1,501 research outputs found
The (B) conjecture for uniform measures in the plane
We prove that for any two centrally-symmetric convex shapes , the function is log-concave. This
extends a result of Cordero-Erausquin, Fradelizi and Maurey in the two
dimensional case. Possible relaxations of the condition of symmetry are
discussed.Comment: 10 page
Adapting Real Quantifier Elimination Methods for Conflict Set Computation
The satisfiability problem in real closed fields is decidable. In the context
of satisfiability modulo theories, the problem restricted to conjunctive sets
of literals, that is, sets of polynomial constraints, is of particular
importance. One of the central problems is the computation of good explanations
of the unsatisfiability of such sets, i.e.\ obtaining a small subset of the
input constraints whose conjunction is already unsatisfiable. We adapt two
commonly used real quantifier elimination methods, cylindrical algebraic
decomposition and virtual substitution, to provide such conflict sets and
demonstrate the performance of our method in practice
Truth Table Invariant Cylindrical Algebraic Decomposition by Regular Chains
A new algorithm to compute cylindrical algebraic decompositions (CADs) is
presented, building on two recent advances. Firstly, the output is truth table
invariant (a TTICAD) meaning given formulae have constant truth value on each
cell of the decomposition. Secondly, the computation uses regular chains theory
to first build a cylindrical decomposition of complex space (CCD) incrementally
by polynomial. Significant modification of the regular chains technology was
used to achieve the more sophisticated invariance criteria. Experimental
results on an implementation in the RegularChains Library for Maple verify that
combining these advances gives an algorithm superior to its individual
components and competitive with the state of the art
Speeding up Cylindrical Algebraic Decomposition by Gr\"obner Bases
Gr\"obner Bases and Cylindrical Algebraic Decomposition are generally thought
of as two, rather different, methods of looking at systems of equations and, in
the case of Cylindrical Algebraic Decomposition, inequalities. However, even
for a mixed system of equalities and inequalities, it is possible to apply
Gr\"obner bases to the (conjoined) equalities before invoking CAD. We see that
this is, quite often but not always, a beneficial preconditioning of the CAD
problem.
It is also possible to precondition the (conjoined) inequalities with respect
to the equalities, and this can also be useful in many cases.Comment: To appear in Proc. CICM 2012, LNCS 736
Electroproduction of the d* dibaryon
The unpolarized cross section for the electroproduction of the isoscalar
di-delta dibaryon is calculated for deuteron target using a
simple picture of elastic electron-baryon scattering from the and the components of the deuteron. The calculated
differential cross section at the electron lab energy of 1 GeV has the value of
about 0.24 (0.05) nb/sr at the lab angle of 10 (30) for the
Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross
section decreases rapidly with increasing dibaryon mass. A large calculated
width of 40 MeV for combined with a small
experimental upper bound of 0.08 MeV for the decay width appears to have
excluded any low-mass model containing a significant admixture of the
configuration.Comment: 11 journal-style pages, 8 figure
A simple expression for the ADM mass
We show by an almost elementary calculation that the ADM mass of an
asymptotically flat space can be computed as a limit involving a rate of change
of area of a closed 2-surface. The result is essentially the same as that given
by Brown and York. We will prove this result in two ways, first by direct
calculation from the original formula as given by Arnowitt, Deser and Misner
and second as a corollary of an earlier result by Brewin for the case of
simplicial spaces.Comment: 9 pages, 1 figur
The Ecology and Species Richness of the Different Plant Communities Within Selected Wetlands on the Maputaland Coastal Plain, South Africa
Selenium Concentrations in Forage on Some High Northwestern Ranges
Forages produced on some high northwestern ranges were
analyzed for selenium concentration to determine the
hazard of white muscle disease (WMD) in calves and
lambs. The selenium concentration in 94 forage samples
ranged from 0.01 to 0.78 ppm, of which 20 samples contained
more than 0.10 ppm. The remaining 74 samples
contained less than 0.10 ppm and 59 of those contained
Less than 0.05 ppm. Approximately 90% of the summer
ranges studied produce forage containing less than 0.10
ppm selenium. Thus, the hazard of WMD on these northwestern
ranges may be high. Ranchers should work individually
and in groups to ascertain losses from the
disease and minimize them by injecting the animals with
selenium
Selenium Concentrations in Alfalfa from Several Sources Applied to a Low Selenium, Alkaline Soil
Two laboratory-prepared ferric hydroxy bi-selenites and
CuSeO? applied to Portneuf silt ham in the field provided
slowly available Se to alfalfa, resulting in Se concentration adequate
but nontoxic for livestock. These materials have potential
as Se fertilizers at low application rates. The ferric hydroxy
bi-selenites offer little or no advantage over CuSeO?. Se from
BaSeO? alone, BaSeO?—BaSO? mixtures, and CuSeO? was
absorbed by alfalfa in concentrations toxic to livestock. A small
fraction of applied elemental Se was available immediately
after application, providing adequate Se to alfalfa for livestock.
The remaining elemental Se was rather inert, and supplies only
slightly more Se to alfalfa than did the untreated soil the year
following application
Effect of Phosphorus Fertilization on the Selenium Concentration in Alfalfa (Medicago sativa)
A study was conducted to determine the effect of P fertilization
on the Se concentration in alfalfa. Adding P to the soil increased
the Se concentration in alfalfa grown in the greenhouse
on six of 14 soils from the northwestern United States. The Se
concentration increase in alfalfa resulting from P addition was
noted on some alkaline and some acid soils. Phosphorus addition
increased the availability to alfalfa of both native and
applied Se in the Portneuf silt loam. Applying 160 kg P/ha
either as H?PO? or concentrated superphosphate to Gooding
sandy loam in the field increased the Se concentration in alfalfa
from a level marginal for animal requirements to an adequate
level
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