摘要:

Current transformers with resistive loads are examined experimentally to determine some of the limitations to high frequency response. Coil resonances are avoided by placement of damping resistors around the secondary winding. This permits a relatively large number of secondary turns (50 or 100), improving low frequency response and increasing thei×tproduct, even for the highest frequency transformers. Uniform response to several gigahertz is obtained in a transformer with 6.4 mm window, while a range ∼1 Hz to ∼300 MHz is found in a larger transformer (12.7 cm diam and 2.5 cm window). Both ferrite and iron alloy cores are utilized.

ISSN:0034-6748    

DOI:10.1063/1.1685307

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The temperature dependence of the dielectric constant of KCl crystals doped with Li+ions has been shown to provide a useful measure of temperature over the range of 1–30 K, that is (at least between 1–10 K), independent of magnetic fields up to at least 100 kOe. The magnetic field dependence, measured by calibrating the thermometer at zero, then at high field, is immeasurably small and certainly less than the absolute temperature uncertainty (about 0.2%) at 4.2 K. The capacitanceCvaries with temperatureTapproximately asC=A+B/T, whereAandBare positive constants. For a thermometer withA∼30 pF andB∼15 pF·deg the sensitivity &dgr; lnC/&dgr; lnT=−B/(AT+B) is about 0.3 at 1 K. Using a GR type 1615 A bridge a sensitivity of 0.3 mK at 1 K, and of 3.6 mK at 4.2 K was obtained. The thermometer calibration is reproducible to better than 0.2% on cycling between room temperature and helium temperature. A long range stability problem, possibilities for higher sensitivities, other geometric arrangements, and similar further development questions are briefly mentioned.

ISSN:0034-6748    

DOI:10.1063/1.1685308

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Potassium chloride crystals doped with OH−or CN−ions are shown to be excellent magnetic field independent thermometers between 0.1 and 10 K. A procedure for making rugged capacitance thermometers, their sensitivity to temperature, and their independence of magnetic field at 1.2 and 4.2 K are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1685309

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An objectionable feature of electron spectra taken with a retarding potential analyzer, for example, as in Auger electron spectroscopy, is the large background that is characteristic of the general shape of the secondary electron distribution function. It is shown that an electron analog of the secondary electron emission from a specimen can be injected at the signal source of a retarding potential analyzer so as to cancel the secondary emission function. The result is that the annoying background that characterizes Auger electron spectra taken with retarding potential analyzers is removed, the error in the magnitude of Auger peaks due to secondary emission background is eliminated, ``washed‐out'' fine structure accompanying large Auger signals may be recovered, and uniform amplifier gain is useful throughout the energy range of the detector circuit. The technique employs one of two analog functions for an approximation to the secondary electron emission and does not attempt an exact fit. The mathematical properties of these functions are described as well as criteria for choosing the appropriate function for the best approximation. It has been found that the functional behavior of the major component of the secondary electron energy spectrum from Ni (110) (i.e., ignoring superimposed Auger electron contributions) is essentially constant from 10 to 1000 eV. Consequently, there is no experimentally observed demarcation between true secondary emission and rediffused primaries. The general energy distribution function can be represented asN(E)=A(E+E0)−m.

ISSN:0034-6748    

DOI:10.1063/1.1685310

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The dual wavelength spectrophotometer, noted for its high sensitivity and accuracy in the recording of oxidation‐reduction and other reactions of membrane bound components in turbid suspensions of biological materials, has now been modified to scan the spectrum of these components over a reasonable wavelength range (40 nm) and in a short time (rates as rapid as 20 nm/sec). The baseline precision is not remarkable (approximately 1% error) but the method retains the intrinsic noise rejection properties of the dual wavelength technique. Two forms of the apparatus are discussed, one a simple modification involving a previously described time sharing compensating circuit, and the other incorporating a tapped potentiometer for more precisely correcting the baseline, and a comparator and error detector for correcting wavelength dependent sensitivity error.

ISSN:0034-6748    

DOI:10.1063/1.1685311

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Internal diameters of a long, small bore metal tube were calculated from the measured capacitances between it and a cylindrical coaxial probe of known characteristics. The tube and the probe were used as the electrodes of a three‐lead capacitor, measurable with high accuracy in a transformer ratio arm bridge. For tubes of 0.1 cm bore or less, average diameters as a function of position can be determined by this method with an over‐all uncertainty of ±6×10−5cm over lengths of 1 m. The method can readily be extended to larger bores and greater lengths.

ISSN:0034-6748    

DOI:10.1063/1.1685312

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Cellular fluorochromes, pyridine nucleotides (PN), and flavoproteins (Fp) reflect the redox state of the cytoplasmic space and mitochondria of the intact cells and tissues and afford a direct readout of essential parameters of cell metabolism. A time sharing fluorometer which alternates every 8 msec the overlapping emission and excitation wavelengths of both fluorochromes enables nearly simultaneous recording of the two components. From a spot of several millimeters in diameter an adequate signal‐to‐noise ratio can be obtained at a response time of less than 0.1 sec. In conjunction with the regenerative flow apparatus, the fluorescence of the components can be recorded in times down to 20 msec. Applicability to reaction kinetics in perfused organs and in suspensions of mitochondria as well as to other systems with double fluorescence labels is indicated.

ISSN:0034-6748    

DOI:10.1063/1.1685313

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

We describe a new microwave gated radiometer for traveling wave measurement of the radiation temperature of low temperature plasma afterglows independent of plasma absorptivity and reflection coefficients. Since this radiometer is unaffected by a medium power heating microwave, it is particularly well suited for keeping a close control on temperature during microwave cross modulation experiments.

ISSN:0034-6748    

DOI:10.1063/1.1685314

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A technique is presented for generating a complete Langmuir probe characteristic in 2 &mgr;sec with sweep speeds greater than 150 V/&mgr;sec. Probe construction with stable lead capacitance is necessary when compensating for the cable displacement current with a current transformer. The probe characteristic is displayed using the X‐Y capabilities of a 'scope and results are given for an electron cyclotron resonance heated hydrogen plasma confined in a toroidal quadrupole.

ISSN:0034-6748    

DOI:10.1063/1.1685315

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A mathematical model of a quadrispherical electrostatic analyzer is formulated to give the response of such an instrument to a monoenergetic, unidirectional charged particle beam. The model is developed taking into account the aperture and collector geometry and it does not rely on the usual simplifying assumptions that the ratio of the analyzer plate separation to the mean radius is small or that any of the angular or energy acceptance windows are negligible. The model is compared to calibration data and is found to agree well. It is also readily adaptable to the determination of the response function of electrostatic analyzers with other patrial spherical geometries utilizing an arbitrary charged particle distribution input function.

ISSN:0034-6748    

DOI:10.1063/1.1685316

出版商:AIP    

年代:1971

数据来源: AIP