Perez Zagorin: Hobbes and the Law of Nature

Hobbes, Law of Nature, instrumental rationality, justice, liberty, homo oeconomicus

Cost of phosphate removal in municipal wastewater treatment plants

Construction and operating costs of advanced wastewater treatment for phosphate removal at municipal wastewater treatment plants have been investigated on orders from the Federal Environmental Bureau in Berlin. Particular attention has been paid to applicable kinds of precipitants for pre-, simultaneous and post-precipitation as well as to different phosphate influent and effluent concentrations. The article offers detailed comments on determination of technical data, investments, capital costs, operating costs and annual costs as well as potential cost reductions resulting from precipitation. Selected results of the cost investigation are shown in graphical form as specific investments, operating and annual costs depending on wastewater flow

The shadow of exit from NATO

President Donald Trump has not been shy about trying to coerce close allies. This inclination has led to concerns that the president poses a unique threat to American alliances. Theoretically, these concerns are consistent with an influential line of argument pointing to strategic restraint and reassurance—via binding institutions—as what sets American alliances apart. However, the Trump presidency is not the first time that the shadow of exit has hung over the United States’ commitment to Europe. Indeed, a closer look at the North Atlantic Treaty Organization’s (NATO) formative period shows that the United States actively considered leaving Europe throughout the 1950s. Even after resigning itself to staying in the early 1960s, the United States used threats of abandonment to put down the Franco-German revolt—the most significant challenge to its preponderant position in the NATO alliance. The primary implication is that American alliance relations have been characterized by more uncertainty—and less restraint and reassurance—than institutionalists have cared to emphasize, which paradoxically suggests that NATO, and the United States’ broader alliance network, is robust enough to survive President Trump’s attempts at coercion.Published versio

Dynamics of magnetic flux tubes in close binary stars I. Equilibrium and stability properties

Surface reconstructions of active close binary stars based on photometric and spectroscopic observations reveal non-uniform starspot distributions, which indicate the existence of preferred spot longitudes (with respect to the companion star). We consider the equilibrium and linear stability of toroidal magnetic flux tubes in close binaries to examine whether tidal effects are capable to initiate the formation of rising flux loops at preferred longitudes near the bottom of the stellar convection zone. The tidal force and the deviation of the stellar structure from spherical symmetry are treated in lowest-order perturbation theory assuming synchronised close binaries with orbital periods of a few days. The frequency, growth time, and spatial structure of linear eigenmodes are determined by a stability analysis. We find that, despite their small magnitude, tidal effects can lead to a considerable longitudinal asymmetry in the formation probability of flux loops, since the breaking of the axial symmetry due to the presence of the companion star is reinforced by the sensitive dependence of the stability properties on the stellar stratification and by resonance effects. The orientation of preferred longitudes of loop formation depends on the equilibrium configuration and the wave number of the dominating eigenmode. The change of the growth times of unstable modes with respect to the case of a single star is very small.Comment: 11 pages, 11 figures, accepted for publication in A&

Are the strengths of solar cycles determined by converging flows towards the activity belts?

It is proposed that the observed near-surface inflows towards the active regions and sunspot zones provide a nonlinear feedback mechanism that limits the amplitude of a Babcock-Leighton-type solar dynamo and determines the variation of the cycle strength. This hypothesis is tested with surface flux transport simulations including converging latitudinal flows that depend on the surface distribution of magnetic flux. The inflows modulate the build-up of polar fields (represented by the axial dipole) by reducing the tilt angles of bipolar magnetic regions and by affecting the cross-equator transport of leading-polarity magnetic flux. With flux input derived from the observed record of sunspot groups, the simulations cover the period between 1874 and 1980 (corresponding to solar cycles 11 to 20). The inclusion of the inflows leads to a strong correlation of the simulated axial dipole strength during activity minimum with the observed amplitude of the subsequent cycle. This in agreement with empirical correlations and in line with what is expected from a Babcock-Leighton-type dynamo. The results provide evidence that the latitudinal inflows are a key ingredient in determining the amplitude of solar cycles.Comment: accepted in A&

Features and technologies of ERS-1 (ESA) and X-SAR antennas

Features and technologies of planar waveguide array antennas developed for spaceborne microwave sensors are described. Such antennas are made from carbon fiber reinforced plastic (CFRP) employing special manufacturing and metallization techniques to achieve satisfactory electrical properties. Mechanical design enables deployable antenna structures necessary for satellite applications (e.g., ESA ERS-1). The slotted waveguide concept provides high aperture efficiency, good beamshaping capabilities, and low losses. These CFRP waveguide antennas feature low mass, high accuracy and stiffness, and can be operated within wide temperature ranges

A necessary extension of the surface flux transport model

Customary two-dimensional flux transport models for the evolution of the magnetic field at the solar surface do not account for the radial structure and the volume diffusion of the magnetic field. When considering the long-term evolution of magnetic flux, this omission can lead to an unrealistic long-term memory of the system and to the suppression of polar field reversals. In order to avoid such effects, we propose an extension of the flux transport model by a linear decay term derived consistently on the basis of the eigenmodes of the diffusion operator in a spherical shell. A decay rate for each eigenmode of the system is determined and applied to the corresponding surface part of the mode evolved in the flux transport model. The value of the volume diffusivity associated with this decay term can be estimated to be in the range 50--100 km^2/s by considering the reversals of the polar fields in comparison of flux transport simulations with observations. We show that the decay term prohibits a secular drift of the polar field in the case of cycles of varying strength, like those exhibited by the historical sunspot record.Comment: for further information visit: http://solweb.oma.be/users/baumann