摘要:

Experimental studies were carried out on laser systems to investigate the excitation mechanisms of the upper laser level (0001) of carbon dioxide in an electrical discharge, and the parts played by helium and nitrogen in mixed systems. Used as constituent gases were carbon dioxide, carbon dioxide‐nitrogen, and carbon dioxide‐helium. Pulsed electrical excitation was used with an arrangement for varying the time delay between the discharge pulse and the alignment of aQ‐switch mirror. The upper‐level‐to‐ground radiation was observed from the side of the tube to study the behavior of the upper level following the current pulse and when the upper level population is suddenly decreased by theQ‐switch. It is concluded that the primary excitation mechanism is electron impact for pure carbon dioxide. Nitrogen is shown to contribute by acting as a storage mechanism for energy prior to resonant transfer, and a value of 1.6×104sec−1Torr−1was obtained for the rate constant of the N2→CO2vibrational energy transfer process. Helium was found to contribute to increased output primarily through causing a favorable shift in electron temperature.

ISSN:0021-8979    

DOI:10.1063/1.1658080

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The temperature dependence of the critical fields of V3Ga has been measured up to 70 kOe using ac and dc magnetization techniques. For a material with a transition width of 26 mdeg at a transition temperature,Tc, of 14.19°K, one calculates from the slope (dHc2/dT=−43.2 kOe/deg) and curvature of theHc2vsTcurve, the Ginzburg—Landau parameter, &kgr;=40±2, the Pauli paramagnetism parameter &agr;=2.28±0.04, and the spin—orbit scattering constant &lgr;so=0.6±0.1. No evidence forHc3was detected and the experimentally difficult upper limit toHc1appears to be about three times as large as calculated from the theories.

ISSN:0021-8979    

DOI:10.1063/1.1658081

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The theory of superconducting bolometer operation is presented and a small‐signal equivalent circuit developed. This circuit contains a portion that represents dynamic thermal effects and a portion resulting from superconductive phenomena. It is shown that the incremental impedance is greater than the dc resistance even for the limit of zero‐frequency modulation. A peaking phenomenon is predicted in the incremental impedance versus temperature for this circuit. The characteristic parameters of a tin superconducting bolometer are presented to indicate the usefulness of incremental impedance measurements in determining these parameters.

ISSN:0021-8979    

DOI:10.1063/1.1658082

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A simple model for the motion of a domain wall in most magnetic materials is presented. The real flexible wall is represented by an equivalent rigid plane wall. The motion of the plane is impeded by springs which are attached to the wall and to defects in the material in the wake of the plane. A spring breaks when the force it exerts on the wall reaches a value characteristic of the defect, and the energy stored in it is lost to the motion. The model is similar to one developed earlier but is based on a more plausible view of the interaction of a wall with a defect. In common with the earlier model, it describes both reversible and irreversible flux changes; it predicts a small‐signal hysteresis loop which is similar to, but significantly different from, the Rayleigh loop; it explains the frictional nature of magnetic hysteresis without invoking anyad hocenergy‐loss mechanisms. It is sufficiently simple to be applied to complex problems. It agrees with the results of exact dynamic calculations to good accuracy and is exact when applied to quasistatic problems. The model is derived by considering the motion of an anisotropic flexible wall pinned by a periodic array of defects. The springs of the model represent the distortions of the wall in the vicinity of the defects. It is shown that the forcefexerted by the defect on the wall and the energyWper defect stored in wall distortions are related approximately to the average displacementz¯of the wall from the defect by the equationsf(t)=kz¯(t),   W(t)=kz¯2(t)/2,wherekis a spring constant associated with wall deformation. These relations justify the spring model. Finally, a comparison is made amongf, W, andz¯calculated as functions of time for a step of applied field from both the exact equations and from the spring model. The agreement is, in all cases, better than 10% of the final values. After the wall breaks free from a defect the energy stored in distortion is dissipated in viscous damping. It does not affect the average wall position and is thus lost to the motion in agreement with the model.

ISSN:0021-8979    

DOI:10.1063/1.1658083

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Conductivity measurements in various polycrystalline ferrites have shown that the temperature dependence of the conductivity has to be described by two different activation energies, one which is attributed to the bulk material and the other which is due to the poorly conducting layers introduced by Koops. Activation energies as derived from the results of magnetic relaxation measurements of the initial permeability for samples of the BaFe12−2&dgr;3+Fe2&dgr;2+O19−&dgr;system are compared with those determined from the conductivity measurements. It appears that the activation energy as derived from the dc conductivity should not always be related to those determined from the magnetic relaxation. Both the high‐frequency conductivity and the magnetic relaxation losses are related to an electron transfer between Fe2+and Fe3+ions. The activation energies depend on the Fe2+content of the sample.

ISSN:0021-8979    

DOI:10.1063/1.1658084

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The spin‐wave instability theory of nonlinear effects in ferromagnetic insulators developed by Suhl for perpendicular pumping and by Schlo¨mann for parallel pumping has been extended to include pumping with an arbitrary microwave field configuration. The theory is applicable to samples of ellipsoidal shape, magnetized to saturation along one principal axis, but not necessarily an axis of rotational symmetry as in the Suhl theory. The theory, in its present form, is quite versatile and applicable to a large variety of situations which are not accessible on the basis of the earlier calculations. Equations are developed specifically for first‐order processes. Several examples are considered to demonstrate the versatility of the theory: (1) Perpendicular pumping with a linearly polarized microwave field; (2) oblique pumping with a linearly polarized field at an angle between 0° and 90° to the static field; (3) perpendicular pumping with a circularly polarized field rotating in the anti‐Larmor sense.

ISSN:0021-8979    

DOI:10.1063/1.1658085

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An integral/matrix‐equation technique for the calculation of a magnetic field produced by stationary current in the presence of permeable material is presented. Utilizing this technique, magnetic fields are computed on the basis of a two‐dimensional model for the plated‐wire memory element. This model essentially represents a planar‐memory element since the plated wire is simulated by a slab of permeable material. Numerical results are presented for different permeabilities of the keepers and the simulated wire. These results show quantitatively how the keepers enhance the magnetic field between the current straps, where the information is to be stored, and how they reduce the fringing fields outside. The field enhancement can be interpreted as reduction in current or power for a given field at the center due to the use of keepers. The technique presented is sufficiently simple and efficient to be a useful tool in designing magnetic memories, as well as in determining the effect of mechanical tolerances on their performance.

ISSN:0021-8979    

DOI:10.1063/1.1658086

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The geometrical aberrations of the objective lens of a scanning electron microscope limit the electron beam diameter to a few tens of angstroms. However, the resolving power generally obtained is of the order of 200–500 Å. This discrepancy is explained by the noise coming from the secondary electron emission which must be considered as a supplementary aberration.

ISSN:0021-8979    

DOI:10.1063/1.1658087

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An experiment was performed to show that the coherence of a laser beam can be maintained over a 5‐cm path in a GaAs parallelepiped. The temperature coefficient of the refractive index was measured from the temperature dependence of the intensity of radiation transmitted through the sample. The value of this coefficient was found to be (5.64±0.28)×10−5(°C)−1for semi‐insulating GaAs at room temperature and 10.6‐&mgr; wavelength. The absorption coefficient of the material used was measured calorimetrically and found to be 0.012±0.002 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.1658088

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Molecules or ions of the form BOx−nlack a center of symmetry whenever the B atom has a nonbonded pair of electrons. The problem of generating an acentric crystal can be approached by using these acentric oxygen polyhedrons as building blocks. A very high incidence of acentricity is found in compounds based on distorted BO3−noctahedra, such as XeO3, AIO3(A=H, Li, Na, K, Rb, Cs, NH4, and Tl), and MTeO3(M=Ca, Sr, Ba, Zn, Cd, Hg, Pb, Ni). Since these materials also have large indices of refraction, the concept of acentricity via nonbonded electrons provides a new and important guideline in the search for nonlinear optical materials.

ISSN:0021-8979    

DOI:10.1063/1.1658089

出版商:AIP    

年代:1969

数据来源: AIP