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931.
932.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. L. Seaman Y. Dalichaouch M. B. Maple J. D. Garrett 《Hyperfine Interactions》1991,64(1-4):517-522
We have performed both zero field and high transverse field measurements at dilution refrigerator temperatures on a number of heavy electron systems, examining the superconducting and magnetic properties of these interesting materials. Among the materials studied to date are UBe13, URu2Si2 and U6Fe. The magnetic field penetration depth in the superconducting state of UBe13 is greater than 10000 Å, as no increase in the transverse field relaxation rate is observed belowT c . A sharp increase in the precession frequency is seen, starting atT c . This frequency shift shows little temperature dependence at low temperature; we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we have observed relaxation in high transverse field due to the formation of a flux lattice in U6Fe, a material where the electron effective mass is rather lighter than in other heavy fermion systems. The relaxation exhibits a sharp onset atT c=3.9 K, and is flat at low temperatures as expected for a conventional superconductor. 相似文献
933.
Fundamental and dual variational principles of magnetostatics of superconductors are formulated. It is shown how test fields can be expressed in terms of vector and scalar potentials. General consequences of the variational magnetostatic formulation are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 97–102, September, 1991. 相似文献
934.
The occurrence of charge on recoil56Mn produced by the (n,γ) reaction in polycrystalline potassium permanganate has been examined using the ‘charge plate technique’.
From considerations of capture gamma ray decay schemes and internal conversion it appears that, in a condensed medium, the
recoil atom develops charge after losing much of its initial kinetic energy which allows collection on charged electrodes.
Preliminary findings were presented at the International Symposium on Radiochemistry and Radiation Chemistry, RC-41 BARC,
Bombay, Feb. 4–6 (1991). 相似文献
935.
Quantitative dependence of MR signal intensity on tissue concentration of Gd(HP-DO3A) in the nephrectomized rat. 总被引:3,自引:0,他引:3
P Wedeking C H Sotak J Telser K Kumar C A Chang M F Tweedle 《Magnetic resonance imaging》1992,10(1):97-108
Cardiac-gated SE 20/224 +/- 20 MR images were obtained from nephrectomized rats before and after intravenously administering 153Gd-Gd(HP-DO3A). The concentration of Gd, [Gd], was linear in dose in myocardium, skeletal muscle, and blood. Under steady-state conditions, where d[Gd]/dt = 0, image intensities (IIN) in regions of interest were compared with the measured [Gd]. IIN was linear in myocardium at less than or equal to 0.61 mumol/g-myocardium (less than or equal to 0.5 mmol/kg dose) and in skeletal muscle at less than or equal to 0.63 mumol/g-muscle (less than or equal to 0.75 mmol/kg). Above 0.6 mumol Gd/g-tissue, IIN did not increase further. The in vivo data were consistent with measured ex vivo and in vivo relaxivities. A 29% greater slope for IIN versus [Gd] in myocardium [14,439 +/- 4350 IIN (mumol/g)] than in muscle [10,258 +/- 5,296 IIN/(mumol/g)] was attributed to a significant difference in blood content: 25% versus 2% weight blood in myocardium and skeletal muscle, respectively. Two components were apparent from plots of ex vivo 1/T1 versus [Gd] in myocardium and muscle, and only one for blood. 相似文献
936.
P Camilleri 《Biomedical chromatography : BMC》1991,5(3):128-132
Many drugs are racemic and therefore much effort has to be devoted towards the stereoselective synthesis of the most effective or less harmful component of a racemic mixture. High performance liquid chromatography will play an important role in the clinical analysis of racemic drugs in anticipation of regulations that are currently being discussed and are expected to be enforced by the end of this decade. In this review a number of methods for chiral resolution are outlined. These include the formation of diastereoisomers and the use of chiral stationary phases or chiral mobile phase additives. 相似文献
937.
938.
Rate constants have been measured by pulse radiolysis for the reactions of the carbonate radical, CO3·?, with a number of organic and inorganic reactants as a function of temperature, generally over the range 5 to 80°C. The reactants include the substitution-inert cyano complexes of FeII, MoIV, and WIV, the simple inorganic anions SO32?, ClO2?, NO2?, I?, and SCN?, several phenolates, ascorbate, tryptophan, cysteine, cystine, methionine, triethylamine, and allyl alcohol. The measured rate constants ranged from less than 105 to 3 × 109 M?1 s?1, the activation energies ranged from ?11.4 to 18.8 kJ mol?1, and the pre-exponential factors ranged from log A = 6.4 to 10.7. The activation energies for the metal complexes and inorganic anions generally decrease with increasing driving force for the reaction, as expected for an outer sphere electron transfer. For highly exothermic reactions, however, the activation energy appears to increase, probably reflecting the temperature dependence of diffusion. For many of the organic reactants, the activation energies were low and independent of driving force, suggesting that the oxidation is via an inner sphere mechanism. 相似文献
939.
940.
O. P. Gorelik G. A. Dyuzhev D. V. Novikov V. M. Oichenko A. A. Sitnikova 《Technical Physics》2002,47(10):1337-1340
Electron microscopy is used in a study of nanoclusters of the carbon soot deposited on a probe in different areas of arc discharge during graphite vaporization under conditions favorable for fullerene synthesis. It is found that the spatial network of soot nanoclusters consists of alternating regions of higher density or associates of carbon particles. Two types of nanoclusters have been identified with the correlation radii of the associates equal to 0.6–0.8 and 1.6–2.2 nm, respectively. Type I nanoclusters are dominant in the soot microparticles, and their structure shows practically no variations with increasing separation r of the soot collector from the discharge axis over the range of distances studied, r=1–9 cm. The effective radius R 0 of the “elementary” particles making up the associates in the soot nanoclusters of Type I calculated with the use of scaling relationships is 0.15–0.17 nm and is close to the gas-kinetic radius of carbon atoms. Type II nanoclusters have been identified in soot collected at r>3 cm. Values of R 0 calculated in this case are 0.6–0.9 nm and decrease with increasing r, which indicates the presence of fullerene molecules in these nanocluster associates. 相似文献