摘要:

Flows of ferromagnetic fluids (colloidal suspensions) are obtained by coupling to the suspended single‐domain particles with a rotating magnetic field. It is shown that very high rotation rates are possible by this technique. Nonmechanical torque‐driven flows represent a hitherto unexplored area in the physics of fluids that has interesting potential technological application. A ferromagnetic pump based upon the present principle could be of great value in fluidic systems and open up new applications in space, ocean, biological and other environments.

ISSN:0003-6951    

DOI:10.1063/1.1754952

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Two phase‐matched four‐frequency mixing experiments in calcite are reported: &ohgr;0(6943 Å) + &ohgr;1(8727 Å) = &ohgr;2(1.175 &mgr;) + &ohgr;3(5764 Å) and 2&ohgr;0(6943 Å) = &ohgr;2(8727 Å) + &ohgr;3(5764 Å) where for index matching, &thgr; = 7.40° and 5.25°, respectively.

ISSN:0003-6951    

DOI:10.1063/1.1754953

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The relationships between the third‐order elastic constants of monocrystalline and polycrystalline (quasi‐isotropic, randomly oriented) solids of cubic symmetry are derived according to elastic strain energy balances assuming negligibly small elastic strain energy contribution from mismatching of the grain boundaries. The relationships between the three third‐order isotropic Lame´ coefficients (&ggr;1, &ggr;2, &ggr;3, Brugger convention) and the six third‐order single‐crystal elastic constants are given by:&ggr;1=135(C111+18C112−30C144−12C166+16C123+16C456)&ggr;2=135(C111+4C112+19C144+2C166−5C123−12C456)&ggr;3=135(C111−3C112−9C144+9C166+2C123+9C456).Good agreement was found between the experimentally evaluated &ggr;1, &ggr;2, &ggr;3values and those derived from the above equations using the six third‐order single‐crystal elastic constants for bcc columbium at room temperature.

ISSN:0003-6951    

DOI:10.1063/1.1754986

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The usefulness of vitreous silica in a variety of high‐frequency ultrasonic and acousto‐optical devices is often limited by the acoustic properties of the material. The purpose of this Letter is to report recent findings on (1) the acoustic loss‐vs‐frequency dependence for shear waves in vitreous silica and (2) the magnitude of the fluctuation in the shear wave phase velocity. Information on the shear wave propagation characteristics is most important for ultrasonic delay line applications for which the shear mode of propagation is predominantley used.

ISSN:0003-6951    

DOI:10.1063/1.1754987

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

When a plane‐polarized light beam is passed through an anisotropic medium, the extraordinary ray can become retarded or advanced relative to the ordinary ray. This leads to a periodic longitudinal extinction of (&lgr;/&Dgr;n) along the light path which provides a quick accurate visual method for determining the birefringence of a material which is both transparent and a good scatterer of light.

ISSN:0003-6951    

DOI:10.1063/1.1754989

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In high‐mobility piezoelectric semiconductors such as InSb, a transverse magnetic field greatly reduces the electron drift velocity required to form an acoustoelectric domain. We have developed a theory which predicts this effect reasonably well. We have also shown that when these materials are used as acoustic amplifiers, the magnetic field reduces the dc power dissipation at maximum acoustic gain to such a large degree that CW amplification of sound waves can easily be achieved.

ISSN:0003-6951    

DOI:10.1063/1.1754990

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An instability of the electron concentration is predicted in a semiconductor with a nearly saturating drift velocity and a diffusion constant which increases with increasing electric field. A small signal analysis shows under what conditions fluctuations of the carrier concentration will be unstable.

ISSN:0003-6951    

DOI:10.1063/1.1754991

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The ``dark‐sheath'' region in plasmoidal discharges is known to be a high field region, and measurements of the relative emission rates from molecular oxygen ions and neutral oxygen atoms show that only the intensity of the molecular ion lines drop sharply in the ``dark‐sheath.'' It is proposed that the dark‐sheath region occurs because the lifetimes of the excited states of the molecular ions are long enough to permit an appreciable fraction of newly created ions to be swept away by the static electric field prior to radiative de‐excitation.

ISSN:0003-6951    

DOI:10.1063/1.1754992

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Negative resistance and oscillations were observed in germanium diodes, operating in forward direction. Conductance and noise measurements were done in the post‐negative resistance region, where the current voltage characteristic obeys the cube law for a plasma injected into an insulator. The conductancegshows a transit time effect, and the h.f. noise can be represented by a noise current generator (4kTg&Dgr;f)1/2in parallel to the device.

ISSN:0003-6951    

DOI:10.1063/1.1754993

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A new technique useful to set a lower limit for the lifetime of the intermediate state of two‐photon absorption processes is described. The technique is applied to the case of two‐photon absorption in CdS.

ISSN:0003-6951    

DOI:10.1063/1.1754994

出版商:AIP    

年代:1967

数据来源: AIP