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981.
Calcium lanthanide oxyborate doped with rare-earth ions LnCa4O(BO3)3:RE3+ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band Ect were calculated and compared with their excitation spectra.Eu3+ and Tb3+ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce3+ ions do not show efficient luminescence and quench the luminescence of Tb3+ ions when Tb3+ and Ce3+ ions are co-doped into LnCOB. GdCOB doped with Dy3+ shows yellowish white light under irradiation of 254 nm light for the reason that Gd3+ ions transfer the energy from itself to Dy3+. Because of the existence of Gd3+, the samples of GdCOB:RE3+ show higher excitation efficiency than LaCOB:RE3+ and YCOB:RE3+, around 188 nm, which indicates that the Gd3+ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb3+, Dy3+ and Eu3+. 相似文献
982.
We give a concise review and extension of S-procedure that is an instrumental tool in control theory and robust optimization analysis. We also discuss the approximate S-Lemma as well as its applications in robust optimization.The many suggestions and detailed corrections of an anonymous referee are gratefully acknowledged. 相似文献
983.
C. Devaux J.P. Chapel E. Beyou Ph. Chaumont 《The European physical journal. E, Soft matter》2002,7(4):345-352
Thin layers of polystyrene were grown from surface-grafted nitroxide initiators via controlled “living” free radical polymerization.
The “reactive” Langmuir-Blodgett deposition method allowed an effective control of the initiator layer density leading to
PS brushes with different and high grafting density and stretching. The influence of the grafting density on the layer structure
was studied. Comparison with theoretical predictions for monodispersed brushes in bad solvent was discussed. The thickness
was found to vary linearly with molecular weight and the density dependence was shown using wetting measurements. Special
features of controlled radical nitroxide polymerization from a surface were discussed. A direct comparison of the molecular
weight and polydispersity between surface and bulk polymers was made by de-grafting the brushes into a toluene/HF solution.
Finally, some evidence of a “surface Fischer” effect was shown from re-initiated layers.
Received 20 December 2001 相似文献
984.
985.
C W Thorpe R H Bates S M Dawson 《The Journal of the Acoustical Society of America》1991,90(6):2931-2934
A sonar system's echolocation capabilities can be inferred from the ambiguity distribution (defined here in terms of the conventional signal response function) of each of its transmitted signals. Several records of sounds emitted by Hector's dolphin are analyzed. The computed ambiguity distributions indicate that the sonar clicks of Hector's dolphins should be capable of resolving the ranges of targets as close together as 2 cm apart, but that target velocities cannot be resolved to any useful degree from a single echo. 相似文献
986.
In this paper we study a widely used zero equation model of turbulence. The governing equations are derived by applying to the incompressible Navier-Stokes equations the Reynolds time averaging procedure. We achieve closure by employing the eddy viscosity concept. Using the Implicit Function Theorem we obtain an existence and uniquencess result. We also discuss the existence of nonsingular solutions. Finally, we present an algorithm for solving the modeled equations. 相似文献
987.
Sydney C. K. Chu 《The Journal of the Operational Research Society》1989,40(9):771-778
This paper reports the actual implementation of a location-allocation study, which is one aspect of the overall Passive Cooling (Thailand) Project conducted in Northern Thailand since 1985. The goal has been to generate decision supports for ‘optimal’ placements of cooling facilities and the assignment of sites to these facilities as part of the post-harvest handling-chain operation of agricultural products. The basic questions addressed in this work are the issues of how many facilities to set up and where to locate them for maximum utility. Our selected approach is to use discrete location-allocation modelling, as, among other reasons, the problem at hand has a most natural network setting. Direct methods as well as efficient heuristics are examined, and sample numerical results are reported as illustrations of the continual implementation. 相似文献
988.
Determination of some hydroxycholesterols in human serum samples 总被引:4,自引:0,他引:4
B J Koopman J C van der Molen B G Wolthers J B Vanderpas 《Journal of chromatography. A》1987,416(1):1-13
The simultaneous determination of some hydroxycholesterols in human serum samples is described. The procedure is based on hydrolysis and extraction of these compounds in serum samples, followed by removal of especially cholesterol (making use of reversed-phase high-performance liquid chromatography) and derivatization of the purified compounds to their trimethylsilyl ethers and subsequent gas chromatography using flame ionization detection. Serum levels of 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol and 26-hydroxycholesterol were determined in several groups of patients: normals, untreated patients suffering from cerebrotendinous xanthomatosis, patients suffering from cerebrotendinous xanthomatosis and treated with either chenodeoxycholic acid or cholic acid in an effective dose, patients suffering from cerebro-hepato-renal syndrome, patients suffering from hypercholesterolemia and treated with cholestyramine for prolonged periods and one patient presumed to be suffering from an inborn error of metabolism in bile acid synthesis. It can be concluded that the 7 alpha-hydroxycholesterol concentration in serum is a good parameter for establishing disorders involving the metabolic conversion of 7 alpha-hydroxycholesterol towards bile acids. In addition, 26-hydroxycholesterol levels in patients suffering from cerebrotendinous xanthomatosis are beyond detectable limits, even during treatment with bile acids in an effective dose, whereas in all other conditions this compound is substantially present. 相似文献
989.
990.
This paper reports a direct jet-based polymerisation by polycondensation approach to forming a self-supporting scaffold structure.
The processing technique is electrospraying, which is also known as electrohydrodynamic atomization. A specially formulated
ethanolic siloxane sol derived from alkoxysilanes was synthesised and electrosprayed using a ring-shaped ground electrode
configuration. The medium was seen to electrospray in the stable cone-jet mode, which later gave rise to the growing or forming
of “fir-tree” like structures. The materials were characterised using microscopy, solid state NMR, FTIR, XRD and DSC. Hence
this paper explains the direct controlled polycondensation from the siloxane sol and further presents the basis by which these
scaffolds take shape. 相似文献