摘要:

The analysis of transient phenomena originating from relaxation processes is a tool for material and device characterization. The time constants of the transients provide information about the energy levels involved, and the transient amplitude is coupled to the density of occupied states. A convenient method for the analysis of exponential transients is the use of correlation‐spectroscopic techniques. An example is deep level transient spectroscopy, a capacitance method for the study of deep impurities in semiconductors. The correlation with a weighting function is in this case conventionally made by hardwired instruments. We demonstrate here how shortcomings of this method can be avoided and higher flexibility can be achieved by separating the signal processing from the data acquisition. The hardware is a high‐resolution capacitance measurement system with a resolution of 0.002 pF in capacitance and 5 &mgr;s in time. As a result of the measurement, which is considerably faster than analog methods, a data array describes the response of the sample with regard to time and temperature. Several signal processing routines are applied to the data to filter out specific information.

ISSN:0034-6748    

DOI:10.1063/1.1136396

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A procedure suitable for laboratory practice is described to prepare large‐area self‐supporting silicon thin crystals with (100), (110) and (111) orientations. Windows up to 2 cm in diameter and 2000 A˚ in thickness can be produced. Variation in the thickness across the sample can be as low as ±60 A˚ as measured by4He+backscattering spectrometry.

ISSN:0034-6748    

DOI:10.1063/1.1136404

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A new technical method of thermal conductivity measurements of uniaxially compressed samples, at liquid helium temperatures, has been tested. This method allows rigorous guiding and alignment of the sample while the problems linked to the thermal insulation of the sample are also minimized. Good reproducibility of the results was obtained after the sample was taken off and mounted again.

ISSN:0034-6748    

DOI:10.1063/1.1136405

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We describe a thermal conductivity cell for the measurements of the composition of binary gas mixtures. The main advantage of the cell is that its response is pressure independent in the range 20–100 Torr. The apparatus, of the parallel plate type, uses a very thin printed circuit film as the hot plate in order to achieve a fast response time. The cell was designed and operated to determine the ortho‐para‐composition of hydrogen gas samples but it also works reliably as an analyser of3He–4He gas mixtures. In both cases the precision of the instrument is better than 10−2for the mole fraction.

ISSN:0034-6748    

DOI:10.1063/1.1136406

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A fast (NTSC TV‐rate), low cost, simple histogram equalization processor is described. In this apparatus, the histogram equalization processing is carried out by the table look‐up method at TV‐rate. The characteristics of the processor, and its applications to the real time and on‐line processing of weak contrast images from the Ultra‐High Voltage Electron Microscope (Osaka University) are described. With this apparatus, equilevel processing, level compression, and level slicing may also be easily carried out.

ISSN:0034-6748    

DOI:10.1063/1.1136407

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A novel microwave cavity is presented in which a conducting sample can be excited by a strong microwave field and, simultaneously, its response can be measured over a wide frequency range surrounding the excitation frequency.

ISSN:0034-6748    

DOI:10.1063/1.1136408

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A new method for measuring the autocorrelation function of stationary, Gaussian distributed, differentiable or nondifferentiable noise is presented. This method does not require real‐time digitizing or analog multiplying and can be easily realized since it is based on the use of either a sampling oscilloscope or a boxcar averager. The method requires the measurement of the ensemble average of the multiple traces generated by internally triggering the oscilloscope or averager on the noise. Expressions for interpreting this average to obtain the autocorrelation function as well as examples of measurements made by this technique are given and discussed.

ISSN:0034-6748    

DOI:10.1063/1.1136409

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A constriction resistance measuring system was designed for evaluating the performance of residential branch wiring circuit connections. The measurement system separates the bulk from the constriction resistance by utilizing the nonlinear voltage‐current behavior of a connection. The method overcomes some of the past problems with the nonlinear technique by employing a pulse stimulus current coupled to a high‐speed data acquisition system under computer control. A least squares nonlinear fit program is used to obtain the best fit of the voltage‐current data to an equation which serves as the nonlinear model. The model was verified by simulating connections with a ’’true 4‐wire crossed rod’’ measurement technique. Measurements on connections formed with aluminium and copper conductors agree closely with the parameters predicted by the model. The method is shown to have the ability to accurately measure the constriction resistance of practical connectors in the presence of widely changing values of bulk resistance. A modification of the technique is proposed and shown to have a potential threefold increase in sensitivity.

ISSN:0034-6748    

DOI:10.1063/1.1136410

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An ultracentrifuge based on the air turbine of a dental drill attains 400,000–600,000 rpm and a centrifugal force 2 to 3 million ×g. It is used for the examination of cell suspentions and homogenates and can be applied to macromolecular solutions. Microcuvettes with volumes ranging from less than 1 mm3to 0.001 mm3(suitable for single cells) are of disk and square capillary form and are made of polycarbonate or glass. A special microscope is used to obtain a stopped image of the rotating cuvette. A new method to preserve the centrifugal state of the contents is tested: deep freezing of a rotating cuvette for subsequent freeze‐drying and microscopical examination. Experiments on cells include centrifugal intercellular movement of nuclei and cytoplasmic particles, cell fusion, and homogenization.

ISSN:0034-6748    

DOI:10.1063/1.1136411

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A laser doppler velocimeter (LDV) has been designed and constructed for use in measuring ocean water flow velocity in the immediate vicinity of marine organisms anchored inside a water tunnel. The principal innovation reported here is the use of a microprocessor to produce an ’’intelligent’’ instrument which automatically calculates and displays the flow velocity. The resulting electronics design represents a considerable simplification over existing instruments which generally require the use of a separate autocorrelator and/or multi‐channel analyzer (MCA) plus an external minicomputer. The LDV configuration employed is a crossed‐beam design using a 2‐mW He–Ne laser and inexpensive optics. A 48‐channel 1‐bit clipped autocorrelation function is implemented using a modified TTL design reported previously by Chen and co‐workers. A Motorola 6800 micromodule updates the contents of each channel by direct memory access and displays the resulting correlogram on a CRT monitor. The velocity is periodically calculated (±5%) and displayed by LED digits.

ISSN:0034-6748    

DOI:10.1063/1.1136412

出版商:AIP    

年代:1980

数据来源: AIP