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.     

Preparation and properties of close-packed composite materials

Monodisperse silica particles of about 0.3m diameter are suspended in methacrylate monomer using a carefully selected dispersant. Many steric dispersants are hydrocarbon chains with a reactive end-group. These are not effective as dispersants for silica in moderately polar solvents, such as esters and the methacrylate monomers. Good dispersion was obtained with a methacrylate polymer terminated by a chlorosilane end group. Settling or centrifugation of these unagglomerated dispersions gives well-packed particle beds. Polymerization of the surrounding monomer produces composite materials with high packing fractions and a high degree of regularity. Moduli and strengths of these composites are reported.     

Is fluoridation a fraud?

During the past 15 years tooth decay rates have declined markedly amongst children in many parts of the industrialised world. Over the same period, however, decay rates have increased dramatically in children in developing countries. For many years it has been claimed that water fluoridation is the most important and cost-effective method for controlling dental caries. A series of recent papers in the scientific literature have challenged the 'fluoridation hypothesis', since the decline in decay reported in the developed countries has occurred in both fluoridated and unfluoridated areas. In some countries of the developing world, tooth decay is now reaching crisis proportions, hence it is important to know whether fluoridation really can "reduce tooth decay by about 60 per cent", or if the dental profession has been promoting a 'flawed' hypothesis for more than 40 years.     

The coming revolution in information systems

A revolution is coming--is absolutely essential--in healthcare. The chief information officer must be among the generals who plan battle strategies and lead the campaigns to fight inflating costs and overwhelming demands. Without their leadership and expertise, armies of healthcare providers are destined to fail, and legions of citizens will fall victim to a system inadequate to meet their needs.     

Aspects of modeling the frequency response of a two-port waveguide-coupled SAW resonator-filter

Coupling-of-modes-in-time and coupling-of-modes-in-space analyses are applied to the modeling of a two-port two-pole waveguide-coupled SAW resonator filter. Modeling is applied to a lumped equivalent circuit and a distributed circuit. While the accuracy of the coupling estimation dictates the exact mode-splitting and bandwidth, the ensuing computations can give a good representation of the amplitude and phase response, including the effect of degenerate transverse modes.     

Subcritical crack growth in partially stabilized ZrO2(MgO)

The room temperature slow crack growth resistance in air ( 50% relative humidity) and in water for large cracks in MgO-partially stabilized zircoba (PSZ) improves with increase in critical fracture toughness,K _lc. Ageing the as-fired PSZ at 1400° C for 8 h results in decreasing K_lc from 8.5 MPa m^1/2 to 6 M Pa M^1/2. The ageing treatment also promotes the growth of eutectoid decomposition products on grain boundaries that is accompanied by a decrease in the dependence (A the change in Region I crack velocity with a change in the applied stress intensity. Calculated times to failures are markedly decreased in the aged as compared to the as-fired PSZ ceramic.     

Comparison of mainline and alternate approaches to fusion energy

The tokamak and tandem mirror concepts are compared with alternate confinement concepts using the criteria established in DOE/ET-0047, An Evaluation of Alternate Magnetic Fusion Concepts 1977. The concepts are evaluated and rated in each of three broad categories: confidence in physics and technology, and reactor desirability. The STARFIRE and MARS reactors are used as a basis for comparing the mainline tokamak and tandem mirror concepts with the alternate concepts evaluated in DOE/ET-0047. Two recent alternate concepts, theohmically heated toroidal experiment (OHTE) and thecompact reversed field pinch reactor (CRFPR), are also evaluated. Results indicate that the physics of the mainline tokamaks and tandem mirrors is better understood than that of most alternate concepts. Both mainline concepts rank near the middle for technology requirements, and both rank near or at the bottom when compared with the reactor desirability of alternate concepts.     

A 2.5n lower bound on the monotone network complexity of T 3 n

Summary The k-th threshold function, T _k ⁿ , is defined as: where x _i{0,1} and the summation is arithmetic. We prove that any monotone network computing T _3/n(x ₁,...,x _n) contains at least 2.5n-5.5 gates.This research was supported by the Science and Engineering Research Council of Great Britain, UK     

Environmental Control Symposium

MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.