Kinetic control of catalytic CVD for high-quality graphene at low temperatures.

Low-temperature (∼600 °C), scalable chemical vapor deposition of high-quality, uniform monolayer graphene is demonstrated with a mapped Raman 2D/G ratio of >3.2, D/G ratio ≤0.08, and carrier mobilities of ≥3000 cm(2) V(-1) s(-1) on SiO(2) support. A kinetic growth model for graphene CVD based on flux balances is established, which is well supported by a systematic study of Ni-based polycrystalline catalysts. A finite carbon solubility of the catalyst is thereby a key advantage, as it allows the catalyst bulk to act as a mediating carbon sink while optimized graphene growth occurs by only locally saturating the catalyst surface with carbon. This also enables a route to the controlled formation of Bernal stacked bi- and few-layered graphene. The model is relevant to all catalyst materials and can readily serve as a general process rationale for optimized graphene CVD.

SOI membrane-based pressure sensor in stress sensitive differential amplifier configuration

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar). © 2012 IEEE.

Self-assembled multilayer graphene oxide membrane and carbon nanotubes synthesized using a rare form of natural graphite

The fabrication of flexible multilayer graphene oxide (GO) membrane and carbon nanotubes (CNTs) using a rare form of high-purity natural graphite, vein graphite, is reported for the first time. Graphite oxide is synthesized using vein graphite following Hummer's method. By facilitating functionalized graphene sheets in graphite oxide to self-assemble, a multilayer GO membrane is fabricated. Electric arc discharge is used to synthesis CNTs from vein graphite. Both multilayer GO membrane and CNTs are investigated using microscopy and spectroscopy experiments, i.e., scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), core level photoelectron spectroscopy, and C K-edge X-ray absorption spectroscopy (NEXAFS), to characterize their structural and topographical properties. Characterization of vein graphite using different techniques reveals that it has a large number of crystallites, hence the large number of graphene sheets per crystallite, preferentially oriented along the (002) plane. NEXAFS and core level spectra confirm that vein graphite is highly crystalline and pure. Fourier transform infrared (FT-IR) and C 1s core level spectra show that oxygen functionalities (-C-OH, -CO,-C-O-C-) are introduced into the basal plane of graphite following chemical oxidation. Carbon nanotubes are produced from vein graphite through arc discharge without the use of any catalyst. HRTEM confirm that multiwalled carbon nanotube (MWNTs) are produced with the presence of some structure in the central pipe. A small percentage of single-walled nanotubes (SWNTs) are also produced simultaneously with MWNTs. Spectroscopic and microscopic data are further discussed here with a view to using vein graphite as the source material for the synthesis of carbon nanomaterials. © 2013 American Chemical Society.

α-Synuclein senses lipid packing defects and induces lateral expansion of lipids leading to membrane remodeling.

There is increasing evidence for the involvement of lipid membranes in both the functional and pathological properties of α-synuclein (α-Syn). Despite many investigations to characterize the binding of α-Syn to membranes, there is still a lack of understanding of the binding mode linking the properties of lipid membranes to α-Syn insertion into these dynamic structures. Using a combination of an optical biosensing technique and in situ atomic force microscopy, we show that the binding strength of α-Syn is related to the specificity of the lipid environment (the lipid chemistry and steric properties within a bilayer structure) and to the ability of the membranes to accommodate and remodel upon the interaction of α-Syn with lipid membranes. We show that this interaction results in the insertion of α-Syn into the region of the headgroups, inducing a lateral expansion of lipid molecules that can progress to further bilayer remodeling, such as membrane thinning and expansion of lipids out of the membrane plane. We provide new insights into the affinity of α-Syn for lipid packing defects found in vesicles of high curvature and in planar membranes with cone-shaped lipids and suggest a comprehensive model of the interaction between α-Syn and lipid bilayers. The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking.

Outer membrane proteins induced by iron deficiency in Anabaena sp PCC 7120

Iron deficiency can induce cyanobacteria to synthesize siderophore receptor proteins on the outer membrane to enhance the uptake of iron. In this study, an outer membrane of high purity was prepared from Anabaena sp. PCC 7120 based on aqueous polymer two-phase partitioning and discontinuous sucrose density ultra-centrifugation, and the induction of outer membrane proteins by iron deficiency was investigated using 2-D gel electrophoresis. At least. five outer membrane proteins were newly synthesized or significantly up-regulated in cells transferred to iron-deficient conditions, which were all identified to be siderophore receptor proteins according to MALDI-TOF-MS analyses. Bacterial luciferase reporter genes luxAB were employed to monitor the transcription of the encoding genes. The genes were induced by iron deficiency at the transcriptional level in different responsive modes. Luciferase activity expressed from an iron-regulated promoter may be used as a bioreporter for utilizable iron in natural water samples. (C) 2009 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Determination of PAH, PCB, and OCP in water from the Three Gorges Reservoir accumulated by semipermeable membrane devices (SPMD)

Bioavailable water concentrations of polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and organochlorine pesticides (OCP) were measured in the water column from Three Gorges Reservoir (TGR) collected in May 2008 using semipermeable membrane devices (SPMDs). The sampling sites spanned the whole reservoir from the upstream Chongqing to the great dam covering more than 600 km long distance with water flow velocities ranging from <0.05 to 1.5 m s(-1). This is the first experience of SPMD application in the biggest reservoir in the world. The results of water sampling rates based on performance reference compounds (PRC) were tested to be significantly correlated with water flow velocities in the big river. Results of back-calculated aqueous concentrations based on PRC showed obvious regional variations of PAH, PCB and OCP levels in the reservoir. Total PAH ranged from 13.8 to 97.2 ng L-1, with the higher concentrations occurring in the region of upstream and near the dam. Phenanthrene, fluoranthene, pyrene and chrysene were the predominant PAH compounds in TGR water. Total PCB ranged from 0.08 to 0.51 ng L-1, with the highest one occurring in the region near the dam. PCB 28, 52, 101, 138, 153, 180, 118 were the most abundant PCB congeners in the water. The total OCP ranged from 2.33 to 3.60 ng L-1 and the levels showed homogenous distribution in the whole reservoir. HCH, DDT and HCB, PeCB were the major compounds of OCP fingerprints. Based on water quality criteria, the TGR water could be designated as being polluted by HCB and PAH. Data on PAH, PCB and OCP concentrations found in this survey can be used as reference levels for future POP monitoring programmes in TGR. (C) 2009 Elsevier Ltd. All rights reserved.

Twin plane re-entrant mechanism for catalytic nanowire growth.

A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center. We suggest that the nucleation barrier at the twin-plane re-entrant groove is effectively reduced by the line energy, and hence the twin acts as a preferential nucleation site that dictates the lateral step flow cycle which constitutes nanowire growth.

Bacterial diversity in activated sludge from a consecutively aerated submerged membrane bioreactor treating domestic wastewater

The bacterial diversity of activated sludge from submerged membrane bioreactor (SMBR) was investigated. A 16S rDNA clone library was generated, and 150 clones were screened using restriction fragment length polymorphism (RFLP). Of the screened clones, almost full-length 16S rDNA sequences of 64 clones were sequenced. Phylogenetic tree was constructed with a database containing clone sequences from this study and bacterial rDNA sequences from NCB1 for identification purposes. The 90.6% of the clones were affiliated with the two phyla Bacteroidetes (50%) and Proteobacteria (40%), and beta-, -gamma-, and delta-Proteobacteria accounted for 7.8%, 28.1%, and 4.7%, respectively. Minor portions were affiliated with the Actinobacteria and Firmicutes (both 3.1%). Only 6 out of 64 16S rDNA sequences exhibited similarities of more than 97% to classified bacterial species, which indicated that a substantial fraction of the clone sequences were derived from unknown taxa. Rarefaction analysis of operational taxonomic units (orrUs) clusters demonstrated that 150 clones screened were still insufficient to describe the whole bacterial diversity. Measurement of water quality parameter demonstrated that performance of the SMBR maintained high level, and the SMBR system remained stable during this study.

Co-catalytic absorption layers for controlled laser-induced chemical vapor deposition of carbon nanotubes.

The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.

Proteomic analysis of the sarcosine-insoluble outer membrane fraction of Flavobacterium columnare

Outer membrane proteins (OMPs) of bacteria are key molecules interacting with the host environment. Flavobacterium columnare, a pathogen-causing columnaris disease of fish worldwide, was studied in order to understand the composition of its OMPs. The sarcosine-insoluble membrane fraction of the OMPs was analysed using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) in combination with reverse-phase high-performance liquid chromatography-tandem mass spectrometry (RP-HPLC MS/MS). Thirty-six proteins were identified, including proteins involved in cell wall/membrane biogenesis, specific transport of various nutrients and in essential metabolism. The present study is the first report on the OMPs of F. columnare, and may serve as the basis for understanding the pathogenesis of the bacterium.

Effects of ytterbium ion on the growth, metabolism and membrane fluidity of Tetrahymena thermophila

Power-time curves and metabolic properties of Tetrahymena thermophila BF5 exposed to different Yb3+ stop levels were studied by ampoule method of isothermal calorimetry at 28 degrees C. Metabolic rate (r) decreased significantly while peak time (PT) increased with the increase of Yb3+ stop. These results were mainly due to the inhibition of cell growth, which corresponded to the decrease of cell number obtained by cell counting. Compared with cell counting, calorimetry was sensible, easy to use and convenient for monitoring the toxic effects of Yb3+ stop on cells and freshwater ecosystem. It was also found that cell membrane fluidity decreased significantly under the effects of Yb3+ stop, which indicated that Yb3+ could be membrane active molecules with its effect on cell membranes as fundamental aspect of its toxicity.

Optimization of operational conditions in a submerged membrane bioreactor

In this study, optimization of operational conditions of a submerged membrane bioreactor treating municipal waste-water was studied. Mixed liquid suspended solid (MLSS), membrane flux (J(v)), aeration (Q), ratio of pumping, time to break time (t(p)/t(b)), and ratio of up flow area to down flow area (A Ad) were chosen as the easily manipulable parameters to study their effects on removal efficiency and membrane fouling. Totally, 16 different runs were designed to compare and select the best combination of the 5 parameters. The results showed that the optimal operational conditions were MLSS = 7g(.)L(-1), J(v) = 10L(.)m(-2.)h(-1), Q = 6 m(3.)h(-1), t(p)/t(b)= 4 min/1 min, and A(r)/A(d) = 1.7 m(2)/m(2). Under such conditions, the SMBR could achieve a double win of high removal efficiency and low membrane fouling.

Characterization of two membrane-associated protease genes obtained from screening out-membrane protein genes of Flavobacterium columnare G(4)

In order to identify genes encoding the outer membrane proteins (OMPs) of the myxobacter Flavobacterium columnare G(4), the expression library of the bacterium was screened by using rabbit antisera developed against its OMPs. Positive colonies of Escherichia coli M15 containing fragments encoding the bacterial OMPs were selected for cloning the relevant genes by genomic walking methods. Two genes encoding a membrane-associated zinc metalloprotease and prolyl oligopeptidase are reported in this paper. The membrane-associated zinc metalloprotease gene (map) is 1800 bp in length, coding for 449 amino acids (aa). Despite the presence of a conserved motif HEXXH for all metalloproteases, the special HEXXH similar to 32 aa similar to E motif of the F. columnare G(4) Map and its low level of identity with other reported zinc-containing metalloproteases may imply that the membrane-associated zinc metalloprotease of F. columnare G(4) represents a new family of zincins. The gene encoding prolyl oligopeptidase (Pop), a serine proteinase, is 2352 bp in length, coding for 649 aa. Sequence homology analysis revealed that the Pop is also novel as it has <50% identity with other reported prolyl oligopeptidase family proteins. The present study represents the first to employ anti-fish bacterial OMP sera to screen genes of membrane-associated proteases of fish pathogenic bacteria, and to provide necessary information for the examination of the role of the two genes in the infection and pathogenesis of F. columnare.

A TPR-family membrane protein gene is required for light-activated heterotrophic growth of the cyanobacterium Synechocystis sp PCC 6803

The unicellular cyanobacterium Synechocystis sp. PCC6803 can grow heterotrophically in complete darkness, given that a brief period of illumination is supplemented every day (light-activated heterotrophic growth, LAHG), or under very weak ( < 0.5 mumol m(-2) s(-1)) but continuous light. By random insertion of the genome with an antibiotic resistance cassette, mutants defective in LAHG were generated. In two identical mutants, sll0886, a tetratricopeptide repeat (TPR)-family membrane protein gene, was disrupted. Targeted insertion of sll0886 and three downstream genes showed that the phenotype was not due to a polar effect. The sll0886 mutant shows normal photoheterotrophic growth when the light intensity is at 2.5 mumol m(-2) s(-1) or above, but no growth at 0.5 mumol m(-2) s(-1). Homologs to sll0886 are also present in cyanobacteria that are not known of LAHG. sll0886 and homologs may be involved in controlling different physiological processes that respond to light of low fluence. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.