摘要:

The possibilities for the use of a scanning force microscope as a machining tool for the modification of gold surfaces were investigated. For this purpose, a scanning force microscope for the creation of structures with constant load and with a force modulation technique was constructed. With this instrument, we are able to create and characterize structures like lines and circles in thin gold films on mica. Especially the force modulation technique is suitable for producing structures with well defined geometry. Further investigations of the shape and the stability of the structures were made. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147632

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel miniature superconducting quantum interference device magnetometer with direct readout electronics has been developed. A high flux-to-voltage transfer factor of up to2500  &mgr;V/&Fgr;0is achieved without additional positive feedback (&Fgr;0is the flux quantum). A flux resolution of8×10−7 &Fgr;0/Hz1/2, corresponding to a magnetic moment sensitivity of approximately2×10−20 A m2/Hz1/2, has been measured. This magnetometer can be used to study the dynamic magnetization properties (including nuclear magnetic resonance and magnetic resonance imaging) of micron and submicron size particles and for high-resolution surface magnetometry. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147633

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An electronic circuit is described that allows the use of an inexpensive Hall probe as a high-performance magnetic-field sensor. The circuit contains a high-precision voltage reference, a proportional control thermostat, a 16 bit serial analog-to-digital converter, and a digital control subsystem integrated into a single programmable logic device. The precision of the probe is of about 4 &mgr;T. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147634

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The pulsed nuclear magnetic resonance (NMR) field measurement system is suitable for high-accuracy field homogeneity measurement for accelerator dipole magnets. The measurement has to use NMR probes as small as a few mm in diameter. The coaxial cable connecting the NMR probe and preamplifier has a length of 10 m or more. The coaxial cable has to be treated as a distributed-constant circuit for high-field measurement. We studied the optimum condition of the radio-frequency signal propagation in the coaxial cable, and found that a cable length ofn&lgr;NMR/2(n=1,2,&ellip;) gives optimum propagation characteristics. In accordance with this result, we designed and fabricated a prototype field measurement system using pulsed NMR. The use of a phase-locked loop circuit facilitated the measurement of the frequency of the free-induction-decay signal. To confirm the performance of this system, the magnetic field in the 2 T region of the superconducting solenoid magnet was measured with the NMR probe of which the shape was a cylinder of 4 mm in diameter. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147952

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This paper presents closed form equations based on a modification of those originally derived by Paros and Weisbord in 1965, for the mechanical compliance of a simple monolithic flexure hinge of elliptic cross section, the geometry of which is determined by the ratio &egr; of the major and minor axes. It is shown that these equations converge at &egr;=1 to the Paros and Weisbord equations for a hinge of circular section and at &egr; ⇒∞ to the equations predicted from simple beam bending theory for the compliance of a cantilever beam. These equations are then assessed by comparison with results from finite element analysis over a range of geometries typical of many hinge designs. Based on the finite element analysis, stress concentration factors for the elliptical hinge are also presented. As a further verification of these equations, a number of elliptical hinges were manufactured on a CNC milling machine. Experimental data were produced by applying a bending moment using dead weight loading and measuring subsequent angular deflections with a laser interferometer. In general, it was found that predictions for the compliance of elliptical hinges are likely to be within 12&percent; for a range of geometries with the ratio&bgr;x (=t/2ax)between 0.06 and 0.2 and for values of &egr; between 1 and 10. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147635

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The wavelet transform has emerged as an important tool for the analysis of intermittent and nonstationary signals. This article addresses implementation issues of a digital continuous wavelet transform that is sufficiently general that any continuous wavelet can be used. Working equations are derived for wavelet sampling, aliasing, and scale population by using the band-pass filter interpretation of wavelet functions. The implementation procedure is applied to the Morlet wavelet in detail as an example. Finally, the Morlet wavelet is applied to velocity fluctuations measured in a subsonic wake undergoing transition to turbulence. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147636

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as10−4can be created and held stable for extended periods of time. Dimensional control of the liquid bridges approaches one part in10−4for the aspect ratio and volume. The apparatus has been tested by measuring the static stability limits of axisymmetric bridges and comparing the results with previous theoretical predictions. Experimental error for the apparatus is &dgr;Bo/Bo=0.03,&dgr;&Lgr;/&Lgr;=0.001and&dgr;V/V=0.001, where Bo is the Bond number, &Lgr; is the aspect ratio of the bridge, andVis the dimensionless (relative) volume of the bridge. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147637

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A microcalorimetry technique allowing one to measure the specific heat of bulk single crystals of a mass typically10 &mgr;g, with a relative resolution&Dgr;c/cof10−4is presented. The well known ac steady state technique is employed. The sample holder is a polymer membrane with lithographically patterned thermometer and heaters made out of metallic thin films. The diameter of the useful area is 0.6 mm and the specific heat of the addendum is1.5 &mgr;J/Kat 100 K. The sample is thermally coupled to the membrane through a gold thin film sputtered on its surface. The thermal coupling time constant of the sample is∼5 ms, allowing to work at frequencies of 10 Hz. The method was applied to small single crystals of YBCO, providing the specific heat jump at the superconducting transition with a relative resolution of10−2and a precision of10−1. The method is optimized at the temperature range 40–160 K, but can easily be modified for lower temperatures. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147938

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermal conductivity of nickel and gold films on quartz (thickness 0.4–8 &mgr;m) was measured by a modulated thermoreflectance technique recording the surface temperature profile. Model calculations predict an optimum frequency for measuring thermal transport within the film. Measurements on films with various thicknesses reveal a thermal conductivity close to the bulk value for nickel while gold films exhibit a reduced conductivity with decreasing film thickness. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147638

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the development of a technique to measure transport properties using a new diamond anvil cell and helium as pressure transmitting medium to ensure hydrostatic conditions. The chamber pressure is measured at any working temperature below 300 K by the ruby fluorescence method. This technique has been used to pressures up to 3 GPa atT=5 K to measure the effect of hydrostatic pressure and magnetic field on the superconducting transition temperature of a single crystal of the anisotropic cuprate superconductor Bi2.1Sr1.9−yLayCuO6+&dgr;. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147639

出版商:AIP    

年代:1997

数据来源: AIP