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

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

Welfare to Web to Work: Internet Job Searching Among Former Welfare Clients in Florida

This study provides the first empirical test of whether searching for jobs on the Internet can help people gain access to high quality jobs. Using new data from former welfare clients in Florida, we present results from a multivariate regression analysis of Internet job searching on wages and on a number of job benefits. On average, Internet job searchers receive better jobs than people who conducted more traditional job searches, net of numerous control variables. These findings suggest that welfare recipients have a great deal to gain from searching for their jobs on the Internet

Why the extensive use of executive orders by state governors may not be a threat to democracy

Like the president, state Governors frequently make use of executive orders in order to pursue their agendas. But do these unilateral actions undermine democracy? No, argue Alexandra G. Cockerham and Robert E. Crew, Jr, who find that legislatures can be willing to delegate policy-making authority to governors if they are of the same party or if the legislature is fragmented

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

Διερεύνηση Πλημυρικής Κατάκλυσης σε συνθήκες μη μόνιμης ροής με τη χρήση Λογισμικών Υδραυλικής Προσομοίωση. Εφαρμογή στον Πηνειό Θεσσαλίας.

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Επιστήμη και Τεχνολογία Υδατικών Πόρων