A 119 GHz planar Schottky diode mixer for a space application

A planar single-ended GaAs Schottky diode mixer has been designed, built, and tested at 119 GHz. The mixer front end includes also a waveguide filter for image rejection, and a temperature compensated ring filter. Measurements at room temperature showed a conversion loss of 7 dB and a noise temperature of 900 K (SSB). At 100 K the measured noise temperature of the mixer was 500 K (SSB).     

Jitter characteristics of an on-chip voltage reference-locked time-to-digital converter

The noise and jitter characteristics of an on-chip voltage reference-locked ring oscillator used in the time-to-digital converter (TDC) of the integrated receiver of a pulsed time-of-flight laser rangefinder are presented. The frequency of the ring oscillator, 683 MHz, was locked to the on-chip voltage reference by means of a frequency-to-voltage converter, resulting in better than 90 ppm/°C stability. The noise and jitter transfer characteristics of the loop were derived, and simulations were performed to see the effects of different noise types (white and 1/f noise) on the cumulative jitter of the locked ring oscillator. Finally, these results were verified by jitter measurements performed using an integrated time-to-digital converter (TDC) fabricated on the same die (0.18 μm CMOS process). The cumulative jitter of the on-chip reference-locked ring oscillator was less than 30 ps (sigma value) over a time range of 70 ns, which made it possible to use this oscillator as the heart of a TDC when aiming at centimetre-level precision (1 cm = 67 ps) in laser ranging.     

Dependence between $$\varvec{\upeta }$$-factor and crack location relative to a fusion boundary between hard and soft materials in a SE(B) specimen

The current solutions in ASTM E1820 and E1921 for the calculation of the J-integral are not necessary directly applicable for strength mismatched welds. The problem is connected to the \(\eta \)-factor relating the experimentally measured work to the J-integral. Previous, investigations on \(\eta \)-factors for welds have focused mainly on cracks at the center of the weld. However, characterisation of the \(\eta \)-factor at other locations is also important since the crack can form anywhere in the weld. In this study, the \(\eta \)-factors for SE(B) specimens were investigated, with focus on the effect of the crack location relative to the fusion boundary between a hard base metal and a soft weld metal of a dissimilar metal weld. The results show a dependence between the \(\eta ^{\textit{CMOD}}\)-factor, the distance of the crack to the fusion boundary, the size of the remaining ligament, and the size of the plastic deformation zone. This dependence cannot be generalised based on this study alone, but the results give insight for developing an analytical \(\eta ^{\textit{CMOD}}\)-equation for strength mismatched specimens.     

Semiconductor and thermoluminescent dosimetry of pulsed soft X ray plasma sources

A multichannel detection system having a dynamic range of approximately 1 x 10(-9) Gy --20 Gy was developed with the use of commercially produced Si-photodiodes and TLDs for accurate measurement of X ray energy emitted from plasma-focus facility and from laser-produced plasmas. The proof of linearity of the employed detectors accomplished by a comparison of their responses to a broad band spectrum of X rays emitted from plasmas, is reported. It is demonstrated that TLDs irradiated with no protective filter show an incorrect response due to overloading in the sub-keV range and repopulation of dosimetric peaks induced by the UV radiation. The measurement of the power of undesirable secondary X ray sources driven by the primary plasma inside the interaction chamber was performed on the basis of analysis of space dependence of X ray intensity with respect to the assumed r(-2) decrease in the intensity far away from the plasma.     

Optimising the refrigeration cycle with a two-stage centrifugal compressor and a flash intercooler

The optimisation of a refrigeration process with a two-stage centrifugal compressor and flash intercooler is presented in this paper. The two-stage centrifugal compressor stages are on the same shaft and the electric motor is cooled with the refrigerant. The performance of the centrifugal compressor is evaluated based on semi-empirical specific-speed curves and the effect of the Reynolds number, surface roughness and tip clearance have also been taken into account. The thermodynamic and transport properties of the working fluids are modelled with a real-gas model. The condensing and evaporation temperatures, the temperature after the flash intercooler, and cooling power have been chosen as fixed values in the process. The aim is to gain a maximum coefficient of performance (COP). The method of optimisation, the operation of the compressor and flash intercooler, and the method for estimating the electric motor cooling are also discussed in the article.     

Bayesian Robust PCA of Incomplete Data

We present a probabilistic model for robust factor analysis and principal component analysis in which the observation noise is modeled by Student-t distributions in order to reduce the negative effect of outliers. The Student-t distributions are modeled independently for each data dimensions, which is different from previous works using multivariate Student-t distributions. We compare methods using the proposed noise distribution, the multivariate Student-t and the Laplace distribution. Intractability of evaluating the posterior probability density is solved by using variational Bayesian approximation methods. We demonstrate that the assumed noise model can yield accurate reconstructions because corrupted elements of a bad quality sample can be reconstructed using the other elements of the same data vector. Experiments on an artificial dataset and a weather dataset show that the dimensional independency and the flexibility of the proposed Student-t noise model can make it superior in some applications.     

Refining visualization reference model for context information

Context-awareness can be used to decrease the need for interaction with a mobile device. This is increasingly important since the functionality of mobile devices and personal digital assistants gets more and more complex while the input and output capabilities remain restricted. An important aspect of context-awareness is to present the current context to the user. We propose a model for visualizing contextual information on the mobile terminal screen. The model is a refinement of a well-known visualization reference model; it takes into account the specific characteristics of mobile use and context information. We present the design of the model in detail, and discuss its applicability for a variety of contexts and tasks by providing a full-fledged use case.     

The photovoltage signals of bacteriorhodopsin in Langmuir–Blodgett films with different molecular orientations

The photoresponse of bacteriorhodopsin (bR) has been studied in Langmuir–Blodgett (LB) films bR was deposited by vertical dipping as x- or z-type monolayers and as z-type multi layers between stearic acid LB films. The electrodes used were a transparent vacuum-deposited ITO on a quartz substrate and an InGa metal alloy. The signals were observed from samples containing a single bR layer or five bR layers both at room humidity and in water-saturated conditions. The photoelectric signals of x- and z-type monolayers had opposite polarities and both had two exponential kinetics on a microsecond time scale with time constants of about 10 and 70 μs. The amplitude of the fast negative component of the signal of a bR monolayer was 0.4 mV, in the opposite direction to that in which protons were pumped. The amplitude due to five layers was five times as high as that due to a monolayer. The ratio between the amplitudes of the fast negative component and the slow positive part of the signal, in the proton-pumping direction, was 1:3. The photoresponse signal saturated with a light intensity of about 1.7 mJ cm^?2, which is equivalent to a photon density of 0.5 Å^?2. The activation energy of the bR photovoltage was 75 ± 5 kJ mol^?1 in the temperature range between 17 and 35°C.     

Measurement and evaluation of wood fuel

Measurement of fuelwood is done by volume or weight scaling. Evaluation determines quality in terms of moisture content, density, heating value, chemical properties and impurities. Both measurement and evaluation involve sampling. The report surveys the existing measurement and evaluation methods, sampling for moisture content, heating values and other fuel properties including nonwood materials.