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报告内容
摘 要
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The Earth-Moon system gives the product GME accurate to better than one part in 108.
Unfortunately, G cannot be determined from this since the mass of the
Earth ME cannot be measured independently. We discuss a cryogenic experiment in which
four magnetically levitated test masses form a planetary system around a
heavy source mass. The test masses are
coupled by superconducting circuits to form a sensitive two-axis superconducting
gravity gradiometer. The entire
apparatus is rotated about the vertical to precisely balance the
gravitational field with centrifugal acceleration. This brings in numerous benefits: (1) the
experiment is free from anelasticity associated with a mechanical support;
(2) the gradiometer is used as a null detector, alleviating the need for its
calibration and eliminating errors associated with scale-factor nonlinearity;
(3) the angular velocity can be calibrated to high precision unambiguously by
measuring the time it takes to make a complete turn; and (4) the source mass
can be shaped to alleviate the stringent metrology requirements for the test
masses. This experiment aims at
determining G with an uncertainty <
10 ppm.
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