3,064 research outputs found

    Marginally Deformed Starobinsky Gravity

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    We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form R2(1āˆ’Ī±)R^{2(1 -\alpha)}, with RR the Ricci scalar and Ī±\alpha a positive parameter, smaller than one half, can account for the recent experimental observations by BICEP2 of primordial tensor modes. We also suggest natural microscopic (non) gravitational sources of these corrections and demonstrate that they lead generally to a nonzero and positive Ī±\alpha. Furthermore we argue, that within this framework, the tensor modes probe theories of grand unification with a large scalar field content.Comment: 5 pages, 1 figure, 2 column

    Non-linear elastic effects in phase field crystal and amplitude equations: Comparison to ab initio simulations of bcc metals and graphene

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    We investigate non-linear elastic deformations in the phase field crystal model and derived amplitude equations formulations. Two sources of non-linearity are found, one of them based on geometric non-linearity expressed through a finite strain tensor. It reflects the Eulerian structure of the continuum models and correctly describes the strain dependence of the stiffness. In general, the relevant strain tensor is related to the left Cauchy-Green deformation tensor. In isotropic one- and two-dimensional situations the elastic energy can be expressed equivalently through the right deformation tensor. The predicted isotropic low temperature non-linear elastic effects are directly related to the Birch-Murnaghan equation of state with bulk modulus derivative Kā€²=4K'=4 for bcc. A two-dimensional generalization suggests K2Dā€²=5K'_{2D}=5. These predictions are in agreement with ab initio results for large strain bulk deformations of various bcc elements and graphene. Physical non-linearity arises if the strain dependence of the density wave amplitudes is taken into account and leads to elastic weakening. For anisotropic deformations the magnitudes of the amplitudes depend on their relative orientation to the applied strain.Comment: 16 page

    Dynamic compression of diopside and salite to 200 GPa

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    New Hugoniot data on single crystal diopside, CaMgSi_2O_6 (Di), suggest that transformation to a high-pressure thermomechanical state begins at āˆ¼50 GPa and is complete above 100 GPa, in agreement with other pyroxenes and silicates of geophysical interest. Comparison of the new high pressure phase (HPP) data for Di and salite, CaMg_(0.82)Fe_(0.18)Si_2O_6 (Sa) with appropriate mixed oxide and perovskite models implies compatibility between either model and the data. Conversely, least-squares fits to the HPP Di data favor lower (3.6 - 3.9 Mg/mĀ³) values of zero-pressure, room-temperature density than the models (4.0 - 4.1 Mg/mĀ³). Similar comments apply to porosity-corrected HPP hedenbergite (Hd) data. The HPP Di, Sa, and Hd data also imply much larger density differences between these compositions in the HPP regime (e.g., ā‰ˆ0.8 Mg/mĀ³ between Di and Hd) than at STP (0.38 Mg/mĀ³). This may represent the influence of multiple transition processes (e.g., polymorphism and Fe^(2+) high-low spin) as a function of Fe content across the Di-Hd series. The new HPP Sa data closely parallel (ā‰ˆ0.1 Mg/mĀ³ less dense) the lower mantle density profile from āˆ¼90 GPa to 136 GPa. Our results are consistent with the speculations of Jeanloz and Ahrens on the possibility of significant Ca in the lower mantle

    Shock-induced temperatures of CaMgSi_2O_6

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    Optical radiation from CaMgSi_2O_6 crystal (diopside) shock-compressed to 145ā€“170 GPa yields shock-induced temperatures of 3500ā€“4800 K, while that from CaMgSi_2O_6 glass, with a density 86% that of CaMgSi_2O_6 crystal, shock-compressed to 96ā€“98 GPa, yields shock-induced temperatures of 3700ā€“3900 K. The observed radiation histories of of the targets containing CaMgSi_2O_6 crystal and glass imply that the shock-compressed states of both are highly absorptive, with effective absorption coefficients of ā‰„ 500ā€“1000 m^(āˆ’1). Calculated shock-compressed states for both CaMgSi_2O_6 crystal and glass, when compared to experimental results, imply the presence of a high-pressure phase (HPP) along both Hugoniots over the respective pressure ranges. The CaMgSi_2O_6 crystal experimental results are consistent with a standard temperature and pressure (STP) HPP mass density of 4100Ā±100 kg/m^3, a STP HPP bulk modulus of 250Ā±50 GPa, and a difference in specific internal energy (SIE) between (metastable) HPP and the CaMgSi_2O_6 crystal states at STP (ā€œenergy of transitionā€) of 2.2Ā±0.5 MJ/kg. The CaMgSi_2O_6 glass results are ā€œbest-fitā€ by the same (median) values of all three parameters; except for the STP SIE difference between the CaMgSi_2O_6 glass and HPP states, however, they are less sensitive to parameter variations than the crystal results because they are at lower pressure. All these model constraints are insensitive to the range of values (1ā€“2) assumed for the STP HPP Gruneisen's parameter. The relatively high value of the STP SIE difference between HPP and CaMgSi_2O_6 crystal or glass most likely implies that CaMgSi_2O_6 glass and crystal experience both solid-solid and solid-liquid phase transformations along their respective Hugoniots below 96 and 144 GPa, respectively. The HPP CaMgSi_2O_6 Hugoniot constrained by the crystal experimental results lies between 2500ā€“3000 K in the pressure range (110ā€“135 GPa) of the lowermost mantle (Dā€²ā€²)] our results imply that CaMgSi_2O_6 is at least partly molten at these pressures and temperatures. Seismically constrained compositional models for this region of Earth's lower mantle suggest that it could contain a significant amount of Ca (25ā€“30 wt % CaO). If so, our results imply that the temperature of the Dā€²ā€² region must be below ā‰ˆ 3000 K, since the finite S-wave velocity of the Dā€²ā€² region implies that it must be (at least at seismic frequencies) predominantly solid

    Relationship of Health-Related Quality of Life to Functional Fitness in Rural Cancer Survivors

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    Silvopasture principles and potential in Saskatchewan

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    Non-Peer ReviewedSilvopasture is a concept in which woody species are intentionally combined with forage crops and livestock in a production system that optimizes the productivity or the economic benefits of the trees and the animals in a sustainable way. A review is presented of silvopasture research relevant to Saskatchewan conditions. In particular, silvopasture principles, as they apply to the co-management of animals with planted or natural forest stands will be explored. Silvopasture practices that are more or less commonly found in Canada include: the use of livestock to control weeds in new plantations; the planting or management of trees and shrubs as livestock windbreaks or for shade; and livestock grazing in natural deciduous, conifer or mixed forests

    Beyond the local approximation to exchange and correlation: the role of the Laplacian of the density in the energy density of Si

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    We model the exchange-correlation (XC) energy density of the Si crystal and atom as calculated by variational Monte Carlo (VMC) methods with a gradient analysis beyond the local density approximation (LDA). We find the Laplacian of the density to be an excellent predictor of the discrepancy between VMC and LDA energy densities in each system. A simple Laplacian-based correction to the LDA energy density is developed by means of a least square fit to the VMC XC energy density for the crystal, which fits the homogeneous electron gas and Si atom without further effort.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
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