Correlations of non-affine displacements in metallic glasses through the yield transition

We study correlations of non-affine displacement during simple shear deformation of Cu-Zr bulk metallic glasses in molecular dynamics calculations. In the elastic regime, our calculations show exponential correlation with a decay length that we interpret as the size of a shear transformation zone in the elastic regime. This correlation length becomes system-size dependent beyond the yield transition as our calculation develops a shear band, indicative of a diverging length scale. We interpret these observations in the context of a recent proposition of yield as a first-order phase transition.Comment: 23 pages, 8 figure

Screened empirical bond-order potentials for Si-C

Typical empirical bond-order potentials are short ranged and give ductile instead of brittle behavior for materials such as crystalline silicon or diamond. Screening functions can be used to increase the range of these potentials. We outline a general procedure to combine screening functions with bond-order potentials that does not require to refit any of the potential's properties. We use this approach to modify Tersoff's [Phys. Rev. B 39, 5566 (1989)], Erhart & Albe's [Phys. Rev. B 71, 35211 (2005)] and Kumagai et al.'s [Comp. Mater. Sci. 39, 457 (2007)] Si, C and Si-C potentials. The resulting potential formulations correctly reproduce brittle materials response, and give an improved description of amorphous phases

Surface flaws control strain localization in the deformation of Cu∣\vertAu nanolaminates

We carried out matched experiments and molecular dynamics simulations of the compression of nanopillars prepared from Cu$\vert$Au nanolaminates with 25 nm layer thickness. The stress-strain behavior obtained from both techniques are in excellent agreement. Variation of the layer thickness in simulations reveals an increase of the strength with decreasing layer thickness. Pillars fail through the formation of shear bands whose nucleation we trace back to the existence of surface flaws. Our combined approach demonstrates the crucial role of contact geometry in controlling the deformation mode and suggests that modulus-matched nanolaminates should be able to suppress strain localization while maintaining controllable strength.Comment: 11 pages, 4 figures, supplementary material (5 pages, 4 figures

On the validity of the method of reduction of dimensionality: area of contact, average interfacial separation and contact stiffness

It has recently been suggested that many contact mechanics problems between solids can be accurately studied by mapping the problem on an effective one dimensional (1D) elastic foundation model. Using this 1D mapping we calculate the contact area and the average interfacial separation between elastic solids with nominally flat but randomly rough surfaces. We show, by comparison to exact numerical results, that the 1D mapping method fails even qualitatively. We also calculate the normal interfacial stiffness $K$ and compare it with the result of an analytical study. We attribute the failure of the elastic foundation model to the neglect of the long-range elastic coupling between the asperity contact regions.Comment: 5 pages, 4 figures, 29 reference

HPC with Python: An MPI-parallel implementation of the Lattice Boltzmann Method

The Lattice Boltzmann Method is well suited for high performance computational fluid dynamics. We show by means of a common two-dimensional test case, the lid-driven cavity problem, that excellent parallel scaling can be achieved in an implementation based on pure Python, using the numpy library and the Message Passing Interface. We highlight opportunities and pitfalls for the implementation of parallel high-performance codes in the high-level language Python

Elastic shakedown and roughness evolution in repeated elastic-plastic contact

Surface roughness emerges naturally during mechanical removal of material, fracture, chemical deposition, plastic deformation, indentation, and other processes. Here, we use continuum simulations to show how roughness which is neither Gaussian nor self-affine emerges from repeated elastic-plastic contact of a rough and rigid surface on a flat elastic-plastic substrate. Roughness profiles change with each contact cycle, but appear to approach a steady-state long before the substrate stops deforming plastically and has hence "shaken-down" elastically. We propose a simple dynamic collapse for the emerging power-spectral density, which shows that the multi-scale nature of the roughness is encoded in the first few indentations. In contrast to macroscopic roughness parameters, roughness at small scales and the skewness of the height distribution of the resulting roughness do not show a steady-state, with the latter vanishing asymptotically with contact cycle

Otyłość a ryzyko rozwoju cukrzycy typu 2 i niektórych nowotworów złośliwych

  Obesity, type 2 diabetes mellitus and cancers are the most common chronic diseases. Data collected by world organizations for protection and promotion of health show a rapid increase in the prevalence of these illnesses over the last few decades. The rapid increase in prevalence of excess body weight globally is believed to be related to the growing proportion of people living in urban areas and the resulting changes in dietary and physical activity patterns. The epidemic of overweight and obesity and the clear connection between raised BMI and many non-communicable diseases (such as cardiovascular diseases, type 2 diabetes, and cancers) make this issue a public health priority all over the world. Estimates of future overweight and obesity prevalence assume that while keeping the current growth rate of prevalence, the numbers of people affected around the globe will rise to 2.16 billion for overweight and 1.12 billion for obesity in 2030. These numbers combined will constitute 58% of the world’s population. Considering the above, we should expect a proportional increase in prevalence of the most serious health consequences of overweight and obesity — type 2 diabetes mellitus and some cancers, including breast cancer in postmenopausal women, endometrial, colonic and renal cancers. In this paper we discussed the available data on prevalence of overweight and obesity and analysed a causal relationship between excess body weight, type 2 diabetes mellitus and selected types of malignancies.    Zarówno otyłość, jak i cukrzycę typu 2 oraz nowotwory złośliwe należy zaliczyć do najczęściej występujących obecnie schorzeń przewlekłych. Dane gromadzone przez światowe organizacje zajmujące się ochroną i promocją zdrowia wskazują na gwałtowny wzrost zapadalności na te choroby w ciągu ostatnich kilku dziesięcioleci. Przyczyn wzrostu rozpowszechnienia nadmiernej masy ciała na świecie upatruje się w zwiększającym się odsetku osób zamieszkujących tereny miejskie oraz wiążącym się z tym trybem życia. Wzrastający odsetek nadwagi oraz otyłości w populacji światowej oraz jej związek z występowaniem wielu schorzeń czyni je istotnym wyzwaniem dla zdrowia publicznego i priorytetem światowej polityki zdrowotnej. Prognozy dotyczące występowania nadwagi i otyłości zakładają, że przy utrzymaniu aktualnego tempa wzrostu rozpowszechnienia częstość ich występowania na świecie wzrośnie do 2,16 mld osób w przypadku nadwagi oraz 1,12 mld osób w przypadku otyłości w 2030 roku, co łącznie będzie stanowić 58% populacji świata. Mając na względzie powyższe dane, należy spodziewać się równie nasilonego wzrostu występowania najpoważniejszych konsekwencji zdrowotnych otyłości, jakimi są m.in. cukrzyca typu 2 oraz wybrane nowotwory złośliwe, w tym nowotwory piersi u kobiet będących po menopauzie, nowotwory endometrium, jelita grubego oraz nerki. W publikacji omówiono dostępne dane dotyczące epidemiologii oraz związku przyczynowo-skutkowego pomiędzy nadmierną masą ciała a ryzykiem rozwoju cukrzycy typu 2 oraz wybranych nowotworów złośliwych.