Geometric recovery

Key words Severe plastic deformation, strain path, fragmentation, geometric recovery, strain efficiency, equivalent strain... 

The importance of geometric recovery is quite plausible when the strain path is reversed. It is not so obvious when the strain path changes in more complicated ways. Experiments on the cold swaging of copper [10,12,13] indicate that geometric recovery is also important for an irregular sequence of strain paths. This problem should therefore be looked at more closely for ECA-pressing. 

For a comparison of the efficiency of different SPD techniques to produce such structures the traditional concept of equivalent strain based on equal mechanical work is problematic, especially when strain is accumulated in steps with varying strain path where geometric recovery must be taken into account. 

The properties of flexible polymer chains moving in porous structures, that is, in structures with geometric constraints such as tubes or slits, apart from their Tclevance for various applications such as filtration, gel permeation chromatography, oil recovery, etc., pose an exciting problem of statistical... 

A ductile material can be stretched uniformly only when stable flow occurs. The stable flow of materials has been investigated by Hart who described the transition from the stable to unstable flow. The beginning of geometrical instability and localisation of strain is the limit of the stable flow. At temperatures above 0.5 T (at equilibrium between recovery and hardening) the strain rate sensitivity parameter "m" may be derived from the expression ... 

Moholkar et al. [11] studied the effect of operating parameters, viz. recovery pressure and time of recovery in the case of hydrodynamic cavitation reactors and the frequency and intensity of irradiation in the case of acoustic cavitation reactors, on the cavity behavior. From their study, it can be seen that the increase in the frequency of irradiation and reduction in the time of the pressure recovery result in an increment in the lifetime of the cavity, whereas amplitude of cavity oscillations increases with an increase in the intensity of ultrasonic irradiation and the recovery pressure and the rate of pressure recovery. Thus, it can be said that the intensity of ultrasound in the case of acoustic cavitation and the recovery pressure in the case of hydrodynamic cavitation are analogous to each other. Similarly, the frequency of the ultrasound and the time or rate of pressure recovery, are analogous to each other. Thus, it is clear that hydrodynamic cavitation can also be used for carrying out so called sonochemical transformations and the desired/sufficient cavitation intensities can be obtained using proper geometric and operating conditions. 

Experimentally, as indicated in Fig. 12.13, we find that D/Dq depends on the shear stress at the wall xw (a flow variable) and the molecular weight distribution (MWD) (a structural variable) (22). The length-to-diameter ratio of the capillary (a geometric variable) also influences D/Dq. The swelling ratio at constant xw decreases exponentially with increasing L/Dq and becomes constant for L/Dq > 30. The reason for this decrease can be explained qualitatively as follows. Extrudate swelling is related to the ability of polymer melts and solutions to undergo delayed elastic strain recovery, as discussed in... 

The quantity of quartz on a sample filter is determined by multiplying the quantity of quartz on a standardized filter by the absorbance of the 800 cm peak of a sample filter divided by the absorbance of the 800 cm peak of the standardized filter. This technique has been used to analyze 53 PAT filters and the results are shown in Table III. Redeposition was not done due the similar deposition technique used to prepare the Standard Reference Filters in the PAT Program (8). The first fourteen samples in Table III were filters that had been retained by the lab from previous PAT Rounds. The actual results on the rest were submitted in the PAT Program to NIOSH. (PAT Filter Number S-35-2 has not been included because half of the filter was initially analyzed backwards in the MIR sample holder resulting in a quartz loss on the support pad.) The % recovery was calculated based upon the PAT Geometric Mean. 

PAT Filter Number PAT Geometric Mean, mg MIR-IR Result, mg % Recovery... 

When free-molecule flow is encountered, Oppenheim [8] has given convenient charts for calculating recovery factors and heat-transfer coefficients for flow over standard geometric shapes. Figures 12-16 and 12-17 give samples of these charts. The molecular speed ratio S used in these charts is defined by... 

G. Iverson and M. D Zmura, Color Constancy Spectral Recovery Using Trichromatic Bilinear Models, in R. D. Luce, M. D Zmura, D. D. Hoffman, G. Iverson, and K. Romney, Eds., Geometric Representations of Perceptual Phenomena, Lawrence Erlbaum, Mahawah, NJ, 169-185 (1995). 

Improvement of the geometric structure of the working electrode by a well-controlled PEVD process benefits the performance of a CO sensor in many ways. To optimize kinetic behavior, the response and recovery times of CO potentiometric sensors were studied at various auxiliary phase coverages. This was realized by a unique experimental arrangement to deposit the Na COj auxiliary phase in-situ at the working electrode of type III potentiometric CO sensors by PEVD in a step-wise fashion. Since the current and flux of solid-state transported material in a series of PEVD processes can be easily moiutoredto control the amount of deposit... 

The response and recovery times of both samples at each PEVD step are compared at a working electrode flow rate of 40 seem in Figures 25a and b, respectively. Because of the inability to fabricate a consistent Pt thick film at the working electrode of both sensors, the response and recovery curves do not exactly match. However, the curves from both samples follow the same trends. Taking into account the geometric factor for both samples, the results from this study can be considered to be fairly consistent. 

The results indicate that sensor response behavior is not only related to the thickness of the auxiliary phase, but is also controlled by other working electrode geometric factors - most likely the aspect ratio of the working electrode surface. Because of the high aspect ratio, the response and recovery times of the sensor are... 

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