1,138 research outputs found
A new species of \u3ci\u3eAtaenius\u3c/i\u3e Harold (Coleoptera: Scarabaeidae: Aphodiinae) from the southeastern United States, with a lectotype designation
A new species of Ataenius Harold, Ataenius thomasi Schnepp and Ashman (Coleoptera: Scarabaeidae: Aphodiinae), from Florida, Georgia, and Mississippi, U.S.A. is described. The lectotype for Ataenius brevis Fall is designated.
In the United States and Canada the genus Ataenius Harold (Coleoptera: Scarabaeidae: Aphodiinae) contains 46 species (Stebnicka 2007; Smith 2009). The most recent faunal review of this genus in these countries was completed by Cartwright (1974). However, several species in that paper have been moved to other genera or synonymized (Stebnicka 2007). Stebnicka and Lago (2005) provide a key and catalog to the Ataenius strigatus group. Specimens of a putative new species of Ataenius occurring in northern Florida were located in the Florida State Collection of Arthropods (FSCA). This new species is similar to Ataenius brevis Fall, but several morphological differences have been identified and are outlined in this paper. In looking for supplementary material, additional specimens of the new species were found in the Snow Entomological Museum Collection (SEMC) and United States National Museum of Natural History (USNM). After consulting the original description of A. brevis, it was discovered that no holotype was designated and that two specimens were present in the type series. Syntypes of A. brevis were borrowed to confirm the new species is morphologically distinct and a lectotype is designated to eliminate potential confusion with the new species and to fix the name to a single specimen
Modeling the dynamical evolution of the M87 globular cluster system
We study the dynamical evolution of the M87 globular cluster system (GCS)
with a number of numerical simulations. We explore a range of different initial
conditions for the GCS mass function (GCMF), for the GCS spatial distribution
and for the GCS velocity distribution. We confirm that an initial power-law
GCMF like that observed in young cluster systems can be readily transformed
through dynamical processes into a bell-shaped GCMF. However,only models with
initial velocity distributions characterized by a strong radial anisotropy
increasing with the galactocentric distance are able to reproduce the observed
constancy of the GCMF at all radii.We show that such strongly radial orbital
distributions are inconsistent with the observed kinematics of the M87 GCS. The
evolution of models with a bell-shaped GCMF with a turnover similar to that
currently observed in old GCS is also investigated. We show that models with
this initial GCMF can satisfy all the observational constraints currently
available on the GCS spatial distribution,the GCS velocity distribution and on
the GCMF properties.In particular these models successfully reproduce both the
lack of a radial gradient of the GCS mean mass recently found in an analysis of
HST images of M87 at multiple locations, and the observed kinematics of the M87
GCS.Our simulations also show that evolutionary processes significantly affect
the initial GCS properties by leading to the disruption of many clusters and
changing the masses of those which survive.The preferential disruption of inner
clusters flattens the initial GCS number density profile and it can explain the
rising specific frequency with radius; we show that the inner flattening
observed in the M87 GCS spatial distribution can be the result of the effects
of dynamical evolution on an initially steep density profile. (abridged)Comment: 15 pages,14 figures;accepted for publication in The Astrophysical
Journa
Small Momentum Evolution of the Extended Drell--Hearn--Gerasimov Sum Rule
We investigate the momentum dependence of the extended Drell-Hearn-Gerasimov
sum rule. An economical formalism is developed which allows to express the
extended DHG sum rule in terms of a single virtual Compton amplitude in forward
direction. Rigorous results for the small momentum evolution are derived from
chiral perturbation theory within the one-loop approximation. Furthermore, we
evaluate some higher order contributions arising from
intermediate states and relativistic corrections. (2 figures available upon
request).Comment: 12 pages, TeX, BUTP-92/51 and CRN-92-5
Novel Quark Fragmentation Functions and the Nucleon's Transversity Distribution
We define twist-two and twist-three quark fragmentation functions in Quantum
Chromodynamics (QCD) and study their physical implications. Using this
formalism we show how the nucleon's transversity distribution can be measured
in single pion inclusive electroproduction.Comment: 10 pages, uses PHYZZX macro package, 2 PostScript figures (added
using FIGURES). MIT-CTP-215
Experimental and Theoretical Results for Weak Charge Current Backward Proton Production
In this paper, we do three things in the study of deuteron break-up by high
energy neutrino beams. (1) We present previously unpublished data on neutrino
induced backward protons from deuteron targets; (2) we calculate the
contributions from both the two-nucleon (2N) and six-quark (6q) deuteron
components, which depend upon the overall normalization of the part that is 6q;
and (3) we suggest other signatures for distinguishing the 2N and 6q clusters.
We conclude that the 6q cluster easily explains the shape of the high momentum
backward proton spectrum, and its size is nicely explained if the amount of 6q
is one or a few percent by normalization of the deuteron. There is a crossover,
above which the 6q contribution is important or dominant, at 300--400 MeV/c
backward proton momentum.Comment: 8 pages, 5 figure
QCD Sum Rule Calculation of Twist-4 Corrections to Bjorken and Ellis-Jaffe Sum Rules
We calculate the twist-4 corrections to the integral of in the
framework of QCD sum rules using an interpolating nucleon field which contains
explicitly a gluonic degree of freedom. This information can be used together
with previous calculations of the twist-3 contribution to the second moment of
to estimate the higher-twist corrections to the Ellis-Jaffe and
Bjorken sum rules. We get and
. Numerically our results roughly agree
with those obtained by Balitsky, Braun and Kolesnichenko based on a sum rule
for a simpler current. Our calculations are far more stable as tested within
the sum rule approach but are more sensitive to less well known condensates.Comment: 18pp., 1 figure (uuencoded eps-file), Late
QCD Sum Rule Calculation of Twist-3 Contributions to Polarized Nucleon Structure Functions
Using the framework of QCD sum rules we predict the twist-3 contribution to
the second moment of the polarized nucleon structure function . As the
relevant local operator depends explicitely on the gluon field, we employ a
recently studied interpolating nucleon current which contains three quark field
and one gluon field operator. Despite the fact that our calculation is based on
the analysis of a completely different correlation function, our estimates are
consitent with those of Balitsky, Braun and Kolesnichenko who used a
three-quark current.Comment: 16pp. , 2 figures (uuencoded eps-files), LateX. Some misprints
corrected, results unchange
Associated production as a probe of the polarized gluon distribution
Associated production of and a has recently been proposed
as clean probe of the gluon distribution. The same mechanism can be used to
probe the polarized gluon content of the proton in polarized proton-proton
collisions. We study production at both polarized fixed
target and polarized collider energies.Comment: 16 pages (10 figures available from M.A.D.), MAD/PH/745, SNUTP 93-6,
YUMS 93-
The Nucleon ``Tensor Charges'' and the Skyrme Model
The lowest moment of the twist-two, chiral-odd parton distribution
of the nucleon can be related to the so-called ``tensor charges'' of the
nucleon. We consider the tensor charges in the Skyrme model, and find that in
the large-, SU(3)-symmetric limit, the model predicts that the octet
isosinglet tensor charge, , is of order with respect to the
octet isovector tensor charge, . The predicted ratio is then 1/3,
in the large- limit. These predictions coincide with the Skyrme model
predictions for the octet charges, and . (The
prediction for the axial charges differs from the commonly quoted
prediction of 5/9, which is based on an inconsistent treatment of the
large- limit.) The model also predicts that the singlet tensor charge,
, is of order with respect to .Comment: 9 single-spaced pages, no figures, MIT-CTP-212
HST Imaging of Globular Clusters in the Edge--on Spiral Galaxies NGC 4565 and NGC 5907
We present a study of the globular cluster systems of two edge-on spiral
galaxies, NGC4565 and NGC5907, from WFPC2 images in the F450W and F814W
filters. The globular cluster systems of both galaxies appear to be similar to
the Galactic globular cluster system. In particular, we derive total numbers of
globular clusters of N_{GC}(4565)= 204+/-38 {+87}{-53} and
N_{GC}(5907)=170+/-41 {+47}{-72} (where the first are statistical, the second
potential systematic errors) for NGC4565 and NGC5907, respectively. This
determination is based on a comparison to the Milky Way system, for which we
adopt a total number of globular clusters of 180+/-20. The specific frequency
of both galaxies is S_N~0.6: indistinguishable from the value for the Milky
Way. The similarity in the globular cluster systems of the two galaxies is
noteworthy since they have significantly different thick disks and
bulge-to-disk ratios. This would suggest that these two components do not play
a major role in the building up of a globular cluster system around late-type
galaxies.Comment: Accepted for publication in the Astronomical Journal, 17 pages incl 5
figures, AAS style two columns. Also available at
http://www.eso.org/~mkissler, Color version of figure 1 only available at
http://www.eso.org/~mkissler (B/W version included
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