3,272 research outputs found
A New Solution of The Cosmological Constant Problems
We extend the usual gravitational action principle by promoting the bare
cosmological constant (CC) from a parameter to a field which can take many
possible values. Variation leads to a new integral constraint equation which
determines the classical value of the effective CC that dominates the wave
function of the universe. In a realistic cosmological model, the expected value
of the effective CC, is calculated from measurable quantities to be O(t_U), as
observed, where t_U is the present age of the universe in Planck units,. Any
application of our model produces a falsifiable prediction for in
terms of other measurable quantities. This leads to a specific falsifiable
prediction for the observed spatial curvature parameter of Omega_k0=-0.0055.
Our testable proposal requires no fine tunings or extra dark-energy fields but
does suggest a new view of time and cosmological evolution.Comment: 5 pages; v3: version accepted by Phys. Rev. Let
Optimal Conditions for Kinetic Study of Succinate Dehydrogenase in Rat Liver
Succinate dehydrogenase (SDH) commonly is assayed as a marker enzyme for mitochondrial activity. The literature presents numerous conditions for conducting this assay due to the fact that, it has been difficult to get sufficient reduction of the acceptor dye, 2,3,5-triphenyl-2H-tetrazolium chloride (TTC). This study was undertaken to optimize the SDH-catalyzed reduction of TTC dye by evaluation of a greater range of molor ratios of TTC to succinate and by further evaluation of additives reported as beneficial. Improvement in enzyme specific activity was achieved by liver perfusion via the left cardiac ventricle with homogenizing solution. Increase in TTC from 1 to 10 mM and further increase to 20 mM resulted in major improvement in color production. The greatest improvement in apparent activity was achieved by addition of 1 mM phenozine methosulfate, a hydrogen transfer mediator. Use of CaCI₂. EDTA, Triton X-100, NaN₃ and KCN was not beneficial. The above modifications of the SDH assay resulted in greater sensitivity, the conduct of a greater number of assays with less tissue and the sacrifice of fewer animals
Using the forest vegetation simulator as a teaching tool
The Forest Vegetation Simulator (FVS) is a tree-level, spatially non-explicit growth model. It is an outgrowth of the Stand Prognosis model that the U.S. Forest Service began developing in the late 1960s. Local variants of FVS now cover most of the forest types of the United States. Development of two complementary programs, Suppose and the Stand Visualization System (SVS), have opened the possibilities for using FVS as a teaching tool in forestry classes
An Approximate Variational Method for Improved Thermodynamics of Molecular Fluids
For a certain class of thermodynamic perturbation theories, a generalization of the Gibbs-Bogoliubov inequality holds through second order of perturbation theory and for a subset of terms the inequality is true to infinite order. Using this approximate variational principle, a perturbation theory is chosen for which the Helmholtz free energy of the reference system is minimized under the constraint that the first order term is identically zero. We apply these ideas to the determination of effective spherical potentials that accurately reproduce the thermodynamics of nonspherical molecular potentials. For a diatomic-Lennard-Jones (DLJ) potential with l ∕σ = 0.793, the resulting spherical reference potential is identical to the median average over angles for the repulsive part of the potential, but differs in the attractive well. The variational effective spherical potential leads to more accurate thermodynamics than the median, however, particularly in the triple point region
The Local Effects of Cosmological Variations in Physical 'Constants' and Scalar Fields I. Spherically Symmetric Spacetimes
We apply the method of matched asymptotic expansions to analyse whether
cosmological variations in physical `constants' and scalar fields are
detectable, locally, on the surface of local gravitationally bound systems such
as planets and stars, or inside virialised systems like galaxies and clusters.
We assume spherical symmetry and derive a sufficient condition for the local
time variation of the scalar fields that drive varying constants to track the
cosmological one. We calculate a number of specific examples in detail by
matching the Schwarzschild spacetime to spherically symmetric inhomogeneous
Tolman-Bondi metrics in an intermediate region by rigorously construction
matched asymptotic expansions on cosmological and local astronomical scales
which overlap in an intermediate domain. We conclude that, independent of the
details of the scalar-field theory describing the varying `constant', the
condition for cosmological variations to be measured locally is almost always
satisfied in physically realistic situations. The proof of this statement
provides a rigorous justification for using terrestrial experiments and solar
system observations to constrain or detect any cosmological time variations in
the traditional `constants' of Nature.Comment: 30 pages, 3 figures; corrected typo
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