摘要:

A hardware/software computer interface for control of a digital frequency synthesizer is described. This synthesizer is controlled by selection of a suitable oscillator between 2.5 and 60.2 MHz, which in turn is controlled by two 8‐bit modulo N counters. The ratio of the two integers (Q /P) selected as the moduli of the counters determines the ratio of synthesized to reference frequency. The interface described directly selects these functions and thus permits computer calculation and setting of the required ratio. Addition of a manually controlled offset frequency completes the synthesis. In this way, frequencies can be synthesized with a maximum error of approximately 10 Hz or less. The interface therefore allows rapid and accurate synthesis of any desired frequency within the 2.5–60.2 MHz range. This method is of utility in both spin‐spin decoupling experiments in NMR spectroscopy and as a central element of a variable frequency NMR spectrometer system. The algorithm for computing the necessary values ofQandPis described. Such an interface is easily adaptable to any minimal laboratory computer system. In the present case an 8K word Varian 620/i computer was used.

ISSN:0034-6748    

DOI:10.1063/1.1686376

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The construction of a new zero‐field paramagnetic resonance (ZFPMR) spectrometer is discussed. Spectrometer organization and construction details are presented for both resonant cavities and broadband traveling‐wave helices as sample holders. A new circuit diagram for a square wave magnetic field modulator with fast rise time is given. The performance of each kind of spectrometer is discussed with particular emphasis on investigation of paramagnetic rare earth ions with zero‐field splittings in diamagnetic host lattices.

ISSN:0034-6748    

DOI:10.1063/1.1686377

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A single beam device which measures continuously as a function of wavelength reflectance and transmittance is described. The unit is attached to a McPherson 218 monochromator, but it can be adapted for any monochromator. A notable feature of the device is that with a specially constructed vacuum evaporator this system enables the study of the optical properties of thin films without exposing them to air. Described also is a feedback light control system designed to compensate for signal intensity variations with wavelength caused by various optical components.

ISSN:0034-6748    

DOI:10.1063/1.1686378

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A type of laser velocimeter termed a laser vector velocimeter (LVV) resolves the 180° directional ambiguity problem of the conventional laser velocimeter by exploiting optical frequency translation techniques and frequency division demultiplexing techniques. This paper defines some fundamental LVV system signal characteristics and signal conditioning and data acquisition problems. The signal conditioning electronics for a three velocity component LVV system are described. Data obtained from atmospheric wind velocity measurements using a two velocity component LVV system are presented to illustrate the vector velocity measurement capabilities of the system. The operational status LVV systems presently in use are two orthogonal velocity component units. However, a laboratory status LVV system has been used to make three‐dimensional vector velocity measurements.

ISSN:0034-6748    

DOI:10.1063/1.1686379

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple bridge circuit using a platinum resistance thermometer is described which generates a signal proportional to 1/T. The error is less than 0.1% over wide ranges. Direct plotting of the temperature response of appropriate physical systems in a useful form is thus expedited. The superiority of platinum over other materials is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686380

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A furnace and electrical measurement system is described that is capable of a wide range of time‐temperature relationships while allowing for the simultaneous measurement of sample temperature and resistance over any 3–4 decades in the range 10−2–107&OHgr;. The furnace system consists of a servo‐controlled push rod moving a sample fixture in a gradient furnace. The servo system is controlled by a cam wheel driven by a stepping motor whose speed can easily be changed during rotation to provide for increased profile versatility. Two‐ or four‐terminal resistance measurements and temperature measurements are possible with four lead wires; each is monitored with a chart recorder. Possible applications and examples of performance are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686381

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Approximate expressions are given for the fraction of scattering events which contribute to the attenuation of the transmitted electron current in cylindrically symmetric electron spectrometers, with and without an imposed axial magnetic field. The sensitivity to scattering is shown to decrease strongly with increasing magnetic field strength owing to the trapping of scattered electrons by the magnetic field and multiple scattering effects due to the path length being a function of the magnetic field strength. The effect of applying a retarding electric field to electrons leaving the interaction region is shown to leave the conclusions substantially the same.

ISSN:0034-6748    

DOI:10.1063/1.1686382

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The classical electric pulse technique has been adapted to measurements of specific heat at high pressure. A wire specimen is heated by a 100 &mgr;sec pulse, stabilized atI= 50 A. The resulting temperature rise is extracted from the voltage dropUover the sample by means of a bridge circuit. The specific heat is obtained from the formulacp= C(T,P)U I / m e˙, whereC(T,P)is a function to be experimentally determined for a given sample,mthe mass of the sample, ande˙the time derivative of the bridge output voltage. A procedure has been developed forin situcorrections ofe˙for heat loss to the medium surrounding the wire. Digital techniques are used for the pulse analysis. The method has been used to ascertain the pressure dependence ofcpfor Cu up to 100 kilobars at room temperature. The relative change incpwas found to be 2.8 × 10−4/kilobar.

ISSN:0034-6748    

DOI:10.1063/1.1686383

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A gravity‐feed, pneumatic‐ejection sample changer has been developed. The changer is suitable for both flat and well‐type detectors and permits the continuous use of gamma‐ray spectroscopy equipment 24 h a day, 7 days a week. The electronic circuitry has a fail‐safe feature which stops the operation of the changer if a malfunction occurs.

ISSN:0034-6748    

DOI:10.1063/1.1686384

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper describes a simple current measuring device which has better response than the Rogowski belt for very high currents and fast rise times and better response than the Rogowski belt and transformer under all conditions. The device consists entirely of passive components, does not require calibration, and is easily adjusted so that there is no linear (in time) component to the droop.

ISSN:0034-6748    

DOI:10.1063/1.1686385

出版商:AIP    

年代:1973

数据来源: AIP