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  • 1
    Electronic Resource
    Electronic Resource
    The frequency fluctuations of an electronically cooled rotor (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2833-2837 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calculations show that even a modest-sized laboratory rotor can exhibit stability comparable to that of good frequency standards if it is sufficiently undisturbed and if its moment of inertia is constant enough. Further, they show that electronic cooling, by derivative feedback, can cause these properties to be exhibited in much more useful regimes of time and frequency. This paper describes theoretical and experimental efforts to evaluate the effects of such feedback on a practical rotor, presently far from ideal. The stability measurements are presented in the context of averaging or observing times and are given as Allan variances. Representative results for a small (few centimeters) rotor with a magnetic suspension bearing show noise 4–5 orders of magnitude above the ideal, i.e., noise caused only by molecular bombardment. These analyses are in the region of averaging times from 10 to 100 000 s, and the measurements were in a laboratory in which the temperature fluctuates a few degrees Centigrade. Measured and calculated transfer functions from temperature variations show that a significant part of the excess noise is caused by these variations. Electronic cooling by feedback behaves as expected in modifying the noise spectrum. The changes in the excess noise are the same as those calculated for molecular bombardment noise, thus indicating that the excess noise comes from frequency-independent driving torques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341593
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetically suspended centrifuge for studies of nonlinear phenomena in stratified fluids: Developmental aspects (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3293-3300 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Design studies of a novel magnetically suspended centrifuge suggest that such a device would be useful for investigating the nonlinear dynamics of interfacial waves in a rotating two-phase liquid. In its final form, the apparatus would use magnetic bearings, a directly-driven rotor, precision temperature control, and vibration isolation. The mechanical noise in the magnetic suspension coil of a preliminary apparatus was measured to be 3-μm rms in a 5-kHz bandwidth. However, these vibrations were attenuated by an active differentiator to the point where there was no observable oscillation in a 183-gram suspended test mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140568
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  • 3
    Electronic Resource
    Electronic Resource
    Using the fast Fourier transform to determine the period of a physical oscillator with precision (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 778-782 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Measuring the period of torsion pendulums with precision has long been a formidable challenge in gravitation experiments, particularly those measuring the Newtonian gravitational constant G. An alternative method to fitting the position signal of the pendulum to a sine wave is the use of the power spectrum generated by the fast Fourier transform (FFT) as the source of information from which the period of oscillation can be determined. There are, however, known limitations to the use of a FFT to measure the period of a physical oscillator with precision. These limitations include two effects due to the finiteness of the duration of the sinusoidal data record and one effect due to the uncertainty of the starting phase of the oscillator relative to the window imposed by this duration. We have done a phenomenological study of the FFT using a desktop computer to imitate a precision oscillator having the physical characteristics of a finite damping constant and drift in the zero potential-energy position. Also, we have taken extensive data with a torsion pendulum, and analyzed them in this way. These studies show that for a real oscillator, such as the classical torsion pendulum, the FFT is a useful tool for determining the period of oscillation with the precision usually associated with larger, more complex, fitting algorithms. With good signal-to-noise ratio and under conditions appropriate to a torsion pendulum, the FFT method can measure the frequency or period to five parts in 106 or better.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139828
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  • 4
    Electronic Resource
    Electronic Resource
    Torsion balances, torsion pendulums, and related devices (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 283-309 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The torsion pendulum is not only a mainstay instrument in the world of precision measurement and gravitational physics, but is important in electrical science, biophysics, petrology, metallurgy, and various other fields of endeavor. Whether used in the "static'' (deflection) mode, the "dynamic'' (oscillating) mode, or in some more complex configuration, instrumentation of this kind enables one to isolate and measure weak effects that would otherwise be difficult if not impossible to observe against the background gravitational field of the earth. In this review, we present a brief history of fiber-suspended apparatus and assess the fundamental limits of performance of the dumbbell pendulum. We then inventory the different versions of such systems presently used by gravitational physicists and discuss the various interrogation techniques used to monitor the movement of the suspended test mass. Next, we tabulate some of the applications for torsion instruments outside of gravitational physics, and close with a few comments on the direction of research in this area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144248
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic manipulation instrumentation for medical physics research (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 533-562 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The noncontact magnetic manipulation of probe masses within the body is an area of research that has received substantial attention from the medical physics community, especially during the past three decades. The therapeutic and diagnostic possibilities arising from such technology include site-specific drug delivery within the central nervous system, advancement of techniques for navigation and selective catheterization of vessels within the cardiovascular and cerebrovascular systems, and the nonsurgical exploration of the alimentary and respiratory tracts. In this review, we examine the physical principles underlying in vivo magnetic manipulation systems, and catalog the various types of instrumentation used for such purposes to date. Thereafter, we evaluate the different methods of image-based localization used to identify the position of the probe within the body. Finally, we appraise an emerging technology known as nonlinear magnetic stereotaxis, a technique that permits minimally invasive access to difficult-to-approach parts of the brain. We close the review with a few comments on the directions for future work within this field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145242
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamic measurement of matter creation (1978)
    [s.l.] : Nature Publishing Group
    Nature 271 (1978), S. 228-229 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Figure 1 shows the elements of the experiment. Two cylinders of highly temperature-stable ceramic rotate concentrically about the axis of rotation of a precision turntable. The outer cylinder is connected to the turntable which rotates with an integral speed constancy limited only by the precision ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/271228a0
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental determination of the force required for insertion of a thermoseed into deep brain tissues (1990)
    Springer
    Annals of biomedical engineering 18 (1990), S. 299-313 
    Details
    ISSN: 1573-9686
    Keywords: Implant ; Force ; Magnetic ; Insertion ; Brain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Our laboratories are developing a new technique for delivering localized hyperthermia to deep-seated brain tumors. In this technique, a spherical thermoseed is stereotactically navigated through the brain and tumor tissues via the noncontact application of an external magnetic force. The force required to produce motion of a 3 mm diameter sphere through in vitro brain tissues was measured to be 0.07 ± 0.03 N. This result was obtained from a series of experiments performed on whole brain specimens extracted from adult canines. Data were also taken with a 3 mm × 3 mm cylinder and a 5 mm sphere. An experimental procedure simulating physiological conditions was developed prior to testing. Evaluations of systematic effects included determinations of the calibration uncertainties, tests of the dependence of the measured force on temperature, and studies of the effects of method of storage of the tissue specimens. The results obtained are compared with (and confirmed by) two different series of experiments performed in vivo on adult canines and with another series of experiments using brain phantom gelatin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368444
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  • 8
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    Magnetic manipulation instrumentation for medical physics research (1994)
    American Institute of Physics
    Details
    Publication Date: 1994-03-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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  • 9
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    Torsion balances, torsion pendulums, and related devices (1993)
    American Institute of Physics
    Details
    Publication Date: 1993-02-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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  • 10
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    Magnetically suspended centrifuge for studies of nonlinear phenomena in stratified fluids: Developmental aspects (1989)
    American Institute of Physics
    Details
    Publication Date: 1989-10-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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