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Detection of earth rotation with a diamagnetically levitating gyroscope
Abstract
Strong magnetic fields allow levitation of apparently nonmagnetic substances due to their weak but not negligible diamagnetic response of about 10−5. Importantly, the diamagnetic force compensates gravity on the level of individual atoms and molecules and, therefore, can be used to mimic a continuous zero-gravity environment that, otherwise, is only achievable on board of a space station. Here we employ this earth-bound low gravity to demonstrate a simple mechanical gyroscope with sensitivity already comparable to that achieved by quantum and military gyroscopes. Our gyroscope can serve as a “shooting range” for the development of precision orbiting gyroscopes that have been a subject of intensive discussions regarding possible tests of general relativity.
... Le déplacement du barreau le long de son axe obture plus le faisceau d'un côté que de l'autre. Cette différence de flux de photons est [GEI01]. Ils mesurent la vitesse de rotation de la terre (Ω T = 7,29.10 ...
... . 1.2 : (a) Vues en coupe et (b) perspective cavalière d'un inclinomètre à lévitation diamagnétique[SIM68].Fig. 1.3: Principe d'un gyroscope à masse lévitante[GEI01]. ...
Diamagnetic levitation is one of the rare way to compensate action of gravity. This kind of repulsion is negligible at our scale. However, at microscale, this effect becomes significant and can achieve levitation of diamagnetic objects. Through the development of micromagnets of numerical and analytical models as well as experimental achievements , these works explore the potential of diamagnetic levitation microdroplets and particles in a paramagnetic environment. They especially demonstrate the ability to accurately measure the interaction between charged droplets levitated . These studies analyze further the study of this levitation combined with dielectrophoretic force . This study opens new perspectives for sorting diamagnetic ball based on their size or susceptibility. Dielectrophoresis opens possibilities in the field for actuating contactless microbeads levitated.
... The researchers at Nijmegen found a way to levitate even a permanent magnet by using the strongly diamagnetic Bi in a magnet [142,143,148]. In addition, an experiment to detect the earth's rotation was made by using a plastic levitating gyroscope in vacuum [157]. It seems to be possible to apply this technique to navigation and geophysical studies, as well as to tests of general relativity. ...
Along with pressure and temperature, the magnetic field is one of the physical parameters that are used for the investigation of matter. It is an important tool for investigating magnetic and electronic properties from both the microscopic and macroscopic points of view. The interaction energy of a substance with a magnetic field, i.e. Zeeman energy or Landau energy, is small even at a field of 2 T as can be provided by a conventional electromagnet. Compared with the inner energies of a substance, magnetic fields as high as possible have been required for obtaining fine and detailed information on the internal structure and energy states. Due to the strong Maxwell stress, however, it is quite difficult to obtain a magnetic field higher than 50 T and much effort has been dedicated to the development of magnets ever since the laboratory electromagnet was invented.The purpose of this paper is to describe the physical effects that have been investigated and the phenomena that have been revealed using high magnetic fields, as well as the development of magnet technology and measurement technology. In addition, application to materials processing is mentioned as an active application of high magnetic fields.
... Sensors incorporating electrostatically or magnetically levitated spinning disks were reported (e.g., see[3,[6][7][8]). Although these devices are promising and demonstrated several advantages, the implementation of intricate feedback control approaches is necessary in order to stabilize intrinsically unstable levitated bodies. ...
In this work we introduce a new class of fully compliant structures performing vibratory motion, yet characterized by non-zero averaged momentum, appearing due to time-dependency of the inertial parameters. The work is motivated by microelectromechancial systems (MEMS) applications, where an implementation of unidirectional, non-vibratory motion involving relative motion of parts is not desirable for reliability reasons. Instead of changing the mass, which is challenging on the microscale, the moment of inertia of the proof mass performing tilting vibrations is controlled in such a way that it is higher or lower depending on the sign of the velocity. This results in a non-zero angular momentum averaged over the period. The equations describing the dynamics of a generic structure with a time-varying inertia and in a rotating coordinate frame are derived by using a variational principle. Simple approximate expressions for the averaged momentum and steady tilting angle are obtained and validated numerically. Based on the model results for different operational scenarios, we demonstrate that these devices can be efficiently used in fully compliant actuators and vibratory angular rate sensors (microgyros) with a steady response in a sensing mode ("pseudospinning disk gyros"), as well as in a parametrically excited gyro. The structure can be viewed also as a first step toward the realization of dynamic materials (DM) which are substances with material properties that may change in space and time.
... Andre Geim, who won the 2010 Nobel Prize in physics, listed H.A.M.S. ter (pronounced "hamster") Tisha as co-author of a paper published in 2001 in Physica B: Condensed Matter, a peerreviewed journal. 4 Tisha, the hamster, supposedly helped Prof. Geim with his famous levitation experiments. Another researcher, Polly Matzinger, studied the human immune system at NIH. ...
Large-scale passive resonant gyroscopes (PRGs) have been utilized in the measurement of Earth rotation. We report on a scheme of phase-sensitive heterodyne detection in large-scale PRGs. By injecting three separated beams into different longitudinal modes of the ring cavity and self-demodulating the detected signals, the backscattering disturbance and the cavity length fluctuation effect both can be isolated. With the implementation of this new scheme, we can obtain the Earth rotation signal with a Sagnac frequency that is twice of that of the traditional scheme, which enhance the equivalent scale factor of the laser gyroscopes. On the other hand, the quantum noise limit of the instrument can also be further suppressed due to the improvement of the signal-to-noise ratio. With this new scheme, the theoretical rotational sensitivity of a 3 m × 3 m large scale PRG can be as low as 10-12 rad/s/Hz. With this rotational sensitivity, the measurement of the length of day or the test of the general relativity can be realized.
La lévitation est un moyen fascinant de se soustraire à l'action de la gravité. Le diamagnétisme est le seul phénomène physique permettant une lévitation stable, statique et passive à température ambiante. Toutefois, cet effet magnétique est généralement insignifiant aux échelles usuelles. Parmis les différents moyens d'augmenter l'amplitude de ce phénomène, la réduction d'échelle est une voie prometteuse. Ces travaux contribuent à l'exploration des possibilités et des potentialités de la lévitation dans le domaine des microsystèmes. La diminution en taille permet d'une part d'augmenter les forces diamagnétiques volumiques et d'autre part de diminuer les forces diamagnétiques absolues. Ces propriétés ont été mises en oeuvre à travers la conception et la fabrication de microcapteurs (accéléromètre, inclinomètre, capteur de force) et de microactionneurs (manipulation de microparticule par inclinaison ou au moyen d'un laser). Ces réalisations ouvrent des perspectives novatrices et des fonctionnalités nouvelles dans le micromonde.
The effect of magnetic field on water mist (diamagnetic) was investigated by both experimental and numerical methods. Water mist was produced by an ultrasonic atomizer and fed from the top of a cylinder that was located in a vertical bore of a superconducting magnet of 10 T or less. Water mist descends due to gravity at 0 T, but at 10 T it mostly levitates above the magnetic coil. In the numerical computation, water mist was simulated by 1000 water droplets 0.1-5 μ m in diameter d . Due to the small sizes of the water droplets, Brownian motion was considered and the Langevin equation was solved. At d≪1 μ m , the particles are driven by the Brownian motion extensively and the magnetic and gravitational forces have almost no effect on them. At d≥1 μ m , the trajectories of particles are greatly deformed by the magnetic field when they go through the magnetic coil. At γ<sub>f</sub>=1000 (10.8 T for 9 cm cylinder diameter), the bulk of the water mist took an hourglass shape above the coil just as observed experimentally. At γ<sub>f</sub>=2000 (15.2 T), the water droplets were computed to be levitated against the gravitational acceleration.
The first production of graphene was awarded the 2010 Nobel Prize in Physics. This discovery has implications for chemistry
and within it for structural chemistry as well.
KeywordsGraphene-Andre Geim-Konstantin Novoselov-Diamagnetic levitation-Fullerenes
S. Earnshaw, a mathematical physicist born in England two centuries ago, was the author of studies on the transmission of
sound and light. His theory on the transmission of light by “detached particles” has also influenced some studies on the stability
of bodies in potential fields, particularly studies on the levitation of permanent magnets, i.e. on passive magnetic levitation.
This theorem was so well known that even Maxwell mentioned it, and is today cited almost as an axiom in the ambit of passive
magnetization. However, what is less well known is that the theory actually only relates to magnetostatics. In this paper,
the mathematic model of the theory that refers to stability is outlined, along with some works that refer to it, in particular
those on passive magnetic levitation. It is then pointed out that spaces of low instability exist in magnetostatics, and that
stability may exist in the magneto-stationary and in magneto-dynamic ambit.
In a pioneering move, one hundred and fifty years ago the Russian organic chemist Aleksandr Butlerov (1828–1886) coined the
term “chemical structure.” He called for basing our understanding of the chemical composition of substances on the concepts
of atomicity and structure.
KeywordsAleksandr Butlerov–Chemical structure–Stereochemistry
The behavior of carbon particles was numerically studied for various sizes (0.01-5 mum) in the air on which a gradient magnetic field was imposed. One thousand particles were released randomly in one of the vertical cylindrical cross sections whose height is equal to its radius. An electric coil was placed coaxially at the bottom level of the enclosure to produce a magnetic field. The Brownian motion was taken into consideration and the Langevin equation was solved for the particle motion. The effect of the magnetic field on the particle movement increased with the particle size, but the Brownian motion decreased. For those particles with diameter d less than or equal to 1 mum, the Brownian motion was so strong that the magnetic and gravitational fields had almost no effects on the particle behavior. For the particles of d greater than or equal to 1 mum, the Brownian motion could be ignored mostly, and the particles accumulated at the bottom or upper walls of the enclosure depending on the magnetic strength.
Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.
The behaviour of a water droplet was numerically studied in natural and magnetic convection of air. The magnetic field was computed using Biot-Savart's law. The Newton's equation of motion was solved for a particle and the Stokes' law of resistance was taken into account for the drag force. The results show that the magnetic field enhances the natural convection of air in the cubical cavity greatly. The influence of the flow field on the motion of a particle increases with the increase in the Ra number. The influence of the magnetic field on the particle increases with the increase in γ which represents the strength of the magnetic field. A particle is levitated in the combined field at larger γ. The initial position of a particle affects its behaviour and its final position. The final position does not depend on the initial velocity if it is not too high.
Nowadays scientists can easily levitate diamagnetic substances in the powerful field of a superconducting magnet. Pyrolytic graphite and strong NdFeB permanent magnets can be bought by every levitation enthusiast for building his own levitation device. But the way towards this was long. First of all diamagnetism had to be discovered and investigated in detail. Then the theoretical fundament for diamagnetic levitation had to be set. And of course suitable technologies had to be developed and tested for practical demonstrations of diamagnetic levitation. At all it took 161 years from discovery of diamagnetism to the first practical levitation demonstration. This paper gives an overview on this historical development and additionally emphasises the most important achievements from the very beginning up to now.
High precision gyroscopes are often used to find the north direction or determine the orientation by detecting the horizontal component of the earth's rotation rate in the field of north-seeking, oil drilling and mining. The ability to measure the earth's rotation rate accurately for gyroscopes can be applied as a basic criterion in those areas. MEMS gyroscopes were thought unable to measure the earth's rotation rate because of its noise and low precision. The detection methods of earth's rotation rate with a MEMS gyroscope were proposed, including the static and dynamic methods. Several major factors that influence the accuracy were analyzed and compensated carefully. The multi-position static and dynamic experiments were completed with a MEMS gyroscope. For the 36-position static measurement method, a single test takes 720 seconds, the 10 times' average error is less than 0.03%. For the dynamic experiments with a period of 18 seconds, a single test takes 108 seconds, the 10 times' average error is less than 1%. The experimental results indicate that the MEMS gyroscopes have great potentials in the field of north-seeking and orientating.
Animals have made an immense contribution to science and medical practice as experimental models in basic research, to study human disease and for drug development. Over the last few decades, animal rights activism and concerns for animal welfare in general have led to an increasing emphasis on and adoption of the “3R” approach (Replace, Reduce and Refine) in biomedical research. This was originally proposed in 1959 by William Russell and Rex Burch with the overall aim of reducing animal suffering while improving the quality of experiments that rely on animal models (see Box 1). Nonetheless, in addition to having no choice in the matter, animals receive no credit for their sacrifice, with the exception of some “celebrities” such as Dolly the famous cloned sheep. In this article, we explore whether animals should also receive more recognition for their vital contribution to research via credit in publications.
### Box 1:From 3R to 4R
> At least in theory, animals other than humans do not seem equipped to become formal authors.
Authorship and contributorship are essential aspects of scientific publishing and widely discussed issues. While considerable attention is paid to whether bylines are too long [1] or too short and to ghost and guest authorship, the possibility of …
Neo-liberal policies have the same general effect in the universities as they do in society as a whole. In society, their tendency has been to form large inequalities in the distribution of income and wealth. Similarly, in the case of higher education and scientific research, more and more funding is going to a few privileged universities and their researchers at the expense of the others. This is justified on the grounds that these universities and researchers are better than the others, so that it more efficient to concentrate funding on them. To find out how to distribute funding regular research assessments are conducted. But how accurate are these research assessments in picking out the researchers who are better from those who are not so good? It is argued that research evaluation as well as the pressure to reward the top-excellence is enhancing conformism and thus it is stifling the diversification of research, the essential element to develop innovations and new technologies. Is competition increasing researchers productivity and differentiation of research projects? How to test that a method of organization and evaluation of science is more efficient than another? Historical examples of discoveries in physics and mathematics in the past thirty years, as the super-high-temperature conductivity, the scanning tunneling microscope, graphene, and others, allow us to clarify how scientific research proceeds and how the findings of basic research are transformed into technological innovations.
With the diamagnetic material property, diamagnetic levitation possesses the special advantages of passive static and stable levitation at room temperature, which has attracted many scholars. Especially in the recent three decades, with the development of strong magnetic field equipment and micro technology, increasing publications on diamagnetic levitation research are appearing. Many foreign researches have done the relative investigations; however, the domestic researches in this field are relatively few and narrow. Aimed at this situation, a review of diamagnetic levitation technology including diamagnetic theory, diamagnetic characteristics and relative application research works is presented. The diamagnetic levitation technology not only possesses free-contact, no-lubrication and low energy consumption merits, but also permits advantages such as passive static and stable levitation at room temperature, micro-nano application and low supporting stiffness, which may possess potential and promising application ranging from micro rotating machinery, energy harvesting, high sensitive MEMS-sensor to cell/particle manipulation. A review of diamagnetic levitation is provided, which is helpful for the domestic researchers.
This paper describes a feasibility study of creating a small low friction and low maintenance generator using a diamagnetically stabilized levitating rotor. The planar rotor described in this paper uses a triangular configuration of magnets that generates emf by passing over coils placed below the rotor. Equations were developed to predict the generated emf from coils with two different coil geometries. Additionally, this paper provides a method for estimating optimal coil size and position for the planar rotor presented for both segmental arc and circular coils to obtain maximum power output. Experiments demonstrated that the emf generated in the coils matches well with the predicted wave forms for each case, and the optimization theory gives good prediction to outcome of induced waveforms. For the segmental arc coil design, the induced emf was 1.7 mV at a radial frequency of 21.8 rad/s. For the circular coil design, the emf was 1.25 mV at a radial frequency of 28.1 rad/s.
The effect of the rotation of the Earth, Omega⊕, on a superfluid resonator equipped with a 4.0 cm2 rotation pickup loop and with a microaperture is reported. The velocity circulation induced in the loop by the rotation is detected by phase-slippage techniques. The magnitude of Omega⊕ is measured to better than 1%, and the north direction to +/-0.5° for a 10 h observation time. This experiment is the superfluid counterpart of interferometric measurements based on the Sagnac effect.
We have measured the phase shift induced by rotation of an atom interferometer at rates of -2 to +2 earth rates and obtained 1% agreement with the predicted Sagnac phase shift for atomic matter waves. The rotational rms noise of our interferometer was 42 milliearth rates for 1 sec of integration time, within 9% of shot noise. The high sensitivity and agreement of predicted and measured behavior suggest useful future scientific applications of atom interferometers as inertial sensors. {copyright} {ital 1997} {ital The American Physical Society}
The levitation of various diamagnetic liquid and solid substances such as water, ethanol, acetone, bismuth, antimony, graphite, wood and plastic has been achieved at room temperature in a strong inhomogeneous static magnetic field. These experiments were performed in the hybrid magnet at the Service National des Champs Intenses (CNRS, Grenoble). These findings show that high field superconducting magnets could be used to provide a contactless, low gravity environment for the elaboration of a wide range of materials. En utilisant les forts champs magnétiques produits par la bobine hybride du Service National des Champs Intenses (CNRS, Grenoble), nous avons obtenu à température ambiante la lévitation de substances diamagnétiques solides ou liquides telles que l'eau, l'alcool, l'acétone, le bismuth, l'antimoine, le graphite, le bois et le plastique. Ces résultats montrent que les bobines supraconductrices peuvent être utilisées pour l'élaboration de nombreux matériaux en gravité réduite, sans contact avec un contenant.
Over twenty years have elapsed since Leonard Schiff at Stanford and, independently, George E. Pugh at the Defense Department predicted that a gyroscope in orbit about Earth would precess as a consequence of Einstein's general theory of relativity. Such behavior depends on an aspect of the theory of gravity that remains untested to this day. Although the concept is simple, the experiment is formidable: The precession is about 44 milliarcsec/year, to be measured with an accuracy of 1 milliarc‐sec per year. Undaunted, Schiff, together with Stanford colleagues William Fairbank and Robert Cannon, respectively, set up a program to develop the experiment. Since 1962, a Stanford team led by Francis Everitt and later having the support of NASA's Marshall Space Flight Center, has patiently and persistently toppled many technical barriers, bringing the experiment from the realm of the improbable into the world of the possible. In late 1980, a committee of 16 scientists and engineers convened by NASA spent five days reviewing the technical readiness of the experiment, which is called the Gravity Probe B. They gave it a sound endorsement and concluded it was now ready to proceed to its flight phase.
We report the demonstration of a Sagnac-effect atom interferometer gyroscope which uses stimulated Raman transitions to coherently manipulate atomic wave packets. We have measured the Earth's rotation rate, and demonstrated a short-term sensitivity to rotations of 2×10-8(rad/s)/√Hz.
It has long been recognized that the macroscopic quantum properties of superfluid helium could form the basis of a technique for measuring the state of absolute rotation of the containment vessel1-5: circulation of superfluid helium is quantized, so providing a reference state of zero rotation with respect to inertial space. Here we provide experimental proof of this concept by detecting the rotation of the Earth using the spatial phase coherence of superfluid 4He, thus providing independent corroboration of an earlier report6 that demonstrated the feasibility of making such a measurement. Our superfluid container is constructed on a centimetre-size silicon wafer, and has an essentially toroidal geometry but with the flow path interrupted by partition incorporating a sub-micrometre aperture. Rotation of the container induces a measurable flow velocity through the aperture in order to maintain coherence in the quantum phase of the super-fluid. Using this device, we determine the Earth's rotation rate to a precision of 0.5% with a measurement time of one hour, and argue that improvements in sensitivity of several orders of magnitude should be feasible.
We discuss new opportunities that present themselves with the advent of very high magnetic field resistive magnets with appreciable central bore access. A detailed description of the parameters of the magnetic force environment for the case of diamagnetic materials in a water-cooled Bitter-type resistive magnet is provided for the reader who may have an interest in low-gravity experiments. We discuss emerging research activities involving novel uses of magnetic forces in high field resistive magnets at the National High Magnetic Field Laboratory. Particular attention is given to the area of diamagnetic materials that allow a low or “zero” gravity state, i.e., magnetic levitation. These include studies involving plant growth, protein crystallization, and dynamics of single particles and granular materials. In the latter case, unique aspects of the magnetic force environment allow low gravity experiments on particulates that cannot be performed on the Space Shuttle due to the lack of a weak confining potential in space. © 2000 American Institute of Physics.
Contrary to our intuition, apparently nonmagnetic substances can be levitated in a magnetic field and can stabilize free levitation of a permanent magnet. Most substances are weakly diamagnetic and the tiny forces associated with this property make the two types of levitation possible. Living things mostly consist of diamagnetic molecules (such as water and proteins) and components (such as bones) and therefore can be levitated and can experience low gravity. In this way, frogs have been able to fly in the throat of a high field magnet. Stable levitation of one magnet by another with no energy input is usually prohibited by Earnshaw’s Theorem. However, the introduction of diamagnetic material at special locations can stabilize such levitation. A magnet can even be stably suspended between (diamagnetic) fingertips. © 2000 American Institute of Physics.
The Melting of glass materials levitated in high magnetic fields has
been carried out without a crucible by using a hybrid magnet and a
CO2 laser. A cubic glass with 6 mm sides has become a
complete sphere through melting and cooling in the air. This new method
will provide opportunities for obtaining high-purity and new
heterogeneous materials.
Diamagnetic objects are repelled by magnetic fields. If the fields are strong enough, this repulsion can balance gravity, and objects levitated in this way can be held in stable equilibrium, apparently violating Earnshaw's theorem. In fact Earnshaw's theorem does not apply to induced magnetism, and it is possible for the total energy (gravitational + magnetic) to possess a minimum. General stability conditions are derived, and it is shown that stable zones always exist on the axis of a field with rotational symmetry, and include the inflection point of the magnitude of the field. For the field inside a solenoid, the zone is calculated in detail; if the solenoid is long, the zone is centred on the top end, and its vertical extent is about half the radius of the solenoid. The theory explains recent experiments by Geim et al, in which a variety of objects (one of which was a living frog) was levitated in a field of about 16 T. Similar ideas explain the stability of a spinning magnet above a magnetized base plate. Stable levitation of paramagnets is impossible.
Samenvatting. Magnetische velden stoten diamagnetische voorwerpen af. Zulke velden kunnen zo sterk zijn dat zij de zwaartekracht opheffen. Het is op deze wijze mogelijk zulke voorwerpen te laten zweven. Dit vormt een stabiel evenwicht, wat in tegenspraak schijnt te zijn met Earnshaw's Theorema. Echter Earnshaw's Theorema is niet langer geldig als het magnetisme veld geinduceerd is. De totale energie (bevattende bijdragen van het magnetisme en de zwaartekracht) kan toch een lokaal minimum vertonen. Algemene criteria voor zo'n minimum zullen worden opgesteld. Verder zal worden aangetoond dat voor een cilindrisch symmetrisch veld, langs zijn symmetrie as altijd een zone gevonden kan worden waarin een stabiel evenwicht bestaat. Voor het veld binnen een soleno?de zal deze zone in detail bepaald worden. Als deze spoel voldoende land is bevindt deze zone zich aan het uiteinde van de spoel. De lengte van deze zone langs de symmetrie as van het veld is ongeveer de helft van de straal van de spoel. Deze theorie geeft een goede verklaring voor de experimenten van Geim et al. In deze experimenten werden een grote verscheidenheid aan verschillende voorwerpen (waaronder een levende kikker) tot zweven gebracht in velden van ongeveer 16 T. Analoge theori?n verklaren de stabiliteit van een roterend permanent magneetje boven een magneetische grondplaat. Het is onmogelijk om paramagnetische voorwerpen stabiel te doen zweven.
Magnetic levitation experiments of some diamagnetic materials in high magnetic fields have been done by using a hybrid magnet of Tohoku University. Water located near the edge of the water-cooled magnet, for example, becomes a globe and levitates when a held at the center of the magnet is above 20.5 T. As the first application of water levitation, we tried to make an ice crystal at the levitating condition and it turned out that the crystallization process shows complicated and strange behavior at supercooled -10 degrees C. Synthesis of a dendrite ice crystal was also tried and it was first found that the directions of growing branches are different. But this effect seems to be not due to the levitation effect but due to the orientation effect.
A high-accuracy orbiting relativity experiment is described. A pure unsupported gyroscope in a spinning drag-free satellite at ambient temperatures with conventional optical instrumentation can measure relativity drifts with errors as low as 3-0.1 arc musec/yr, an improvement of 102-103 over the current GP-B experiment. Recent theoretical work has suggested that the post-Newtonian parameter 1-gamma~1/omegaBD might lie in the range 10-4- 10-8, signaling the presence of a massless scalar field. The experiment described here could measure gamma to an accuracy between 10-7 and 10-8; for the highest accuracies, the measurement depends critically on future microarcsecond astrometry or a two-gyro version of the experiment.
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