ISSN:0034-6748    

DOI:10.1063/1.1751595

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

The electrical motor drive and the magnetic support for the vacuum type ultracentrifuge have been revised and improved. The drive is a two‐phase motor and the support a solenoid which attracts a solid steel cylinder fastened to the rotating parts. The armature of the motor consists of a solid steel cylinder and a magnetic core support mounted coaxially on a stainless steel tubular shaft. Cooling water passes through the tubular shaft. A two‐phase salient pole stator produces the rotating magnetic field when actuated by the output of a transitron oscillator and power amplifier. Condensers in series with the motor field windings split the phase and match the load to the power amplifier. At an oscillator frequency of 1188 cycles per second and an input to the motor of 1 kw, the rotating magnetic field produces a torque of 600 g‐cm throughout the starting period up to about 10 percent slip (about ½ hp at 1000 r.p.s.). A 7½‐lb rotor (6¼″ diameter, moment of inertia of 81,000 g‐cm2) has been accelerated to 1000 r.p.s. in about 18 min. Upon reaching the desired operating speed, a slip speed control actuated by a magnetic pick‐up on the centrifuge shaft sharply reduces the power input to the motor and automatically holds the rotational speed constant to within 0.05 percent. When the slip is not too large, the mechanism provides a satisfactory ultracentrifuge drive which is ``run‐away proof'' and which automatically maintains its speed within ½ r.p.s. from day to day.

ISSN:0034-6748    

DOI:10.1063/1.1751596

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

The conditions affecting the reproducibility of a thin‐walled all‐glass type counter used with the Neher‐Harper quenching circuit have been investigated. The plate voltage and grid bias on the quenching tube are the most critical factors, and experimental arrangements for holding them constant are described. An upward drift in counting rate is noted at rates of the order of 100 per sec., and methods for minimizing the effect of this drift on the accuracy of the measurements are described. A new method of calibrating a counter circuit is used. The activity ofa sample of radon is measured under the same geometrical conditions at different times, and by use of the accurately known half‐life of radon, the counting losses at various speeds are determined. A variation of the multiple‐addition method of calibration is also used with concordant results. It is found that with proper precautions the counter can be used to measure counting rates in the range from 30 to 200 per sec. with an accuracy of 0.2 to 0.3 percent.

ISSN:0034-6748    

DOI:10.1063/1.1751597

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

The theory and design of an a.c. operated d.c. amplifier with large current output are presented. A d.c. phase inverter using cathode in‐phase degeneration drives the push‐pull output stage. The output is linear over a range of 160 ma.

ISSN:0034-6748    

DOI:10.1063/1.1751598

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

In the field of physiology, the measurement of action potentials is rapidly increasing in importance as time progresses. The paper describes recent progress in instruments adapted particularly for making low voltage measurements in this field. Detailed description is given of the integrating voltmeter, its characteristics and its use.

ISSN:0034-6748    

DOI:10.1063/1.1751599

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

To overcome the difficulties and limitations of earlier methods for obtaining absorption spectra of detailed microscopic structures, it has been found necessary to impose more rigid demands upon the monochromator and to introduce improvements in densitometry. The optical properties of the microscope and the spectral properties of the source together determine the requirements which must be made upon the monochromator. These requirements are analyzed and a convenient method of quantitative densitometry is described together with the results of a simple test of this method.

ISSN:0034-6748    

DOI:10.1063/1.1751600

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751601

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751603

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751604

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751605

出版商:AIP    

年代:1940

数据来源: AIP