Learning rules for graph transformations by induction from examples

The input to the described program, in learning mode, consists of examples of starting graph and result graph pairs. The starting graph is transformable into the result graph by adding or deleting certain edges and vertices. The essential common features of the starting graphs are stored together with specifications of the edges and vertices to be deleted or added. This latter information is obtained by mapping each starting graph onto the corresponding result graph. On subsequent input of similar starting graphs without a result graph, the program, in performance mode, recognizes the characterizing set of features in the starting graph and can perform the proper transformation on the starting graph to obtain the corresponding result graph. The program also adds the production to its source code so that after recompilation it is permanently endowed with the new production. If any feature which lacks the property "ordinary" is discovered in the starting graph and only one example has been given, then there is feedback to the user including a request for more examples to ascertain whether the extraordinary property is a necessary part of the situation.     

Dynamics of the Inversion Reaction

Three examples are presented of homolytic bimolecular substitutions, F + CH₃I, H + CD₄, and H + SiD₄. All are shown by laser techniques to proceed by inversion. For the latter two reactions, the proof is based on the demonstration that the entering H atom and the leaving D atom have approximately parallel velocities. The isotopic substitution reactions are almost vibrationally adiabatic in the sense that the departing D atom carries away about 80% of the kinetic energy of the incoming H atom.     

Photodissociation with Polarized Light

This is a review of a small part of the work on photodissociation with polarized light performed by Kent Wilson and his students [1–4] at the University of California at San Diego and the author and his students [5–7] at Columbia. The physics of the experiment has been presented in a recent review by R.N. Zare [8] who was the first to suggest the utility of such work. We comment on the photodissociation of three molecules — I₂,Cd(CH₃), and α-iodonaphthalene.     

Time-resolved spectroscopy of hemoglobin and its complexes with subpicosecond optical pulses

Subpicosecond optical pulses have been used to study the photolysis of hemoglobin conplexes. Photodissociation of carboxyhemoglobin is found to occur in less than 0.5 picosecond. In hemoglobin and oxyhemoglobin a nondissociative excited state recovery in 2.5 picoseconds is observed.     

Molecular photodissociation by an ultraviolet photon

The laser has greatly expanded the study of photodissociation dynamics. By generating large concentrations of fragments using monochromatic light, the laser enables the measurement of their final state distribution. This distribution over translational, vibrational, and rotational states combined with the conservation of energy and linear and angular momentum allows us, in principle, to calculate the forces acting in the excited state. A review of experimental results so far obtained shows that: 1) for diatomics the quantum states of the dissociated atoms can now be directly determined, 2) for triatomics the excess of photon energy over dissociation energy appears in comparable amounts in vibrational and translational energy with rotational energy often substantial as well (ICN and H2S are exceptions), 3) in complex molecules optical energy is absorbed in one part of the molecule and utilized in another with resulting intramolecular transfer of energy.