Microstructural Evidence for Diffusion-Driven Tetragonal-to-Orthorhombic Phase Transformation in Y-Ba-Cu-O Superconductor

Microstructures of Y-Ba-Cu-O superconductor were observed using a polarized microscope. Orthorhombic and tetragonal phases were easily distinguished by the optical etching with cross-polarized light. In the specimen cooled rapidly in oxygen, it was possible to see the path of oxygen diffusion by observing the variation of the twin concentration. At the boundary between transformed and untransformed materials, evidence for diffusion-driven transformation could be clearly seen.     

Theory of asymmetric organocatalysis of Aldol and related reactions: rationalizations and predictions

Computational studies have led to models to understand some classic and contemporary asymmetric reactions involving organocatalysts. The Hajos-Parrish-Eder-Sauer-Wiechert reaction and intermolecular aldol reactions as well as Mannich reactions and oxyaminations catalyzed by proline and other amino acids, and Diels-Alder reactions catalyzed by MacMillan's chiral amine organocatalysts have been studied with density functional theory. Quantitative predictions for several new catalysts and reactions are provided.     

Electrochemical incineration of benzoquinone in aqueous media using a quaternary metal oxide electrode in the absence of a soluble supporting electrolyte

Electrochemical incineration of p-benzoquinone was evaluated as a model for the mineralization of carbon in toxic aromatic compounds. A Ti or Pt anode was coated with a film of the oxides of Ti, Ru, Sn and Sb. This quaternary metal oxide film was stable; elemental analysis of the electrolysed solution indicated the concentration of these metal ions to be 3g L–1 or less. The anode showed good reactivity for the electrochemical incineration of benzoquinone. The use of a dissolved salt matrix as the so-called supporting electrolyte was eliminated in favor of a solid-state electrolyte sandwiched between the anode and cathode. This substitution permitted the electrolysis solution to be analysed by electrospray mass spectrometry (ESMS); however, as a consequence, electrolysis periods were excessively long. Total organic carbon (TOC) and chemical oxygen demand (COD) decreased to 1–2 mgL–1 after 64h of electrolysis. The solution pH changed from 5 to 4. Phenolic and carboxylic acid intermediate products such as hydroquinone, maleic acid, fumaric acid, succinic acid, malonic acid, acetic acid and formic acids were identified and quantified using solid phase microextraction with gas chromatography with mass spectrometric detection (GCMS) or liquid chromatography (LC) with conductivity detection, absorbance detection, or electrosprary mass spectrometry (ESMS). Less than 1% of the carbon in benzoquinone was converted to acetone and acetaldehyde.     

Attenuation of matrix effects in inductively coupled plasma mass spectrometry with a supplemental electron source inside the skimmer

Electrons are added from a heated filament at the base of the skimmer to reduce the space charge repulsion in the ion beam. This technique improves the analyte sensitivity moderately and also minimizes the matrix effects caused by other elements in the sample significantly. The suppression of signal for even the most troublesome combination of light analyte and heavy matrix elements can be attenuated from 90 to 99% to only 2-10% for 2 mM matrix solutions with an ultrasonic nebulizer. The supplemental electron current can be adjusted to "titrate" out the matrix effects as desired.     

A cerebellar model of timing and prediction in the control of reaching

A simplified model of the cerebellum was developed to explore its potential for adaptive, predictive control based on delayed feedback information. An abstract representation of a single Purkinje cell with multistable properties was interfaced, using a formalized premotor network, with a simulated single degree-of-freedom limb. The limb actuator was a nonlinear spring-mass system based on the nonlinear velocity dependence of the stretch reflex. By including realistic mossy fiber signals, as well as realistic conduction delays in afferent and efferent pathways, the model allowed the investigation of timing and predictive processes relevant to cerebellar involvement in the control of movement. The model regulates movement by learning to react in an anticipatory fashion to sensory feedback. Learning depends on training information generated from corrective movements and uses a temporally asymmetric form of plasticity for the parallel fiber synapses on Purkinje cells.     

Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS2 Nanosheets

Understanding the collaborative behaviors of the excitons and phonons that result from light–matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton‐coupled phonon vibration from molybdenum disulfide (MoS₂) nanosheets in a pre‐excitonic resonance condition is reported. A strong rise‐to‐decay profile for the transient second‐harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A‐exciton. The time‐dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm^?1 (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS₂ samples of varying thicknesses, the speed of the supersonic waves generated in the out‐of‐plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS₂ monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low‐dimensional materials and their hybrids with ultrahigh fidelity.