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101.
An ultrasonic velocity borehole logger has been developed for use in small diameter boreholes drilled in rock for probing ahead of tunnels. The paper gives details of its design and construction and examples of its use in logging boreholes drilled in a laboratory trial and in an underground stone quarry. Two special features of the logging tool are that the transducers are mechanically pressed against the rock in the borehole wall and therefore no liquid is needed in the borehole to provide a coupling for the signal, and that the whole tool has been made compact enough to fit into a 56 mm diameter borehole. The instrument measures the compressional wave velocity of the rock, which may be interpreted to provide a qualitative indication of rock properties. In addition a method of deriving the rock strength from the velocity is suggested and demonstrated for the two test boreholes. Recommendations for developing the prototype into an instrument for routine use are made. 相似文献
102.
103.
The mechanisms of collection and release of sixteen elements in atom-trapping atomic absorption spectrometry with a water-cooled silica trap in an air-acetylene flame are examined. Ag, Au, Cd, Co, Cu, Fe, Ni, Pb, Se and Zn appear to accumulate as metals whilst K, Li, Na, Cr, Mg and Mn are trapped as silicates or oxides. Al and V are also trapped as oxides, but were not studied further. No evidence could be found that the surface temperature of the trap exceeds 1700 K during the release cycle. Plots of appearance time of atoms vs. m.p. suggest that while direct evaporation can play a part in atomization, sputtering by energetic species in the scouring flame gases may explain the appearance of gaseous atoms at the relatively low temperatures involved. The atomization phenomena are related to those observed with electrothermal atomizers based on carbon and tantalum. It is suggested that sputtering processes may also be involved in such atomizers. 相似文献
104.
105.
106.
107.
The application of Schlieren and shadow techniques for the study of flame processes is discussed in relation to analytically useful premixed flames. The information obtained, particularly with shadowgraphs, may be correlated with the measured signals and signal noise in atomic-absorption and flame-emission spectrometry. 相似文献
108.
M.?BiasiniEmail author R. D.?Gann L. N.?Pfeiffer K. W.?West X. P.A.?Gao B. C.D.?Williams J. A.?Yarmoff A. P.?MillsJr 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(2):305-314
The conductivity of an Al0.24Ga0.76As/GaAs
quantum well was studied as a function of the surface charge
generated by electron bombardment of the sample in the absence of
an externally applied surface electric field. Under a suitable
rate of electron irradiation, it was possible to completely shut
off the conductive channel, implying a surface density
. Light illumination quenches the
increase of the resistivity, apparently due to photoemission from
the metastable surface states. Upon turning off the electron
bombardment the surface charge on adsorbed layers of xenon and
water at 8 K decays in room temperature darkness with a lifetime
τ= 0.30 ±0.02 s. The average charging efficiency, is
μ0 ≃0.001. Surface charging is shown to be an effective
method for contactless gating of field effect devices. 相似文献
109.
We have investigated the integer quantum Hall plateau-to-plateau transition in two-dimensional electrons confined to AlxGa(1-x)As-Al0.33Ga0.67As heterostructures over a broad range of Al concentration x. For x between 0.65% and 1.6%, where the dominant contribution to disorder is from the short-range alloy potential fluctuations, we observe a perfect power-law scaling in the temperature range from 30 mK to 1 K with a critical exponent kappa = 0.42 +/- 0.01. 相似文献
110.
In this Letter we report on lateral diffusion measurements of excitons at low temperature in double quantum wells of various widths. The structure is designed so that excitons live up to 30 micros and diffuse up to 500 microm. Particular attention is given to establishing that the transport occurs by exciton motion. The deduced exciton diffusion coefficients have a very strong well width dependence, and obey the same power law as the diffusion coefficient for electrons. 相似文献