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The thermomechanical processing of NiTi shape memory alloys usually involves several steps of hot and/or cold deformation. The present work presents the structural characterization of a Ni-rich NiTi alloy bar, produced by vacuum-induced melting and thermomechanical processing in laboratory scale, aiming at massive production in the future. This study focused on the first step of hot working at 800 °C during rotary forging. Microstructural characterization was performed using differential scanning calorimetry, high- and low-temperature X-ray diffraction (XRD) using a laboratory source and synchrotron XRD. Thus, it was possible to obtain the phase transformation characteristics of the material: the transformation temperatures and the transformation sequence. Proposed thermomechanical processing is intended for production of bars and wires that will be subsequently drawn to get thin wires, for different applications, including orthodontic arch wires.
Archaeological materials present unique records on natural processes allowing the study of long-term material behaviors such as structural modifications and degradation mechanisms. The present work is focused on the chemical and microstructural characterization of four prehistoric arsenical copper artifacts. These artifacts were characterized by micro-energy dispersive X-ray fluorescence spectrometry, optical microscopy, scanning electron microscopy with X-ray microanalysis, micro-X-ray diffraction and synchrotron radiation micro-X-ray diffraction. Cu3As is the expected intermetallic arsenide in arsenical copper alloys, reported in the literature as exhibiting a hexagonal crystallographic structure. However, a cubic Cu3As phase was identified by X-ray diffraction in all of our analyzed archaeological artifacts, while the hexagonal Cu3As phase was clearly identified only in the artifact with higher arsenic content. Occurrence of the cubic arsenide in these particular objects, suggests that it was precipitated due to long-term aging at room temperature, which points to the need of a redefinition of the Cu-As equilibrium phase constitution. These results highlight the importance of understanding the impact of structural aging for the assessment of original properties of archaeological arsenical copper artifacts, such as hardness or color.
Resonant optical dipole antennas, consisting either of two arms coupled by a small gap or of a single, uncoupled arm only, are fabricated by the application of electron beam lithography and gold evaporation. Using dark-field microscopy, scattering spectra of structures with varied antenna arm length and varied gap size are obtained. The results show not only a spectral redshift for coupled structures compared to single arm structures, but also that the far-field scattering intensity is significantly higher for two arm structures with gap. In addition to the dipole structures, first fabrication results on quadrupole antennas and split-ring antennas are presented, offering novel pathways for an enhancement of the optical response function.
The restriction of phage λ.C by K(P1) cells is reduced when the cells are subjected to an EDTA cold-wash treatment which has been shown to remove surface-localized enzymes. We conclude that a surface-localized enzyme plays an essential role in host-controlled restriction.
Growth of K(P1) bacteria under conditions which lead to a reduction in the level of nucleases also leads to a reduction of their ability to restrict the growth of λ.C. Experiments designed to estimate the time after adsorption at which restriction takes place indicate that phage DNA is probably restricted by a nuclease while passing through the periplasm.
Cu–Ag alloy films prepared by magnetron cosputtering were characterized by using x-ray diffraction. A two-phase nanocrystalline structure of Cu grains supersaturated with Ag and Ag grains saturated with Cu was always observed. When alloying Ag with Cu or Cu with Ag, the grain sizes decreased dramatically, and the supersaturation increased with the amount of the alloying element. On annealing, the grain sizes of the Cu–Ag films increased and the solubilities decreased. To shed light on the mechanisms in play during the phase formation and subsequent phase changes, additional in situ real-time measurements were carried out using a high-intensity x-ray beam from the synchrotron at the European Synchrotron Radiation Facility in Grenoble, France. Based on the experimental findings, the phase formation and the subsequent changes during annealing are discussed.
The nanostructural evolution during heat treatments of direct-current magnetron-sputtered Ag films, deposited at room temperature at different substrate bias voltages, was experimentally studied. A growth chamber equipped with a magnetron and Kapton windows for in-situ x-ray diffraction was mounted on a six-circle goniometer at a synchrotron beam line. Bragg–Brentano x-ray diffraction was used to monitor the (111) Bragg peak during thermal annealing of the Ag films. In addition, to investigate the 〈111〉 fiber texture, one-dimensional pole figures were measured ex situ. The thermal stability of the nanostructure was sensitively dependent on the substrate bias voltage. Increasing the bias voltage resulted in significantly lower rates of grain growth, which we ascribe mainly to the formation of Ar bubbles. Furthermore, the grain size in the as-deposited films decreased with increasing bias voltage while the width of the one-dimensional pole figures increased.
The evolution during growth and subsequent annealing of the <111> fiber texture in magnetron-sputtered nanocrystalline Au films has been studied experimentally using X-ray diffraction with synchrotron radiation. To quantitatively investigate this fiber texture, grain orientation distributions were recorded in situ during growth and during subsequent annealing using Bragg-Brentano geometry. The (111) diffraction intensity was measured as a function of the sample tilt χ, the tilt axis lying at the intersection of the film surface and the scattering plane. As a quantitative measure of the texture, we used the width of the orientation distributions. The grain-orientation distributions narrowed during annealing. The activation energy for the process behind this texture change was found to be 0.64 ± 0.05 eV, close to the activation energy for grain boundary self-diffusion in nanocrystalline Au. This and the narrowing of the grain orientation distributions led us to suggest that the observed changes in texture originated from grain rotations and not from grain growth. Grain growth did not take place at the lower temperatures, where changes in orientation distributions were observed.
Scanning tunneling microscopy experiments show that the unstable growth morphology observed during molecular beam homoepitaxy on slightly vicinal Si(001) surfaces consists of straight step bunches. The instability occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. An instability with the same characteristics is observed in a 2D Kinetic Monte Carlo model of growth with incorporated Si(001)-like diffusion anisotropy. This provides strong evidence that the diffusion anisotropy destabilizes growth on Si(001) and similar surfaces towards step bunching. This new instability mechanism is operational without any additional step edge barriers.
In the final chapter, possible new ways for the study of urban human biology are discussed. Although various approaches might be possible, two approaches, one of them epidemiological, the other one, anthropological, are considered most pertinent. The use of epidemiological techniques with clearly defined urban variables within an adaptability framework has much mileage, as has the use of ethnography, modernisation studies and studies of urban pathways, for the identification of new, urban characteristics that impact on human biology. Vital to the future of urban human biology is the reformulation of human ecology within an adaptability framework, in which social and organisational constructs are regarded as components of the stress environment.
The human biology of the future must acknowledge the urban existence of human populations, the ways in which they shape their urban environments, and the ways in which their urban environments impact on their health and well-being. Human response to changing environments is a key issue in human adaptability research, and the colonisation of the urban environment is a major adaptive challenge (Boyden 1987; Huss-Ashmore and Thomas, 1997; Schell 1988, 1984), and can be studied at the population and individual levels. Human ecology has contributed significantly to the study of urbanism.