Instruments stress-optical

The diagnostics applied to shock experiments can be characterized as either prompt or delayed. Prompt instrumentation measures shock velocity, particle velocity, stress history, or temperature during the initial few shock transits of the specimen, and leads to the basic equation of state information on the specimen material. Delayed instrumentation includes optical photography and flash X-rays of shock-compression events, as well as post-mortem examinations of shock-produced craters and soft-recovered debris material. 

As discussed in section 7.1.6.4, semidilute solutions of rodlike polymers can be expected to follow the stress-optical rule as long as the concentration is sufficiently below the onset of the isotropic to nematic transition. Certainly, once such a system becomes nematic and anisotropic, the stress-optical rule cannot be expected to apply. This problem was studied in detail using an instrument capable of combined stress and birefringence measurements by Mead and Larson [109] on solutions of poly(y benzyl L-glutamate) in m-cresol. A pretransitional increase in the stress-optical coefficient was observed as the concentration approached the transition to a nematic state, in agreement of calculations based on the Doi model of polymer liquid crystals [63]. In addition to a dependence on concentration, the stress-optical coefficient was also seen to be dependent on shear rate, and on time for transient shear flows. 

Instrumental measurement of whiteness has been the subject of much research. The parameters needed for unambiguous characterisation in the assessment of whiteness and tint of fluorescent substrates have been reviewed [21]. The importance of seeking good correlation between different instruments is stressed [20]. Various trials have demonstrated that it is possible to adjust modern instruments used to measure the optical characteristics of FBA-treated samples of paper so that the results agree with a standard deviation of the order of one CIE whiteness unit [22]. 

Eqs. (4.140) and (4.150)-(4.152) are used to evaluate the response of the model composites in cyclic loading and the displacements 6 and 8, can be expressed as a function of the alternating stress, Aff, and the number of cycles, N. In experiments, degradation of the interface properties, e.g., the coefficient of friction, p or A(= 2pjfc/a), can also be expressed in terms of the cyclic loading parameters, Aoptical methods (with a microscope) or by means of more complicated instruments (see for example Naaman et al. (1992)) in fiber pull-out. Alternatively, they can be directly determined from the load and load-point displacement records in the case of fiber push-out. 

Figure 15.2—Two instruments with spark ionisation. On the left, a Jobin-Yvon model JY-50E instrument. The opened spark chamber can be seen in the photograph. On the right, a model ARC Met-900 instrument from Metorex. The spark is produced by a gun connected by fibre optic to the spectrometer and situaied in the console (reproduced by permission of American Stress Technologies).

The critical phase of either a creep test or a stress relaxation test is in the first few seconds. It is here that the transducer can be overloaded or the optical encoder can give a noisy response. Most controlled-strain instruments will give an audible error signal if the transducer is overloaded. For controlled-stress instruments, the noise level is determined by the resolution of the optical encoder. 

The measurement of the polarization properties of light can be automated and improved by introducing a modulation of the polarization. Here a regular, time-dependent variation is introduced onto the optical properties of certain devices within either (or both) the PSG or PSA sections of the instrument. The modulation can be one of two types rotation of an optical element with fixed optical properties, or the modulation of the optical properties (retardation, for example) of an element with a fixed orientation. These are referred to as rotary modulators or field effect modulators, respectively. The latter name reflects the use of external fields (stress, electric or magnetic) to impart the modulation in these devices. In any case, a periodic oscillation is introduced into the signals that are measured that can effectively isolate specific optical properties in the sample. 

Ion selective membranes are the active, chemically selective component of many potentiometric ion sensors (7). They have been most successfully used with solution contacts on both sides of the membrane, and have been found to perform less satisfactorily when a solid state contact is made to one face. One approach that has been used to improve the lifetime of solid state devices coated with membranes has been to improve the adhesion of the film on the solid substrate (2-5). However, our results with this approach for plasticized polyvinylchloride (PVC) based membranes suggested it is important to understand the basic phenomena occurring inside these membranes in terms of solvent uptake, ion transport and membrane stress (4,6). We have previously reported on the design of an optical instrument that allows the concentration profiles inside PVC based ion sensitive membranes to be determined (7). In that study it was shown that water uptake occurs in two steps. A more detailed study of water transport has been undertaken since water is believed to play an important role in such membranes, but its exact function is poorly understood, and the quantitative data available on water in PVC membranes is not in good agreement (8-10). One key problem is to develop an understanding of the role of water uptake in polymer swelling and internal stress, since these factors appear to be related to the rapid failure of membranes on solid substrates. 

It must be stressed that the raw curves are not size distributions and calibration is required to convert to absolute values [29]. The importance of the correction for the breakdown in the laws of geometric optics is stressed by Weiner et. al. [30] who show excellent agreement between theoty and experiment when this is done correctly. They also use the Brookhaven disc photocentrifuge to characterize ASTM carbon blacks.[3 i ] This method has been used to characterize void-containing latex particles [32]. Commercial instruments are available from Joyce-l.oebI, CPS Instruments and Brookhaven. 

In thermomechanical analysis (TMA) the deformation of the sample under stress is monitored against time or temperature while the temperature increases or decreases proportionally to time. Changes are detected by mechanical, optical, or electrical transducers. The stress may be a compression, penetration, tension, flexure, or torsion. Generally the instruments are also able to measure the sample dimensions, a technique called thermodilatometry. The stress F/A) expressed in N/m or Pa may be a normal tensile stress cr, a tangential shearing stress x, or a pressure change Ap the force applied is F and A is the area. 

Figure 14.6 Atomic emission instrument with spark ionization. Left, Jobin-Yvon model JY-50. Details of the spark chamber in the open position. Right, mobile post of Metorex ARC Met-900 industrial analysis. The spark is produced by a gun, linked by an optical fibre to the spectrophotometer situated in the console (reproduced courtesy of Jobin-Yvon and American Stress Technologies).

In our discussion of instrumentation foctors, we will stress their effects on excitation and emission spectra. However, similar concerns are inqx>rtant in the measurement of fluorescence lifetimes and anisotropies, which will be described in Chapters 4, 5, and 10. Additionally, the optical prc rties of the samples, such as optical density and turbidity, can also affect the spectra. Specific examples are given to clarify these effects and the means to avoid them. 

Recent papers on the relationship between optical rotatory dispersion and circular dichroism of optically active systems have stressed the superiority of the latter in interpreting the data. Unfortunately, circular dichroism measurements have been either difficult or expensive to obtain. Recently available instruments are costly and the reliability of the data these instruments afford certainly has not reached its maximum. Universal polarimeters have been described, but they require either major changes in existing insttuments or special construction of new instruments. This paper describes a method of modifying the RUDOLPH Spectropolarimeter, Model 200 AS, to measure the ellipticity of elliptically polarized light and thus indirectly measure circular dichroism. This modification requires no major changes and virtually no expense. 

There are numerous potential biomedical applications for on-line breath analysis instruments. For example, as shown in one of the projects described above, laser spectroscopic on-line monitoring of C2H6 in exhaled breath could serve as a non-invasive means of acquiring information on oxidative stress status. However, it should be emphasized that any clinical reliance on exhaled biomarkers will depend strongly on the availability of rugged, fast and inexpensive detection systems. But it is foreseeable that the rapid advances in optical technologies will most likely result in smaller devices in the near future, which are also cheaper and easier to use than the current pre-commercial measurement set-ups. Specifically, innovations in IR lasers and spectroscopic instrumentation may soon enable laser-... 

The indentation test is one of the simplest ways to measure mechanical properties of a material. The micromechanical behavior of polymers and the correlation with microstrnctnre and morphology have been widely investigated over the past two decades (23). Conventional microindentation instruments are based on the optical measnrement of the residual impression produced by a sharp indenter penetrating the specimen surface under a given load at a known rate. Microhardness is obtained by dividing the peak load by the contact area of impression. From a macroscopic point of view, hardness is directly correlated to the yield stress of the material, ie, the minimnm stress at which permanent strain is produced when the stress is snbseqnently removed. 

Recently introduced instruments from TA Instruments include the DMA Q800 analyser [4, 5]. The instrument can be used for the testing of mechanical properties of a broad range of viscoelastic materials at temperatures ranging from -150 °C to 600 °C. The DMA Q800 is claimed to provide unmatched performance in stress-strain control and measurement. It uses a proprietary non-contact linear motor to provide precise stress control, and optical encoder technology for unmatched sensitivity and resolution in strain deflection. 

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