Off-axis geometry

To enhance the overlap of the IR beam with the trapped ion cloud, the copper excite-electrodes of the ICR cell are polished and serve as a multipass reflection cell for the laser beam the curvature of the electrodes naturally refocuses the beam (in one direction only) on each pass. The off-axis geometry of the PEL beam has the additional advantage that a second laser beam can access the imi cloud on-axis. A C02-laser can, for instance, be used in addition to the PEL to induce dissociation, so that product ions can be mass-isolated and spectroscopically investigated. Moreover, a C02-laser can be employed to enhance the fragmentation yield. 

Fresnel and Kubelka-Munk) is eliminated by accessories with an off-axis geometry, such as the one shown in Figure 16.3. Although the optical efficiency of these devices, as measured by the signal at the detector from a nonabsorbing standard, is lower than that of on-axis accessories, the proportion of Fresnel reflection is decreased significantly. The result is that bandshapes are more symmetrical and the linearity of plots of/(/ oo) versus concentration extend to higher concentration. 

Following on the above, we consider the departure of off-axis paraboloidal segments from a sphere of the same vertex radius. Figure 1 shows the geometry of an arbitrary segment, taken to be circular for ease of argument. 

PBDS will also be useful in a related area for the examination of catalysts which are opaque not because of high unit absorption but because they are physically large, i.e., entire catalyst pellets. This is made possible by the favourable geometry of the apparatus and detection device. As indicated schematically in Fig. 1, the sample is merely placed at the focus of the IR beam (an off-axis elliptical mirror is used to focus the IR beam about 1 cm from the edge of the mirror) and a laser beam grazes the surface. The "sample space of the spectrometer is thus of indefinite volume and can be made as large as needed to examine massive objects (in the present apparatus, a sphere of about 20 cm diameter could be accomodated). An example is shown in Fig. 8. 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

The [10°] off axis tension specimen shown in Fig 3.23 is another simple specimen similar in geometry to that of the [ 45 ]s tensile test. This test uses a unidirectional laminate with fibers oriented at 10° to the loading direction and the biaxial stress state (i.e. longitudinal, transverse and in-plane shear stresses on the 10° plane) occurs when it is subjected to a uniaxial tension. When this specimen fails under tension, the in-plane shear stress, which is almost uniform through the thickness, is near its critical value and gives the shear strength of the unidirectional fiber composites based on a procedure (Chamis and Sinclair, 1977) similar to the [ 45°]s tensile test. 

The reflectron is situated behind the field-free region opposed to the ion source. The detector is positioned on the source side of the ion mirror to capture the arrival of ions after they are reflected. There are two common methods of positioning the detector. It may be coaxial with the initial direction of the ion beam. This detector has a central hole to transmit the ions leaving the source. However, the most common instrument geometry has the detector off-axis with respect to the initial direction of the ion beam. Indeed, adjusting the reflectron at a small angle in respect to the ions leaving the source allows the detector to be positioned adjacent to the ion source. 

Tensile test specimens have been fabricated based on ASTM D 3039 for off-axis angles. The materials chosen for fiber and matrix were E-Glass UD-weaves and ML-506 Epoxy resin, respectively. UD-weave fiber lay-up and test specimen geometry are shown in Figure 1 and Figure 2 ... 

The linearity of the K-M function has been investigated for several different conditions. For caffeine, as diluted in KCl powder and reaching up to 100% of weight, maxima of weak and strong absorption bands were tested for this important analytical parameter. It was found that under the conditions given, the use of an accessory with off-axis optical geometry and with application of crossed polarizers before and after the sample, reduced contributions from specular Fresnel reflection from particles on the upper sample surface. As a result, the linear region... 

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