Impact of hyperthermic regional perfusion therapy on cell metabolism of malignant melanoma monitored by 31P MR spectroscopy

For the first time, the influence of hyperthermic regional perfusion therapy on tumor cell metabolism has been monitored by means of 31P MR spectroscopy. Shortly after treatment, a complete depletion of high energy phosphates, a significant increase of inorganic phosphate, phosphomono- and phosphodiester resonances and a decrease of pH have been observed. Healthy muscle tissue showed only minor effects caused by this aggressive therapy. The time course of the transient variation of phosphate metabolite concentrations is explained in the framework of a simple pathophysiological model. The results demonstrate that the imediate effect of chemotherapy on tumor tissue can be detected by 31P MRS before any clinical signs of tumor response are visible.     

Single rotational lifetimes of formaldehyde in a hypersonic jet

Radiationless transitions have recently been shown to also depend on their rotational energy content. Careful documentation of this effect demand lifetime measurements of single rotational states. These must, however, be documentable by a complete computer simulation. The molecule cannot be too large to afford complete spectroscopic separability of lines and accurate spectroscopy for use in the computer simulation. Furthermore measurements should be carried out in a beam to avoid the almost impossible extrapolation to the rotationally “collisionless” regime. Formaldehyde is apprarently a good candidate due to its highly documented spectroscopy including magnetic perturbations. The latter is particularly prominent for the 2²4¹ vibronic absorption, but the rotational transitions are still grossly congested (1902 transitions with a peak intensity above 1% are calculated to contribute to the band contour). Experiments in a hypersonic jet cool the molecules to 17 K without leading to aggregates. The rotational states are well separated and very pure, as shown by detailed computer simulation for the asymmetric rotor including contrifugal distortion. Lifetimes of some 18 states are reported as a function of rotational quantum numbers and shown to vary substantially. The symmetric and antisymmetric nuclear spin forms of formaldehyde here show up as separate isomers during the expansion.     

A proof of Price's Law on Schwarzschild black hole manifolds for all angular momenta

Price's Law states that linear perturbations of a Schwarzschild black hole fall off as t−2?−3 for t→∞ provided the initial data decay sufficiently fast at spatial infinity. Moreover, if the perturbations are initially static (i.e., their time derivative is zero), then the decay is predicted to be t−2?−4. We give a proof of t−2?−2 decay for general data in the form of weighted L¹ to L^∞ bounds for solutions of the Regge–Wheeler equation. For initially static perturbations we obtain t−2?−3. The proof is based on an integral representation of the solution which follows from self-adjoint spectral theory. We apply two different perturbative arguments in order to construct the corresponding spectral measure and the decay bounds are obtained by appropriate oscillatory integral estimates.     

Evolutionary insights on the willingness to communicate

While in previous models of pre-play communication players are forced to communicate, we investigate what happens if players can choose not to participate in this cheap talk. Outcomes are predicted by analyzing evolutionary stability in a population of a priori identical players. If the game following the communication rewards players who choose the same action then an efficient outcome is only guaranteed when participation in the pre-play communication is voluntary. If however players aim to coordinate on choosing different actions in the underlying game and there are sufficiently many messages then the highest payoff is selected when players are forced to talk to each other before playing the game. Received: September 2000/Revised: March 2003     

Do large molecules ionize?

A possible mechanism for the ionization or lack thereof in large molecules is discussed. The experimental observation is that the ionization efficiency rapidly decreases with increasing weight, whether one uses electron impact, single-photon or multi-photon ionization. Possible mechanisms for this decline in the yield of ions are considered. It is suggested that in larger molecules ionization occurs through the intermediate formation of charge pairs which can ionize in a unimolecular-like fashion due to an energy fluctuation. A more probable route is however for the charge pairs to recombine. Possible experimental tests of the proposed mechanism are considered and a scaling law for the mass-dependence is derived and shown to fit the available data.     

Molecular two-photon spectroscopy with two synchronized tunable dye lasers

Two tunable dye lasers, with differing wavelength and polarization, were synchronized to produce a two-photon spectrum in gas phase benzene. Simultaneous absorption of two photons from one laser beam was precluded by choosing appropriate wavelengths. All possible ratios have been measured for a totally-symmetric two-photon transition demonstrating a strong analogy between two-photon absorption and Raman scattering.     

The temporal development of intracavity absorption in a dye laser

Intercavity absorptions is known to lead to an enormous enhancement in the detectability of absorbing species. Here the time development of this enhancement of this enhancement is investigated in order to fix a typical time scale such measurements. This is done with a Pockles cell in front and inside a flashlamp pumped dye laser resonator. The enhancement of absorption steeply increases at laser threshold and then levels off during the letter part of the laser pulse. By Q-switching a dye laser it is demonstrated that on a time resolution of 20 nsec extinctions as low as 10^-4 can be measured with an enhancement of two orders of magnitude.