STUDIES ON PLANT BILE PIGMENTS-6. PHOTOCHEMICALLY ASSISTED REACTION OF A-DIHYDROBILINDIONE WITH NUCLEOPHILES AS A MODEL FOR PHYTOCHROME INTERCONVERSION

From the A-dihydrobilindione 3. the pyridinium derivatives 6a,b and analogues thereof have been obtained by a formal nucleophilic substitution. The reaction is rationalized as a photochemically assisted oxidation of 3 with a subsequent regioselective addition of pyridine at C-5. By thermolysis. 6a.b yields back the parent bilin 3, together with an oxidation product. The significance of the reaction with respect to the phytochrome interconversion is discussed

Non-Gaussian wave functionals in Coulomb gauge Yang--Mills theory

A general method to treat non-Gaussian vacuum wave functionals in the Hamiltonian formulation of a quantum field theory is presented. By means of Dyson--Schwinger techniques, the static Green functions are expressed in terms of the kernels arising in the Taylor expansion of the exponent of the vacuum wave functional. These kernels are then determined by minimizing the vacuum expectation value of the Hamiltonian. The method is applied to Yang--Mills theory in Coulomb gauge, using a vacuum wave functional whose exponent contains up to quartic terms in the gauge field. An estimate of the cubic and quartic interaction kernels is given using as input the gluon and ghost propagators found with a Gaussian wave functional.Comment: 27 pages, 21 figure

Colombian Purchasing Power Parity Analysed Using a Framework of Multivariate Cointegration

This paper tests for purchasing power parity (PPP)between Colombia and its main trading partners using the Johansen framework of multivariate cointegration. The tests shows that PPP does not hold in the strong sense, but a clear purchasing power relationschip is, nevertheless, shown to exist. The model is, furthermore, shown to have significant forecasting power. It outperforms a random walk in out-of sample forecasting on the 12 and 24 month horizont but not on the 3 and 6-month horizon.