What can we say about seed fields for galactic dynamos?

We demonstrate that a quasi-uniform cosmological seed field is a much less suitable seed for a galactic dynamo than has often been believed. The age of the Universe is insufficient for a conventional galactic dynamo to generate a contemporary galactic magnetic field starting from such a seed, accepting conventional estimates for physical quantities. We discuss modifications to the scenario for the evolution of galactic magnetic fields implied by this result. We also consider briefly the implications of a dynamo number that is significantly larger than that given by conventional estimates

Studies on the hill reaction activity of soluble chloroplast extracts final report

Hill reaction activity of soluble chloroplast extracts from spinac

Flip-flop phenomenon: observations and theory

In many active stars the spots concentrate on two permanent active longitudes which are 180 degrees apart. In some of these stars the dominant part of the spot activity changes the longitude every few years. This so-called flip-flop phenomenon has up to now been reported in 11 stars, both single and binary alike, and including also the Sun. To explain this phenomenon, a non-axisymmetric dynamo mode, giving rise to two permanent active longitudes at opposite stellar hemispheres, is needed together with an oscillating axisymmetric magnetic field. Here we discuss the observed characteristics of the flip-flop phenomenon and present a dynamo solution to explain them.Comment: 4 pages, 5 figures, contribution to the conference "Dynamos of the Sun, Stars and Planets", to be published in AN Volume 32

Phase transition in a mean-field model for sympatric speciation

We introduce an analytical model for population dynamics with intra-specific competition, mutation and assortative mating as basic ingredients. The set of equations that describes the time evolution of population size in a mean-field approximation may be decoupled. We find a phase transition leading to sympatric speciation as a parameter that quantifies competition strength is varied. This transition, previously found in a computational model, occurs to be of first order.Comment: accepted for Physica

RATES OF RETURN IN THE FARM AND NON-FARM SECTORS: A TIME SERIES COMPARISON

Financial Economics,

Rarefied flow past a flat plate at incidence

Results of a numerical study using the direct simulation Monte Carlo (DSMC) method are presented for the transitional flow about a flat plate at 40 deg incidence. The plate has zero thickness and a length of 1.0 m. The flow conditions simulated are those experienced by the Shuttle Orbiter during reentry at 7.5 km/s. The range of freestream conditions are such that the freestream Knudsen number values are between 0.02 and 8.4, i.e., conditions that encompass most of the transitional flow regime. The DSMC simulations show that transitional effects are evident when compared with free molecule results for all cases considered. The calculated results demonstrate clearly the necessity of having a means of identifying the effects of transitional flow when making aerodynamic flight measurements as are currently being made with the Space Shuttle Orbiter vehicles. Previous flight data analyses have relied exclusively on adjustments in the gas-surface interaction models without accounting for the transitional effect which can be comparable in magnitude. The present calculations show that the transitional effect at 175 km would increase the Space Shuttle Orbiter lift-drag ratio by 90 percent over the free molecule value

Impact of Capital Gains and Urban Pressure on Farmland Values: A Spatial Correlation Analysis

Farmland is a major component of wealth in the farm sector as well as wealth of farm households. This study contributes to our knowledge of variations in farmland prices by examining the extent to which farmland values are spatially correlated and to what extent that this spatial correlation can be explained by income to farmland.land values, spatial correlation, Land Economics/Use,

The Effect of US Energy Policy and Farm Program Payments on the Bio-Fuel Sector: A Regime-Switching Approach

Resource /Energy Economics and Policy,

THE MEASUREMENT OF INEQUALITY IN CANADIAN AND U.S. AGRICULTURAL INCOME BY COMPONENTS OF NET VALUE ADDED

This paper examines changes in net value added generated through Canadian and U.S. farm production, 1970-2000. We consider how the structural changes in Canadian and U.S. agriculture have affected the size and distribution of net value added and its components: rent, capital, labor, and to net farm income. We use the Theil Measure of Inequality (TMI) to compare and explain changes in 1) the between and within-region distribution of net value added, and 2) changes in the distribution of factor shares of net value added in Canada and in the U.S. Results show that in Canada (1960-2000), net value added has become somewhat more equally distributed relative to the number of farms per province, but has varied widely from 1972-1988. Between-region inequality in net value added accounted for from 0.5 to 85.5 percent of this inequality from 1960-2000. In the U.S. (1949-2000), net value added has become more unequally distributed. About half of the variation in net value added in the U.S. is due to between-region variation and about half to within-region variation in net value added. We find that most of the variation in the components of net value added (returns to capital, labor, nonoperator landlords, and to farm operators) in Canada and the United States is due to variations across regions, rather than to variations in the components of net value added themselves. These variations have generally been due to macroeconomic differences in regions, such as shifts in enterprise specialization, urbanization, changes in government programs, and to other structural changes in agriculture.Agricultural Finance,