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21.
The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.  相似文献   
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A trial was carried out to determine the optimal height of feeding troughs above floor level and the spacing between pen railings which would enable sheep to access feed troughs but prevent them from getting out of pens during sea voyages. The trial involved a group of 16 large (79 kg) wether sheep and 24 small (30 kg) wether lambs which were held in pens and trained to eat lucerne pellets. Feed troughs similar to those used on ships were constructed 260 mm deep and 220 mm wide. A system of adjustable railings were used to alter the trough height and to determine the optimal spacing to allow the large sheep to get their heads through, but to prevent small sheep from escaping. In order that sheep of various sizes can access feed from the bottom of feed troughs, the height of the top edge of the trough should not exceed 360 mm above floor level for 30 kg sheep or 460 mm for mature sheep. This range is due to differences between the groups in their shoulder height, and variation between individuals within each group. Shoulder heights of the small sheep used in this trial ranged from 505 to 590 mm, and for the 16 mature animals the range was 610-715 mm. It is important that the feed troughs are low enough for all animals to access the feed on offer. Mature sheep were able to pass their heads between rails spaced at 200 mm without difficulty, but some difficulty was experienced when the space was reduced to 180 mm. The maximum rail spacing which prevented the escape of 30 kg lambs could not be determined with certainty because they could pass through a space of only 180 mm when laid on their side, but the smallest space through which they passed voluntarily was 220 mm. Hence the optimal spacing between railings which would allow all sheep good access to feed and would prevent almost all small sheep from escaping is about 190-210 mm.  相似文献   
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Partially purified thymus products were used to evaluate the maturation of T lymphocytes in immunodeficient mice. Three different bovine thymic extracts, designated thymic extracts A, B, and C, were successful in increasing the longevity of conventionally raised nude mice. Daily injection of bovine thymic extracts A, B, and C and mouse thymus extracts failed to mature a population of T lymphocytes and restore the capacity to reject heart allografts. Preincubation of normal syngeneic bone marrow with thymic extract B in vitro before injection into nude mice also failed to reconstitute the host's ability to reject heart grafts. The number of antibody plaque-forming cells of sheep red blood cells in lethally irradiated, bone marrow-reconstituted mice could be increased by preincubating the bone marrow cells with bovine thymic extract fraction B before injection followed by daily injections. A similar but less marked increase in plaque-forming cells was obtained by the daily injection of bovine thymic extract fraction C. Complete functional maturation of T lymphocytes in immunodeficient animals appears to require more than thymic extract stimulation of bone marrow cells or pre-T lymphocytes.  相似文献   
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Lactation in the mare is associated with changes in the release of metabolic as well as reproductive hormones. Plasma glucose concentration is constantly reduced in lactating compared with non-lactating mares. Several metabolic signals have been proposed to link nutrition and somatic metabolism with reproductive function. The following experiment was performed to study the effect of acute hypoglycaemia on the release of insulin-like growth factor-1 (IGF-1) and luteinizing hormone (LH) in cyclic mares. Different doses of insulin (0.1 and 0.2 IU/kg body weight) were given to induce a decrease in plasma glucose concentration, as existent in lactating mares. All horses treated with insulin developed a hypoglycaemia over a time period of nearly 10 h. The IGF-1 and LH were analysed before and after insulin administration. At no point of time, a significant difference between the two insulin treatments and the control treatment was observed. Therefore, the hypoglycaemic horse is apparently able to provide the brain with sufficient glucose. Short-term hypoglycaemia does not affect the hypothalamo-pituitary-ovarian axis, and concentrations of IGF-1 and LH remained stable during insulin-induced hypoglycaemia. An acute change in plasma glucose concentration is thus not or at least not the only metabolic signal that links nutrition and somatic metabolism with reproductive function in the horse mare.  相似文献   
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