all the steps of the light reactions may lead to the formation of dangerous oxidative species. Chlorophyll a, the green heart of oxygenic photosynthesis, is also its main Achilles' heel, due to a high intersystem crossing (ISC) probability that leads to the production of excited triplet state, an efficient singlet oxygen sensitizer. Photosynthetic organisms have consequently developed several photoprotective mechanisms aimed to avoid photo-oxidative stress originated from the excess of absorbed light, that otherwise would ultimately lead to cell death. Photoprotection is pivotal for life on Earth, however a full comprehension of the molecular mechanisms is still lacking for several of the processes that photosynthetic organisms employ. The knowledge of the diverse adaptations of the photoprotective response to the various natural conditions in which photosynthetic organisms have evolved promises to highlight the essential characteristics that an efficient mechanism has to display. This understanding of the key molecular requirements for an efficient photoprotection may be exploited for the design of bio-mimetic molecular systems in the fields of artificial photosynthesis, photodynamic therapies and photocatalysis, to make them more durable in virtue of specifically tailored photoprotective mechanisms. The quickest of the photoprotective processes taking place in natural photosystems relies on the capability of carotenoids to photoprotect the system, either by directly quenching the triplet state of chlorophyll through triplet-triplet energy transfer, or by deactivation of the photosensitized singlet oxygen once it is formed. With the aim of studying this pivotal trait of photosynthetic organisms, in the course of my graduate research I characterized the role of carotenoids in the photoprotection of the two major components of the oxygenic photosynthetic machinery, namely Photosystem I and Photosystem II. Due to the high complexity of the studied samples, consisting of multi-subunit complexes formed by the assembly of Reaction Centers with numerous bound antenna complexes, an Optically Detected Magnetic Resonance (ODMR) approach has been utilized. ODMR, being a double resonance technique, makes possible to disentangle the different triplet state contributions and extract the information regarding the triplet states populated upon illumination in the multi-chromophore complex of interest. A comparative approach, involving either differences in the size of the complexes or mutations, allowed to get insight into the energy transfer pathways and into the differential role that β-carotene and xanthophylls play in the photoprotection of the two photosystems. With the aim to extend the study of natural photoprotective mechanisms and understand them at a molecular level, we started to work on an unusual chlorophyll binding protein, the Water-Soluble Chlorophyll-binding Protein (WSCP). This research has been conduct in the framework of a joint project between the university of Padova and the university of Mainz. WSCP remarkably differs from the other known chlorophyll-binding proteins, being not involved in the photosynthetic process. WSCP has been shown to be an incredibly stable complex, being able to protect its chlorophylls towards photodamage. Interestingly this protein does not contain carotenoids, in contrast to every other known chlorophyll-binding protein. By combining biochemical and spectroscopic methodologies, we discovered a mechanism for the photoprotection of chlorophylls in WSCP completely new in the landscape of photoprotection We demonstrated that the observed resistance of the WSCP-bound chlorophylls to singlet oxygen damage depends on the localization of the phytyls moieties between the chlorophylls forming a tight dimer in WSCP. We were able to propose a photoprotective mechanism based on the capability of the phytyls to limit the singlet oxygen accessibility to the oxidizable sites of the chlorophylls