摘要:

A theory of friction is presented that may be more applicable to geologic materials than the classic Bowden and Tabor theory. In the model, surfaces touch at the peaks of asperities and sliding occurs when the asperities fail by brittle fracture. The coefficient of friction, &mgr;, was calculated from the strength of asperities of certain ideal shapes; for cone‐shaped asperities, &mgr; is about 0.1 and for wedge‐shaped asperities, &mgr; is about 0.15. For actual situations which seem close to the ideal model, observed &mgr; was found to be very close to 0.1, even for materials such as quartz and calcite with widely differing strengths. If surface forces are present, the theory predicts that &mgr; should decrease with load and that it should be higher in a vacuum than in air. In the presence of a fluid film between sliding surfaces, &mgr; should depend on the area of the surfaces in contact. Both effects are observed. The character of wear particles produced during sliding and the way in which &mgr; depends on normal load, roughness, and environment lend further support to the model of friction presented here.

ISSN:0021-8979    

DOI:10.1063/1.1710026

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The noise theory for a self‐sustaining avalanche discharge, which was published recently by Hines, is verified experimentally for low frequencies. It was found, in general, that the open‐circuit spectral voltage density, ⟨u2⟩Av/&Dgr;f, arises from three contributions: (1) the inherent avalanche noise calculated by Hines and given by ⟨u02⟩Av/&Dgr;f=a2Vb2/I, wherea2=3.3×10−20A/Hz,Vb= breakdown voltage andI= avalanche current; (2) excess noise at low current densities caused by nonuniformities of avalanche breakdown (even in microplasma‐free diodes); and (3) excess noise at high current densities which seems to be caused by thermal effects. The temperature dependence of the noise is entirely due to the two excess‐noise contributions. The experimental results are discussed with respect to their application in the design of noise generators, low‐noise and low‐current avalanche diodes, microwave oscillators, and negative‐resistance amplifiers.

ISSN:0021-8979    

DOI:10.1063/1.1710027

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Magnetic susceptibility of nickel‐chromium alloys, containing 2.2, 5.6, 7.8, 11.2, 13.3, 16.6, 22.0, and 25.0 at. % chromium, have been studied up to 1500°K. Our data do not exhibit any anomalies of the type observed recently by Chechernikov and Pop from which they inferred the existence of antiferromagnetism in the nickel‐rich nickel‐chromium solid solutions. In this respect the present measurements are in satisfactory agreement with the older studies by Manders. Small irregularities are observed in the inverse magnetic susceptibility vs temperature curves for 16.6, 22.0, and 25.0 at. % chromium samples. The origin of these observations is not clearly understood but, likely, results from the existence of Ni2Cr phase in these alloys.

ISSN:0021-8979    

DOI:10.1063/1.1710028

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes dynamic magnetization experiments in hard‐drawn niobium‐silver Permalloy wire of the type used in domain‐wall shift registers. In particular, it reports evidence for the compression, under the influence of an applied bucking field, of the transition region separating two domains of antiparallel longitudinal magnetization. In the absence of external field, the transition region is characterized by a domain wall roughly conical in shape, with a minimum length of about 1 cm for wire of 0.005‐cm diameter. The length of the transition region is inversely proportional to the longitudinal derivative of flux, which may also be referred to as magnetic pseudocharge. The latter quantity was measured by a bifilar pickup coil wound around the wire, and subsequent electronic integration. Dynamic experiments employing ac bucking fields with or without an additional homogeneous field result in hysteresis loops of particularly simple and predictable types. Identifiable individual processes within the cycle are nucleation, compression and expansion of the transition region, and wall motion. A compression of the longitudinal dimension of the domain wall by a factor four is observed with a bucking field of 17 Oe. The curved portion of the loops is, with good accuracy, described by a parabolic dependence. This shape is expected from magnetostatic arguments which predict a domain‐wall length proportional to (HB±HW)−½, whereHBis the applied bucking field andHWis the wall‐motion threshold.

ISSN:0021-8979    

DOI:10.1063/1.1710029

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of current‐voltage characteristics have been performed on Au‐Si3N4‐Mo and Au‐Si3N4‐Si (degenerate substrate) structures of various nitride‐film thicknesses from 300 Å to 3000 Å and over a range of temperatures. The films are deposited by the process of reaction of SiCl4with NH3. It is found that at any given temperature and electric field, the current transport is essentially independent of the substrate material, the film thickness, or the polarity of the electrodes.It is proposed that the current‐transport mechanisms are bulk controlled rather than electrode controlled. The conduction‐current density,J, is the sum of three contributions:J=J1+J2+J3, whereJ1∼Eexp {−q[&phgr;1− (qE/&pgr;&egr;0&egr;d)½]/kT},J2∼E2exp (−E2/E), andJ3∼Eexp (−q&phgr;3/kT). At high fields and high temperaturesJ1dominates the current conduction (the Poole‐Frenkel effect or internal Schottky effect); one obtains a barrier height of (1.3±0.2) V for &phgr;1and a value of 5.5±1 for the dynamic dielectric constant &egr;d. At high fields and low temperaturesJ2dominates as a result of field ionization of trapped electrons (presumably from the same centers as forJ1) into the conduction band; one obtains a value for the fieldE2of the order of 6×107V/cm. At low fields and moderate temperaturesJ3dominates because of the hopping of thermally excited electrons from one isolated state to another yielding Ohmic characteristics and a thermal‐activation energyq&phgr;3of about 0.1 eV.At low temperatures the maximum dielectric strength approached ∼107V/cm. At high temperatures whereJ1dominates the current conduction, the maximum dielectric strength, which is limited by thermal instability, decreases as (&phgr;1−CT)2, whereCis a function of the thermal conductivity of the nitride films.

ISSN:0021-8979    

DOI:10.1063/1.1710030

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Single crystals of GaAs [(110), (111), and (1¯1¯1¯) faces] were sputtered by normally incident low‐energy (0–140 eV) argon ions in the source of a mass spectrometer. For each face, approximately 99.4% of the collected ions were neutral Ga and As atomic species; the balance were neutral GaAs molecules. No neutral Ga2, As2or (GaAs)2molecules, or negative Ga−, As−, or (GaAs)−ions, with the characteristics of sputtered particles, were detected. Sputtering ``yields'' for the three faces were found to be: ``Y'' (111) ≈ ``Y'' (1¯1¯1¯) > ``Y'' (110).

ISSN:0021-8979    

DOI:10.1063/1.1710031

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Using an optical‐transmission method, the deposition of sputtered Ni atoms on a glass collector in an abnormal glow discharge is measured in Ar and Ar‐H2mixture at 5 Torr. The distribution of atoms deposited on a glass collector is found to be determined by the diffusion process of sputtered atoms in the gases. The results show that the sputtering rate is proportional to the square of the current, and the sputtering rate of 100% Ar is about twice as large as that of 70% Ar‐30% H2mixture.

ISSN:0021-8979    

DOI:10.1063/1.1710032

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In this paper the phase relationships between self‐locked modes in lasers are investigated. The calculations are based on a self‐consistency condition. The electric field in the cavity produces in the medium nonlinear polarization terms. These polarization terms may then be considered acting as source terms onto which the mode oscillations lock. The self‐consistency condition imposed on the phases arises from the fact that the phase‐locked modes must reproduce the originally assumed electric field. We find the calculated phase relationships in essential agreement with earlier predictions based on the maximum‐emission principle. The latter principle assumes that the phase relations which maximize the total rate of‐stimulated emission should grow most rapidly and should be the ones that establish themselves in lasers. The present paper gives additional evidence for the validity of the maximum‐emission principle. In either calculation the basic physical mechanism that is responsible for the phase‐locking effect is the nonlinear saturation in the laser medium or some saturable absorber.

ISSN:0021-8979    

DOI:10.1063/1.1710033

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Sputtering yields have been measured during normally incident 1‐ to 5‐keV Ar+ion irradiation of polycrystalline Au, ⟨100⟩, ⟨110⟩, and ⟨111⟩ Au monocrystals, a ⟨111⟩ Al monocrystal, and several ⟨0kl⟩ Cu monocrystals of previously unreported orientations. Onderdelinden's transparency model is found to account satisfactorily for the orientation dependence of the yields of low‐index Cu, Au, and Ge crystals. The importance of the recording geometry in governing the appearance of sputtering ejection patterns is demonstrated. The so‐called ⟨114⟩ ejection‐pattern spots from ⟨111⟩ fcc crystals are attributed to assisted focusing sequences along ⟨100⟩, the most probable ejection direction being shifted because the last focusing ``lens'' is incomplete.

ISSN:0021-8979    

DOI:10.1063/1.1710034

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The nucleation and the growth of the {101¯2} ⟨101¯1¯⟩ type twins in zinc single crystals have been investigated by applying concentrated loads in the [0001¯] direction and on the (0001) surface of such crystals with point indenters as a mechanical means of stress concentration. Assuming the crystals to be a semi‐infinite anisotropic elastic medium, the resolved shear stress for the twins to grow is calculated to be 130±50 g/mm2.

ISSN:0021-8979    

DOI:10.1063/1.1710035

出版商:AIP    

年代:1967

数据来源: AIP