Probing the Brønsted Acidity of the External Surface of Faujasite-Type Zeolites

We outline two methodologies to selectively characterize the Brønsted acidity of the external surface of FAU-type zeolites by IR and NMR spectroscopy of adsorbed basic probe molecules. The challenge and goal are to develop reliable and quantitative IR and NMR methodologies to investigate the accessibility of acidic sites in the large pore FAU-type zeolite Y and its mesoporous derivatives often referred to as ultra-stable Y (USY). The accessibility of their Brønsted acid sites to probe molecules (n-alkylamines, n-alkylpyridines, n-alkylphosphine- and phenylphosphine-oxides) of different molecular sizes is quantitatively monitored either by IR or ³¹P NMR spectroscopy. It is now possible, for the first time to quantitatively discriminate between the Brønsted acidity located in the microporosity and on the external surface of large pore zeolites. For instance, the number of external acid sites on a Y (LZY-64) zeolite represents 2 % of its total acid sites while that of a USY (CBV760) represents 4 % while the latter has a much lower framework Si/Al ratio.     

Yet another geometric programming dual algorithm

We describe an algorithm for the geometric programming dual problem which uses an adaptation of the generalized LP algorithm, proposed by Dantzig et al. twenty-five years ago for the chemical equilibrium problem, and show the slack primal constraints pose no numerical difficulties for this algorithm as they do for previous dual-based algorithms.     

Collisional activation by fourier-transform mass spectrometry : A study of target gas excitation

Studies on the charge-transfer reactions between translationally excited polyatomic ions and the neutral target gas used for collisional activation/collision-induced dissociation are described. These studies demonstrate an additional area where Fourier-transform mass spectrometry can be used to probe the fundamentals of ion/neutral interactions, viz., target gas excitation which competes with collision-induced dissociation.     

Solving Posynomial Geometric Programming Problems via Generalized Linear Programming

This paper revisits an efficient procedure for solving posynomial geometric programming (GP) problems, which was initially developed by Avriel et al. The procedure, which used the concept of condensation, was embedded within an algorithm for the more general (signomial) GP problem. It is shown here that a computationally equivalent dual-based algorithm may be independently derived based on some more recent work where the GP primal-dual pair was reformulated as a set of inexact linear programs. The constraint structure of the reformulation provides insight into why the algorithm is successful in avoiding all of the computational problems traditionally associated with dual-based algorithms. Test results indicate that the algorithm can be used to successfully solve large-scale geometric programming problems on a desktop computer.     

Studies of gold,platinum and palladium indicating electrodes in strongly oxidizing aqueous solutions

A comparison of the behavior of gold, platinum and palladium indicating electrodes in various strongly oxidizing solutions with the behavior observed when these electrodes are oxidized anodically reveals that the same reaction are occurring at the electrodes These reactions are attributed to oxide (or hydroxide) film formation because the potentials at which these various reactions occur agree reasonably well with the potential of known oxide-metal transitions The present study emphasizes the transient potential-time response of an indicating electrode when immersed in a strongly oxidizing solution It is concluded that all “inert” indicating electrodes undergo stepwise chemical oxidation in strongly oxidizing media.     

Vibrational Spectrum and Space Group of Cesium Dichromate

Cesium dichromate forms triclinic crystals which are apparently isomorphous with potassium dichromate.¹ The only published x-ray study of this compound consists of powder pattern results², and no determination of the space group has been presented. The only possible space groups for triclinic cesium dichromate are P1-C¹ ₁ and P1-C¹ ₁, which are distinguished by the presence and absence of inversion symmetry, respectively. Since inversion symmetry precludes coincidence between the infrared and Raman spectra, vibrational spectroscopy may be applied to the determination of the space group. This approach has been used recently to verify the space group of potassium dichromate.³ The present note presents the infrared and Raman spectra of crystalline cesium dichromate and our conclusions as to the space group.     

Auxiliary functions of the PsbO, PsbP and PsbQ proteins of higher plant Photosystem II: a critical analysis

Numerous studies over the last 25 years have established that the extrinsic PsbO, PsbP and PsbQ proteins of Photosystem II play critically important roles in maintaining optimal manganese, calcium and chloride concentrations at the active site of Photosystem II. Chemical or genetic removal of these components induces multiple and profound defects in Photosystem II function and oxygen-evolving complex stability. Recently, a number of studies have indicated possible additional roles for these proteins within the photosystem. These include putative enzymatic activities, regulation of reaction center protein turnover, modulation of thylakoid membrane architecture, the mediation of PS II assembly/stability, and effects on the reducing side of the photosystem. In this review we will critically examine the findings which support these auxiliary functions and suggest additional lines of investigations which could clarify the nature of the functional interactions of these proteins with the photosystem.     

Computational comparison on the partitioning strategies in multiple choice integer programming

In this paper we review the theoretical background of two partitioning strategies, the Weighted-Mean-Method (WMM) and the Reformulation-and-Transformation-Technique (RTT), incorporated in the special ordered set branch-and-bound procedures leading to the global optimum in Multiple Choice Integer Programming (MCIP). Procedure flow is developed with a numerical example presented to illustrate the effect of these two partitioning strategies in the algorithm. This procedure flow is then coded using IBM APL2. A total of 24 test problems are solved by this APL2 code for MCIP to analyze the performance of WMM and RTT in MCIP. The preliminary computational results indicate that, on the average, RTT produces smaller branching trees than does WMM. Its performance tends to be better for those MCIP problems having more multiple choice sets and a fewer average number of variables in each set. However, the average CPU time consumed by using RTT does not differ much from that consumed by using WMM.