18,926 research outputs found
Anatomy and Histology of the Male Reproductive Complex of the Onion Maggot Fly, \u3ci\u3eDelia Antiqua\u3c/i\u3e, (Diptera: Anthomyiidae) Including Some Comparisons With \u3ci\u3eD. Platura\u3c/i\u3e and \u3ci\u3eD. Radicum\u3c/i\u3e
In Delia antiqua (Meigen) (Diptera: Anthomyiidae), the male reproductive complex is composed of a pair of testes, paired vas deferens connecting the testes to the anterior ejaculatory duct, and a pair of paragonial (accessory) glands. Each D. antiqua paragonial gland consists of a single layer of secretory epithelial cells surrounded by a thin sheath of muscle tissue. The paragonial cells appear to be largely homogeneous in form, however a minor number of cells exhibit unique staining characteristics distinct from the main cells of the gland. This is preliminary evidence for a secondary cell type as has been found for Drosophila and Aedes paragonial glands. In contrast to the testis and vas deferens, where most of the growth occurs during the pupal stage, the D. antiqua paragonial glands expanded markedly due to secretory accumulation during the first days of adult life. Based on histochemical analyses, the paragonial secretion contained abundant protein, with evidence of glycoprotein. The reproductive complex in all three Delia species (D. antiqua, D. radicum (Bouche) and D. platura (Meigen)) appears similar, with the exception of size differences and timing of paragonial secretory accumulation and sperm maturation. Paragonial glands of D. radicum were the largest in both length and width, and only this species possessed abundant sperm upon eclosion. Of the three species, D. radicum appears most capable of mating immediately after eclosion based on the histology of its reproductive complex, which is consistent with biochemical and behavioral observations made earlier in this laboratory
Structural trends in clusters of quadrupolar spheres
The influence of quadrupolar interactions on the structure of small clusters
is investigated by adding a point quadrupole of variable strength to the
Lennard-Jones potential. Competition arises between sheet-like arrangements of
the particles, favoured by the quadrupoles, and compact structures, favoured by
the isotropic Lennard-Jones attraction. Putative global potential energy minima
are obtained for clusters of up to 25 particles using the basin-hopping
algorithm. A number of structural motifs and growth sequences emerge, including
star-like structures, tubes, shells and sheets. The results are discussed in
the context of colloidal self-assembly.Comment: 8 pages, 6 figure
A Simple Linearized Hot-Wire Anemometer
The circuit and application of an inexpensive simple linearized hot wire anemometer especially suited to turbulence research in incompressible media is described. Special features of the design are very high stability, simple bridge adjustment, and a linearizer having an adjustable exponent and very high transfer function accuracy. Measured frequency response is in excess of 100 kilohertz for the bridge 7.5 kilohertz for the linearizer
Computing toric degenerations of flag varieties
We compute toric degenerations arising from the tropicalization of the full
flag varieties and embedded in a
product of Grassmannians. For and we
compare toric degenerations arising from string polytopes and the FFLV polytope
with those obtained from the tropicalization of the flag varieties. We also
present a general procedure to find toric degenerations in the cases where the
initial ideal arising from a cone of the tropicalization of a variety is not
prime.Comment: 35 pages, 6 figure
GRO J1744-28, search for the counterpart: infrared photometry and spectroscopy
Using VLT/ISAAC, we detected 2 candidate counterparts to the bursting pulsar
GRO J1744-28, one bright and one faint, within the X-ray error circles of
XMM-Newton and Chandra. In determining the spectral types of the counterparts
we applied 3 different extinction corrections; one for an all-sky value, one
for a Galactic Bulge value and one for a local value. We find the local value,
with an extinction law of alpha = 3.23 +- 0.01 is the only correction that
results in colours and magnitudes for both bright and faint counterparts
consistent with a small range of spectral types, and for the bright
counterpart, consistent with the spectroscopic identification. Photometry of
the faint candidate indicates it is a K7/M0 V star at a distance of 3.75 +- 1
kpc. This star would require a very low inclination angle (i < 9deg) to satisfy
the mass function constraints; however it cannot be excluded as the counterpart
without follow-up spectroscopy to detect emission signatures of accretion.
Photometry and spectroscopy of the bright candidate indicate it is most likely
a G/K III star. The spectrum does not show Br-gamma emission, a known indicator
of accretion. The bright star's magnitudes are in agreement with the
constraints placed on a probable counterpart by the calculations of Rappaport &
Joss (1997) for an evolved star that has had its envelope stripped. The mass
function indicates the counterpart should have M < 0.3 Msol for an inclination
of i >= 15deg; a stripped giant, or a main sequence M3+ V star are consistent
with this mass-function constraint. In both cases mass-transfer, if present,
will be by wind-accretion as the counterpart will not fill its Roche lobe given
the observed orbital period. The derived magnetic field of 2.4 x 10^{11} G will
inhibit accretion by the propeller effect, hence its quiescent state.Comment: 12 pages, 6 figures, 4 table, MNRAS accepted Changes to the content
and an increased analysis of the Galactic centre extinctio
Particle Acceleration in Active Galactic Nuclei
The investigation of stochastic particle acceleration through resonant interactions with plasma waves that populate the magnetosphere surrounding an accreting black hole is presented. Stochastic acceleration has been successfully applied to the problem of ion and electron energization in solar flares, and is capable of accounting for a wide range of both neutral and charged particle emissions. It is also a component in diffusive shock acceleration, since pitch-angle scattering (which is necessary for multiple shock crossings) is accompanied by diffusion in momentum space, which in turn yields a net systematic energy gain; however, stochastic energization will dominate the first-order shock process only in certain parameter regimes. Although stochastic acceleration has been applied to particle energization in the lobes of radio galaxies, its application to the central regions of AGNs (active galactic nuclei) has only recently been considered, but not in detail. We proposed to systematically investigate the plasma processes responsible for stochastic particle acceleration in black hole magnetospheres along with the energy-loss processes which impede particle energization. To this end, we calculated acceleration rates and escape time scales for protons and electrons resonating with Alfven waves, and for electrons resonating with whistlers. We also considered the "hot" topic of gamma-ray line emission from the Orion complex. We proposed that the observed gamma-ray lines are produced by energetic ions that are stochastically accelerated by cascading Alfven waves in the accretion plasma near a black hole. Related research papers that were published in journals are listed
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