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This paper is a brief review of some of the properties and applications of liquid crystals. By studying the references, a reader can gain a more extensive insight into the liquid crystalline state. Classifications of liquid crystalline materials and nomenclature characteristic of the field give the reader a working knowledge of the subject. Polymorphism is one of the common properties of liquid crystalline materials; the subject is covered in the text and summarized in tabular forms. The fundamental properties of liquid crystals are correlated with some of the behaviors and uses of liquid crystals. Optical properties, curvature elastic properties, surface effects, external field effects and hydrodynamics of the liquid crystalline state are discussed as necessary to describe recent practical applications; these include displays, storage of images and other electrooptic devices. [ABSTRACT FROM AUTHOR]

Considerable attention has recently been paid to the investigation of the optical properties of twisted fibres. It has been shown that, if the ratio of the total twist angle to the total phase retardation is small, the rotation of the plane of polarization equals the twist angle. However, no effective method has been proposed for the experimental determination of the twist angle and of the total phase retardation in the general case, although the problem has been theoretically considered by Desai and Patel. It is the aini of this paper to show that some results gained in photoelasticity for the uniform rotation of principal axes are directly applicable to the investigation of twisted fibres. A method for the determination of the twist angle and of the total phase retardation of a twisted fibre in the general case is presented. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented about the optical properties of fabrics.

The burn injury hazard of fabrics has been conceptually related to laboratory test methods. The relation is to be de rived from the description of the relevant processes which lead to burn injury. Among these processes stand out the ig nition, the burn and the tissue denaturalization processes as predominately deterministic because of predictable fabric response.Presented here are the results of an experimental and analytical investigation into the fabric ignition process. Thermo physical fabric properties relevant to the description of the ignition process have been presented. Fabric ignition times were measured under radiative heating. Modeling rules for the ignition process are presented. [ABSTRACT FROM PUBLISHER]

The choice of appropriate infrared transmitting materials for high-power laser applications necessitates a knowledge of various optical parameters. Because experimental data is often scant or unreliable in frequency regions of interest it has become important to be able to predict optical parameters from either theoretical or phenomenological models. This requires identification of the major physical mechanisms, and translation of this information into a useful model. Considerable progress has been made recently, especially with regard to the frequency dependence of refraction, absorption α and photoelasticity. It has been found, for example, that frequency dispersion is important at 10.6μm for all three of the latter quantities in most alkali-halides. For most semiconductors, on the other hand, only the effects on α are significant. It is shown that the mix of existing experimental data with recent theory is now providing us, for the first time, with a fairly comprehensive view of the magnitude, frequency dependence, and temperature dependence of optical parameters of infrared transmitting materials. [ABSTRACT FROM AUTHOR]

The reflection and transmission properties of an anisotropic plasma slab immersed in a static magnetic field normal to the plane of incidence are studied for the case of oblique incidence of a parallel-polarized plane wave. The emphasis is on 'the thin-film reflection properties', namely, the oscillations in the reflection coefficient due to constructive interference of internally reflected waves from the front and back surfaces of the slab geometry. The effect of the slab width, the angle of incidence and the strength of the magnetic field on the nature of the oscillations in the power reflection coefficient are discussed.
The general nature of variation of power reflection coefficient for the slab can be predicted from the nature of the characteristic root q. In the range of real q the power reflection coefficient is oscillatory and the oscillations with increasing amplitude will be more and more crowded as q increases, finally giving rise to an infinite number of oscillations around the point where q is real and infinite. As q approaches asymptotically a value C (C= cos , where is the angle of incidence), the oscillations will be of decreasing amplitude and increasing width. When q equals C the value of is zero. In the range of imaginary q, is non-oscillatory. While in this range, for the semi-infinite case is 1, for the slab is less than 1, showing the tunnelling of power through the slab. approaches 1 as the magnitude of imaginary q approaches infinity. [ABSTRACT FROM AUTHOR]

Experiments are reported in which changes in the appearance of carpet samples after treatment ranging from 2 × 104 to 20 × 104 revolutions in a Tetrapod Walker were assessed with the aid of photographs of the new and treated samples. It was found that photographs, taken under controlled conditions, can be used as a record and basis for the assessment of changes in appearance resulting mainly from changes in texture, without much disturbing effect from colour and pattern. The ranking of carpets, based on changes in their appearance, did not alter significantly after 5 × 104 revolutions in the Tetrapod Walker. Results from the Tetrapod Walker are compared with those from a floor trial, where the effects of soiling caused further interference with the assessment. [ABSTRACT FROM AUTHOR]

Reflectance methods have been investigated for measuring the ability of the fiber in dyed carpeting to retard or "hide" soil. The ideal method should be able to eliminate the effect of color which may mask or accentuate apparent soil. A method which approaches this ideal consists of measuring reflectance before and after soiling by using an interference filter with a bandpass centered at a wavelength close to the dominant wavelength of each color. This method reduces the effect of color sufficiently that the average calculated apparent soil for a set of 16 differently colored carpets soiled equally is significantly different from that of the same set of carpets after the addition of a small amount of soil (0.06% owf). Two other methods, one with a Y-tristimulus filter and another with three tristimulus filters (total color change), are not suitable for this type of evaluation. [ABSTRACT FROM PUBLISHER]