摘要:

A theoretical analysis of the method of time averaging is made with special emphasis on the correlation effects caused by non‐white noise. It is shown that only in special cases is the signal‐to‐noise ratio improved exactly according to the square root of the number of successive scans through the investigated spectrum. This is shown in detail for random noise with an exponential‐cosine autocorrelation function. In the case of random noise with a pure exponential autocorrelation function, the deviation from the proportionality to the square root of the number of scans does not exceed a factor √2. If the frequency dependence of the power spectrum of the noise is given by |f|−&lgr;, 0≤&lgr;≤1, then the proportionality to the square root of the number of scans holds exactly. A peak in the noise power spectrum at a multiple of the repetition frequency of the scanning does affect the time averaging only if its width is smaller than the repetition frequency.

ISSN:0034-6748    

DOI:10.1063/1.1719443

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Intermediate passage conditions in magnetic resonance experiments are investigated to determine the optimum performance conditions for maximum sensitivity, particularly in connection with time averaging methods. The possible increase in signal height by increasing the sweep rate can be utilized in time averaging methods to enhance the sensitivity. The optimization of the conditions described here is based on numerical solutions of the Bloch equations. The results are given in graphical form and show the optimum conditions for many magnetic resonance experiments where the absorption mode signal is recorded. The improvement of the sensitivity, which is possible if instead of a slow passage, single scan experiment a fast passage, multiple scan experiment is made, is higher for a high ratio of the relaxation timesT1/T2. The possible gain is limited by the maximum allowed line broadening and line shift. The conditions are nearly optimum if the sweep ratea(cps/sec) and the rf field strength &ggr;H1(rad/sec) are related bya/(&ggr;H1)2=0.332. Additionally, it is shown that the shift of the resonance maximum due to the intermediate passage conditions can have a negative sign and that an increase of the sweep rate can cause a narrowing of the resonance line under certain conditions.

ISSN:0034-6748    

DOI:10.1063/1.1719444

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A high power, solid state device to switch direct current on and off for the controlled pulsing of a high intensity light source is described. Using 400 A (continuous rating) silicon controlled rectifiers, the switch has a design maximum power rating of 5000 A at 450 V for a 1 msec pulse.

ISSN:0034-6748    

DOI:10.1063/1.1719445

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A systematic investigation of the design variables for a high pressure cell with supported taper pistons has been undertaken. The variables studied include: the effect of center thickness, the effect of flat diameter and piston diameter, the pressure gradient across the flat, the pressure gradient on the taper, and the effect of different materials supporting the center. It is concluded that any scaling up in size from the dimensions used in the electrical resistance cell previously described in the literature (2.29 mm diam flat and 0.33 mm center thickness) results in a drastic reduction in pressure range. Scaling down the flat size results in a modest increase in pressure range. The pressure is remarkably independent of radius in the region of the flat which contains the electrical resistance sample. A piston with a double taper might suppy a greater degree of support for the piston tip.

ISSN:0034-6748    

DOI:10.1063/1.1719446

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An electro‐optical system is described for automatically measuring the spectral response of a photosensitive material or device and its output under an arbitrary light spectrum. The system has been used to obtain the spectral response and the short circuit current of solar cells in outer space sunlight. A comparison of the outer space short circuit current of n‐p silicon solar cells measured by this system and by a commercially available solar simulator shows an agreement of better than 2.1%.

ISSN:0034-6748    

DOI:10.1063/1.1719447

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A light source is described for generation of intense constant shape pulses of width as short as 20 nsec at demonstrated repetition rates up to 5 kc. The radiated power in the violet‐green region (3000–5000 Å) of the spectrum was measured at 0.5 W/sr perpendicular to the lamp axis. Lamp configuration, pulser circuitry, and applications to spectroscopy and optical radar are discussed. A simple computer to facilitate the determination of fluorescent lifetimes is described.

ISSN:0034-6748    

DOI:10.1063/1.1719448

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An apparatus, based on thin‐rod resonance techniques, has been used to determine both Young's and shear moduli as functions of temperature during a single experiment. The advantages of this method, its accuracy, and its limitations are discussed, along with the constructional details of the apparatus.

ISSN:0034-6748    

DOI:10.1063/1.1719449

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An instrument has been developed which measures the rate of phototaxis in a suspension of microorganisms by recording the increase in optical density which results when the organisms accumulate in a beam of stimulating light. Intensity and spectral quality of the actinic light, as well as of randomly scattered background illumination, can be controlled. Density changes are measured with a dual chopped beam arrangement using infrared light. Thermostatic control of the temperature of the sample is provided.

ISSN:0034-6748    

DOI:10.1063/1.1719450

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A direct current voltage measuring and recording system having high sensitivity (0.02 &mgr;V) and high accuracy has been developed using commercially available components. The performance of the system exceeds the nominal specifications of the individual portions of the system because of selection of components and careful shielding, guarding, and grounding practices.

ISSN:0034-6748    

DOI:10.1063/1.1719451

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The variable ``moire´ pattern,'' formed when a 1:1 image of an 8 &mgr; grating connected to a Mo¨ssbauer drive is reflected back onto itself, is utilized to measure the instantaneous velocity of the drive. A photodiode converts the intensity modulated light from the pattern into an electrical signal. From this signal pulses are derived that correspond to shifts of the grating by multiples of 2 &mgr;. These pulses can be applied to a multichannel analyzer used as a part of the Mo¨ssbauer spectrometer and thus yield a velocity calibration spectrum. Instantaneous velocities can be measured with accuracies down to about 1 &mgr;/sec.

ISSN:0034-6748    

DOI:10.1063/1.1719452

出版商:AIP    

年代:1965

数据来源: AIP