Conformal mapping of the unit circle or of the upper half plane onto a polygon

The aim of this paper is to reduce the problem of conformal mapping onto a polygon and the inverse mapping problem to simple engineering exercises. In particular, both analytical and numerical methods are combined to eliminate the need for complicated mathematical analysis. A FORTRAN IV-program is presented which offers many conveniences to the user including graphic representation of the mapping. Finally, the results of 15 examples relating to quadrilaterals, pentagons and heptagons are given for reference. The high degree of accuracy of the calculated values, to about 10 significant digits, should be noted.     

Recent achievements in single photon detectors and their applications

Abstract

Solid state single photon detectors are receiving more and more attention in a number of areas of applied physics: optical sensors, communications, quantum cryptography, optical ranging and Lidar, time resolved spectroscopy, opaque media imaging and ballistic photon identification. This paper reports on results of research and development in the field of solid state single photon detectors at the Czech Technical University in Prague over the last 20 years. Avalanche photodiodes specifically designed for single photon counting devices have been developed based on various semiconductor materials: Si, Ge, GaP, GaAs and InGaAs. Electronic circuits for biasing, quenching and control of these detectors have been developed and optimized for different applications. The sensitivity of solid state photon counters spans from 0.1 nanometre X-rays up to 1800 nanometres in the near infrared region. Timing resolution of solid state photon counters as high as 50 picoseconds full width at a half maximum has been achieved when detecting single photon signals. Circuits permitting operation of solid state photon counters in both single and multiple photon signal regimes have been developed and applied. The compact and rugged design, radiation resistance, and low operating voltage are attractive features of solid state photon counters in various space projects.     

Time interval measurement device based on surface acoustic wave filter excitation, providing 1 ps precision and stability

This article deals with the time interval measurement device, which is based on a surface acoustic wave (SAW) filter as a time interpolator. The operating principle is based on the fact that a transversal SAW filter excited by a short pulse can generate a finite signal with highly suppressed spectra outside a narrow frequency band. If the responses to two excitations are sampled at clock ticks, they can be precisely reconstructed from a finite number of samples and then compared so as to determine the time interval between the two excitations. We have designed and constructed a two-channel time interval measurement device which allows independent timing of two events and evaluation of the time interval between them. The device has been constructed using commercially available components. The experimental results proved the concept. We have assessed the single-shot time interval measurement precision of 1.3 ps rms that corresponds to the time of arrival precision of 0.9 ps rms in each channel. The temperature drift of the measured time interval on temperature is lower than 0.5 ps/K, and the long term stability is better than +/-0.2 ps/h. These are to our knowledge the best values reported for the time interval measurement device. The results are in good agreement with the error budget based on the theoretical analysis.     

Positron lifetimes in ZnO single crystals

Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.     

Multichannel Cross Modulation in CATV Amplifier

The Volterra series approach is used to derive a simplified expression relating the single channel and multichannel cross modulation in a CATV amplifier. The cross modulation from n unwanted carriers synchronously modulated is seen to be dependent upon the phase versus frequency variation of the third-order Volterra transfer function of an amplifier. Only when the phase is constant for any frequency of interest is the increase in the magnitude of the cross-modulation vector given by 20 log n, n being the number of synchronously modulated carriers.     

Kontinuierliche Staubmessung an Arbeitsplätzen und Industrieanlagen

Registrierende Meßverfahren auf kontaktelektrischer Basis. Wirkungsweise, Aufbau und Eichung des Meßgerätes ?Konitest?. Einfluß der stofflichen Zusammensetzung und der Körnung des Staubes. Staubgehaltsmessung im Hochofengichtgas. Staubkonzentrationsmessung der Atemluft an staubgefährdeten Arbeitsplätzen. Erhöhung der Nachweisempfindlichkeit des Konitests. Registrierende Messung der lungengängigen Feinstaubkonzentration und der Staubkonzentration der Außenluft.     

Electrical conductivity of internally oxidized Ag-Mg and Ag-Al alloys

Conclusions A study was made of the electrical conductivity of internally oxidized Ag-Mg alloys containing 0.5, 0.8, 1, 1.35, and 1.85 at.% Mg and of internally oxidized Ag-Al alloys with 0.5, 1.0, and 1.5 at.%A1. The results obtained are analyzed. The investigation has shown that internal oxidation decreases the electrical conductivity of such alloys, the extent of the decrease depending upon the oxidation temperature and the concentration of the alloying component. The electrical conductivity of oxidized Ag-Mg alloys is higher than that of oxidized Ag-Al alloys. Plastic deformation leads to a further fall in electrical conductivity, which, however, can be partly offset by high-temperature annealing.Translated from Poroshkovaya Metallurgiya, No. 2 (146), pp. 103–107, February, 1975.     

Peltier-Cooled and Actively Quenched Operation of InGaAs/InP Avalanche Photodiodes as Photon Counters at a 1.55-mum Wavelength

The performance of commercially available InGaAs/InP avalanche photodiodes as single-photon detectors at a 1.55-mum wavelength has been investigated. A new active quenching and gating circuit, tailored for operation of these diodes at temperatures in the range from room temperature to -60 degrees C and achievable by means of thermoelectrical cooling, has been developed. Careful tuning of the diodes' operating conditions resulted in a significant reduction of afterpulsing effects; it permitted operation of the detectors with high repetition rates. A noise-equivalent power of 7 x 10(-16) W/Hz(1/2) was obtained at a 1.55-mum wavelength.