bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation, Preservation, and Cleavage of the Disulfide Bond by Vanadium
Authors: Wang Dongren , Behrens Axel , Farahbakhsh Mahin , Gätjens Jessica , Rehder Dieter
Published: April 2003

Reaction of the disulfide {HpicanS}2 (HpicanS is the carboxamide based on picolinate (pic) and o‐mercaptoaniline (anS); the {} brackets are used to denote disulfides) with [VOCl2(thf)2] leads to reductive scission of the disulfide bond and formation of the mixed‐valence (VIV/VV) complex anion [(OVpicanS)2μ‐O]− (1), with the dianionic ligand coordinating through the pyridine‐N atom, the deprotonated amide‐N atom, and thiophenolate‐S atom. Reductive cleavage of the SS bond is also observed as [VCl2(tmeda)2] (tmeda=tetramethylethylenediamine) is treated with the disulfides {HsalanS}2 or {HvananS}2 (HsalanS and HvananS are the Schiff bases formed between o‐mercaptoaniline and salicylaldehyde (Hsal) or vanillin (Hvan), respectively), yielding the VIII complexes [VCl(tmeda)(salanS)] (2 a), or [VCl(tmeda)(vananS)] (2 b). The disulfide bond remains intact in the aerial reaction between {HsalanS}2 and [VCl3(thf)3] to yield the VV complex [VOCl{salanS}2] (3), where (salanS)2− coordinates through the two phenolate and one of the imine functions. The SS bond is also preserved as [VO(van)2] or [VO(nap)2] (Hnap=2‐hydroxynaphthalene‐1‐carbaldehyde) is treated with bis(2‐aminophenyl)disulfide, {anS}2, a reaction which is accompanied by condensation of the aldehyde and the diamine, and complexation of the resulting bis(Schiff bases) {HvananS}2 or {HnapanS}2 to form the complexes [VO{vananS}2] (4 a) or [VO{napanS}2] (4 b). In 4 a and 4 b, the phenolate and imine functions, and presumably also one of the disulfide‐S atoms, coordinate to VIV. 2Mercaptophenyl‐2′‐pyridinecarboxamide (H2picanS) retains its identity in the presence of VIII; reaction between [VCl3(thf)3] and H2picanS yields [V{picanS}2]− (5). The dithiophenolate 2,6‐bis(mercaptophenylthio)dimethylpyridine (6 a) is oxidized, mediated by VO2+, to the bis(disulfide) octathiadiaza‐cyclo‐hexaeicosane 6 b. The relevance of these reactions for the speciation of vanadium under physiological conditions is addressed. [HNEt3]‐1⋅0.5 NEt3, 3⋅3 CH2Cl2, {HsalanS}2, [HNEt3]‐5, and 6 b⋅4 THF have been characterized by Xray diffraction analysis.
Transannular Reactions of Two Parallel 1,3‐Butadiynes: Syntheses, Structures, and Reactions of 1Azacyclotetradeca‐3,5,10,12‐tetrayne Derivatives
Authors: Schmidt Erik M. , Gleiter Rolf , Rominger Frank
Published: April 2003

The synthesis of 1alkyl and 1aryl‐1‐azacyclotetradeca‐3,5,10,12‐tetraynes was achieved in a stepwise approach. The key intermediate was 1,13‐dibromotrideca‐2,4,9,11‐tetrayne (18). Reaction with methyl‐ (19 a), ethyl‐ (19 b), isopropyl‐ (19 c), n‐butyl‐ (19 d), and tert‐butylamine (19 e) as well as aniline (19 f) and p‐methoxyaniline (19 g) gave the corresponding 14‐membered tetraynes 20 a–20 g. The ring inversion process of 20 b was studied by variable temperature 1H NMR spectroscopy. From these measurements a value of 10.6 kcal mol−1 was calculated for ΔG≠. Xray investigations on single crystals of 20 b, 20 c, and 20 f revealed the axial position for the substituent at each nitrogen atom. For 20 b we encountered the chair conformation, for 20 c both chair and boat conformations, and for 20 f the boat conformation in the solid state. The reaction of 20 c with concentrated HCl in ethanol yielded 2,10‐dichloro‐6‐isopropyl‐6‐azatricyclo[9.3.0.04,8]tetradeca‐1(11),2,4(8),9‐tetraene (25 c). Compound 25 c was oxidized by 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) to 27 c. The structure of the latter was confirmed by Xray investigations. The reaction of 20 c in aqueous HCl lead to the formation of 10‐chloro‐2‐isopropyl‐1,3,4,6,7,8‐hexahydro‐2H‐benzo[g]isoquinolin‐9‐one (37 c). The structure of 37 c was verified by Xray studies on single crystals.
A Versatile Approach Towards Regioselective Platinated DNA Sequences
Authors: Heetebrij Robert J. , de Kort Martin , Meeuwenoord Nico J. , den Dulk Hans , van der Marel Gijs A. , van Boom Jacques H. , Reedijk Jan
Published: April 2003

Undesired N7 platination of 2′‐deoxyguanosine residues at predetermined sites in an oligodeoxynucleotide (ODN) sequence is prevented by applying the sterically demanding diphenylcarbamoyl (DPC) as an O6‐protecting group. The presence of a base‐labile oxalyl linker between the immobilized 3′‐nucleotide and controlled pore glass (CPG) allows cleavage of the protected ODN from the support and leaves DPC protection unaffected. This method provides an ODN with specifically blocked guanine‐N7 sites for platination. In the hexanucleotides prepared in this study, 5′‐GGBGGT‐3′(for B=T, C and A), a platinum GG adduct is introduced at G4,G5. These site‐specific platinated hexamers were isolated in a yield of 65 %, and were fully characterized by using reversed‐phase HPLC (high performance liquid chromotography), LCMS (liquid chromatography‐mass spectrometry), MALDI‐TOF MS (matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry), PAGE (polyacrylamide gel electrophoresis) and Maxam–Gilbert sequencing analysis.
Progress in the Palladium‐Catalyzed Cyanation of Aryl Chlorides
Authors: Sundermeier Mark , Zapf Alexander , Mutyala Sateesh , Baumann Wolfgang , Sans Jürgen , Weiss Stefan , Beller Matthias
Published: April 2003

The development of new palladium catalysts for the cyanation of various aryl and heteroaryl chlorides is described. The combination of amine co‐catalysts with chelating phosphine ligands, for example, 1,4‐bis(diphenylphosphino)butane (dppb) or 1,5‐bis(diphenylphosphino)pentane (dpppe), allows an efficient cyanation of chloroarenes with simple potassium cyanide. General palladium‐catalyzed cyanation of nonactivated and deactivated chloroarenes is possible for the first time. Studies of the oxidative addition of aryl halides to palladium triphenylphosphine complexes in the presence and absence of amines suggest that the co‐catalyst is capable of preventing catalyst deactivation caused by the presence of excess cyanide ions in solution.
Criteria for the Elucidation of the Pseudopericyclic Character of the Cyclization of (Z)‐1,2,4,6‐Heptatetraene and Its Heterosubstituted Analogues: Magnetic Properties and Natural Bond Orbital Analysis
Authors: Rodríguez‐Otero Jesús , Cabaleiro‐Lago Enrique M.
Published: April 2003

The electrocyclization of heterosubstituted derivatives of (Z)‐1,2,4,6‐heptatetraene, (2Z)‐2,4,5‐hexatrien‐1‐imine and (2Z)‐2,4,5‐hexatrienal exhibit some features which suggest a pseudopericyclic mechanism. In order to examine this, a comprehensive study including the determination of magnetic properties to estimate aromaticity and an NBO analysis throughout the reaction path was conducted. The cyclization of 5oxo‐2,4‐pentadienal, a process of unequivocal pseudopericyclic nature, was studied for comparison. The results suggest that, although the lone electron pair on the heteroatom in the heptatetraene derivatives seemingly plays a crucial role in the reaction mechanism, it does not suffice to deprive the reaction from the essential features of a pericyclic disrotatory electrocyclization.
Stereodynamics and Characterization of the Hexa(4‐n‐dodecylbiphenylyl)benzene Hexaanion that Includes a Twisted Benzene Core
Authors: Eshdat Lior , Hoffman Roy E. , Fechtenkötter Andreas , Müllen Klaus , Rabinovitz Mordecai
Published: April 2003

Hexa(4‐n‐dodecylbiphenylyl)benzene (HDBB) was reduced by a series of alkali metals in THF under high vacuum. Three reduction states were identified by NMR spectroscopy, namely the dianion, tetraanion and hexaanion. The NMR spectra of HDBB6− revealed a remarkable distortion of symmetry, which is interpreted by adoption of a twisted conformation of the central benzene ring and a slow rotation of the inner phenylene rings of the biphenyl units. Due to the surprising thermal stability of the hexaanion, a dynamic NMR investigation revealed the pseudorotation of the twisted conformation and the phenylene rotation mentioned above.
[ReO3(bipy)]+[X]−‐Catalyzed Aldehyde Olefination: Carbene and Phosphorane Intermediates
Authors: Zhang Xiangyang , Chen Peter
Published: April 2003

The aldehyde olefination reaction, catalyzed by cationic high‐valent oxorhenium complexes, shows evidence of the intermediacy of both carbene complexes and phosphoranes. The solution‐phase reaction is facile and amenable to tuning and is, hence, likely to prove to be of practical significance. Individual steps in the catalytic cycle are observed in the gas phase. Catalytic competence of each of the putative intermediates can be demonstrated.
The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity
Authors: Floquet Sébastien , Ouali Nadjet , Bocquet Bernard , Bernardinelli Gérald , Imbert Daniel , Bünzli Jean‐Claude G. , Hopfgartner Gérard , Piguet Claude
Published: April 2003

The segmental tris‐tridentate ligand L7 reacts with stoichiometric quantities of LnIII (Ln=La–Lu) in acetonitrile to give the complexes [Ln2(L7)3]6+ and [Ln3(L7)3]9+. Formation constants point to negligible size‐discriminating effects along the lanthanide series, but Scatchard plots suggest that the self‐assembly of the trimetallic triple‐stranded helicates [Ln3(L7)3]9+ is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively [Ln3(L7)3](CF3SO3)9 (Ln=La, Eu, Gd, Tb, Lu) and the Xray crystal structure of [Eu3(L7)3](CF3SO3)9⋅(CH3CN)9⋅(H2O)2 (Eu3C216H226N48O35F27S9, triclinic, P$\bar 1$, Z=2) shows the three ligand strands wrapped around a pseudo‐threefold axis defined by the three metal ions rigidly held at about 9 Å. Each metal ion is coordinated by nine donor atoms in a pseudo‐trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo‐trigonal symmetries in the solid state and in solution. High‐resolution luminescence analyses evidence a low‐lying LMCT state affecting the central EuN9 site, so that multi‐metal‐centered luminescence is essentially dominated by the emission from the two terminal EuN6O3 sites in [Eu3(L7)3]9+. New multicenter equations have been developed for investigating the solution structure of [Ln3(L7)3]9+ by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce–Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second‐rank crystal‐field parameters, obtained by LIS analysis, for the LnN6O3 and LnN9 sites with respect to the parameters extracted for EuIII from luminescence data, suggests that the geometry of the central LnN9 site is somewhat relaxed in solution.
Stabilizing Bolaform Amphiphile Interfacial Assemblies by Introducing Mesogenic Groups
Authors: Wang Mingfeng , Qiu Dengli , Zou Bo , Wu Tao , Zhang Xi
Published: April 2003

We describe the synthesis and characterization of the mesogen‐bearing bolaform amphiphile 4,4′‐dihydroxybiphenylbis(11‐pyridinium‐N‐yl‐undecanoic ester) dibromide (BP‐10) and its solid/liquid interfacial self‐assembly. Cylindrical micelles are directly observed by atomic force microscopy (AFM) at the interface between mica and the aqueous solution above the critical micelle concentration (cmc). In situ and ex situ AFM studies indicate that the cylindrical micelles are stable both at the mica/solution interface and in the dry state. The enhanced stability of the micellar structures enables a detailed investigation of their self‐assembly behavior and supramolecular structures at the interface. The adsorption model proposed here is supported by the variation of the interfacial self‐assemblies on changing the solution concentration and substrate temperature.
Insektizide für die Landwirtschaft: Chemische Schädlingsbekämpfung
Authors: Beckmann Marion , Haack Karl‐Josef
Published: April 2003

Ein Überblick über chemische Schädlingsbekämpfung in der Landwirtschaft wird geboten, indem Grundlagen zu Schädlingsarten, heute verwendete Wirkstoffe und Substanzklassen, deren biochemische Wirkmechanismen und Wirkprofile dargestellt werden.
Herbizide für die Landwirtschaft: Chemische Unkrautbekämpfung
Authors: Seitz Thomas , Hoffmann Michael G. , Krähmer Hansjörg
Published: April 2003

Dieser Artikel beschreibt die momentan wichtigsten marktrelevanten Herbizide sowie deren molekulare Wirkmechanismen und pflanzenphysiologische Effekte. Darüber hinaus wird auch auf neue herbizide Wirkmechanismen und die Bedeutung von Safenern eingegangen.
Synthese‐Entwicklung unter speziellen Randbedingungen: Patentsituation und Kostenoptimierung
Authors: Haack Karl‐Josef
Published: April 2003

Dieser Artikel beschreibt Herstellwege für ausgewählte Wirkstoffe im chemischen Pflanzenschutz. Es werden Methoden und zentrale Zwischenstufen bei den Synthesen von Glyphosate, Glyphosine, Glufosinate, Thiamethoxam, Clothianidin, Fipronil, Kresoxim‐methyl, Trifloxystrobin, Abamectin, Emamectin, (S‐)Metolachlor, Indoxacarb und Deltamethrin vorgestellt.
Moderne Fungizide: Pilzbekämpfung in der Landwirtschaft
Authors: Henningsen Michael
Published: April 2003

In den letzten Jahren wurde eine große Anzahl von neuen Fungiziden in die Landwirtschaft eingeführt. Auf Grund ihres breiten Wirkspektrums haben sich die Strobilurine zu einer der wichtigsten fungiziden Substanzklassen entwickelt. Diese Übersicht stellt die Neuentwicklungen seit 1995 vor, beschreibt die Wirkmechnismen und die wesentlichen Zielkulturen.
Lebensmittelinhaltsstoffe und ‐kontaminanten: Aus toxikologischer Sicht
Authors: Schrenk Dieter
Published: April 2003

Unsere Lebensmittel enthalten Stoffen natürlichen Ursprungs, die bei zu häufigem oder übermäßigem Verzehr zu Gesundheitsstörungen führen können. Hierzu zählen beispielsweise die Glucosinolate in Kohlarten oder Trypsin‐Inhibitoren in (ungegarten) Leguminosen. Ferner können bestimmte Inhaltsstoffe wie das Vicin der Ackerbohne oder die Glycyrrhetinsäure in Lakritz für bestimmte Gruppen von Verbrauchern (z.B. mit Erkrankungen wie Bluthochdruck oder bei bestimmten genetischen Defekten) Gefahren bergen. Gesetzlich zugelassene Lebensmittelzusatzstoffe wie Konservierungsstoffe, Emulgatoren oder Farbstoffe sind in der Regel sehr gründlich toxikologisch geprüft und bewertet worden und können daher als sehr sicher gelten. Im Gegensatz dazu stammen Rückstände und Kontaminanten häufig aus unsachgemäßer oder gesetzwidriger Herstellung oder Behandlung von Lebensmitteln oder Rohstoffen. Bei niedrigeren Gehalten können sie Hintergrundkontaminationen z.B. aus der Umwelt widerspiegeln. Schließlich müssen auch Nahrungsergänzungsmittel und ‚funktionelle Lebensmittel’︁ auf toxikologische Eigenschaften überprüft werden, da nicht alle Stoffe, die in einem bestimmten Dosisbereich als ‚gesund’︁ gelten, auch in höherer Dosierung günstig wirken bzw. sicher sind.
(K)ein süßes Leben
Authors: Hübner Karl
Published: April 2003

Er war einer der regesten Wissenschaftler im Berlin seiner Zeit. Mit seiner Begründung der industriellen Gewinnung von Zucker aus Rüben schuf er zudem ein gewaltiges praxisrelevantes Erbe. Und doch ist der sein Leben lang von Geldsorgen geplagte heute weitgehend vergessen. Nicht einmal das Römpp‐Chemielexikon führt seinen Namen. Nur unter dem Begriff Saccharose taucht er kurz auf — als derjenige, der 1801 die erste Rübenzuckerfabrik der Welt gründete: In diesem Jahr, am 28. April, jährt sich sein Geburtstag zum 250. Mal.
Berliner Blau: Alte Farbe in neuem Glanz
Authors: Roth Klaus
Published: April 2003

Die Entdeckung des Berliner Blaus war reiner Zufall. 1704 erhielt der Berliner Färber Diesbach wohl zu seiner eigenen großen Überraschung aus Eisenvitriol und Kalilauge eine dunkelblaue Lösung. Heute wissen wir, dass die verwendete Kalilauge mit dem damals noch unbekannten Kaliumhexacyanoferrat K4[Fe(CN)6] verunreingt gewesen sein muss. Über die Entdeckung wurde 1710 berichtet [1]: der Farbstoff war ungiftig und ließ sich trotz seiner Unlöslichkeit in Wasser, Öl und anderen Flüssigkeiten sehr fein verteilen. Insgesamt ein ideales Pigment, das als Berliner oder Preußisch Blau die Welt eroberte. Zwar änderte sich mit dem Herstellungsort der Name, aber egal ob Pariser Blau, Miloriblau, Antwerpener Blau, Persischblau, Turnbulls Blau, Hamburger Blau u.s.w., als Mal‐, Druck‐oder Textilfarbe, zum Färben von Leder oder Kunststoffen und in der Kosmetik, Berliner Blau blieb bis heute eines der farbintensivsten und schönsten Blaupigmente.
Höhepunkte aus Liebigs Experimentalvorlesung
Authors: Schwedt Georg
Published: April 2003

Liebigs Geburtstag jährt sich am 12. Mai 2003 zum 200. Mal. Aus diesem Anlass werden einzelne Experimente bzw. Versuchsreihen, die noch heute eine grundlegende Bedeutung haben, aus seiner in Gießen entwickelten Experimentalvorlesung vorgestellt. Sie stammen aus dem im Nachlass seines Sohnes, des Arztes Georg von Liebig (1827—1903), im Jahre 1906 aufgefundenen Vorlesungsbuch, das 1983 veröffentlicht wurde.
Entwicklung von Analysenmethoden
Authors: Dobrat Walter
Published: April 2003

CIPAC ist eine internationale Vereinigung unabhängiger Wissenschaftler, die sich mit der Entwicklung und Herausgabe von Analysenmethoden für Pflanzenschutzmittel und Methoden für die Bestimmung von physikalischen Eigenschaften befassen.
Phänomene aus der Konserve
Authors: Hildebrandt Henry , Höfker Uwe
Published: April 2003

Chemische Experimente werden schon seit längerer Zeit auf „Celluloid gebannt”︁, aber auch hier revolutioniert (oder ‚evolutioniert’︁) das Internet die Zugänglichkeit und kann — recht verstanden — die Lehre in Hochschule und Schule bereichern und ein größeres chemieinteressiertes Publikum ansprechen. Neben die Realaufnahmen von chemischen Versuchen treten dabei immer häufiger mehr oder weniger interaktive Veranschaulichungen von Modellvorstellungen durch Computeranimationen.
Sternförmige Hohlschalen aus Metalloxiden
Authors: Feil Sylvia
Published: April 2003

Sie bilden nicht nur schöne Muster — die Strukturen der Hohlschalen von Kieselalgen (Diatomeen) und Strahlentierchen (Radiolarien) faszinieren auch durch andere Eigenschaften: Diese Einzeller haben hierarchisch geordnete Strukturebenen, die eine biomimetische Nachahmung interessant machen.
Ein Calciumatom als Computer
Authors: Groß Michael
Published: April 2003

Ein Quantenzustand kann — zumindest theoretisch — der Informationsverarbeitung dienen. Denken Sie etwa an einen Kernspin im Magnetfeld, der sich mittels Anregung mit Radiowellen zwischen zwei verschiedenen Zuständen umschalten lässt. Dafür braucht man nicht mehr als ein handelsübliches NMR‐Spektrometer. Ein solches Zustandspaar definiert ein Qubit, das quantenmechanische Analogon zum Bit der Computertechnik.
Doubly tunable double ring surface coil
Authors: Volotovskyy Vyacheslav , Tomanek Boguslaw , Corbin Ian , Buist Richard , Tuor Ursula I. , Peeling James
Published: April 2003

To perform multinuclear magnetic resonance spectroscopy and imaging, a coil with a high signal‐to‐noise ratio and spatially uniform B1 field that covers the same volume of interest at several frequencies is preferred. The design of a surface coil that reduces contaminating signals from the surface‐lying tissues and improves uniformity of the B1 field within the same preselected volume for both31P and 1H is described. Testing of the coil demonstrated acquisition of proton images and 31P spectra from a selected voxel in rat liver at 7 T. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 11–16, 2003.
The relationship between the Nyquist criterion and the point spread function
Authors: Sarty Gordon E.
Published: April 2003

It is well known that to avoid aliasing in the reconstruction of functions on ℝn that have support on a compact set B (having n‐volume |B|), it is necessary to sample k‐space with a density equal to or higher than one sample per 1/|B| n‐volume of k‐space. It is also well known that undersampling any particular region of k‐space will lead to an aliasing, or “folding in” of image information containing the spatial frequency information of the undersampled region. Here a simple description of what it means to fold in specific spatial frequency information is given in terms of the structure of the point spread function. The description should be useful for designers of k‐space sampling schemes that deliberately incorporate undersampled regions. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 17–24, 2003.
NMR spiral surface microcoils: Design, fabrication, and imaging
Authors: Eroglu Sertac , Gimi Barjor , Roman Brian , Friedman Gary , Magin Richard L.
Published: April 2003

NMR investigation of volume‐limited chemical and biological samples requires a radio frequency (RF) microcoil with high signal‐to‐noise ratio (SNR) over the region of interest. Conventional approaches using solenoidal microcoils provide high sensitivity (RF field strength per unit current) and spectral resolution but require the sample and sample container to be enclosed by the coil. Planar surface microcoils provide an alternative configuration that allows direct access to the sample, but with the sacrifice of RF field uniformity. In this study we evaluate a family of planar RF microcoils (500 MHz, Archimedean geometry, 1–6 turns, inner radius 0.75 to 4 mm, and conductor widths of 75, 100, and 200 μm). The design, fabrication, and performance (electrical and NMR) of the coils are described. This coil configuration exhibits a high local SNR, easy fabrication, good electrical properties, and moderate spectral uniformity (suitable for imaging and low resolution NMR spectroscopy). This design can also be scaled to smaller dimensions. These results suggest that planar spiral RF microcoils will find applications in multimodality microscopy and microfludic devices where sample manipulation and coil integration with the microanalysis systems is necessary. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 1–10, 2003.
CORBA request portable interceptors: analysis and applications
Authors: Baldoni R. , Marchetti C. , Verde L.
Published: April 2003

Interceptors are an emerging middleware technology enabling the addition of specific network‐oriented capabilities to distributed applications. By exploiting interceptors, developers can register code within interception points, extending the basic middleware mechanisms with specific functionality, e.g. authentication, flow control, caching, etc. Notably, these extensions can be achievedwithout modifyingeither the application or the middleware code.

In this paper we report the results of our experiences with CORBA request portable interceptors. In particular, we point out (i) the basic mechanisms implementable by these interceptors, i.e. request redirection and piggybacking and (ii) we analyze their limitations. We then propose a proxy‐based technique to overcome the interceptors' limitations. Successively, we present a performance analysis carried out on three Java‐CORBA platforms currently implementing the portable interceptors specification. Finally, we conclude our work with a case study in which portable interceptors are used to implement the fault‐tolerant CORBA client invocation semantic without impacting on the client application code and on the CORBA ORB. We also release fragments of Java code for implementing the described techniques. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of a prototype intelligent network interface
Authors: Underwood Keith D. , Ligon Walter B. , Sass Ron R.
Published: April 2003

With a focus on commodity PC systems, Beowulf clusters traditionally lack the cutting edge network architectures, memory subsystems, and processor technologies found in their more expensive supercomputer counterparts. Many users find that what Beowulf clusters lack in technology, they more than make up for with their significant cost advantage. In this paper, an architectural extension that adds reconfigurable computing to the network interface of Beowulf clusters is proposed. The proposed extension, called an intelligent network interface card (or INIC), enhances both the network and processor capabilities of the cluster, which has a significant impact on the performance of a crucial class of applications. Furthermore, for some applications, the proposed extension partially compensates for weaknesses in the PC memory subsystem. A prototype of the proposed architecture was constructed and analyzed. In addition, two applications, the 2D Fast Fourier Transform (2D‐FFT) and integer sorting, which benefit from the resulting architecture, are discussed and analyzed on the proposed architecture. Specifically, results indicate that the 2D‐FFT is performed 15–50% faster when using the prototype INIC rather than the comparable Gigabit Ethernet. Early simulation results also indicate that integer sorting will receive a 21–32% performance boost from the prototype. The significant improvements seen with a relatively limited prototype lead to the conclusion that cluster network interfaces enhanced with reconfigurable computing could significantly improve the Beowulf architecture. Copyright © 2003 John Wiley & Sons, Ltd.
Using multirail networks in high‐performance clusters
Authors: Coll Salvador , Frachtenberg Eitan , Petrini Fabrizio , Hoisie Adolfy , Gurvits Leonid
Published: April 2003

Using multiple independent networks (also known as rails) is an emerging technique which is being used to overcome bandwidth limitations and enhance fault tolerance of current high‐performance parallel computers. In this paper, we present and analyze various algorithms to allocate multiple communication rails, including static and dynamic allocation schemes. An analytical lower bound on the number of rails required for static rail allocation is shown. We also present an extensive experimental comparison of the behavior of various algorithms in terms of bandwidth and latency. We show that striping messages over multiple rails can substantially reduce network latency, depending on average message size, network load and allocation scheme. The methods compared include a static rail allocation, a basic round‐robin rail allocation, a local‐dynamic allocation based on local knowledge and a dynamic rail allocation that reserves both communication endpoints of a message before sending it. The last method is shown to perform better than the others at higher loads: up to 49% better than local‐knowledge allocation and 37% better than the round‐robin allocation. This allocation scheme also shows lower latency and it saturates at higher loads (for long enough messages). Most importantly, this proposed allocation scheme scales well with the number of rails and message size. In addition we propose a hybrid algorithm that combines the benefits of the local‐dynamic allocation for short messages with those of the dynamic algorithm for large messages. Copyright © 2003 John Wiley & Sons, Ltd.
Cover Picture: Ab Initio Calculation of Parity‐Violating Chemical Shifts in NMR Spectra of Chiral Molecules (ChemPhysChem 4/2003)
Authors: Laubender Guido , Berger Robert
Published: April 2003

The cover picture shows an intriguing effect in molecular systems, which is caused by the parity‐violating weak interactions: The chemical shifts of magnetic nuclei are predicted to differ for the two enantiomers of a chiral compound! While in the R enantiomer the nucleus (red) of the yellow center gives rise to the red NMR signal, the corresponding nucleus of the S enantiomer (green) is expected to absorb at a slightly different frequency. The ab initio approach presented by Laubender and Berger on pp. 395–399 allows for a prediction of the resulting parity‐violating line splitting (shown in the black curve) and for the identification of molecular candidates that are well‐suited to the first successful measurement of parity‐violating effects in molecules.
Surface Tension Measurements in Microgravity and their Relevance to Marangoni Convection
Authors: Egry Iván
Published: April 2003

The physical properties of liquids, such as surface tension, Marangoni convection and surface segregation are important in many technical fields and are of fundamental interest. However, inaccuracy of experiments has prevented us from fully understanding these phenomena. Recent advances in experimental techniques, such as the containerless technique and the utilization of microgravity, are described.
Alkyl Monolayer Passivated Metal–Semiconductor Diodes: 2: Comparison with Native Silicon Oxide
Authors: Liu Yong‐Jun , Yu Hua‐Zhong
Published: April 2003

To understand the electrical properties at passivated metal–semiconductor interfaces, two types of mercury–insulator–silicon (n‐type) junctions, Hg|C10H21Si and Hg|SiO2Si, were fabricated and their current–voltage and capacitance–voltage characteristics compared. Both of them exhibited near‐ideal rectifying characteristics with an excellent saturation current at reverse bias, which is in contrast to the previously reported ohmic behavior of an unmodified mercury–silicon junction. The experimental results also indicated that the n‐decyl monolayer passivated junction possesses a higher effective barrier height, a lower ideality factor (that is, closer to unity), and better reproducibility than that of native silicon oxide. In addition, the dopant density and build‐in potential, extracted from capacitance–voltage measurements of these passivated mercury–silicon junctions, revealed that alkyl monolayer derivatization does not alter the intrinsic properties of the silicon substrate. The calculated surface state density at the alkyl monolayer|silicon interface is lower than that of the silicon oxide|silicon interface. The present study increases the possibility of using advanced organic materials as ultrathin insulator layers for miniaturized, silicon‐based microelectronic devices.
High Lithium Ionic Conductivity in the Lithium Halide Hydrates Li3‐n(OHn)Cl (0.83≤n≤2) and Li3‐n(OHn)Br (1≤n≤2) at Ambient Temperatures
Authors: Schwering Georg , Hönnerscheid Andreas , van Wüllen Leo , Jansen Martin
Published: April 2003

Lithium ionic conductivity and phase transitions in a series of lithium halides hydrates and hydroxides with general formula Li3‐n(OHn)X (0.83≤n≤2; X=Cl,Br) were studied using impedance measurements and 1H and 7Li NMR spectroscopy. All compounds studied in this work crystallize in the antiperovskite structure or are closely related to this structure type. With the exception of LiCl⋅H2O, all compounds with integer lithium content exhibit good lithium ionic conductivity in their high temperature cubic phases above T=33 °C. Lithium doping of samples LiX⋅H2O and Li2(OH)X leads to a suppression of the phase transition into the noncubic phases and the good ionic conductivity is extended down to lower temperatures (T<0 °C). Thus, lithium doping of the lithium halide hydrates provides a promising tool for tailoring the ionic conductivity at ambient temperatures to its optimum value.
OLED and PLED Devices Employing Electrogenerated, Intramolecular Charge‐Transfer Fluorescence
Authors: Goes Marijn , Verhoeven Jan W. , Hofstraat Hans , Brunner Klemens
Published: April 2003

The light generating mechanism of a series of light emitting diodes with electron donor–bridge–acceptor systems (D–b–A) as the emitting species was examined by constructing model diodes based on small organic molecules (OLEDs) as well as on molecularly doped electroactive (poly‐N‐vinylcarbazole, PVK) and insulating (polystyrene, PS) polymers (PLEDs). The direct electrogeneration of an intramolecular charge‐transfer (CT) fluorescence of the donor–bridge–acceptor systems occurred readily in OLED devices with a D–b–A system as the emissive layer. In diodes with PS as the host matrix, hole‐injection and electron‐injection occurred directly in the D–b–A molecules residing close to the anode and the cathode, respectively. In the PVK diodes, hole‐injection occurred primarily into PVK and the positive charge carrier was subsequently trapped on the D–b–A molecule, whereas electron‐injection at the cathode side occurred directly into the D–b–A molecules. Charge‐hopping between neighboring molecules then occurred until a hole and electron resided on the same molecule, which is equivalent to the formation of the CT excited state, and which finally relaxed by intramolecular charge recombination under the emission of CT fluorescence.
On the Temperature–Pressure Free‐Energy Landscape of Proteins
Authors: Ravindra Revanur , Winter Roland
Published: April 2003

We studied the thermodynamic stability of a small monomeric protein, staphylococcal nuclease (Snase), as a function of both temperature and pressure, and expressed it as a 3D free‐energy surface on the p,T‐plane using a second‐order Taylor expansion of the Gibbs free‐energy change ΔG upon unfolding. We took advantage of a series of different techniques (small‐angle Xray scattering, Fourier‐transform infrared spectroscopy, differential thermal analysis, pressure perturbation calorimetry and densitometry) in the evaluation of the conformation of the protein and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The calculated results of the free‐energy landscape of the protein are in good agreement with experimental data of the p,T‐stability diagram of the protein over a temperature range from 200 to 400 K and at pressures from ambient pressure to 4000 bar. The results demonstrate that combined temperature–pressure‐dependent studies can help delineate the free‐energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. The approach presented may also be used for studying other systems with so‐called re‐entrant or Tamman loop‐shaped phase diagrams.
An Ab Initio Study on the Mechanism of the Atmospheric Reaction NH2+O3→H2NO+O2
Authors: Peiró‐García Julio , Nebot‐Gil Ignacio , Merchán Manuela
Published: April 2003

The atmospheric reaction NH2+O3→H2NO+O2 has been investigated theoretically by using MP2, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. At the MP2 level of theory, the hypersurface of the potential energy (HPES) shows a two step reaction mechanism. Therefore, the mechanism proceeds along two transition states (TS1 and TS2), separated by an intermediate designated as Int. However, when the single‐reference higher correlated QCISD and the multiconfigurational CASSCF methodologies have been employed, the minimum structure Int and TS2 are not found on the HPES, which thus confirms a direct reaction mechanism. Single‐reference high correlated and multiconfigurational methods consistently predict the barrier height of the reaction to be within the range of 3.9 to 6.6 kcal mol−1, which is somewhat higher than the experimental value.1 The calculated reaction enthalpy is −67.7 kcal mol−1.
Hydration and Ion Pairing in Aqueous Sodium Oxalate Solutions
Authors: Buchner Richard , Samani Faradj , May Peter M. , Sturm Peter , Hefter Glenn
Published: April 2003

Dielectric spectra have been measured for aqueous sodium oxalate solutions up to the saturation concentration (0.04≤c [mmol L−1]≤0.25) at 25 °C over the approximate frequency range 0.2≤ν [GHz]≤20. The spectra exhibit a process at about 1 GHz associated with the presence of ion pairs, in addition to the dominant solvent relaxation process at about 18 GHz. Detailed analysis of the solvent dispersion amplitude indicates that the oxalate ion is highly hydrated but that its solvation sheath is “fragile”, decreasing quickly with increasing solute concentration. The NaOx(aq)− ion pair is shown to be of the double‐solvent‐separated (2SIP) type, with an infinite dilution association constant KA=1.04±0.02. Analysis of the ion‐pair relaxation time as a function of solute concentration gave rate constants for the formation (k12=(7.3±0.4)109 L mol−1 s−1) and dissociation (k21=(6.7±0.5)108 s−1) of the ion pair. These values are reasonably close to the diffusion‐controlled values predicted by the Eigen theory, consistent with a 2SIP structure for the ion pair.
Some unmeasured crystal properties
Authors: Raab R. E.
Published: April 2003

The subject of this paper is three macroscopic properties of crystals: Jones birefringence, non‐reciprocal linear birefringence along a cube edge in certain magnetic cubic crystals, and the static magneto‐electric coefficient of magnetic cubic crystals which exhibit this effect. As each of these properties has a particular theoretical interest, and as they remain, as yet, unmeasured, a background account is presented of each, together with the theory, in multipole form, of experiments which would allow the three properties to be measured.
Solid state recrystallization: a promising technique for the growth of semiconductor materials
Authors: Triboulet R.
Published: April 2003

Experimental results related to the growth by solid state recrystallization of different semiconductors such as HgCdTe, HgMnTe, CdTe, ZnSe and ZnS are reported and reviewed. The importance of the initial texture and of the deviation from stoichiometry is stressed and the essential role of metal vacancies is emphasized.
YVO4 crystals – puzzles and challenges
Authors: Ryba‐Romanowski W.
Published: April 2003

Work on optical properties of undoped and rare‐earth doped YVO4 crystals is briefly reviewed. Fundamental spectroscopic parameters relevant to laser performance of YVO4 containing erbium, thulium and holmium, derived from absorption and emission spectra and from excited state relaxation dynamics, have been presented. Laser performance of YVO4:Er has been reported and laser potential of YVO4 doped with thulium and holmium has been assessed. Anomalous phenomenon of up‐conversion of IR radiation into red emission in YVO4:Yb,Ho and puzzling anti Stokes emission in nominally undoped YVO4 have been discussed.
Advances in modeling of wide‐bandgap bulk crystal growth
Authors: Bogdanov M. V. , Demina S. E. , Karpov S. Yu. , Kulik A. V. , Ramm M. S. , Makarov Yu. N.
Published: April 2003

We review key aspects of sublimation growth of wide‐bandgap semiconductors like SiC, AlN and GaN, and show how modeling can help to solve a number of practical problems. As the temperature distribution in the growth chamber is the most critical factor in the sublimation technology, we discuss in detail specific features of heat transfer with the focus on the porous materials normally involved in the growth system: powder source, thermal insulation, and graphite. The species transport is simulated using advanced models accounting for a multicomponent vapor and the kinetics of chemical interaction of nitrogen‐containing species with the surface of group‐III nitrides. The effect of growth conditions on parasitic phase formation is analyzed. To optimize the growth system design and operating conditions, we suggest an inverse‐problem approach instead of commonly used trial‐and‐error methods. This simulation procedure has proved quite efficient for getting design solutions, which could hardly be found by conventional straightforward methods. In particular, we demonstrate the effectiveness of the inverse modeling for finding the growth conditions, which provide crystals of desired shapes. A special analysis is made to establish a correlation between the growth conditions and defect distribution in the grown crystal, with the focus on thermoelastic stress produced by temperature gradients. The high‐temperature dynamics of gliding dislocations and consequent plastic stress relaxation in the material is examined. The prospective of global modeling of wide‐bandgap crystal growth by sublimation and still open questions are discussed.
Scanning probe microscopy and computer simulations: Complementary techniques for nanostructured materials and thin films
Authors: Richter A. , Smith R.
Published: April 2003

It is demonstrated how scanning force microscopy in combination with recent simulation techniques and computer power can be used in a complementary way in the analysis and explanation of thin film growth and nanoindentation on crystal surfaces. Simulation techniques such as Monte Carlo models and molecular dynamic models are applied for thin film growth and nanoindentation. The formation of the first molecular layers in the growth of C60 films on silicon can be modelled by classical molecular dynamics to show the different bonding behaviour between C60 molecules, which results in hexagonal and cubic structures with stacking faults within the C60 film. Ab initio calculations of C60 bonding sites to the silicon surface classify bond types by the length and the energy of the C‐Si bonds. Strong binding energies between the C60 molecule and the Si atoms are obtained to fix the C60 molecule at a definite position. Different growth modes such as island and layer growth of C60 films can be studied by Monte Carlo simulations, including diffusion of atoms within the cluster and cluster diffusion over the surface itself. A brief experimental view of the nanoindentation process is given in combination with molecular dynamics simulations for the penetration of the tip into a C60 surface. The crystal symmetry is reflected during the plastic deformation in the pile‐up structure around the indentation hole in relation to the orientation of the indenter and the crystal surface. As an example of these investigations results are given for nanoindentation into the Fe{110} single crystal surface.
Mixtures of organic macrocycles for applications in solar cell devices
Authors: Boguta A. , Wróbel D. , Hoffmann T. J. , Mazurkiewicz P.
Published: April 2003

In this paper we present spectroscopic and photoelectric studies of two families of macrocycles and their mixtures: phthalocyanines and naphthalocyanines complexed with various ions. The dyes are characterized by significant light absorption and each dye absorbs in a different spectral region and covers only a part of the solar light spectrum. The use of the dyes mixture extends the light absorption region and can lead to the enhancement of photovoltaic effects. The spectroscopic properties are studied to establish the radiative and non–radiative deactivation pathways of the dye excited states as processes competitive to charge separation. As it is shown, the excitation energy transfer improve the efficiency of light energy to electric energy conversion. The dynamics of the electromagnetic field in the phthalocyanine–naphthalocyanine–solvent system as a multicomponent body in the sense of extended phenomenological electrodynamics is also presented. Lagrange–Hamilton formalism can be used in the investigation of the local electromagnetic field in the dyes–solvent mixture. The presented results seem to be essential in the determination of the conditions required for the enhancement of the photoeffects in the photoelectrochemical cell based on the organic materials.
Rb3Lu(PO4)2:Ce and Cs3Lu(PO4)2:Ce – new promising scintillator materials
Authors: Wisniewski D. , Wojtowicz A. J. , Drozdowski W. , Farmer J. M. , Boatner L. A.
Published: April 2003

Cs3Lu(PO4)2:Ce and Rb3Lu(PO4)2:Ce single crystals have been studied under gamma‐, x‐ray and UV excitation. For all types of excitation the luminescence of these materials is dominated by a broad Ceemission band positioned at the UV/visible light boundary. Highly efficient and relatively fast scintillation of both materials identify them as promising scintillators.
Growth and TEM and HREM characterisation of TiC crystals grown from high‐temperature solutions
Authors: Strzeciwilk D. , Wokulski Z. , Tkacz P.
Published: April 2003

The results of TiC crystals and Ni microstructure studies by means of transmission electron microscope are presented. It was shown that Ni may be used as high temperature solvent for obtaining TiC crystals. This paper reports the results of morphology and growth of TiC crystals. The obtained TiC crystals with application of Ni as high temperature solvent were mainly of {001} cubic form, although irregular forms were also observed. Detailed TEM and HREM studies have shown that dislocations are formed in the vicinity of incoherent TiC precipitates in Ni matrices.
Preparation of semi‐insulating CdTe doped with group IV elements by post growth annealing
Authors: Turkevych I. , Grill R. , Franc J. , Höschl P. , Belas E. , Moravec P. , Fiederle M. , Benz K. W.
Published: April 2003

Thermodynamic conditions for post‐growth annealing to prepare near stoichiometric semi‐insulating CdTe are studied for undoped, and Sn and Ge‐doped single crystals. The main aim of the annealing procedure was to obtain high resistive material with the minimal concentration of native and foreign defects. The high temperature (200 – 1000 °C) in‐situ conductivity σ and Hall effect measurements were used to control the native defect density and to determine the Cd pressure pCd at which shallow defects are compensated. It is shown that contrary to the undoped samples in which the change of the type of conductivity by variations of pCd is easy, the Sn‐ and Ge‐doped samples exhibit a much more stable behavior due to the Sn (Ge) selfcompensation. It was found that: the temperatures near 500 °C is optimum for the real‐time annealing of bulk samples, the chemical diffusion is sufficiently fast at these temperatures while the uncontrolled change of defect density distribution during the subsequent cooling process is minimized. The time‐dependent charge measurement technique was used to characterize the room‐temperature specific resistivity distribution in the as‐grown crystals, which indirectly controls the dynamic of solidification process. This allows us to consider the specific resistivity distribution along the growth direction of each crystal in terms of superposition of segregation and self‐compensation phenomena.
Application of tungsten films for substrate masking in liquid phase epitaxial lateral overgrowth of GaAs
Authors: Dobosz D. , Zytkiewicz Z. R. , Piotrowski T.T. , Kaminska E. , Papis E. , Piotrowska A.
Published: April 2003

Liquid phase epitaxial lateral overgrowth of GaAs layers on GaAs substrates masked by tungsten films was studied. We show that at our growth conditions perfect growth selectivity was obtained, so the layers started growing from the openings cut in the mask only. However, serious damage of the mask during epitaxial growth was observed. As this deteriorates crystallographic quality of the layers a procedure was elaborated to eliminate degradation of the tungsten film by the melt. In particular, reduction of growth temperature and deposition of Au/Zn wetting layers between tungsten film and the GaAs substrate were found important to avoid degradation of the mask and for successful lateral growth of the layers. Tungsten masked GaAs substrates were then used for lateral overgrowth of GaAs by liquid phase electroepitaxy. Preliminary results are presented showing that application of electrically conductive tungsten mask, which allows a direct DC current flow from the melt to the substrate, results in much wider and thinner electroepitaxial layers than those grown on the substrates coated by insulating film.
Stress‐induced structural changes in thin InAs layers grown on GaAs substrate
Authors: Bak‐Misiuk J. , Shalimov A. , Kaniewski J. , Misiuk A. , Dynowska E. , Reginski K. , Trela J. , Przesławski T. , Hartwig J.
Published: April 2003

Effect of high temperature‐high pressure treatment on strain state of the lattice mismatched InAs layers grown on the GaAs substrate was investigated by means of X‐ray diffraction methods. The InAs layers were grown on (100) oriented GaAs by molecular beam epitaxy. Measurements of the rocking curve width and lattice parameters were carried out using high resolution diffractometer. Annealing of the InAs/GaAs structure performed at high pressure changes its strain state and defect structure. Especially, annealing at the growth temperature at high pressure was found to be effective in improvement of the structural perfection of the layer. It means that thin InAs layers having comparatively low dislocation density can be produced by high temperature ‐ high pressure procedure. The relative changes of threading dislocation density were sensitive to the temperature of the treatment, however they were independent of the primary defect structure of the samples.