Spectral characterisation and frame synchronisation of optical fibre digital PPM

The discrete time decoding of data in pulse position modulation calls for accurate timing synchronisation, particularly at the frame rate. The spectral properties of optical fibre digital PPM are considered. An original expression is presented for predicting the spectrum and it is shown that, unlike satellite PPM, a component exists at the frame rate which may be used for timing extraction purposes. Further, it is illustrated that the modulation index can be used to enhance this component by up to 19 dB. This has been verified practically, with the results agreeing to within 1 dB of those predicted from the original expression presented.<>     

Analysis of slots in nonradiating dielectric waveguide using the modal expansion method

A modal expansion method is used with the reciprocity and Poynting theorems to derive the admittance of inclined slots cut in the metal wall of a nonradiating dielectric (NRD) waveguide. Theoretical values of normalised conductance and susceptance are compared with previously reported experimental results and are found to be in good agreement.<>     

New wire interface for graded 3-D TLM

A new 3-D graded TLM model for thin radiating wires is presented. The model differs from previous TLM models because the wire is modelled at the interfaces between cells, rather than through the centre of the node. The connection between the TLM symmetrical condensed-node link lines and the line forms a 'wire interface'. The scattering algorithm for the interface and simulation results are given.<>     

Performance of 1700 m2 solar pond operation in arid zone

A 1700 m² solar pond was constructed in the desert of Kuwait where severe weather conditions prevail in all seasons. The paper describes in detail a diffuser design for the gradient establishment, gradient stability, and thermal performance of the pond. The main problem encountered in operating the pond was mixing between the upper zone and the gradient zone, even when the wind speed was as low as 5 m/s. No mixing between the gradient and the lower connective zone was observed. The wind effect was severe in causing mixing even when the upper convective zone increased to 0.90 m.     

Optical properties of Bi2Te2Se thin films

Some optical parameters of Bi₂Te₂Se thin films, determined from the measured absorbance and transmittance at normal incidence in the visible spectral range, were studied as functions of film thickness and annealing temperature. These parameters were found to be sensitive to both film thickness and microstructure change caused by annealing in a film. The effect of thickness and temperature of annealing on the optical gap was interpreted in terms of elimination of defects and change of disordering in the amorphous matrix.     

Numerical modeling of nonsteady transient processes in a sphere with cavity subjected to internal dynamic load

The article suggests a numerical algorithm for investigating shock-wave processes in a hollow sphere with limited thickness subjected to internal dynamic surface loads. On the example of actual boundary conditions the article evaluates the contribution of all groups of elastic waves to the formation of an overall structure of rapidly occurring wave processes within the medium under consideration. The effect of the boundary conditions on the distribution field of the components of displacements, speeds, strains and stresses across the hollow sphere upon multiple passage of stress waves was discovered, and some aspects of the realized numerical algorithm connected with the stability of the scheme were investigated.Translated from Problemy Prochnosti, No. 8, pp. 15–19, August 1992.     

Face recognition: combining cognitive psychology and imageengineering

Many cognitive tasks that are easy for humans to perform are proving difficult to emulate in computer systems. Combining the disciplines of psychology and engineering may offer a solution to some of these problems. A connectionist or neural network model of face recognition by humans which incorporates aspects of a model proposed by cognitive psychologists is presented. A comparative set of experiments has been performed using this simulation and human subjects for familiar face recognition. By employing the same stimuli for both humans and the computer model, it is possible to advance not only our understanding of human cognition but also to develop improved automated systems for face recognition     

Energy method of longevity calculation under an irregular loading. Report 2. Longevity under programmed block loading

A method of calculating longevity to macrocrack development under a programmed loading in the form of a block repeated many times to failure is proposed. Relationships are derived for calculation of longevity under blocks with stepwise variation in stress amplitude, and also blocks assigned by the probability-distribution density of the stress amplitudes and tables of the differential frequency of repetition of peak and average stresses. Consideration of variation in the material's endurance limit under an irregular cyclic loading is demonstrated. It is shown that a specific type of relationships can be derived for the material under investigation with allowance for its kinetic cyclic-strain diagrams. An example of the longevity calculation, which is compared with experimental data for the block loading of steel 40Kh specimens, is cited.Translated from Problemy Prochnosti, No. 8, pp. 3–11, August, 1995.     

Improved Prediction of Ozone Levels in Urban and Rural Atmospheres

Based on data obtained in terms of the first International cooperative program on the effects of acidic precipitations on materials (ICP Materials) of the United Nations European Commission on Economics (UN ECE), the relations between the ozone O₃ and nitrogen dioxide NO₂ concentrations in combination with the sunshine effect (taken into account either as the solar radiation (Rad) or the sunshine duration (Sun)) are considered. Analysis based on monthly and annual averages led to a new equation recommended for predicting ozone levels over rural, urban, and industrial areas of Europe as a function of NO₂ concentration and Sun parameter. Using Rad instead of Sun provides similar results, but, for practical usage, the equation involving a more easily available parameter Sun was recommended. The new equation corrects and improves the earlier proposed one, in which the concentration of ozone was given as a function of NO₂ concentration solely, and is included in the UN ECE Manual on mapping critical loads / levels and geographical areas where they are exceeded.