56,569 research outputs found
An Analytic Method of Interpretation of Electron Diffraction Photographs of Gases
An analytic procedure to be used in the interpretation of electron diffraction photographs for gases is developed. The experimentally determined positions of the maxima and minima are employed to solve directly for the interatomic distances through successive approximations. The method is then generalized so as to be applicable to molecules in which rotations or large oscillations about a bond are permitted. As a test, three sets of data which have already been published are recalculated yielding somewhat altered values for the molecular parameters. New diffraction photographs of propane are analyzed. It is pointed out that the number of theoretical intensity curves which must be computed to obtain the correct structure is thereby greatly reduced
Hydrogen ions
Hydrogen ion production and distribution in upper atmospher
The cosmological constant and the relaxed universe
We study the role of the cosmological constant (CC) as a component of dark
energy (DE). It is argued that the cosmological term is in general unavoidable
and it should not be ignored even when dynamical DE sources are considered.
From the theoretical point of view quantum zero-point energy and phase
transitions suggest a CC of large magnitude in contrast to its tiny observed
value. Simply relieving this disaccord with a counterterm requires extreme
fine-tuning which is referred to as the old CC problem. To avoid it, we discuss
some recent approaches for neutralising a large CC dynamically without adding a
fine-tuned counterterm. This can be realised by an effective DE component which
relaxes the cosmic expansion by counteracting the effect of the large CC.
Alternatively, a CC filter is constructed by modifying gravity to make it
insensitive to vacuum energy.Comment: 6 pages, no figures, based on a talk presented at PASCOS 201
Solar-wind control of the extent of planetary ionospheres
In our solar system there are at least four magnetic planets: Earth, Jupiter, Mercury, and Mars; while at least one planet, Venus, appears to be essentially nonmagnetic. The ionospheres of the magnetic planets are imbedded in their magnetosphere and thus shielded from the solar wind, whereas the ionosphere of Venus, at least, interacts directly with the solar wind. However, the solar wind interaction with the planetary environment, in both cases, affects the behavior of their ionospheres. The role the solar wind interaction plays in limiting the extent of the ionospheres of both magnetic and nonmagnetic planets is discussed
Repeatability of evolution on epistatic landscapes
Evolution is a dynamic process. The two classical forces of evolution are
mutation and selection. Assuming small mutation rates, evolution can be
predicted based solely on the fitness differences between phenotypes.
Predicting an evolutionary process under varying mutation rates as well as
varying fitness is still an open question. Experimental procedures, however, do
include these complexities along with fluctuating population sizes and
stochastic events such as extinctions. We investigate the mutational path
probabilities of systems having epistatic effects on both fitness and mutation
rates using a theoretical and computational framework. In contrast to previous
models, we do not limit ourselves to the typical strong selection, weak
mutation (SSWM)-regime or to fixed population sizes. Rather we allow epistatic
interactions to also affect mutation rates. This can lead to qualitatively
non-trivial dynamics. Pathways, that are negligible in the SSWM-regime, can
overcome fitness valleys and become accessible. This finding has the potential
to extend the traditional predictions based on the SSWM foundation and bring us
closer to what is observed in experimental systems
Spruce Budworm Weight and Fecundity: Means, Frequency Distributions, and Correlations for Two Populations (Lepidoptera: Tortricidae)
Pupal weights and fecundities of spruce budworm from Minnesota had different means, coefficients of variation, and frequency distributions than spruce budworm from New Hampshire. The two variables were correlated in one of the populations but not the other
The Orientation of Unsymmetrical Molecules at Interfaces
A function giving the distribution of the angles of orientation of the molecular axes from the normal to the interface can be obtained if one makes use of a number of special assumptions regarding the forces of orientation. This is compared with the distribution calculated on assuming an extreme form of Langmuir's principle of independent surface action. The importance of having such a function is pointed out
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