5,346 research outputs found

    Drying and cracking mechanisms in a starch slurry

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    Starch-water slurries are commonly used to study fracture dynamics. Drying starch-cakes benefit from being simple, economical, and reproducible systems, and have been used to model desiccation fracture in soils, thin film fracture in paint, and columnar joints in lava. In this paper, the physical properties of starch-water mixtures are studied, and used to interpret and develop a multiphase transport model of drying. Starch-cakes are observed to have a nonlinear elastic modulus, and a desiccation strain that is comparable to that generated by their maximum achievable capillary pressure. It is shown that a large material porosity is divided between pore spaces between starch grains, and pores within starch grains. This division of pore space leads to two distinct drying regimes, controlled by liquid and vapor transport of water, respectively. The relatively unique ability for drying starch to generate columnar fracture patterns is shown to be linked to the unusually strong separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments

    Drying and cracking mechanisms in a starch slurry

    Get PDF
    Starch-water slurries are commonly used to study fracture dynamics. Drying starch-cakes benefit from being simple, economical, and reproducible systems, and have been used to model desiccation fracture in soils, thin film fracture in paint, and columnar joints in lava. In this paper, the physical properties of starch-water mixtures are studied, and used to interpret and develop a multiphase transport model of drying. Starch-cakes are observed to have a nonlinear elastic modulus, and a desiccation strain that is comparable to that generated by their maximum achievable capillary pressure. It is shown that a large material porosity is divided between pore spaces between starch grains, and pores within starch grains. This division of pore space leads to two distinct drying regimes, controlled by liquid and vapor transport of water, respectively. The relatively unique ability for drying starch to generate columnar fracture patterns is shown to be linked to the unusually strong separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments

    Diffusion on a heptagonal lattice

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    We study the diffusion phenomena on the negatively curved surface made up of congruent heptagons. Unlike the usual two-dimensional plane, this structure makes the boundary increase exponentially with the distance from the center, and hence the displacement of a classical random walker increases linearly in time. The diffusion of a quantum particle put on the heptagonal lattice is also studied in the framework of the tight-binding model Hamiltonian, and we again find the linear diffusion like the classical random walk. A comparison with diffusion on complex networks is also made.Comment: 5 pages, 6 figure

    Letter from W. H. Elson, Edwin B. Cox, C. N. Kendall, F. T. Oldt, and A. W. Rankin

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    Letter concerning resolutions being voted on concerning the National Educational Association

    Concepts of microdosimetry

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    This is the first part of an investigation of microdosimetric concepts relevant to numerical calculations. The definitions of the microdosimetric quantities are reviewed and formalized, and some additional conventions are adopted. The common interpretation of the quantities in terms of energy imparted to spherical sites is contrasted with their interpretation as the result of a diffusion process applied to the initial spatial pattern of energy transfers in the irradiated medium

    Robust Inference of Trees

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    This paper is concerned with the reliable inference of optimal tree-approximations to the dependency structure of an unknown distribution generating data. The traditional approach to the problem measures the dependency strength between random variables by the index called mutual information. In this paper reliability is achieved by Walley's imprecise Dirichlet model, which generalizes Bayesian learning with Dirichlet priors. Adopting the imprecise Dirichlet model results in posterior interval expectation for mutual information, and in a set of plausible trees consistent with the data. Reliable inference about the actual tree is achieved by focusing on the substructure common to all the plausible trees. We develop an exact algorithm that infers the substructure in time O(m^4), m being the number of random variables. The new algorithm is applied to a set of data sampled from a known distribution. The method is shown to reliably infer edges of the actual tree even when the data are very scarce, unlike the traditional approach. Finally, we provide lower and upper credibility limits for mutual information under the imprecise Dirichlet model. These enable the previous developments to be extended to a full inferential method for trees.Comment: 26 pages, 7 figure

    Resistance Training may Mitigate Age-related Decline in Physical Function

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    Aging is often accompanied with the onset of sarcopenia, defined by low muscle mass, strength, and physical function. Regular resistance exercise may mitigate this loss; however, data are lacking that compare younger and older adults who do and do not perform resistance training for general health on skeletal muscle mass and physical function. PURPOSE: The aim of this study was to identify differences in muscle mass and physical function between younger and older adults who did and did not perform resistance training for general health. METHODS: Healthy younger (23.8 ± 0.4 yrs) and older (68.5 ± 1.2 yrs) men and women (n = 76) who either did or did not regularly participate in resistance training were placed into 4 groups: young trained (YT: n = 22), young not trained (YNT: n = 16), old trained (OT: n = 17), and old not trained (ONT: n = 21). Dual energy x-ray absorptiometry assessed appendicular skeletal muscle mass (SMI). Participants performed 4 physical function tests: stair climb (SC), 30s sit-to-stand (30sSTS), 6-min walk test (6MWT), and timed-up-and-go (TUG). ANOVAs were used to compare groups for all measures, p ≤ 0.05. Data are reported as mean ± SE. RESULTS: Differences were found between groups for SMI, SC, 30sSTS, 6MWT, and TUG (p ≤ 0.05). SMI was higher for YT compared to YNT (p = 0.001), ONT (p \u3c 0.0001) and OT (p = 0.032) (YT: 8.67 ± 0.36 kg/m2, YNT: 7.08 ± 0.23 kg/m2, OT: 7.73 ± 0.29 kg/m2, ONT: 7.11 ± 0.27 kg/m2). SC performance was slower for ONT compared to YT (p \u3c 0.0001), YNT (p \u3c 0.0001), and OT (p = 0.032); however, YT and was faster than OT (p = 0.002) (YT: 2.37 ± 0.05s, YNT: 2.60 ± 0.10s, OT: 2.94± 0.15s, ONT: 3.32 ± 0.16s). For 30sSTS, OT completed more reps than ONT (p \u3c 0.0001) and YNT (p = 0.001). YT completed more reps than YNT (p \u3c 0.0001) and ONT (p \u3c 0.0001) (YT: 22.8 ± 0.5 reps, YNT: 18.4 ± 0.7 reps, OT: 22.1 ± 1.1 reps, ONT: 16.7 ± 0.6 reps). OT (p = 0.001), YT (p \u3c 0.0001), and YNT (p = 0.046) walked farther in the 6MWT compared to ONT, and YT walked farther than YNT (p = 0.048) (YT: 837.0 ± 16.7 yds, YNT: 783.2 ± 14.5 yds, OT: 819.9 ± 23.3 yds, ONT: 728.3 ± 18.9 yds). For TUG, OT (p = 0.001) and YT (p = 0.046) were faster than ONT (YT: 5.81 ± 0.17s, YNT: 5.87 ± 0.25s, OT: 5.31 ± 0.19s, ONT: 6.35 ± 0.21s). 30sSTS, 6MWT and TUG were not different between OT and YT. 6MWT and SC were not different between OT and YNT (p \u3e 0.05). All other comparisons were not significantly different (p \u3e 0.05). CONCLUSION: Resistance trained older adults outperformed their nonresistance trained peers and these data suggest that older adults who engage in regular resistance training may maintain physical function similar to that of younger adults

    Testing of quantum phase in matter wave optics

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    Various phase concepts may be treated as special cases of the maximum likelihood estimation. For example the discrete Fourier estimation that actually coincides with the operational phase of Noh, Fouge`res and Mandel is obtained for continuous Gaussian signals with phase modulated mean.Since signals in quantum theory are discrete, a prediction different from that given by the Gaussian hypothesis should be obtained as the best fit assuming a discrete Poissonian statistics of the signal. Although the Gaussian estimation gives a satisfactory approximation for fitting the phase distribution of almost any state the optimal phase estimation offers in certain cases a measurable better performance. This has been demonstrated in neutron--optical experiment.Comment: 8 pages, 4 figure
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