11,957 research outputs found
M-Theory on the Orbifold C^2/Z_N
We construct M-theory on the orbifold C^2/Z_N by coupling 11-dimensional
supergravity to a seven-dimensional Yang-Mills theory located on the orbifold
fixed plane. It is shown that the resulting action is supersymmetric to leading
non-trivial order in the 11-dimensional Newton constant. This action provides
the starting point for a reduction of M-theory on G_2 spaces with co-dimension
four singularities.Comment: 33 pages, Late
Phosphorus and arsenic distributions in a seasonally-stratified, iron- and manganese-rich lake: microbiological and geochemical controls
Seasonal stratification in temperate lakes greater than a few metres deep provides conditions amenable to pronounced vertical zonation of redox chemistry. Such changes are particularly evident in eutrophic systems where high phytoplankton biomass often leads to seasonally-established anoxic hypolimnia and profound changes in geochemical conditions. In this study, we investigated the behaviour of trace elements in the water column of a seasonally-stratified, eutrophic lake. Two consecutive years of data from Lake Ngapouri, North Island, New Zealand, demonstrate the occurrence of highly correlated profiles of phosphorus (P), arsenic (As), iron (Fe) and manganese (Mn), all of which increased in concentration by 1-2 orders of magnitude within the anoxic hypolimnion. Stoichiometric and mass-balance considerations demonstrate that increases in alkalinity in hypolimnetic waters were consistent with observed changes in sulfate, Fe and Mn concentrations with depth, corresponding to dissimilatory reduction of sulfate, Fe(III) and Mn(IV) hydroxides. Thermodynamic constraints on Fe, Mn and Al solubility indicate that amorphous Fe(III), Mn(IV) hydroxides most probably controlled Fe and Mn in the surface mixed layer (~0 to 8 m) while Al(III) hydroxides were supersaturated throughout the entire system. Surface complexation modelling indicated that iron hydroxides (HFO) potentially dominated As speciation in the lake. It is likely that other colloidal phases such as allophanic clays also limited HPO42- activity, reducing competition for HAsO42- adsorption to iron hydroxides. This research highlights the coupling of P, As, Fe and Mn in Lake Ngapouri, and the apparent role of multiple colloidal phases in affecting P and As activity within overarching microbiological and geochemical processes
Halo-Independent Direct Detection Analyses Without Mass Assumptions
Results from direct detection experiments are typically interpreted by
employing an assumption about the dark matter velocity distribution, with
results presented in the plane. Recently methods which are
independent of the DM halo velocity distribution have been developed which
present results in the plane, but these in turn require an
assumption on the dark matter mass. Here we present an extension of these
halo-independent methods for dark matter direct detection which does not
require a fiducial choice of the dark matter mass. With a change of variables
from to nuclear recoil momentum (), the full halo-independent
content of an experimental result for any dark matter mass can be condensed
into a single plot as a function of a new halo integral variable, which we call
. The entire family of conventional halo-independent
plots for all DM masses are directly found from the single
plot through a simple rescaling of axes. By considering
results in space, one can determine if two experiments are
inconsistent for all masses and all physically possible halos, or for what
range of dark matter masses the results are inconsistent for all halos, without
the necessity of multiple plots for different DM masses.
We conduct a sample analysis comparing the CDMS II Si events to the null
results from LUX, XENON10, and SuperCDMS using our method and discuss how the
mass-independent limits can be strengthened by imposing the physically
reasonable requirement of a finite halo escape velocity.Comment: 23 pages, 8 figures. v2: footnote and references adde
THE ECONOMICS OF CLEANING WINTER WHEAT FOR EXPORT: AN EVALUATION OF PROPOSED FEDERAL "CLEAN GRAIN" STANDARDS
Buyer complaints about poor quality U.S. wheat have led to proposals to enforce minimum dockage standards for exports. An economic-engineering approach is used to evaluate costs and benefits of cleaning wheat in order to meet these standards for 13 possible cleaning configurations. These results are used in an optimization framework to estimate costs and benefits of cleaning all U.S. export wheat. The estimates indicate that cleaning U.S. export winter wheat to .35% dockage would cost an average of 1 cent/bu., requiring an initial capital investment of $28 million. Value of wheat lost in cleaning is a significant cost that previously has been overlooked.Agricultural and Food Policy,
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