摘要:

A mechanical arcless dc circuit breaker is proposed and has been constructed. A rectifying device is used to block the reverse current of the breaker, allowing the breaker to open under zero current condition created by the discharge of a commutation circuit. A diode and a saturable reactor are used as the rectifying device, with a leakage current of ∼1 and ∼10 A, respectively. The duration of mechanical motion is about 20 ms, and its jitter is 2 ms, which is too long to make an economical system using a commutation capacitor. In order to avoid the dead time, the commutation circuit is started after the breaker kicks in and the final jitter is reduced to 20 &mgr;s. Arcless current interruption is achieved at 10 kA and 9.1 kV. Since a strong arc plasma is not generated between the contacts, a long lifetime of the breaker can be expected and a disconnecting switch can be used instead of a circuit breaker, reducing the size of the switch. These characteristics of the new breaker can be expanded for many applications.

ISSN:0034-6748    

DOI:10.1063/1.1143252

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We developed a two‐dimensional x‐ray detector for x‐ray beam profile analysis. The detector was built from commercially available parts, which included a low‐cost 8‐bit CCD camera, and a zoom lens coupled to a close‐up lens, to which was attached a fiber‐optic faceplate coated with (Gd2O2S:Tb) phosphor to a surface density of (10 mg/cm2). Testing of the detector unit has shown good linearity of response to the incident x‐ray intensity (within ±4%), and good spatial linearity. The advantages of this detector lie mainly in its compactness, its ease of maneuverability, and the fact that it can be remotely controlled by a PC/AT computer at a reasonable cost (∼$1000 without the PC/AT).

ISSN:0034-6748    

DOI:10.1063/1.1143253

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A method for the high‐temperature generation of reactive species in supersonic molecular beams has been developed. Pyrolysis temperatures (25–1800 °C) can be maintained for longer than 100 h for extended experiments. Short contact time (≊10 &mgr;s) of the seeded (<1 Torr partial pressure in 2 atm inert carrier gas) precursor molecules suppresses recombination of the product radicals. Number densities for radicals are estimated to be ≊1014cm−3at the sonic orifice with radical fluxes of ≊1016s−1.

ISSN:0034-6748    

DOI:10.1063/1.1143254

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An automated ac susceptibility measuring system based on an ac mutual inductance bridge is described. A personal computer and a digital‐analog converter are used to control the amplitude and phase of the compensatory signal which balances the bridge. An analog multiplier and a variable‐resistance photocoupler are used in the amplitude and phase control circuits, respectively. The magnetic moment of a sample for a 1‐&mgr;V output voltage is 3.8×10−6emu/&mgr;V. Sufficient sensitivity was confirmed for an application to oxide superconductors.

ISSN:0034-6748    

DOI:10.1063/1.1143255

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A small, single piezoXYZtranslator has been developed. The device has been used as a scanner for a scanning tunneling microscope and has been tested successfully in air and in UHV. Its simple design results in a rigid and compact scanning unit which permits high scanning rates.

ISSN:0034-6748    

DOI:10.1063/1.1143256

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Two low phase‐noise Gunn diodeX‐band oscillators intended for use in electron paramagnetic resonance (EPR) spectroscopy are described. In the first, a 250‐mW MA49159 Gunn diode oscillator (M/A‐COM, Burlington, MA) is mounted in a coaxial transmission line that is closely coupled to a TE011transmission cavity that in turn is loosely coupled to the output transmission line. The output power is 50 mW and the phase noise is −145 dBc/Hz at 100 kHz offset. In the second, two such coaxial assemblies are used with 500‐mW MA49110 diodes for increased power. The output power is 150 mW and the phase noise is −150 dBc/Hz at 100‐kHz offset. These phase noise values are in the range of 24–29 dB better than the specification for a normal high quality klystron used in commercial spectrometers.

ISSN:0034-6748    

DOI:10.1063/1.1143257

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A small ring‐shaped vacuum chamber has been constructed and connected to the piezotube used for scanning samples in the atomic force microscope (AFM). Samples made up of any material, up to 50 mm in diameter, can be firmly attached onto the piezotube without causing damage to the sample. A 50‐lbeer container forms a buffer between vacuum pump and chamber. With this supply of vacuum, the AFM can be operated for a 4–8 h period without turning on the vacuum pump again. Samples can be changed within 30 s. The scan frequency when using microscope slides is limited to 40 Hz due to resonance effects of the microscope slides.

ISSN:0034-6748    

DOI:10.1063/1.1143258

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Impact shocks produced by the closed‐cycle refrigerator produce jitter in the output frequency of a diode laser. An electronic device is described which allows triggering of the data acquisition system when the influence of the vibration‐induced noise is at a minimum.

ISSN:0034-6748    

DOI:10.1063/1.1143259

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A portable device that easily maintains a desired humidity at room temperature ranging from 50% to 95% in a small, closed environment is described. This device permits extended x‐ray and spectroscopic analysis of crystals that require a humidified environment by passing a stream of air over heated water. An electronic controller coupled with a humidity sensor provides feedback and control.  

ISSN:0034-6748    

DOI:10.1063/1.1143260

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An easily implemented scheme for the fabrication of glass micropipettes is described using a high‐velocity pneumatic piston for the production of a strong pulling force. The piston is incorporated into a standard two‐stage pipette puller and is capable of producing both patch‐ and ultramicro‐type pipettes. The system has the versatility of a solenoid puller with a greater simplicity and lower cost.

ISSN:0034-6748    

DOI:10.1063/1.1143261

出版商:AIP    

年代:1992

数据来源: AIP