17,388 research outputs found
Mid-IR period-magnitude relations for AGB stars
Asymptotic Giant Branch variables are found to obey period-luminosity
relations in the mid-IR similar to those seen at K_S (2.14 microns), even at 24
microns where emission from circumstellar dust is expected to be dominant.
Their loci in the M, logP diagrams are essentially the same for the LMC and for
NGC6522 in spite of different ages and metallicities. There is no systematic
trend of slope with wavelength. The offsets of the apparent magnitude vs. logP
relations imply a difference between the two fields of 3.8 in distance modulus.
The colours of the variables confirm that a principal period with log P > 1.75
is a necessary condition for detectable mass-loss. At the longest observed
wavelength, 24 microns, many semi-regular variables have dust shells comparable
in luminosity to those around Miras. There is a clear bifurcation in LMC
colour-magnitude diagrams involving 24 micron magnitudes.Comment: 5 pages, 4 figure
Energy Transport in the Vaidya System
Energy transport mechanisms can be generated by imposing relations between
null tetrad Ricci components. Several kinds of mass and density transport
generated by these relations are studied for the generalized Vaidya system.Comment: J.Math. Phys. (to appear
A Spacetime in Toroidal Coordinates
We present an exact solution of Einstein's field equations in toroidal
coordinates. The solution has three regions: an interior with a string equation
of state; an Israel boundary layer; an exterior with constant isotropic
pressure and constant density, locally isometric to anti-de Sitter spacetime.
The exterior can be a cosmological vacuum with negative cosmological constant.
The size and mass of the toroidal loop depend on the size of the cosmological
constant.Comment: to appear in J. Math. Phy
Quasigeometric Distributions and Extra Inning Baseball Games
Each July, the eyes of baseball fans across the country turn to Major League Baseball’s All-Star Game, gathering the best and most popular players from baseball’s two leagues to play against each other in a single game. In most sports, the All-Star Game is an exhibition played purely for entertainment. Since 2003, the baseball All-Star Game has actually ‘counted’, because the winning league gets home field advantage in the World Series. Just one year before this rule went into effect, there was no winner in the All-Star Game, as both teams ran out of pitchers in the 11th inning and the game had to be stopped at that point. Under the new rules, the All-Star Game must be played until there is a winner, no matter how long it takes, so the managers need to consider the possibility of a long extra inning game. This should lead the managers to ask themselves what the probability is that the game will last 12 innings. What about 20 innings? Longer?
In this paper, we address these questions and several other questions related to the game of baseball. Our methods use a variation on the well-studied geometric distribution called the quasigeometric distribution. We begin by reviewing some of the literature on applications of mathematics to baseball. In the second section we will define the quasigeometric distribution and examine several of its properties. The final two sections examine the applications of this distribution to models of scoring patterns in baseball games and, more specifically, the length of extra inning games
Scale Symmetries of Spherical String Fluids
We consider homothetic maps in a family of spherical relativistic star
models. A generalization of Vaidya's radiating metric provides a fluid
atmosphere of radiation and strings. The similarity structure of the string
fluid is investigated.Comment: to appear in J. Math. Physic
Trace metal requirements for microbial enzymes involved in the production and consumption of methane and nitrous oxide
Fluxes of greenhouse gases to the atmosphere are heavily influenced by microbiological activity. Microbial enzymes involved in the production and consumption of greenhouse gases often contain metal cofactors. While extensive research has examined the influence of Fe bioavailability on microbial CO_2 cycling, fewer studies have explored metal requirements for microbial production and consumption of the second- and third-most abundant greenhouse gases, methane (CH_4), and nitrous oxide (N_2O). Here we review the current state of biochemical, physiological, and environmental research on transition metal requirements for microbial CH_4 and N_2O cycling. Methanogenic archaea require large amounts of Fe, Ni, and Co (and some Mo/W and Zn). Low bioavailability of Fe, Ni, and Co limits methanogenesis in pure and mixed cultures and environmental studies. Anaerobic methane oxidation by anaerobic methanotrophic archaea (ANME) likely occurs via reverse methanogenesis since ANME possess most of the enzymes in the methanogenic pathway. Aerobic CH_4 oxidation uses Cu or Fe for the first step depending on Cu availability, and additional Fe, Cu, and Mo for later steps. N_2O production via classical anaerobic denitrification is primarily Fe-based, whereas aerobic pathways (nitrifier denitrification and archaeal ammonia oxidation) require Cu in addition to, or possibly in place of, Fe. Genes encoding the Cu-containing N_2O reductase, the only known enzyme capable of microbial N_2O conversion to N_2, have only been found in classical denitrifiers. Accumulation of N_2O due to low Cu has been observed in pure cultures and a lake ecosystem, but not in marine systems. Future research is needed on metalloenzymes involved in the production of N_2O by enrichment cultures of ammonia oxidizing archaea, biological mechanisms for scavenging scarce metals, and possible links between metal bioavailability and greenhouse gas fluxes in anaerobic environments where metals may be limiting due to sulfide-metal scavenging
Adding Twist to Anisotropic Fluids
We present a solution generating technique for anisotropic fluids which
preserves specific Killing symmetries. Anisotropic matter distributions that
can be used with the one parameter Ehlers-Geroch transform are discussed.
Example spacetimes that support the appropriate anisotropic stress-energy are
found and the transformation applied. The 3+1 black string solution is one of
the spacetimes with the appropriate matter distribution. Use of the transform
with a black string seed is discussed.Comment: to appear in J. Math. Phy
Two-Fluid Atmosphere for Relativistic Stars
We have extended the Vaidya radiating metric to include both a radiation
fluid and a string fluid. This paper expands our brief introduction to
extensions of the Schwarzschild vacuum which appeared in 1998 Phys. Rev. D Vol
57, R5945. Assuming diffusive transport for the string fluid, we find new
analytic solutions of Einstein's field equations.Comment: to appear in Classical and Quantum Gravit
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