Archaeal ubiquity

In the seventeenth century, Antoine von Leeuwenhook used a simple microscope to discover that we live within a previously undetected microbial world containing an enormously diverse population of creatures. The late nineteenth and early twentieth century brought advances in microbial culture techniques and in biochemistry, uncovering the roles that microbes play in all aspects of our world, from causing disease to modulating geochemical cycles. In the last 25 years, molecular biology has revealed the complexity and pervasiveness of the microbial world and its importance for understanding the interactions that maintain living systems on the planet. The paper by Preston et al. (1) in this issue of the Proceedings provides a clear illustration of the power of these molecular techniques to describe new biological relationships and to pose important questions about the mechanisms that drive evolution. The analysis of ribosomal RNA gene sequences is one molecular approach that has radically altered our view of microbial diversity. Its application can be extended and expedited by the use of PCR. The confluence of these techniques has stimulated the rapid assembly of sequence information from homologues rRNA gene regions derived from virtually all classes of organisms. The data collected thus far support the scheme first presented by Woese et al. (2), which holds that the relationships among organisms can be summarized in the form of a universal phylogenetic tree comprised of one eukaryotic and two prokaryotic domains: the Eucarya, the Bacteria, and the Archaea (Fig. 1)

Housing and labor market distortions in Poland : linkages and policy implications

Poland's housing and macroeconomic policies have restricted investments in housing and urban infrastructure to a level well below that of other European countries. This has resulted in a shortage of housing typified by 15 to 20 year waits for government sponsored housing. Shortages of this magnitude are likely to cause distortions with impacts on patterns of savings and consumption, the price level, and on the functioning of labor markets. This paper focuses particularly on how housing market distortions are transmitted to labor markets, with impacts on rates of migration, relative wage levels among different regions, and, by implication, on the productivity of the Polish work force. The basic thesis of the paper is that if housing markets are prevented from reaching their competitive equilibrium that labor markets will similarly be prevented. Evidence is examined on the extent of housing and labor market disequilibria, and estimates econometric models that relate internal migration and relative wages to alternative measures of housing market disequilibria. From these analyses it is concluded that labor markets are in fact distorted by housing market distortions, with potentially major macroeconomic costs.Banks&Banking Reform,Municipal Financial Management,Housing&Human Habitats,Public Sector Economics&Finance,Urban Housing

The Order of Phase Transitions in Barrier Crossing

A spatially extended classical system with metastable states subject to weak spatiotemporal noise can exhibit a transition in its activation behavior when one or more external parameters are varied. Depending on the potential, the transition can be first or second-order, but there exists no systematic theory of the relation between the order of the transition and the shape of the potential barrier. In this paper, we address that question in detail for a general class of systems whose order parameter is describable by a classical field that can vary both in space and time, and whose zero-noise dynamics are governed by a smooth polynomial potential. We show that a quartic potential barrier can only have second-order transitions, confirming an earlier conjecture [1]. We then derive, through a combination of analytical and numerical arguments, both necessary conditions and sufficient conditions to have a first-order vs. a second-order transition in noise-induced activation behavior, for a large class of systems with smooth polynomial potentials of arbitrary order. We find in particular that the order of the transition is especially sensitive to the potential behavior near the top of the barrier.Comment: 8 pages, 6 figures with extended introduction and discussion; version accepted for publication by Phys. Rev.

Mechanism of spontaneous formation of stable magnetic structures on the Sun

One of the puzzling features of solar magnetism is formation of long-living compact magnetic structures; such as sunspots and pores, in the highly turbulent upper layer of the solar convective zone. We use realistic radiative 3D MHD simulations to investigate the interaction between magnetic field and turbulent convection. In the simulations, a weak vertical uniform magnetic field is imposed in a region of fully developed granular convection; and the total magnetic flux through the top and bottom boundaries is kept constant. The simulation results reveal a process of spontaneous formation of stable magnetic structures, which may be a key to understanding of the magnetic self-organization on the Sun and formation of pores and sunspots. This process consists of two basic steps: 1) formation of small-scale filamentary magnetic structures associated with concentrations of vorticity and whirlpool-type motions, and 2) merging of these structures due to the vortex attraction, caused by converging downdrafts around magnetic concentration below the surface. In the resulting large-scale structure maintained by the converging plasma motions, the magnetic field strength reaches ~1.5 kG at the surface and ~6 kG in the interior; and the surface structure resembles solar pores. The magnetic structure remains stable for the whole simulation run of several hours with no sign of decay.Comment: 13 pages, 4 figures, submitted to the Astrophysical Journa

Numerical constraints on the model of stochastic excitation of solar-type oscillations

Analyses of a 3D simulation of the upper layers of a solar convective envelope provide constraints on the physical quantities which enter the theoretical formulation of a stochastic excitation model of solar p modes, for instance the convective velocities and the turbulent kinetic energy spectrum. These constraints are then used to compute the acoustic excitation rate for solar p modes, P. The resulting values are found ~5 times larger than the values resulting from a computation in which convective velocities and entropy fluctuations are obtained with a 1D solar envelope model built with the time-dependent, nonlocal Gough (1977) extension of the mixing length formulation for convection (GMLT). This difference is mainly due to the assumed mean anisotropy properties of the velocity field in the excitation region. The 3D simulation suggests much larger horizontal velocities compared to vertical ones than in the 1D GMLT solar model. The values of P obtained with the 3D simulation constraints however are still too small compared with the values inferred from solar observations. Improvements in the description of the turbulent kinetic energy spectrum and its depth dependence yield further increased theoretical values of P which bring them closer to the observations. It is also found that the source of excitation arising from the advection of the turbulent fluctuations of entropy by the turbulent movements contributes ~ 65-75 % to the excitation and therefore remains dominant over the Reynolds stress contribution. The derived theoretical values of P obtained with the 3D simulation constraints remain smaller by a factor ~3 compared with the solar observations. This shows that the stochastic excitation model still needs to be improved.Comment: 11 pages, 9 figures, accepted for publication in A&

Fisheries Management under Irreversible Investment: Does Stochasticity Matter?

We present a continuous, nonlinear, stochastic and dynamic model for capital investment in the exploitation of a renewable resource. Both the resource stock and capital stock are treated as state variables. The resource owner controls fishing effort and the investment rate in an optimal way. Biological stock growth and capital depreciation rate are stochastic in the model. We find that the stochastic resource should be managed conservatively. The capital utilization rate is found to be a non-increasing function of stochasticity. Investment could be either higher or lower depending on the interaction between the capital and the resource stocks. In general a stochastic capital depreciation rate has only weak influence on optimal management. In the long run, the steady state harvest for a stochastic resource becomes lower than the deterministic level.Physical capital; irreversible investment; stochastic growth; long-term sustainable optimal

Continuous harvesting costs in sole-owner fisheries with increasing marginal returns

We develop a bioeconomic model to analyze a sole-owner fishery with fixed costs as well as a continuous cost function for the generalized Cobb-Douglas production function with increasing marginal returns to effort level. On the basis of data from the North Sea herring fishery, we analyze the consequences of the combined effects of increasing marginal returns and fixed costs. We find that regardless of the magnitude of the fixed costs, cyclical policies can be optimal instead of the optimal steady state equilibrium advocated in much of the existing literature. We also show that the risk of stock collapse increases significantly with increasing fixed costs as this implies higher period cycles which is a quite counterintuitive result as higher costs usually are considered to have a conservative effect on resources.Bioeconomic modelling; Stock collapse; Fixed costs; Pulse fishing; Cyclical dynamics; Increasing marginal returns