Metal-organic frameworks are a novel family of chemically diverse materials, which are of interest across engineering, physics, chemistry, biology and medicine-based disciplines. Since the ...development of the field in its current form more than two decades ago, priority has been placed on the synthesis of new structures. However, more recently, a clear trend has emerged in shifting the emphasis from material design to exploring the chemical and physical properties of structures already known. In particular, although such nanoporous materials were traditionally seen as rigid crystalline structures, there is growing evidence that large-scale flexibility, the presence of defects and long-range disorder are not the exception in metal-organic frameworks, but the rule. Here we offer some perspective into how these concepts are perhaps inescapably intertwined, highlight recent advances in our understanding and discuss how a consideration of the interfaces between them may lead to enhancements of the materials' functionalities.
SUMMARY
A large variety of foregut symptoms can occur in patients with gastroesophageal reflux disease (GERD), which can overlap with other disorders such as somatoform disorders and dyspepsia. Due ...to unclear diagnostic situations, these patients are often not adequately treated. The aim of this study was the evaluation of patients with foregut symptoms, referred for possible antireflux surgery, regarding their relationship with GERD and somatization tendencies based on control data from an unselected population. Symptom evaluation and somatization screening were initiated both in volunteers and in patients with foregut symptoms and GERD. Unselected volunteers from a village population were also evaluated by symptom analysis and for somatisation tendency. In addition, patients with foregut symptoms were diagnosed for GERD, and symptom analysis and psychodiagnostic evaluation were performed. There is no major significant difference in the symptom-spectrum in patients with foregut symptoms, whether they have a proven pathologic acid exposure from GERD or not. The probability for the risk of somatization was 5.6% in the unselected population of nonpatient volunteers (n = 267). In patients with foregut symptoms (n = 750), the probability for the presence of somatoform tendencies was approximately 20%, independent whether these patients had a documented GERD or a normal esophageal acid exposure, implicating further diagnostic work-up for the selection of patients for antireflux surgery. There is a remarkable symptom load and variety in patients with GERD, in patients with foregut symptoms, and in an unselected population of volunteers. There is no difference in the risk for somatization between patients with foregut symptoms and those with documented GERD. Therapeutic decision making especially prior to antireflux surgery requires an awareness of mental and emotional challenges.
We performed ab initio calculations of the elastic constants of five flexible metal-organic frameworks (MOFs): MIL-53(Al), MIL-53(Ga), MIL-47, and the square and lozenge structures of DMOF-1. ...Tensorial analysis of the elastic constants reveals a highly anisotropic elastic behavior, some deformation directions exhibiting very low Young's modulus and shear modulus. This anisotropy can reach a 400:1 ratio between the most rigid and weakest directions, in stark contrast to the case of nonflexible MOFs such as MOF-5 and ZIF-8. In addition, we show that flexible MOFs can display extremely large negative linear compressibility. These results uncover the microscopic roots of stimuli-induced structural transitions in flexible MOFs, by linking the local elastic behavior of the material and its multistability.
While all multinational organizations face the challenge of managing tensions between local integration and global responsiveness, they are increasingly required to pursue additional, often ...paradoxical, objectives – such as social and commercial goals. However, we know little about how these tensions at the core of the MNC strategy interact. Based on an inductive qualitative study of four headquarters–subsidiary relationships in a Latin American Multinational Hybrid Organization, we develop a model showing the interplay of multiple tensions and management approaches to address them. This allows us to contribute to research on subsidiary roles, which we found to differ depending on how multiple tensions are addressed. Furthermore, we add to the literature on hybridity in multinational organizations by pointing out how regional differences between units of a single organization unfold. Finally, we provide some practical recommendations for the management of multinational hybrid organizations.
The South Asian monsoon-pollution pump and purifier Lelieveld, J; Bourtsoukidis, E; Brühl, C ...
Science (American Association for the Advancement of Science),
2018-Jul-20, 2018-07-20, 20180720, Letnik:
361, Številka:
6399
Journal Article
Recenzirano
Odprti dostop
Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the ...wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth's surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.
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•An introductory review of the computational chemistry methods commonly used in the field of metal–organic frameworks.•Prediction of crystal structures, geometrical properties and ...large-scale screening of hypothetical MOFs.•Thermal, mechanical and electronic properties of MOFs.•Simulation of adsorption of fluids and fluid mixtures in MOFs.
In this introductory review, we give an overview of the computational chemistry methods commonly used in the field of metal–organic frameworks (MOFs), to describe or predict the structures themselves and characterize their various properties, either at the quantum chemical level or through classical molecular simulation. We discuss the methods for the prediction of crystal structures, geometrical properties and large-scale screening of hypothetical MOFs, as well as their thermal and mechanical properties. A separate section deals with the simulation of adsorption of fluids and fluid mixtures in MOFs.
We examine the relationship between electric vehicle battery chemistry and supply chain disruption vulnerability for four critical minerals: lithium, cobalt, nickel, and manganese. We compare the ...nickel manganese cobalt (NMC) and lithium iron phosphate (LFP) cathode chemistries by (1) mapping the supply chains for these four materials, (2) calculating a vulnerability index for each cathode chemistry for various focal countries and (3) using network flow optimization to bound uncertainties. World supply is currently vulnerable to disruptions in China for both chemistries: 80% 71% to 100% of NMC cathodes and 92% 90% to 93% of LFP cathodes include minerals that pass through China. NMC has additional risks due to concentrations of nickel, cobalt, and manganese in other countries. The combined vulnerability of multiple supply chain stages is substantially larger than at individual steps alone. Our results suggest that reducing risk requires addressing vulnerabilities across the entire battery supply chain.
We report on a bottom-up approach of the selective and precise growth of subnanometer wide straight and chevron-type armchair nanoribbons (GNRs) on a stepped Au(788) surface using different specific ...molecular precursors. This process creates spatially well-aligned GNRs, as characterized by STM. High-resolution direct and inverse photoemission spectroscopy of occupied and unoccupied states allows the determination of the energetic position and momentum dispersion of electronic states revealing the existence of band gaps of several electron volts for straight 7-armchair, 13-armchair, and chevron-type GNRs in the electronic structure.
We provide a general thermodynamic framework for the understanding of guest-induced structural transitions in hybrid organic−inorganic materials. The method is based on the analysis of experimental ...adsorption isotherms. It allows the determination of the free energy differences between host structures involved in guest-induced transitions, especially hard to obtain experimentally. We discuss the general case of adsorption in flexible materials and show how a few key quantities, such as pore volumes and adsorption affinities, entirely determine the phenomenology of adsorption, including the occurrence of structural transitions. On the basis of adsorption thermodynamics, we then propose a taxonomy of guest-induced structural phase transitions and the corresponding isotherms. In particular, we derive generic conditions for observing a double structural transition upon adsorption, often resulting in a two-step isotherm. Finally, we show the wide applicability and the robustness of the model through three case studies of topical hybrid organic−inorganic frameworks: the hysteretic hydrogen adsorption in Co(1,4-benzenedipyrazolate), the guest-dependent gate-opening in Cu(4,4′-bipyridine)(2,5-dihydroxybenzoate)2 and the CO2-induced “breathing” of hybrid material MIL-53.
Much attention has recently been focused on soft porous crystals, a fascinating subclass of metal–organic frameworks that behave in a remarkable stimuli-responsive fashion, presenting structural ...changes of large amplitude in response to guest adsorption, mechanical pressure, or variations in temperature. In this Perspective, we summarize the recently developed thermodynamic and mechanical theoretical models for the understanding of these materials, based on the concepts of adsorption stress and osmotic thermodynamic ensemble. We show how these models provide a coherent picture of adsorption-induced deformation and structural transitions in flexible metal–organic frameworks, all the way from the length scale of the unit cell to that of the full crystal. In particular, we highlight the new perspectives opened by these models, as well as some of the important open questions in the field.
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