Temperature-independent Strain Research Articles

Temperature independent strain measurement with a fiber grating tapered cavity sensor

A novel fiber grating tapered cavity sensor used for encoding strain into its spectral profile independently and its experimental demonstration are presented. The sensor possesses two spectral peaks within its main reflection band and the normalized power difference between the two peaks changes linearly with applied strain while it is independent of temperature variation. The accuracy of this particular sensor in measuring strain is estimated to be /spl plusmn/29 /spl mu//spl epsi/ in a range of 1200 /spl mu//spl epsi/.

Temperature-independent strain sensor system using a tilted fiber Bragg grating demodulator

We experimentally demonstrate a new approach for the demodulation of a fiber Bragg grating (FBG) strain sensor by combining a tilted FBG demodulator with a temperature-independent property and a dual head FBG sensor with a temperature-discriminating property. This technique guarantees a stable measurement independent of temperature perturbation at both sides of sensor and demodulator without any additional temperature-isolation or temperature-referencing process and has the minimum resolvable strain of 10 /spl mu/strain. The ranges of operating temperature at the sensor and at the demodulator which guarantee a dynamic range of 1800 /spl mu/strain corresponding to the wavelength difference 2.2 nm between two notches of the tilted FBG spectrum are from room temperature to 180/spl deg/C and 140/spl deg/C, respectively.

Temperature-independent strain sensor using a chirped Bragg grating in a tapered optical fibre

A novel, temperature-independent strain sensor is demonstrated using a chirped fibre grating in a tapered optical fibre. The effective bandwidth of the grating is uniquely dependent on strain and is essentially temperature-independent. The interrogation simply involves monitoring the back-reflected intensity from the grating. A strain resolution of 0.1% over a strain measurement range of 4066 mu epsilon has been experimentally achieved. >

The quantum theory of crystal deformation: the harmonic approximation and rotational invariance

In order that such thermodynamic quantities as the stress tensor, elastic constants and piezoelectric coefficients have the correct index symmetries when evaluated theoretically, it is necessary that the theory be consistent with the rotational invariance property of the particle interaction potential function. In this work, the conditions under which the harmonic lattice model is consistent with this property are found and it is shown that the harmonic lattice potential coefficients must then have a certain simple form. In general, the usual harmonic model does not satisfy these conditions. The dynamical properties of a rotationally invariant harmonic model are described. It is shown rigorously for such a model that on deformation the phonon spectrum is unchanged and that there is no internal strain, so that the stress tensor and elastic constants are temperature independent. The rotationally invariant harmonic model is used to provide a zero-order Hamiltonian for the treatment of the deformation of an anharmonic crystal. This approach, besides being completely consistent with the rotational invariance property, has the advantage that the momentum perturbation term, recently introduced into the theory of deformation, is completely absorbed into the zero-order Hamiltonian. The perturbation diagram treatment is thus simplified. By summing over an infinite number of a certain type of diagram, a new formula is obtained for the temperature-independent internal strain contribution to the second-order elastic constants of the ordinary (that is, not necessarily rotationally invariant) harmonic model of common use. The consequences of crystal symmetry for this model are discussed.

Temperature-dependent conversion of sexual agglutinability in Saccharomyces cerevisiae

Temperature dependency of sexual agglutinability in Saccharomyces cerevisiae was found. In almost all strains tested that were derived from several different sources, the agglutinability was constitutive when grown at 25° C but inducible when grown at 36° C, suggesting that the temperature-dependent conversion of sexual agglutinability is general nature in Saccharomyces. Cycloheximide and 8-hydroxyquinoline inhibited completely both cell division and the conversion of the agglutinability from constitutive to inducible type. N-Hydroxyurea and 5-fluorouracil which allowed cell growth to some extent inhibited the conversion slightly. Hence, the conversion of the agglutinability from constitutive to inducible type may be achieved in cells newly born after temperature shift. The reverse conversion of the agglutinability was gradual in comparison with the conversion from constitutive to inducible type. This conversion of the agglutinability was regulated by a single gene closely linked to mating type locus, which is recognizable by using a temperature-independent constitutive strain.