Stress concentrations in nanoscale defective graphene

Defect-free graphene nanosheets are the strongest material known but manufactured graphene tends to contain flaws of different forms and dimensions, leading to the degradation of mechanical performance. Here we report a quantitative mechanical approach to quantitatively evaluate the influence of defects within exfoliated pristine graphene sheets. Results indicate stress concentrations around defects within graphene sheets that lower strength. The description of stress concentration broadly follows a Griffith strength approach for continuum materials, despite the non-continuum structure of graphene, but has little impact on the Young’s modulus

On the Strength of Defective Graphene Materials.

PhDGraphene is the first 2D material consisting of carbon atoms densely packed into planar structures. Graphene oxide (GO) is the intermediate derivative of chemically-produced graphene, which retains 2D basal plane structures but is also decorated with functional groups along the basal plane and edges. This functionality allows self-assembly of planar sheets into a paper-like material. However, formations of both intrinsic defects within the sheet structures as well as larger scale extrinsic defects in the paper are expected to significantly degrade mechanical performance. Strength provides the most direct evidence of defect related mechanical behaviour and is therefore targeted for understanding defect effects in GO paper. Such evaluations are crucial both from a technological perspective of realizing designed functions and from a fundamental interest in understanding structure-mechanics in 2D nanomaterials. A complete strategy of performing mechanical testing at different length scales is thus reported to provide a comprehensive description of GO strength. Both conventional larger scale mechanical testing as well as novel smaller length scale evaluations, using in situ atomic force microscopy (AFM) combined with scanning electron microscopy (SEM) and optical microscopy as well as structural probing using synchrotron FT-IR microspectroscopy, were applied to GO materials. Results showed that large structural defects determined mechanical properties of GO papers due to stress concentration effects whereas smaller scale intrinsic effects were defined by interfacial defects and stress concentrations within sheets. Synchrotron FT-IR microspectroscopy provided molecular deformation mechanisms in GO paper, which highlighted the interaction between in-plane C=C and cross-linking C=O bonds. A comprehensive description of macroscopic GO paper using evaluations of strength at the range of length scales studied was attempted, with a good correlation between predictions and experimental observations. This thesis therefore provides a hierarchical understanding of the defects impact on the strength of graphene-based materials from the macroscale to the nanoscale

Dynamic Modelling of Zenith Wet Delay in GNSS Measurements

Proper modelling of the temporal correlations of the zenith wet delay (ZWD) is important in some of the Global Navigation Satellite Systems (GNSS) applications such as estimation of the Perceptible Water Vapour (PWV), and methods such as Precise Point Positioning (PPP). The random walk (RW) and the first-order Gauss- Markov (GM) autocorrelation model are commonly used for the dynamic modelling of ZWD in Kalman filtering of GNSS measurements. However, it was found that the GM model consistently underestimates the temporal correlations that exist among the ZWD estimates. Therefore, a new autocorrelation dynamic model is proposed in a form similar to that of a hyperbolic function. The impact of the proposed dynamic model on the near-real time estimation of the ZWD was tested and its results were compared to that of the GM model as well as the RW model. In this test, GPS dual-frequency data collected on the 25th Jan 2010 at two Western Australian IGS stations, namely, Yarragadee and Karratha, were used. Results showed that the proposed model outperformed the GM model, and when added to hydrostatic models were able to provide near real-time (with 30 seconds intervals) ZTD estimates to within a few cm accuracy

Context-dependent regulation of P-body composition and mRNA turnover in Saccharomyces cerevisiae

Control of gene expression is crucial for cells surviving in a changing environment. In eukaryotes, gene expression can be regulated at different levels, among which posttranscriptional control is of special importance, as it can rapidly modulate the level of gene products. It typically includes mRNA processing, export, translation, decay as well as protein degradation. One type of cytoplasmic granules, which is involved in repression of translation, mRNA decay, mRNA surveillance/quality control and mRNA storage are P-bodies. They consist of mRNP aggregates, constitute the 5’ to 3’ mRNA decay machinery in yeast cells and can be induced in response to various stress conditions. This thesis contains three studies carried out in S. cerevisiae aimed to uncover the mRNA contents of P-bodies, their role in mRNA turnover, as well as to better understand how P-body formation and function are regulated. Unlike protein components, the mRNA species sequestered by P-bodies are poorly characterized. In the first part of this thesis, an approach to isolate P-body localized transcripts was established. This method was used to identify, subsequently, common and stress-specific mRNA subsets associated with P-bodies. We further examined the fates of these transcripts, and discovered two major types of transcripts. One type was decayed within P-bodies, yet the decay occurred with different kinetics. The second type remained stable for at least 1 h after stress induction. Moreover, we identified transcript-specific cis- and trans-elements that affect P-body targeting and/or degradation including the 3’UTR and RNA binding protein Puf5p. In yeast, P-bodies were observed in close proximity to the ER, implying that the ER may play a role in mRNA regulation (Kilchert et al., 2010). In the second study, we identified Scp160p and Bfr1p as polysome-associated ER localized proteins. Loss of either Bfr1p or Scp160p led to numerous Dcp2p positive foci under normal growth condition. Dcp2p is a core constituent of P-bodies, and served as a marker in this study. Therefore, this observation suggests that they might serve as inhibitors preventing P-body formation under unstressed condition. However, general translation was unaffected, indicating that P-body formation and translation attenuation were uncoupled in the absence of Bfr1p and Scp160p. In the third part of this thesis, we identified Pby1p as a facultative P-body component, Pby1p P-body localization was observed under glucose starvation but not when hyper osmotic shock was applied. Interestingly, loss of Pby1p caused a great reduction of cellular Dcp2p concentration without preventing P-body formation. Furthermore, the decay of particular P-body associated transcripts was slightly delayed in a Δpby1 strain, suggesting its possible role in regulating mRNA stability and P-body function

Research on reverse logistics location under uncertainty environment based on grey prediction

AbstractThis article constructs reverse logistic network based on uncertain environment, integrates the reverse logistics network and distribution network, and forms a closed network. An optimization model based on cost is established to help intermediate center, manufacturing center and remanufacturing center make location decision. A gray model GM (1, 1) is used to predict the product holdings of the collection points, and then prediction results are carried into the cost optimization model and a solution is got. Finally, an example is given to verify the effectiveness and feasibility of the model

Microscopic Phase Structure of Mo-based Catalyst and Its Catalytic Activity for Soot Oxidation

The MoO3 catalysts supported on nano-scale TiO2 with various loading rates (5%, 10%, 20%, and 40%) were prepared by an impregnation method. The phase structures of nano-scale MoO3/TiO2 catalysts were characterized by Brunner-Emmet-Teller, Fourier Transform Infrared Spectra, X-ray Diffraction, and Scanning Electron Microscope. The oxidation activities of catalysts over diesel soot were performed in a Thermogravimetric Analysis system. The kinetics of the catalytic oxidation process was analyzed based on Starink method. The characterization results showed that the phase structure of MoO3 supported on TiO2 depends heavily on the molybdenum contents, which put great effects on soot oxidation. The orthorhombic crystal system (α-MoO3) appeared on the surface of the catalysts when the MoO3 exceeds 10%. Due to the low melting point and good surface mobility of MoO3, the catalytic activity was increased and the characteristic temperatures were decreased with the increase in MoO3 contents. As a result, the activities of catalysts with different loading rates for soot oxidation can be ranked as: Mo5<Mo10<Mo2

Sudden death of entanglement with Hamiltonian ensemble assisted by auxiliary qubits

In this paper, we theoretically propose a method to simulate the longitudinal relaxation of a single qubit by coupling it to an auxiliary qubit. In order to mimic the finite-temperature relaxation, we utilize the Hamiltonian-ensemble approach [Kropf, Gneiting, and Buchleitner, Phys. Rev. X 6, 031023 (2016)] and in each realization the auxiliary qubit possesses a random level spacing. The longitudinal relaxation arises as a consequence of the ensemble average and the interaction between the working qubit and the auxiliary qubit. Furthermore, we apply this approach to investigate the influence of the longitudinal relaxation and the transverse relaxation on the entanglement dynamics of two qubits. It is discovered that the sudden death of the entanglement will occur as long as the longitudinal relaxation is present. The transverse relaxation assists the longitudinal relaxation and thus accelerates the finite-time disentanglement.Comment: 8 pages,7 figure