Dislocation interactions mediated by grain boundaries

The dynamics of dislocation assemblies in deforming crystals indicate the emergence of collective phenomena, intermittent fluctuations and strain avalanches. In polycrystalline materials, the understanding of plastic deformation mechanisms depends on grasping the role of grain boundaries on dislocation motion. Here the interaction of dislocations and elastic, low angle grain boundaries is studied in the framework of a discrete dislocation representation. We allow grain boundaries to deform under the effect of dislocation stress fields and compare the effect of such a perturbation to the case of rigid grain boudaries. We are able to determine, both analytically and numerically, corrections to dislocation stress fields acting on neighboring grains, as mediated by grain boundary deformation. Finally, we discuss conclusions and consequences for the avalanche statistics, as observed in polycrystalline samples.Comment: 13 pages, 5 figure

Теоретичний аналіз динаміки розвитку творчої активності дошкільника

(uk) У статті проаналізовано динаміку розвитку творчої активності дошкільника. Зазначається, що процес формування особистості дошкільника досягається під час самореалізації її в творчій діяльності. Особлива увага приділена характеристиці етапів розвитку свідомості та творчій взаємодії «дитина – дорослий». Обґрунтовується необхідність створення сприятливих умов щодо творчої активності дошкільника.(ru) В статье проанализирована динамика развития творческой активности дошкольника. Отмечается, что процесс формирования личности дошкольника достигается во время самореализации ее в творческой деятельности. Особое внимание уделено характеристике этапов развития сознания и творческому взаимодействию «ребенок – взрослый». Обосновывается необходимость создания благоприятных условий относительно творческой активности дошкольника

Plate-impact loading of cellular structures formed by selective laser melting

Porous materials are of great interest because of improved energy absorption over their solid counterparts. Their properties, however, have been difficult to optimize. Additive manufacturing has emerged as a potential technique to closely define the structure and properties of porous components, i.e. density, strut width and pore size; however, the behaviour of these materials at very high impact energies remains largely unexplored. We describe an initial study of the dynamic compression response of lattice materials fabricated through additive manufacturing. Lattices consisting of an array of intersecting stainless steel rods were fabricated into discs using selective laser melting. The resulting discs were impacted against solid stainless steel targets at velocities ranging from 300 to 700 m s-1 using a gas gun. Continuum CTH simulations were performed to identify key features in the measured wave profiles, while 3D simulations, in which the individual cells were modelled, revealed details of microscale deformation during collapse of the lattice structure. The validated computer models have been used to provide an understanding of the deformation processes in the cellular samples. The study supports the optimization of cellular structures for application as energy absorbers. © 2014 IOP Publishing Ltd

Modelling the small punch tensile behaviour of an aerospace alloy

The small punch (SP) test is a widely accepted methodology for obtaining mechanical property information from limited material quantities. Much research has presented the creep, tensile and fracture responses of numerous materials gathered from small-scale testing approaches. This is of particular interest for alloy down selection of next-generation materials and in situ mechanical assessments. However, to truly understand the evolution of deformation of the miniature disc specimen, an accurate and detailed understanding of the progressive damage is necessary. This paper will utilise the SP test to assess the tensile properties of several Ti–6Al–4V materials across different temperature regimes. Fractographic investigations will establish the contrasting damage mechanisms and finite element modelling through DEFORM software is employed to characterise specimen deformation

Atomic-scale modeling of the deformation of nanocrystalline metals

Nanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be modeled with the computational resources available today. We present molecular dynamics simulations of nanocrystalline copper with grain sizes up to 13 nm. Two different deformation mechanisms are active, one is deformation through the motion of dislocations, the other is sliding in the grain boundaries. At the grain sizes studied here the latter dominates, leading to a softening as the grain size is reduced. This implies that there is an ``optimal'' grain size, where the hardness is maximal. Since the grain boundaries participate actively in the deformation, it is interesting to study the effects of introducing impurity atoms in the grain boundaries. We study how silver atoms in the grain boundaries influence the mechanical properties of nanocrystalline copper.Comment: 10 pages, LaTeX2e, PS figures and sty files included. To appear in Mater. Res. Soc. Symp. Proc. vol 538 (invited paper). For related papers, see http://www.fysik.dtu.dk/~schiotz/publist.htm

Infrared seeded parametric four-wave mixing for sensitive detection of molecules

We have developed a sensitive resonant four-wave mixing technique based on two-photon parametric four-wave mixing with the addition of a phase matched ''seeder'' field. Generation of the seeder field via the same four-wave mixing process in a high pressure cell enables automatic phase matching to be achieved in a low pressure sample cell. This arrangement facilitates sensitive detection of complex molecular spectra by simply tuning the pump laser. We demonstrate the technique with the detection of nitric oxide down to concentrations more than 4 orders of magnitude below the capability of parametric four-wave mixing alone, with an estimated detection threshold of 10(12) molecules/cm(3)

Non-Equilibrium Evolution Thermodynamics Theory

Alternative approach for description of the non-equilibrium phenomena arising in solids at a severe external loading is analyzed. The approach is based on the new form of kinetic equations in terms of the internal and modified free energy. It is illustrated by a model example of a solid with vacancies, for which there is a complete statistical ground. The approach is applied to the description of important practical problem - the formation of fine-grained structure of metals during their treatment by methods of severe plastic deformation. In the framework of two-level two-mode effective internal energy potential model the strengthening curves unified for the whole of deformation range and containing the Hall-Petch and linear strengthening sections are calculated.Comment: 7 pages, 1 figur

WPA position statement on prisoner mental and public health care

As a group, prisoners have a tendency not to engage effectively with healthcare services while they are in the community because they have so many other competing priorities. Other priorities may include access to adequate finance, finding a place to sleep that is dry and safe, having sufficient food for themselves and their families, or the need to meet existing addictions. However, as a group, they present with high levels of health morbidity across domains of physical and mental health and addictions. It is widely established that screening people for healthcare conditions at the point when they are received into prison can assist in identifying a range of medical conditions. Although the process has limitations, the practice of screening is recommended internationally. After screening has taken place, healthcare services are meant to be provided in prisons to the same extent and quality as would be available in the community, yet across the world, there have often been problems in ensuring the adequacy of prison healthcare systems. Prison healthcare departments have often lagged behind regarding funding, and many countries have reported problems with the quality and consistency of delivery. Also, issues with training and continuous professional development are often cited as problematic in this area. This curriculum has been prepared to assist countries in ensuring that systems are in place for the effective training and continuous professional development of staff. It is meant to assist those who design such programs for local use