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This work investigates solute transport due to self-interstitial defects and radiation induced segregation tendencies in dilute ferritic alloys, by computing the transport ...coefficients of each system based on ab initio calculations of binding energies, migration rates, as well as formation and migration vibrational entropies. The implementation of the self-consistent mean field method in the KineCluE code allows for the calculation of transport coefficients extended to arbitrary interaction ranges, crystal structures, and diffusion mechanisms. In addition, the code gives access to the diffusion and dissociation rates of small solute-defect clusters – in this case, vacancy- and dumbbell-solute pairs. The results show that the diffusivity of P, Mn, and Cr solute atoms is dominated by the dumbbell mechanism, that of Cu by vacancies, while the two mechanisms might be in competition for Ni and Si, despite the fact that the corresponding mixed dumbbells are not stable. Systematic positive radiation-induced segregation (RIS) at defect sinks is expected for P and Mn solutes due to dumbbell diffusion, and for Si due mainly to vacancy drag. Vacancy drag is also responsible for Cu and Ni enrichment at sinks below 1085 K. The RIS behavior of Cr is the outcome of a fine balance between enrichment due to the dumbbell diffusion mechanism and depletion due to the vacancy one. Therefore, for dilute Cr concentrations global enrichment occurs below 540 K, and depletion above. This threshold temperature grows with solute concentration. The findings are in qualitative agreement with experimental observations of RIS and clustering phenomena, and confirm that solute-defect kinetic coupling plays an important role in the formation of solute clusters in reactor pressure vessel steels and other alloys.
Endosomal sequestration of lipid-based nanoparticles (LNPs) remains a formidable barrier to delivery. Herein, structure-activity analysis of cholesterol analogues reveals that incorporation of C-24 ...alkyl phytosterols into LNPs (eLNPs) enhances gene transfection and the length of alkyl tail, flexibility of sterol ring and polarity due to -OH group is required to maintain high transfection. Cryo-TEM displays a polyhedral shape for eLNPs compared to spherical LNPs, while x-ray scattering shows little disparity in internal structure. eLNPs exhibit higher cellular uptake and retention, potentially leading to a steady release from the endosomes over time. 3D single-particle tracking shows enhanced intracellular diffusivity of eLNPs relative to LNPs, suggesting eLNP traffic to productive pathways for escape. Our findings show the importance of cholesterol in subcellular transport of LNPs carrying mRNA and emphasize the need for greater insights into surface composition and structural properties of nanoparticles, and their subcellular interactions which enable designs to improve endosomal escape.
Crystal plasticity involves the motion of dislocations under stress. So far, atomistic simulations of this process have predicted Peierls stresses, the stress needed to overcome the crystal ...resistance in the absence of thermal fluctuations, of more than twice the experimental values, a discrepancy best-known in body-centred cubic crystals. Here we show that a large contribution arises from the crystal zero-point vibrations, which ease dislocation motion below typically half the Debye temperature. Using Wigner's quantum transition state theory in atomistic models of crystals, we found a large decrease of the kink-pair formation enthalpy due to the quantization of the crystal vibrational modes. Consequently, the flow stress predicted by Orowan's law is strongly reduced when compared with its classical approximation and in much closer agreement with experiments. This work advocates that quantum mechanics should be accounted for in simulations of materials and not only at very low temperatures or in light-atom systems.
In the last two decades, Fourier Transform Infrared (FTIR) and Raman spectroscopies turn out to be valuable tools, capable of providing fingerprint-type information on the composition and structural ...conformation of specific molecular species. Vibrational spectroscopy's multiple features, namely highly sensitive to changes at the molecular level, noninvasive, nondestructive, reagent-free, and waste-free analysis, illustrate the potential in biomedical field. In light of this, the current work features recent data and major trends in spectroscopic analyses going from in vivo measurements up to ex vivo extracted and processed materials. The ability to offer insights into the structural variations underpinning pathogenesis of diseases could provide a platform for disease diagnosis and therapy effectiveness evaluation as a future standard clinical tool.
The diffusion of defects in crystalline materials
controls macroscopic behaviour of a wide range of processes, including alloying, precipitation, phase transformation and creep
. In real materials, ...intrinsic defects are unavoidably bound to static trapping centres such as impurity atoms, meaning that their diffusion is dominated by de-trapping processes. It is generally believed that de-trapping occurs only by thermal activation. Here, we report the direct observation of the quantum de-trapping of defects below around one-third of the Debye temperature. We successfully monitored the de-trapping and migration of self-interstitial atom clusters, strongly trapped by impurity atoms in tungsten, by triggering de-trapping out of equilibrium at cryogenic temperatures, using high-energy electron irradiation and in situ transmission electron microscopy. The quantum-assisted de-trapping leads to low-temperature diffusion rates orders of magnitude higher than a naive classical estimate suggests. Our analysis shows that this phenomenon is generic to any crystalline material.
•Multi-stage cycles and parallel compression are included in two-stage cascades.•Forty different combinations of cycles are simulated.•Low global-warming potential natural refrigerants R-290 and ...R-170 are considered.•The influence of each cycle on the whole configuration is analyzed.•–80 °C refrigeration coefficient of performance is increased.
In response to the COVID-19 pandemic, some vaccines have been developed requiring ultralow-temperature refrigeration, and the number of these freezers has been increased worldwide. Ultralow-temperature refrigeration operates with a significant temperature lift and, hence, a massive decrease in energy performance. Therefore, cascade cycles based on two vapor compression single-stage cycles are traditionally used for these temperatures. This paper proposes the combination of six different cycles (single-stage with and without internal heat exchanger, vapor injection, liquid injection, and parallel compression with and without economizer) in two-stage cascades to analyze the operational and energy performance in ultralow-temperature freezers. All this leads to 42 different configurations in which the intermediate cascade temperature is optimized to maximize the coefficient of performance. Ultra-low global warming potential natural refrigerants such as R-290 (propane) and R-170 (ethane) for the cascade high- and low-temperature stage have been considered. From the thermodynamic analysis, it can be concluded that liquid and vapor injection cascade configurations are the most energy-efficient. More specifically, those containing a vapor injection in the low-temperature stage (0.89 coefficient of performance, 40 % higher than traditional configurations). Then, using an internal heat exchanger for such low temperatures is unnecessary in terms of energy performance. The optimum intermediate cascade temperature varies significantly among cycles, from −37 °C to 2 °C, substantially impacting energy performance. Parallel compression configuration improves energy performance over single-stage cycles, but not as much as multi-stage (between 20 % and 30 % lower coefficient of performance). For most of low-temperature cycles, the high-temperature stage can be based on a single-stage cycle while keeping the maximum coefficient of performance.
Modeling point defects at an atomic scale requires careful treatment of the long-range atomic relaxations. This elastic field can strongly affect point defect properties calculated in atomistic ...simulations because of the finite size of the system under study. This is an important restriction for ab initio methods which are limited to a few hundred atoms. We propose an original approach coupling ab initio calculations and linear elasticity theory to obtain the properties of an isolated point defect for reduced supercell sizes. The reliability and benefit of our approach are demonstrated for three problematic cases: the self-interstitial in zirconium, clusters of self-interstitials in iron, and the neutral vacancy in silicon.
The purpose of this Special Issue is to present the impact in clinical practice as well as in medical research of novel molecules that have been introduced in the treatment of diabetes mellitus, ...dyslipidaemia, and cardiovascular disease ....
The primary aim of this research was to explore the feasibility of producing environmentally friendly composite materials by employing diverse hybrid matrices consisting of dammar natural resin, ...supplemented with small proportions of two synthetic resins: one epoxy and the other acrylic. A blend of paper and chicken feathers served as the reinforcing elements. The fabrication of these composite materials utilized a hand layup technique. Targeted for applications in the furniture industry or interior design, their mechanical properties were assessed through various tests. Specimens were obtained from the manufactured samples and subjected to evaluations for tensile strength, compression, flexure, vibrations, Shore hardness, and water absorption. Results indicated that irrespective of the testing method employed, the mechanical strength properties exhibited a decline with an increase in the percentage of dammar in the hybrid resins, whereas the elasticity properties demonstrated an increase with this percentage.
Wound dressing design is a dynamic and rapidly growing field of the medical wound-care market worldwide. Advances in technology have resulted in the development of a wide range of wound dressings ...that treat different types of wounds by targeting the four phases of healing. The ideal wound dressing should perform rapid healing; preserve the body’s water content; be oxygen permeable, non-adherent on the wound and hypoallergenic; and provide a barrier against external contaminants—at a reasonable cost and with minimal inconvenience to the patient. Therefore, choosing the best dressing should be based on what the wound needs and what the dressing does to achieve complete regeneration and restoration of the skin’s structure and function. Biopolymers, such as alginate (ALG), chitosan (Cs), collagen (Col), hyaluronic acid (HA) and silk fibroin (SF), are extensively used in wound management due to their biocompatibility, biodegradability and similarity to macromolecules recognized by the human body. However, most of the formulations based on biopolymers still show various issues; thus, strategies to combine them with molecular biology approaches represent the future of wound healing. Therefore, this article provides an overview of biopolymers’ roles in wound physiology as a perspective on the development of a new generation of enhanced, naturally inspired, smart wound dressings based on blood products, stem cells and growth factors.
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