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

Influence of severe plastic deformation on the precipitation hardening of a FeSiTi steel

The combined strengthening effects of grain refinement and high precipitated volume fraction (~6at.%) on the mechanical properties of FeSiTi alloy subjected to SPD processing prior to aging treatment were investigated by atom probe tomography and scanning transmission electron microscopy. It was shown that the refinement of the microstructure affects the precipitation kinetics and the spatial distribution of the secondary hardening intermetallic phase, which was observed to nucleate heterogeneously on dislocations and sub-grain boundaries. It was revealed that alloys successively subjected to these two strengthening mechanisms exhibit a lower increase in mechanical strength than a simple estimation based on the summation of the two individual strengthening mechanisms

Role of electromagnetically induced transparency in resonant four-wave-mixing schemes.

Published versio

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)

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

Intercomparison of methods of coupling between convection and large-scale circulation: 1. Comparison over uniform surface conditions

As part of an international intercomparison project, a set of single column models (SCMs) and cloud-resolving models (CRMs) are run under the weak temperature gradient (WTG) method and the damped gravity wave (DGW) method. For each model, the implementation of the WTG or DGW method involves a simulated column which is coupled to a reference state defined with profiles obtained from the same model in radiative-convective equilibrium. The simulated column has the same surface conditions as the reference state and is initialized with profiles from the reference state. We performed systematic comparison of the behavior of different models under a consistent implementation of the WTG method and the DGW method and systematic comparison of the WTG and DGW methods in models with different physics and numerics. CRMs and SCMs produce a variety of behaviors under both WTG and DGW methods. Some of the models reproduce the reference state while others sustain a large-scale circulation which results in either substantially lower or higher precipitation compared to the value of the reference state. CRMs show a fairly linear relationship between precipitation and circulation strength. SCMs display a wider range of behaviors than CRMs. Some SCMs under the WTG method produce zero precipitation. Within an individual SCM, a DGW simulation and a corresponding WTG simulation can produce different signed circulation. When initialized with a dry troposphere, DGW simulations always result in a precipitating equilibrium state. The greatest sensitivities to the initial moisture conditions occur for multiple stable equilibria in some WTG simulations, corresponding to either a dry equilibrium state when initialized as dry or a precipitating equilibrium state when initialized as moist. Multiple equilibria are seen in more WTG simulations for higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations

Each baby counts in 2018 – lessons learned and future directions

The Royal College of Obstetricians and Gynaecologists (RCOG) launched the Each Baby Counts (EBC) project in 2015. The aim of the project is to reduce the number of stillbirths, early neonatal deaths and severe brain injuries in term babies born following labour by 50% by the year 2020. The first full report focussed on the quality of local reviews, fetal monitoring, individual human factors and neonatal care. For this article we have not focussed on the neonatal issues but have summarized the main points from each chapter. The aim of EBC will be achieved by focusing on three themes: (i) improving the quality of reviews of these babies, prompting local units to address their systematic failings that led to the outcome; (ii) development of toolkits and resources to support units to implement the recommendations in the report; (iii) improving care by establishing a platform for shared learning between units in order to adopt a more proactive approach to reducing babies who are harmed during labour

Agonist-induced alteration in the membrane form of muscarinic cholinergic receptors

Incubation of 1321N1 human astrocytoma cells with carbachol resulted in a rapid loss of binding of [3H]N-methylscopolamine ([3H]NMS) to muscarinic cholinergic receptors measured at 4 degrees C on intact cells; loss of muscarinic receptors in lysates from the same cells measured with [3H]quinuclidinyl benzilate [( 3H]QNB) at 37 degrees C occurred at a slower rate. Upon removal of agonist from the medium, the lost [3H]NMS binding sites measured on intact cells recovered with a t1/2 of approximately 20 min, but only to the level to which [3H]QNB binding sites had been lost; no recovery of "lost" [3H]QNB binding sites occurred over the same period. Based on these data and the arguments of Galper et al. (Galper, J. B., Dziekan, L. C., O'Hara, D. S., and Smith, T. W. (1982) J. Biol. Chem. 257, 10344-10356) regarding the relative hydrophilicity of [3H]NMS versus [3H]QNB, it is proposed that carbachol induces a rapid sequestration of muscarinic receptors that is followed by a loss of these receptors from the cell. These carbachol-induced changes are accompanied by a change in the membrane form of the muscarinic receptor. Although essentially all of the muscarinic receptors from control cells co-purified with the plasma membrane fraction on sucrose density gradients, 20-35% of the muscarinic receptors from cells treated for 30 min with 100 microM carbachol migrated to a much lower sucrose density. This conversion of muscarinic receptors to a "light vesicle" form occurred with a t1/2 approximately 10 min, and reversed with a t1/2 approximately 20 min. In contrast to previous results in this cell line regarding beta-adrenergic receptors (Harden, T. K., Cotton, C. U., Waldo, G. L., Lutton, J. K., and Perkins, J. P. (1980) Science 210, 441-443), agonist binding to muscarinic receptors in the light vesicle fraction obtained from carbachol-treated cells was still regulated by GTP. One interpretation of these data is that agonists induce an internalization of muscarinic receptors with the retention of their functional interaction with a guanine nucleotide regulatory protein