1,560 research outputs found
A contribution to the study of sex-determination in the anura
The problem of sex -determination possesses
a peculiar fascination for the student of. animate
Nature and the fact that it remains as yet unsolved,
permits one to set out on the great adventure of its
solution with high hopes and, if one is young, with
confidence.But with the experience of the difficulties
and complexities of the subject comes a chastened
mind, and at the journey's end one is left with just
the hope that in the results of the work which has
enslaved by its all -absorbing fascination, there may
be found some suggestion as to the direction in which
the truth of the matter really lies.In this study the question of sex- determination is approached through a consideration of the abnormalities of the reproductive system which have
been recorded in Zoological literature. Often an
appreciation of the abnormal can illumine the mechanism of the normal.The typical sexual characters are first
briefly described, so as to furnish standards to
which the abnormalities may be referred. The abnormalities are then tabulated and analysed. A
brief consideration of the embryology of the reproductive system naturally follows and the investigation is brought to a close by a review of what is
known of the sex-ratio. An account is given of certain experiments.It is intended to demonstrate that the abnormalities obviously suggest that in the case of the
frog, sex is not irreversible; that the facts of embryology lend support to this view; and that a .study of
the variations of the sex -ratio supplies conclusive
proof that sax- reversal can and does occur. The graduated degrees of abnormality as portrayed, are shown . to provide a clear view of the process by which sex-reversal is effected
Higher dimensional Calabi-Yau manifolds of Kummer type
Based on Cynk-Hulek method we construct complex Calabi-Yau varieties of
arbitrary dimensions using elliptic curves with automorphism of order 6. Also
we give formulas for Hodge numbers of varieties obtained from that
construction. We shall generalize result of Katsura and Sch\"utt to obtain
arbitrarily dimensional Calabi-Yau manifolds which are Zariski in any
characteristic Comment: 13 pages, 2 figure
Black-Footed Ferret Recovery
The captive population of black-footed ferrets increased from 24 to 58 animals in 1988, and was split to provide the species added protection against extinction. Experimental reintroductions may begin in 1991. In some areas, experimental population designations as authorized under Section 10 (j) of the Endangered Species Act may be used to provide wider management latitude. The Black-footed Ferret Interstate Coordinating Committee oversees much of the work related to reintroduction. Expanded effort to locate wild ferrets now includes a $10,000 reward offer. Research focuses on captive breeding, reintroduction techniques, disease, and habitat. A new Recovery Plan was approved in 1988
Black-Footed Ferret Recovery
The captive population of black-footed ferrets increased from 24 to 58 animals in 1988, and was split to provide the species added protection against extinction. Experimental reintroductions may begin in 1991. In some areas, experimental population designations as authorized under Section 10 (j) of the Endangered Species Act may be used to provide wider management latitude. The Black-footed Ferret Interstate Coordinating Committee oversees much of the work related to reintroduction. Expanded effort to locate wild ferrets now includes a $10,000 reward offer. Research focuses on captive breeding, reintroduction techniques, disease, and habitat. A new Recovery Plan was approved in 1988
Evolving outer heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer
The first all-sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow ribbon of enhanced ENA emissions. In this study we compare the second set of sky maps to the first in order to assess the possibility of temporal changes over the 6 months between views of each portion of the sky. While the large-scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale. In particular, we find that (1) the overall ENA emissions coming from the outer heliosphere appear to be slightly lower in the second set of maps compared to the first, (2) both the north and south poles have significantly lower (similar to 10-15%) ENA emissions in the second set of maps compared to the first across the energy range from 0.5 to 6 keV, and (3) the knot in the northern portion of the ribbon in the first maps is less bright and appears to have spread and/or dissipated by the time the second set was acquired. Finally, the spatial distribution of fluxes in the southernmost portion of the ribbon has evolved slightly, perhaps moving as much as 6 degrees (one map pixel) equatorward on average. The observed large-scale stability and these systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy and help inform possible mechanisms for producing the IBEX ribbon
Precision Pointing of IBEX-Lo Observations
Post-launch boresight of the IBEX-Lo instrument onboard the Interstellar
Boundary Explorer (IBEX) is determined based on IBEX-Lo Star Sensor
observations. Accurate information on the boresight of the neutral gas camera
is essential for precise determination of interstellar gas flow parameters.
Utilizing spin-phase information from the spacecraft attitude control system
(ACS), positions of stars observed by the Star Sensor during two years of IBEX
measurements were analyzed and compared with positions obtained from a star
catalog. No statistically significant differences were observed beyond those
expected from the pre-launch uncertainty in the Star Sensor mounting. Based on
the star observations and their positions in the spacecraft reference system,
pointing of the IBEX satellite spin axis was determined and compared with the
pointing obtained from the ACS. Again, no statistically significant deviations
were observed. We conclude that no systematic correction for boresight geometry
is needed in the analysis of IBEX-Lo observations to determine neutral
interstellar gas flow properties. A stack-up of uncertainties in attitude
knowledge shows that the instantaneous IBEX-Lo pointing is determined to within
\sim 0.1\degr in both spin angle and elevation using either the Star Sensor
or the ACS. Further, the Star Sensor can be used to independently determine the
spacecraft spin axis. Thus, Star Sensor data can be used reliably to correct
the spin phase when the Star Tracker (used by the ACS) is disabled by bright
objects in its field-of-view. The Star Sensor can also determine the spin axis
during most orbits and thus provides redundancy for the Star Tracker.Comment: 22 pages, 18 figure
Focusing on size and energy dependence of electron microbursts from the Van Allen radiation belts
Eukaryotic initiation factor-4E in superficial and muscle invasive bladder cancer and its correlation with vascular endothelial growth factor expression and tumour progression
Vascular endothelial growth factor (VEGF) is an important factor mediating tumour angiogenesis. VEGF mRNA is differentially expressed in bladder cancer with high expression in superficial tumours (stage pTaand pT1) contrasting with low expression in muscle invasive tumours (stage ≥ pT2). To investigate mechanisms regulating VEGF expression in bladder cancer, VEGF mRNA and protein were measured in normal bladder (n = 12) and primary bladder cancers (n = 57). VEGF protein levels correlated with mRNA expression in normal bladder (r = 0.68, P = 0.02) and bladder cancer (r = 0.46, P = 0.0007). Whilst VEGF mRNA expression was threefold higher in superficial compared to muscle invasive bladder cancers (P = 0.0001) there was no difference in VEGF protein (P = 0.81). Accordingly, the median protein:mRNA ratios increased more than 15-fold with increasing tumour stage (P< 0.0001) suggesting translational regulation. Expression of the eukaryotic initiation factor-4E (eIF-4E), a factor implicated in the translational regulation of VEGF, was greater in tumours than normal bladder (P< 0.0001) and correlated with VEGF protein:mRNA ratios (n = 43, r = 0.54, P = 0.0004) pointing to its role in the regulation of VEGF. In superficial tumours (n = 37) high expression of eIF-4E was associated with a poor prognosis and reduced stage progression-free survival (P = 0.04, Cox proportional hazards model). The study demonstrates that eIF-4E may be involved in translational regulation of VEGF in bladder cancer and might have a role as a prognostic factor in bladder cancer. © 2000 Cancer Research Campaig
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