Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope

The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions.Comment: V2: update to conform to the published article; new choice for internal inductance of torus; updated Fig. 2; new Figs. 3, 5, and

Simulated Gas Turbine Casing Response to Rotor Blade Pressure Excitation

Non-intrusive measurement of blade condition within gas turbines is of major interest within all areas of their use. It is proposed that the measurement of the casing vibration, due to the aerodynamic-structural interaction within the turbine, could provide a means of blade condition monitoring and modal parameter estimation. In order to understand the complex relationship between blade vibrations and casing response, an analytical model of the casing and simulated pressure signal associated with the rotor blades is presented. A mathematical formulation is undertaken of the internal pressure signal due to both the rotating bladed disk as well as individual blade vibrations and the solution of the casing response is formulated. Excitation by the stator blades and their contribution to the casing response is also investigated. Some verification of the presented analytical model is provided by comparison with Finite Element Analysis results for various rotor rotational speeds

Prepotentials for local mirror symmetry via Calabi-Yau fourfolds

In this paper, we first derive an intrinsic definition of classical triple intersection numbers of K_S, where S is a complex toric surface, and use this to compute the extended Picard-Fuchs system of K_S of our previous paper, without making use of the instanton expansion. We then extend this formalism to local fourfolds K_X, where X is a complex 3-fold. As a result, we are able to fix the prepotential of local Calabi-Yau threefolds K_S up to polynomial terms of degree 2. We then outline methods of extending the procedure to non canonical bundle cases.Comment: 42 pages, 7 figures. Expanded, reorganized, and added a theoretical background for the calculation

Indeterminacy and instability in Petschek reconnection

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate

Does Habitat Management for Northern Bobwhites Benefit the Red Imported Fire Ant?

Red imported fire ants (Solenopsis invicta) have caused damage to agricultural, economic, and wildlife resources since their accidental introduction. Previous studies have suggested that red imported fire ant (RIFA) mound densities are positively correlated to habitats maintained through disturbance. Prescribed burning and disking are two techniques commonly used to disturb portions of the landscape to maintain early successional habitats for northern bobwhite (Colinus virginianus). We tested the hypothesis that prescribed burning and disking would increase RIFA mound densities. This study was conducted in Refugio County, Texas in the Texas Coastal Prairie on Loamy Prairie range sites. Red imported fire ant mound densities were different between years (F = 5.05, df = 2, P = 0.0148). However, burning and disking had no impact (F = 0.22, df = 2, P = 0.8044) on RIFA mound densities. Initially high RIFA mound densities in our study area coupled with the territoriality of predominantly monogyne (single-queen) colonies may have limited increases in RIFA mound density in response to treatments on these study sites

WMAP Haze: Directly Observing Dark Matter?

In this paper we show that dark matter in the form of dense matter/antimatter nuggets could provide a natural and unified explanation for several distinct bands of diffuse radiation from the core of the Galaxy spanning over 12 orders of magnitude in frequency. We fix all of the phenomenological properties of this model by matching to x-ray observations in the keV band, and then calculate the unambiguously predicted thermal emission in the microwave band, at frequencies smaller by 10 orders of magnitude. Remarkably, the intensity and spectrum of the emitted thermal radiation are consistent with--and could entirely explain--the so-called "WMAP haze": a diffuse microwave excess observed from the core of our Galaxy by the Wilkinson Microwave Anisotropy Probe (WMAP). This provides another strong constraint of our proposal, and a remarkable nontrivial validation. If correct, our proposal identifies the nature of the dark matter, explains baryogenesis, and provides a means to directly probe the matter distribution in our Galaxy by analyzing several different types of diffuse emissions.Comment: 16 pages, REVTeX4. Updated to correspond with published version: includes additional appendices discussing finite-size effect

The Fate of Nephrons in Congenital Obstructive Nephropathy: Adult Recovery is Limited by Nephron Number Despite Early Release of Obstruction

Urinary tract obstruction and reduced nephron number often occur together as a result of maldevelopment of kidneys and urinary tract. We wished to determine the role of nephron number on the adaptation of remaining nephrons of mice subjected to neonatal partial unilateral ureteral obstruction (UUO) and followed through adulthood

Degraded Rangeland: Can the Balance Be Restored in the Absence of Satisfactory Range Management Practices?

The rangelands of KwaZulu-Natal play a fundamental role in the wealth and security of communal populations who are dependent on these forage-producing lands for their livelihoods. In most communal areas of the Province, there is an absence of satisfactory range management practices and the utilization of resources is generally non-sustainable. A major threat to the productivity of rangeland is inappropriate land use, such as overgrazing and incorrect burning practices, leading to extensive degradation of both the vegetative and soil components. Range vegetation and soil reserves show vastly reduced productivity. Degradation also results in increased susceptibility to erosion, loss of vegetative cover and palatable species, loss of biodiversity and reduced productivity, directly threatening food security of vast numbers of people in the rural areas. Social issues such as weakened and marginalized traditional authorities and reduced control of resource utilization is partly responsible. In addition, the value placed on livestock for draught power, meat, milk and other products, and for financial security against calamity, entrenches a reluctance to diminish stock numbers. Alternative strategies to reduce pressure on stressed range systems need to be formulated in participation with affected communities to, among other benefits, increase the contribution from animals to household security

Strangelet dwarfs

If the surface tension of quark matter is low enough, quark matter is not self bound. At sufficiently low pressure and temperature, it will take the form of a crystal of positively charged strangelets in a neutralizing background of electrons. In this case there will exist, in addition to the usual family of strange stars, a family of low-mass large-radius objects analogous to white dwarfs, which we call "strangelet dwarfs". Using a generic parametrization of the equation of state of quark matter, we calculate the mass-radius relationship of these objects.Comment: 10 pages, LaTeX, added discussion of CFL phase and strangelet pollution, version to appear in journal. arXiv admin note: text overlap with arXiv:0808.067