A method for using a time interval counter to measure frequency stability

An interval timer is used in a single-mixer frequency-stability measurement system in place of an event timer. The dead-time problem is avoided with the aid of a reference pulse train and an algorithm for ambiguity resolution. The noise floor test and the unfolding algorithm are described. Advantages of the technique are high precision, convenient interfacing, and low cost. A disadvantage is the vulnerability of the technique to missing data.     

A theoretical and experimental study of low-loss SAW filters with interdigitated interdigital transducers

A study of low-loss surface-acoustic-wave (SAW) interdigitated interdigital transducer (IIDT) structures is presented. A model based on mixed scattering matrices was used in the analysis. It is shown that the inherent comb frequency response of the IIDT can be smoothed by slanting the transducers in the structure. Alternatively, the combs can be enhanced to produce a compact low-loss feedback element for potential application in multimode oscillators. Experimental verification of the analysis is provided by a 3:2 slanted-finger IIDT filter with a 10% relative bandwidth of 5.9-dB insertion loss, and a comb filter with 13.4-dB insertion loss and comb spacing of about 3 MHz. The measured responses agree quite well with the theory.     

Thermo-mechanical behaviour of wood and wood products

The dynamic mechanical behaviour of solid wood, fibreboard, and wood laminates has been examined in the temperature range –100 to +150° C. Two events are apparent in the response of the solid wood, a low-temperature (–50° C) transition which is interpreted as being associated with the onset of movement of bound water, and a higher temperature (40 to 120° C) thermal softening process. With fibreboard, the relationship between the shear storage modulus and density is shown to be described by a simple packing efficiency factor applicable over a wide range of temperature. The behaviour of the laminates is strongly dependent upon the orientation of the outer ply. A model is proposed which analyses the response of the laminate in terms of its constituent plies and allows calculation of numerical values of the component shear storage moduli. With both the fibreboard and the laminates the binder, urea-formaldehyde resin, is shown to have a significant influence on the absolute values of tan observed.     

A technique for assessment of torso kinesiology

A technique is described for monitoring and analysis of the angular displacement of the human torso. The technique is based on the use of miniature electromechanical inclinometers and video recording. The system was developed for continuous measurement of the angular displacement of spinal segments in the sagittal plane during all stages of lifting. Angular displacements of the cervical, thoracic and lumbar regions were obtained from a dynamic lifting case study using a digital processing system. The geometrical changes of the torso during five prescribed stages were measured. The system revealed good accuracy with high correlation coefficient scores for a wide range of lifting tasks in a comparative laboratory study. This paper describes the monitoring technique; the system's advantages, disadvantages and measuring accuracy are discussed.     

Conservation of mechanical energy and circulation in the theory of inviscid fluid sheets

In the theory of thin fluid sheets, governing equations are derived with specific reference to an assumed simple kinematic structure of the flow. There is a separate set of governing equations associated with each degree of complexity of the kinematic structure, forming a hierarchy of models (Green and Naghdi [3] and Shields and Webster [8]). If one is interested in the velocity profile across the sheet, the kinematic structure can be used again to interpret the variables in the governing equations as an approximate flow. This paper is concerned with the properties of this approximate flow.Two important consequences of the field equations (Euler's equations) in the classical, three-dimensional theory of ideal fluids are: conservation of mechanical energy, and conservation of circulation (Kelvin's theorem). The research reported herein provides a proof that mechanical energy is exactly conserved for the approximate flow in each level in this hierarchy. Two types of circulation are considered in the approximate flow: in-sheet circulation which is computed about circuits lying a fixed fractional distance between the top and bottom surfaces of the sheet, and cross-sheet circulation which is computed about circuits lying in a vertical cylindrical surface. It was found that K moments of the in-sheet circulation and K – 1 weighted moments of the cross-sheet circulation are conserved in the Kth level approximate flow.     

Screening model for assessing ‘cost’ of minimum flow requirements in the Svartå River,Sweden

The minimum flow requirements in the Svartå River in Sweden are directed at maintaining fishlife and providing suitable dilution for waste flows. The implications of varying the minimum flow requirements in the river are examined using a mixed integer optimisation model. The model is formulated as a modified method-of-weights technique with the economic issues of hydro-electricity generation, irrigation and urban water supply placed in the objective function and the minimum flows specified within the constraint set. The integer component of the model is required to model the operating policy at the major flow regulation facility in the system and the restricted validity of the irrigation permits. Application of the model shows that in dry years where competition between minimum flow levels and the other economic uses, is most intense, the levels achieved by the various economic objectives are only slightly reduced even with significant increases in the minimum flow requirements. Variations in minimum flow requirements of up to 45% only produce changes of 10% or less in the economic objectives. The lack of sensitivity of the objective levels is due primarily to the level of control exerted indirectly on the whole system in dry years by the release regulation policy and the restricted validity of the irrigation permits. In normal to wet years these policies are not as restrictive and more choice is available. In such years, however, there is generally sufficient water to satisfy all requirements and allocation is not a critical issue. The model itself is formulated generally so that a range of scenarios beyond those examined specifically in the paper can be considered.     

An approximate expression for the motional capacitance of a lateral field resonator

A simple approximate expression is obtained for the motional capacitance of a lateral-field quartz resonator. Comparison with measured values for fundamental-mode and third-overtone SC-cut resonators shows agreement within 10-50%