Highly efficient and chemoselective acetalization of carbonyl compounds catalyzed by new and reusable zirconyl triflate,ZrO(OTf)2

Various types of aromatic aldehydes were efficiently converted to their corresponding 1,3‐dioxanes and 1,3‐dioxolane with 1,3‐propanediol and ethylene glycol, respectively, in the presence of catalytic amount of ZrO(OTf)₂ in acetonitrile at room temperature. The catalyst can be reused several times without loss of its catalytic activity. Very short reaction times, selective acetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones, very mild reaction conditions, reusability of the catalyst, and easy workup are noteworthy advantages of this method. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:131–135, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20523     

Atomic-scale studies of impurities in superconductors with a scanning tunneling microscope

Imaging and spectroscopy with a cryogenic scanning tunneling microscope (STM) have been used to study the local variation of electronic states on the atomic scale in both low-T_c and high-T_c superconductors. These experiments provide an atomic-scale perspective of impurity scattering by directly probing the localized excitations that are induced by individual impurities.     

Dirac Nodal Arc Semimetal PtSn4: An Ideal Platform for Understanding Surface Properties and Catalysis for Hydrogen Evolution

Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn₄. The determined turnover frequency (TOF) for each active site of PtSn₄ is 1.54 H₂ s^?1 at 100 mV. This sets a benchmark for HER catalysis on Pt‐based noble metals and earth‐abundant metal catalysts. We make use of the robust surface states of PtSn₄ as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn₄ displays excellent chemical and electrochemical stabilities after long‐term exposure in air and long‐time HER stability tests.     

All optical 2-bit analog to digital converter using photonic crystal based cavities

A novel design for realizing all optical analog to digital converter will be proposed in this paper. The proposed structure consists of two main parts; a nonlinear 3-channel demultiplexer, followed by an optical coder. The nonlinear demultiplexer will be used to quantize the input analog signal according to its optical intensity and the coder will convert the quantized levels into 2-bit binary codes. The nonlinear demultiplexer will be realized using three nonlinear resonant cavities. At appropriate values of input signal optical intensity one of the cavities can drop the optical beam to its corresponding output port. The proposed structure is capable of supporting maximum sampling rate up to 52 GS/s and total footprint of the structure is about 924 µm².     

Semi-discrete optimal transport: hardness,regularization and numerical solution

Mathematical Programming - Semi-discrete optimal transport problems, which evaluate the Wasserstein distance between a discrete and a generic (possibly non-discrete) probability measure, are...