Analytical approaches to investigate transmitter content and release from single secretory vesicles

The vesicle serves as the primary intracellular unit for the highly efficient storage and release of chemical messengers triggered during signaling processes in the nervous system. This review highlights conventional and emerging analytical methods that have used microscopy, electrochemistry, and spectroscopy to resolve the location, time course, and quantal content characteristics of neurotransmitter release. Particular focus is on the investigation of the synaptic vesicle and its involvement in the fundamental molecular mechanisms of cell communication.     

Dimroth-type rearrangement of 1-benzyl- and 1-glycosyl-5-aminoimidazoles to 4-(N-substituted amino)imidazoles

An efficient route is described to an unusual exocyclic 4-β-d-ribofuranosyl-aminoimidazole nucleoside, related 4-N-benzylaminoimidazoles and imidazole analogues of precursors in the de novo biosynthesis of purines, via a regiospecific and stereoselective base-catalysed Dimroth-type rearrangement of 1-ribofuranosyl and 1-benzyl-5-aminoimidazoles. Use of a ¹⁵N labelled precursor showed the unequivocal endo- to exocyclic translocation of the nitrogen atom during the rearrangement.     

Controlling the structure and size of Au nanocrystals by annealing and ion sputtering

In situ thermal annealing was used for the first time to observe directly that Au nanoparticles, which were originally fully embedded in the near-surface region of TiO(2), can be tailored into hemispheres exposed at the surface at elevated temperature. Precise control of the size of the Au hemispheres was achieved by subsequent low-energy ion sputtering. This method can be used to control the structure and size of a wide variety of nanoparticles in a matrix where surface structure and particle size are required to obtain specific material properties.     

Forecasting wind speed with recurrent neural networks

This research presents a comparative analysis of the wind speed forecasting accuracy of univariate and multivariate ARIMA models with their recurrent neural network counterparts. The analysis utilizes contemporaneous wind speed time histories taken from the same tower location at five different heights above ground level. A unique aspect of the study is the exploitation of information contained in the wind histories for the various heights when producing forecasts of wind speed for the various heights. The findings indicate that multivariate models perform better than univariate models and that the recurrent neural network models outperform the ARIMA models. The results have important implications for a variety of engineering applications and business related operations.     

Reliable and efficient error control for an adaptive Galerkin-characteristic method for convection-dominated diffusion problems

An efficient and reliable a-posteriori error estimator is developed for a characteristic-Galerkin finite element method for time-dependent convection-dominated problems. An adaptive algorithm with variable time and space steps is proposed and studied. At each time step in this algorithm grid coarsening occurs solely at the final iteration of the adaptive procedure, meaning that only time and space refinement is allowed before the final iteration. It is proved that at each time step this adaptive algorithm is capable of reducing errors below a given tolerance in a finite number of iteration steps. Numerical results are presented to check the theoretical analysis.     

Structural stability and phase transitions in WO3 thin films

Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (lambda = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of approximately 60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30-500 degrees C. The phase transitions in the WO3 thin films occur in sequence as the temperature is increased: monoclinic --> orthorhombic --> hexagonal. Distortion and tilting of the WO6 octahedra occurs with the phase transitions and significantly affects the electronic properties and, hence, the electrochemical device applications of WO3.     

Multilevel Preconditioners for Mixed Methods for Second Order Elliptic Problems

A new approach for constructing algebraic multilevel preconditioners for mixed finite element methods for second order elliptic problems with tensor coefficients on general geometry is proposed. The linear system arising from the mixed methods is first algebraically condensed to a symmetric, positive definite system for Lagrange multipliers, which corresponds to a linear system generated by standard nonconforming finite element methods. Algebraic multilevel preconditioners for this system are then constructed based on a triangulation of the domain into tetrahedral substructures. Explicit estimates of condition numbers and simple computational schemes are established for the constructed preconditioners. Finally, numerical results for the mixed finite element methods are presented to illustrate the present theory.     

Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens

The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B?B double bond enables reactions with Se⁰ and Te⁰. The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions.     

Structural changes of (K,Gd)2Ta2O7 pyrochlore at high pressure

The structure of K-bearing tantalate pyrochlore (K_2-xGd_x)Ta₂O_6+x(x∼0.4) was studied at high pressures using in situ X-ray diffraction and Raman scattering methods. Experimental results indicated that (K_2-xGd_x)Ta₂O_6+x(x∼0.4) retains the pyrochlore structure up to 40 GPa, but partial amorphization occurred at pressures above 23 GPa. The amorphous phase was also confirmed in the quenched sample by means of transmission electron microscopy. The tantalate pyrochlore lattice is more stable than pyrochlore compounds in other systems, such as rare earth titanates, zirconates and stannates. The structural stability of pyrochlore tantalate may be mainly related to the size ratio of cations on the 16d and 16c sites in the lattice.