Pressure-distance curves

Methods of measuring underwater shock waves by crusher gauges, diaphragm gauges piezoelectric gauges are thoroughly described by Cole (Ref 3) in Chapter 7. Cook (Ref 7) describes the use of a 16- to 64-frame/sec camera to measure the free surface vel produced by a shock wave at the surface, and the determination of the underwater pressure-distance curve for TNT... 

FIGURE 3.12 A plot of the internal kappa values Km obtained from the pressure-distance curves against I /. where is the average observed cZ-spacing. 

Significant primary blast injury only occurs in those who have been exposed to high blast loading and are consequently very close to the point of detonation (remember the pressure distance curve. Fig. 3.2). As a result, most such casualties will have died from secondary or tertiary injuries. However, reflection and summation in closed spaces may be associated with a significant incidence of primary injuries in survivors of atrocities in areas such as bars and buses. In one Israeli bus bomb incident, incidences of 76% for eardrum perforation, 38% for blast lung and 14% for abdominal blast injury were found. 

Hertzian mechanics alone cannot be used to evaluate the force-distance curves, since adhesive contributions to the contact are not considered. Several theories, namely the JKR [4] model and the Derjaguin, Muller and Torporov (DMT) model [20], can be used to describe adhesion between a sphere and a flat. Briefly, the JKR model balances the elastic Hertzian pressure with attractive forces acting only within the contact area in the DMT theory attractive interactions are assumed to act outside the contact area. In both theories, the adhesive force is predicted to be a linear function of probe radius, R, and the work of adhesion, VFa, and is given by Eqs. 1 and 2 below. 

Measurement of detonation pressure) 363-69 (Peak pressure-distance relationships curves) 41) Cook (1958), 32-35 (Measurement of deton pressure) 265-68 (Maximum available work and peak blast pressure) 4la) I. Ginsburgh, JAppl-Phys 29, 1381-82(1958) (Abnormal pressures in a shock tube) 41b) D. Price, ChemRevs 59, 801-25(1959) (Substituted in her discussions the term "detonation pressure for "brisance and "detonation energy for "power ) 42) Baum, Stanyu-kovich Shekhter (1959), 139-43 (Bichel bomb for detn of pressure) 43) Bandurin Rukin (1959), 69-74 (Pressure of gases formed on expln in a closed vessel)... 

In addition to measuring shock wave and bubble energies, underwater tests also can measure the shock wave impulse, another indicator of explosive strength. The shock wave impulse is derived by measuring the area under the pressure-time curve for a selected integration time interval at a known distance from the explosion... 

Thus, we seek an asymptotic solution of the one-dimensional gasdynamic equations for a given pressure evolution curve, f(t/r), which is characterized by a sufficiently rapid pressure decrease. In a slightly different way, we may formulate the problem thus preserving the form of the dimensionless function f(t/r), we let the pressure duration go to zero and the maximum pressure to infinity, and look for the asymptotic solution—the distribution of the velocity, pressure and other quantities—after a finite time t, at a finite distance x. 

In the case of cross-flow hltration, one can expect that the gel-layer thickness and the surface concentration of the solute wUl vary with distance from the channel entrance. As a consequence, the local permeate flux will also vary with longitudinal position. In a highly recommended article, Denisov [53] presented a mathematically rigorous theory of concentration polarization in cross-flow ultraflltration, which takes into account the nonuniformity of the local permeate membrane flux. He derived equations describing the pressure/flux curve. 

In parallel, another important (although less direct) technique for measuring forces between macromolecules or lipid bilayers was developed, namely, the osmotic stress method [39-41]. A dispersion of vesicles or macromolecules is equilibrated with a reservoir solution containing water and other small solutes, which can freely exchange with the dispersion phase. The reservoir also contains a polymer that cannot diffuse into the dispersion. The polymer concentration determines the osmotic stress acting on the dispersion. The spacing between the macromolecules or vesicles is measured by X-ray diffraction (XRD). In this way, one obtains pressure-versus-distance curves. The osmotic stress method is used to measure interactions between lipid bilayers, DNA, polysaccharides, proteins, and other macromolecules [36]. It was particularly successful in studying the hydration... 

A pressure-time curve representing one point of the diagram pressure vs distance is also shown. 

The pressure history was measured by a PCB 113 A24 piezoelectric transducer with a sensitivity of 735 mV/Mpa, which was installed on the tube wall at a distance of 900 mm from the bottom. The maximum rate of pressure rise was calculated from the slope- of the tangent of the pressure-time curve at its inflection point. The flame arrival was detected by eight ionization probes on the axis of the test tube, biased at a 400 Vdc potential. The combustion tube and the obstacles were carefully cleaned after each test. 

Thus, it was questioned if there were any intrinsic hydration layers on a lipid membrane. The oscillatory profile observed in the A/ versus distance curve obtained by FM-AFM revealed the existence of the hydration layer on a DPPC bilayer (Fig. 18.8a). In FM-AFM, the force is measured with a tip having a nanometer-scale cross section, while the force measured by SFA and the osmotic pressure method is averaged over a micrometer-scale area. Such global averaging may smear out the local distance dependence, showing the oscillatory profile. The result clearly showed the importance of having local spatial resolution in the investigations on interfacial phenomena. 

From Figs. 10.17 and 10.18 it follows that because of the significant duration of the rarefaction phase at F < 0.7, the rarefaction wave effect is more dangerous for some targets than the pressure wave effect. Figure 10.19 presents TNT equivalents based on the rarefaction phase pressure Kp (curves 1,2) and the compression phase pressure Kp+ (curves 3, 4) at various distances from the blast epicenter. Within the accuracy of the measured rarefaction wave parameters, the pressure TNT equivalent of the rarefaction phase does not depend on the distance and everywhere is not less than the TNT equivalent for the compression phase. 

Fig. 10.20 TNT pressure impulse equivalent of a gas detonation for rarefaction (1,2) and compression (3) phases versus relative distance curves 1,3 -Ef= 46 MJ/kg curves 237 MJ/kg...

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