POMzites: a roadmap for inverse design in metal oxide chemistry

Computationally exploring the space generated by the self‐assembly of known molecular metal oxides and the ability to predict new architectures is a challenging task. As a proof of concept, here, we propose narrowing it down to a new family of all‐inorganic porous materials named POMzites. Structures with new topologies, but aiming for pure inorganic systems, will be targeted initially. POMzites are composed of ring‐shaped tungsten oxide building blocks connected with transition metal linkers forming zero to three dimensional frameworks. Despite POMzites and zeolites having similar structures, the library of POMzites is an order of magnitude smaller than that of zeolites (14 POMzites vs 213 zeolites). The idea proposed in this perspective article is to accelerate the discovery of new POMzite porous frameworks materials using inverse design approaches

Theoretical view on the origin and implications of structural distortions in polyoxometalates

Structural features of polyoxometalates (POMs) —versatile inorganic clusters of academic and technological interest— are discussed in the present article. POMs are, in general, very regular structures presenting a high symmetry in most cases. Distortions are, however, important for some electronic and magnetic properties. We herein discuss some particular geometric features that are crucial for the theoretical treatment and comprehension of well-known experimental phenomena. For instance, we have been able to understand and rationalize the geometrical distortions present in molybdenum POMs. Moreover, we can affirm that these geometrical distortions are caused by a pseudo Jahn Teller effect. In what concerns NMR chemical shifts, we present a discussion on the importance of geometry for the correct description of the signals and the key role played by the interatomic distances. Finally, a study on the adsorption of Keggin clusters on silver surfaces shows how the POM structure looses its regular shape to adapt to that new situation

Design and implementation of low complexity adaptive optical OFDM systems for software-defined transmission in elastic optical networks

Due to the increasing global IP traffic and the exponential growing demand for broadband services, optical networks are experimenting significant changes. Advanced modulation formats are being implemented at the Digital Signal Processing (DSP) level as key enablers for high data rate transmission. Whereas in the network layer, flexi Dense Wavelength-Division Multiplexing (DWDM) grids are being investigated in order to efficiently use the optical spectrum according to the traffic demand. Enabling these capabilities makes high data rate transmission more feasible. Hence, introducing flexibility in the system is one of the main goals of this thesis. Furthermore, minimizing the cost and enhancing the Spectral Efficiency (SE) of the system are two crucial issues to consider in the transceiver design. This dissertation investigates the use of Optical Orthogonal Frequency Division Multiplexing (O-OFDM) based either on the Fast Fourier Transform (FFT) or the Fast Hartley Transform (FHT) and flexi-grid technology to allow high data rate transmission over the fiber. Different cost-effective solutions for Elastic Optical Networks (EON) are provided. On the one hand, Direct Detection (DD) systems are investigated and proposed to cope with present and future traffic demand. After an introduction to the principles of OFDM and its application in optical systems, the main problems of such modulation is introduced. In particular, Peak-to-Average Power Ratio (PAPR) is presented as a limitation in OFDM systems, as well as clipping and quantization noise. Hence, PAPR reduction techniques are proposed to mitigate these impairments. Additionally, Low Complexity (LC) PAPR reduction techniques based on the FHT have also been presented with a simplified DSP. On the other hand, loading schemes have also been introduced in the analyzed system to combat Chromatic Dispersion (CD) when transmitting over the optical link. Moreover, thanks to Bit Loading (BL) and Power Loading (PL), flexible and software-defined transceivers can be implemented maximizing the spectral efficiency by adapting the data rate to the current demand and the actual network conditions. Specifically, OFDM symbols are created by mapping the different subcarriers with different modulation formats according to the channel profile. Experimental validation of the proposed flexible transceivers is also provided in this dissertation. The benefits of including loading capabilities in the design, such as enabling high data rate and software-defined transmission, are highlighted.Degut al creixement del tràfic IP i de la demanda de serveis de banda ampla, les xarxes òptiques estan experimentant canvis significatius. Els formats avançats de modulació, implementats a nivell de processat del senyal digital, habiliten la transmissió a alta velocitat. Mentre que a la capa de xarxa, l'espectre òptic es dividit en ranures flexibles ocupant l'ample de banda necessari segons la demanda de tràfic. La transmissió a alta velocitat és fa més tangible un cop habilitades totes aquestes funcionalitats. D'aquesta manera un dels principals objectius d'aquesta tesis es introduir flexibilitat al sistema. A demés, minimitzar el cost i maximitzar l'eficiència espectral del sistema són també dos aspectes crucials a considerar en el disseny del transmissor i receptor. Aquesta tesis investiga l'ús de la tecnologia Optical Orthogonal Frequency Division Multiplexing (OFDM) basada en la transformada de Fourier (FFT) i la de Hartley (FHT) per tal de dissenyar un sistema flexible i capaç de transmetre a alta velocitat a través de la fibra òptica. Per tant, es proposen diferent solucions de baix cost vàlides per a utilitzar en xarxes òptiques elàstiques. En primer lloc, s'investiguen i es proposen sistemes basats en detecció directa per tal de suportar la present i futura demanda. Després d'una introducció dels principis d' OFDM i la seva aplicació als sistemes òptics, s'introdueixen alguns dels problemes d'aquesta modulació. En particular, es presenten el Peak-to-Average Power Ratio (PAPR) i els sorolls de clipping i de quantizació com a limitació dels sistemes OFDM. S'analitzen tècniques de reducció de PAPR per tal de reduir l'impacte d'aquests impediments. També es proposen tècniques de baixa complexitat per a reduir el PAPR basades en la FHT. Finalment, s'utilitzen algoritmes d'assignació de bits i de potència, Bit Loading (BL) i Power Loading (PL), per tal de combatre la dispersió cromàtica quan es transmet pel canal òptic. Amb la implementació dels algoritmes de BL i PL, es poden dissenyar transmissors i receptors flexibles adaptant la velocitat a la demanda del moment i a les actuals condicions de la xarxa. En particular, els símbols OFDM es creen mapejant cada portadora amb un format de modulació diferent segons el perfil del canal. El sistema és validat experimentalment mostrant les prestacions i els beneficis d'incloure flexibilitat per tal de facilitar la transmissió a alta velocitat i cobrir les necessitats de l'Internet del futurDebido al crecimiento del tráfico IP y de la demanda de servicios de banda ancha, las redes ópticas están experimentando cambios significativos. Los formatos avanzados de modulación, implementados a nivel de procesado de la señal digital, habilitan la transmisión a alta velocidad. Mientras que en la capa de red, el espectro óptico se divide en ranuras flexibles ocupando el ancho de banda necesario según la demanda de tráfico. La transmisión a alta velocidad es más tangible una vez habilitadas todas estas funcionalidades. De este modo uno de los principales objetivos de esta tesis es introducir flexibilidad en el sistema. Además, minimizar el coste y maximizar la eficiencia espectral del sistema son también dos aspectos cruciales a considerar en el diseño del transmisor y receptor. Esta tesis investiga el uso de la tecnologia Optical Orthogonal Frequency Division Multiplexing (OFDM) basada en la transformada de Fourier (FFT) y en la de Hartley (FHT) con tal de diseñar un sistema flexible y capaz de transmitir a alta velocidad a través de la fibra óptica. Por lo tanto, se proponen distintas soluciones de bajo coste válidas para utilizar en redes ópticas elásticas. En primer lugar, se investigan y se proponen sistemas basados en detección directa con tal de soportar la presente y futura demanda. Después de una introducción de los principios de OFDM y su aplicación en los sistemas ópticos, se introduce el principal problema de esta modulación. En particular se presentan el Peak-to-Average Power Ratio (PAPR) y los ruidos de clipping y cuantización como limitaciones de los sistemas OFDM. Se analizan técnicas de reducción de PAPR con tal de reducir el impacto de estos impedimentos. También se proponen técnicas de baja complejidad para reducir el PAPR basadas en la FHT. Finalmente, se utilizan algoritmos de asignación de bits y potencia, Bit Loading (BL) y Power Loading (PL), con tal de combatir la dispersión cromática cuando se transmite por el canal óptico. Con la implementación de los algoritmos de BL y PL, se pueden diseñar transmisores y receptores flexibles adaptando la velocidad a la demanda del momento y a las actuales condiciones de la red. En particular, los símbolos OFDM se crean mapeando cada portadora con un formato de modulaci_on distinto según el perfil del canal. El sistema se valida experimentalmente mostrando las prestaciones y los beneficios de incluir flexibilidad con tal de facilitar la transmisión a alta velocidad y cubrir las necesidades de Internet del futuro

Carotid artery image segmentation

Treballs Finals de Grau d'Enginyeria Informàtica, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2016, Director: Laura Igual MuñozThe main process causing most cardiovascular diseases is atherosclerosis, which is responsible for the thickening of the major arteries walls. Concretely, the intimamedia thickness (IMT) of the carotid artery wall is an early and effective marker of atherosclerosis progression. The measurement of the IMT is directly extracted from the segmentation of two different layers of the carotid artery wall. In this project, we present three fully automated techniques to perform the segmentation of these two layers of the carotid artery wall using B-mode ultrasound images. The segmentation of the carotid artery wall is a challenging problem due to image noise, artefacts and image shape, intensity and resolution variability. One of the developed methods is based on lumen detection. It first detects the lumen region of the carotid artery and then it seeks the both layers using the differences between the intensity values of the image. The other two methods are based on a classification system, considering the image segmentation problem as a classification problem of the image pixels into interior or exterior of the region formed by the two layers. One of them uses the random forest classifier and the other one uses the stacked sequential learning scheme with random forest as a base learner. We validate the proposed techniques using a data set of B-mode images obtained from a clinical institution and we compare its performances

Optimization and evaluation of variability in the programming window of a flash cell with molecular metal-oxide storage

We report a modeling study of a conceptual nonvolatile memory cell based on inorganic molecular metal-oxide clusters as a storage media embedded in the gate dielectric of a MOSFET. For the purpose of this paper, we developed a multiscale simulation framework that enables the evaluation of variability in the programming window of a flash cell with sub-20-nm gate length. Furthermore, we studied the threshold voltage variability due to random dopant fluctuations and fluctuations in the distribution of the molecular clusters in the cell. The simulation framework and the general conclusions of our work are transferrable to flash cells based on alternative molecules used for a storage media

Comparison between bulk and FDSOI POM flash cell: a multiscale simulation study

In this brief, we present a multiscale simulation study of a fully depleted silicon-on-insulator (FDSOI) nonvolatile memory cell based on polyoxometalates (POMs) inorganic molecular clusters used as a storage media embedded in the gate dielectric of flash cells. In particular, we focus our discussion on the threshold voltage variability introduced by random discrete dopants (random dopant fluctuation) and by fluctuations in the distribution of the POM molecules in the storage media (POM fluctuation). To highlight the advantages of the FDSOI POM flash cell, we provide a comparison with an equivalent cell based on conventional (BULK) transistors. The presented simulation framework and methodology is transferrable to flash cells based on alternative molecules used as a storage media

Molecular Based Flash Cell for Low Power Flash Application: Optimization and Variability Evaluation

The field of molecular electronics continues to spur interest in the quest for miniaturization and reduction of operational power of electron devices. Most of the systems described in the literature are based on organic molecules, such as benzene, ferrocene and fullerenes. However, the use of inorganic molecules known as polyoxometalates (POMs) (see Fig.l and Fig.2) could offer several important advantages over the conventional and organic based devices. Our present work shows that POMs are more compatible with existing CMOS processes than organic molecules and they can replace the polysilicon floating gate in contemporary flash cell devices [2]. The interest in POMs for flash cell applications stems from the fact that POMs are highly redox active molecules and that they can also be doped with electronically active heteroatoms [3]. They can undergo multiple reversible reductions/oxidations, which makes them attractive candidates for multi-bit storage in flash memory cells. The molecular charge storage is localised, thus minimising cross-cell capacitive coupling, which arises from charge redistribution on the sides of a poly-Si floating gate (FG) and is one of the most critical issues with flash memories. Although this benefit is presently realised in floating gates by charge-trapping dielectric or by a metallic nano-cluster array, both technologies exhibit large variability. Charge-trap memories suffer variation in trap-density and trap energy and the size and density of nano-clusters is difficult to control. This precludes their ultimate miniaturization. In fact, the concept of using molecules as storage centers has already been demonstrated for organic redox-active molecules [1]. Here, using full 3D simulations, we evaluate correlation between the device performance (in terms of threshold voltage VT) and statistical variability, arising from the random dopant fluctuations (RDF) and POM fluctuations (POMF)

Computational study into the effects of countercations on the [P8W48O184]40– polyoxometalate wheel

Porous metal oxide materials have been obtained from a ring-shaped macrocyclic polyoxometalate (POM) structural building unit, [P8W48O184]40–. This is a tungsten oxide building block with an integrated “pore” of 1 nm in diameter, which, when connected with transition metal linkers, can assemble frameworks across a range of dimensions and which are generally referred to as POMzites. Our investigation proposes to gain a better understanding into the basic chemistry of this POM, specifically local electron densities and locations of countercations within and without the aforementioned pore. Through a rigorous benchmarking process, we discovered that 8 potassium cations, located within the pore, provided us with the most accurate model in terms of mimicking empirical properties to a sufficient degree of accuracy while also requiring a relatively small number of computer cores and hours to successfully complete a calculation. Additionally, we analyzed two other similar POMs from the literature, [As8W48O184]40– and [Se8W48O176]32–, in the hopes of determining whether they could be similarly incorporated into a POMzite network; given their close semblance in terms of local electron densities and interaction with potassium cations, we judge these POMs to be theoretically suitable as POMzite building blocks. Finally, we experimented with substituting different cations into the [P8W48O184]40– pore to observe the effect on pore dimensions and overall reactivity; we observed that the monocationic structures, particularly the Li8[P8W48O184]32– framework, yielded the least polarized structures. This correlates with the literature, validating our methodology for determining general POM characteristics and properties moving forward

First Principle Simulations of Current Flow in Inorganic Molecules: Polyoxometalates (POMs)

In this work we present a simulation study of current flow in inorganic molecular metal oxide clusters known as polyoxometalates (POMs). The simulations are carried out by using combination of the density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. To investigate the current flow in POMs, we investigate two possible ways to place the POM cluster between two gold (Au) electrodes - vertical and horizontal. Our results show that the position of the POM molecule and the contact between the molecule and the Au electrodes determines the current flow. Overall, the vertical configuration of the molecule between the two Au electrodes shows better current flow in comparison to the horizontal configuration. In this work we also establish a link between the underlying electronic structure and transmission spectra and conductance

Synthesis of polyoxometalate clusters using carbohydrates as reducing agents leads to isomer-selection

By using sugars as the reducing agents, we demonstrate that it is possible to control the self-assembly of polyoxomolybdates through selective preparation of a single heteropolyanion isomer. D-(−)-Fructose has been proved to be an effective reducing sugar compared to the chemically similar carbohydrate D-(+)-glucose. The gentle reduction results in favourable formation of the Wells–Dawson type gamma isomer in 6-fold reduced form at room temperature