Effect of defects on fracture strength of graphene sheets

With a hexagonal monolayer network of carbon atoms, graphene has demonstrated exceptional electrical 22 and mechanical properties. In this work, the fracture of graphene sheets with Stone–Wales type defects and vacancies were investigated using molecular dynamics simulations at different temperatures. The initiation of defects via bond rotation was also investigated. The results indicate that the defects and vacancies can cause significant strength loss in graphene. The fracture strength of graphene is also affected by temperature and loading directions. The simulation results were compared with the prediction from the quantized fracture mechanics.

Generation of uniform plasmas by crossed internal oscillating current sheets : key concepts and experimental verification

The results of comprehensive experimental studies of the operation, stability, and plasma parameters of the low-frequency (0.46 MHz) inductively coupled plasmas sustained by the internal oscillating rf current are reported. The rf plasma is generated by using a custom-designed configuration of the internal rf coil that comprises two perpendicular sets of eight currents in each direction. Various diagnostic tools, such as magnetic probes, optical emission spectroscopy, and an rf-compensated Langmuir probe were used to investigate the electromagnetic, optical, and global properties of the argon plasma in wide ranges of the applied rf power and gas feedstock pressure. It is found that the uniformity of the electromagnetic field inside the plasma reactor is improved as compared to the conventional sources of inductively coupled plasmas with the external flat coil configuration. A reasonable agreement between the experimental data and computed electromagnetic field topography inside the chamber is reported. The Langmuir probe measurements reveal that the spatial profiles of the electron density, the effective electron temperature, plasma potential, and electron energy distribution/probability functions feature a high degree of the radial and axial uniformity and a weak azimuthal dependence, which is consistent with the earlier theoretical predictions. As the input rf power increases, the azimuthal dependence of the global plasma parameters vanishes. The obtained results demonstrate that by introducing the internal oscillated rf currents one can noticeably improve the uniformity of electromagnetic field topography, rf power deposition, and the plasma density in the reactor.

Discharge mode transitions in low-frequency inductively coupled plasmas with internal oscillating current sheets

Transitions between the two discharge modes in a low-frequency (∼460 kHz) inductively coupled plasma sustained by an internal oscillating radio frequency (rf) current sheet are studied. The unidirectional rf current sheet is generated by an internal antenna comprising two orthogonal sets of synphased rf currents driven in alternately reconnected copper litz wires. It is shown that in the low-to-intermediate pressure range the plasma source can be operated in the electrostatic (E) and electromagnetic (H) discharge modes. The brightness of the E -mode argon plasma glow is found remarkably higher than in inductively coupled plasmas with external flat spiral "pancake" coils. The cyclic variations of the input rf power result in pronounced hysteretic variations of the optical emission intensity and main circuit parameters of the plasma source. Under certain conditions, it appears possible to achieve a spontaneous E→H transition ("self-transition"). The observed phenomenon can be attributed to the thermal drift of the plasma parameters due to the overheating of the working gas. The discharge destabilizing factors due to the gas heating and step-wise ionization are also discussed. © 2005 American Vacuum Society.

Graphene-type sheets of Nb1-xWxS2 : synthesis and in situ functionalization

Enlightened by the discovery of graphenes, a variety of inorganic analogues have been synthesized and characterized in recent years. Solvated Nb1-xWxS2 analogues of graphene-type sheets were prepared by lithiation and exfoliation of multistacked Nb1-xWxS2 coin roll nanowires (CRNWs), followed by in situ functionalization with gold nanoparticles to synthesize gold-loaded Nb1-xWxS2/Au nanocomposites. The Nb1-xWxS2 nanosheets and the corresponding Nb1-xWxS2/Au nanocomposites were characterized by high resolution electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM), dynamic light scattering (DLS) and scanning force microscopy (AFM). The graphene-type sheets are stable in water and other solvents and can be functionalized similarly as chalcogen-terminated surfaces (e.g. with Au nanoparticles).

Mechanism of kaolinite sheets curling via the intercalation and delamination process

Kaolinite naturally occurs in the plate form for the interlayer hydrogen bond and the distortion and adaption of tetrahedron and octahedron. But kaolinite sheets can be exfoliated to nanoscrolls artificially in laboratory through multiple-step displacement intercalation. The driving force for kaolinite sheet to be curled nanoscroll originates from the size discrepancy of Si–O tetrahedron and Al–O octahedron. The displacement intercalation promoted the platy kaolinite sheets spontaneously to be scrolled by eliminating the interlayer hydrogen bond and atomic interaction. Kaolinite nanoscrolls are hollow tubes with outer face of tetrahedral sheet and inner face of octahedral sheet. Based on the theoretical calculation it is firstly reported that the minimum interior diameter for a single kaolinite sheet to be scrolled is about 9.08 nm, and the optimal 24.30 nm, the maximum 100 nm, which is verified by the observation of scanning electron microscope and transmission electron microscope. The different adaption types and discrepancy degree between tetrahedron and octahedron generate various curling forces in different directions. The nanoscroll axes prefer the directions as [100], [1 �10], [110], [3 �10], and the relative curling force are as follows, [3 �10] > [100] = [1�10] > [110].

Real time maximum power conversion tracking and resonant frequency modification for high power piezoelectric ultrasound transducer

Piezoelectric ultrasound transducers are commonly used to convert mechanical energy to electrical energy and vice versa. The transducer performance is highly affected by the frequency at which it is excited. If excitation frequency and main resonant frequency match, transducers can deliver maximum power. However, the problem is that main resonant frequency changes in real time operation resulting in low power conversion. To achieve the maximum possible power conversion, the transducer should be excited at its resonant frequency estimated in real time. This paper proposes a method to first estimate the resonant frequency of the transducer and then tunes the excitation frequency accordingly in real time. The measurement showed a significant difference between the offline and real time resonant frequencies. Also, it was shown that the maximum power was achieved at the resonant frequency estimated in real time compare to the one measured offline.

Decellularized periodontal ligament cell sheets with recellularization potential

The periodontal ligament is the key tissue facilitating periodontal regeneration. This study aimed to fabricate decellularized human periodontal ligament cell sheets for subsequent periodontal tissue engineering applications. The decellularization protocol involved the transfer of intact human periodontal ligament cell sheets onto melt electrospun polycaprolactone membranes and subsequent bi-directional perfusion with NH4OH/Triton X-100 and DNase solutions. The protocol was shown to remove 92% of DNA content. The structural integrity of the decellularized cell sheets was confirmed by a collagen quantification assay, immunostaining of human collagen type I and fibronectin, and scanning electron microscopy. ELISA was used to demonstrate the presence of residual basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) in the decellularized cell sheet constructs. The decellularized cell sheets were shown to have the ability to support recellularization by allogenic human periodontal ligament cells. This study describes the fabrication of decellularized periodontal ligament cell sheets that retain an intact extracellular matrix and resident growth factors and can support repopulation by allogenic cells. The decellularized hPDL cell sheet concept has the potential to be utilized in future "off-the-shelf" periodontal tissue engineering strategies.

Numerical analysis for the interlayer toughening of piezoelectric smart composite plate

The piezoelectric composite material could engender stress concentration resulting from small cracks during layers easily, as the cracks growth will lead to the failure of the whole structure. In this paper, a finite element model for piezoelectric composite materials by ABAQUS including interlayer crack was established, and the J integral and crack tip stress of different types PZT patches were calculated by using the equivalent integral method. Then, the J integral for adhesive layers with different thickness, elastic modulus considering and not considering piezoelectricity was investigated. The results show that the J integral of mode I, II reduces with thicker adhesive layer and lower elastic modules, and the J integral of mode II decreases more sharply than that of mode I.

The impact of home loan key facts sheets on borrowers' comparisons of loan costs

This thesis evaluates the effectiveness of the prescribed design and distribution requirements of the Australian Government's home loan key facts sheets (KFS) aimed at helping borrowers compare loan costs. The findings show that despite effectively improving borrower decision-making, few borrowers were aware of their existence and function. It was also demonstrated that KFS have had limited market impact over the four year window since introduction, likely due to the requirement that KFS provision is not required unless formally requested by a borrower. Recommendations include transferring the burden of disclosure to lenders in the first instance to address this information gap.

Indentation strength of a piezoelectric ceramic: Experiments and simulations

The spherical indentation strength of a lead zirconate titanate (PZT) piezoelectric ceramic was investigated under poled and unpoled conditions and with different electrical boundary conditions (arising through the use of insulating or conducting indenters). Experimental results show that the indentation strength of the poled PZT is higher than that of the unpoled PZT. The strength of a poled PZT under a conducting indenter is higher than that under an insulating indenter. Poling direction (with respect to the direction of indentation loading) did not significantly affect the strength of material. Complementary finite element analysis (FEA) of spherical indentation of an elastic, linearly coupled piezoelectric half-space is conducted for rationalizing the experimental observations. Simulations show marked dependency of the contact stress on the boundary conditions. In particular, contact stress redistribution in the Coupled problem leads to a change in the fracture initiation, from Hertzian cracking in the unpoled material to Subsurface damage initiation in poled PZT. These observations help explain the experimental ranking of strength the PZT in different material conditions or under different boundary conditions.

Identification and analysis of extended strands and beta-sheets in globular proteins

A method to identify β-sheets in globular proteins from extended strands, using only α-carbon positions, has been developed. The strands that form β-sheets are picked up by means of simple distance criteria. The method has been tested by applying it to three proteins with accurately known secondary structures. It has also been applied to ten other proteins wherein only α-carbon coordinates are available, and the list of β-sheets obtained. The following points are worth noting: (i) The sheets identified by the algorithm are found to agree satisfactorily with the reported ones based on backbone hydrogen bonding, wherever this information is available. (ii) β-Strands that do not form parts of any sheet are a common feature of protein structures. (iii) Such isolated β-strands tend to be short. (iv) The conformation corresponding to the preferred right-handed twist of the sheet is overwhelmingly observed in both the sheet-forming and isolated β-strands.

Texture dependent stress corrosion failure of commercial titanium sheets in bromine-methanol solution

The stress corrosion cracking (SCC) characteristics of agr-titanium sheets in a bromine-methanol solution have been studied in the annealed and cold-rolled conditions using longitudinal and transverse specimens. The times to failure for annealed longitudinal specimens were longer than those for similarly tested transverse specimens. The cold-rolled specimens developed resistance to SCC, but failed by cleavage when notched, unlike the intergranular separation in annealed titanium. The apparent activation energy was found to be texture dependent and was in the range 30 to 51 kJ mol–1 for annealed titanium, and 15kJ mol–1 for cold-rolled titanium. The dependence of SCC behaviour on the texture is related to the changes in the crack initiation times. These are caused by changes in the passivation and repassivation characteristics of the particular thickness plane. The thickness planes are identified with the help of X-ray pole figures obtained on annealed and cold-rolled material. On the basis of the activation energy and the electrochemical measurements, the mechanism of SCC in annealed titanium is identified to be the one involving stress-aided anodic dissolution. On the other hand, the results on the cold-rolled titanium are in support of the hydrogen embrittlement mechanism consisting of hydride precipitation. The cleavage planes identified from the texture data match with the reported habit planes for hydride formation.

Fungal Planet description sheets: 128-153

Novel species of microfungi described in the present study include the following from Australia: Catenulostroma corymbiae from Corymbia, Devriesia stirlingiae from Stirlingia, Penidiella carpentariae from Carpentaria, Phaeococcomyces eucalypti from Eucalyptus, Phialophora livistonae from Livistona, Phyllosticta aristolochiicola from Aristolochia, Clitopilus austroprunulus on sclerophyll forest litter of Eucalyptus regnans and Toxicocladosporium posoqueriae from Posoqueria. Several species are also described from South Africa, namely: Ceramothyrium podocarpi from Podocarpus, Cercospora chrysanthemoides from Chrysanthemoides, Devriesia shakazului from Aloe, Penidiella drakensbergensis from Protea, Strelitziana cliviae from Clivia and Zasmidium syzygii from Syzygium. Other species include Bipolaris microstegii from Microstegium and Synchaetomella acerina from Acer (USA), Brunneiapiospora austropalmicola from Rhopalostylis (New Zealand), Calonectria pentaseptata from Eucalyptus and Macadamia (Vietnam), Ceramothyrium melastoma from Melastoma (Indonesia), Collembolispora aristata from stream foam (Czech Republic), Devriesia imbrexigena from glazed decorative tiles (Portugal), Microcyclospora rhoicola from Rhus (Canada), Seiridium phylicae from Phylica (Tristan de Cunha, Inaccessible Island), Passalora lobeliaefistulosis from Lobelia (Brazil) and Zymoseptoria verkleyi from Poa (The Netherlands). Valsalnicola represents a new ascomycete genus from Alnus (Austria) and Parapenidiella a new hyphomycete genus from Eucalyptus (Australia). Morphological and culture characteristics along with ITS DNA barcodes are also provided. © 2012 Nationaal Herbarium Nederland & Centraalbureau voor Schimmelcultures.

Fungal Planet description sheets: 281–319

Novel species of fungi described in the present study include the following from South Africa: Alanphillipsia aloeicola from Aloe sp., Arxiella dolichandrae from Dolichandra unguiscati, Ganoderma austroafricanum from Jacaranda mimosifolia, Phacidiella podocarpi and Phaeosphaeria podocarpi from Podocarpus latifolius, Phyllosticta mimusopisicola from Mimusops zeyheri and Sphaerulina pelargonii from Pelargonium sp. Furthermore, Barssia maroccana is described from Cedrus atlantica (Morocco), Codinaea pini from Pinus patula (Uganda), Crucellisporiopsis marquesiae from Marquesia acuminata (Zambia), Dinemasporium ipomoeae from Ipomoea pes-caprae (Vietnam), Diaporthe phragmitis from Phragmites australis (China), Marasmius vladimirii from leaf litter (India), Melanconium hedericola from Hedera helix (Spain), Pluteus albotomentosus and Pluteus extremiorientalis from a mixed forest (Russia), Rachicladosporium eucalypti from Eucalyptus globulus (Ethiopia), Sistotrema epiphyllum from dead leaves of Fagus sylvatica in a forest (The Netherlands), Stagonospora chrysopyla from Scirpus microcarpus (USA) and Trichomerium dioscoreae from Dioscorea sp. (Japan). Novel species from Australia include: Corynespora endiandrae from Endiandra introrsa, Gonatophragmium triuniae from Triunia youngiana, Penicillium coccotrypicola from Archontophoenix cunninghamiana and Phytophthora moyootj from soil. Novelties from Iran include Neocamarosporium chichastianum from soil and Seimatosporium pistaciae from Pistacia vera, Xenosonderhenia eucalypti and Zasmidium eucalyptigenum are newly described from Eucalyptus urophylla in Indonesia. Diaporthe acaciarum and Roussoella acacia are newly described from Acacia tortilis in Tanzania. New species from Italy include Comoclathris spartii from Spartium junceum and Phoma tamaricicola from Tamarix gallica. Novel genera include (Ascomycetes): Acremoniopsis from forest soil and Collarina from water sediments (Spain), Phellinocrescentia from a Phellinus sp. (French Guiana), Neobambusicola from Strelitzia nicolai (South Africa), Neocladophialophora from Quercus robur (Germany), Neophysalospora from Cotymbia henryi (Mozambique) and Xenophaeosphaeria from Grewia sp. (Tanzania). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.