Showing papers by "Polytechnic University of Valencia published in 2017"

Metal–organic and covalent organic frameworks as single-site catalysts

Abstract: Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.

A chemical genetic roadmap to improved tomato flavor

Abstract: Modern commercial tomato varieties are substantially less flavorful than heirloom varieties. To understand and ultimately correct this deficiency, we quantified flavor-associated chemicals in 398 modern, heirloom, and wild accessions. A subset of these accessions was evaluated in consumer panels, identifying the chemicals that made the most important contributions to flavor and consumer liking. We found that modern commercial varieties contain significantly lower amounts of many of these important flavor chemicals than older varieties. Whole-genome sequencing and a genome-wide association study permitted identification of genetic loci that affect most of the target flavor chemicals, including sugars, acids, and volatiles. Together, these results provide an understanding of the flavor deficiencies in modern commercial varieties and the information necessary for the recovery of good flavor through molecular breeding.

Network Traffic Classifier With Convolutional and Recurrent Neural Networks for Internet of Things

Abstract: A network traffic classifier (NTC) is an important part of current network monitoring systems, being its task to infer the network service that is currently used by a communication flow (e.g., HTTP and SIP). The detection is based on a number of features associated with the communication flow, for example, source and destination ports and bytes transmitted per packet. NTC is important, because much information about a current network flow can be learned and anticipated just by knowing its network service (required latency, traffic volume, and possible duration). This is of particular interest for the management and monitoring of Internet of Things (IoT) networks, where NTC will help to segregate traffic and behavior of heterogeneous devices and services. In this paper, we present a new technique for NTC based on a combination of deep learning models that can be used for IoT traffic. We show that a recurrent neural network (RNN) combined with a convolutional neural network (CNN) provides best detection results. The natural domain for a CNN, which is image processing, has been extended to NTC in an easy and natural way. We show that the proposed method provides better detection results than alternative algorithms without requiring any feature engineering, which is usual when applying other models. A complete study is presented on several architectures that integrate a CNN and an RNN, including the impact of the features chosen and the length of the network flows used for training.

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D

Abstract: Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation–reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene. Encapsulation of single-atom and particulate gold within growing zeolite frameworks generates active catalysts with exceptionally high thermal stability.

Open Ephys: an open-source, plugin-based platform for multichannel electrophysiology.

Abstract: Objective. Closed-loop experiments, in which causal interventions are conditioned on the state of the system under investigation, have become increasingly common in neuroscience. Such experiments can have a high degree of explanatory power, but they require a precise implementation that can be difficult to replicate across laboratories. We sought to overcome this limitation by building open-source software that makes it easier to develop and share algorithms for closed-loop control. Approach. We created the Open Ephys GUI, an open-source platform for multichannel electrophysiology experiments. In addition to the standard 'open-loop' visualization and recording functionality, the GUI also includes modules for delivering feedback in response to events detected in the incoming data stream. Importantly, these modules can be built and shared as plugins, which makes it possible for users to extend the functionality of the GUI through a simple API, without having to understand the inner workings of the entire application. Main results. In combination with low-cost, open-source hardware for amplifying and digitizing neural signals, the GUI has been used for closed-loop experiments that perturb the hippocampal theta rhythm in a phase-specific manner. Significance. The Open Ephys GUI is the first widely used application for multichannel electrophysiology that leverages a plugin-based workflow. We hope that it will lower the barrier to entry for electrophysiologists who wish to incorporate real-time feedback into their research.

Frequently asked questions about chlorophyll fluorescence, the sequel

Abstract: Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121–158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additional Chl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F V /F M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge from different Chl a fluorescence analysis domains, yielding in several cases new insights.

Multipurpose silicon photonics signal processor core

Abstract: Integrated photonics changes the scaling laws of information and communication systems offering architectural choices that combine photonics with electronics to optimize performance, power, footprint, and cost. Application-specific photonic integrated circuits, where particular circuits/chips are designed to optimally perform particular functionalities, require a considerable number of design and fabrication iterations leading to long development times. A different approach inspired by electronic Field Programmable Gate Arrays is the programmable photonic processor, where a common hardware implemented by a two-dimensional photonic waveguide mesh realizes different functionalities through programming. Here, we report the demonstration of such reconfigurable waveguide mesh in silicon. We demonstrate over 20 different functionalities with a simple seven hexagonal cell structure, which can be applied to different fields including communications, chemical and biomedical sensing, signal processing, multiprocessor networks, and quantum information systems. Our work is an important step toward this paradigm.Integrated optical circuits today are typically designed for a few special functionalities and require complex design and development procedures. Here, the authors demonstrate a reconfigurable but simple silicon waveguide mesh with different functionalities.

Combination of Poly(lactic) Acid and Starch for Biodegradable Food Packaging

Abstract: The massive use of synthetic plastics, in particular in the food packaging area, has a great environmental impact, and alternative more ecologic materials are being required. Poly(lactic) acid (PLA) and starch have been extensively studied as potential replacements for non-degradable petrochemical polymers on the basis of their availability, adequate food contact properties and competitive cost. Nevertheless, both polymers exhibit some drawbacks for packaging uses and need to be adapted to the food packaging requirements. Starch, in particular, is very water sensitive and its film properties are heavily dependent on the moisture content, exhibiting relatively low mechanical resistance. PLA films are very brittle and offer low resistance to oxygen permeation. Their combination as blend or multilayer films could provide properties that are more adequate for packaging purposes on the basis of their complementary characteristics. The main characteristics of PLA and starch in terms of not only the barrier and mechanical properties of their films but also of their combinations, by using blending or multilayer strategies, have been analyzed, identifying components or processes that favor the polymer compatibility and the good performance of the combined materials. The properties of some blends/combinations have been discussed in comparison with those of pure polymer films.

Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene.

Abstract: The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

Active sites on graphene-based materials as metal-free catalysts

Abstract: Graphenes and related materials have attracted growing interest as metal-free catalysts The present review is focused on describing the active sites that have been proposed to be responsible for the catalytic activity observed for such systems It will be shown that diverse defects and chemical functionalities on the graphene layers can catalyze reactions, including oxygenated functional groups, carbon vacancies and holes, edge effects, and the presence of dopant elements Besides discrete active sites, the catalytic activity arising from the collective properties of graphenes as materials by adsorbing substrates and reagents and activating them by charge transfer is also commented The review has an introductory general section summarizing the general methodologies that have been used to support the proposed structure of the active sites, including theoretical calculations, comparison of the catalytic activity of graphene samples with different compositions, the use of organic molecules as models of the active centers, and selective masking of functional groups The review is concluded with our view on future developments in the field

On the Use of PLA-PHB Blends for Sustainable Food Packaging Applications

Abstract: Poly(lactic acid) (PLA) is the most used biopolymer for food packaging applications. Several strategies have been made to improve PLA properties for extending its applications in the packaging field. Melt blending approaches are gaining considerable interest since they are easy, cost-effective and readily available processing technologies at the industrial level. With a similar melting temperature and high crystallinity, poly(hydroxybutyrate) (PHB) represents a good candidate to blend with PLA. The ability of PHB to act as a nucleating agent for PLA improves its mechanical resistance and barrier performance. With the dual objective to improve PLAPHB processing performance and to obtain stretchable materials, plasticizers are frequently added. Current trends to enhance PLA-PHB miscibility are focused on the development of composite and nanocomposites. PLA-PHB blends are also interesting for the controlled release of active compounds in the development of active packaging systems. This review explains the most relevant processing aspects of PLA-PHB based blends such as the influence of polymers molecular weight, the PLA-PHB composition as well as the thermal stability. It also summarizes the recent developments in PLA-PHB formulations with an emphasis on their performance with interest in the sustainable food packaging field. PLA-PHB blends shows highly promising perspectives for the replacement of traditional petrochemical based polymers currently used for food packaging.

Are Multidimensional Recurrent Layers Really Necessary for Handwritten Text Recognition

Abstract: Current state-of-the-art approaches to offline Handwritten Text Recognition extensively rely on Multidimensional Long Short-Term Memory networks However, these architectures come with quite an expensive computational cost, and we observe that they extract features visually similar to those of convolutional layers, which are computationally cheaper This suggests that the two-dimensional long-term dependencies, which are potentially modeled by multidimensional recurrent layers, may not be essential to achieve a good recognition accuracy, at least in the lower layers of the architecture In this work, an alternative model is explored that relies only on convolutional and one-dimensional recurrent layers that achieves better or equivalent results than those of the current state-of-the-art architecture, and runs significantly faster In addition, we observe that using random distortions during training as synthetic data augmentation dramatically improves the accuracy of our model Thus, are multidimensional recurrent layers really necessary for Handwritten Text Recognition? Probably not

Silicon Nitride Photonic Integration Platforms for Visible, Near-Infrared and Mid-Infrared Applications

Abstract: Silicon nitride photonics is on the rise owing to the broadband nature of the material, allowing applications of biophotonics, tele/datacom, optical signal processing and sensing, from visible, through near to mid-infrared wavelengths. In this paper, a review of the state of the art of silicon nitride strip waveguide platforms is provided, alongside the experimental results on the development of a versatile 300 nm guiding film height silicon nitride platform.

Energy performance evaluation of R1234yf, R1234ze(E), R600a, R290 and R152a as low-GWP R134a alternatives.

Abstract: In 2014, the Directive 517/2014 was introduced by European Parliament to reduce the use of high-GWP greenhouse gases in the European area in order to limit global climate change in accordance with the objectives marked by the EU Research and Innovation programme Horizon 2020. These restrictions affect the large majority of artificial refrigerants among which R134a is included due to its relatively high GWP100 (1301). The widely used of R134a in the refrigeration and air conditioning fields reveals the need to identify new low-GWP alternatives. Accordingly, in this work five low-GWP R134a possible choices have been tested and compared in an identical refrigerating facility equipped with a hermetic compressor, under the same operating conditions. The refrigerants used in this analysis are: R290 and R600a (HCs); R134a and R152a (HFCs), and finally, R1234yf and R1234ze(E) (HFOs). All of them have been assayed without changes in the facility, that is, as direct drop-ins. The results obtained from the experimental tests are presented and commented in this work from the energetic point of view.

The MOF-driven synthesis of supported palladium clusters with catalytic activity for carbene-mediated chemistry.

Abstract: The development of catalysts able to assist industrially important chemical processes is a topic of high importance. In view of the catalytic capabilities of small metal clusters, research efforts are being focused on the synthesis of novel catalysts bearing such active sites. Here we report a heterogeneous catalyst consisting of Pd4 clusters with mixed-valence 0/+1 oxidation states, stabilized and homogeneously organized within the walls of a metal-organic framework (MOF). The resulting solid catalyst outperforms state-of-the-art metal catalysts in carbene-mediated reactions of diazoacetates, with high yields (>90%) and turnover numbers (up to 100,000). In addition, the MOF-supported Pd4 clusters retain their catalytic activity in repeated batch and flow reactions (>20 cycles). Our findings demonstrate how this synthetic approach may now instruct the future design of heterogeneous catalysts with advantageous reaction capabilities for other important processes.

Conditional Variational Autoencoder for Prediction and Feature Recovery Applied to Intrusion Detection in IoT.

Abstract: The purpose of a Network Intrusion Detection System is to detect intrusive, malicious activities or policy violations in a host or host's network. In current networks, such systems are becoming more important as the number and variety of attacks increase along with the volume and sensitiveness of the information exchanged. This is of particular interest to Internet of Things networks, where an intrusion detection system will be critical as its economic importance continues to grow, making it the focus of future intrusion attacks. In this work, we propose a new network intrusion detection method that is appropriate for an Internet of Things network. The proposed method is based on a conditional variational autoencoder with a specific architecture that integrates the intrusion labels inside the decoder layers. The proposed method is less complex than other unsupervised methods based on a variational autoencoder and it provides better classification results than other familiar classifiers. More important, the method can perform feature reconstruction, that is, it is able to recover missing features from incomplete training datasets. We demonstrate that the reconstruction accuracy is very high, even for categorical features with a high number of distinct values. This work is unique in the network intrusion detection field, presenting the first application of a conditional variational autoencoder and providing the first algorithm to perform feature recovery.

Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory

Abstract: The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV–EeV energy range using the Antares, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within ±500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.

“Ab initio” synthesis of zeolites for preestablished catalytic reactions

Abstract: Unlike homogeneous catalysts that are often designed for particular reactions, zeolites are heterogeneous catalysts that are explored and optimized in a heuristic fashion. We present a methodology for synthesizing active and selective zeolites by using organic structure-directing agents that mimic the transition state (TS) of preestablished reactions to be catalyzed. In these zeolites, the pores and cavities could be generated approaching a molecular-recognition pattern. For disproportionation of toluene and isomerization of ethylbenzene into xylenes, the TSs are larger than the reaction products. Zeolite ITQ-27 showed high disproportionation activity, and ITQ-64 showed high selectivity for the desired para and ortho isomers. For the case of a product and TS of similar size, we synthesized a catalyst, MIT-1, for the isomerization of endo-dicyclopentane into adamantane.

Arabidopsis m6A demethylase activity modulates viral infection of a plant virus and the m6A abundance in its genomic RNAs.

Abstract: N6-methyladenosine (m6A) is an internal, reversible nucleotide modification that constitutes an important regulatory mechanism in RNA biology. Unlike mammals and yeast, no component of the m6A cellular machinery has been described in plants at present. m6A has been identified in the genomic RNAs of diverse mammalian viruses and, additionally, viral infection was found to be modulated by the abundance of m6A in viral RNAs. Here we show that the Arabidopsis thaliana protein atALKBH9B (At2g17970) is a demethylase that removes m6A from single-stranded RNA molecules in vitro. atALKBH9B accumulates in cytoplasmic granules, which colocalize with siRNA bodies and associate with P bodies, suggesting that atALKBH9B m6A demethylase activity could be linked to mRNA silencing and/or mRNA decay processes. Moreover, we identified the presence of m6A in the genomes of two members of the Bromoviridae family, alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV). The demethylation activity of atALKBH9B affected the infectivity of AMV but not of CMV, correlating with the ability of atALKBH9B to interact (or not) with their coat proteins. Suppression of atALKBH9B increased the relative abundance of m6A in the AMV genome, impairing the systemic invasion of the plant, while not having any effect on CMV infection. Our findings suggest that, as recently found in animal viruses, m6A modification may represent a plant regulatory strategy to control cytoplasmic-replicating RNA viruses.

Towards a unified analysis of brain maturation and aging across the entire lifespan: A MRI analysis.

Abstract: Previous literature about the structural characterization of the human cerebellum is related to the context of a specific pathology or focused in a restricted age range. In fact, studies about the cerebellum maturation across the lifespan are scarce and most of them considered the cerebellum as a whole without investigating each lobule. This lack of study can be explained by the lack of both accurate segmentation methods and data availability. Fortunately, during the last years, several cerebellum segmentation methods have been developed and many databases comprising subjects of different ages have been made publically available. This fact opens an opportunity window to obtain a more extensive analysis of the cerebellum maturation and aging. In this study, we have used a recent state-of-the-art cerebellum segmentation method called CERES and a large data set (N = 2,831 images) from healthy controls covering the entire lifespan to provide a model for 12 cerebellum structures (i.e., lobules I-II, III, IV, VI, Crus I, Crus II, VIIB, VIIIA, VIIIB, IX, and X). We found that lobules have generally an evolution that follows a trajectory composed by a fast growth and a slow degeneration having sometimes a plateau for absolute volumes, and a decreasing tendency (faster in early ages) for normalized volumes. Special consideration is dedicated to Crus II, where slow degeneration appears to stabilize in elder ages for absolute volumes, and to lobule X, which does not present any fast growth during childhood in absolute volumes and shows a slow growth for normalized volumes.

A monolithic integrated photonic microwave filter

Abstract: Meeting the increasing demand for capacity in wireless networks requires the harnessing of higher regions in the radiofrequency spectrum, reducing cell size, as well as more compact, agile and power-efficient base stations that are capable of smoothly interfacing the radio and fibre segments. Fully functional microwave photonic chips are promising candidates in attempts to meet these goals. In recent years, many integrated microwave photonic chips have been reported in different technologies. To the best of our knowledge, none has monolithically integrated all the main active and passive optoelectronic components. Here, we report the first demonstration of a tunable microwave photonics filter that is monolithically integrated into an indium phosphide chip. The reconfigurable radiofrequency photonic filter includes all the necessary elements (for example, lasers, modulators and photodetectors), and its response can be tuned by means of control electric currents. This is an important step in demonstrating the feasibility of integrated and programmable microwave photonic processors. A tunable photonic microwave filter is monolithically integrated in an InP chip. The filter includes all of the required elements — a laser, a modulator and a photodetector — and its response can be tuned by controlling the electric currents.

Are Health Videos from Hospitals, Health Organizations, and Active Users Available to Health Consumers? An Analysis of Diabetes Health Video Ranking in YouTube.

Abstract: Health consumers are increasingly using the Internet to search for health information. The existence of overloaded, inaccurate, obsolete, or simply incorrect health information available on the Internet is a serious obstacle for finding relevant and good-quality data that actually helps patients. Search engines of multimedia Internet platforms are thought to help users to find relevant information according to their search. But, is the information recovered by those search engines from quality sources? Is the health information uploaded from reliable sources, such as hospitals and health organizations, easily available to patients? The availability of videos is directly related to the ranking position in YouTube search. The higher the ranking of the information is, the more accessible it is. The aim of this study is to analyze the ranking evolution of diabetes health videos on YouTube in order to discover how videos from reliable channels, such as hospitals and health organizations, are evolving in the ranking. The analysis was done by tracking the ranking of 2372 videos on a daily basis during a 30-day period using 20 diabetes-related queries. Our conclusions are that the current YouTube algorithm favors the presence of reliable videos in upper rank positions in diabetes-related searches.