Knowledge of the thermodynamic potential in terms of the independent variables allows to characterize the macroscopic state of the system. However, in practice, it is difficult to access this ...potential experimentally due to irreversible transitions that occur between equilibrium states. A showcase example of sudden transitions between (meta)stable equilibrium states is observed for soft porous crystals possessing a network with long-range structural order, which can transform between various states upon external stimuli such as pressure, temperature and guest adsorption. Such phase transformations are typically characterized by large volume changes and may be followed experimentally by monitoring the volume change in terms of certain external triggers. Herein, we present a generalized thermodynamic approach to construct the underlying Helmholtz free energy as a function of the state variables that governs the observed behaviour based on microscopic simulations. This concept allows a unique identification of the conditions under which a material becomes flexible.
Quality for a sustainable future Vandenbrande, Willy W.
Total quality management & business excellence,
04/2021, Letnik:
32, Številka:
5-6
Journal Article
Recenzirano
There is a growing number of organisations working on sustainable development and there is no lack of events organised or papers published on the subject. These activities are related to high level ...policies that appeal to political leaders. As far as businesses are concerned the target group mainly consists of large and globally active organisations. Very often small or medium sized enterprises (SMEs) are not involved, although they form the vast majority of companies. Quality management has the methods and the tools to bring sustainability to the SME level, facilitating action and leading to tangible results for the organisation. We present a general framework that allows any SME to take steps in sustainability by using quality management methods. An implementation path is given, related to the current maturity level of the company. This allows the sustainability movement to gain momentum and be spread out much more widely. But as many planetary problems are bringing us dangerously close to tipping points (global warming, mass extinction of species, ...) this may not be enough. A new definition of sustainability is presented that can be used as a starting point for developing quality based economic and social systems.
The methanol-to-olefins process over H-SAPO-34 is characterized by its high shape selectivity toward light olefins. The catalyst is a supramolecular system consisting of nanometer-sized inorganic ...cages, decorated by Brønsted acid sites, in which organic compounds, mostly methylated benzene species, are trapped. These hydrocarbon pool species are essential to catalyze the methanol conversion but may also clog the pores. As such, diffusion of ethene and propene plays an essential role in determining the ultimate product selectivity. Enhanced sampling molecular dynamics simulations based on either force fields or density functional theory are used to determine how molecular factors influence the diffusion of light olefins through the 8-ring windows of H-SAPO-34. Our simulations show that diffusion through the 8-ring in general is a hindered process, corresponding to a hopping event of the diffusing molecule between neighboring cages. The loading of different methanol, alkene, and aromatic species in the cages may substantially slow down or facilitate the diffusion process. The presence of Brønsted acid sites in the 8-ring enhances the diffusion process due to the formation of a favorable π-complex host–guest interaction. Aromatic hydrocarbon pool species severely hinder the diffusion and their spatial distribution in the zeolite crystal may have a significant effect on the product selectivity. Herein, we unveil how molecular factors influence the diffusion of light olefins in a complex environment with confined hydrocarbon pool species, high olefin loadings, and the presence of acid sites by means of enhanced molecular dynamics simulations under operating conditions.
Methods A literature study via MEDLINE and Embase search with keywords 'PRIS', 'lactic acid', 'propofol' and 'sedation'. ...we completed differential diagnosis of lactic acidosis and found that not ...all possible causes (for example, hyperglycemia, ketonemia, pharmacologic confounders as biguanides, epinephrine) were ruled out in most cases.
Atomic partial charges appear in the Coulomb term of many force-field models and can be derived from electronic structure calculations with a myriad of atoms-in-molecules (AIM) methods. More advanced ...models have also been proposed, using the distributed nature of the electron cloud and atomic multipoles. In this work, an electrostatic force field is defined through a concise approximation of the electron density, for which the Coulomb interaction is trivially evaluated. This approximate “pro-density” is expanded in a minimal basis of atom-centered s-type Slater density functions, whose parameters are optimized by minimizing the Kullback–Leibler divergence of the pro-density from a reference electron density, e.g., obtained from an electronic structure calculation. The proposed method, Minimal Basis Iterative Stockholder (MBIS), is a variant of the Hirshfeld AIM method, but it can also be used as a density-fitting technique. An iterative algorithm to refine the pro-density is easily implemented with a linear-scaling computational cost, enabling applications to supramolecular systems. The benefits of the MBIS method are demonstrated with systematic applications to molecular databases and extended models of condensed phases. A comparison to 14 other AIM methods shows its effectiveness when modeling electrostatic interactions. MBIS is also suitable for rescaling atomic polarizabilities in the Tkatchenko–Scheffler scheme for dispersion interactions.
Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate ...frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and extrusion mechanisms under realistic, high-rate deformation conditions. Here, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate dependence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable and reusable impact energy absorbers for challenging new applications.
Hypertrophic obstructive cardiomyopathy remains one of the more common inherited cardiac disorders with often a major impact on quality of life. Even today, most frequently a sternotomy is performed ...to conduct the myectomy. Several minimally invasive procedures, under direct vision or through transmitral access, have been demonstrated to operate on these patients. However, we believe our video-assisted transaortic approach could provide a more precise and complete resection than other minimally invasive approaches because of a clearer visualization of the septum and outflow tract. This could further increase the benefits for these patients and potentially make more frail patients eligible for surgical intervention.
Thermal engineering of metal–organic frameworks for adsorption-based applications is very topical in view of their industrial potential, in particular, since heat management and thermal stability ...have been identified as important obstacles. Hence, a fundamental understanding of the structural and chemical features underpinning their intrinsic thermal properties is highly sought-after. Herein, we investigate the nanoscale behavior of a diverse set of frameworks using molecular simulation techniques and critically compare properties such as thermal conductivity, heat capacity, and thermal expansion with other classes of materials. Furthermore, we propose a hypothetical thermodynamic cycle to estimate the temperature rise associated with adsorption for the most important greenhouse and energy-related gases (CO2 and CH4). This macroscopic response on the heat of adsorption connects the intrinsic thermal properties with the adsorption properties and allows us to evaluate their importance.
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