Melt processing and characterisation of lightweight metal composites reinforced by nanocarbon

Increasing the specific strength of lightweight structural metals such as magnesium, which has two-thirds the density of aluminium, has the potential to significantly widen their application and improve the system energy efficiency and performance across transport and defence industries. Reinforcing magnesium matrices with nano-sized particles to form metal matrix nanocomposites (MMNCs) has shown promise as a way of achieving an increase in specific properties, albeit without the traditionally associated decrease in ductility. This study manufactured and characterised magnesium-based MMNCs to investigate the impact of nanoparticle reinforcements on the mechanical properties of the composites, their microstructure and the theoretical models used for the potential strengthening mechanisms. Multi-walled carbon nanotubes (MWCNTs) can be considered as the ideal reinforcing nanoparticle due to their exceptional mechanical properties, geometry and low density, which can take full advantage of the proposed strengthening mechanisms that occur when nanoparticles are added to a metal matrix. MWCNTs are however notoriously difficult to be homogenously dispersed in a metal matrix and are poorly wetted by molten metal; therefore, nickel coated MWCNTs (NiCNTs) and silicon carbide nanoparticles are also investigated as a potential solution for wettability in this study. Magnesium alloy AZ91D was used as the metal matrix material and the MMNCs were made using metal melt-stirring combined with a nanoparticle pre-dispersion technique. Melt processing and casting techniques are favoured in component manufacturing processes due their scalability and cost-effectiveness. The melt stirring processing parameters such as casting temperature, stirring time and stirring speed were thoroughly examined and modified to successfully produce MMNC samples. The compression mechanical properties of the AZ91D-MWCNT composites showed no change for a range of MWCNT concentrations for the melt stirring processing parameters tested. Theoretical studies of nanoparticle dispersion and wettability combined with electron microscopy of the cross sections of the samples showed that the pre-dispersion and melt stirring processes were insufficient to homogenously disperse the MWCNTs in the metal matrix, therefore NiCNTs were utilised. Whilst no significant differences in compression mechanical properties were seen for the AZ91D-NiCNT samples, a 13% increase in hardness was achieved. An 11% and 20% increase in hardness was achieved for samples of AZ91D composites reinforced with equal concentration of silicon carbide nanoparticles and whiskers, respectively. The poor wettability of MWCNTs by AZ91D melt, apparent from SEM imaging of the composite fracture surfaces, suggested that in order to take advantage of the superior mechanical properties of MWCNTs, a coherent interface between the MWCNT and the Mg matrix is necessary. The nickel coating and silicon carbide nanoparticles, known to wet with molten magnesium, may have provided a coherent interface that resulted in the measured increase in hardness.Open Acces

Low-lying eigenmodes of the Wilson-Dirac operator and correlations with topological objects

The probability density of low-lying eigenvectors of the hermitian Wilson-Dirac operator is examined. Comparisons in position and size between eigenvectors, topological charge and action density are made. We do this for standard Monte-Carlo generated SU(3) background fields and for single instanton background fields. Both hot and cooled SU(3) background fields are considered. An instanton model is fitted to eigenmodes and topological charge density and the sizes and positions of these are compared.Comment: v3: 20 pages, 11 figures, Colour versions of Fig. 1 and Fig. 4 and additional colour figures can be obtained at http://www.physics.adelaide.edu.au/cssm/lattice Revised version contains additional discussions about the topological charge used and greatly improved readability of the plots, Corrected Fig.

O Z-Degree de Tidewater e o modelo INTRO para a Adoção Sustentável dos REA

A growing body of research confirms the financial and academic benefits that accrue to students whose faculty adopt open educational resources, or OER. While there are no content licensing costs associated with using OER, there are several real costs that must be incurred by an institution that chooses to support its faculty in adopting OER. The Z-Degree initiative at Tidewater Community College utilizes only OER for the 21 courses, providing a pathway for students to earn an associate of science degree in business administration without ever buying a textbook. The authors introduce and illustrate the INTRO (INcreased Tuition Revenue through OER) model for sustaining the provision of OER adoption services. The adoption of OER as part of the Z-Degree decreases drop rates among Tidewater students, allowing the institution to retain tuition revenue it would otherwise have refunded. This retained revenue provides a renewable source of funds to sustainably support the adoption of OER.Un creciente cuerpo de investigaciones reafirman los beneficios económicos y académicos que reportan sobre los estudiantes universitarios el uso de recursos educativos abiertos (REA) por parte de sus docentes. Sin embargo, las instituciones que deciden apoyan a sus docentes en el uso de REA tienen que asumir una gran cantidad de costes reales, a pesar de no contar con costes asociados a las licencias de contenido. La iniciativa Z-Degree llevada a cabo por la Tidewater Community College utiliza solo REA en 21 asignaturas del Diploma de Asociado en Ciencias de Administración de Empresas, proporcionando una vía para que los estudiantes puedan obtener el título universitario sin tener que comprar un solo libro de texto. Los autores presentan e ilustran el modelo Aumento de los Ingresos por Matrículas a través de REA (INTRO, por sus siglas en inglés) para sostener la prestación de servicios que supone la adopción de los REA. La adopción de los REA como parte de la Z-Degree disminuye las tasas de abandono entre los estudiantes Tidewater, lo que permite a la institución mantener los ingresos por las matrículas. Esta retención de ingresos proporciona una fuente renovable de fondos para apoyar de forma sostenible la adopción de los REA.Um crescente corpo de pesquisa confirma os benefícios financeiros e acadêmicos que para os alunos cujos professores adotam recursos educacionais abertos, ou REA. Ainda que não há nemhum custo de licença de conteúdo associado com usar REA, sim há custos reais que devem ser incorridos por uma institucao que decide apoiar sua faculdade na adoção dos REA. A iniciativa de Z-Degree, em Tidewater College utiliza apenas REA para os vinte-uns cursos porem provendo um caminho para que os alunos ganham uma diploma de Associate’s de ciencia em administração de empresas sem nunca compra um livro. Os autores apresentam e ilustram o INTRO (Increased Tuition Revenue atraves de REA) modelo para sustentar a prestação de serviços para a adoção dos REA. A adoção de REA como parte do Z-Degree diminui taxas de abandono entre os alunos de Tidewater, permitindo que a instituição retenha a receita de matrícula que em outra situação teria devolvido. Este receita retida fornece uma fonte renovável de fundos para apoiar de forma sustentável a adopção de REA

Geospatial Data on Parade: The Results and Implications of the GIS Analysis of Remote Sensing and Archaeological Excavation Data at Fort York’s Central Parade Ground

This article presents a case study on the application of geographical information systems (GIS) in the context of military archaeology at the Fort York National Historic Site (AjGu-26) in Toronto, Ontario. By employing GIS to amalgamate data from historic mapping, ground penetrating radar, LiDAR, and 30 years of archaeological investigation, the authors reconstruct the historic landscape at the central parade ground of this national historic site. In doing so, they identify the remains of an early 19th-century vice-regal building that served as the official residence of the lieutenant governors of Upper Canada before the American forces burned it down in 1813—an important event that later provided the justification for the British destruction of the White House. With the successful application of GIS to amalgamate multiple lines of evidence, the article serves as another case for the broader acceptance of digital data technologies into the standard methodological toolkits of archaeologists

Geospatial Data on Parade: The Results and Implications of GIS Analysis of Remote Sensing and Archaeological Excavation Data at Fort York’s Central Parade Ground

Source at https://orb.binghamton.edu/neha/vol44/iss1/6.This article presents a case study on the application of geographical information systems (GIS) in the context of military archaeology at the Fort York National Historic Site (AjGu-26) in Toronto, Ontario. By employing GIS to amalgamate data from historic mapping, ground penetrating radar, LiDAR, and 30 years of archaeological investigation, the authors reconstruct the historic landscape at the central parade ground of this national historic site. In doing so, they identify the remains of an early 19th-century vice-regal building that served as the official residence of the lieutenant governors of Upper Canada before the American forces burned it down in 1813—an important event that later provided the justification for the British destruction of the White House. With the successful application of GIS to amalgamate multiple lines of evidence, the article serves as another case for the broader acceptance of digital data technologies into the standard methodological toolkits of archaeologists

Comparing short gamma-ray burst jet structure models

A structured gamma-ray burst (GRB) jet could explain the dimness of the prompt emission observed from GRB 170817A, but the exact form of this structure is still ambiguous. However, with the promise of future joint gravitational wave (GW) and GRB observations, we shall be able to examine populations of binary neutron star (BNS) mergers rather than on a case-by-case basis. We present an analysis that considers GW triggered BNS events both with and without short GRB counterparts assuming that events without a counterpart were observed off-axis. This allows for Bayes factors to be calculated to compare different jet structure models. We perform model comparison between a Gaussian and power-law apparent jet structure on simulated data to demonstrate that the correct model can be distinguished with a log Bayes factor of >5 after fewer than 100 events. Constraints on the apparent structure jet model parameters are also made. After 25(100) events the angular width of the core of a power-law jet structure can be constrained within a 90% credible interval of width ~9.1(4.4)°, and the outer beaming angle to be within ~19.9(8.5)°. Similarly, we show the width of a Gaussian jet structure to be constrained to ~2.8(1.6)°

Formation of the coherent heavy fermion liquid at the 'hidden order' transition in URu2Si2

In this article we present high-resolution angle-resolved photoemission (ARPES) spectra of the heavy-fermion superconductor URu$_2$Si$_2$. Measurements as a function of both excitation energy and temperature allow us to disentangle a variety of spectral features, revealing the evolution of the low energy electronic structure across the hidden order transition. Already above the hidden order transition our measurements reveal the existence of weakly dispersive states below the Fermi level that exhibit a large scattering rate. Upon entering the hidden order phase, these states transform into a coherent heavy fermion liquid that hybridizes with the conduction bands.Comment: 5 pages, 4 figure