1,921 research outputs found

    Continuous Elastic Phase Transitions in Pure and Disordered Crystals

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    We review the theory of second--order (ferro--)elastic phase transitions, where the order parameter consists of a certain linear combination of strain tensor components, and the accompanying soft mode is an acoustic phonon. In three--dimensional crystals, the softening can occur in one-- or two--dimensional soft sectors. The ensuing anisotropy reduces the effect of fluctuations, rendering the critical behaviour of these systems classical for a one--dimensional soft sector, and classical with logarithmic corrections in case of a two--dimensional soft sector. The dynamical critical exponent is z=2z = 2, and as a consequence the sound velocity vanishes as cs∝∣Tβˆ’Tc∣1/2c_s \propto | T - T_c |^{1/2}, while the phonon damping coefficient is essentially temperature--independent. Disorder may lead to a variety of precursor effects and modified critical behaviour. Defects that locally soften the crystal may induce the phenomenon of local order parameter condensation. When the correlation length of the pure system exceeds the average defect separation nDβˆ’1/3n_{\rm D}^{-1/3}, a disorder--induced phase transition to a state with non--zero average order parameter can occur at a temperature Tc(nD)T_c(n_{\rm D}) well above the transition temperature Tc0T_c^0 of the pure crystal. Near Tc0T_c^0, the order--parameter curve, susceptibility, and specific heat appear rounded. For T<Tc(nD)T < T_c(n_{\rm D}) the spatial inhomogeneity induces a static central peak with finite qq width in the scattering cross section, accompanied by a dynamical component that is confined to the very vicinity of the disorder--induced phase transition.Comment: 26 pages, Latex (rs.sty now IS included), 11 figures can be obtained from U.C. T\"auber ([email protected]); will appear in Phil. Trans. Roy. Soc. Lond. A (October 1996

    Carabid and Staphylinid beetles from agricultural land in the lower Fraser Valley, British Columbia

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    Pit-traps were emptied every two or three days for two seasons in crop, fallow, and grass plots to determine the species and population density of Carabidae and Staphylinidae associated with agricultural land, and their relationship with brassica crops. Half of the plots were enclosed by plastic barriers and the beetles were trapped to extinction: half were not enclosed. Thirty-three carabid and 16 staphylinid species were captured. The dominant species was the small, generalized. European carabid predator, &lt;i&gt;Bembidion lampros&lt;/i&gt;, which had a population on crop and fallow land of about 29000/hectare. It was almost absent in grass. Other numerous carabids were &lt;i&gt;Harpalus aeneus&lt;/i&gt;, &lt;i&gt;Calathus fuscipes&lt;/i&gt;, and &lt;i&gt;Clivina fossor&lt;/i&gt;, all introduced European spp., with populations of almost 2000, 5600, and llOOO/hectare respectively. The first and third of these were scarce in grassland but the second was abundant. In plots of Brussels sprouts &lt;i&gt;Aleochara bilineata&lt;/i&gt;, a staphylinid, was effectively parasitic on root maggots, and averaged more than 6000/hectare. Soil cores taken in October centred on a Brussels sprouts plant averaged 26.4 &lt;i&gt;Hylemya puparia&lt;/i&gt; per core of which 44% were parasitized by &lt;i&gt;A. bilineata&lt;/i&gt;

    Resistance to insecticides in root maggots in British Columbia

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    Fully Point-wise Convolutional Neural Network for Modeling Statistical Regularities in Natural Images

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    Modeling statistical regularity plays an essential role in ill-posed image processing problems. Recently, deep learning based methods have been presented to implicitly learn statistical representation of pixel distributions in natural images and leverage it as a constraint to facilitate subsequent tasks, such as color constancy and image dehazing. However, the existing CNN architecture is prone to variability and diversity of pixel intensity within and between local regions, which may result in inaccurate statistical representation. To address this problem, this paper presents a novel fully point-wise CNN architecture for modeling statistical regularities in natural images. Specifically, we propose to randomly shuffle the pixels in the origin images and leverage the shuffled image as input to make CNN more concerned with the statistical properties. Moreover, since the pixels in the shuffled image are independent identically distributed, we can replace all the large convolution kernels in CNN with point-wise (1βˆ—11*1) convolution kernels while maintaining the representation ability. Experimental results on two applications: color constancy and image dehazing, demonstrate the superiority of our proposed network over the existing architectures, i.e., using 1/10∼\sim1/100 network parameters and computational cost while achieving comparable performance.Comment: 9 pages, 7 figures. To appear in ACM MM 201
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