摘要:

A new device capable of measuring minute dc voltages is described, and a simple theory which describes the operation and predicts the performance is presented. Experimental amplifiers have demonstrated dc sensitivities which closely approach the maximum attainable by any device. Their performance characteristics agree satisfactorily with the theory. Sensitivities of 4×10−14V with a source resistance of 4×10−7&OHgr; and a time constant of ≈ 1 sec have been obtained at 4.2°K. The ultimate sensitivity appears to be limited only by the noise present in the source itself.

ISSN:0034-6748    

DOI:10.1063/1.1721066

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The dynamic and optical properties of the cylindrical capacitor for nonrelativistic charged particles were studied for certain arrangements of the source and some interesting features were found. A point source embedded in the inner cylinder on the common axis of the capacitor can be imaged for any angle of emission &thgr;0between 0 and &pgr;/2. Each angle &thgr;0has its correspondingK0factor incorporating the geometrical and electrical parameters of the device.K0and &thgr;0together determine uniquely the distance between the source and its image on the common axis of the capacitor. There exists a first order focus for all angles of emission except &thgr;0=42°18.5′; for the latter there is a second order focus. The figures of merit of this analyzer concerning resolution and transmission were found to be better than those of other forms of the cylindrical analyzer. However, the deflecting voltages required in the new device are higher. The calculations were checked experimentally for &thgr;0=&pgr;/4.

ISSN:0034-6748    

DOI:10.1063/1.1721067

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The capability of the Naval Applied Science Laboratory for direct simulation of thermal effects due to nuclear weapons has been extended to low yield devices [as small as 10 kilotons (kt)] by the installation of a high performance servo‐driven shutter in a carbon arc imaging furnace. The system can simulate thermal radiation pulses from atmospheric detonations with yields of from 10 kt to the largest devices. It can deliver a maximum irradiance of 190 J cm−2sec−1over an effective spot diameter (irradiance at least 90% of maximum) of approximately 17 mm using a single ellipsoidal mirror. With the addition of a second mirror, a maximum irradiance of over 850 J cm−2sec−1can be obtained with an effective spot diameter of about 4 mm. Arbitrary pulse shapes can also be delivered. Provision is made to record irradiance histories and source characteristics during each exposure without appreciably interfering with sample irradiation.

ISSN:0034-6748    

DOI:10.1063/1.1721068

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The application of the internal electronics of a commercial sampling oscilloscope, modified by a few additional components which do not interfere with the normal functions of the oscilloscope, as a very fast time‐to‐amplitude converter for measurements of short time differences is described. The electronic modifications and their functions are reported. The electronic time resolution has a FWHM of 3.2×10−11sec, a slope decayt1/2of 5×10−12sec, and certainly can be improved. The range of measurable time differences lies between some picoseconds and some milliseconds.

ISSN:0034-6748    

DOI:10.1063/1.1721069

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A device has been designed and constructed, largely of commercially available operational amplifiers, to measure the voltage‐current relations in biological membranes due to the ion flux through them. The device operates in three modes: to clamp the voltage across the membrane to some predetermined value and record the current, to clamp the current through the membrane and record the trans‐membrane voltage, and to recorddV/dI, the resistance of the membrane measured in a time short compared to the ion redistribution time.

ISSN:0034-6748    

DOI:10.1063/1.1721070

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The design of a gauge capable of measuring gas pressures in the range from atmospheric pressure to 10−4mm Hg by acoustic techniques is presented. The principles of acoustic transmission in the classical and geometrical relaxation regimes of gas dynamics are reviewed for the case of a confined volume of gas. The geometrical conditions for the feasibility of a sonic pressure gauge following a linear law are obtained. Practical limitations in the sound source used give rise to a change in the sensitivity of the gauge in the transition from classical to geometrical relaxation regime. Transducer and electronic design and a calibration curve of the gauge are given. The experimental results are in general agreement with the analysis.

ISSN:0034-6748    

DOI:10.1063/1.1721071

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A cryostat to transmit the load of a 270 ton press to a chamber at liquid helium temperatures is described. The pressure transmitting columns are made of an epoxy resin‐bonded glass fiber laminate. The liquid helium consumption is ∼10 liters to cool from ∼70 to 4.2°K, and the boiloff rate is ∼1.2 liters. Measurements of the electrical resistance of bismuth between 4.2 and 77°K at different pressures up to ∼85 kilobars were made using a Bridgman anvil (1.27 cm face) geometry.

ISSN:0034-6748    

DOI:10.1063/1.1721072

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A switching circuit using a high powr silicon‐controlled rectifier to discharge a high energy (5 kJ), low voltage (450 V) capacitor bank into pulse coils immersed in liquid helium is described. A free‐wheeling diode assures that the pulses remain unidirectional. The circuit has successfully operated with inductance‐resistance‐capacitance (LRC) combinations yielding pulses having rise times &tgr;Rand decay times &tgr;Din the ranges 0.80 msec ≤&tgr;R≤0.25 sec and 2.2 msec ≤&tgr;D≤1.2 sec, respectively. Another SCR is used to shunt unwanted capacitor energy to an auxiliary circuit at any desired time during the pulse duration. This function is used to protect the pulse coils from overheating and to conserve liquid helium. The use of special, fixed‐geometry copper coils is described which enables one to obtain initial rates of change of the applied magnetic fieldH˙0which varied over many orders of magnitude (102<H˙0<108Oe/sec). The circuit, while generally useful in most solid‐state studies requiring pulsed‐magnetic fields, was used to study flux‐jumping, rate effects, and critical currents in tubes and wires made of type II superconducting materials. Some of these experiments are described.

ISSN:0034-6748    

DOI:10.1063/1.1721073

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A unique system has been developed with the capability for use as a voltage monitor or regulated voltage source to a stability level as good as 1 ppm/12 h, or 0.1 ppm/15 min. The system employs a precision capacitor charged to a voltage level matching the level of interest, so that it provides optimum discrimination against amplifier noise and also obviates the need for a voltage divider. A useful voltage range from 1 kV to 10 kV has been demonstrated and there is reason to hope that the technique can be applied at higher voltage levels. The short term stability, for time intervals of 1 hour or less, is superior to that obtainable from a conventional system containing the usual voltage reference, voltage divider, and dc amplifier.

ISSN:0034-6748    

DOI:10.1063/1.1721074

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

After a short theoretical exposition of a method for compensating inaccuracies in parallel‐diode switch‐gates, a linear gate circuit is presented which is based on the described principle. Accurate measurements of differential linearity error in the whole dynamic range (0–10 V) have been done. The results of experimental checks of rise time, pedestal, rejection factor, and thermal stability are also given. The circuit which operates with gating pulses longer than 30 nsec is believed to introduce a considerable improvement in comparison with previously given solutions, mainly from the linearity point of view.

ISSN:0034-6748    

DOI:10.1063/1.1721075

出版商:AIP    

年代:1967

数据来源: AIP