摘要:

An ac calorimeter is developed for the measurement of heat capacity in liquid including the aqueous suspension of biological materials in the temperature range between 270 and 400 K. Using this apparatus we perform the measurement of heat capacity at the main phase transition of lipid suspended in water. Additionally a new method to determine the absolute value of the heat capacity is proposed.

ISSN:0034-6748    

DOI:10.1063/1.1137546

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simple conductimetric method for measuring the hematocrit value of blood is described. Using a conventional electronic conductivity meter having a two‐electrode cell, the conductivity between the electrodes dipped in a diluted sample of the blood is measured and related quantitatively to the strength of suspended erythrocytes (that is, to the hematocrit value) in the test suspension. The extent of diluting the sample prior to the measurement is optimally determined on the basis of theoretical considerations. The merits of this instrumentation in terms of simplicity, economy, and linearity are compared with those of conventional methods of hematocrit determination. Possibilities of improving the present method by using inductive‐type conductivity meters and/or by using vhf (very high frequency) resonant circuit sensors are suggested. Relevant theoretical considerations and experimental results are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137547

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The ac in‐phase and out‐of‐phase response of type II superconductors is discussed in terms of dc magnetization curves. Hysteresis in the dc magnetization is shown to lead to a dependence of the ac response on the rate at which an external field is swept. This effect allows bothHc1andHc2to be measured by ac techniques. A relatively simple mutual inductance bridge for making such measurements is described in the text, and factors affecting bridge sensitivity are discussed in the Appendix. Data for the magnetic superconductor ErRh4B4obtained using this bridge are reported.

ISSN:0034-6748    

DOI:10.1063/1.1137548

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A sound resonator is described which allows concentration measurements in binary‐gas mixtures. The apparatus is particularly useful for relative measurements between a mixture and a pure gas.

ISSN:0034-6748    

DOI:10.1063/1.1137549

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A method for measuring magnetoresistance of metals and metallic alloys in a pulse magnetic field of high intensity is presented. The accuracy of the sample magnetoresistance &Dgr; &rgr;/&rgr;0is ±12% and ±5% for &Dgr; &rgr;/&rgr;0values of 10−3and 10−1, respectively. This accuracy can be achieved for sample resistances of the order of 10−1–102&OHgr;.

ISSN:0034-6748    

DOI:10.1063/1.1137550

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The infrared spectra of the antisymmetric stretching bands of dilute solutions of nitrite and nitrate ions in sodium bromide are proposed as pressure gauges for use with anvils and other apparatuses. Their frequencies, which are at 1279.0 and 1401.3 cm−1respectively at zero pressure, were measured up to 186 kbar relative to theR1fluorescence line of ruby. The pressure is related to the shift &Dgr;&ngr; of the frequency of the nitrite ion at 22 °C from the zero‐pressure value by the equationp/kbar=2.356(&Dgr;&ngr;/cm−1)−1.334(&Dgr;&ngr;/cm−1)exp(−&Dgr;&ngr;/92 cm−1), and to the shift &Dgr;&ngr; of the frequency of the nitrate ion by the equationp/kbar=1.775(&Dgr;&ngr;/cm−1)−0.7495(&Dgr;&ngr;/cm−1) ×exp(−&Dgr;&ngr;/78 cm−1). Both equations were fitted by least squares, assuming that the error is in the pressure only, and the standard deviation of the pressure is 1.1 and 1.4 kbar, respectively.

ISSN:0034-6748    

DOI:10.1063/1.1137551

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In order to investigate the phase behavior of mixtures at high pressures we have developed a system consisting of a diamond‐anvil cell with a high‐pressure vessel to match. The diamond cell can be filled at room temperature and pressures up to 10 kbar with a gaseous mixture of known composition. The cell is constructed such that a constant volume method can be used to measure the dew‐ and bubble‐point curves of a mixture.

ISSN:0034-6748    

DOI:10.1063/1.1137563

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The stability of 12 commercial carbon resistance thermometers has been tested at three temperatures, 12.6, 20.3, and 30 K, when the sensors were exposed to cycling between 12.6 and 293 K. The resistances of the thermometers changed markedly over 20 such cycles by amounts equivalent to temperature changes of between 0.07 and 0.57 K at 20.3 K. Both abrupt and gradual changes were observed. A few measurements were made at 4.2 K to explore the correlation between changes in resistance at various temperatures. A two‐point recalibration method is shown to be accurate to 1 mK over the range 12.6 to 30 K and can be used to 4.2 K.

ISSN:0034-6748    

DOI:10.1063/1.1137552

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Two infrared radiometers were constructed for use in shock wave and detonation research. Fast detectors were combined with wide‐band amplifiers to achieve an overall response of about 5 ns, which was confirmed by experiments on planar shocked copper plates. Detonation experiments show the merits of a new optical technique for probing detonation wave structure and for reactive and nonreactive shock wave research.

ISSN:0034-6748    

DOI:10.1063/1.1137553

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An experimental technique for directly measuring strain‐induced stiffening effects in individual carbon fibers has been developed. The technique involves the superposition of a small amplitude oscillating strain (&Dgr;&egr;∼10−4) on a slow linearly increasing strain (∼1.1×10−3s−1). Synchronous detection of the resultant ac component of the measured stress yields a signal proportional to the slope of the stress versus strain curve provided the modulation amplitude is small compared to the ultimate strain at failure (∼0.005). The experimental arrangement has been designed for use in conjunction with an Instron tensile test apparatus. A novel design for a fiber gripping apparatus which permits direct measurement of the strain is also described. The technique has been applied to carbon fibers produced from two different precursor materials: polyacrylonitrile and mesophase pitch. Fibers from both precursors exhibited strain‐induced stiffening. The modulus of the pitch‐based fibers increased in proportion to the square root of the strain, whereas that of the PAN‐based fibers showed an almost linear increase.

ISSN:0034-6748    

DOI:10.1063/1.1137554

出版商:AIP    

年代:1983

数据来源: AIP