7,339 research outputs found
Mechanochemistry as an emerging tool for molecular synthesis: what can it offer?
Mechanochemistry is becoming more widespread as a technique for molecular synthesis with new mechanochemical reactions being discovered at increasing frequency. Whilst mechanochemical methods are solvent free and can therefore lead to improved sustainability metrics, it is more likely that the significant differences between reaction outcomes, reaction selectivities and reduced reaction times will make it a technique of interest to synthetic chemists. Herein, we provide an overview of mechanochemistry reaction examples, with âdirectâ comparators to solvent based reactions, which collectively seemingly show that solid state grinding can lead to reduced reaction times, different reaction outcomes in product selectivity and in some instances different reaction products, including products not accessible in solution
Recent Advances Concerning Certain Class of Geophysical Flows
This paper is devoted to reviewing several recent developments concerning
certain class of geophysical models, including the primitive equations (PEs) of
atmospheric and oceanic dynamics and a tropical atmosphere model. The PEs for
large-scale oceanic and atmospheric dynamics are derived from the Navier-Stokes
equations coupled to the heat convection by adopting the Boussinesq and
hydrostatic approximations, while the tropical atmosphere model considered here
is a nonlinear interaction system between the barotropic mode and the first
baroclinic mode of the tropical atmosphere with moisture.
We are mainly concerned with the global well-posedness of strong solutions to
these systems, with full or partial viscosity, as well as certain singular
perturbation small parameter limits related to these systems, including the
small aspect ratio limit from the Navier-Stokes equations to the PEs, and a
small relaxation-parameter in the tropical atmosphere model. These limits
provide a rigorous justification to the hydrostatic balance in the PEs, and to
the relaxation limit of the tropical atmosphere model, respectively. Some
conditional uniqueness of weak solutions, and the global well-posedness of weak
solutions with certain class of discontinuous initial data, to the PEs are also
presented.Comment: arXiv admin note: text overlap with arXiv:1507.0523
Mechanochemical Activation of Zinc and Application to Negishi Cross-Coupling
A form independent activation of zinc, concomitant generation of organozinc species and engagement in a Negishi crossâcoupling reaction via mechanochemical methods is reported. The reported method exhibits a broad substrate scope for both C(sp3)âC(sp2) and C(sp2)âC(sp2) couplings and is tolerant to many important functional groups. The method may offer broad reaching opportunities for the inâ
situ generation organometallic compounds from base metals and their concomitant engagement in synthetic reactions via mechanochemical methods
Complete mitochondrial genome sequence of Urechis caupo, a representative of the phylum Echiura
BACKGROUND: Mitochondria contain small genomes that are physically separate from those of nuclei. Their comparison serves as a model system for understanding the processes of genome evolution. Although hundreds of these genome sequences have been reported, the taxonomic sampling is highly biased toward vertebrates and arthropods, with many whole phyla remaining unstudied. This is the first description of a complete mitochondrial genome sequence of a representative of the phylum Echiura, that of the fat innkeeper worm, Urechis caupo. RESULTS: This mtDNA is 15,113 nts in length and 62% A+T. It contains the 37 genes that are typical for animal mtDNAs in an arrangement somewhat similar to that of annelid worms. All genes are encoded by the same DNA strand which is rich in A and C relative to the opposite strand. Codons ending with the dinucleotide GG are more frequent than would be expected from apparent mutational biases. The largest non-coding region is only 282 nts long, is 71% A+T, and has potential for secondary structures. CONCLUSIONS: Urechis caupo mtDNA shares many features with those of the few studied annelids, including the common usage of ATG start codons, unusual among animal mtDNAs, as well as gene arrangements, tRNA structures, and codon usage biases
Translating solid state organic synthesis from a mixer mill to a continuous twin screw extruder
A study on the translation of a solid-state synthetic reaction from a mechanochemical mixer-mill to a continuous twin-screw extruder is discussed herein. The study highlights some considerations to be made and parameters to be tested in the context of a model fluorination reaction, which is the first organic fluorination to be attempted using extrusion. Upon optimization, which features the first use of grinding auxiliary solids to enable effective synthetic extrusion, the difluorination reaction was successfully translated to the extruder, leading to a 100-fold improvement in Space Time Yield (STY); 29 kg mâ3 dayâ1 in a mixer mill to 3395 kg mâ3 dayâ1 in a twin screw extruder
Parent-Child Communication About Educational Aspirations: Experiences of Adolescents in Rural China
The importance of parents in the transmission of educational aspirations to children is well-established. However, little is known about the quality of parent-child communication about educational aspirations and how this communication relates to childrenâs educational aspirations in socioeconomically disadvantaged families in rural China. In this study, we sought to gain insight into parent-child communication around educational aspirations from the perspective of Chinese rural adolescents. Twenty-three grade-9 students were recruited from middle schools in Songzi, a poor rural county in central China. Participants comprised 12 boys and 11 girls aged 14 to 16 years (M = 14.65 years, SD = 0.59). Students completed one-to-one qualitative interviews about parent-child communication and their educational aspirations in June 2020. Thematic analysis revealed that adolescentsâ educational aspirations were strongly influenced by their parentsâ beliefs and aspirations for them, with fulfilling parental aspirations and achieving economic success being important influences on rural adolescentsâ educational aspirations. However, parent-child communication quality was undermined when parents had an authoritarian communication style and when parents were absent due to rural-urban migration, in which case adolescents reported stress and perceived lack of support in achieving their goals. In addition, mothers were viewed as playing a more vital role in communication than fathers. The implications of the findings for school and community-based interventions promoting rural parentsâ ability to communicate effectively with their children about academic concerns are discussed
Delayed crack propagation in barium titanate single crystals in humid air
2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Resting-state EEG power and coherence vary between migraine phases
© 2016, The Author(s). Background: Migraine is characterized by a series of phases (inter-ictal, pre-ictal, ictal, and post-ictal). It is of great interest whether resting-state electroencephalography (EEG) is differentiable between these phases. Methods: We compared resting-state EEG energy intensity and effective connectivity in different migraine phases using EEG power and coherence analyses in patients with migraine without aura as compared with healthy controls (HCs). EEG power and isolated effective coherence of delta (1â3.5 Hz), theta (4â7.5 Hz), alpha (8â12.5 Hz), and beta (13â30 Hz) bands were calculated in the frontal, central, temporal, parietal, and occipital regions. Results: Fifty patients with episodic migraine (1â5 headache days/month) and 20 HCs completed the study. Patients were classified into inter-ictal, pre-ictal, ictal, and post-ictal phases (n = 22, 12, 8, 8, respectively), using 36-h criteria. Compared to HCs, inter-ictal and ictal patients, but not pre- or post-ictal patients, had lower EEG power and coherence, except for a higher effective connectivity in fronto-occipital network in inter-ictal patients (p <.05). Compared to data obtained from the inter-ictal group, EEG power and coherence were increased in the pre-ictal group, with the exception of a lower effective connectivity in fronto-occipital network (p <.05). Inter-ictal and ictal patients had decreased EEG power and coherence relative to HCs, which were ânormalizedâ in the pre-ictal or post-ictal groups. Conclusion: Resting-state EEG power density and effective connectivity differ between migraine phases and provide an insight into the complex neurophysiology of migraine
Superconductivity in iron telluride thin films under tensile stress
By realizing in thin films a tensile stress state, superconductivity of 13 K
was introduced into FeTe, an non-superconducting parent compound of the iron
pnictides and chalcogenides, with transition temperature higher than that of
its superconducting isostructural counterpart FeSe. For these tensile stressed
films, the superconductivity is accompanied by the softening of the first-order
magnetic and structural phase transition; and also, the in-plane extension and
out-of-plane contraction are universal in all FeTe films independent of sign of
lattice mismatch, either positive or negative. Moreover, the correlations were
found exist between the transition temperatures and the tetrahedra bond angles
in these thin films.Comment: 4 pages, 4 figures, accepted by Physical Review Letter
Metrics with Prescribed Ricci Curvature near the Boundary of a Manifold
Suppose is a manifold with boundary. Choose a point . We
investigate the prescribed Ricci curvature equation \Ric(G)=T in a
neighborhood of under natural boundary conditions. The unknown here is
a Riemannian metric. The letter in the right-hand side denotes a
(0,2)-tensor. Our main theorems address the questions of the existence and the
uniqueness of solutions. We explain, among other things, how these theorems may
be used to study rotationally symmetric metrics near the boundary of a solid
torus . The paper concludes with a brief discussion of the Einstein
equation on .Comment: 13 page
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