Dithiocarbamates: new organic catalysts for the photochemical generation of radicals

En la meva tesis doctoral hem pres els anions dithiocarbamat i xantat com a organocatalitzadors per generar radicals sota condicions fotocatalítiques. Aquesta nova classe de catalitzadors ens ha sorprès en utilitzar mecanismes distinctius i complementaris als anteriorment descrits per activar diferents substractes de forma radicalaria. Particularment, l'alta nucleofilitat del nostre catalitzador ditiocarbamat ens ha permès generar radicals intermedis des de (pseudo)halurs d'alquil comercials a través d'un mecanisme tipus SN2. Posteriorment, aquests radicals han sigut acoplats amb enolats de silil èter aconseguint la formació de cetones á-alquilades. La nostra nova metodologia, que funciona en condicions suaus i tolera una gran varietat de grups funcionals, ens ha permès instal·lar substituents que no són possibles d'obtindre amb metodologies aniòniques més clàssiques. A més a més, sota aquestes noves condicions, el procediment permet l'ús d'un nou catalitzador d'amina que posteriorment ha estat utilitzat de forma efectiva per fer de forma enantioselectiva l'alquilació de cetones cícliques.activar una varietat de precursors radicalaris i generar aquests radicals de forma fotocatalítica amb energia fotònica de baixa intensitat. Aquestes noves estratègies catalítiques aporten noves tècniques molt útils al camp de la química orgànica sintètica. En mis estudios de doctorado hemos usado los aniones ditiocarbamato y xantato como organocatalizadores para la generación de radicales en condiciones fotoquímicas. Curiosamente, esta nueva clase de catalizadores podría utilizar mecanismos distintos y complementarios para activar diferentes sustratos hacia la formación de radicales. En particular, la alta nucleofilidad de nuestro catalizador de ditiocarbamato nos permitió generar intermediarios de capa abierta a partir de (pseudo) haluros de alquilo fácilmente disponibles vía SN2. Los radicales resultantes han sido atrapados por silil enol éteres para liberar cetonas á-alquiladas. Las condiciones de reacción suaves del método y la tolerancia del grupo funcional nos permitieron instalar, en la posición á de las cetonas, restos no compatibles con los procesos aniónicos clásicos. Además, las condiciones redox neutrales de este proceso lo hicieron tolerante a un catalizador de amina a base de cinchona, que se utilizó para desarrollar un protocolo efectivo para la alquilación asimétrica de cetonas cíclicas. Por otro lado, la alta donicidad de electrones de los donantes de ditiocarbamato y xantogenato se ha explotado para activar el precursor de radicales activos redox a través de un colector complejo aceptor de donantes de electrones (EDA) catalítico.En conclusión, se ha demostrado que los aniones ditiocarbamato y xantato son una clase versátil de organocatalizadores útiles para activar una variedad de precursores de radicales y generar intermediarios de capa abierta bajo fotoirradiación con fotones de baja energía. Las estrategias catalíticas desarrolladas pueden enriquecer las herramientas disponibles en química orgánica sintética. In my doctoral studies, I have exploited dithiocarbamate and xanthate anions as organocatalysts for the generation of radicals under photochemical conditions. Interestingly, this new class of catalysts could use distinct and complementary mechanisms to activate different substrates towards radical formation. In particular, the high nucleophilicity of our dithiocarbamate catalyst allowed us to generate open-shell intermediates from readily available alkyl (pseudo)halides through an SN2 pathway. The ensuing radicals have been trapped by silyl enol ethers to deliver á-alkylated ketones. The method's mild reaction conditions and functional group tolerance allowed us to install, at the ketones' á-position, moieties not compatible with classical anionic processes. In addition, the redox neutral conditions of this process made it tolerant of a cinchona-based amine catalyst, which was used to develop an effective protocol for the asymmetric alkylation of cyclic ketones. On the other hand, the high electron-donicity of dithiocarbamate and xanthogenate donors have been exploited to activate redox active radical precursor through a catalytic electron donor acceptor (EDA) complex manifold. The radicals generated via the catalytic EDA approach have been exploited in redox-neutral and net-reductive transformations

Detecting single-trial EEG evoked potential using a wavelet domain linear mixed model: application to error potentials classification

Objective. The main goal of this work is to develop a model for multi-sensor signals such as MEG or EEG signals, that accounts for the inter-trial variability, suitable for corresponding binary classification problems. An important constraint is that the model be simple enough to handle small size and unbalanced datasets, as often encountered in BCI type experiments. Approach. The method involves linear mixed effects statistical model, wavelet transform and spatial filtering, and aims at the characterization of localized discriminant features in multi-sensor signals. After discrete wavelet transform and spatial filtering, a projection onto the relevant wavelet and spatial channels subspaces is used for dimension reduction. The projected signals are then decomposed as the sum of a signal of interest (i.e. discriminant) and background noise, using a very simple Gaussian linear mixed model. Main results. Thanks to the simplicity of the model, the corresponding parameter estimation problem is simplified. Robust estimates of class-covariance matrices are obtained from small sample sizes and an effective Bayes plug-in classifier is derived. The approach is applied to the detection of error potentials in multichannel EEG data, in a very unbalanced situation (detection of rare events). Classification results prove the relevance of the proposed approach in such a context. Significance. The combination of linear mixed model, wavelet transform and spatial filtering for EEG classification is, to the best of our knowledge, an original approach, which is proven to be effective. This paper improves on earlier results on similar problems, and the three main ingredients all play an important role

Modeling Merging Galaxies using MINGA - Improving Restricted N-body by Dynamical Friction

Modeling interacting galaxies to reproduce observed systems is still a challenge due to the extended parameter space (among other problems). Orbit and basic galaxy parameters can be tackled by fast simulation techniques like the restricted N-body method, applied in the fundamental work by Toomre & Toomre (1972). This approach allows today for the study of millions of models in a short time. One difficulty for the classical restricted N-body method is the missing orbital decay, not allowing for galaxy mergers. Here we present an extension of the restricted N-body method including dynamical friction. This treatment has been developed by a quantitative comparison with a set of self-consistent merger simulations. By varying the dynamical friction (formalism, strength and direction), we selected the best-fitting parameters for a set of more than 250000 simulations. We show that our treatment reliably reproduces the orbital decay and tidal features of merging disk galaxies for mass ratios up to q=1/3 between host and satellite. We implemented this technique into our genetic algorithm based modeling code MINGA and present first results.Comment: To be published in the proceedings of the "Galactic and Stellar Dynamics 2008" conference. 4 pages, 4 figures, 2 table

High resolution in z-direction: The simulation of disc-bulge-halo galaxies using the particle-mesh code SUPERBOX

SUPERBOX is known as a very efficient particle-mesh code with highly-resolving sub-grids. Nevertheless, the height of a typical galactic disc is small compared to the size of the whole system. Consequently, the numerical resolution in z-direction, i.e. vertically with respect to the plane of the disc, remains poor. Here, we present a new version of SUPERBOX that allows for a considerably higher resolution along z. The improved code is applied to investigate disc heating by the infall of a galaxy satellite. We describe the improvement and communicate our results. As an important application we discuss the disruption of a dwarf galaxy within a disc-bulge-halo galaxy that consists of some 10^6 particles.Comment: Comments: 4 pages, 5 figures, pre-peer reviewed version. In: Galactic and stellar dynamics in the era of high-resolution surveys, Boily C., Combes F., Hensler G., eds., Strasbourg (France), March 2008, in press (Astronomische Nachrichten

La realizzazione della sede del TIFPA

In questa nota è illustrata l'attività svolta durante il primo anno di effettiva operatività del TIFPA allo scopo di realizzare un progetto per la ristrutturazione degli spazi da destinare a sede del Centro, all'interno dell'edificio di proprietà dell'Università degli Studi di Trento che ospita le attività del Dipartimento di Fisica. Vengono descritte le successive fasi di evoluzione del progetto, da quelle iniziali di definizione delle linee guida generali, fino alle attività conclusive di allestimento dei locali e dei laboratori

Il Medioevo tra mito e realtà

Prendendo in considerazione le diverse fasi della storia dell’uomo risulta evidente che ogni periodo ha avuto via via una connotazione talvolta positiva talvolta negativa. A tal proposito, è giusto puntualizzare che tra tutti i periodi storici, quello che ha subito una maggiore mitizzazione e deformazione prospettica, in senso fortemente negativo, è indubbiamente l’epoca medievale. L’idea generale che si ha del Medioevo è quella di un lungo periodo di riempimento della storia, compreso tra la caduta dell’Impero Romano d’Occidente (476 dc) e l’età dell’Umanesimo e del Rinascimento (XIV sec.). Già l’idea stessa del Medioevo come “periodo intermedio”, quindi mobile, confuso e caotico è da considerarsi sbagliata. In effetti, nel corso della storia è impossibile distinguere fasi di movimento e trasformazione, da fasi di pura immobilità. Proprio per questa sua collocazione tra due epoche che, alla luce delle fonti forniteci degli intellettuali dall’epoca moderna in poi, potremmo definire “positivi”, si tende a conferire al Medioevo una condizione di negatività che lo accosta in maniera spontanea al concetto ormai consolidato dei “secoli bui

A Protocol for Continual Explanation of SHAP

Continual Learning trains models on a stream of data, with the aim of learning new information without forgetting previous knowledge. Given the dynamic nature of such environments, explaining the predictions of these models can be challenging. We study the behavior of SHAP values explanations in Continual Learning and propose an evaluation protocol to robustly assess the change of explanations in Class-Incremental scenarios. We observed that, while Replay strategies enforce the stability of SHAP values in feedforward/convolutional models, they are not able to do the same with fully-trained recurrent models. We show that alternative recurrent approaches, like randomized recurrent models, are more effective in keeping the explanations stable over time.Comment: ESANN 2023, 6 pages, added link to cod