Justifying the parameters of dredging in various types of stopes and massive productive strata

Introduction. Due to a wide variety of placer dredging conditions, traditional methods of dredging parameters calculation do not always take into account all aspects of productive strata mining. It is first of all true for deep placers operation and mining with side cuts. Research aim is to improve the methods of calculating dredging parameters and the capacity of pilesupported bucket chain dredgers. Methodology. Existing methods of calculating dredging parameters and dredgers capacity do not take into account the applied mining method, stope type, and upper stope cave-in conditions. The indicated factors greatly influence the parameters of productive strata excavation and washery refuse disposal. Taking these ISSN 0536-1028 «Известия вузов. Горный журнал», № 3, 2020 13 factors into account makes it possible to forecast the indicators of the pile-support dredgers more accurately. Results. Investigation of some aspects of dredging trenches and side cuts has made it possible to establish the dependence of dredger maneuvering angle in pit face and capacity on cutting depth when mining massive productive strata; spoil dumps parameters dependence on the type of stoping; the interrelation between the daily capacity and the width of the front bank under various vertical distribution of rock. The indicated dependences allow to determine dredging parameters and indicators for particular conditions. Summary. The proposed approach, which calculates dredging parameters when using side cuts and when mining deep placers with non-uniform thickness of sands, makes it possible to calculate the chips size, buckets filling ratio and sand fragmentation ratio in a more substantiated way; it makes it possible to more effectively manage the process of sand mining, thus increasing the capacity of dredges.

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Disappearance Voltage Determinations Using a Convergent Beam

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064979 ◽

1971 ◽

Vol 29 ◽

pp. 184-185

Author(s):

W. L. Bell

Keyword(s):

Second Order ◽

Objective Method ◽

Uniform Thickness ◽

Rocking Curve ◽

Crystal Perfection ◽

Kikuchi Line ◽

Central Maximum ◽

Diffraction Patterns ◽

Convergent Beam ◽

Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

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Comparison of Techniques for EELS Mapping in Biology

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100163964 ◽

1996 ◽

Vol 54 ◽

pp. 300-301

Author(s):

R.D. Leapman ◽

S.B. Andrews

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Image Data ◽

Beam Current ◽

Quantitative Information ◽

Acquisition Time ◽

Uniform Thickness ◽

Electron Dose ◽

Array Detectors ◽

Transmission Electron

Elemental mapping of biological specimens by electron energy loss spectroscopy (EELS) can be carried out both in the scanning transmission electron microscope (STEM), and in the energy-filtering transmission electron microscope (EFTEM). Choosing between these two approaches is complicated by the variety of specimens that are encountered (e.g., cells or macromolecules; cryosections, plastic sections or thin films) and by the range of elemental concentrations that occur (from a few percent down to a few parts per million). Our aim here is to consider the strengths of each technique for determining elemental distributions in these different types of specimen.On one hand, it is desirable to collect a parallel EELS spectrum at each point in the specimen using the ‘spectrum-imaging’ technique in the STEM. This minimizes the electron dose and retains as much quantitative information as possible about the inelastic scattering processes in the specimen. On the other hand, collection times in the STEM are often limited by the detector read-out and by available probe current. For example, a 256 x 256 pixel image in the STEM takes at least 30 minutes to acquire with read-out time of 25 ms. The EFTEM is able to collect parallel image data using slow-scan CCD array detectors from as many as 1024 x 1024 pixels with integration times of a few seconds. Furthermore, the EFTEM has an available beam current in the µA range compared with just a few nA in the STEM. Indeed, for some applications this can result in a factor of ~100 shorter acquisition time for the EFTEM relative to the STEM. However, the EFTEM provides much less spectral information, so that the technique of choice ultimately depends on requirements for processing the spectrum at each pixel (viz., isolated edges vs. overlapping edges, uniform thickness vs. non-uniform thickness, molar vs. millimolar concentrations).

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