Interaction between stray electrostatic fields and a charged free-falling test mass

We present an experimental analysis of force noise caused by stray electrostatic fields acting on a charged test mass inside a conducting enclosure, a key problem for precise gravitational experiments. Measurement of the average field that couples to the test mass charge, and its fluctuations, is performed with two independent torsion pendulum techniques, including direct measurement of the forces caused by a change in electrostatic charge. We analyze the problem with an improved electrostatic model that, coupled with the experimental data, also indicates how to correctly measure and null the stray field that interacts with the test mass charge. Our measurements allow a conservative upper limit on acceleration noise, of 2 (fm/s2)/Hz(1/2) for frequencies above 0.1 mHz, for the interaction between stray fields and charge in the LISA gravitational wave mission.     

Size and density control of silicon oxide nanowires by rapid thermal annealing and their growth mechanism

In this work, we demonstrate a fast approach to grow SiO₂ nanowires by rapid thermal annealing (RTA). The material characteristics of SiO₂ nanowires are investigated by field emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field (HAADF) imaging, electron energy loss spectroscopy (EELS), and energy-filtered TEM (EFTEM). The HAADF images show that the wire tip is predominantly composed of Pt with brighter contrast, while the elemental mappings in EFTEM and EELS spectra reveal that the wire consists of Si and O elements. The SiO₂ nanowires are amorphous with featureless contrast in HRTEM images after RTA at 900°C. Furthermore, the nanowire length and diameter are found to be dependent on the initial Pt film thickness. It is suggested that a high SiO₂ growth rate of >1 μm/min can be achieved by RTA, showing a promising way to enable large-area fabrication of nanowires.     

An expeditious and high-yield formal synthesis of hirsutene using Rh(I)-catalyzed [(5+2)+1] cycloaddition

An expeditious and high-yield formal synthesis of hirsutene has been achieved. This synthesis features Rh(I)-catalyzed [(5+2)+1] cycloaddition to construct a bicyclic cyclooctenone, which can be efficiently transformed to bicyclic diketone, an advanced intermediate for racemic and asymmetric syntheses of hirsutene.     

One single standard substance for the determination of multiple anthraquinone derivatives in rhubarb using high-performance liquid chromatography-diode array detection

Due to the complexity of the chemical constitution of traditional Chinese medicines (TCMs), now there is a trend to establish methods, using multi-components analysis, for the effective quality control of TCMs. However, the limited availability of multiple reference substances hinders the wide popularization for routine quality control of TCMs. Using an easily available single component contained in the analyte as an internal standard to determine multiple analogues should be a practical option. In this study, we selected rhubarb rhizome as an example, and used emodin, the easily available active component, as the external standard to determine directly the content of emodin in rhubarb, and the same component as the internal standard to simultaneously determine the other six anthraquinones in rhubarb. Compared with the results obtained using the external standard method, this alternative method was found to have no statistically significant differences in our laboratory as verified by the F-test (p = 95%, n = 6). However, due to weak robustness caused by the fluctuation of relative response factors in different laboratories, such a method can only serve as a practical measure to solve the lack of so many chemical standard substances when relative response factors have been determined. This alternative method can then be used without reference substances. Once the corresponding chemical standards are available and are acceptable as well as cost-effective, then the external standard method for the simultaneous determination of multiple components (SDMC) in TCMs will prevail.     

Preparation and characterization of size-controlled CeO2 nanoparticles coated with SiO2

CeO₂@SiO₂ (core@shell) nanoparticles were prepared by means of chemical precipitation technique. Results from X-ray diffraction, transmission electron microscopy (TEM), and Zeta-potential analyses provide strong microscopic and spectroscopic evidences to prove that CeO₂ particles have been encapsulated inside amorphous SiO₂ shell. As revealed from TEM investigations, the average grain size of CeO₂@SiO₂ is significantly smaller than that of uncoated CeO₂ nanoparticles prepared under the same conditions, indicating it is an effective method to restrict the grain enlargement of nanocrystalline CeO₂ by coating a thin layer of SiO₂ at elevated temperatures. The CeO₂@SiO₂ nanoparticles display a similar surface electric character behavior to that of SiO₂, and its dispersibility in water is improved.     

Phenanthroline‐Catalyzed Stereoretentive Glycosylations

Carbohydrates are essential moieties of many bioactive molecules in nature. However, efforts to elucidate their modes of action are often impeded by limitations in synthetic access to well‐defined oligosaccharides. Most of the current methods rely on the design of specialized coupling partners to control selectivity during the formation of glycosidic bonds. Reported herein is the use of a commercially available phenanthroline to catalyze stereoretentive glycosylation with glycosyl bromides. The method provides efficient access to α‐1,2‐cis glycosides. This protocol has been performed for the large‐scale synthesis of an octasaccharide adjuvant. Density‐functional theory calculations, together with kinetic studies, suggest that the reaction proceeds by a double S_N2 mechanism.     

Intense red and cyan luminescence in europium doped silicate glasses

The photoluminescence properties of silicate glasses, singly doped with europium ions and co-doped with europium ions and Al powder, have been characterized by the absorption, excitation, and emission spectroscopies. The absorption edge in the absorption spectra shows a large red shift from 320 nm to 405 nm. Under near-ultraviolet (NUV) excitation, sample, doped with Eu³⁺ emit intense red light while those co-doped with Eu³⁺ and Al give intense cyan emission. The influences of the glass compositions on the spectroscopic properties are also discussed. These glasses may be potential candidates for light-emitting diodes (LEDs).     

MOFs-derived carbon covered alumina (CCA) supported Pt nanoparticles as catalyst for enantioselective hydrogenation

A one-step approach was developed to prepare carbon covered alumina (CCA) material by using Al-based MOFs (Al-PCP) as sacrificial template. Pt/CCA nanoparticle catalysts were characterized by using XRD, TGA, XPS, N₂ sorption, SEM, TEM and elemental analysis and revealed that they retained the mesostructure with high Pt dispersion and had a CCA structure. Moreover, after reduced at 800 °C, Pt/CCA-800 afforded the highest enantiomeric excess (84.8%) after chirally modified with cinchonidine at the second time reaction and can be recycled for more than 8 times without distinct loss of activity or enantioselectivity in the asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate.