Covalent organic frameworks (COFs) are crystalline and porous materials with bi- or three-dimensional structures built up by connecting their molecular precursors by dynamic covalent bonds. Using ...bottom-up or top-down strategies, bi-dimensional COFs can be obtained as single- or few-layer materials, thus enlarging the family of 2D-materials based on graphene. The main advantage of 2D-materials based on COFs is the fact that they can be chemically designed, thus allowing the formation of
á la carte
materials with well-designed functionalities including their size and features of their pores. The aim of this perspective review is to illustrate in a rational way the current state-of-the-art in the field of COF nanosheet formation using the two general approaches of material nano-structuring. This article reviews a selected collection of samples that illustrates the essential concepts, strategies of preparation following the two general approaches, bottom-up and top-down, and a selection of COF nanolayers showing seminal properties and potential material applications. Finally, we provide some perspectives of this novel research field.
Covalent organic frameworks are crystalline porous materials with 2- or 3-dimensional structures designed modularly from their molecular precursors. Using bottom-up or top-down strategies, single- or few-layer materials can be obtained from them.
Deubiquitinases (DUBs) have fundamental roles in the ubiquitin system through their ability to specifically deconjugate ubiquitin from targeted proteins. The human genome encodes at least 98 DUBs, ...which can be grouped into 6 families, reflecting the need for specificity in their function. The activity of these enzymes affects the turnover rate, activation, recycling and localization of multiple proteins, which in turn is essential for cell homeostasis, protein stability and a wide range of signaling pathways. Consistent with this, altered DUB function has been related to several diseases, including cancer. Thus, multiple DUBs have been classified as oncogenes or tumor suppressors because of their regulatory functions on the activity of other proteins involved in tumor development. Therefore, recent studies have focused on pharmacological intervention on DUB activity as a rationale to search for novel anticancer drugs. This strategy may benefit from our current knowledge of the physiological regulatory mechanisms of these enzymes and the fact that growth of several tumors depends on the normal activity of certain DUBs. Further understanding of these processes may provide answers to multiple remaining questions on DUB functions and lead to the development of DUB-targeting strategies to expand the repertoire of molecular therapies against cancer.
Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are ...generally obtained from cellulose and hemicellulose fractions of biomass
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the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.
This review presents recent advances in the production of biomass derived furfural and 5-hydroxymethylfurfural and in their catalytic conversion into chemicals and fuels
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transfer hydrogenation, photocatalytic and electrocatalytic processes.
Drought‐related tree mortality is now a widespread phenomenon predicted to increase in magnitude with climate change. However, the patterns of which species and trees are most vulnerable to drought, ...and the underlying mechanisms have remained elusive, in part due to the lack of relevant data and difficulty of predicting the location of catastrophic drought years in advance. We used long‐term demographic records and extensive databases of functional traits and distribution patterns to understand the responses of 20–53 species to an extreme drought in a seasonally dry tropical forest in Costa Rica, which occurred during the 2015 El Niño Southern Oscillation event. Overall, species‐specific mortality rates during the drought ranged from 0% to 34%, and varied little as a function of tree size. By contrast, hydraulic safety margins correlated well with probability of mortality among species, while morphological or leaf economics spectrum traits did not. This firmly suggests hydraulic traits as targets for future research.
We took advantage of an exceptionally strong El Niño‐related drought in 2015 to understand the effects on tree mortality in a diverse, seasonally dry tropical forest. Tree mortality rates differed widely among species, ranging from 0% to 34%, and varied little as a function of tree size. We correlated the mean mortality rates by species with a large number of potential explanatory variables and found that hydraulic safety margins correlated well with probability of mortality among species, while soft traits such as wood density did not. This firmly suggests hydraulic traits as targets for future research.
The topology of the composite flow fields reconstructed by linear superposition of a two-dimensional boundary layer flow with an embedded laminar separation bubble and its leading three-dimensional ...global eigenmodes has been studied. According to critical point theory, the basic flow is structurally unstable; it is shown that in the presence of three-dimensional disturbances the degenerate basic flow topology is replaced by a fully three-dimensional pattern, regardless of the amplitude of the superposed linear perturbations. Attention has been focused on the leading stationary eigenmode of the laminar separation bubble discovered by Theofilis et al. (Phil. Trans. R. Soc. Lond. A, vol. 358, 2000, pp. 3229–3324); the composite flow fields have been fully characterized with respect to the generation and evolution of their critical points. The stationary global mode is shown to give rise to a three-dimensional flow field which is equivalent to the classical U-shaped separation, defined by Hornung & Perry (Z. Flugwiss. Weltraumforsch., vol. 8, 1984, pp. 77–87), and induces topologies on the surface streamlines that are resemblant to the characteristic stall cells observed experimentally.
•Technical impacts of PV integration into power systems are reviewed.•The PV characteristics causing the impacts, as well as the level and timeframe at which they occur are identified.•PV penetration ...limits reported in the literature are examined.•The tools and models to analyse the power system impacts are elaborated.
As the number of photovoltaic (PV) installations across the world keeps on increasing, their impacts on power systems are becoming more visible and more severe. In this two-part review, the implications of high PV penetration on the stability and reliability of power systems are comprehensively assessed. This paper, the first of the two, reviews the impacts of PV on the power systems’ voltage, frequency, protection, harmonics, rotor angle stability, and flexibility requirement in detail. Factors contributing to those impacts, as well as the level and timeframe at which they occur, are carefully analysed. Subsequently, the limits of PV penetration observed in the literature are reviewed. To allow the readers to verify these impacts and limits, the tools and models typically employed in power system analysis are also elaborated. The second part of the review then completes the investigation by assessing the existing solutions to the PV integration challenges and suggesting the way forward.
•Progressive collapse fragility of steel MRFs with semi-rigid bolted connections was studied.•Fragility models were derived and accompanied by tornado diagrams for sensitivity evaluation.•Fibre and ...component modelling were combined for pushdown-based capacity assessment.•Sensitivity of progressive collapse to design criteria and column-loss scenarios was quantified.•Different fragility levels were established for different analysis scenarios and code provisions.
Robustness is a key factor in the safety of structures and structural components or sub-assemblies against progressive or disproportionate collapse, the latter term being classically used to indicate a significant disproportion in size between the initial and final damage configurations. Particularly for a steel moment-resisting frame (MRF), the connections play a pivotal role in the robustness and redundancy of the structural system because an alternative load path could be mobilised when/if the beam-column joints have enough capacity to sustain the abnormal extra-loads developed following the loss or notional removal of a support element as consequence of a triggering event.
Although the latter is usually but not exclusively related to terrorist attacks (e.g. faulty construction, uncontrolled gas releases, etc.) and the structural behaviour inherently involves uncertainties in loads and system capacity, progressive collapse has been probabilistically assessed in a few studies, mainly focussed on reinforced concrete structures. In light of this, delving more into probabilistic approaches could be timely, and this paper presents the main results of sensitivity and fragility analysis of steel MRFs featuring top-and-seat with web angle connections, leading to the derivation of both tornado diagrams as well as fragility models. The former ones quantify the progressive collapse sensitivity to design parameters, whilst the latter ones provide the probability of failure as a function of a given intensity measure. Uncertainties in material and geometrical properties of building portfolios were modelled and propagated through Monte Carlo simulation, whereas component-based modelling was integrated with the pushdown methodology for damage analysis of the randomly sampled building realisations. The obtained results show the influence of the studied parameters/random variables on progressive collapse behaviour/fragility and provide insights into the effect of changing the seismic intensity for the design and the column-removal scenario for the assessment of a bolted-angle joint system that has not been probabilistically treated up until now.
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