Vibrating reed

Eor the preparation of suspensions and emulsions, coUoid mills and homogenizers, respectively, are used. Ultrasonic mills that utilize vibrating reeds in restricted chambers to reduce the particle size of the dispersed ingredients can also be employed (see Colloids Ultrasonics). 

Resonance-Forced Vibration. Resonance-forced vibration devices drive the vibration of the specimen. This can be over a range of frequencies that includes the resonant frequency, which is detected as a maximum in the ampHtude, or the instmment can be designed to detect the resonant frequency and drive the specimen at that frequency. An example of the resonance-forced vibration technique is the vibrating reed. A specimen in... 

Dosimetry. Ion current measurements required for absolute dosimetry were performed with a Cary 31 ionization chamber and vibrating reed electrometer. Dry nitrogen was used as filling gas for the chamber, and a W value of 34.9 e.v./ion pair was assumed for H-3 beta rays in N2 (27). Deuterium pressures in each of the reaction mixtures were great enough to ensure that less than 1% of the H-3 beta rays reached the walls of the reaction vessel (7). 

Flow-Type Ionization Chamber (PFC). The Flow -Type Ionization Chamber Method (PFC) has been developed for continuously measuring radon gas in the atmospheric air. The detail of the device has been described elsewhere (Shimo, 1985). Briefly, measurements are continuously carried out by drawing air through the detector at 1.0 2.0 /min. The ionization currentdue to alpha particles from radon and its daughters is detected with a vibrating reed electrometer (VRE) in the same manner as the DSC. The sensitivity... 

Figure 6 Typical amplitude-frequency curve obtained with a vibrating reed ap-paraius. [From L. E. Nielsen,...

The unsuitable nature of many commercial instruments which are in common use clearly illustrates the confusion prevalent in the field of viscometric measurements. Many instruments measure some combination of properties which depend only partly on the fluid consistency since the flow is not laminar. In others the shear rates are indeterminate and the data cannot be interpreted completely. Examples of such units include rotational viscometers with inserted baffles, as in the modified Stormer instruments in which the fluid flows through an orifice, as in the Saybolt or Engler viscometers instruments in which a ball, disk, or cylinder falls through the fluid, as in the Gardiner mobilometer. Recently even the use of a vibrating reed has been claimed to be useful for measurement of non-Newtonian viscosities (M14, W10), although theoretical studies (R6, W10) show that true physical properties are obviously not obtainable in these instruments for such fluids. These various instru-... 

The quadrupole mass filter (QMF) is a mass analyzer on whose operation use of an MEM is not necessarily dependent. The ion currents produced are of sufficient magnitude to be measured by means of a Faraday cage and a suitable amplifier such as a vibrating-reed electrometer. The QMF is a true M/z filter which requires no magnetic fields. Since first being proposed by Paul and Steinwedel (30), the QMF has been investigated extensively, and the principles and methods of operation are well known (see, for example, ref. 31). 

The Plasma Chromatograph (PC, registered trademark of the Franklin GNO Corp.) is also an instrument which does not depend on the use of magnetic fields (33). It should be well suited for the study of macroions because (a) the currents measured are well within the range of a Faraday cage-vibrating-reed electrometer detector system, and (b) the instrument operates at atmospheric pressure, thus making unnecessary the reduction in pressure from that of the electrospray chamber. 

The transverse vibrations of a beam are used in the test method known as the vibrating reed and the solution used is that of the differential equation (see e.g. Thomson241)... 

Higher harmonic than the fundamental can be detected with the vibrating reed device and the variation of E with frequency studied. 

As in the simple 3- or 4-point bending of a beam the vibrating reed device assumes the validity of the differential Eq. (2.2) which is due to Euler. Timoshenko25 included both rotary inertia and shear deformation deriving a more exact differential equation which reduces to the Euler equation as a special case. Use of the Timoshenko beam theory for anisotropic materials has been made by Ritchie et al.26 who derive a pair of equations for torsion-flexure coupling (which will always occur unless the axis of the beam coincides with the symmetry axis of the anisotropic material). 

For measurements of ultraviolet light from a quartz mercury arc passes through a quartz monochromator, silica lens, and window, and is focused onto the crystal at an angle of incidence of about 45°. The saturated photocurrent is collected by the surrounding metal drum to determine ip by the Fowler method (4). A vacuum thermopile measures the light intensity. Photoelectric and diffraction currents are measured by a vibrating reed electrometer. Ultra-high-vacuum techniques are employed, which result in residual pressures of less than 10-9 mm. of Hg. 

Various methods (1-1) have used to determine the dynamic mechanical properties of polymers. Many of the instruments described are well known and are widely used (torsional pendulum, rheovibron, vibrating reed, and Oberst beam ASTM D4065-82). Newer instruments like the torqued cylinder apparatus (4), resonant bar apparatus (5) and Polymer Laboratories Dynamic Mechanical Thermal Analyzer (6) are becoming more popular in recent times. 

CONTACT POTENTIAL FROM VIBRATING REED ELECTRODE STUDIES... 

There are two practical difficulties. One is the measurement of the very small photocurrent, which may be as low as 10" amp, requiring the use of a vibrating reed electrometer or similar instrument. The second is that, for work functions above 5 eV, Vq lies in the far ultraviolet. This makes the study of some adsorptions very difficult and 6 eV is about the practical limit of such measurements. A suitable light source is the quartz mercury arc. The energy of the incident beam can be measured with a calibrated photocell, a vacuum thermopile or a radiometer. A suitable cell for adsorption studies is shown in Fig. 11. The sample being studied forms the cathode B. It can be a metal foil or a film formed by evaporation from the filament E. A wire C is fused through the glass to make contact with the... 

The speed of a centrifuge should be checked at least once every 3 months. The procedure should use a stroboscopic light or a vibrating-reed external tachometer of known accuracy. The measured speed should not differ by more than 5% from the rated speed under specified conditions. All the speeds at which the centrifuge is commonly operated should be checked. The centrifuge timer should be checked weekly against a reference timer (such as a stopwatch) and should not be more than 10% in error. Commutators and brushes should be checked at least every 3 months. Brushes (where used) should be replaced when they show considerable wear. However, in many modern induction-drive motors, brushes have been eliminated thus removing a source of dust that can cause motor failure. 

The lowest temperature 6 peak appears at approximately -160 C in the vibrating reed measurement whereas only the onset of 6 relaxation can be seen near -18O C in the torsional pendulum test. As discussed below, this peak is not present in the Nafion acid or in its salt membranes in both mechanical and dielectric measurements. 

The G" (or E") and tan 6 peaks occuring in the temperature range from -20 to -120 C are extremely broad and skewed in both vibrating reed and torsion pendulum experiments. These peaks are considered to be the sum of two overlapping peaks—the 8 and Y relations. The highest temperature a relaxation is seen around 5 to 20 C on the tan 6 curves the drastic drop in G (or E ) and the sharpness of the tan <5g peak are characteristic of typical glass transition behavior of a neutral amorphous polymer. 

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