Role of carbon nanotube dispersion in fracture toughening of plasma sprayed aluminum oxide - carbon nanotube nanocomposite coating

Aluminum oxide (A1203, or alumina) is a conventional ceramic known for applications such as wear resistant coatings, thermal liners, heaters, crucibles, dielectric systems, etc. However applications of A1203 are limited owing to its inherent brittleness. Due to its excellent mechanical properties and bending strength, carbon nanotubes (CNT) is an ideal reinforcement for A1203 matrix to improve its fracture toughness. The role of CNT dispersion in the fracture toughening of the plasma sprayed A1203-CNT nanocomposite coating is discussed in the current work. Pretreatment of powder feedstock is required for dispersing CNTs in the matrix. Four coatings namely spray dried A1203 (A-SD), A1203 blended with 4wt.% CNT (A4C-B), composite spray dried A1203-4wt.% CNT (A4C-SD) and composite spray dried A1203-8wt.% CNT (A8CSD), are synthesized by plasma spraying. Owing to extreme temperatures and velocities involved in the plasma spraying of ceramics, retention of CNTs in the resulting coatings necessitates optimizing plasma processing parameters using an inflight particle diagnostic sensor. A bimodal microstructure was obtained in the matrix that consists of fully melted and resolidified structure and solid state sintered structure. CNTs are retained both in the fully melted region and solid-state sintered regions of processed coatings. Fracture toughness of A-SD, A4C-B, A4C-SD and A8C-SD coatings was 3.22, 3.86, 4.60 and 5.04 MPa m1/2 respectively. This affirms the improvement of fracture toughness from 20 % (in A4C-B coating) to 43% (in A4C-SD coating) when compared to the A-SD coating because of the CNT dispersion. Fracture toughness improvement from 43 % (in A4C-SD) to 57% (in A8C-SD) coating is evinced because of the CNT content. Reinforcement by CNTs is described by its bridging, anchoring, hook formation, impact alignment, fusion with splat, and mesh formation. The A1203/CNT interface is critical in assisting the stress transfer and utilizing excellent mechanical properties of CNTs. Mathematical and computational modeling using ab-initio principle is applied to understand the wetting behavior at the A1203/CNTinterface. Contrasting storage modulus was obtained by nanoindentation (~ 210, 250, 250-350 and 325-420 GPa in A-SD, A4C-B, A4C-SD, and A8C-SD coatings respectively) depicting the toughening associated with CNT content and dispersion.

Giant enhancement of n-type carrier mobility in highly strained germanium nanostructures

First-principles electronic structure methods are used to predict the rate of n-type carrier scattering due to phonons in highly-strained Ge. We show that strains achievable in nanoscale structures, where Ge becomes a direct bandgap semiconductor, cause the phonon-limited mobility to be enhanced by hundreds of times that of unstrained Ge, and over a thousand times that of Si. This makes highly tensile strained Ge a most promising material for the construction of channels in CMOS devices, as well as for Si-based photonic applications. Biaxial (001) strain achieves mobility enhancements of 100 to 1000 with strains over 2%. Low temperature mobility can be increased by even larger factors. Second order terms in the deformation potential of the Gamma valley are found to be important in this mobility enhancement. Although they are modified by shifts in the conduction band valleys, which are caused by carrier quantum confinement, these mobility enhancements persist in strained nanostructures down to sizes of 20 nm.

First-principles calculation of alloy scattering in GexSi1-x

First-principles electronic structure methods are used to find the rates of intravalley and intervalley n-type carrier scattering due to alloy disorder in Si1-xGex alloys. The required alloy scattering matrix elements are calculated from the energy splitting of nearly degenerate Bloch states which arises when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Scattering parameters for all relevant Delta and L intravalley and intervalley alloy scattering are calculated. Atomic relaxation is found to have a substantial effect on the scattering parameters. f-type intervalley scattering between Delta valleys is found to be comparable to other scattering channels. The n-type carrier mobility, calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys.

Amino acid racemization for several DSDP samples (Table 1)

Kinetic parameters for the epimerization of isoleucine in multispecific foraminiferal asemblages were used to establish the effects of burial depth and the geothermal gradient on the extent of reaction. It was observed that with a little as thirty meters of burial in a normal thermal regime there were differences between the extent of epimerization measured and that which would have been predicted for thermal equilibrium with bottom water temperatures. As would be expected, these differences are greatest when the heat flow (the geothermal gradient) and/or the sedimentation rates are highest. These effects were observed in most of the DSDP samples studied, and have been used to estimate the average heat flux since the time of sample deposition. Occasional anomalous effects were observed which could not be related to past or present heat flux. These were determined to be due to such geologic occurrences as slumping and reworking or to recent sample contamination. Other problems emerged related to bottom water temperatures including changes over geologic time which are unknown and could not be deduced. Thus, the presence of epimerization anomalies in DSDP cores as noted above limits the effectiveness of amino acid geochronology in such cores, unless these anomalies can be recognized as ab initio.

Interplay of Defects, Magnetism, Ripples and Strain in Graphene

We present a comprehensive study based on first-principles calculations about the interplay of four important ingredients on the electronic structure of graphene: defects + magnetism + ripples + strain. So far they have not been taken into account simultaneously in a set of ab initio calculations. Furthermore, we focus on the strain dependence of the properties of carbon monovacancies, with special attention to magnetic spin moments. We demonstrated that such defects show a very rich structural and spin phase-diagram with many spin solutions as function of strain. At zero strain the vacancy shows a spin moment of 1.5 Bohrs that increases up to 2 Bohrs with stretching. Changes are more dramatic under compression: the vacancy becomes non-magnetic under a compression larger than 2%. This transition is linked to the structural modifications associated with the formation of ripples in the graphene layer. Our results suggest that such interplay could have important implications for the design of future spintronics devices based on graphene derivatives, as for example a spin-strain switch based on vacancies.

Vector Graphics: From PostScript and Flash to SVG

The XML-based specification for Scalable Vector Graphics (SVG), sponsored by the World Wide Web consortium, allows for compact and descriptive vector graphics for the Web. SVG s domain of discourse is that of graphic primitives whose optional attributes express line thickness, fill patterns, text size and so on. These primitives have very different properties from those of traditional document components (e.g. sections, paragraphs etc.) that XML is normally called upon to express. This paper describes a set of three tools for creating SVG, either from first principles or via the conversion of existing formats. The ab initio generation of SVG is effected from a server-side CGI script, using a PERL library of drawing functions; later sections highlight the problems of converting Adobe PostScript and Macromedia s Shockwave format (SWF) into SVG.

Quiralidade, superfície de energia potencial e dinâmica de complexos envolvendo H2O2 + gases nobres

Tese (doutorado)—Universidade de Brasília, Instituto de Física, 2015.

On the temperature dependence of the rate coefficient of formation of C2+ from C + CH+

[EN] We carry out quasi-classical trajectory caculations for theC + CH+ → C2+ + H reaction on an ad hoc computed high-level ab initio potential energy surface. Thermal rate coefficients at the temperatures of relevance in cold interstellar clouds are derived and compared with the assumed, temperature-independent estimates publicly available in kinetic databases KIDA and UDfA. For a temperature of 10 K the database value overestimates by a factor of two the one obtained by us (thus improperly enhancing the destruction route of CH+ in astrochemical kinetic models) which is seen to double in the temperature range 5–300 K with a sharp increase in the first 50 K. The computed values are fitted via the popular Arrhenius–Kooij formula and best-fitting parameters α = 1:32 X 10-9 cm3s-1, β = 0:10 and γ = 2:19 K to be included in the online mentioned databases are provided. Further investigation shows that the temperature dependence of the thermal rate coefficient better conforms to the recently proposed so-called ‘deformed Arrhenius’ law by Aquilanti and Mundim.

A gestão da qualidade no ensino superior: Percursos e recursos

Este artigo condensa um conjunto de reflexões baseadas em factos relacionados com a gestão da qualidade nas Instituições de Ensino Superior (IES). São identificados factores internos e externos favoráveis à melhoria da qualidade dos serviços prestados por estas organizações, bem como algumas das barreiras que se lhe opõem. Relativamente às abordagens da qualidade, nestas organizações são consideradas: de um lado as que resultam da Supervisão do Estado e do outro as que estão associadas a sistemas de natureza voluntária, designadas aqui por Abordagem Qualidade, em que sobressai a Certificação baseada na norma ISO 9001 e os sistemas de Gestão pela Qualidade Total (GQT) também designados de Excelência Organizacional. São identificadas algumas das insuficiências dos modelos assentes na Supervisão do Estado e defendida a importância de atender ao conjunto de “boas práticas” já existentes, ao invés de abordagens que tratam desta problemática numa perspectiva ab initio, sem contemplar o conhecimento acumulado neste domínio da gestão das organizações.

Estudo do genoma do vírus causador da mionecrose infecciosa em camarões e desenvolvimento de métodos para detecção de polimorfismos

Shrimp farming is one of the activities that contribute most to the growth of global aquaculture. However, this business has undergone significant economic losses due to the onset of viral diseases such as Infectious Myonecrosis (IMN). The IMN is already widespread throughout Northeastern Brazil and affects other countries such as Indonesia, Thailand and China. The main symptom of disease is myonecrosis, which consists of necrosis of striated muscles of the abdomen and cephalothorax of shrimp. The IMN is caused by infectious myonecrosis virus (IMNV), a non-enveloped virus which has protrusions along its capsid. The viral genome consists of a single molecule of double-stranded RNA and has two Open Reading Frames (ORFs). The ORF1 encodes the major capsid protein (MCP) and a potential RNA binding protein (RBP). ORF2 encodes a probable RNA-dependent RNA polymerase (RdRp) and classifies IMNV in Totiviridae family. Thus, the objective of this research was study the IMNV complete genome and encoded proteins in order to develop a system differentiate virus isolates based on polymorphisms presence. The phylogenetic relationship among some totivirus was investigated and showed a new group to IMNV within Totiviridae family. Two new genomes were sequenced, analyzed and compared to two other genomes already deposited in GenBank. The new genomes were more similar to each other than those already described. Conserved and variable regions of the genome were identified through similarity graphs and alignments using the four IMNV sequences. This analyze allowed mapping of polymorphic sites and revealed that the most variable region of the genome is in the first half of ORF1, which coincides with the regions that possibly encode the viral protrusion, while the most stable regions of the genome were found in conserved domains of proteins that interact with RNA. Moreover, secondary structures were predicted for all proteins using various softwares and protein structural models were calculated using threading and ab initio modeling approaches. From these analyses was possible to observe that the IMNV proteins have motifs and shapes similar to proteins of other totiviruses and new possible protein functions have been proposed. The genome and proteins study was essential for development of a PCR-based detection system able to discriminate the four IMNV isolates based on the presence of polymorphic sites

Assessing the activity coefficients of water in cholinium-based ionic liquids: experimental measurements and COSMO-RS modeling

The vapor liquid-equilibrium of water + ionic liquids is relevant for a wide range of applications of these compounds. It is usually measured by ebulliometric techniques, but these are time consuming and expensive. In this work it is shown that the activity coefficients of water in a series of cholinium-based ionic liquids can be reliably and quickly estimated at 298.15K using a humidity meter instrument. The cholinium based ionic liquids were chosen to test this experimental methodology since data for water activities of quaternary ammonium salts are available in the literature allowing the validation of the proposed technique. The COSMO-RS method provides a reliable description of the data and was also used to understand the molecular interactions occurring on these binary systems. The estimated excess enthalpies indicate that hydrogen bonding between water and ionic liquid anion is the dominant interaction that governs the behavior of water and cholinium-based ionic liquids systems, while the electrostatic-misfit and van der Walls forces have a minor contribution to the total excess enthalpies.

Structure-properties correlations in divalent metal phosphonates

Crystalline metal phosphonates may offer acidic sites, structural flexibility and guest molecules (H2O, heterocyclics, etc.) which can act as proton carriers. In addition, some frameworks are also amenable for post‐synthesis modifications in order to enhance desired properties [1,2]. In this work, we present the synthesis and structural characterization of two hydroxyphosphonoacetates hybrids based on magnesium, [Mg5(O3PCHOHCOO)2(HO3PCHOHCOO)2·8H2O] [Mg5(HPAA)2(H1HPAA)2·8H2O], and zinc, [Zn6K(O3PCHOHCOO)4(OH)·6.5H2O] [Zn6K(HPAA)4(OH)·6.5H2O]. Both solids present three-dimensional frameworks and their crystal structures were solved ab initio from X-ray powder diffraction. The proton conductivity of [Zn6K(HPAA)4(OH)·6.5H2O] as well as ammonia derivatives of M(II)(HO3PCHOHCOO)·2H2O [M(II)=Zn, Mg] will be reported and discussed.

El fenotipo "basal-her2" en el cáncer de mama: caracterización clínico-molecular e implicaciones terapéuticas

Clinically HER2+ (cHER2+) breast cancer (BC), as exclusively determined by immunohistochemistry of HER2 protein overexpression and/or fluorescence in situ hybridization of HER2 gene amplification, has been largely considered a single disease entity in terms of clinical outcome and in the susceptibility to the anti-HER2 monoclonal antibody trastuzumab (Herceptin). However, although the adjuvant/neoadjuvant use of the trastuzumab has been shown to significantly reduce recurrence risk when added to standard chemotherapy in women with early-stage cHER2+ BC, not all cases derive similar benefit from trastuzumab because a significant number of cHER2+ BC patients develop disease recurrence. Unfortunately, the identification of a robust clinical predictor of trastuzumab benefit, including HER2 itself, has proven challenging in the adjuvant/neoadjuvant setting. Thus, we suggest that a new generation of research needs to refine the prognostic taxonomy of cHER2+ BC and develop easy-to-use, clinicbased prediction algorithms to distinguish between good- and poor- responders to trastuzumab-based therapy ab initio. This study offered two hypotheses: 1.) HER2 overexpression can unexpectedly take place in a molecular background owned by basal-like BC (a commonly HER2-negative BC subtype which possesses many epithelial-mesenchymal transition (EMT) characteristics and exhibits robust cancer stem cell [CSC]-like features), thus generating a so-called basal/cHER2+ BC subtype; 2.) the basal/cHER2+ phenotype confers poor prognosis and delineates a subgroup of intrinsically aggressive cHER2+ BC with primary resistance to trastuzumab...