Yi Lv

Microbial communities of aerobic granules: Granulation mechanisms

Aerobic granulation is an advanced biological wastewater treatment technology. This study for the first time identified the microbial communities of sliced samples of mature granules by polymerase chain reaction (PCR) amplification and denaturing gradient gel electrophoresis (DGGE) technique and those of whole growing granules by high-throughput sequencing technique. The sliced sample study revealed that mature granules have a spherical core with anaerobic Rhodocyclaceae covered by an outer spherical shell with both aerobic and anaerobic strains. The growing granule study showed that the flocculated flocs were first transited to young granules with increased abundances of Flavobacteriaceae, Xanthomonadaceae, Rhodobacteraceae and Microbacteriaceae, then the abundances of anaerobic strains were increased owing to the formation of anaerobic core. Since the present granules were cultivated from flocculated flocs, the microbial community data suggested that granules were formed via a deterministic rather than via a random aggregation-disintegration mechanism.

Layer-dependent nanoscale electrical properties of graphene studied by conductive scanning probe microscopy

The nanoscale electrical properties of single-layer graphene (SLG), bilayer graphene (BLG) and multilayer graphene (MLG) are studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). The quantum capacitance of graphene deduced from SCM results is found to increase with the layer number (n) at the sample bias of 0 V but decreases with n at -3 V. Furthermore, the quantum capacitance increases very rapidly with the gate voltage for SLG, but this increase is much slowed down when n becomes greater. On the other hand, the magnitude of the EFM phase shift with respect to the SiO2 substrate increases with n at the sample bias of +2 V but decreases with n at -2 V. The difference in both quantum capacitance and EFM phase shift is significant between SLG and BLG but becomes much weaker between MLGs with a different n. The layer-dependent quantum capacitance behaviors of graphene could be attributed to their layer-dependent electronic structure as well as the layer-varied dependence on gate voltage, while the layer-dependent EFM phase shift is caused by not only the layer-dependent surface potential but also the layer-dependent capacitance derivation.

Drying and re-cultivation of aerobic granules

Aerobic granules stored in liquid medium can lose structural integrity during storage. This study demonstrated that the aerobic granules cultivated by seeding activated sludge into column-type sequential batch reactors and fed with synthetic wastewater at organic loading rate of 1.5 kg/m3-d can be dried by acetone gradient method to moisture content less than 1%. Then, the dried granules can be reactivated through a re-cultivation process to recover their organic degradation capacity in 12 h, or their appearance in 5 d. During the drying and recovery, the granules experienced volume and weight losses by >80% and >85%, respectively, with minimal loss in structural integrity. The microbial communities of the dried and re-cultivated granules were probed using polymerase chain reaction-denaturing gradient gel electrophoresis technique. The family Xanthomonadaceae and the family Comamonas can survive in dried granules and could contribute to maintain structural integrity in re-cultivation stage.

Influencing factors on the size uniformity of self-assembled SiGe quantum rings grown by molecular beam epitaxy

The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concentration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape or even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×10(8) cm(-2) are obtained at the optimized growth temperature of 640°C.

Electrical properties of individual self-assembled GeSi quantum rings

The nanoscale electrical properties of self-assembled GeSi quantum rings (QRs) were investigated by conductive scanning probe microscopy at room temperature. The current distribution of individual GeSi QRs measured by conductive atomic force microscopy (CAFM) shows a low conductivity at the central hole as compared to the rim; however, the QRs’ composition distribution obtained by selective chemical etching combined with AFM observation reveals that within the QRs’ central holes, the Ge content is high, which should lead to a high conductivity instead of a low one as observed. Together with the results obtained by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM), it is supposed that the GeSi QRs’ electrical properties are mainly determined by the ring-shaped topography, rather than by the complete oxidation of the QRs’ central hole or their composition distributions.

DRWSC — To simplify dynamic invocation for RESTful Web services

Dynamic invocation has always been a hot issue in Web services in order to take full advantage of the flexibility of services computing. One key underlying enabling technology is a self-descriptive contact between the service consumer and provider. In the SOAP-based environment, WSDL has been proven a successful description language which is widely accepted. But for many years, we cannot get the equivalent in the RESTful, another dominant style of Web services. Thanks for the announcement of WSDL 2.0 which has been designed with RESTful Web service in mind and became a recommend in 2007, developers can use it as the APIs for RESTful Web services which are attracting more and more attention of Web applications all over the world. Unfortunately, the vision is almost unfulfilled due to rare reference implementations. To fill the gap between the vision and practice, we present a useful tool for dynamically invoking RESTful Web services based on the information extracted from WSDL 2.0. Our implementation demonstrates the feasibility that dynamic invocations in general RESTful Web services can be done as easy as in SOAP-based ones.

Growth and memory effect of Er-stabilized β-MnO2 films grown on Si substrates

A memory effect is reported for Er-stabilized beta-MnO2 films made of highly orientation-aligned textured nanocrystals. The films are composed of nanocrystals with a size of about 20 nm. The crystalline direction along the growth direction is almost along beta-MnO2 , but the one in the plane is disordered. Er doping can effectively enhance the thermal stability of beta-MnO2 up to 850 degrees C, which is essential for its future application in industry. A memory effect has been observed for both as-grown and annealed samples. The mechanism of the memory effect was found by analysis to be charge trapping by carrier injection, from either the bottom or the top electrode. For the annealed sample, a low leakage current was achieved, which is about 5 orders of magnitude smaller than that of the as-grown sample. The results show that beta-MnO2 is a promising candidate material for nonvolatile memory applications.