New Copoly(bisphenol-A)carbonates,Having Hydrophilic Porphyrin Units as End-Groups,Synthesized by Melt-Reacting Processes

The synthesis of some poly(bisphenol-A)carbonates (PCs) containing hydrophilic porphyrin units as end groups, by thermal treatment of commercial PC and 5,10,15-tri{p[ω-methoxy-poly(oxyethylene)]phenyl}20(p-hydroxy phenyl)porphyrin (I) blends, is reported. A suitable choice of reaction temperature, molar composition and reaction time, allowing the extent of the outer-inner transesterification reactions, leads to a gradual insertion of porphyrin units in the polymer chains. The composition of the obtained materials was inferred by GPC and MALDI-TOF mass spectrometric analysis.     

Conformational analysis of model compounds of vitamin D by theoretical calculations

A conformational analysis of two model compounds of vitamin D was carried out by means of theoretical computations, Ab initio calculations were carried out using the standard 6-31G* basis set at the Hartree–Fock (HF) level of theory. In addition, the Møller–Plesset (MP2) correlation treatment was applied on the simplest model. Semiempirical calculations were also performed using the AM1 Hamiltonian. The results predict stable A-ring twist forms with energies in the order of 4–6 kcal/mol relative to the global minimum, significantly higher than those reported from molecular mechanics calculations. In addition, a folded conformation was found by the HF optimizations; however, its stability is predicted to be very poor. Comparison of the theoretical results with experimental data is discussed. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1647–1655, 1997     

On Covering Methods for D.C. Optimization

Covering methods constitute a broad class of algorithms for solving multivariate Global Optimization problems. In this note we show that, when the objective f is d.c. and a d.c. decomposition for f is known, the computational burden usually suffered by multivariate covering methods is significantly reduced. With this we extend to the (non-differentiable) d.c. case the covering method of Breiman and Cutler, showing that it is a particular case of the standard outer approximation approach. Our computational experience shows that this generalization yields not only more flexibility but also faster convergence than the covering method of Breiman-Cutler.     

On the best approximation matrix problem for integrable matrix functions

In this paper positive definite matrix functionals defined on a set of square integrable matrix valued functions are introduced and studied. The best approximation problem is solved in terms of matrix Fourier series. Riemann-Lebesgue matrix property and a Bessel-Parseval matrix inequality are given.     

A value for multichoice games

A multichoice game is a generalization of a cooperative TU game in which each player has several activity levels. We study the solution for these games proposed by Van Den Nouweland et al. (1995) [Van Den Nouweland, A., Potters, J., Tijs, S., Zarzuelo, J.M., 1995. Cores and related solution concepts for multi-choice games. ZOR-Mathematical Methods of Operations Research 41, 289–311]. We show that this solution applied to the discrete cost sharing model coincides with the Aumann-Shapley method proposed by Moulin (1995) [Moulin, H., 1995. On additive methods to share joint costs. The Japanese Economic Review 46, 303–332]. Also, we show that the Aumann-Shapley value for continuum games can be obtained as the limit of multichoice values for admissible convergence sequences of multichoice games. Finally, we characterize this solution by using the axioms of balanced contributions and efficiency.     

Finding GM-estimators with global optimization techniques

In this note we address the problem of finding the GM-estimator for the location parameter of a univariate random variable. When this problem is non-convex but d.c. one can use a standard covering method, which, in the one-dimensional case has a simple form. In this paper we exploit the structure of the problem in order to obtain d.c. decompositions with certain optimality properties in the application of the algorithm. Numerical results show that this general-purpose algorithm outperforms previous ad-hoc methods for this problem.     

Replication invariance on NTU games

Two concepts of replication (conflictual and non-conflictual) are extended from the class of pure bargaining games to the class of NTU games. The behavior of the Harsanyi, Shapley NTU, Egalitarian and Maschler-Owen solutions of the replica games is compared with that of the Nash and Egalitarian solutions in pure bargaining games. Received June 1995/Final version February 2000     

Identification of pyrolysis products of polysulphides by collisionally activated decomposition linked scanning mass spectrometry

Collisionally activated decomposition (CAD) linked scan mass spectra have been used in the identification of pyrolysis products obtained by the direct pyrolysis of some polysulphides in a mass spectrometer. Structures were determined by comparing the CAD spectra of the pyrolysis products with those of authentic compounds. The results are of help in elucidating the thermal degradation mechanisms that occur in the pyrolysis of the polysulphides investigated.     

Theoretical study of the ethane ionization spectra within the correlation hole model

This work is an extension of a previous study on the assignment of the peaks of the photoionization spectrum of C₂H₆ [1]. The model of the correlation hole is reconsidered in order to carry out a new study of the states² A _1g ,² E _g ,² E _u and² A _2u of the C₂H ₆ ⁺ The qualitative relations which the average mass of the electrons in the Coulomb hole must have for the four states of the C₂H ₆ ⁺ , lead to a new criterion for the assignation of the peaks of the spectrum. The arrangement obtained for the two lower peaks is in agreement with those obtained previously [1].     

A millimeter-wave monolithic grid amplifier

A 36-element monolithic grid amplifier has been fabricated. The peak gain is 5 dB at 40.8 GHz with a 3-dB bandwidth of 1.4 GHz. The active elements are pairs of heterojunction-bipolar-transistor's (HBT's). The individual transistors in the grid have a maximum oscillation frequency,f _max , of 100 GHz. The grid includes base stabilizing capacitors which result in a highly stable grid. This is the first report of a successful monolithic grid amplifier.