Formation and bleaching of optically-induced absorption bands in CdS:Cd,Cu crystals

Our earlier work has revealed the occurrence of three photoinduced bands in cadmium sulphide crystals appropriately doped with both cadmium and copper: one in the visible and two in the near IR region of the optical absorption spectrum. This investigation is now extended by examining the growth kinetics, their dependences on the temperature and on the excitation-light intensity, as well as the kinetics of thermal bleaching of the induced absorption. The data obtained are discussed in terms of the formation of photochemical complexes which give rise to the visible band. The IR bands are attributed to centers which are also responsible for the IR quenching of the photoconductivity.     

Electron trapping and untrapping during the dark decay of flash-produced KC1 F′ and F′ > A(Na) bands between 290–350°K

Both the thermal lifetimes of the F′(F′_A) centers and the ratios of the electron trapping cross-sections of (F_A) to α(α_A) centers were derived from the decay kinetics of flash-produced F′(F′_A) bands. In particular, the ratios dropped steeply with the temperature possibly due to a thermally activated de-excitation following excited state pre-trapping of the electron by the anion vacancy.     

Evaluation of a method for controlling molecular scaffold diversity in de novo ligand design

We describe an algorithm for the automated generation of molecular structures subject to geometric and connectivity constraints. The method relies on simulated annealing and simplex optimization of a penalty function that contains a variety of conditions and can be useful in structure-based drug design projects. The procedure controls the diversity and complexity of the generated molecules. Structure selection filters are an integral part and drive the algorithm. Several procedures have been developed to achieve reliable control. A number of template sets can be defined and combined to control the range of molecules which are searched. Ring systems are predefined. Normally, the ring-system complexity is one of the most elusive and difficult factors to control when fusion-, bridge- and spiro-structures are built by joining templates. Here this is not an issue; the decision about which systems are acceptable, and which are not, is made before the run is initiated. Queries for inclusion and exclusion spheres are incorporated into the objective function, and, by using a flexible notation, the structure generation can be directed and more focused. Simulated annealing is a reliable optimizer and converges asymptotically to the global minimum. The objective functions used here are degenerate, so it is likely that each run will produce a different set of good solutions.     

Characterizing invariants for local extensions of current algebras

ParisA of local quantum field theories are studied, whereA is a chiral conformal quantum field theory and is a local extension, either chiral or two-dimensional. The local correlation functions of fields from have an expansion with respect toA into conformal blocks, which are non-local in general. Two methods of computing characteristic invariant ratios of structure constants in these expansions are compared: (a) by constructing the monodromy representation of the braid group in the space of solutions of the Knizhnik-Zamolodchikov differential equation, and (b) by an analysis of the local subfactors associated with the extension with methods from operator algebra (Jones theory) and algebraic quantum field theory. Both approaches apply also to the reverse problem: the characterization and (in principle) classification of local extensions of a given theory.     

Structural and spectroscopic analysis of dipeptide <Emphasis Type="SmallCaps">l</Emphasis>-methionyl-glycine and its hydrochloride

Dipeptide l-methionyl-glycine (Met-Gly) hydrochloride was characterized structurally by means of solid-state linear polarized IR (IR-LD) spectroscopy of oriented samples as colloidal suspension in nematic liquid crystal. Quantum chemical ab initio calculations and vibrational analysis support the experimental data. ¹H and ¹³C nuclear magnetic resonance (NMR) data, mass spectrometry (ESI-MS and FAB-MS) techniques, thermogravimetry (TGV), and differential scanning calorimetry (DSC) method were employed as well. The experimental and theoretical data of hydrochloride salt were compared with analogous data of the neutral dipeptide with the aim to explain the role of intermolecular hydrogen bonding on the conformational behavior and spectroscopic properties of the compound studied.