Experiments involving the laser vaporization of graphite have indicated that one particular duster of carbon, C(60), is preeminently stable; this special stability may be evidence that C(60) can readily take the form of a hollow truncated icosahedron (a sort of molecular soccerball). If true, this structure for C(60) would be the first example of a spherical aromatic molecule. In fact, because of symmetry properties unique to the number 60, it may be the most perfecty spherical, edgeless molecule possible. Its rapid formation in condensing carbon vapors and its extreme chemical and photophysical stability may have far-reaching implications in a number of areas, particularly combustion science and astrophysics. For these reasons C(60) and other dusters of carbon have continued to be the subject of intense research. This article provides a short review of the many new experimental probes of the properties of C(60) and related carbon dusters. 相似文献
The T.M.E. System of Feed Evaluation. I.R. Sibbald, Animal Research Centre Contribution 83‐1, Animal Research Centre, Ottawa, Ontario, Canada.
Physiology and Behaviour of the Pigeon, edited by M. Abs. 1983. 360 pages, illustrated. London, Academic Press Ltd. Price £34.00. ISBN 0 12 042950 0. 相似文献
1. The ovulatory cycle of the domestic hen (Gallus domesticus) was postulated to be the result of the interaction of two independent systems.
2. A circadian system was postulated to control the restriction of ovulation to an 8‐h period of the day under conventional 14 h light: 10 h dark regimes.
3. The final phase of follicular maturation was postulated to commence after ovulation of the preceding ovum in the hierarchy.
4. Ovulation was postulated to occur when a mature follicle was present in the ovary during the appropriate phase of the circadian‐linked system.
5. The predicted times of oviposition were within the standard error of the observed times of oviposition under 21‐, 24‐ and 28‐h photoschedules.
6. It was concluded that this hypothesis for the control of the ovulatory cycle of the hen is consistent with current knowledge. 相似文献
1. To test the preferences of hens for particular social conditions when laying, they were provided with choices of nest‐sites varying in seclusion. Three experimental conditions were used.
2. In Experiment 1, nest‐site selection by members of a group of light hybrids was studied in a complex pen‐system. Eggs were clumped in distribution ; only one individual laid in the most secluded part of the system.
3. Experiment 2 provided light hybrids with an extensive outdoor area, but similarly clumped laying was observed; there was no indication that hens attempted to find concealment for nesting.
4. In Experiment 3, hens from a group of light hybrids just coming into lay and from a group of mature medium hybrids were tested singly, in an area that included a cage containing some of their flockmates. Most subjects from both groups laid near the other birds rather than in isolation.
5. In semi‐intensive conditions, the majority of hens are apparently gregarious rather than solitary in their nesting behaviour. 相似文献
1. Glycerol is an effective cryoprotective for fowl spermatozoa, but after thawing the frozen semen it must be reduced in concentration from the level adequate to protect spermatozoa during freezing, otherwise it has a contraceptive action.
2. A series of alternative cryoprotective compounds were tested for their effect on fertility when fowl spermatozoa were inseminated fresh in their presence. Under these circumstances dimethylsulphoxide, dimethylaceta‐mide, ethane‐diol, propane‐diol and methylpyrrolidone did not depress fertility when used in concentrations equivalent to that of glycerol or in amounts reported previously to be non‐toxic and adequate to protect cells during freezing.
3. Dimethylacetamide was compared with propane‐diol for use in freezing fowl semen and the former enabled encouraging levels of fertility to be obtained. 相似文献
Necropsy records of 36 sows with torsion of abdominal organs involving individually the stomach, the spleen, a liver lobe or the intestine were reviewed for the years 1970 to 1983, and the age, the clinical signs and the gross lesions were recorded. These acute abdominal accidents were characterized clinically by sudden death. Dry sows from large breeding units were affected. Twenty-six cases were diagnosed between January 1981 and December 1983 while only ten cases had been seen between 1970 and 1980. Gastric torsion was the most common condition (40% of the cases) and the other three conditions were equally represented (20% each). Management practises that could be responsible for the apparent increase in occurrence of this problem are discussed. 相似文献
The objective of this study was to investigate the development of maternal-filial social attachments between ewes and alien lambs using the technique of "restraint fostering." Forty-eight to 72 h after parturition, 22 Targhee -type ewes were separated from their natural lambs, placed in restraining devices ( stanchions ) and each exposed to a single alien lamb. After a period of 1 or 4 d of restraint, the ewes were subjected to five 10-min lamb acceptance tests over a 48-h period. The observer recorded butts and butt attempts by the ewe and successful and unsuccessful suckle attempts by the lamb. The ewe-lamb pairs were then housed in pens with other groups of ewes and lambs and observed intermittently for acceptance behaviors. Six of the 14 ewes restrained for 4 d and none of the eight ewes restrained for 24 h met the criterion for successful adoption within 48 h. After being housed in group pens, adoptions were achieved by three ewes in the 1-d group and an additional four ewes in the group restrained for 4 d. Ewes restrained for 24 h were significantly more aggressive toward fostered young than ewes restrained for 4 d. In addition, the proportion of successful suckling attempts was significantly lower for lambs fostered on ewes in the 1-d group. Both groups showed a decline in butts and butt attempts over successive acceptance tests, but while the proportion of successful suckling attempts declined for lambs housed with 1-d ewes, they increased over time for lambs fostered on ewes restrained for 4 d.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
A stranded young pygmy sperm whale was nursed for four days in a pool, fed an artificial diet via a stomach tube and injected intramuscularly with antibiotics and corticosteroids. Initially unable to maintain her balance or to swim, she showed progressive improvement and by the third day could swim and dive quite strongly. Early on the fifth day her condition rapidly worsened and she died. An autopsy revealed extensive deep bruising in the head and mid-abdominal regions consistent with injuries sustained during the stranding. 相似文献