bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass‐transfer coefficients in washcoated monoliths
Authors: Bhattacharya Madhuchhanda , Harold Michael P. , Balakotaiah Vemuri 
Published: October 2004

AbstractThe asymptotic mass‐transfer coefficients are determined in washcoated monoliths of various geometric shapes by solving the convection–diffusion equation in the fluid phase coupled with the diffusion–reaction equation in the washcoat. The dependency of the asymptotic Sherwood number (Sh∞) on washcoat properties (relative effective washcoat thickness λ, ratio of diffusivity of reactant in the fluid phase to that in the washcoat δ, and the catalyst loading ϕ) is examined. It is found that in the kinetic regime (ϕ → 0), Sh∞ approaches a new asymptote (Shw,∞) which depends on the flow as well as washcoat geometries. For δ → 0, Shw,∞ approaches Sh corresponding to flow geometry, whereas for δ → ∞ it approaches Sh of flow geometry. As can be expected, in the mass transfer controlled regime, Sh∞ approaches ShT,∞ (flow geometry), which is independent of washcoat properties. It is also found that the variation of Sh∞ with catalyst loading is not always monotonic when washcoat distribution around the channel perimeter is nonuniform. Numerical results, describing the variation of Sh∞ with washcoat properties, are presented for some commonly used channel geometries. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2939–2955, 2004
Simulation and optimal design of multiple‐bed pressure swing adsorption systems
Authors: Jiang Ling , Fox V. Grant , Biegler Lorenz T. 
Published: October 2004

AbstractPressure swing adsorption (PSA) is a very versatile technology for gas separation and purification. The widespread industrial application of PSA has called for an efficient set of simulation, design, and optimization methodologies. In previous work by Jiang and co‐workers, we used a Newton‐based approach to quickly converge the cyclic steady state and design constraints, and a simultaneous tailored approach with the state‐of‐art nonlinear optimization strategy to design optimal PSA processes. In this work we extend the simulation and optimization strategies to multiple bed systems. Both unibed and multibed frameworks are adopted to describe bed behaviors. The unibed framework models only one bed over a cycle and uses storage buffers to mimic the bed interactions. The multibed framework simultaneously solves all beds but only for a portion of the cycle. Challenges and implementation details of both frameworks are discussed. A five‐bed, 11‐step hydrocarbon separation process, which separates H2 from a mixture of H2, N2, CO2, CO, and CH4, is used for illustration. By manipulating valve constants, step times, flow rates, and bed geometry, the optimizer successfully maximizes H2 recovery, while meeting product purity and pressure specifications. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2904–2917, 2004
Time‐integrated pointers for enabling the analysis of detailed reaction mechanisms
Authors: Androulakis Ioannis P. , Grenda Jeffrey M. , Bozzelli Joseph W. 
Published: October 2004

AbstractA procedure for deriving time‐integrated pointers to capture element transformations during numerical integration runs, on complex chemical mechanisms, is introduced. The principal advantage is that the resulting temporally integrated pointers allow derivation of importance criteria; and these weight the contribution of all species and reactions during the reaction interval. This approach quantifies the sources and sinks of reactions active over a period of time in terms of element flux. It provides identification of key reaction pathways and the derivation of a reduced skeletal representation at minimum computational cost, in the elementary mechanism analysis. We extend the analysis to more complex systems, such as burner‐stabilized flames, that are governed by both reaction and diffusion. Here, we illustrate how some reaction pathways are altered in the presence of diffusion. Finally a new coupling of mechanism generation and mechanism reduction, which significantly reduces the computational burden associated with automated kinetic mechanism generation, is presented. The concepts are demonstrated with examples involving high‐ and low‐temperature oxidation of hydrocarbons. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2956–2970, 2004
Monoliths as multiphase reactors: A review
Authors: Roy Shaibal , Bauer Tobias , Al‐Dahhan Muthanna , Lehner Peter , Turek Thomas 
Published: October 2004

AbstractMonolith reactors are being studied as a replacement for conventional multiphase reactors such as trickle‐bed reactors, slurry reactors, and slurry bubble column reactors for gas–liquid–solid reactions. Reactors with monolith catalyst packing have been found to be hydrodynamically superior to existing industrial reactors. This review covers multiphase reactions carried out in monolith reactors by various researchers. It first defines the monolith reactor and looks into the geometrical aspects of monolith. The section dealing with hydrodynamics reviews pressure drop, phase holdup, flow distribution, and dispersion characteristics. This study also considers the tools used to characterize the hydrodynamic parameters and their typical values. Although the available literature is scarce, monoliths are considered to have superior mass transfer characteristics. This review lists the mass transfer correlations for each category (gas–liquid, gas–solid, liquid–solid). The last section discusses the reaction aspects of monolith reactors. The ultimate goal is to implement such reactors for multiphase reactions. This section also compares the performance of monolith reactors with conventional multiphase reactors and lists the various reactor models reported to predict the overall performance of monolith reactors. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2918–2938, 2004
Phenotypic manifestations of the OCTN2 V295X mutation: Sudden infant death and carnitine‐responsive cardiomyopathy in Roma families
Authors: Melegh Béla , Bene Judit , Mogyorósy Gábor , Havasi Viktória , Komlósi Katalin , Pajor László , Oláh Éva , Kispál Gyula , Sumegi Balázs , Méhes Károly 
Published: October 2004

AbstractIn two non‐consanguineous Hungarian Roma (Gypsy) children who presented with cardiomyopathy and decreased plasma carnitine levels, we identified homozygous deletion of 17081C of the SLC22A5 gene that results in a frameshift at R282D and leads ultimately to a premature stop codon (V295X) in the OCTN2 carnitine transporter. Carnitine treatment resulted in dramatic improvement of the cardiac symptoms, echocardiographic, and EKG findings in both cases. Family investigations revealed four sudden deaths, two of them corresponded to the classic SIDS phenotype. In postmortem tissue specimens available from three of them we could verify the homozygous mutation. In liver tissue reserved from two patients lipid droplet vacuolization could be observed; the lipid vacuoles were located mainly in the peripherolobular regions of the acini. In the heart tissue signs of generalized hypertrophy and lipid vacuoles were seen predominantly in the subendocardial areas in both cases; some aggregates of smaller lipid vacuoles were separated, apparently by membranes. Review of all OCTN2 deficiency cases reported so far revealed that this is the first presentation of histopathology in classic familial sudden infant death syndrome (SIDS) with an established SLC22A5 mutation. In addition to the two affected homozygous cardiomyopathic children and three homozygous sudden death patients, the genetic analysis in 25 relatives showed 14 carriers. The mutant gene derived from five non‐consanguineous grandparents, each of them having 6–14 brothers and sisters. This alone suggests a wide ancestral spread of the mutation in certain Roma subpopulations. © 2004 Wiley‐Liss, Inc.
Anforderungen an Umkehrdächer mit Trennlage: Erläuterungen zur Anwendung von EN ISO 6946
Authors: Leimer Hans‐Peter , Bednar Thomas , Dreyer Jürgen , Künzel Hartwig M. , Palier Pierre , Rode Carsten , Tejchmann‐Konarzewski Jacek 
Published: October 2004

AbstractDieser Beitrag soll für unterschiedliche Regionen in Europa die Anwendung der Norm EN ISO 6946 im Hinblick auf Wärmeverluste beim Umkehrdach erläutern. In der Fassung dieser Norm von Oktober 2003 wird bei der Bestimmung des Wärmedurchgangskoeffizienten bei Umkehrdächern ein zusätzlicher, niederschlagsbedingter Wärmeverlust berücksichtigt. Die zusätzlichen Wärmeverluste eines Daches, die bedingt durch den Abfluß von erwärmten Niederschlägen unterhalb der Wärmedämmung entstehen, können somit rechnerisch erfaßt werden. Die Größe der Wärmeverluste ist abhängig von der Niederschlagsmenge und dem Anteil der Wassermenge, die direkt zwischen Dachabdichtung und Wärmedämmung abläuft. Diese Veröffentlichung soll die Anwendung der Norm für unterschiedliche Regionen in Europa erläutern. Hierzu werden ergänzend Klimadaten und Randbedingungen verschiedener Regionen dargestellt. Zudem werden bei Umkehrdächern mit Trennlage die Anforderungen an die Trennlage beschrieben. Hierbei werden die niederschlagsbedingten Wärmeverluste in der Folge soweit verringert, daß diese rechnerisch unberücksichtigt bleiben können.
Vorgehensweise zur gesundheitlichen Bewertung von VOC‐ und SVOC‐Emissionen aus Bauprodukten: Bewertungskonzept des Ausschusses zur gesundheitlichen Bewertung von Bauprodukten (AgBB)
Authors: Witten Jutta 
Published: October 2004

AbstractInnenraumrelevante Bauprodukte können als bedeutsame Emissionsquellen von flüchtigen organischen Stoffen auftreten und dabei in erheblichen Maß die Qualität der Raumluft beeinflussen. Öffentlich rechtliche Anforderungen an Bauprodukte zum Gesundheitsschutz der Raumnutzer sind in der europäischen Bauproduktenrichtlinie (89/106/EWG) und durch Umsetzung in nationales Recht im Bauproduktengesetz bzw. den Landesbauordnungen verankert. Mit der europäischen Bauprodukten‐Richtlinie werden die notwendige Anforderungen an die Bereiche “Gesundheit, Hygiene und Umwelt” definiert, die im Grundlagendokument 3 der europäischen Kommission ausgeführt sind. Hierzu gehören besonders die Anforderungen Schadstoffemissionen aus Bauprodukten sowie Vermeidung und Begrenzung von flüchtigen organischen Verbindungen (VOC) in Innenräumen. Da für die Umsetzung dieser gesundheitsbezogenen Anforderungen eine offiziell anerkannte Vorgehensweise bisher nicht vorliegt, hat der Bund‐/Länderausschuss zur gesundheitlichen Bewertung von Bauprodukten (AgBB) Prüfkriterien zur gesundheitlichen Beurteilung von flüchtigen organischen Verbindungen (VOC‐ und SVOC‐Emissionen) aus Bauprodukten konkretisiert und veröffentlicht. Diese am Baurecht angelehnte Verfahrensweise stellt mit dem Ziel der Beschränkung von Emissionen von flüchtigen organischen Verbindungen aus Bauprodukten standardisierte Prüfnachweise sowie gesundheitlich relevante Bewertungsgrundlagen zur Verfügung. Vor dem Hintergrund bauaufsichtlicher Erfordernisse ermöglicht diese objektivierbare und besonders transparente Vorgehensweise zukünftig Verbrauchern, Architekten, Planern und auch Bauproduktherstellern innenraumrelevante Bauprodukte bereits im Vorfeld nach ihrer Schadstoff‐ und Emissionsrelevanz zu erkennen und zielgerecht einzusetzen.
Modellierung des Single Burning Item Tests
Authors: Hofmann Anja 
Published: October 2004

AbstractIm Rahmen der Vereinheitlichung der Normen in Europa wurde der Single Burning Item (SBI) Test als neuer europäischer Brandtest für Bauprodukte für das mittlere Beanspruchungsniveau entwickelt. In diesem Test wird ein Entstehungsbrand in einer Zimmerecke nachgestellt, der durch einen einzelnen brennenden Gegenstand, z.B. durch einen brennenden Papierkorb, ausgelöst wird. Der SBI‐Test wurde von der Bundesanstalt für Materialforschung und ‐prüfung (BAM) und der TU Berlin mit numerischen Modellen untersucht und diese anhand von Experimenten validiert. Es zeigt sich ein signifikanter Einfluß der Belüftung des Brandraums und der Umgebungstemperatur auf die Temperatur‐ und Strömungsverhältnisse im Brandraum. In DIN EN 13823 sind jedoch für beide Parameter nicht feste Werte, sondern Bereiche angegeben. Neue Experimente, in der die einzelnen Parameter Belüftung, Umgebungstemperatur und möglicherweise auch Luftfeuchte der Umgebungsluft gezielt variiert werden, wären zur weiteren Klärung notwendig. Die vorhandenen Daten und die numerischen Ergebnisse geben Anlaß zu der Frage, ob die Bereiche, in denen die Belüftung und die Umgebungstemperatur variiert werden dürfen, in der Norm zu weit gefaßt sind.
High‐Temperature Synthesis of Stable Ordered Mesoporous Silica Materials by Using Fluorocarbon–Hydrocarbon Surfactant Mixtures
Authors: Li Defeng , Han Yu , Song Jiangwei , Zhao Lan , Xu Xianzhu , Di Yan , Xiao Feng‐Shou 
Published: October 2004

AbstractHighly ordered hexagonal mesoporous silica materials (JLU‐20) with uniform pore sizes have been successfully synthesized at high temperature (150–220 °C) by using fluorocarbon–hydrocarbon surfactant mixtures. The fluorocarbon–hydrocarbon surfactant mixtures combine the advantages of both stable fluorocarbon surfactants and ordered hydrocarbon surfactants, giving ordered and stable mixed micelles at high temperature (150–220 °C). Mesoporous JLU‐20 shows extraordinary stability towards hydrothermal treatment (100 % steam at 800 °C for 2 h or boiling water for 80 h), thermal treatment (calcination at 1000 °C for 4 h), and toward mechanical treatment (compressed at 740 MPa). Transmission electron microscopy images of JLU‐20 show well‐ordered hexagonal arrays of mesopores with one‐dimensional (1D) channels and further confirm that JLU‐20 has a two‐dimensional (2D) hexagonal (P6 mm) mesostructure. 29Si HR MAS NMR spectra of as‐synthesized JLU‐20 shows that JLU‐20 is primarily made up of fully condensed Q4 silica units (δ=−112 ppm) with a small contribution from incompletely cross‐linked Q3 (δ=−102 ppm) as deduced from the very high Q4/Q3 ratio of 6.5, indicating that the mesoporous walls of JLU‐20 are fully condensed. Such unique structural features should be directly attributed to the high‐temperature synthesis, which is responsible for the observed high thermal, hydrothermal, and mechanical stability of the mesoporous silica materials with well‐ordered hexagonal symmetry. Furthermore, the concept of “high‐temperature synthesis” is successfully extended to the preparation of three‐dimensional (3D) cubic mesoporous silica materials by the assistance of a fluorocarbon surfactant as a co‐template. The obtained material, designated JLU‐21, has a well‐ordered cubic Im3m mesostructure with fully condensed pore walls and shows unusually high hydrothermal stability, as compared with conventional cubic mesoporous silica materials such as SBA‐16.
Structure and Dynamics of Homoleptic Beryllocenes: A Solid‐State 9Be and 13C NMR Study
Authors: Hung Ivan , Macdonald Charles L. B. , Schurko Robert W. 
Published: October 2004

AbstractThe correlation between anisotropic 9Be NMR (quadrupolar and chemical shielding) interactions and the structure and dynamics in [Cp2Be], [${{\rm Cp}{{\ast \hfill \atop 2\hfill}}}$Be], and [(C5Me4H)2Be] is examined by solid‐state 9Be NMR spectroscopy, as well as by ab initio and hybrid density functional theory calculations. The 9Be quadrupole coupling constants in the three compounds correspond well to the relative degrees of spherical ground‐state electronic symmetry of the environment about beryllium. Theoretical computations of NMR interaction tensors are in excellent agreement with experimental values and aid in understanding the origins of NMR interaction tensors and their correlation to molecular symmetry. Variable‐temperature (VT) 9Be and 13C NMR experiments reveal a highly fluxional structure in the condensed phase of [Cp2Be]. In particular, the pathway by which the Cp rings of [Cp2Be] ‘invert’ coordination modes is examined in detail using hybrid density functional theory in order to inspect variations of the 9Be NMR interaction tensors. The activation energy for the ‘inversion’ process is found to be 36.9 kJ mol−1 from chemical exchange analysis of 13C VT CP/MAS NMR spectra. The low‐temperature (ca. −100 °C) X‐ray crystal structures of all three compounds have been collected and refined, and are in agreement with previously reported structures. In addition, the structure of the same Cp2Be crystal was determined at 20 °C and displays features consistent with increased intramolecular motion, supporting observations by 9Be VT NMR spectroscopy.
New Types of Soluble Polymer‐Supported Bisphosphine Ligands with a Cyclobutane Backbone for Pd‐Catalyzed Enantioselective Allylic Substitution Reactions
Authors: Zhao Dongbo , Sun Jie , Ding Kuiling 
Published: October 2004

AbstractA highly efficient and practical optical resolution of anti head‐to‐head racemic coumarin dimer 7 has been achieved by molecular complexation with TADDOL, (−)‐8, through a hydrogen bonding interaction to afford the corresponding two enantiomers, (−)‐ and (+)‐7, in 70 and 75 % yields, respectively, with >99 % ee. Starting from enantiopure (−)‐7, a new type of C2‐symmetric bisphosphine ligand (S,S,S,S)‐3 with a cyclobutane backbone has been synthesized in good yield by facile transformations. The asymmetric induction efficiency of these chiral bisphosphine ligands in Pd‐catalyzed asymmetric allylic substitution reactions was evaluated. Under the experimental conditions, the allylic substitution products could be obtained in excellent yields (up to 99 %) and enantioselectivities (up to 98.9 % ee). By taking advantage of the high enantioselectivity of this catalytic reaction and the easily derivable carboxylate groups on the cyclobutane backbone of ligand (S,S,S,S)‐3, a new type of analogous ligand (S,S,S,S)‐4 as well as the MeO‐PEG‐supported soluble ligand (S,S,S,S)‐5 (PEG=polyethylene glycol) have also been synthesized and utilized in asymmetric allylic substitution reactions. In particular, the MeO‐PEG supported (S,S,S,S)‐5 b had a synergistic effect on the enantioselectivity of the reaction compared with its nonsupported precursor (S,S,S,S)‐4 c, affording the corresponding allylation products 14 a and 14 b with excellent enantioselectivities (94.6 and 97.2 % ee, respectively). Moreover, the Pd complex of (S,S,S,S)‐5 b could easily be recovered and recycled several times without significant loss of enantioselectivity and activity in the allylic substitution reactions.
By What Mechanisms Are Metal Cyclobutadiene Complexes Formed from Alkynes?
Authors: Veiros Luís F. , Dazinger Georg , Kirchner Karl , Calhorda Maria José , Schmid Roland 
Published: October 2004

AbstractThe mechanism of formation of an η4‐cyclobutadiene complex from a metallacycle, generated by oxidative coupling of two acetylenes with the fragments CpRuCl, [CpRu(PH3)]+, CpCo, and CpRh, was investigated by means of DFT/B3LYP calculations. Two distinct pathways can be envisaged. 1) A multistep reaction, which can be denoted the Vollhardt mechanism, proceeding via a cyclopropenyl carbene and a tetrahedrane‐type intermediate. 2) A one‐step transformation involving the formation of a third MC bond with rearrangement of the metallacyclic ring. Although path 2 is definitely favored over path 1, both pathways are energetically prohibitive unless substituents are present on the acetylene. For the CpRuCl system with HCCR the barrier varies with R in the series H≈Ph>Me≫SiMe3. On going from H to SiMe3, the barrier for path 2 drops from 41.1 to 26.8 kcal mol−1. This latter value is already reachable, in agreement with experiment. Whereas the reaction mechanisms involving the fragments CpCo, CpRh, and CpRuCl are very similar (but not identical owing to the additional ligand in CpRuCl), those of [CpRu(PH3)]+ reveal a modification with serious consequences. In both paths 1 and 2, the originally planar metallacycle experiences first a bending distortion induced by the σ‐donor strength of P (in contrast to Cl), which compensates the loss of electrons from the ring brought about by bending. The bent metallacycle is already electronically asymmetric and thus the further course of the reaction is facilitated.
Hydrogen‐Bonded Polyrotaxane‐like Structure Containing Cyclic (H2O)4 in [Zn(OAc)2(μ‐bpe)]⋅2 H2O: X‐ray and Neutron Diffraction Studies
Authors: Ng Meng Tack , Deivaraj Theivanayagam C. , Klooster Wim T. , McIntyre Garry J. , Vittal Jagadese J. 
Published: October 2004

AbstractThe reaction of 4,4′‐bipyridylethane (bpe) and 4,4′‐dipyridyl disulfide (dpds) with Zn(OAc)2⋅2 H2O has led to the formation of two coordination polymers, [Zn(OAc)2(μ‐bpe)]⋅2 H2O (1) and [Zn(OAc)2(μ‐dpds)] (2). Both the compounds have zigzag coordination polymeric structures as revealed by X‐ray crystallography. However, the presence of two lattice water molecules in 1 results in an interesting difference between the crystal structures. In 1, the carboxylate carbonyl oxygen atoms of the Zn(OAc)2 groups from two different adjacent zigzag polymers and four lattice water molecules form 24‐membered hydrogen‐bonded rings (graph set notation, R66(24)). One of the two bpe ligands associated with each ZnII center passes through the center of this ring to form a two‐dimensional hydrogen‐bonded coordination polymeric structure. In the solid state, the adjacent 24‐membered hydrogen‐bonded rings further fuse together through OH⋅⋅⋅O hydrogen bonds among four waters to form cyclic (H2O)4. This results in a one‐dimensional hydrogen‐bonded ribbon‐like polymer comprising fused alternating 24‐ and eight‐membered OH⋅⋅⋅O hydrogen‐bonded rings. One of the bpe ligands passes through the center of the larger ring to produce an unexpected single self‐penetrating three‐dimensional hydrogen‐bonded network with polyrotaxane‐like association. A neutron diffraction study provides a detailed description of the hydrogen bonds involved.
Illuminating Zinc in Biological Systems
Authors: Lim Nathaniel C. , Freake Hedley C. , Brückner Christian 
Published: October 2004

AbstractZinc is the second most abundant transition metal in the human body, fulfilling a multitude of biological roles, but the mechanisms underlying its physiology are poorly understood. The lack of knowledge is, in part, due to the hitherto limited techniques available to track zinc in biological systems. The recent emergence of a number of zinc‐specific molecular sensors has provided a new tool to image zinc in live cells and tissue samples. This contribution highlights the concepts behind using zinc‐specific fluorescent molecular sensors to gain information about zinc action in biological samples, and provides representative examples of images recorded.
A New Class of Non‐Racemic Chiral Macrocycles: A Conformational and Synthetic Study
Authors: Gibson Susan E. , Mainolfi Nello , Kalindjian S. Barret , Wright Paul T. , White Andrew J. P. 
Published: October 2004

AbstractAmino alcohols have been used to introduce non‐racemic chirality into macrocycles using a modular approach that relies on a Heck macrocyclisation reaction. A wide variety of macrocycles have been synthesised, and their structures studied using X‐ray crystallography and molecular modelling. A fragmentation reaction encountered during the use of (S)‐1,1‐dimethylvalinol revealed that carboxylic acids generate acylals under reaction conditions often used for Heck reactions.