49 research outputs found
Shortest path based decision making using probabilistic inference
Despite the extensive use of boron-modified
phenolâformaldehyde
polymers as insulating materials in soft magnetic composites (SMCs),
the structure and arrangement of the inorganic cross-linking units
in these systems have not been fully elucidated. To clarify the structure,
configuration, and distribution of the boron cross-links in these
materials, phenolâformaldehyde resins modified by boric acid
were synthesized and characterized using advanced multiple-quantum <sup>11</sup>Bâ<sup>11</sup>B MAS NMR correlation techniques combined
with the quantum chemical geometry optimizations and the subsequent <sup>11</sup>B NMR chemical shielding calculations. The analyses of the
resulting spectra revealed a well-evolved (high-density) phenolâformaldehyde
polymer network additionally strengthened by nitrogen and boron cross-links.
The boron-based cross-links were attributed to monoester (ca. 10%)
and diester (ca. 90%) complexes (six-membered spirocyclic borate anions)
with strictly tetrahedral coordination (B<sup>IV</sup>). During the
thermal treatment, the monoester and diester borate complexes underwent
additional transformation in which the spirocyclic borate anions were
more tightly incorporated into the polymer matrix via additional <i>N</i>-type (amino) cross-links. A <sup>11</sup>Bâ<sup>11</sup>B double-quantum correlation MAS NMR experiment revealed
that the majority of the monoester and diester borate complexes (ca.
80%) were uniformly distributed within and effectively isolated by
the polymer matrix, with an average <sup>11</sup>B···<sup>11</sup>B interatomic distance greater than 6 Ă
. A non-negligible
part of the spirocyclic borate anion complexes (ca. 20%), however,
existed in pairs or small clusters in which the average <sup>11</sup>B···<sup>11</sup>B interatomic distance was less than
5.5 Ă
. In addition, the formation of homodimers (diesterâdiester)
was demonstrated to be preferred over the formation of heteroclusters
(monoesterâdiester)
Perovskite-molecule composite thin films for efficient and stable light-emitting diodes
Abstract: Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives
Spatial clusters of Varroa destructor control strategies in Europe
Publication history: Accepted - 18 May 2022; Published online - 29 June 2022Beekeepers have various options to control the parasitic mite Varroa destructor in honey bee colonies, but no empirical data
are available on the methods they apply in practice. We surveyed 28,409 beekeepers maintaining 507,641 colonies in 30
European countries concerning Varroa control methods. The set of 19 diferent Varroa diagnosis and control measures was
taken from the annual COLOSS questionnaire on honey bee colony losses. The most frequent activities were monitoring of
Varroa infestations, drone brood removal, various oxalic acid applications and formic acid applications. Correspondence
analysis and hierarchical clustering on principal components showed that six Varroa control options (not necessarily the most
used ones) signifcantly contribute to defning three distinctive clusters of countries in terms of Varroa control in Europe.
Cluster I (eight Western European countries) is characterized by use of amitraz strips. Cluster II comprises 15 countries from
Scandinavia, the Baltics, and Central-Southern Europe. This cluster is characterized by long-term formic acid treatments.
Cluster III is characterized by dominant usage of amitraz fumigation and formed by seven Eastern European countries. The
median number of diferent treatments applied per beekeeper was lowest in cluster III. Based on estimation of colony numbers
in included countries, we extrapolated the proportions of colonies treated with diferent methods in Europe. This suggests that
circa 62% of colonies in Europe are treated with amitraz, followed by oxalic acid for the next largest percentage of colonies.
We discuss possible factors determining the choice of Varroa control measures in the diferent clustersOpen access funding provided by University of Graz. The authors have no relevant financial or non-financial interests to disclose. COLOSS and its supporters had no influence on the study design or the decision to publish
Enantiotropy of Simvastatin as a Result of Weakened Interactions in the Crystal Lattice: Entropy-Driven Double Transitions and the Transient Modulated Phase as Seen by Solid-State NMR Spectroscopy
In crystalline molecular solids, in the absence of strong intermolecular interactions, entropy-driven processes play a key role in the formation of dynamically modulated transient phases. Specifically, in crystalline simvastatin, the observed fully reversible enantiotropic behavior is associated with multiple order–disorder transitions: upon cooling, the dynamically disordered high-temperature polymorphic Form I is transformed to the completely ordered low-temperature polymorphic Form III via the intermediate (transient) modulated phase II. This behavior is associated with a significant reduction in the kinetic energy of the rotating and flipping ester substituents, as well as a decrease in structural ordering into two distinct positions. In transient phase II, the conventional three-dimensional structure is modulated by periodic distortions caused by cooperative conformation exchange of the ester substituent between the two states, which is enabled by weakened hydrogen bonding. Based on solid-state NMR data analysis, the mechanism of the enantiotropic phase transition and the presence of the transient modulated phase are documented
NMR Crystallography of the Polymorphs of Metergoline
Two polymorphs of the drug compound metergoline (C25H29N3O2) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum chemical calculations that were performed for molecular crystals. In this way, it was possible to assign the total of 40 1H–13C correlation pairs in a highly complex system, namely, in the dynamically disordered polymorph with two independent molecules in the unit cell of a large volume of 4234 Å3. For the simpler polymorph, which exhibits only small-amplitude motions and has just one molecule in the unit cell with a volume of 529.0 Å3, the values of the principal elements of the 13C chemical shift tensors were measured. Additionally, for this polymorph, a set of crystal structure predictions were generated, and the {13C, 1H} isotropic and 13C anisotropic chemical shielding data were computed while using the gauge-including projector augmented-wave approach combined with the “revised Perdew-Burke-Ernzerhof“ exchange-correlation functional (GIPAW-RPBE). The experimental and theoretical results were combined in an application of the newly developed strategy to polymorph discrimination. This research thus opens up new routes towards more accurate characterization of the polymorphism of drug formulations
Potential and Limitations of 2D 1 H- 1 H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids
Solid-state NMR study of biodegradable starch/polycaprolactone blends
International audienc
Study of biodegradable starch/polycaprolactone blends by solid-state NMR methods
International audienc
Self-Organization, Structure, Dynamic Properties, and Surface Morphology of Silica/Epoxy Films As Seen by Solid-State NMR, SAXS, and AFM
Study of biodegradable starch/polycaprolactone blends by solid-state NMR methods
International audienc