摘要:

Techniques are described for making large ultrahigh vacuum beryllium windows for use in synchrotron radiation installations. Procedures are given for affecting both hard brazed seals and demountable seals involving either lead or copper gaskets. Brazed seals can be made to either stainless steel or copper. Possible alternative methods are suggested.

ISSN:0034-6748    

DOI:10.1063/1.1139060

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A commercial scanning acoustic microscope operating in the frequency range of 50–2000 MHz is described. It has a stable scan mechanism suitable for the high‐frequency end to give high‐resolution images and modes to allow for material characterization at the low‐frequency end. The high‐frequency electronics permitting a wideband operation with a variety of acoustic lenses are described. Microprocessors control many parts of the the instrument to release the user from the routine adjustments, resulting in a user‐friendly interface. Images are presented to show the resolution and penetration abilities of the instrument at several frequencies, along with comparative optical images.

ISSN:0034-6748    

DOI:10.1063/1.1139061

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A magnetic monopole detector with a sensitivity range down to extremely small magnetic charge is described. Backgrounds in the detector are discussed and representative background distributions are given. Appropriate steps to minimize these backgrounds are detailed. The region of sensitivity of the detector to magnetic monopoles in terms of monopole charge and monopole mass is given.

ISSN:0034-6748    

DOI:10.1063/1.1139062

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

This paper describes an assessment of the behavior of a differential scanning calorimeter and the development of satisfactory calibration, operation, and data reduction procedures, which depend on performance characteristics of the individual instrument. Factors that contribute to thermal lag are identified; suggestions for evaluating and compensating for it are given.

ISSN:0034-6748    

DOI:10.1063/1.1139063

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new instrument is presented for measuring complex adiabatic compressibility and adiabatic pressure‐induced temperature variation (∂T/∂P)Sof liquids in the low‐frequency range from 0.5 Hz to 2 kHz. The relative accuracy of the measurement is of the order of 10−3–10−4. The velocity and absorption coefficient of sound in the low‐frequency range give us information on slow relaxational phenomena. (∂T/∂P)S, which is directly related to the ratio of thermal expansion coefficient to specific heat, can be measured accurately by ac method. The measurement of these quantities provides us with new information on thermodynamic or low‐frequency relaxational behavior of liquids, including critical liquids, liquid crystals near their phase transitions, and biological materials.

ISSN:0034-6748    

DOI:10.1063/1.1139064

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The design and operation of a graphite element drop‐tube reactor system for a study of the fundamental mechanisms and reaction rates of sulfur dioxide (SO2) removal by high‐temperature injection of limestone‐based sorbents is described. The reactor system is designed for laminar flow in an environment that allows for control of reaction temperature, sorbent particle residence time, and atmosphere composition. The sorbent injection system allows variable feed rates to as low as 1 mg/min for particles as small as 1 &mgr;m in diameter. The water‐cooled sorbent collection system arrests the high‐temperature reaction upon capture and allows analysis of the sorbent’s efficiency of SO2capture andinsituparticle‐size distribution. The results presented show the reactivity of different types of sorbents at varying conditions of system operation.

ISSN:0034-6748    

DOI:10.1063/1.1139065

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A simple, efficient helium‐3 cryostat for Mo¨ssbauer spectroscopy based on a closed‐cycle carbon sorption pump is described. An unexpected variation of the minimum available temperature as a function of measurement time is described and explained as a hydrostatic pressure effect connected to the density maximum of liquid helium‐3 at 0.515 K.

ISSN:0034-6748    

DOI:10.1063/1.1139066

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A simple diode bridge used as a temperature sensor with an accuracy of ±0.5 °C in the temperature range of 25–100 °C has been fabricated and tested. It was first realized using commercially available breadboard transistor arrays and then in two monolithic integrated circuits which differ in the forms of the contact holes. The performance and limitations of these sensors are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139067

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A computer‐assisted instrument was constructed to measure the fundamental physical properties that regulate water transport at the cell level in plants. With this automated pressure probe, we measure a cell’s hydrostatic pressure by inserting an oil‐filled glass capillary into the cell. The capillary is connected to a pressure sensor and to a plunger controlled by a stepper motor. At the capillary tip an interface forms between the cell sap and oil. The image of this interface is directed through a microscope to a video camera. The interface position is detected by a video processor sampling at 60 Hz and is regulated by a microcomputer which advances or retracts the plunger at rates up to 280 steps per second. To determine the hydraulic conductance of cell membranes, the computer carries out pressure‐relaxation and pressure‐clamp experiments. Pressure is recorded with a resolution of 0.02 bar and is regulated in pressure‐clamp experiments at ±0.02 bar. The instrument measures the cell volumetric elastic modulus by injecting or removing small volumes from the cell while simultaneously measuring cell turgor pressure. This system was tested on the cells of pea seedlings and proved superior to the previous techniques, especially for pressure‐clamp experiments and volumetric elastic modulus determinations.

ISSN:0034-6748    

DOI:10.1063/1.1139068

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A theory for the dynamic balancing of the double thin‐film arms Wheatstone bridge, when both of its sensor arms are growing in thickness in vacuum, has been developed. Rate of growth of the imbalancing signal, bridge sensitivity at the null balance, and its decay with the growth of the sensor arm thickness are derived and discussed. It is shown that as long as the bridge remains dynamically balanced, the ratio of the deposition rates of the films on the sensor armsRandSis proportional to the external resistance ratioP/Q. Hence, if the bridge is kept balanced by the feedback system, the composition of the film codeposited on a common substrate will remain constant which can, however, be varied by changing the ratioP/Q. An experiment was performed to test the validity of this theory by evaporating Cu and Cr separately on the two sensor arms of the bridge in the same vacuum chamber. The vapor pressures of both the metals were recorded simultaneously by a RGA scanning 50–70‐amu range. It was found that as long as the bridge remains balanced, the ratiopCu/pCrremains constant. In contrast, when the bridge is imbalanced with either polarity,pCu/pCrvaried in either direction from this constant value. Further, for a ±10% deviation in thepCu/pCrfrom the constant ratio, the signal grows at a rate of ∼10 &mgr;V s−1. This signal is found to be capable of electronic feedback control of the evaporation system.

ISSN:0034-6748    

DOI:10.1063/1.1139069

出版商:AIP    

年代:1986

数据来源: AIP