In the last 30 days

• Open/close The elasticity and strength of paper and other fibrous materials

  H L Cox 1952 Br. J. Appl. Phys. 3 72 Tag this article

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  An analysis is made of the effect of orientation of the fibres on the stiffness and strength of paper and other fibrous materials. It is shown that these effects may be represented completely by the first few coefficients of the distribution function for the fibres in respect of orientation, the first three Fourier coefficients for a planar matrix and the first fifteen spherical harmonics for a solid medium. For the planar case it is shown that all possible types of elastic behaviour may be represented by composition of four sets of parallel fibres in appropriate ratios. The means of transfer of load from fibre to fibre are considered and it is concluded that the effect of short fibres may be represented merely by use of a reduced value for their modulus of elasticity. The results of the analysis are applied to certain samples of resin bonded fibrous filled materials and moderately good agreement with experimental results is found.

• Open/close Thermal expansion of bismuth telluride

  K N R Taylor 1961 Br. J. Appl. Phys. 12 717 Tag this article

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• Open/close Structure-cell data and expansion coefficients of bismuth telluride

  M H Francombe 1958 Br. J. Appl. Phys. 9 415 Tag this article

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  Accurate measurements of the structure-cell parameters of bismuth telluride, Bi ₂Te ₃, have been made using annealed powders and etched rods cut from single-crystal ingots. Previously reported anomalies in the X-ray powder intensity data are found to originate entirely in preferred orientation of the crystallites.

  A study of the thermal expansion of the unit cell over the temperature range -195 to 400° C has revealed a marked anisotropy between the axial expansion coefficients, that for the c axis (22.2 × 10 ^-6 per °C at 20° C) being almost twice that for the a axis (12.9 × 10 ^-6). Near 200° C changes occur in both the principal axial expansions, comparable with those observed at low temperatures in certain hexagonal metal structures.

• Open/close Investigation of the instability of a moving liquid film

  H B Squire 1953 Br. J. Appl. Phys. 4 167 Tag this article

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  The stability of a thin layer of liquid moving in still air is studied theoretically with the object of throwing light on the break-up of films during atomization. It is found that instability occurs if W = T/ρ ₁ U ² h < 1 and that the wavelength for maximum growth factor, for W « 1, is λ = (4π T/ρ ₂ U ²) where ρ ₁ is the liquid density, ρ ₂ is the air density, U is the film velocity, 2 h is the film thickness and T is the surface tension of the liquid. Comparison with experimental data shows fair agreement with the observed wavelengths.

• Open/close Reduction of stainless-steel outgassing in ultra-high vacuum

  R Calder and G Lewin 1967 Br. J. Appl. Phys. 18 1459 Tag this article

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  The outgassing rate of a 2 mm thick stainless-steel sheet was measured in ultra-high vacuum at constant pressure to avoid the readsorption occurring in a `rate of pressure rise' determination. The rate was typically 10 ^-12 torr l. cm ^-2 sec ^-1 and about 99% or more of the gas was hydrogen. Since stainless steel usually contains large amounts of hydrogen and the diffusion coefficient of hydrogen in stainless steel is high, it was suspected that the hydrogen diffuses to the surface from the interior of the metal and is released into the vacuum. Calculations show that the observed outgassing rate could be explained by such a process and should be reduced by several orders of magnitude by a high-temperature treatment. The effects of residual hydrogen in the treatment furnace and hydrogen permeation from the atmosphere are also considered in these calculations. The greater the thickness of the metal, the higher the temperature has to be. Measurements are in reasonable agreement with these calculations.

• Open/close Deposition by thermal evaporation of thin films of titanium and zirconium for tritium targets

  V D Scott and L W Owen 1959 Br. J. Appl. Phys. 10 91 Tag this article

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  Equipment and procedure are described for applying thin films of titanium and zirconium as tritium carriers to backings of copper, gold and platinum. A large proportion of the coatings prepared absorbed high atom ratios of tritium, titanium being more satisfactory in this respect than zirconium. It is suggested that defects in the coating arise mainly from the undesirable reaction of the metals with residual gases, particularly oxygen, during evaporation in the vacuum chamber. Firstly, this causes stress, brittleness, and owing to lack of adhesion, blistering of the deposit; secondly absorption of tritium is inhibited by the oxide film on the metal surface, and the total amount absorbed reduced as a result of there being fewer lattice sites available for the tritium. An electron diffraction examination showed that although the deposits appeared bright and metallic, a thin protective oxide film was present on the evaporated titanium and zirconium.

• Open/close The dielectric constant of zinc oxide over a range of frequencies

  N H Langton and D Matthews 1958 Br. J. Appl. Phys. 9 453 Tag this article

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  The dielectric constant of a colloidal zinc oxide has been measured by the method of mixtures, using cyclohexanol and ethyl acetate as the suspending liquids. The dielectric constant has been found to be 10.4 over the frequency range 105 kc/s to 10 Mc/s, falling to 9.4 at 25 Mc/s, measurements being made at 25° C with an accuracy of 2.3%. The dielectric constant of an acicular zinc oxide has been found to have an apparent value of about 40, over the frequency range 100 kc/s to 10 Mc/s. Results are given of dielectric constant measurements on mixtures of cyclohexanol and ethyl acetate, which appear to disobey Lichteneker's empirical logarithmic mixing rule.

• Open/close What is ferromagnetic resonance?

  R A Waldron 1960 Br. J. Appl. Phys. 11 69 Tag this article

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  It is pointed out that two distinct resonance effects take place in ferrite samples at microwave frequencies, ferromagnetic resonance and an effect due to the shape of the specimen. The latter effect is called Kittel resonance in this paper. It is commonly supposed that the two effects are the same, but it is shown that this is not the case. In ferromagnetic resonance, the diagonal and off-diagonal elements of the permeability tensor (μ and α respectively) exhibit anomalous dispersion, and microwave fields are excluded from the specimen. In Kittel resonance, nothing spectacular is happening to μ and α, but the fields in the specimen become very large, giving rise to a large loss; it is this effect that is observed in resonant cavity experiments. The behaviour of cavities and wave-guides containing ferrites is discussed in the light of these facts, and a new interpretation is arrived at of certain effects in waveguides when μ < α.

• Open/close Kramers-Kronig analysis of reflection data

  D M Roessler 1965 Br. J. Appl. Phys. 16 1119 Tag this article

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  A method is given for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from normal incidence reflectance data when data over only a limited spectral range is available. No assumptions are needed concerning the behaviour of the reflectance data outside the experimental range, and no extrapolations of data are required. As an example, the extreme ultra-violet reflectance data of potassium iodide is analysed by this method.

• Open/close Approximation formulae for the light scattering coefficient of dielectric spheres

  P Walstra 1964 Br. J. Appl. Phys. 15 1545 Tag this article

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  The validity of several approximation formulae for the light scattering coefficient of homogeneous non-absorbing spheres of refractive index ratios between 1 and 1.25 has been investigated by means of comparison with results from the rigorous theory.

  The theories of Rayleigh, Schoenberg and Jung, Rayleigh-Gans, Jöbst, Heller, Hart and Montroll, and of van de Hulst have been considered, and a linear equation valid for a small size range. For large spheres there is as yet no equation giving a close approximation, and a simple semi-empirical formula is derived here. It gives values correct within one per cent, and has a wide range of validity. Also the forward scattering amplitude function is given.