Collective hyperspherical coordinates for polyatomic molecules and clusters

For n-body dynamics an analysis is made of the properties of configuration space within a symmetric hyperspherical framework. Coordinates are conveniently broken up into spatial (or external) rotations, kinematic invariants (related to the inertia moments) and kinematic (or internal) rotations. Their usefulness is demonstrated for the study of constrained intramolecular motions and of concerted reactions and for collective modes of polyatomic molecules and clusters. For a fixed hyperradius, which is a measure of total inertia, the space of kinematic invariants is the surface of a right spherical triangle that leads to the tetrahedral (for n = 4) or octahedral (for n ≥ 5) tessellation of the sphere. Alternative parametrizations are discussed, including the proper one to deal with the umbrella inversion motion of ammonia.     

An impulse integrator for Langevin dynamics

The best simple method for Newtonian molecular dynamics is indisputably the leapfrog Stormer-Verlet method. The appropriate generalization to simple Langevin dynamics is unclear. An analysis is presented comparing an ‘impulse method’ (kick; fluctuate; kick), the 1982 method of van Gunsteren and Berendsen, and the Brünger-Brooks-Karplus (BBK) method. It is shown how the impulse method and the van Gunsteren-Berendsen methods can be implemented as efficiently as the BBK method. Other considerations suggest that the impulse method is the best basic method for simple Langevin dynamics, with the van Gunsteren-Berendsen method a close contender.     

The benefit to consumers from generic scoring models based on credit reports

Received on 1 July 1991. The benefit to consumers from the use of informative creditreports is demonstrated by showing the improvement in creditdecisions when generic scoring models based on credit reportsare implemented. If these models are highly predictive, thenthe truncation of credit reports will reduce the predictivepower of bureau-based generic scoring systems. As a result,more good credit risks will be denied credit, and more poorcredit risks will be granted credit. It is shown that, evenwhen applied to credit applications that had already been screenedand approved, the use of generic scoring models significantlyimproves credit grantors' ability to predict and eliminate bankruptcies,charge-offs, and delinquencies. As applied to existing accounts,bureau-based generic scores are shown to have predictive valuefor at least 3 months, while scores 12 months old may not bevery powerful. Even though bureau-based scores shift towardsthe high-risk end of the distribution during a recession, theycontinue to rank risk very well. When coupled with application-basedcredit-scoring models, scores based on credit-bureau data furtherimprove the predictive power of the model-the improvements beinggreater with more complete bureau information. We conclude thatgovernment-imposed limits on credit information are anti-consumerby fostering more errors in credit decisions.     

SIMULTANEOUS SATURATION OF VARIABLE FLUORESCENCE YIELD AND PHOTOACOUSTICALLY MONITORED THERMAL EMISSION IN THYLAKOID MEMBRANES

Thermal and fluorescence emission from thylakoid membranes were monitored simultaneously in a photoacoustic cell. A close relationship existing between variable fluorescence and variable thermal emissions is demonstrated. The modulated measuring beam of the photoacoustic spectrophotometer was used to study the effect of light intensity on the energy storage yield and on the variable fluorescence yield. The half-saturation light intensities obtained for both parameters were 8.5 and 9.1 W m^?2, respectively. The similar sensitivity of energy storage and variable fluorescence yield to light intensity indicates that electron transfer with plastoquinone as last acceptor is probably responsible for the photoacoustically monitored energy storage.     

CONTRIBUTION A L''ETUDE DE LA LUMINESCENCE DIFFEREE DE COLORANTS EN MILIEU RIGIDE. PHOTOIONISATION DE LA FLUORESCEINE DANS L''ACIDE BORIQUE PAR UN PROCESSUS A DEUX PHOTONS

Abstract— A study of the delayed luminescence and thermoluminescence of fluorescein and others dyes in boric acid glass gives evidence of photoionisation of these compounds. To account for the energetic aspect of the photoionisation, a two photon process involving solute-solvent proton exchange is proposed. The participation of the heterogeneous structure of the glass in the mechanism of the photoionisation is confirmed.