Above threshold Coulomb explosion of molecules in intense laser pulses

We have measured and explained a new mechanism of molecular ionization near the appearance intensity that produces a sequence of peaks in the nuclear kinetic energy spectrum separated by the photon energy. Our interpretation is based on an internally consistent model for the nuclear motion during an intense laser pulse. Within this model, the same concepts and language can be used for both dissociation and ionization, leading to a more unified understanding of the dynamics.     

Enhancing high-order above-threshold dissociation of H2+ beams with few-cycle laser pulses

High-order (three-photon or more) above-threshold dissociation (ATD) of H(2)(+) has generally not been observed using 800 nm light. We demonstrate a strong enhancement of its probability using intense 7 fs laser pulses interacting with beams of H(2)(+), HD(+), and D(2)(+) ions. The mechanism invokes a dynamic control of the dissociation pathway. These measurements are supported by theory that additionally reveals, for the first time, an unexpectedly large contribution to ATD from highly excited electronic states.     

Cyclic antiautomorphisms of directed triple systems

A transitive triple, (a,b,c), is defined to be the set {(a,b), (b,c), (a,c)} of ordered pairs. A directed triple system of order v, DTS(v), is a pair (D,β), where D is a set of v points and β is a collection of transitive triples of pairwise distinct points of D such that any ordered pair of distinct points of D is contained in precisely one transitive triple of β. An antiautomorphism of a Directed triple system, (D,β), is a permutation of D that maps β to β⁻¹, where β ⁻¹ = {(c,b,a)|(a,b,c) E β}. In this article we give necessary and sufficient conditions for the existence of a Directed triple system of order v admitting an antiautomorphism consisting of a single cycle of length d and having v − d fixed points. Further, we give a more general result for partial Directed triple systems in which the missing ordered pairs are precisely those containing two fixed points. © 1996 John Wiley & Sons, Inc.     

Regulation of the receptor-mediated cyclic AMP response of kidney to parathyroid hormone in the vitamin D-deficient rat.

Rats fed a diet deficient in vitamin D were found to exhibit a refractory cyclic AMP response of kidney slices to parathyroid hormone and a marked decrease in membrane parathyroid hormone-dependent adenylate cyclase activity. Both the characteristic calcium deficiency (hypocalcemia) and secondary elevation of circulating parathyroid hormone appeared before the first noticeable decrease in hormone-dependent enzyme activity. After repletion of D-deficient rats with vitamin D2, we found that serum calcium and parathyroid hormone were both restored to normal levels before the depressed enzyme response to the hormone was reversed. Moreover, infusion of parthyroid hormone into vitamin D-replete rats led to a marked reduction in parathyroid hormone-dependent adenylate cyclase activity, which was partly restored to control level 3 hours after discontinuing the hormone infusion. Taken as a whole, this study suggests that the elevated endogenous parathyroid hormone in the vitamin D-deficient rat is involved in the "down-regulation" of renal cyclic AMP responsiveness to the hormone. However, these experiments do not rule out the possibility that calcium deficiency and/or vitamin D per se participate in the regulation of the renal cyclic AMP response to parathyroid hormone.     

Charge transfer and elastic scattering in very slow H(+)+D(1s) half collisions

Charge transfer and elastic scattering probabilities were measured for half collisions between very slow protons and atomic deuterium. Collision energies down to a few meV, lower by more than an order of magnitude and with better energy resolution than previous measurements, were studied using the dissociation of the HD+ electronic ground state. The collision energy is determined a posteriori from the measured momentum vector of the dissociating charged fragments. The experimental results are in good agreement with our coupled channel calculations.     

Absorption of ultrasound by mammalian ovaries

The transient thermoelectric method was employed to determine the ultrasonic absorption coefficient of excised bovine, canine, feline, murine, ovine, and porcine ovaries at 1 MHz. The dynamics of the organ yields significant variations with physiological stage and structure. Values ranged from 0.017 cm-1 for the follicle to 0.050 cm-1 for the corpus luteum, largely reflecting macromolecular content. Little interspecies variation was observed.