Ice tessellation on a hydroxylated silica surface

The adsorption of water on a fully hydroxylated silica surface is studied by using density-functional total-energy and molecular dynamics calculations. The (100) surface of beta(alpha)-cristobalite covered by geminal hydroxyls has been taken as the substrate. A well-ordered and stable two-dimensional ice with quadrangular and octagonal patterns of hydrogen bond (H-bond) networks-an ice tessellation-is found on the surface for the first time. With the vibrational recognition, the four water molecules in the quadrangle are found to be bonded by strong H bonds while the quadrangles are connected to each other by weak H bonds. This configuration is the most stable, because all the water molecules are fully saturated with H bonds either to each other or to the surface hydroxyl groups.     

Octanuclear metallocyclic Ni4Fc4 compound: synthesis, crystal structure, and electrochemical sensing for Mg2+

New, neutral octanuclearmacrocyclic compound Ni(4)Fc(4) was achieved via self-assembly from Ni(BF(4))(2) and a ferrocene-containing bis-tridentate ligand. The compound exhibits a channeled structure with cavities inside and senses the Mg(2+) electrochemically in the solid state.     

Freeze-drying of mononuclear cells and whole blood of human cord blood

The research on haematopoietic stem cells of human cord blood has become more important recently. People have concentrated on the preservation of cord blood stem cells. At present, cord blood can be preserved at ultra-low temperatures. In this study, we try to preserve cord blood and its constituents by freeze-drying. The experiments on both the mononuclear cell content and the whole blood of human cord blood were carried out respectively. The samples were frozen firstly by different cooling protocols in the presence of PVP, sucrose, and mannitol. Afterwards, they were vacuum-dried at a selected shelf temperature of -30 degree C for the main drying stage, and then vacuum-dried at 15 degree C for the second drying stage. The entire time of the freeze drying was 52 hours. Samples were stored at room temperature for 2 days prior to evaluation. Subsequently, the dried samples were suspended in an isotonic phosphate-buffered saline solution. The recovery of the cells were tested by a haemacytometer, and the highest cell numerical count recovery of MNC was 75.0 percent (SD = 4.1 percent) (P = 0.01), obtained in the protocol of 40 percent PVP + 20 percent sucrose + 10 percent Mannitol. The viability of the nucleated cells measured by PI staining and the ratio of the number of CD34+ to the number of lymphocytes (by the FITC anti-human CD34+ conjugated antibody method) were measured using a flow cytometer (FCM). The protocol of 40 percent PVP + 20 percent sucrose + 10 percent fetal bovine serum had the highest viability of 98.6 percent (SD = 0.7 percent) (P = 0.01). The highest ratio of CD34+ to lymphocytes was 1.2%, and the highest recovery of CD34+ was 68.4 percent (SD = 39.5 percent) (P = 0.05). Comparing the results of the lyophilized MNC subfraction with that of the whole blood, the lyophilization of the isolated MNC was more successful than that of whole blood.     

Si-based nanoscale SiO2 islands and light-emitting source array

A SiO₂ nanoscale island array was fabricated on a Si substrate by using anodic porous alumina as a mask. Transmission electron microscopy observation and the atomic force microscopy pattern show that the arrangement of SiO₂ islands has a quasi-hexagonal symmetry. Ge ions with a dose of 1×10¹⁷ cm^-2 were subsequently implanted into the SiO₂ island array to form Ge-related light-emitting centers. The photoluminescence (PL) spectra of as-implanted and annealed samples show three PL bands at 370, 400 and 415 nm. Their intensities reach maximums in the sample with an annealing temperature of 700 °C. Spectral analysis suggests that the 370 and 415 nm PL bands arise from Ge-Ge and Ge-Si defect centers, while the 400 nm PL is related to GeO color centers in the SiO₂ islands. The existence of these PL bands indicates the formation of a Si-based nanoscale light source array. PACS 78.55.Mb; 42.72.Bj; 68.65.+g     

Fullerene-sensitized

[reaction: see text] Fullerene catalyzes the cycloaddition of dimethyliminodiacetate to maleimides under photolysis to form 2,5-dimethoxycarbonylpyrrolidine derivatives.     

High repetition rate, compact micro-pulse all-solid-state laser

A high repetition rate, compact micro-pulse all-solid-state laser is designed. The diffusion bonded crystal of YAG, Nd:YAG, and Cr4+:YAG is taken as a monolithic cavity. The optimized initial transmission,output coupling, and pumping size of Cr4+:YAG are calculated. The experimental results show that the laser satisfies the requirement of a spaceborne laser range finder.     

Multilevel fast multipole algorithm for acoustic wave scattering by truncated ground with trenches

The multilevel fast multipole algorithm (MLFMA) is extended to solve for acoustic wave scattering by very large objects with three-dimensional arbitrary shapes. Although the fast multipole method as the prototype of MLFMA was introduced to acoustics early, it has not been used to study acoustic problems with millions of unknowns. In this work, the MLFMA is applied to analyze the acoustic behavior for very large truncated ground with many trenches in order to investigate the approach for mitigating gun blast noise at proving grounds. The implementation of the MLFMA is based on the Nystrom method to create matrix equations for the acoustic boundary integral equation. As the Nystrom method has a simpler mechanism in the generation of far-interaction terms, which MLFMA acts on, the resulting scheme is more efficient than those based on the method of moments and the boundary element method (BEM). For near-interaction terms, the singular or near-singular integrals are evaluated using a robust technique, which differs from that in BEM. Due to the enhanced efficiency, the MLFMA can rapidly solve acoustic wave scattering problems with more than two million unknowns on workstations without involving parallel algorithms. Numerical examples are used to demonstrate the performance of the MLFMA with report of consumed CPU time and memory usage.     

Aging-induced abnormality of dielectric response under dc bias in Ba(Zr,Ti)O<Subscript>3</Subscript> thin films

The dielectric properties of fresh and aged Ba(Zr_0.25Ti_0.75)O₃ thin films have been investigated. It is found that the aged sample shows a significant decrease in the dielectric constant compared to the fresh one. Furthermore, the aged sample also exhibits abnormal double-peaks-shape butterfly C–V characteristics, which indicates the defect-dipole stabilized domain and/or domain-wall motions. Meanwhile, we found that double-peaks-shape butterfly C–V characteristics become weak and even disappear with increasing of applied electric field and temperature. The present results are discussed in light of the symmetry-conforming principle of point defects.     

Highly efficient TfOH-catalyzed head-to-tail dimerization of vinylarenes

A convenient and efficient TfOH-catalyzed head-to-tail dimerization of vinylarenes has been realized under mild conditions. The present protocol provides an attractive approach to a diverse range of higher olefins in good to excellent yields.