103 research outputs found
Indirect Evidence for L\'evy Walks in Squeeze Film Damping
Molecular flow gas damping of mechanical motion in confined geometries, and
its associated noise, is important in a variety of fields, including precision
measurement, gravitational wave detection, and MEMS devices. We used two
torsion balance instruments to measure the strength and distance-dependence of
`squeeze film' damping. Measured quality factors derived from free decay of
oscillation are consistent with gas particle superdiffusion in L\'evy walks and
inconsistent with those expected from traditional Gaussian random walk particle
motion. The distance-dependence of squeeze film damping observed in our
experiments is in agreement with a parameter-free Monte Carlo simulation. The
squeeze film damping of the motion of a plate suspended a distance d away from
a parallel surface scales with a fractional power between 1/d and 1/d^2.Comment: 5 pages 5 figures accepted for PRD; typo in equation 3 and figure 1
fixe
The kilogram: inertial or gravitational mass?
With the redefinition of the international system of units, the value of the Planck constant was fixed, similarly to the values of the unperturbed ground state hyperfine transition frequency of the Cs-133 atom and speed of light in vacuum. Theoretically and differently from the past, the kilogram is now explicitly defined as the unit of inertial mass. Experimentally, the kilogram is realized by atom count or the Kibble balance. We show that only the former method measures the inertial mass without assuming the universality of free fall. Under ordinary circumstances, the results obtained by the Kibble balance require the equivalence of inertial and gravitational mass. Therefore, the agreement between the two measures can be interpreted as a test of the equivalence principle
Reflections on a Measurement of the Gravitational Constant Using a Beam Balance and 13 Tons of Mercury
In 2006, a final result of a measurement of the gravitational constant
performed by researchers at the University of Z\"urich was published. A value
of G=6.674\,252(122)\times
10^{-11}\,\mbox{m}^3\,\mbox{kg}^{-1}\,\mbox{s}^{-2} was obtained after an
experimental effort that lasted over one decade. Here, we briefly summarize the
measurement and discuss the strengths and weaknesses of this approach.Comment: 13 pages, 5 figures accepted for publication in Phil. Trans. R. Soc.
High Sensitivity Torsion Balance Tests for LISA Proof Mass Modeling
We have built a highly sensitive torsion balance to investigate small forces
between closely spaced gold coated surfaces. Such forces will occur between the
LISA proof mass and its housing. These forces are not well understood and
experimental investigations are imperative. We describe our torsion balance and
present the noise of the system. A significant contribution to the LISA noise
budget at low frequencies is the fluctuation in the surface potential
difference between the proof mass and its housing. We present first results of
these measurements with our apparatus.Comment: 6th International LISA Symposiu
Charge Management for Gravitational Wave Observatories using UV LEDs
Accumulation of electrical charge on the end mirrors of gravitational wave
observatories, such as the space-based LISA mission and ground-based LIGO
detectors, can become a source of noise limiting the sensitivity of such
detectors through electronic couplings to nearby surfaces. Torsion balances
provide an ideal means for testing gravitational wave technologies due to their
high sensitivity to small forces. Our torsion pendulum apparatus consists of a
movable Au-coated Cu plate brought near a Au-coated Si plate pendulum suspended
from a non-conducting quartz fiber. A UV LED located near the pendulum
photoejects electrons from the surface, and a UV LED driven electron gun
directs photoelectrons towards the pendulum surface. We have demonstrated both
charging and discharging of the pendulum with equivalent charging rates of
, as well as spectral measurements of the pendulum
charge resulting in a white noise level equivalent to .Comment: 5 pages, submitted to PR
Temporal Extent of Surface Potentials between Closely Spaced Metals
Variations in the electrostatic surface potential between the proof mass and
electrode housing in the space-based gravitational wave mission LISA is one of
the largest contributors of noise at frequencies below a few mHz. Torsion
balances provide an ideal testbed for investigating these effects in conditions
emulative of LISA. Our apparatus consists of a Au coated Cu plate brought near
a Au coated Si plate pendulum suspended from a thin W wire. We have measured a
white noise level of 30, \uVhz above approximately 0.1, mHz, rising at lower
frequencies, for the surface potential variations between these two closely
spaced metals
New CP-violation and preferred-frame tests with polarized electrons
We used a torsion pendulum containing polarized
electrons to search for CP-violating interactions between the pendulum's
electrons and unpolarized matter in the laboratory's surroundings or the sun,
and to test for preferred-frame effects that would precess the electrons about
a direction fixed in inertial space. We find and for AU. Our preferred-frame constraints, interpreted in
the Kosteleck\'y framework, set an upper limit on the parameter eV that should be compared to the benchmark
value eV.Comment: 4 figures, accepted for publication in Physical Review Letter
First measurements of the flux integral with the NIST-4 watt balance
In early 2014, construction of a new watt balance, named NIST-4, has started
at the National Institute of Standards and Technology (NIST). In a watt
balance, the gravitational force of an unknown mass is compensated by an
electromagnetic force produced by a coil in a magnet system. The
electromagnetic force depends on the current in the coil and the magnetic flux
integral. Most watt balances feature an additional calibration mode, referred
to as velocity mode, which allows one to measure the magnetic flux integral to
high precision. In this article we describe first measurements of the flux
integral in the new watt balance. We introduce measurement and data analysis
techniques to assess the quality of the measurements and the adverse effects of
vibrations on the instrument.Comment: 7 pages, 8 figures, accepted for publication in IEEE Trans. Instrum.
Meas. This Journal can be found online at
http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=1
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