摘要:

A signal generator is described that provides two oscillations of “almost” incommensurate frequencies, along with their sum and difference frequency. There is no phase drift between the outputs since all signals are generated from a single master clock. The concept is based on Fibonacci approximands to the golden mean. Technical implementation requires ordinary digital frequency dividers and a single phase-locked-loop frequency multiplier. Applications are measurements of weak nonlinearities in “almost linear” transfer functions. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148272

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A two-dimensional capacitive position transducer is described which hasx,yand angular outputs and a fixed zero. The prototype has submicron and arcsecond sensitivity, 10 mm range, and a nonlinearity of 0.1&percent;, which is easily corrected to 0.01&percent;. The transducer employs a synthetic dual full-bridge technique and is compact, easily fabricated, and suitable for use in cryogenic environments.©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148273

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. Thef/4probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148274

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A means for sensing relative position and speed of mechanically functional machine members having accessible ferromagnetic portions is described. The method is based on creating, sensing, and annihilating local transitions in the polarity of remanent magnetization in surface regions of such parts while in motion, in analogous fashion to conventional magnetic recording. The presence and location of a transition, sensible by its associated external field, constitutes stored information carried by the member. Bias and “erasure” are provided by a permanent magnet; transitions are “written” by pulsed currents through a coil on a gapped core and “read” by Hall-effect field sensors located at purposeful distances downstream. Transition position is determinable within ±0.1 mm. Velocity is determined by the elapsed time between a recording pulse and its detection. Experimental data from a polyurethane timing belt reinforced with cabled steel wires demonstrates system operation. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148275

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An advanced measurement method for the dynamic current voltage characteristics of fast transversely excited atmosphere excimer laser discharges is presented. In contrast to well-known numerical techniques, inductive components are eliminated from the measured discharge gap voltage directly during operation of the laser by means of a fast video amplifier circuit. Comparison of experimental data obtained from a laboratory KrF*excimer laser with theoretical data shows that the achieved resolution is sufficiently high to reveal actual halogen donor concentration and arcing in the discharge. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148282

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The formation of adducts resulting from interactions between protein ions and residual gases in an electrospray ionization ion trap/time-of-flight mass spectrometer is reported. This instrument utilizes diffusion pumps to achieve high vacuum, and we found that when silicon based diffusion pump fluids were used, characteristic adduct peaks appeared in the mass spectra. These adduct peaks were not detected, however, when a polyphenyl ether (Santovac 5) was used as the diffusion pump fluid. In switching the diffusion pump fluid to Santovac 5, a rigorous cleaning procedure capable of removing residual silicon pump fluid from the instrument was a critical step. This cleaning procedure can also be used for routine cleaning of the ion trap and other source components. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148276

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An accelerometer adaptor, for near field shock wave measurements, is described for applications in which the mounting structure undergoes elasto-plastic deformation. It is of simple construction, light, easy to install and remains attached on the mounting surface during relatively large deformations. The design overcomes the possibility of the accelerometer being projected from the mounting plate, which results from mounting directly on a plate surface. It was successfully employed for measuring peak accelerations up to 100 000g. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148277

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A cryogenically cooled sample holder and support assembly has been constructed for surface x-ray diffraction studies in ultrahigh vacuum. The design combines ease of sample replacementin situwith good mechanical stability and temperature control. This is achieved by locating a rectangular pin on the sample holder in a collet which can be closed from outside the vacuum chamber. Samples up to 10 mm square can be held at a constant temperature between 40 and 1300 K. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148283

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Under routine source conditions, the optimum nozzle-skimmer distance to achieve maximum molecular beam intensities is within the range of a few millimeters. In cases where double skimming is additionally required, the distance between the skimmers should be kept small in order to sample a sufficiently large solid angle of the beam and hence maintain a good enough intensity. These two facts make it normally difficult to isolate the first from the second expansion chamber using a commercial vacuum gate valve due to the lack of remaining space. This note presents the design of a vacuum-tight valve which allows the aperture of a skimmer to be closed by plugging a needle directly against its internal conical wall. The valve can be driven manually or pneumatically from outside the vacuum chamber. The helium conductance of the valve was measured to be better than1×10−8mbar×l×s−1for a helium partial pressure difference of 1 bar. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148284

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is shown that a simple rectangular filter is a good approximation to Wein’s optimal filter for improving the signal-to-noise ratio in a typical modulated reflectance spectroscopy experiment. This enables one to obtain identical information from data recorded with much smaller time constants for data averaging and therefore faster scan speeds. The limitations of this method are also discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148278

出版商:AIP    

年代:1997

数据来源: AIP