Temperature-responsive flexibility in metal-organic frameworks (MOFs) appeals to the imagination. The ability to transform upon thermal stimuli while retaining a given crystalline topology is desired ...for specialized sensors and actuators. However, rational design of such shape-memory nanopores is hampered by a lack of knowledge on the nanoscopic interactions governing the observed behavior. Using the prototypical MIL-53(Al) as a starting point, we show that the phase transformation between a narrow-pore and large-pore phase is determined by a delicate balance between dispersion stabilization at low temperatures and entropic effects at higher ones. We present an accurate theoretical framework that allows designing breathing thermo-responsive MOFs, based on many-electron data for the dispersion interactions and density-functional theory entropy contributions. Within an isoreticular series of materials, MIL-53(Al), MIL-53(Al)-FA, DUT-4, DUT-5 and MIL-53(Ga), only MIL-53(Al) and MIL-53(Ga) are proven to switch phases within a realistic temperature range.
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.
The flexibility of three MIL-47(V)-type materials (MIL-47, COMOC-2, and COMOC-3) has been explored by constructing the pressure versus volume and free energy versus volume profiles at various ...temperatures ranging from 100 to 400 K. This is done with first-principles-based force fields using the recently proposed QuickFF parametrization protocol. Specific terms were added for the materials at hand to describe the asymmetry of the one-dimensional vanadium-oxide chain and to account for the flexibility of the organic linkers. The force fields are used in a series of molecular dynamics simulations at fixed volumes but varying unit cell shapes. The three materials show a distinct pressure–volume behavior, which underlines the ability to tune the mechanical properties by varying the linkers toward different applications such as nanosprings, dampers, and shock absorbers.
The free radical suspension polymerization of vinyl chloride is modelled at the elementary reaction level, systematically taking into account diffusion limitations. The resulting kinetic model ...enables the quantitative description of conversion, molecular mass distribution and the formation of structural defects as a function of polymerization time for a wide range of industrially relevant conditions. By deriving population balance equations for structurally distinct radical species the formation of structural defects could be determined. From model calculations it follows that structural defects are predominantly formed at conversions higher than 75% as the rates of the monomolecular reactions responsible for the formation of structural defects are not limited by diffusion and thus become favoured at higher conversion. This threshold value for the monomer conversion is in good agreement with experimental observations.
Simulation is an effective tool to learn or refresh skills and knowledge, but numerous barriers prevent the routine use of simulation. The purpose of this project was to assess the feasibility and ...acceptability of the use of a low-tech simulation kit by the hospital's personnel for overcoming those barriers. A phenomenological qualitative approach using semistructured interviews was conducted with a convenience sample of 5 Certified Registered Nurse Anesthetists (CRNAs) and a student registered nurse anesthetist at a rural community hospital. Additionally, a CRNA served as the facilitator and was interviewed. Alter the data were independently analyzed by 2 individuals, 6 themes emerged. A low-tech simulation was acceptable, although the sense of stress was difficult to replicate. The facilitator found that simulation preparation and execution were easier and less work than expected. A low-tech simulation kit is a viable option for increasing the frequency of simulating anesthesia emergencies and overcoming the barriers that prevent the frequent use of simulation in the clinical setting. Psychological fidelity can be enhanced through innovative methods (flip book containing screenshots of an electrocardiographic monitor, video) to overcome the limitations of a low-tech simulation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
Myalgias are common in patients treated with electroconvulsive therapy (ECT). The mechanism of this side effect is unknown. Two commonly postulated etiologies are the motor activity during the ...convulsion and the fasciculations induced by succinylcholine. If the former phenomenon accounts for most of themyalgias, then the appropriate strategy will be to increase the succinylcholine dose at subsequent treatments. If, on the other hand, the latter phenomenon is more important in inducing myalgias, then the appropriate strategy may be to decrease succinylcholine dosages (on the theory that lower doses result in less fasciculating). On the other hand, if neither of these factors accounts for myalgias, then succinylcholine dose adjustments may be irrelevant to myalgias in the ECT situation. In this study, we assessed the degree of convulsive movements during the seizure as well as strength of fasciculations caused by succinylcholine to see which, if either, correlates with ultimate complaints of myalgias. The results indicated that neither of these factors, nor dose of succinylcholine, correlated with myalgias. We conclude that dose adjustments to succinylcholine are unlikely to affect complaints of myalgias in ECT patients.
This study presents biochemical, histochemical, morphological and immunological evidence that part of the high molecular weight alkaline phosphatase observed in the serum of patients with liver ...disease and particularly in cases of intrahepatic cholestasis or focal-, extrahepatic obstruction originates from the liver plasma membrane. The high molecular weight protein alkaline phosphatase complex contains several plasma membrane enzymes and behaves like a plasma membrane fragment after isopycnic density gradient ultracentrifugation in sucrose, cesium chloride and metrizamide. Electron microscopic examination revealed a triple-layered vesicle which retained alkaline phosphatase activity. Incubation of human liver cells with anti-serum against purified high molecular weight multienzyme complex resulted in fixation of antibodies on the plasma membrane as shown by positive plasma membrane fluorescence. These plasma membrane fragments in the serum are not of biliary origin.
We compared three current methods (immunoinhibition, "Isomune-CK" immunoprecipitation, and the Tandem-E CKMB II immunoenzymometric assay) for determination of creatine kinase (CK; EC 2.7.3.2) ...isoenzyme MB in serum. Although results inter-correlated well, the immunoinhibition assay gave higher activity values. Atypical CK forms did not interfere with the immunoprecipitation and immunoenzymometric methods. In acute myocardial infarction the catalytic properties of CK decreased with the enzyme's age, as reflected by a steady increase in activation energy of the catalyzed reaction. In septicemia patients with very low CK and CK-MB catalytic activity, mean CK-MB mass concentration exceeded the upper reference limit, suggesting an increased rate of loss of activity concentration in these patients' sera. Because of the assay's lesser susceptibility to conformational changes at the active site of the enzyme, we suggest that measurement of CK-MB mass concentration is better suited for infarct sizing than measurement of catalytic activity.
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