Optimization of the magnetic dynamo

In stars and planets, magnetic fields are believed to originate from the motion of electrically conducting fluids in their interior, through a process known as the dynamo mechanism. In this Letter, an optimization procedure is used to simultaneously address two fundamental questions of dynamo theory: "Which velocity field leads to the most magnetic energy growth?" and "How large does the velocity need to be relative to magnetic diffusion?" In general, this requires optimization over the full space of continuous solenoidal velocity fields possible within the geometry. Here the case of a periodic box is considered. Measuring the strength of the flow with the root-mean-square amplitude, an optimal velocity field is shown to exist, but without limitation on the strain rate, optimization is prone to divergence. Measuring the flow in terms of its associated dissipation leads to the identification of a single optimal at the critical magnetic Reynolds number necessary for a dynamo. This magnetic Reynolds number is found to be only 15% higher than that necessary for transient growth of the magnetic field.Comment: Optimal velocity field given approximate analytic form. 4 pages, 4 figure

A dc to dc converter

The object of the invention is to provide an improved converter for converting one direct current voltage to another. A plurality of phased square wave voltages are provided from a ring counter through amplifiers to a like plurality of output transformers. Each of these transformers has two windings, and S(1) winding and an S(2) winding. The S(1) windings are connected in series, then the S(2) windings are connected in series, and finally, the two sets of windings are connected in series. One of six SCRs is connected between each two series connected windings to a positive output terminal and one of diodes is connected between each set of two windings of a zero output terminal. By virtue of this configuration, a quite high average direct current voltage is obtained, which varies between full voltage and two-thirds full voltage rather than from full voltage to zero. Further, its variation, ripple frequency, is reduced to one-sixth of that present in a single phase system. Application to raising battery voltage for an ion propulsion system is mentioned

Scales for co-compact embeddings of virtually free groups

Let $\Gamma$ be a group which is virtually free of rank at least 2 and let $\mathcal{F}_{td}(\Gamma)$ be the family of totally disconnected, locally compact groups containing $\Gamma$ as a co-compact lattice. We prove that the values of the scale function with respect to groups in $\mathcal{F}_{td}(\Gamma)$ evaluated on the subset $\Gamma$ have only finitely many prime divisors. This can be thought of as a uniform property of the family $\mathcal{F}_{td}(\Gamma)$.Comment: 12 pages; key words: uniform lattice, virtually free group, totally disconnected group, scale function (Error in references corrected in version 2

Organic amendment increases arbuscular mycorrhizal fungal diversity in primary coastal dunes

Plastic pots were inserted beneath seedlings of a shallow-rooted C4 grass species, Ischaemum indicum, with and without a root-impenetrable nylon sachet filled with organic matter (OM) amendment, at seven stations along an interrupted belt transect in which plant community and soil chemistry had been previously surveyed. The transect was perpendicular to mean high-water mark (MH-WM) across a primary coastal dune system in Goa, India, where summer monsoon is the predominant weather feature. The Quadrat survey of plant frequency was made in stations when the above-ground biomass was estimated to be highest. Arbuscular mycorrhiza fungal (AMF) spore density and diversity were determined morphologically in amended and control pots soils, and in OM sachet residues, after host-plant desiccation when monsoon rains had ceased. Twenty-seven AM fungal spore morphotypes were isolated from the pots containing OM amended rhizosphere soils, 19 from controls and 14 from OM residues in the sachets. Gigaspora margarita proved to be the dominant spore in all treatments. Eight morphotypes recovered from amended pots were not recovered from the controls. There was an increasing trend in species diversity in amended pots away from MH-WM. Spore recovery from the three regimes showed variable distribution that indicated differing AMF species strategies

Effects of aircraft noise on flight and ground structures

Acoustic loads measured on jet-powered STOL configurations are presented for externally blown and upper surface blown flap models ranging in size from a small laboratory model up to a full-scale aircraft model. The implications of the measured loads for potential acoustic fatigue and cabin noise are discussed. Noise transmission characteristics of light aircraft structures are presented. The relative importance of noise transmission paths, such as fuselage sidewall and primary structure, is estimated. Acceleration responses of a historic building and a residential home are presented for flyover noise from subsonic and supersonic aircraft. Possible effects on occupant comfort are assessed. The results from these three examples show that aircraft noise can induce structural responses that are large enough to require consideration in the design or operation of the aircraft

Thermal and Non-thermal Plasmas in the Galaxy Cluster 3C 129

We describe new Chandra spectroscopy data of the cluster which harbors the prototypical "head tail" radio galaxy 3C 129 and the weaker radio galaxy 3C 129.1. We combined the Chandra data with Very Large Array (VLA) radio data taken at 0.33, 5, and 8 GHz (archival data) and 1.4 GHz (new data). We also obtained new HI observations at the Dominion Radio Astrophysical Observatory (DRAO) to measure the neutral Hydrogen column density in the direction of the cluster with arcminute angular resolution. The Chandra observation reveals extended X-ray emission from the radio galaxy 3C 129.1 with a total luminosity of 1.5E+41 erg/s. The X-ray excess is resolved into an extended central source of ~2 arcsec (1 kpc) diameter and several point sources with an individual luminosity up to 2.1E+40 erg/s. In the case of the radio galaxy 3C 129, the Chandra observation shows, in addition to core and jet X-ray emission reported in an earlier paper, some evidence for extended, diffuse X-ray emission from a region east of the radio core. The 12 arcsec x 36 arcsec (6 kpc x 17 kpc) region lies "in front" of the radio core, in the same direction into which the radio galaxy is moving. We use the radio and X-ray data to study in detail the pressure balance between the non-thermal radio plasma and the thermal Intra Cluster Medium (ICM) along the tail of 3C 129 which extends over 15 arcmin (427 kpc). Depending on the assumed lower energy cutoff of the electron energy spectrum, the minimum pressure of the radio plasma lies a factor of between 10 and 40 below the ICM pressure for a large part of the tail. We discuss several possibilities to explain the apparent pressure mismatch.Comment: Accepted for publication in MNRAS. Refereed manuscript. 14 pages, 8 figures, additional panel of Fig. 3 shows asymmetric ICM distributio

Hospital Community Benefits After the ACA: Partnerships for Community Health Improvement

Examines states' and localities' efforts to promote community health and systemic change through collaborations focused on community health needs assessments, priority setting, strategic planning, and the implementation of health improvement initiatives

Approximate trajectory data for missions to the major planets

Contour charts and tables on trajectory data for missions to Jupiter, Saturn, Uranus, and Neptune and their moon

CONJOINT ANALYSIS OF GROUNDWATER PROTECTION PROGRAMS

Three conjoint models-a traditional ratings model, a ratings difference specification, and a binary response model-were used to value groundwater protection program alternatives. The last, which is virtually identical to a dichotomous choice contingent valuation specification, produced the smallest value estimates. This suggests that the conjoint model is very sensitive to model specifications and that traditional conjoint models may overestimate economic value because many respondents are not in the market for the commodity being valued.Resource /Energy Economics and Policy,