Fabric evolution and strain localisation in inherently anisotropic specimens of anisometric particles (lentils) under triaxial compression

Granular Matter - Engineered granular materials have gained considerable interest in recent years. For this substance, the primary design variable is grain shape. Optimizing grain form to achieve a...     

Single-crystalline Te microtubes: Synthesis and NO2 gas sensor application

Tellurium tubular crystals were grown by direct thermal evaporation of tellurium metal in an inert atmosphere on quartz substrates at ambient pressure without employing any catalyst. Tellurium powder was evaporated by heating at 600 °C and was condensed at a substrate temperature of 300–350 °C in the downstream of argon gas at a flow rate of 100 mL/min. The structure and chemical composition of the as-synthesized samples were examined by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-rays microanalysis and micro-Raman spectroscopy. Scanning electron microscopy images and X-ray diffraction patterns showed that the as-synthesized Te had a tubular single-crystalline morphology with a hexagonal cross-section. The Te microtubes were typically 0.5–6 mm long, 30–70 μm in external diameter, and 5–20 μm thick. NO₂ gas-sensing properties of the Te microtubes at room temperature were also investigated. They showed a promising sensitivity and response towards tested gas.     

Localised deformation patterning in 2D granular materials revealed by digital image correlation

Tests have been performed on an analogue two-dimensional granular material in a special laboratory apparatus that allows the application of general stress or strain conditions. Digital image correlation of pairs of consecutive photographs taken during the tests has enabled fields of displacement and hence strain to be determined. Thus direct observation of internal displacements and strains has been possible for a series of general strain increments with different orientations of principal strain and different imposed angles of dilation. This analysis has successfully provided clear evidence of evolving internal structures of deformation. The observed evolving structures consist of bands of localised deformation and ‘cells’ of low deformation between the bands. The orientations of the identified localised features and cells are seen to depend on the applied strain path. The characteristic features and dimensions of the bands have been approximately identified.     

Can intergranular force transmission be identified in sand?

This work tackles the challenge of assessment of force distributions in granular media. Spatially resolved neutron and x-ray diffraction are used to measure internal strains of sand grains under load. These approaches are sensitive to the crystallographic strains of the sand grains (quartz crystals) such that each grain acts as a local 3D strain gauge and so, for elastic deformations, a force gauge. First results are presented from recent experiments that provide tantalising indications of the potential of these techniques in the investigation of the mechanics of granular media.     

Observing strain localisation processes in bio-cemented sand using x-ray imaging

In-situ x-ray tomography has been used to follow deformation processes in 3D during two triaxial compression tests, one on a specimen of bio-cemented Ottawa 50?C70 sand and the other on a specimen of the non-cemented sand. The global stress-strain responses show that the bio-cementation process increases the shear strength (peak deviator stress is approximately doubled), and causes the material to exhibit a linear behaviour up until peak, as well as increasing the dilatancy angle. The residual strength of the two samples is very close at large strain. Quantitative 3D digital image analysis (porosity, cement-density and strain field measurements), reveals that a dilatant shear band gradually develops pre-peak in the reference material. The cemented sample however undergoes an abrupt change of deformation mechanism at peak stress: from homogeneous deformation to localised dilatant shearing, which is associated with a local loss of cementation.     

Answer to the remarks on superconductivity in PdH

In this paper, the effect of heating rate on the microwave sintered 90W–7Ni–3Fe heavy alloys was investigated, with the heating rate in the range from 10 to 112 °C/min. When the alloys were sintered at the heating rate from 20 to 105 °C/min, they exhibit excellent properties with the relative density over 99%, tensile strength between 850 and 922 MPa and elongation around 20%. It has been shown that a faster heating rate results in smaller W grain size and larger W–W contiguity. The heating rate of 80 °C/min has the best combination of the microstructure and mechanical performance. Sintering under an optimized condition leads to the enhanced mechanical properties of 1020 MPa in tensile strength and 21% in elongation.     

Effects of low frequency electromagnetic fields on expression of lymphocyte subsets and production of cytokines of men and women employed in a museum

The objective of this study was to analyse the immune response to electromagnetic fields (ELMFs) in seven men and eight women employed in a museum. The workers were exposed in a room to an ELMFs (range 0.2-3.6 microT and 40-120 V/m) induced by 50 Hz electricity for 20 h a week. Control groups consisted of 47 women and 39 men with a similar percentage of atopic subjects, age (range 30-51 years) and smoking habits of the workers included in the study. Levels of blood lead (Pb) and urinary trans-trans muconic acid, a metabolite of benzene (markers of exposure to traffic and smoking) of the control and exposed groups were similar. Lymphocyte subsets were determined in men and women using conjugated antibodies. Serum interleukin (IL) 4 and interferon gamma and their 'in vitro' production by peripheral mononuclear blood cells (PMBCs) stimulated by phytohemoglutinin (PHA), as well as blastogenesis of PMBCs induced by PHA, were determined in women only. ELMF-exposed women showed a significant reduction in the percentage of B and NK CD3(-)-CD25+ lymphocytes and a slight reduction of CD16(+)-56+ NK lymphocytes. They also showed significantly lower levels of interferon gamma in serum, or produced in the supernatants by PMBCs both spontaneously and stimulated by PHA, while they did not show significant changes in serum and 'in vitro' produced IL-4, or in blastogenesis of PMBCs. Men working in the museum showed, in relation to the controls, a statistically significant reduction in both number and percentage of CD16(+)- CD56+ and CD3(-)-CD25+ lymphocyte subsets. On the whole, this investigation demonstrates a reduction of blood NK lymphocytes and of the production of interferon gamma in workers exposed to low frequency ELMFs. Recent studies have shown that stress and poor lifestyle induce the reduction of blood cytotoxic activities possibly acting on nervous functions. This may suggest that ELMFs reduces blood NK lymphocytes by combined effects on the immune and nervous systems.