23 research outputs found
Effect of Repeated Administration of hCG on Ovarian Response in PMSG-superovulated Ouled Djellal Ewes (Algeria)
The objective of this study was to evaluate the effect of repeated administration of hCG on ovarian response in PMSG-superovulated ewes. Intravaginal pessaries containing 40 mg fluorogestone acetate (FGA) were inserted in all ewes (n=9) and remained in situ for 14 days. Two days prior to pessary removal, all ewes were treated with 1000 IU of PMSG. On the day of sponge removal (day 0), the females were randomly assigned to 2 treatments. The first group (n=3) did not receive any hCG, while the second group (n=6) treated inter-muscular with hCG (500 IU) during days 0-2. On day 8, laparotomy was performed to assess numbers of corpora lutea (CL) and anovulatory follicles (AF). Blood samples were collected for analysis of serum progesterone (P4) using radioimmunoassay (RIA) method. The results obtained for first and second group was in number of CL (6.33±1.15 and 10.50±5.54), number of AF (2 ±3.46 and 4.16±5.70), then the levels of P4 (5.75± 4.45 and 13.22±6.80 ng/ml), respectively. These results indicate that the repeated administration of hCG post-sponge removal increases number of CL and improves luteal function in ewes after PMSG-superovulatory treatment
Chatter stability prediction for CNC machine tool in operating condition through operational modal analysis
The stability of high-speed machining operations is crucial in machining process and
presents a key issue for insuring better surface quality, increasing productivity and
protecting both machines and safe workpiece. Stability prediction in milling is based on
experimental modal analysis by the estimation of frequency response functions using a tap
test. One limitation of accurately estimating the stability using such approach is the
change in process and the dynamic characteristics of the machine tool under operation.
This paper proposes a signal processing procedure applied to vibrations in machining
process in order to obtain spindle’s modal variations in operation. The novelty of the
proposed approach consists in removing “virtual modes”, caused by harmonic excitations,
from the system response before performing operational modal analysis. Thus, the proposed
procedure combines two existing techniques that are the Cepstral Editing Procedure and the
Least Square Complex Exponential. The importance of the developed methodology is in
adjusting the chatter stability criterion for material removal on a dynamic basis. The
main work is given as follows: first of all, the Cepstral Editing Procedure (CEP)
algorithm is applied on the acceleration signals for removing deterministic vibrations
caused by harmonic excitations. The residue signal is the system response to white noise
excitation. The frequency response functions (FRF) are then calculated from these signals
at different cutting conditions. The outcome is compared to the result of impact test on
the spindle under static condition. Similarities in the form of FRFs obtained in static
and operational conditions validate the proposed approach while variations of modal
properties under different cutting conditions are successfully captured. Secondly, the
Least Square Complex Exponential (LSCE) method in operational modal analysis is invoked to
find the natural frequencies and damping ratios of the system at different spindle speeds
and cutting depths. Then, the dynamic chatter stability lobes diagrams (SLD) are
established which account for spindle’s speed-dependent modal variations. A significant
change in the stability border is observed which is interesting in machining fields. It
will be shown that some depths of cut that are stable with static stability lobes become
unstable with dynamic stability lobes and vice versa