Global existence for coupled systems of nonlinear wave and Klein-Gordon equations in three space dimensions

We consider the Cauchy problem for coupled systems of wave and Klein-Gordon equations with quadratic nonlinearity in three space dimensions. We show global existence of small amplitude solutions under certain condition including the null condition on self-interactions between wave equations. Our condition is much weaker than the strong null condition introduced by Georgiev for this kind of coupled system. Consequently our result is applicable to certain physical systems, such as the Dirac-Klein-Gordon equations, the Dirac-Proca equations, and the Klein-Gordon-Zakharov equations.Comment: 31 pages. The final versio

Response of PBXs and inert substitutes in launch and impact scenarios

The physical behaviour of a polymer bonded explosive (PBX) fill is important for the development of safe and reliable shells and penetrators. The strain rate environment during launch or impact is generally in the intermediate regime, below shock but above quasi-static. Confidence in the predictions of the constitutive response of PBXs is a necessary pre-requisite for accurate predictions of the likelihood of reactions. The level of deformation and the rate of that deformation can cause ignitions. A number of experiments have been completed with different levels of confinement of both PBXs and PB inerts to obtain data on their behaviour at these strain rates. Instrumentation has included flash X-ray, Digital Speckle Radiography (DSR), VISAR, high speed video and pressure gauges. Experimental data is presented together with hydrocode modelling comparisons. Necessary features of the material models are discussed together with lessons learnt in its application across the strain rate regimes present during launch and impact

Prazosin attenuates the natriuretic response to atrial natriuretic factor in man

Prazosin attenuates the natriuretic response to atrial natriuretic factor in man. The effect of alpha-1-adrenoceptor blockade with 0.25mg oral prazosin on the renal response to atrial natriuretic factor (ANF) 5 pmol/kg/min was examined in eight healthy male volunteers undergoing maximal water diuresis. ANF on its own decreased mean arterial blood pressure (P < 0.05) without altering heart rate or increasing plasma norepinephrine. ANF increased urinary sodium excretion by 130% (P < 0.01) from baseline value with accompanying 18% decrease (P < 0.05) in PAH clearance (ERPF) without changing inulin clearance (GFR). When compared to placebo infusion, ANF infusion caused a significant increase in fractional excretion lithium (FELi), a marker of proximal tubular function. Fractional distal delivery of sodium, another marker of proximal tubular outflow as determined by free water clearance, was also increased during ANF infusion. As expected, ANF decreased distal nephron fractional sodium reabsorption as evaluated by both the “lithium method” and by the conventional “solute-free water method”. Prazosin on its own had no effect on blood pressure, renal function or hormonal parameters. When given in combination with ANF, prazosin blunted the natriuretic effect of ANF from 130% to 35% (P < 0.01). However, prazosin pretreatment did not influence the ANF-induced fall in blood pressure or ERPF nor the ANF-induced suppression of plasma aldosterone. We have therefore found evidence to support the hypothesis that at basal levels of sympathetic tone, the natriuretic effect of ANF in man is dependent on an intact sympathetic nervous system, since sympathetic blockade by prazosin blunts its sodium excretory effects