7,077 research outputs found
Angular reduction in multiparticle matrix elements
A general method for the reduction of coupled spherical harmonic products is
presented. When the total angular coupling is zero, the reduction leads to an
explicitly real expression in the scalar products within the unit vector
arguments of the spherical harmonics. For non-scalar couplings, the reduction
gives Cartesian tensor forms for the spherical harmonic products, with tensors
built from the physical vectors in the original expression. The reduction for
arbitrary couplings is given in closed form, making it amenable to symbolic
manipulation on a computer. The final expressions do not depend on a special
choice of coordinate axes, nor do they contain azimuthal quantum number
summations, nor do they have complex tensor terms for couplings to a scalar.
Consequently, they are easily interpretable from the properties of the physical
vectors they contain.Comment: This version contains added comments and typographical corrections to
the original article. Now 27 pages, 0 figure
Effects of Government Programs on Corn, Soybeans, and Wheat Production in the U.S.
Agricultural Finance, Farm Management, Production Economics,
Importance of Baryon-Baryon Coupling in Hypernuclei
The coupling in --hypernuclei and coupling in --hypernuclei produce novel
physics not observed in the conventional, nonstrange sector. Effects of
conversion in H are reviewed.
The role of coupling suppression in the
--hypernuclei due to Pauli blocking is highlighted, and the
implications for the structure of B are explored.
Suppression of conversion in He is hypothesized as the reason that the
matrix element is small. Measurement of H is
proposed to investigate the full interaction. The
implication for analog states is discussed.Comment: 17 pages LATEX, 1 figure uuencoded postscrip
Assessing statistical significance of periodogram peaks
The least-squares (or Lomb-Scargle) periodogram is a powerful tool which is
used routinely in many branches of astronomy to search for periodicities in
observational data. The problem of assessing statistical significance of
candidate periodicities for different periodograms is considered. Based on
results in extreme value theory, improved analytic estimations of false alarm
probabilities are given. They include an upper limit to the false alarm
probability (or a lower limit to the significance). These estimations are
tested numerically in order to establish regions of their practical
applicability.Comment: 7 pages, 6 figures, 1 table; To be published in MNRA
Abundances of Disk Planetary Nebulae in M31 and the Radial Oxygen Gradient
We have obtained spectra of 16 planetary nebulae in the disk of M31 and
determined the abundances of He, N, O, Ne, S and Ar. Here we present the median
abundances and compare them with previous M31 PN disk measurements and with PNe
in the Milky Way. We also derive the radial oxygen gradient in M31, which is
shallower than that in the Milky Way, even accounting for M31's larger disk
scale length.Comment: 2 pages, 1 figure, 1 table, to appear in the proceedings of IAU
Symposium No. 283, Planetary Nebulae: An Eye to the Futur
Abundances of PNe in the Outer Disk of M31
We present spectroscopic observations and chemical abundances of 16 planetary
nebulae (PNe) in the outer disk of M31. The [O III] 4363 line is detected in
all objects, allowing a direct measurement of the nebular temperature essential
for accurate abundance determinations. Our results show that the abundances in
these M31 PNe display the same correlations and general behaviors as Type II
PNe in the Milky Way Galaxy. We also calculate photoionization models to derive
estimates of central star properties. From these we infer that our sample PNe,
all near the peak of the Planetary Nebula Luminosity Function, originated from
stars near 2 M_sun. Finally, under the assumption that these PNe are located in
M31's disk, we plot the oxygen abundance gradient, which appears shallower than
the gradient in the Milky Way.Comment: 48 pages, including 12 figures and 8 tables, accepted by
Astrophysical Journa
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