10 research outputs found
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Mapping the phase diagram of alkyl ligands on nanoparticle surfaces with molecular simulations and field theoretic models
Some of the most important and interesting phenomena in physical chemistry, such as heterogeneous catalysis, semi-conduction, and self-assembly depend crucially upon the surface properties of the material under consideration. This is particularly relevant for nanoscopic objects, whose surface-to-volume ratio is much higher than macroscopic materials. Thus, it is often necessary to carefully engineer nanoparticle surfaces so as to prevent them rom coalescing or reacting with their environment. This is achieved by using passivating ligands that stabilize nanoparticle surfaces and consequently, modify the chemical, optical, and electrical properties of nanocrystals and modulate inter-nanoparticle interactions. As a result, gaining an understanding of ligand behavior is essential to synthesizing new nanomaterials with useful technological applications; particularly because probing ligand structure is experimentally difficult.We approach this problem by performing atomistic computer simulations of alkyl ligands on a semiconducting nanocrystal facet to elucidate their phase behavior at different temperatures and solvent conditions. These simulations provide a detailed description of the structure of the ligand molecules, specifically providing insight into the order-disorder transition they undergo as the temperature is varied. This phase transition changes the arrangement of the surface ligands, affecting how a nanoparticle interacts with solvent and other nanoscale objects in its environment. We proceed to map the observed statistics of ligand orientation onto a coarse-grained field theoretic model of the ordering transition, which is parametrized by physical properties obtained from simulation data. By extracting the underlying physics of the transition and removing irrelevant atomistic details, this coarse-grained model considerably reduces computational costs, while still describing the collective behavior of ligand molecules on a nanoparticle surface. This new understanding can be leveraged to describe ligand ordering when multiple nanoparticle surfaces are close to each other and its effect on the phase behavior of ligand passivated nanocrystals
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Mapping the phase diagram of alkyl ligands on nanoparticle surfaces with molecular simulations and field theoretic models
Some of the most important and interesting phenomena in physical chemistry, such as heterogeneous catalysis, semi-conduction, and self-assembly depend crucially upon the surface properties of the material under consideration. This is particularly relevant for nanoscopic objects, whose surface-to-volume ratio is much higher than macroscopic materials. Thus, it is often necessary to carefully engineer nanoparticle surfaces so as to prevent them rom coalescing or reacting with their environment. This is achieved by using passivating ligands that stabilize nanoparticle surfaces and consequently, modify the chemical, optical, and electrical properties of nanocrystals and modulate inter-nanoparticle interactions. As a result, gaining an understanding of ligand behavior is essential to synthesizing new nanomaterials with useful technological applications; particularly because probing ligand structure is experimentally difficult.We approach this problem by performing atomistic computer simulations of alkyl ligands on a semiconducting nanocrystal facet to elucidate their phase behavior at different temperatures and solvent conditions. These simulations provide a detailed description of the structure of the ligand molecules, specifically providing insight into the order-disorder transition they undergo as the temperature is varied. This phase transition changes the arrangement of the surface ligands, affecting how a nanoparticle interacts with solvent and other nanoscale objects in its environment. We proceed to map the observed statistics of ligand orientation onto a coarse-grained field theoretic model of the ordering transition, which is parametrized by physical properties obtained from simulation data. By extracting the underlying physics of the transition and removing irrelevant atomistic details, this coarse-grained model considerably reduces computational costs, while still describing the collective behavior of ligand molecules on a nanoparticle surface. This new understanding can be leveraged to describe ligand ordering when multiple nanoparticle surfaces are close to each other and its effect on the phase behavior of ligand passivated nanocrystals
Contribution of Laboratory Findings in Assessing the Severity of Covid-19 Infection: In A Tertiary Care Hospital
Background: In December 2019 first case of Coronavirus disease (COVID-19) was reported in China and then has spread across the world. With the use of biomarkers categorising patients becomes easier and can help clinicians in identifying patients with higher risk of disease progression and initiating effective management in time and thereby reducing the mortality due to COVID-19. Methods: The Data was collected retrospectively from medical records of 126 hospitalized patients diagnosed with COVID-19 from a tertiary care hospital between August and September 2020. Laboratory parameters on admission in patients who required intensive care unit (ICU) support and those who did not require ICU support were compared. Results: The patients who required ICU care (n = 47) were older (median, 55 vs. 49 years), with more underlying comorbidities (42.5% vs. 17.7%). ICU patients had higher leucocytes, neutrophils, Neutrophil to Lymphocyte Ratio (NLR), urea, creatinine, lactate dehydrogenase (LDH), and D-dimer but lower lymphocyte count when compared with non-ICU patients (p < 0.05). Conclusions: Elevated D-dimer and NLR appear to be independent biomarkers for severe COVID-19 infection. These laboratory parameters may help the clinicians to determine the patients who have a higher risk of disease progression and thus initiate effective treatment in time
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Tailoring Morphology of Cu-Ag Nanocrescents and Core-Shell Nanocrystals Guided by a Thermodynamic Model.
The ability to predict and control the formation of bimetallic heterogeneous nanocrystals is desirable for many applications in plasmonics and catalysis. Here, we report the synthesis and characterization of stable, monodisperse, and solution-processed Cu-Ag bimetallic nanoparticles with specific but unusual elemental arrangements that are consistent with a recently developed thermodynamic model. Using air-free scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, the distribution of Cu and Ag positions was unambiguously identified within individual nanocrystals (NCs), leading to the discovery of a Cu-Ag nanocrescent shape. A simple yet versatile thermodynamic model was applied to illustrate how the interplay between surface and interface energies determines the particle morphology. It is found that there exists a range of surface-to-interface energy ratios under which crescent-shaped nanocrystals are the thermodynamically favored products, with the morphology tunable by adjusting the Ag content. We further show the conversion of Cu-Ag nanocrescents into Ag@Cu2O upon mild oxidation, whereas fully core-shell Cu@Ag NCs are robust against oxidation up to 100 °C. The plasmonic and interband absorptions of Cu-Ag NCs depend on the composition and the degree of Cu oxidation, which may find application in light-driven catalysis
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Tailoring Morphology of Cu–Ag Nanocrescents and Core–Shell Nanocrystals Guided by a Thermodynamic Model
The
ability to predict and control the formation of bimetallic
heterogeneous nanocrystals is desirable for many applications in plasmonics
and catalysis. Here, we report the synthesis and characterization
of stable, monodisperse, and solution-processed Cu–Ag bimetallic
nanoparticles with specific but unusual elemental arrangements that
are consistent with a recently developed thermodynamic model. Using
air-free scanning transmission electron microscopy with energy-dispersive
X-ray spectroscopy, the distribution of Cu and Ag positions was unambiguously
identified within individual nanocrystals (NCs), leading to the discovery
of a Cu–Ag nanocrescent shape. A simple yet versatile thermodynamic
model was applied to illustrate how the interplay between surface
and interface energies determines the particle morphology. It is found
that there exists a range of surface-to-interface energy ratios under
which crescent-shaped nanocrystals are the thermodynamically favored
products, with the morphology tunable by adjusting the Ag content.
We further show the conversion of Cu–Ag nanocrescents into
Ag@Cu<sub>2</sub>O upon mild oxidation, whereas fully core–shell
Cu@Ag NCs are robust against oxidation up to 100 °C. The plasmonic
and interband absorptions of Cu–Ag NCs depend on the composition
and the degree of Cu oxidation, which may find application in light-driven
catalysis
Laser-Induced Sub-millisecond Heating Reveals Distinct Tertiary Ester Cleavage Reaction Pathways in a Photolithographic Resist Polymer
Acid-catalyzed, thermally activated ester cleavage reactions are critical for lithographic patterning processes used in the semiconductor industry. The rates of these high-temperature reactions within polymer thin films are difficult to characterize because of the thermal instability of many polymers and a lack of temperature-resolved measurement techniques. Here we introduce the use of transient laser irradiation to heat a methylÂadamantane-protected acrylate copolymer to 600 °C in less than a millisecond. These conditions mediate the removal of the protecting groups and enable accurate kinetic measurements. At sub-millisecond exposure to high temperatures (∼600 °C), the rate of the ester cleavage reaction exhibits the expected first-order dependence on acid concentration. In contrast, the reaction exhibits more complex kinetics when the polymer film is heated to lower temperatures (115 °C) on a conventional hot-plate. We identify distinct methylÂadamantane-derived deprotection products under the high- and low-temperature conditions that are consistent with the observed rate differences. The acid-catalyzed dimerization of 1-methyleneÂadamantane occurs at low temperature, which reduces the acid concentration available for the ester cleavage. This dimerization reaction is minimized during transient laser-induced heating because bimolecular reactions are disfavored under these conditions. We constructed a mathematical model based on these observations that accounts for the competition for the catalyst between the dimerization and ester cleavage processes. This laser-induced, sub-millisecond heating technique provides a means to probe and model temperature and time regimes of thermally activated reactions in polymer films, and these regimes exhibit distinct and advantageous reaction pathways that will inform future advances in high-performance photoÂlithography
Secondary Infections with Ebola Virus in Rural Communities, Liberia and Guinea, 2014–2015
Persons who died of Ebola virus disease at home in rural communities in Liberia and Guinea resulted in more secondary infections than persons admitted to Ebola treatment units. Intensified monitoring of contacts of persons who died of this disease in the community is an evidence-based approach to reduce virus transmission in rural communities