Dwell-time effect

Force measurements made without displacement values are still useful in identifying the dependency of tablet hardness (and other associated characteristics) on compaction force, and also the effect of the tablet press compaction speed on tablet strength (influence of dwell time/effective... 

Force measurements made without displacement values are still useful in identifying the dependency of tablet hardness (and other associated characteristics) on compaction force, and also the effect of the tablet press compaction speed on tablet strength (influence of dwell time/effective contact time). Dwell time dependency is an important scale-up factor for the tableting process, and evaluation of the sensitivity of a formulation to dwell time at small scale is useful, although the actual commercial dwell time is not always achievable on instrumented, small-scale tablet presses. 

This produces high bending moments and hence a relatively greater acceleration of the fibre after junction failure. The opportunity for the secondary junction formation is then reduced since the kinetic frictional force will decrease rapidly with velocity. There is some analogy to the dwell time effect in autoadhesion. 

Adhesion will then increase as a function of time until a new equilibrium is attained. This is a major cause of the adhesive dwell-time effect. 

Figure 8.19. (a) Dwell-time effect (b) adhesive drag and hysteresis. 

A substantial increase in tumor to background ratio was found when the adenoviral vector was coinjected with Lipiodol (Table 22.5). This reflected an increase in the percentage of tumor cells i diich expressed the gene therapy marker as well a decrease in the percentage of normal hepatocytes that expressed the marker. The latter is an expected consequence of embolization. The increase in tumor cell staining suggests that the dwell time effect more than overcame the decrease in blood flow caused by embolization. 

Experiments and results. The viscoelastic material chosen was an optically smooth polyurethane, reconunended for dynamic studies in photoelasticity SM4 Vishay, with E = 3.6 MPa). The surfaces were wiped with an alcohol-soaked cloth, dried with warm air and left, sheltered from dust, for 30 min for the equilibrium with room temperature to be reached. Then, two strips of thickness /i=3.175 mm with various lengths L and widths b varying in the range 5-20 cm and S-20 mm, respectively, w e gently superimposed, and they adhered under only molecular attraction forces, without additional adhesive. In order to avoid the dwell time effect (/9), strips were coupled during the same contact duration 30 min, for all experiments. Moreover, temperature (23°C) and humidity (84%) were kept constant. In these conditions, the reproducibility is better than 3%. 

A loop tack (Fig. 2c) test consists of allowing a tear-shaped loop of conditioned tape to drape into contact with a test surface of specified area (usually 25.4 x 25.4 mm), with the force of contact limited to the weight of the tape itself (ASTM Ref. D-6195). The ends of the loop are held in a tensile tester. After a momentary contact time the tester is engaged and the tape is removed at a specified speed. The maximum in the removal force is ordinarily observed just at the point where the two peel fronts Join. The value is reported in a force per area of tape width, or lb in. -. While this tack test has some popularity, it is perhaps more of a very short dwell time peel test, and it has variables more associated with that test, especially backing effects, since heavier backings lead to higher tack values. 

Figure 16. The effect of net charge. Approximate net charge for each toxin is indicated in parenthesis beside the compound number. Note the strong correlation between net charge and Net charge does not apjiear to have a significant effect on dwell time.

The spectral width SWi associated with the F, frequency domain may be dehned as F, = SWi. The time increment for the ti domain, which is the effective dwell time, DWi for this period, is related to SW as follows DWi = (V2)SW]. The time increments during [Pg.158]

Note The initial kinetic energy of slow ions can be lost upon several collisions, thereby stopping their motion along the cell. [119,120] Under such conditions, the continuous ion current into the cell is the only impetus to push the ions through as a result of space-charge effects. The resulting dwell time of about 10 ms allows up to about 5000 (reactive) collisions to take place at some 5 Pa collision gas (or reagent gas) pressure in an octopole collision cell. [123]... 

LC-MS/MS has dramatically changed the way bionalysis is conducted. Accurate and precise quantitation in the pg ml scale is nowadays possible however one has to be aware of certain issues which are specific to mass spectrometric detection such as matrix effects and metabolite crosstalk. With the current growing interest in the analysis of endogenous biomarkers in biological matrices, quantitative bioanalysis with MS has certainly the potential to contribute further in this field with the development of multicomponent assays. Modern triple quadrupole instruments have the feature to use very short dwell times (5-10 ms), allowing the simultaneous determination of more than 100 analytes within the timescale of an HPLC peak. Due to the selectivity of the MS detection the various analytes... 

The Kirkendall effect (8) is time and temperature dependent, and with some metal couples, it takes place even at room temperature. For instance, adhesion of solder to gold is damaged by heating to about 150°C for about 5 minutes, due to the formation of Kirkendall voids. Naturally, the formation of Kirkendall voids is accelerated by increased temperature and dwelling time. 

Two critical parameters that must be controlled for the process to be effective in a reasonable time period are concentration and dwell time. These parameters will Vary with each instrument, depending on design and capacity of the various units. 

The modeling of residual stress development during cure can be used to optimize the processing conditions to reduce or control residual stresses. The current process model is used next to assess the effects of several processing conditions on residual stresses. Reduced cure temperature, longer dwell times, slower cool down rate, and the use of novel cure cycles are all feasible for the reduction of residual stresses. 

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