摘要:

Near a phase transition the rate of change with temperature of the specific heat and the thermal relaxation time can both become very large with resulting difficulties in the measurement of specific heat by conventional methods. This paper describes a calorimetry method specially adapted to overcome these difficulties, which has proved successful for measurements near the critical point of fluids.

ISSN:0034-6748    

DOI:10.1063/1.1686346

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The inlet and outlet temperatures and the block temperature of a discrete heat exchanger in a dilution refrigerator have been measured. Temperatures measured on the outgoing3He&sngbnd;4He stream were higher than temperatures predicted theoretically; this discrepancy has been attributed to viscous effects within the dilute3He&sngbnd;4He channel which degrade the performance of the heat exchanger significantly below 80 mK.

ISSN:0034-6748    

DOI:10.1063/1.1686347

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The design of an inexpensive ``boxcar'' integrator for improving the signal‐to‐noise (S/N) ratio of low level repetitive signals is described. The design is simplified by using the timing circuits of an oscilloscope to generate the gate and delay for the boxcar. The S/N ratio can be improved up to 60 dB. It is useful for signals from 500 &mgr;V to 30 mV rms containing frequencies up to 50 kHz, at repetition rates to several kHz. Examples of its use for sine and square waves are included.

ISSN:0034-6748    

DOI:10.1063/1.1686348

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A fast acting valve has been developed for quasisteady gas injection with a short rise time. The valve has a structure which is a combination of the conventional poppet and piston valves. From gas density measurements by a fast ionization gauge, the rise time was found to be limited by the expansion of the gas front. The minimum rise time is 70 &mgr;sec for a specific geometry of gas exit. The design criteria are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686349

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method is described with which small magnetic moments of samples can be measured using a superconducting transformer and a commercial flux gate magnetometer. It is applied to nuclear magnetic thermometry in the temperature range from 1.7 mK to 0.5 K using the intermetallic compound AuIn2, which is particularly suitable for this purpose.

ISSN:0034-6748    

DOI:10.1063/1.1686350

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A general method has been developed by which two‐pulse experiments may be largely automated by interfacing a minicomputer to an NMR pulse spectrometer. The necessary pulses and time delays are supplied by the computer and the interface converts these to the levels necessary for the rf oscillator and power amplifier of the spectrometer. Values of the relaxation times (T1,T2,T1&rgr;) are extracted from the collected data by data analysis subroutines which perform a least‐squares fit of the data to an exponential decay. Deviations of the data points from the least‐squares slope are displayed to permit an immediate visual check for experimental errors. The advantages of the simple pulse sequences are retained while their disadvantages, particularly inefficient data collection for very long or very short relaxation times, are greatly reduced. The lower limit of relaxation times which may be measured by this method is about 100 &mgr; sec.

ISSN:0034-6748    

DOI:10.1063/1.1686351

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A gas laser cavity beam is used as monochromatic radiation source for detecting and sizing aerosol particles. The aerosol is forced through the cavity of a (1/2) mW open cavity He&sngbnd;Ne laser having one plane mirror and one spherical mirror. Light scattered from individual particles is collected by a hemispherical mirror and is focused onto a detector. The system has good resolution and sensitivity and has the capability of measuring high aerosol concentrations without dilution.

ISSN:0034-6748    

DOI:10.1063/1.1686352

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A detailed analysis of the transmission properties of low‐energy spherical electrostatic electron spectrometers employing preacceleration or preretardation is presented, which shows that the transmission efficiency of such instruments is not necessarily related inversely to electron energy nor directly to analyzer pass energy. A prescription, which enables observed spectra to be corrected over a wide energy range for intensity variations resulting from instrumental effects, is provided, and a detectable shift (≤ 0.1 eV) in the apparent position of electron lines under certain conditions is predicted. The theory is applied to the design and performance of two spherical photoelectron spectrometers employing ultraviolet and soft x‐ray sources. The analysis may readily be extended to other forms of electrostatic spectrometers employing preacceleration or preretardation.

ISSN:0034-6748    

DOI:10.1063/1.1686353

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Computer analysis of reflected power profiles allows accurate determination of complex dielectric permittivity of low, medium, and high permittivity liquids by one single method if nonideal plunger properties are taken into account. For low loss measurements account is taken of the losses in the waveguide walls. For medium and high permittivity liquids, dumbell plunger design leads to important errors due to higher mode excitation and propagation.

ISSN:0034-6748    

DOI:10.1063/1.1686354

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A time‐of‐flight method for measurement of the lifetime of metastable molecules is described. The method is applicable to a molecules in several different metastable excited states. As compared to methods used previously, the method has the advantages that it does not require selective excitation or quenching of the different states; moreover, it does not require a determination of the relative populations or velocity distributions of molecules in the excited states. The feasibility of the method is demonstrated with a measurement of the lifetime of thea1&pgr;gstate of N2.

ISSN:0034-6748    

DOI:10.1063/1.1686355

出版商:AIP    

年代:1973

数据来源: AIP