Generation, Characterization, and Impact of Mesopores in Zeolite Catalysts

Amongst the current developments in the field of hierarchical pore structures, the creation of mesopores in zeolite crystals is the most frequently employed way to combine micropores with mesopores in one material. In this review an overview is presented of the different approaches to generate and characterize mesopores in zeolite crystals and establish their impact on the catalytic action. Mesopores can be created via several routes from which steaming and acid leaching are the most frequently applied. Novel approaches using secondary carbon templates that are removed after synthesis have recently been launched. For the characterization of mesopores, nitrogen physisorption and electron microscopy are commonly used. More recently, it was shown that electron tomography, a form of three-dimensional transmission electron microscopy, is able to reveal the three-dimensional shape, size, and connectivity of the mesopores. The effect of the presence of mesopores for catalysis is demonstrated for several industrially applied processes that make use of zeolite catalysts: the cracking of heavy oil fractions over zeolite Y, the production of cumene and hydroisomerization of alkanes over mordenite, and synthesis of fine chemicals over Y, ZSM-5, and Beta. For these processes, the mesopores ensure an optimal accessibility and transport of reactants and products, while the zeolite micropores induce the preferred shape-selective properties.     

Illusory conjunctions are an illusion: The effects of target–nontarget similarity on conjunction and feature errors.

The results of previous studies on visual perception suggest that conjunction errors partly derive from imperfect binding of correctly perceived features. However, the paradigms used in these studies do not generally allow one to discriminate between errors of feature binding and errors of target-nontarget confusion. In Experiments 1–4, an altered paradigm was used enabling discrimination between errors of feature binding and errors of target-nontarget confusion. The results showed that conjunction errors between color and identity do not derive from imperfect binding. In Experiments 5 and 6, a typical mainstream paradigm was used. The results indicated that, in such a paradigm, data patterns suggesting the existence of illusory conjunctions are likely to be due to errors of target-nontarget confusion instead of imperfect feature binding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conjugation to Albumin‐Binding Molecule Tags as a Strategy to Improve Both Efficacy and Pharmacokinetic Properties of the Complement Inhibitor Compstatin

The compstatin family of complement inhibitors has shown promise in various immuno‐inflammatory disorders. Although recent analogues show beneficial pharmacokinetics, further extension of the plasma half‐life is expected to benefit systemic application of these peptidic inhibitors. We therefore synthesized conjugates of compstatin analogues and albumin‐binding molecules (ABM) to increase circulatory residence. Equilibrium dialysis in complement‐depleted serum showed a marked increase in plasma protein binding from <8 % to >99 % for a resulting chimera (ABM2‐Cp20). Further analysis confirmed interaction with albumin from different species, primarily via site II. Importantly, ABM2‐Cp20 bound 20‐fold stronger to its target protein C3b (K_D=150 pM ) than the parent peptide. Kinetic and in silico analysis suggested that ABM2 occupies a secondary site on C3b and improves the dissociation rate via additional contacts. Addition of an ABM modifier thereby not only improved plasma protein binding but also produced the most potent compstatin analogue to date with potential implications for the treatment of systemic complement‐related diseases.     

Analysis of geodesic lenses by beam propagation method

It is shown that geodesic lenses can be analysed by means of the propagating beam method. This method allows one to take diffraction effects and anisotropy into account, while requiring only a moderate amount of computer time. To illustrate the method, a few geodesic lenses are analysed.     

Safety stock or safety lead time: coping with unreliability in demand and supply

Safety stock and safety lead time are common measures used to cope with uncertainties in demand and supply. Typically, these uncertainties are studied in isolated instances, ignoring settings with uncertainties both in demand and in supply. The current literature largely neglects case study based contexts and, often, single product situations are investigated in which machine set-ups are not considered. Based on the problems and findings in a case study, we investigate the effects of safety stock and safety lead time on delivery performance in a multi-product setting. The outcomes of the extensive simulation study indicate that utilising a safety lead time results in a higher delivery performance where there is a variable supply, whereas having a safety stock results in a higher delivery performance where there is unreliable demand information. In contrast to earlier findings in the single product situation, this study shows that managers facing the combination of unreliability in demand information and supply variability in a multiple product situation should opt for a safety lead time as the most effective way of improving their delivery performance.     

Intermediate product selection and blending in the food processing industry

This study addresses a capacitated intermediate product selection and blending problem typical for two-stage production systems in the food processing industry. The problem involves the selection of a set of intermediates and end-product recipes characterising how those selected intermediates are blended into end products to minimise the total operational costs under production and storage capacity limitations. A comprehensive mixed-integer linear model is developed for the problem. The model is applied on a data set collected from a real-life case. The trade-offs between capacity limitations and operational costs are analysed, and the effects of different types of cost parameters and capacity limitations on the selection of intermediates and end-product recipes are investigated.     

Investigation of the Substrate Specificity of Lacticin 481 Synthetase by Using Nonproteinogenic Amino Acids

One enzyme, many substrates . The substrate specificity of a lantibiotic biosynthetic enzyme, lacticin 481 synthetase, was probed by using synthetic prepeptides containing a variety of nonproteinogenic amino acids, including unnatural α‐amino acids, β‐amino acids, D ‐amino acids, and peptoids.

     

Illusory conjunctions die hard: A reply to Prinzmetal, Diedrichsen, and Irvy (2001).

M. Donk (see record 1999-11444-003) showed that various data patterns that have been considered as evidence for the existence of illusory conjunctions may be due to errors of target-nontarget confusion, an account that challenges the mere, existence of illusory conjunction. In a reply, W. Prinzmetal, J. Diedrichsen, and R. B. Ivry (see record 2001-06699-002) argued against this conclusion, claiming that some earlier findings can be explained only when one assumes that illusory conjunctions exist. The current article shows that Prinzmetal et al.'s claims cannot refute any of Donk's earlier conclusions, suggesting indeed that one can only conclude that "illusory conjunctions are an illusion." (PsycINFO Database Record (c) 2010 APA, all rights reserved)