摘要:

The design and construction of a superconducting magnet system, producing a maximum magnetic field of 0.6 T with any desired direction, is described. The magnet consists of a pair of Helmholtz coils, which can be rotated about a fixed solenoid. The azimuthal angle of the field is selected manually by rotation of the Helmholtz coils, and the polar angle is selected electronically by adjusting the currents in the Helmholtz coils and solenoid appropriately. The latter is accomplished automatically by means of the associated power supply, which is described in detail. The accuracy of the magnet system is approximately 0.8 mT or ½% of the field magnitude, whichever is greater. This system has proved to be indispensable for studies of the rf size effect in pure metals at low temperatures. temperatures.

ISSN:0034-6748    

DOI:10.1063/1.1686700

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Absolute electric field measurements of a 2 GHz electromagnetic wave in a nonuniform plasma are described. A remote measurement technique with minimum perturbations is used in which the information is obtained at the launching antenna from the backscattered signal of a small movable dipole in the radiation field. The weak scattering signal of the test dipole is discriminated against reflections from metallic walls and the plasma cutoff layer by introducing a small frequency shift (&Dgr;&ohgr;/&ohgr;≃10−3) at the dipole. The dipole contains a passive nonlinear reactive element (varactor diode) which generates multiple sidebands when irradiated with two frequencies. The nonlinear behavior of the sidebands is used to obtain an absolute calibration for the electric field strength at the dipole. Mismatch effects due to the density dependent dipole radiation resistance are minimized by terminating the dipole with a high impedance.

ISSN:0034-6748    

DOI:10.1063/1.1686701

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A sample probe for pulsed nuclear magnetic resonance that replaces the normal resonant circuit by a lumped parameter delay line is described. Theoretical analysis shows that the delay line probe has a signal‐to‐noise ratio and conversion efficiency of power into rotating magnetic field equivalent to a resonant circuit ofQ=(2&pgr;) (delay time) (Larmor frequency). However, the delay line probe has a much wider bandwidth, much shorter transient decay time, and faster recovery from the rf excitation pulse. Experimental results are included that demonstrate submicrosecond recovery times for the observation of the signal.

ISSN:0034-6748    

DOI:10.1063/1.1686702

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The technique of using a pressure‐resisting glass cell for high resolution NMR measurement up to 2000 kg/cm2has been established. The high pressure NMR experiment is shown to be safely conducted on the ordinary high resolution spectrometer. In this report, detailed illustration of the glass cell is described along with the explanation of the device to transmit the pressure, generated in the standard high pressure equipment, to the glass cell located in the high resolution NMR probe.

ISSN:0034-6748    

DOI:10.1063/1.1686703

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Powder neutron diffraction data have been obtained on cesium metal above the two transitions at 42.5 and 43 kilobar using a piston cylinder apparatus. A Lucalox cylinder (high density Al2O3) (35.4 mm o.d., 6.35 mm i.d.) is radially supported by compressing two steel plates with a hydraulic ram leaving a neutron window between the plates ∼6 mm high. A 17° included angle was used between the cylinder and support plates. A tungsten carbide piston, driven by a second hydraulic ram, raised the pressure on the sample at three times the rate of increase of the support pressure.

ISSN:0034-6748    

DOI:10.1063/1.1686704

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A continuously variable time delay correlator was designed for the purpose of measuring velocity. The inverse transit time (velocity) between upstream and downstream detectors is continuously adjusted by a feedback loop which maintains constant the level of cross correlation at two equal intervals from the peak correlation. Variable delay is achieved by changing the clock frequency which controls a digital shift register delay line. The output of the system is linear and identical to that calculated with parallel logic cross correlation computers.

ISSN:0034-6748    

DOI:10.1063/1.1686705

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Design and working principle of a flash x‐ray system is described. A two‐stage Marx generator is used, the charging voltage is 150 kV, the stored energy 1125 J. Anode and cathode are arranged coaxially. The anode consists of a tungsten coated aluminium tube of 20 mm i.d. into which the substances to be irradiated are placed. Measurements of electrical and radiation parameters are described. The x‐ray dose per pulse is 400 rad, the half‐width of the pulse is 0.2 &mgr;sec and the mean quantum energy 44 keV. An example for the application of the system in microsecond pulse radiolysis is presented.

ISSN:0034-6748    

DOI:10.1063/1.1686706

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The laser emission of vibrationally excited OH in the electronic ground state, produced in pulsed electric discharges through O3&sngbnd;H2gas mixtures, has been studied using two transverse discharge systems. Discharges were produced in two electrode and multipin transverse configurations. Stimulated emission between the &ngr; = 3→&ngr; = 2 and &ngr; = 2→&ngr; = 1 levels was observed in the 3 &mgr; wavelength region. The output has been investigated as a function of composition and pressure of O3&sngbnd;H2mixtures, addition of foreign gases, and discharge energy. Output intensities were compared to that of the HF laser emission produced from H2&sngbnd;SF6in the same discharge system. The two discharge configurations gave similar intensities; this OH laser was shown to have approximately 10−2times the power of the HF†laser.

ISSN:0034-6748    

DOI:10.1063/1.1686707

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The construction of a voltage clamp with discontinuous feedback is described. Its main feature is a pulsed membrane current with an amplitude proportional to the voltage error, which is determined by integration in the pulse intervals. A current pulse of 8 &mgr;sec length repeating every 24 &mgr;sec is used. Gain switching assures a fast response to large errors, as well as high steady state accuracy. Membrane voltage changes by 150 mV in 8 &mgr;sec to 1% of the final value. 50 &mgr;sec after such a step, a change of resistive membrane current can be read reliably. Performance is demonstrated with equivalent networks of biological membranes and with applications to black lipid membranes and epithelial membranes.

ISSN:0034-6748    

DOI:10.1063/1.1686708

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A photoionization source of monoenergetic electrons is described and design criteria for such sources are discussed. The present design produces a beam of ≃10−12–10−13A by photoionization of a metastable (1D2) barium beam inside the cavity of a He&sngbnd;Cd laser operating at 3250 Å. The photoelectrons are produced with 17 meV kinetic energy and a calculated energy spread of <1 meV. Energy analysis is provided by measuring the width of the 11.08 eV argon resonance. The observed width of this resonance has, to date, been limited to ∼6 meV, but tests are reported which indicate that this width is largely due to Doppler spreading in the target atomic beam and potential gradients across the collision volume.

ISSN:0034-6748    

DOI:10.1063/1.1686709

出版商:AIP    

年代:1974

数据来源: AIP