摘要:

Tests to determine the usefulness of carbon felt as a cold cathode in high repetition rate x‐ray systems are described. Application of these test results to design and operation of an x‐ray preionizer for an excimer laser system has resulted in a simple, reliable x‐ray source which can be used at pulse rates up to 500 Hz for >2×107shots before the carbon felt must be replaced.

ISSN:0034-6748    

DOI:10.1063/1.1137416

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An electronically sampled vibrating‐reed dc electric field sensor of the chopping field‐mill variety is described. The compact, battery powered, self‐contained sensor, which can be imbedded in any electrode surface, is capable of measuring true dc fields up to the 106V/m range over an indefinite period of time; however, continuous peak sampling of the chopped periodic signal allows transients on the order of 10 ms to be monitored. Measurement in the presence of ionic space charge is made possible by keeping all structural components exposed to the field at a single equipotential.

ISSN:0034-6748    

DOI:10.1063/1.1137417

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simplified vibrating‐reed technique for the measurement of the temperature dependence of Young’s modulus of small thin samples is described. The vibration of the reed is detected optically rather than with a capacitively coupled electrode as has been used by previous investigators. The optical coupling greatly simplifies the sample stage and electronic circuitry. It is made possible by the use of a microminiature Joule–Thomson‐effect refrigerator which mounts directly onto theX–Ystage of a metallurgical microscope. Because of the refrigerator’s small size and lack of mechanical vibrations, the high‐quality room temperature optics of the microscope can be used to detect the small amplitude vibration of the reed over a wide temperature range. We observe the Curie and Neel points of the magnetic phase transitions of terbium atTc=221 K andTN=233 K, respectively. In addition, we measure Young’s modulus at 280 K to be 5.90×1011dyn/cm2.

ISSN:0034-6748    

DOI:10.1063/1.1137418

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An airflow resistivity instrument features a novel specimen holder, especially designed forinsitumeasurement on the earth’s ground surface. This capability eliminates the disadvantages of prior intrusive instruments, which necessitate the removal of a test specimen from the ground. A prototype instrument can measure airflow resistivities in the range 10–5000 cgs rayl/cm, at specimen depths up to 15.24 cm (6 in.), and at differential pressures up to 2490.8 dyn/cm2(1 in. H2O) across the specimen. Because of the close relationship between flow resistivity and acoustic impedance, this instrument should prove useful in acoustical studies of the earth’s ground surface. Results of airflow resistivity measurements on an uncultivated grass field for varying values of moisture content are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137419

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In measuring thermophysical properties using the transient calorimetric method, conduction heat leak from test specimens can be a source of error if not properly accounted for. An analysis method is presented in this paper for determining the magnitude of this leak. The analysis consists of deriving the temperature profiles in the specimen support. These temperatures are then used to determine the heat leak using two different approaches. In the first approach, the heat penetration depth in the support is derived and used to obtain an added thermal capacitance to the specimen. In the second approach, the heat leak was considered to reduce the net heat input. Both small and large heat‐leak cases were analyzed, with the latter estimated by means of two recurrence relations. A chart was also developed for a rapid estimation of this leak. In the absence of a reliable experiment to measure the heat leak, this paper provides a viable alternative for accurate leak determination.

ISSN:0034-6748    

DOI:10.1063/1.1137415

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Hysteretic heating of the crack tip often occurs during tests of fatigue crack propagation. If hysteretic heating occurs to a significant extent at and ahead of the crack tip in a notched polymer specimen, fatigue crack propagation behavior may be altered in a complex way. It is, therefore, important to monitor the temperature at crack tips during testing. Methods of temperature measurement are reviewed, and a semiautomated apparatus incorporating an infrared microscope for measuring temperature profiles during fatigue tests is described.

ISSN:0034-6748    

DOI:10.1063/1.1137420

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In this article improved grid holders for use in a multipurpose electron microscope stage are described. Two models, made from copper, bronze, or brass, both allowing cooling and tilting, provide either (1) a heating capability with the grid in a strip configuration or (2) a full‐circle grid without the heating facility. The mechanical stability, electrical, thermal, and anticontamination characteristics, and tilt movements are excellent.

ISSN:0034-6748    

DOI:10.1063/1.1137421

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We constructed a simple polarizing microscope in which the sample temperature can be controlled with an accuracy of 10−3 °C from room temperature to about 60 °C. The temperature stability at a sample was directly assessed using the temperature‐dependent birefringence of a liquid‐crystal sample.

ISSN:0034-6748    

DOI:10.1063/1.1137422

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This paper investigates the long‐term stability of three different types of thermistor with room‐temperature resistances ranging from 80 to 150 k&OHgr;. Precision measurements of thermistor resistance and temperature were made in a thermal environment controlled to ±3 &mgr;K. Measurements took place in between periods of limited thermal cycling and also during 100 days at constant temperature. Mechanical shock and strain appear to be the cause of the high drift rates observed in some thermistors; the majority of the thermistors were, however, very stable, with drift rates around 0.1 mK per 100 days and were unaffected by thermal cycling. Such low drift rates indicate that certain thermistors could be used as convenient temperature transfer standards with a reproducibility in the submillikelvin range.

ISSN:0034-6748    

DOI:10.1063/1.1137423

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A small probe utilizing the attenuation of the beta emissions from promethium‐147 has been constructed and calibrated for measuring the suspension concentration of dusts in the range of 0.1 to 2.0 kg/m3. The absorption of beta particles (negatively charged electrons) is related to the amount of matter through which the particles pass. The probe discussed here measures the beta absorption through a 3.8‐cm path length at sample rates up to 20 samples per second. The small size of the probe (16 cm overall) allows real‐timeinsitulocal measurements of the suspension of a dust. The basic theory of operation and details of the probe operation are presented. Data from the probe for use in dust flammability experiments are also presented.

ISSN:0034-6748    

DOI:10.1063/1.1137424

出版商:AIP    

年代:1983

数据来源: AIP