摘要:

A new method that allows real time determination of the velocity of a sphere moving through a liquid in high pressure Stokes’ viscometry studies is described. Our electro‐detection method relies on the electrical conductivity contrast between sphere and liquid. The method has been tested on a jadeite melt at pressures of 2.4 and 2.9 GPa and at temperatures of 1350 and 1450 °C, respectively, and yields viscosities (with an associated error of 25%) which are consistent with those determined by the quench and probe method. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1146125

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new rheometer is described. It consists of a transducer unit supplied with an electric impedance analyzing unit. The transducer unit converts a mechanical impedance into an electrical impedance by the piezoelectric effect. A detailed quantitative analysis of the interaction between the sample and the transducer is given. The real and imaginary parts of the shear modulus of a viscoelastic sample can be found in the frequency range of 1 mHz–50 kHz, modulus range of 0.1 MPa–10 GPa, and the temperature range of 150–300 K. The sample volume is 0.3 cm3and the strain amplitude is exceedingly small. The small size of the transducer allows for good temperature control and equilibration. It has a simple construction based on inexpensive components. Results on the supercooled liquid 2‐metyl‐2,4‐pentandiol at the glass transition obtained by the method are included. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146126

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Shock wave speeds are often measured by comparing arrival times at the tips of electrical shorting pins in a hexagonal array over two elevations (called up and down). In the conventional arrangement, the center pin is solely responsible for measuring the curvature of the wave front. Without this datum the shock speed cannot be precisely determined. In some experiments this pin fails frequently enough to be a problem. We report a simple rearrangement between up and down designated pins which eliminates the critical reliance on a single pin. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146523

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this paper we characterize the behavior of a new pulsed gas lens, the colliding shock lens. We show how input energy, electrical diameter, number of discharge electrodes, and enclosing the discharges, affect its optical aperture and focal length. Experimental results are presented for three different lenses and for a 1 cm aperture lens with a focal length of 1.5 m. We derive a simple colliding shock lens scaling law. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146127

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An innovative concept for decentralized processing of the signals of multiple sensors is presented. The basic idea is to connect every sensor via an analog‐to‐digital converter with a high‐performance microprocessor, a transputer, that exclusively collects and processes its signal. The transputers are linked to a powerful network. Exemplarily, a measuring system based on this concept was used for the determination of local parameters of liquid–gas two‐phase flows (e.g., local void fraction and bubble frequency). Up to six fiber‐optical probes were utilized simultaneously to demonstrate the efficiency of the system. The signal processing under that special application may include on‐line evaluation of flow parameters and on‐line correction of errors of measurement due to sensor‐induced effects. The concept of the new system, however, is basically independent of the number and type of sensors, as well as of the method of signal processing. The transputer‐based measuring system thus provides a flexible, efficient tool for applications in which great amounts of data have to be evaluated or manipulated quickly. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146128

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Measurements are recorded for multiwire thermocouples consisting of either two or three wires of unequal diameters. Signals from the multiwire probe are recorded for a reversing gas flow with both a periodic temperature and time constant fluctuation. It is demonstrated that the reconstructed signal from the multiwire thermocouple requires no compensation provided &ohgr;/&ohgr;1<2.3 for two wires or &ohgr;/&ohgr;1<3.6 for three wires where &ohgr;1(=2&pgr;f) is the natural frequency of the smaller wire based on the maximum gas velocity. The latter results were possible provided Fourier transformed data from the wires were used and knowledge of the gas velocity phase angle was available. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146129

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The paper deals with the difficulties of reconstructing a hydrodynamic structural function from a time‐dependent raw signal produced by a sensor. In the presence of two fluid phases, the deformation of a phase interface at a sensor leads to a lag between the occurrence and the detection of the event, and the probe response characteristics may be altered with time for several reasons. A new phase discrimination technique is presented based on man–machine interaction and utilizing genetic optimization. To discriminate the phases, two‐point threshold discrimination is proposed at first. In addition, a man–machine method is introduced which can mimic a human expert observation of a raw signal and his intuitive discrimination procedure. Finally, genetic algorithms are used to search for those threshold settings that produce solutions closest to those defined by an expert. The proposed new method is capable of adaptation to specific flow conditions. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146130

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The assumption of zero contact angle of the Wilhelmy plate method causes error for the surface pressure‐area characteristics of some spread monolayers. To avoid this problem, a video‐enhanced plate method is developed to monitor the dynamic surface tension and contact angle simultaneously. According to this method, the profile of the air–water interface adjacent to a flat plate is captured by an image digitization technique. The surface tension and contact angle are obtained from the best fit between the edge coordinates of the captured image and a theoretical equation derived from the Young–Laplace equation. Preliminary results show satisfactory agreement between the curve of the air–water interface obtained from experimental data and the theoretical curve for obtained values of surface tension and contact angle. Twenty tests for pure water at 25 °C give an average surface tension 72.0±0.2 mN/m, which confirms the accuracy of this method. A preliminary dynamic test also indicates that the effect of the contact angle in the Wilhelmy method can be corrected by dividing the apparent surface tension obtained from the Wilhelmy method by the cosine of contact angle measured by the present method. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146131

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Areas of solid surfaces as small as 1 cm2were determined by krypton adsorption at liquid nitrogen temperature using an adsorption apparatus with a temperature‐compensated, differential tensimeter of symmetrical design. The BET monolayer volume of krypton for 50, 100, or 150 of 1 mm steel ball bearings was proportional to the number of balls used. The coefficient of proportionality agreed with the result on 10 000 ball bearings. The surface area of 50 ball bearings is to 1.57 cm2, which suggests that it is feasible to measure surface areas as small as 1 cm2. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146132

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new, phosphorescence‐based optical instrument for making oxygen tension (PO2) measurements in individual vessels of microvascular preparations is described. Palladium–porphyrin compounds injected into the systemic vasculature are excited by light and the measured phosphorescence emission lifetime used to calculate intravascular PO2. Because this technique is relatively new, we have undertaken a rigorous examination of its usefulness and inherent limitations for microvascular studies. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146133

出版商:AIP    

年代:1995

数据来源: AIP