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This study examined the effects of live mass on ovarian follicular dynamics in heifers before and after the onset of nutritional anoestrus. The effects of decreased live mass on secretion of progesterone, LH and FSH were also investigated. Ovarian characteristics were monitored in 16 postpubertal Brahman heifers using daily transrectal ultrasonography. After two normal oestrous cycles, 11 heifers (treatment group) were allocated to a restricted diet, until the cessation of their oestrous cycles, that resulted in a decrease in live mass of 0.8 kg day−1. Heifers were then fed an ad libitumdiet, resulting in increasing live mass until resumption of oestrous cycles. Five heifers (control group) were fed an unrestricted diet throughout the experimental period. The concentrations of progesterone in plasma were monitored twice a week and the concentrations of LH and FSH were determined on day 6 after ovulation, before initiation of dietary restriction, after a 17% decrease in live mass and after the onset of anoestrus in the treatment group. Onset of anoestrus was preceded by linear decreases in the size of ovarian follicles and corpora lutea, and in the persistence of the first dominant follicles of oestrous cycles. These changes were proportional to the decrease in live mass (P< 0.001). The frequency of pulses of LH or mean concentration of FSH on day 6 of the oestrous cycle were not changed after a 17% decrease in live mass, and did not increase following the onset of anoestrus, although concentrations of progesterone were < 0.2 ng ml−1, suggesting that release of LH was suppressed at this time. Increasing live mass following anoestrus resulted in a linear increase in dominant follicle size and persistence, which were correlated with changing mass (P< 0.001); ovulation resumed when dominant follicles were 105 ± 4% of the size of initial ovulatory follicles.

Summary.Scrotal insulation for 48 h raised subcutaneous scrotal temperature by 4°C in hybrid Bos indicusx Bos taurusbulls. The incidence of decapitated spermatozoa in the ejaculate increased significantly between 6 and 14 days and that of protoplasmic droplets and tail abnormalities between 20 and 23 days after insulation, respectively. Simultaneously, the percentages of spermatozoa with lost and damaged acrosomes increased significantly 12–17 days after insulation. At slaughter 23 days after scrotal insulation sperm production rates and gonadal reserves had not been affected by insulation, but epididymal reserves were markedly reduced, particularly in the cauda. Elevated testicular temperature therefore had an effect on immature spermatozoa in the caput epididymidis and on spermatids, but it is suggested that selective sperm resorption in the rete testis and excurrent ducts may prevent some of these changes being expressed in the ejaculate.

Summary.The hybrids were carrying 50% (N = 4) or 75% (N = 4) zebu (Brahman) blood. The spermatogenic cells were labelled in vivowith [3H]thymidine. The relative frequencies of the seminiferous epithelial cycle stages, determined from examination of 6350 tubule cross-sections, did not differ between the 2 hybrid types examined, between regions of the testis or between testes within animals. Frequencies were generally similar to those for Bos taurusbulls except that the frequency of stage 4 tubules was lower and that of stage 8 tubules higher. The mean duration of the seminiferous epithelial cycle was 13·41 days and was similar for both types of hybrid. The durations of meiosis and spermiogenesis were calculated to be 20·7 and 17·4 days respectively, estimates which are similar to those for Bos taurusbulls. From the relative frequency of cell stages and estimates of the duration of the cycle, a time divisor of 5·11 days is suggested as being appropriate to determine daily sperm production from counts of spermatid reserves in testicular homogenates of these hybrid bulls.

A new observation is reported on the variation of the electrical resistivity of a quenched Al–4·07 wt.-%Cu alloy that has been aged at T1(in the range 110–200° C) and then up-quenched about 20° C to T2. If sufficient time has elapsed at T1a maximum is attained in the relation between resistivity and time at T2with a height commonly < 5 × 10–9Ω cm. It is concluded that the resistance maximum arises from re-solution of intermediate precipitates which may be G.P.[1], “or”, when conditions are such that the operative solvus line is crossed during up-quenching. It is difficult to perform a meaningful quantitative analysis of the data in terms of the position of the operative solvus because the resistivity measurements cannot yield the vital information about the local solute concentration round the small proportion of intermediate precipitates, estimated to involve about 0·3% of the total copper content of the alloy, that revert into solution. No re-solution of could be observed by hot-stage transmission electron microscopy at temperatures below 300° C during up-quenching under conditions that gave rise to an electrical resistivity maximum.

Isochronal annealing of wires of aluminium-12 × 10-6 at.fr. indium that have been quenched into liquid HeI reveals that the electrical resistivity anneals out in two stages, one centred on a temperature of 240 K and the other at about 350 K for a heating rate of 2 K/min. The effective migration energy for the defects annealing out on the first stage has been determined to be 0·44 ± 0·04 eV and is close to the measured value of the migration energy for the annealing of defects in pure aluminium quenched from the same temperature range (0·41±0·04 eV). These energy values suggest that the divacancy is the migrating defect, but a kinetic analysis of the expected resistivity change from divacancy annihilation gave a value of only a quarter of the observed change. The most likely source of the unexplained part of the resistivity changes is clustering of indium atoms, but this has not been studied in the present investigation.

Two types of short-term transient effect have been observed in Al-Cu alloys containing a small amount of impurity. The transients are thought to reflect the migration of vacancies and vacancy impurity atom pairs respectively in reactions which are not maintained in equilibrium during the quenching operation, and hence extend into the observed ageing process.

Further support has been obtained for a suggestion previously made (J. Inst. Metals, 1956–7, 85, 425) that the height of the damping maximum, δp, which develops in quench-ageing Al-Cu-Mg-Si alloys is related to the composition of the α phase at the quenching temperature. Parallel measurements are reported of δpand of the as-quenched electrical resistivity as a function of quenching temperature and of alloy composition. Discontinuities in the damping and resistivity variations showed close agreement and are claimed to coincide with the attainment of the limit of solubility of the α phase at the quenching temperature. A preliminary investigation of the feasibility of using the damping discontinuity to determine the composition limits of the α phase has led to the conclusion that the α/(α + Mg2Si) boundary at 460° C for alloys with 0.85 at.- % copper is close to that estimated by Axon (J. Inst. Metals, 1954–55, 83, 490). The method also confirmed the expected position of the α/(α + θ) boundary but showed unexpected damping behaviour in the two-phase (α + θ) region.

Soundly based metallurgical interest in the internal friction of solids dates from the appearance of Zener's text “Elasticity and Anelasticity of Metals” in 1948. This scholarly and pithy work presents an analysis of the mechanical behaviour which arises if the process of transition between the unstressed and the stressed equilibrium states is delayed and is accompanied by a change in dimensions of the solid. In these circumstances the relation between decrement and frequency of vibration has characteristic maxima which can be used to give information on the specific mechanism causing the peak. Zener has listed and analysed several such processes, for example the thermoelastic effect, ordering of solute atoms under stress, deformation at crystal boundaries, and eddy currents generated by mechanical vibration. Of these loss mechanisms, that of solute-atom ordering has contributed most to new knowledge on the behaviour of alloys; this is evident in the prominence given to it by Nowick in his review of internal friction up to 1951 and in later reviews by Entwistle. More recently, significant new work has appeared to justify making the topic of stress-induced ordering an important part of the present review.