摘要:

A laser crossed‐beam anemometer has been applied to the study of capillary blood flow. Analysis of the various contributions to theS/Nratio of this system is presented, in which the effect of finite detector area is taken into account. Experimental data, takeninvivofrom a rabbit omentum, using a coherent frequency tracker, are included. The frequency tracker also serves as a particularly effective phase‐lock detection system, based upon the rotation of the relative polarization of the two incident beams. The data processing circuits are gated synchronously with the cardiac pulse, thus allowing measurement of flow velocity as a function of phase in the cardiac cycle. In spite of the considerable optical phase distortion incurred upon passage of the laser beams through the tissue covering the blood vessels, the autocorrelation of the fringe field (’’fringe visibility’’) remained high enough to permit useful velocity measurements. Rotation of the fringe direction allows measurement, with a one‐dimensional velocimeter, of randomly oriented flows.

ISSN:0034-6748    

DOI:10.1063/1.1136255

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An apparatus is described which can make force vs. displacement measurements on regions of a living cell. A force on the order of 10−3dyne is applied by a stylus to an area of about 10 &mgr;m2on the upper side of a cell growing on a culture dish. The resulting deformation is deduced from a solution conductance measurement with a sensitivity of 0.1 &mgr;m. The technique is compatible with optical microscopy and electrophysiological recording.

ISSN:0034-6748    

DOI:10.1063/1.1136256

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper presents the description of a pneumatically‐operated particle ejector and its performance under atmospheric ambient conditions. The ejected 100‐&mgr; particles are observed to remain an aggregate for approximately 10 ms prior to dispersion. The particles move at the initial velocity for a short initial period. This observation can be verified by a mathematical analysis. The instant of time at which the particles leave the ejector can be determined within approximately 1 ms.

ISSN:0034-6748    

DOI:10.1063/1.1136257

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We describe an instrument that images the Alcator A tokamak plasma in the soft x‐ray energy range with high temporal resolution. Radiation from a cross section of the plasma column is detected by an array of seventeen surface barrier detectors which provides 1 cm poloidal spatial resolution over a 16 cm field of view. The instrument’s nominal sensitivity lies in the spectral range from 0.27 to 25 keV; this range includes much of the radiation emitted by the Alcator A plasma, whose core temperature is typically in the 0.6 to 1.1 keV range. The frequency response of the detector‐electronics system extends from dc to 170 kHz. We discuss: (1) some design considerations and instrument calibrations, including the instrument’s measured response to 0.28, 1.5, 8.0, and 17.5 keV x‐rays and its theoretical response to a bremsstrahlung spectrum; (2) the detector‐electronics noise levels under various conditions; (3) the instrument’s response to an electrically modulated x‐ray source; (4) the detector x‐ray response as a function of bias voltage and temperature; (5) the detector linearity of response to 1.5 keV x‐rays; and (6) the stability of the detector x‐ray response despite numerous and prolonged vacuum breaks. Sample data, obtained from Alcator A discharges, are presented.

ISSN:0034-6748    

DOI:10.1063/1.1136258

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A variable temperature (4.2 K to 300 K) micromagnetic susceptometer has been designed to maximize sensitivity to the magnetic flux produced by small samples. The susceptometer is based upon a superconductive flux sensor which measures the magnetic flux through a set of coils due to a sample magnetized in a uniform field. A minimum measurable volume susceptibility of 7.5 ×10−8(emu) for a 1 microgram sample of curium has been achieved giving an increase in sensitivity of two orders of magnitude over Faraday devices designed for microgram metallic samples.

ISSN:0034-6748    

DOI:10.1063/1.1136259

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Soft x‐rays (2 to 6 keV) have been observed from transition radiators using electrons at energies of 104 and 66 MeV. The observed spectra agree well with theory. Various stacks of mylar of 2.5, 3.5 and 6.35 &mgr;m thickness were used to produce the radiation. Optimum foil thicknesses and number were calculated and found experimentally to be correct.

ISSN:0034-6748    

DOI:10.1063/1.1136260

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An apparatus is described in which hydrogen atoms were trapped at temperatures down to 1.1 K in the 11 T field of a large volume superconducting magnet. A high sensitivity thermal detector was used to study trapping and recombination of atoms on the detector surface. The apparatus permits the application of extremely high steady state magnetic fields to study the potential effects of electron spin polarization on the stabilization of hydrogen atoms.

ISSN:0034-6748    

DOI:10.1063/1.1136261

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

LEED intensity curves between 0–50 eV contain sharp peaks due to electronic surface resonances. Successful comparison with theory requires an accurate knowledge of the incidence angles and energy resolution ≲0.15 eV. It is shown that these requirements can be achieved with a conventional LEED system. The resolution was obtained by doubly modulating the four grid retarding optics and the electron gun. The incidence angles were found with a simple photographic technique.

ISSN:0034-6748    

DOI:10.1063/1.1136262

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Discharging a capacitor through a constant current ballast into a fuse device provides a repeatable method for fuse characterization. The energy required to burn out the device is easily calculated from the area under the voltage trace. A simple, novel circuit provides this constant current pulse which is self‐terminating.

ISSN:0034-6748    

DOI:10.1063/1.1136263

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A high sensitivity vibrating reed magnetometer useful for measurements on very small ferromagnetic particles is described. The reed is made of gold wire (18 &mgr;m in diameter, 10 mm long). The mechanical vibrations of the reed are converted directly to an ac voltage by a piezoelectric ceramic. Using a lock‐in amplifier magnetic moments as small as 10−9Acm2can be detected.

ISSN:0034-6748    

DOI:10.1063/1.1136264

出版商:AIP    

年代:1980

数据来源: AIP