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991.
992.
An intensity-modulated optical fibre sensor system is described which employs a single LED source to provide the measurand and the reference signals with two separate wavelength bands. The allocated wavelength bands are selected to minimize any differential intensity effects that may arise from LED thermal variations. The sensor system, comprising a transceiver unit connected to an optical displacement sensor using a single optical fibre, provides an output fully referenced for all major common-mode variations that are likely to occur. Performance characteristics for the prototype system are reported which show a linear displacement range of over 20 mm.  相似文献   
993.
Granular films prepared from well-defined In clusters embedded in Kr (? 10-40 at % Kr) show sharp resistance anomalies very close to the superconducting transition temperature. The observed resistance peak(s), which go(es) above the normal state resistance RN and which can be as high as ? 1.5 RN, can be explained by a “mesoscopic” effect: Superconducting percolation aggregates of size ξρ, larger than the superconducting coherence length ξS, but smaller than the quasiparticle relaxation length λQ*, have a superconducting gap, but are not yet able to carry a supercurrent.  相似文献   
994.
The height distribution of the dayside cusp aurora and the relation between optical emissions and net downward electron energy flux are discussed. These two important characteristics of day-side cusp aurora are still unknown. It is instructive to compare particle flux and optical luminosity because these two quantities should be proportional if the cusp aurora is caused by electron impact, as has been found for nighttime aurora in the oval. Furthermore, there should then be a direct relation between auroral altitudes and particle energy. Based on coordinated auroral observations at Svalbard and Greenland, together with simultaneous, overhead F-9 satellite measurements, these quantities have been evaluated  相似文献   
995.
996.
The temperature dependence of magnetization of a nanocrystalline Fe60Co30Zr10 alloy annealed at various temperatures to varying crystal sizes was investigated down to 5 K in the field range up to 5 T. The fitting procedure gave T3/2 as the leading term irrespective of the crystal size. We suggest that the increase of the coefficient by this term for smaller crystals may be connected to an increased relative volume of their surface.  相似文献   
997.
For several years, the study of neighborhood unions of graphs has given rise to important structural consequences of graphs. In particular, neighborhood conditions that give rise to hamiltonian cycles have been considered in depth. In this paper we generalize these approaches to give a bound on the smallest number of cycles in G containing all the vertices of G. We show that if for all x, y ? V(G), |N(x) ∩ N(y)| ≧ 2n/5 + 1, then V(G) is coverable by at most two cycles. Several related results and extensions to t cycles are also given.  相似文献   
998.
New model compounds for poly[N,N′-bis(phenoxyphenyl)pyromellitimide] have been synthesized in order to investigate the formation of imine bonds which are proposed to form during the curing process and lead to crosslinking in the bulk polymer. Raman studies show that terminal amines can react with imide carbonyls during curing to form C?N bonds. The Raman band due to C?N appears at 1656 cm?1 and the band due to C?O closest to the imine bond is observed at 1742 cm?1. These results are in agreement with previously published results on vapor deposited polyimide films.  相似文献   
999.
For a program of surface and interface experiments with the PAC isotope100Pd, a procedure has been developed to chemically separate100Pd from irradiated rhodium and deposit it on surfaces by evaporation under UHV conditions. First results have been obtained for100Pd on an Ni(111) surface.  相似文献   
1000.
Crosslinked poly (methyl methacrylate) and poly (carbonate-urethane) as well as full interpenetrating network on their base (IPN) were characterized by precise heat capacity measurements in the temperature interval 1.2–150 K. As judged by the positive sign of the excess Gibbs free energy in the whole temperature interval above 30 K, the apparently single-phase state of IPN is thermodynamically unstable; however, its kinetic stability is ensured by permanent chamical crosslinks prohibiting the incipient phase separation. © 1994 John Wiley & Sons, Inc.  相似文献   
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