A new procedure to isolate carrier-free isotopes of Nb and Ta after a 12-MeV proton bombardment of a natural Hf foil has been considered. The cross section of the corresponding natHf(p,x)179Ta reaction has been estimated for the first time as 5.4?±?0.5 mb. The isotopes that were produced were subsequently used for development of procedures for the chemical characterization of element 105 (Db). HF/HNO3 and HNO3/H2O2 media have been chosen and the parameters of the experiments have been optimized. Based on the results obtained in this work, off-line experimental procedures have been proposed for the evaluation of the chemical behavior of Db. 相似文献
Because of its ease of implementation and insensitivity to indenter drift, dynamic indentation techniques have been frequently used to measure mechanical properties of bulk and thin film materials as a function of indenter displacement. However, the actual effect of the oscillating tip on the material response has not been examined. Recently, it has been shown that the oscillation used with dynamic indentation techniques alters the measured hardness value of ductile metallic materials, especially at depths less than 200 nm. The alteration in the hardness is due to the added energy associated with the oscillation which assists dislocation nucleation. Atomistic simulations on nickel thin films agree with experiments that more dislocations are nucleated during dynamic indents than with quasi-static indents. Through the analysis of quasi-static and dynamic indents made into nickel single crystals and thin films, a theory to describe this phenomenon is presented. This is coined the Nano-Jackhammer effect, a combination of dislocation nucleation and strain rate sensitivity caused by indentation with a superimposed dynamic oscillation. 相似文献
A detailed study of the spectrofluorimetric determination of malic acid by reaction with /gb-naphthol is reported. As little as 0.1 /smg of malic acid can be determined. The optimum concentration of sulfuric acid is 80% (v/v). The interferences of citric, succinic and tartaric acids are discussed. 相似文献
Field studies indicate that Japanese macaque (Macaca fuscata) communication signals vary with the social situation in which they occur [S. Green, "Variation of vocal pattern with social situation in the Japanese monkey (Macaca fuscata): A field study," in Primate Behavior, edited by L. A. Rosenblum (Academic, New York, 1975), Vol. 4]. A significant acoustic property of the contact calls produced by these primates is the temporal position of a frequency peak within the vocalization, that is, an inflection from rising to falling frequency [May et al., "Significant features of Japanese macaque communication sounds: A psychophysical study," Anim. Behav. 36, 1432-1444 (1988)]. The experiments reported here are based on the hypothesis that Japanese macaques derive meaning from this temporally graded feature by parceling the acoustic variation inherent in natural contact calls into two functional categories, and thus exhibit behavior that is analogous to the categorical perception of speech sounds by humans. To test this hypothesis, Japanese macaques were trained to classify natural contact calls by performing operant responses that signified either an early or late frequency peak position. Then, the subjects were tested in a series of experiments that required them to generalize this behavior to synthetic calls representing a continuum of peak positions. Demonstration of the classical perceptual effects noted for human listeners suggests that categorical perception reflects a principle of auditory information processing that influences the perception of sounds in the communication systems not only of humans, but of animals as well. 相似文献
An electrode has been prepared, consisting of a PVC membrane containing Corning 477316 nitrate liquid ion-exchanger in the chlorate form, which responds to chlorate ions. It has a faster response (1-2 sec) and lower limit of detection (3 x 10(-5)M) than the nitrate electrode for chlorate determination. Selectivity coefficients for the electrode towards several other ions have been measured. 相似文献