摘要:

In this paper a signal model of the rubidium (Rb) atomic frequency standard is developed. The model combines an analysis of the atomic physics required to describe processes occurring within the Rb absorption cell with a feedback analysis of the clock’s servocontrol circuitry, and thus allows clock performance in terms of Allan variance to be predicted from a number of electronic and physical parameters. All previous models of the Rb clock have been limited to an analysis of the clock’s short‐term performance, Allan variance averaging times less than 10 000 s. However, by explicitly including the effects of discharge lamp intensity fluctuations, which are transformed into output frequency variations via the light shift effect, clock performance can be predicted for averaging times greater than 10 000 s. Furthermore, the present model is the first which incorporates the influence of an optically thick Rb vapor, along with the diffusion of optically pumped atoms to the walls of the absorption cell, into the calculation of clock performance. As part of the model’s validation, the calculations are compared with the results from a recent Rb clock long‐term performance experiment. Agreement between measured and predicted Allan variances for both short and long averaging time periods is excellent.

ISSN:0021-8979    

DOI:10.1063/1.336683

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We evaluate the dipolar energy in a periodic multilayer film consisting of alternating ferromagnetic and nonmagnetic layers, for magnetization perpendicular to the plane of the film, arranged in alternately polarized strip domains. The lowest‐energy state for this configuration is calculated for the case of freely mobile domain walls. Within certain limits, the layered film behaves as a uniform medium with an anisotropy arising from the layering. The relevance of the theory to experiments on Pd/Co layered films is discussed.

ISSN:0021-8979    

DOI:10.1063/1.336684

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The sealed‐off CO2laser with La1−xSrxCoO3oxide cathode was found to improve laser performances in both output power and operating life. The maximum output power from 120‐cm discharge length was 62 W and the life defined by the power decrease by 10% was 3500 h at this power level. The power enhancement of this laser is due to the combined effects of catalytic activity and O2emissivity of the oxide cathode, while the life improvement is due to the combined effects of its chemical inertness, O2emissivity, and low sputtering rate.

ISSN:0021-8979    

DOI:10.1063/1.336685

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A multikilojoule deuterium fluoride (DF) chemical laser with a low‐pressure mixture of F2/D2/O2/SF6was developed in which a Lambda‐type electron beam initiation scheme was used. The DF laser output obtained from a 27‐liter active volume was 2.5 kJ with a pulsewidth of about 500 ns. The corresponding electrical efficiency and chemical efficiency are 128% and 10.5%, respectively.

ISSN:0021-8979    

DOI:10.1063/1.336686

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The rate equations for stimulated electronic Raman scattering are presented for a general case, including linear absorption, atom and pump photon depletion, and variable beam geometry. Nondimensional variables are introduced, resulting in a simple procedure for optimization of Raman cell design and performance. A numerical solution of the detailed model is shown for a specific case, and the effects of the various parameters on the conversion efficiency are discussed.

ISSN:0021-8979    

DOI:10.1063/1.336687

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An experiment demonstrating optical pulse narrowing of a 6943‐A˚, 20‐ns ruby laser pulse to a few ns in the isophase of the liquid‐crystal cholesteryl oleate is reported. An analytical expression is derived for the backscattered intensity at the entrance to the scattering cell. Also, rough estimates of the pulse widths, time to reach intensity maximum, and asymmetry of the pulse shape are presented.

ISSN:0021-8979    

DOI:10.1063/1.336688

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The characterization of porosity in solids using the frequency dependence of the ultrasonic attenuation is discussed both from the theoretical and experimental viewpoint. The major thrust of our work is the determination of the volume fraction and size of the voids for the case of dilute porosity (<6%) in structural materials. An aluminum alloy (A357) was chosen for study due to its economic importance in large‐scale casting and the particular suitability of aluminum for this type of study. Following recent papers the attenuation is described by an independent scatterer model for spherical voids. Numerical results are presented in a form suitable for use with a range of materials. A method for determining the volume fraction and pore size is given. Specific tabular results are given for stainless steel, IN‐100, Ti, Si3N4, as well as aluminum. Figures of merit which partially describe those situations in which the method is usable are also presented. In the experimental work a digitized spectrum analysis system was used to measure the frequency dependence of the attenuation coefficient in A357 aluminum cast alloys. In the cast materials the average pore size was in the order of 100 &mgr;m and the pore concentration varied from essentially 0 to 6%. It was found that experimental measurement of the attenuation could be fit by the theoretical model. The resulting parameters yield a good estimate of the pore volume fraction.

ISSN:0021-8979    

DOI:10.1063/1.336689

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Exact analytical solutions of the heat‐diffusion problem encountered in the pulsed photothermal evaluation of layered materials are presented. The analysis relates to the long‐time decay of the front face temperature following the absorption of a surface heat pulse. The configuration of a coating on a substrate is analyzed, and the parameters governing the temperature evolution are identified with a particular emphasis on the thermal contact resistance term. This model provides a new method of measuring the quality of the interface. Previously published data and new experiments with laminated materials and living tissues are analyzed using the proposed analytical solutions.

ISSN:0021-8979    

DOI:10.1063/1.336690

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Electrode erosion (especially anode erosion) is still an important problem for high‐power vortex stabilized arc lamps. A study of the electrode erosion mechanisms has therefore been carried out in vortex stabilized arcs operating at a maximum input power of 40 kW. It was found that three factors are important in the removal of electrode material: evaporation caused by thermal loading, ablation due to time varying stresses, and corrosion resulting from the presence of impurities in the gas. It was also found that the first two factors, and hence the erosion rates, can be affected significantly by the orientation of the electrodes and the presence of an external magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.336691

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A detailed investigation of the behavior of particle orbits in the simultaneous presence of three large amplitude waves such as those encountered in the collective particle accelerator experiment at the Naval Research Laboratory is undertaken. Stochasticity arising out of the resonance overlap of the waves can influence the particle dynamics significantly and thereby affect the outcome of the experimental results. Choice of initial phase and energy for successful operation is identified and discussed.

ISSN:0021-8979    

DOI:10.1063/1.336692

出版商:AIP    

年代:1986

数据来源: AIP