3,064 research outputs found
Marginally Deformed Starobinsky Gravity
We show that quantum-induced marginal deformations of the Starobinsky
gravitational action of the form , with the Ricci scalar
and 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 .
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
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 for bcc. A two-dimensional generalization suggests
. 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
New Hugoniot data on single crystal diopside, CaMgSi_2O_6 (Di), suggest that transformation to a high-pressure thermomechanical state begins at ā¼50 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., ā0.8 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 (ā0.1 Mg/mĀ³ less dense) the lower mantle density profile from ā¼90 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
Optical radiation from CaMgSi_2O_6 crystal (diopside) shock-compressed to 145ā170 GPa yields shock-induced temperatures of 3500ā4800 K, while that from CaMgSi_2O_6 glass, with a density 86% that of CaMgSi_2O_6 crystal, shock-compressed to 96ā98 GPa, yields shock-induced temperatures of 3700ā3900 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„ 500ā1000 m^(ā1). 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 (āenergy of transitionā) of 2.2Ā±0.5 MJ/kg. The CaMgSi_2O_6 glass results are ābest-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 (1ā2) 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 2500ā3000 K in the pressure range (110ā135 GPa) of the lowermost mantle (Dā²ā²)] 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 (25ā30 wt % CaO). If so, our results imply that the temperature of the Dā²ā² region must be below ā 3000 K, since the finite S-wave velocity of the Dā²ā² region implies that it must be (at least at seismic frequencies) predominantly solid
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Patients with ALS show highly correlated progression rates in left and right limb muscles.
ObjectiveAmyotrophic lateral sclerosis (ALS) progresses at different rates between patients, making clinical trial design difficult and dependent on large cohorts of patients. Currently, there are few data showing whether the left and right limbs progress at the same or different rates. This study addresses rates of decline in specific muscle groups of patients with ALS and assesses whether there is a relationship between left and right muscles in the same patient, regardless of overall progression.MethodsA large cohort of patients was used to assess decline in muscle strength in right and left limbs over time using 2 different methods: The Tufts Quantitative Neuromuscular Exam and Accurate Test of Limb Isometric Strength protocol. Then advanced linear regression statistical methods were applied to assess progression rates in each limb.ResultsThis report shows that linearized progression models can predict general slopes of decline with good accuracy. Critically, the data demonstrate that while overall decline is variable, there is a high degree of correlation between left and right muscle decline in ALS. This implies that irrespective of which muscle starts declining soonest or latest, their rates of decline following onset are more consistent.ConclusionsFirst, this study demonstrates a high degree of power when using unilateral treatment approaches to detect a slowing in disease progression in smaller groups of patients, thus allowing for paired statistical tests. These findings will be useful in transplantation trials that use muscle decline to track disease progression in ALS. Second, these findings discuss methods, such as tactical selection of muscle groups, which can improve the power efficiency of all ALS clinical trials
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Non-Peer Reviewe
Relationship of Health-Related Quality of Life to Functional Fitness in Rural Cancer Survivors
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Silvopasture principles and potential in Saskatchewan
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
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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