Ever since Galileo scientists have known that all bodies fall with the same acceleration regardless of their mass and composition. Known as the
Universality of Free Fall, this is the most direct ...experimental evidence of the
Weak Equivalence Principle, a founding pillar of General Relativity according to which the gravitational (passive) mass
m
g
and the inertial mass
m
i
are always in the same positive ratio in all test bodies. A space experiment offers two main advantages: a signal about a factor of a thousand bigger than on Earth and the absence of weight. A new space mission named GALILEO GALILEI (GG) has been proposed (Nobili et al., 1995 J. Astronautical Sciences, 43, 219; GALILEO GALILEI (GG), PRE PHASE A REPORT, ASI (Agenzia Spaziale Italiana), September 1996) aimed at testing the weak Equivalence Principle (EP) to 1 part in 10
17 in a rapidly spinning (5 Hz) drag-free spacecraft at room temperature, the most recent ground experiments having reached the level of 10
−12 (Adelberger et al., 1990 PhRvD, 42, 3267; Su et al., 1994 PhRvD, 50, 3614). Here we present a nondrag-free version of GG which could reach a sensitivity of 1 part in 10
16. The main feature of GG is that, similarly to the most recent ground experiments, the expected (low frequency) signal is modulated at higher frequency by spinning the system, in this case by rotating the test bodies (in the shape of hollow cylinders) around their symmetry axes, the signal being in the perpendicular plane. They are mechanically suspended inside the spacecraft and have very low frequencies of natural oscillation (due to the weakness of the springs that can be used because of weightlessness) so as to allow self-centering of the axes; vibrational noise around the spin/signal frequency is attenuated by means of mechanical suspensions. The signal of an EP violation would appear at the spin frequency as a relative (
differential) displacement of the test masses perpendicularly to the spin axis, and be detected by capacitance sensors; thermal stability across the test masses and for the required integration time is obtained passively thanks to both the fast spin and the cylindrical symmetry. In the nondrag-free version the entire effect of atmospheric drag is retained, but a very accurate balancing of the test bodies must be ensured (through a coupled suspension) so as to reach a high level of
Common Mode Rejection and reduce the differential effects of drag below the target sensitivity. In so doing the complexities of a drag-free spacecraft are avoided by putting more stringent requirements on the experiment. The spacecraft must have a high area-to-mass ratio in order to reduce the effects of nongravitational forces; it is therefore a natural choice to have three pairs of test masses (in three experimental chambers) rather than one as by Nobili et al. (1995) J. Astronautical Sciences, 43, 219 and the mission called GALILEO GALILEI PRE PHASE A REPORT, ASI (Agenzia Spaziale Italiana), September 1996. The GG setup is specifically designed for space; however, a significant EP test on the ground is possible — because the signal is in the transverse plane — by exploiting the horizontal component of the gravitational and the centrifugal field of the Earth. This ground test is underway.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Numerous bacterial and plant genes are expressed specifically during nodule development. The results of a study indicate that the nodM gene coding for glucosamine synthase is required for efficient ...Nod signal production and that function is common in Rhizobium meliloti and Rhizobium leguminosarum.
A large volume of data (temperatures, densities, concentrations, winds, etc.) has been accumulated showing that in addition to seasonal changes in the thermosphere, annual variations are present and ...have a component that is a function of latitude. It appears that the helium concentrations have much larger variations in the southern hemisphere than in the northern hemisphere; the same holds true for the exospheric temperatures deduced from Ogo 6 data. Similarly, satellite drag data in the 250‐ to 400‐km range indicate that the bulge of density tends to stay over the southern hemisphere, whereas winds deduced from Ogo 4 and 6 data show a tendency to blow northward across the equator. If part of the explanation of these asymmetries can be found in a latitude independent component induced by the changing sun‐earth distance between solstices (Volland et al., 1972; Ching and Chiu, 1972, 1973), the fact that an asymmetry is still present at the equinoxes suggests that this is not the sole cause: more energy seems to be available for the thermosphere in the southern hemisphere during the equinoxes; this may be the result of an asymmetry in the geomagnetic field or an asymmetrical dissipation of tidal waves induced by an asymmetrical worldwide ozone distribution.
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