bluuebunny/crossref_metadata_2025 huggingface dataset:
Modellierung von Luftblasen als Rotationsellipsoide anhand paarweiser ebener Projektionen (Modelling of Air Bubbles as Spheroids Based on a Pair of Parallel Planar Projections)
Authors: Hoppe Dietrich , Zaruba Aliaksandr , Prasser Horst-Michael
Published: February 2006

Eine in ruhendem Wasser aufsteigende Luftblase wird parallel zur Wasseroberfläche in zwei zueinander senkrechte horizontale Richtungen parallel projiziert. Diese beiden Projektionen werden zunächst als Ellipsen approximiert. Anhand der Ellipsen wird die Blase dann als Rotationsellipsoid modelliert. Dieses eignet sich zur Analyse der Orientierung der Symmetrieachse der Blase auf ihrem Weg durch das Wasser. Dies wird an einem Ensemble schraubenartig aufsteigender Blasen verdeutlicht.
Pyroelektrische Zeilensensoren und ihre Anwendungen (Pyroelectric Linear Arrays and their Applications)
Authors: Norkus Volkmar , Gerlach Gerald , Köhler Reinhard , Hofmann Günter
Published: February 2006

In den letzten Jahren ist am Institut für Festkörperelektronik eine flexible Herstellungstechnologie für pyroelektrische Infrarotsensoren auf der Basis von Lithiumtantalat (LiTaO3) entwickelt worden. Mit ihr ist es möglich, Sensoren zu entwerfen und zu fertigen, die einen hohen Signal-Rausch-Abstand besitzen und der geplanten Anwendung optimal angepasst sind. So wurden Zeilensensoren mit bis zu 256 empfindlichen Elementen hergestellt, die vorteilhaft in der Temperaturmesstechnik, Gasanalytik und Sicherheitstechnik eingesetzt werden können.
Pyroelektrische Detektoren mit integriertem Operationsverstärker für hohe Modulationsfrequenzen (Pyroelectric Detectors with Integrated Operational Amplifier for High Modulation Frequencies)
Authors: Neumann Norbert , Sänze Hannjo , Heinze Matthias
Published: February 2006

Durch die Entwicklung einer Familie von pyroelektrischen Detektoren mit integriertem Transimpedanzverstärker können die Vorteile des Strombetriebs auch für Modulationsfrequenzen bis in den kHz-Bereich konsequent genutzt, die Applikation solcher Detektoren vereinfacht sowie neue Einsatzfelder wie z. B. die Absorptionsspektroskopie mit Quanten-Kaskaden-Lasern eröffnet werden. Die wesentlichen Vorteile des Transimpedanzverstärkers ergeben sich aus der niedrigen elektrischen Zeitkonstante τE und dem Kurzschlussbetrieb des pyroelektrischen Elements. Um auch bei hohen Modulationsfrequenzen über eine genügend hohe Empfindlichkeit von z. B. 7500 V/W zu verfügen, wird ein möglichst flacher Amplitudengang der Empfindlichkeit bis über 1 kHz angestrebt. Erreicht wird dies durch eine elektrische Zeitkonstante von (0.1…1) ms und eine hohe Bandbreite des Operationsverstärkers von mindestens 1 MHz. Im Einzelnen wird beschrieben, wie die Forderungen umgesetzt werden können und welche Kompromisse einzugehen sind.
Beschleunigungsempfindlichkeit pyroelektrischer Sensoren (Acceleration Sensitivity of Pyroelectric Infrared Detectors)
Authors: Shvedov Dmitry , Norkus Volkmar , Gerlach Gerald
Published: February 2006

In dieser Arbeit wird der Einfluss mechanischer Beschleunigungen auf das Ausgangssignal pyroelektrischer Sensoren (Mikrofonieeffekt) untersucht. Es wurden unterschiedliche Sensorparameter analysiert.
LimoLIT – Licht-modulierte Lock-in-Thermografie zur Solarzellenprüfung (LimoLIT – Light Modulated Lock-in Thermography for Solar Cell Examination)
Authors: Krauß Matthias , Pfengler David , Vollheim Birgit , Mahler Guido
Published: February 2006

Bei der Massenproduktion von Solarzellen gewinnen effiziente Prüfverfahren zur Sicherung der Produktqualität und Optimierung der Prozesse zunehmend an Bedeutung. Mit der Licht-modulierten Lock-in-Thermografie (LimoLIT) können Solarzellen bereits während des Fertigungsprozesses innerhalb kürzester Messzeiten berührungslos geprüft werden. Durch eine periodisch modulierte Beleuchtung der Solarzelle werden lokale Erwärmungen an Defekten (Shunts) hervorgerufen, die mit einer leistungsfähigen Thermografiekamera unter Anwendung des Lock-in-Verfahrens detektiert werden.
Serpentine Locomotion Articulated Chain: ANA II
Authors: Cardona A. M. , Barrero J. I. , Otálora C. , Parra C.
Published: February 2006

When humanity faces challenges in solving problems beyond their technical resources, and has no foundation to solve a problem, engineering must search for an answer developing new concepts and innovative frameworks to excel these limitations and travel beyond our capabilities. This project “Serpentine locomotion articulated chain: ANA II” is a self‐contained robot built to evaluate the behavior of the platform being capable of serpentine movements, in a modular chain mechanical design, based on a master/slave architecture.
High‐light‐induced Changes on Photosynthesis, Pigments, Sugars, Lipids and Antioxidant Enzymes in Freshwater (Nostoc spongiaeforme) and Marine (Phormidium corium) Cyanobacteria
Authors: Bhandari Rupali , Sharma Prabhat Kumar
Published: February 2006

We studied the effects of high‐light exposure (500 μmol m−2 s−1 of photosynthetic active radiation) on the cyanobacteria Nostoc spongiaeforme Agardh, a fresh‐water alga, and Phormidium corium Agardh (Gomont), a marine alga, with respect to photosynthesis, pigments, sugar content, lipid peroxidation, fatty acids composition, antioxidant enzymes activity and DNA. It was seen that the ratio of variable fluorescence (Fv) to maximum fluorescence (Fm), which is indicative of photosynthetic efficiency, decreased because of the light treatment. The damage to photosynthesis occurred in the antenna system and the photosynthetic II reaction center. Photobleaching of photosynthetic pigments was also observed. High‐light treatment also resulted in decreased sugar content, which was probably due to the effect on photosynthesis. Peroxidation of membrane lipids, indicating oxidative damage to lipids and a high level of unsaturation in the cell membrane, was also observed. The activity of antioxidant enzyme superoxide dismutase and ascorbate peroxidase was increased, probably as a result of oxidative damage observed in the form of lipid peroxidation. Quantitative decreases in phospholipid and glycolipid levels were also observed. The level of unsaturated fatty acids in total lipids and glycolipids remained unchanged in both species; however, the level of saturated fatty acids decreased, which slightly changed the ratio in favor of unsaturated fatty acids. Degradation of DNA was also observed in both species. There was a transient plateau 2–4 h after exposure to high‐light treatment in the Fv/Fm ratio and in levels of phycobilisome pigments, sugars and antioxidant enzymes after an initial decrease 1 h after the treatment. These findings may indicate a period of partial adaptation to high light that is due to the efficiency of protective processes operational in the two species, which subsequently failed after a longer exposure duration of 4–6 h.
Hydrogen response in liquid propylene polymerization: Towards a generalized model
Authors: Ali M. Al‐haj , Betlem B. , Roffel B. , Weickert G.
Published: February 2006

Liquid propylene batch experiments in the absence of a gas phase have been carried out using a highly‐active MgCl2/TiCl4/phthalate/silane/AlR3 catalyst at varying temperatures (60‐80°C) and molar hydrogen‐monomer ratios of 0‐10 mmol/mol. With increasing hydrogen concentration the

polymerization rate increases rapidly, reaching a constant value at concentrations above 1.4 mmol/mol;

pseudo‐first‐order catalyst deactivation constant increases;

molecular weight decreases;

polydispersity decreases slightly;

but average molecular weight and polydispersity increase with increasing temperature. Polymerization rate, deactivation constant, and average molecular weight can be modeled based on a consistent dormant site mechanism assuming an (averaged) quasi‐single‐site model. © 2006 American Institute of Chemical Engineers AIChE J,2006
Titelbild: Molecular Recognition of a Three‐Way DNA Junction by a Metallosupramolecular Helicate (Angew. Chem. 8/2006)
Authors: Oleksi Aneta , Blanco Alexandre G. , Boer Roeland , Usón Isabel , Aymamí Joan , Rodger Alison , Hannon Michael J. , Coll Miquel
Published: February 2006

Metallosupramolekulare Helicate mit trigonal‐antiprismatischer Form füllen den zentralen hydrophoben Hohlraum eines Drei‐Wege‐DNA‐Knotenpunkts perfekt aus. Sechs hydrophobe Ringe des Wirkstoffs stapeln sich mit sechs DNA‐Basen und drei weitere sind sandwichartig in die kleinen Furchen eingelagert. Die Zuschrift von M. Coll, M. J. Hannon et al. auf S. 1249 ff. zeigt neue Möglichkeiten für Wechselwirkungen mit DNA und vor allem mit DNA‐Knotenpunkten.
Cover Picture: Molecular Recognition of a Three‐Way DNA Junction by a Metallosupramolecular Helicate (Angew. Chem. Int. Ed. 8/2006)
Authors: Oleksi Aneta , Blanco Alexandre G. , Boer Roeland , Usón Isabel , Aymamí Joan , Rodger Alison , Hannon Michael J. , Coll Miquel
Published: February 2006

Metallosupramolecular helicates with trigonal‐antiprismatic geometry thread through and fit perfectly into the central hydrophobic cavity of a three‐way DNA junction. Six hydrophobic rings of the drug stack on six DNA bases, with three more sandwiched in the minor grooves. This work reveals and enables a new approach to targeting DNA and specifically DNA junctions. For more details, see the Communication by M. Coll, M. J. Hannon, and co‐workers on page 1227 ff.
Assessment of the accuracy of dental enamel thickness measurements using microfocal X‐ray computed tomography
Authors: Olejniczak Anthony J. , Grine Frederick E.
Published: February 2006

Tooth enamel thickness has long been an important character in studies of primate and especially hominin phylogeny, taxonomy, and adaptation. Current methods for accurately assessing enamel thickness involve the physical sectioning of teeth, because measurements of enamel thickness using some radiographic techniques are unreliable. However, because destructive methods limit sample sizes and access to important fossil specimens, it is desirable that they be replaced with nondestructive techniques. Although microfocal X‐ray computed tomography (mCT) has been used recently in studies of enamel thickness, the accuracy of this technique has yet to be established. The present research compares physical sections to computer‐generated mCT sections of teeth from a variety of primate and nonprimate, recent and fossil taxa to examine whether enamel thickness, tooth size, and diagenetic remineralization (fossilization) impact the ability of mCT to measure enamel thickness accurately. Results indicate that recent teeth of varying size and thickness are clearly and accurately depicted in mCT scans, with measurements from nearly identical planes in physical and mCT sections differing by 3–5%. A fossil papionin molar (ca. 2 Myr) was also accurately measured using mCT scans, although thinner enamel in much older therapsid (ca. 263–241 Myr) teeth could not be distinguished from dentine. mCT is thus an accurate technique for measuring enamel thickness in recent taxa, although heavily mineralized teeth pose an obstacle to the ability of mCT to distinguish dental tissues. Moreover, absolutely thin enamel (less than ∼ 0.10 mm) is difficult to resolve adequately in raw mCT images based on pixel values alone. Therefore, caution must be exercised in the application of mCT to the study of fossilized teeth. © 2006 Wiley‐Liss, Inc.
Morphological evidence for existence of IL‐6 receptor alpha in the glomus cells of rat carotid body
Authors: Wang Xi , Zhang Xi‐Jing , Xu Zhen , Li Xin , Li Gai‐Li , Ju Gong , Wang Bai‐Ren
Published: February 2006

The carotid body (CB) senses changes in arterial blood PO2 and modulates respiratory movement. It is generally accepted that the dopaminergic type I cells in the CB are chemoreceptors. However, it has not been clarified whether the carotid body has the ability to perceive the stimulation of proinflammatory cytokines. Interleukin 6 (IL‐6) as a multifunctional cytokine plays a pivotal role in host defense mechanism. In the present study, we observed the expression of IL‐6Rα mRNA and protein in the carotid body using immunohistochemistry, Western blots, and in situ hybridization. The results confirmed the presence of IL‐6Rα proteins and mRNAs in the glomus cells of rat carotid body. These results suggest that the function of the carotid body may be influenced by the proinflammatrory cytokines through their receptors. © 2006 Wiley‐Liss, Inc.
Retrospective analysis of utilization patterns and cost implications of coxibs among seniors in Quebec, Canada: What is the potential impact of the withdrawal of rofecoxib?
Authors: Rahme Elham , Hunsche Elke , Toubouti Youssef , Chabot Isabelle
Published: February 2006

Objective

In September 2004, the manufacturer of rofecoxib announced a voluntary worldwide withdrawal of the drug. The impact of this withdrawal on drug budgets is unclear. This study evaluated average daily doses and costs of rofecoxib and celecoxib and concomitant use of gastroprotective agents (GPAs) in elderly patients with osteoarthritis (OA) or rheumatoid arthritis (RA) in Quebec, prior to the rofecoxib withdrawal.

Methods

This retrospective cohort study used prescription drug and medical service data from the Quebec government health agency administrative database and included coxib users ≥66 years of age with OA or RA who filled ≥3 consecutive rofecoxib or celecoxib prescriptions in 2001–2002. Results were adjusted for gastrointestinal risk factors and other patient baseline characteristics.

Results

Data were analyzed for 11,975 rofecoxib and 12,480 celecoxib users. Mean daily dosages were 20.7 mg for rofecoxib and 231.3 mg for celecoxib. Rofecoxib users consumed a mean ± SD of 0.95 ± 0.43 pills per day, and celecoxib users took 1.34 ± 0.65 pills per day. Mean ± SD unadjusted daily acquisition costs were $1.18 ± $0.53 (Canadian) for rofecoxib and $1.45 ± $0.74 for celecoxib. After adjusting for patient baseline characteristics, the mean daily acquisition cost for rofecoxib was $0.25 lower than for celecoxib. Rofecoxib users were less likely than celecoxib users to fill a GPA coprescription (odds ratio 0.88; 95% confidence interval 0.81, 0.95). Subgroup analyses yielded comparable results.

Conclusion

Celecoxib appears to be a more expensive therapeutic option than rofecoxib due to a relatively higher daily dose and tablet consumption.
Role of RANK ligand in normal and pathologic bone remodeling and the therapeutic potential of novel inhibitory molecules in musculoskeletal diseases
Authors: Cohen Stanley
Published: February 2006

This is the first article in a new series entitled “Clinical Aspects of Molecular Research in Rheumatology,” which will appear regularly in Arthritis Care & Research. As with all health care professionals, our readership is increasingly faced with the reality that in medicine today there is simply “too much to know.” This is particularly true for those confronted by the challenges of interpreting the remarkable advances occurring in the fields of cellular and molecular biology as applied to research in rheumatology. This series will present concise reviews written by leaders in the field that are tailored to nonlaboratory‐based readers. It is hoped that these articles will provide both an overview of cutting edge science in an interpretable format, and provide direction for those desiring to learn more about the precise topics. We welcome reader feedback and ideas for future topics.

Leonard H. Calabrese, DO

Section Editor
Effect of membrane mimicking environment on the conformation of a pore‐forming (xSxG)6peptide
Authors: Thundimadathil Jyothi , Roeske Roger W. , Guo Lili
Published: February 2006

The mechanism of membrane interaction by β‐sheet peptides is important to understand fundamental principles of folding of β‐barrel proteins and various β‐amyloid proteins. Here, we examined the conformational characteristics of a porin‐like channel forming (xSxG)6peptide in solution and membrane‐mimicking environments (CD and ATR–IR) to understand the structural changes of the peptide during membrane association and channel formation. A comparison of the peptide conformations in different microenvironments showed that β‐sheet formation is enhanced in membrane‐mimicking liposomes and SDS‐micelles. The lipid‐induced β‐sheet formation was confirmed by the formation of a characteristic β‐sheet structure on mixing a methanolic solution of the peptide (partially folded) with preformed liposomes. The amphipathicity of the peptide; increased hydrogen bonding, hydrophilicity, and reduction in dimensionality of the membrane surface; membrane–peptide interaction–forces; and presence of flexible glycines might facilitate β‐sheet formation in membranes. Though the CD spectra of both the peptide‐bound and peptide‐incorporated lipids are reminiscent of a β‐sheet structure, a significant variation in the peak positions of the two β‐sheet structures was noticed. The channel characteristics of (xSxG)6in the presence of low ionic strength solutions of NEt3BzCl and glucosammonium chloride are comparable to those reported under high ionic strength solutions. Altogether the data suggest that the channel formation by (xSxG)6proceeds via β‐sheet aggregate formation at the membrane surface, β‐sheet insertion, and rearrangement into a β‐barrel–like structure. The β‐barrel–like channel formation most likely arises from a sequence similarity to β‐barrel porins whereas the lipid‐induced β‐sheet formation is governed by the above‐mentioned factors. © 2006 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 84: 317–328, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Orientational order of Australian spider silks as determined by solid‐state NMR
Authors: Bonev B. , Grieve S. , Herberstein M. E. , Kishore A. I. , Watts A. , Separovic F.
Published: February 2006

A simple solid‐state NMR method was used to study the structure of 13C‐ and 15N‐enriched silk from two Australian orb‐web spider species, Nephila edulis and Argiope keyserlingi. Carbon‐13 and 15N spectra from alanine‐ or glycine‐labeled oriented dragline silks were acquired with the fiber axis aligned parallel or perpendicular to the magnetic field. The fraction of oriented component was determined from each amino acid, alanine and glycine, using each nucleus independently, and attributed to the ordered crystalline domains in the silk. The relative fraction of ordered alanine was found to be higher than the fraction of ordered glycine, akin to the observation of alanine‐rich domains in silk‐worm (Bombyx mori) silk. A higher degree of crystallinity was observed in the dragline silk of N. edulis compared with A. keyserlingi, which correlates with the superior mechanical properties of the former © 2006 Wiley Periodicals, Inc. Biopolymers 82:134–143, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
X‐ray photoelectron spectroscopic and Raman analysis of silk fibroin–Cu(II) films
Authors: Zhou Li , Chen Xin , Dai Weilin , Shao Zhengzhong
Published: February 2006

There is evidence to suggest that Cu(II) is involved in the natural spinning process of a silkworm helping to convert the concentrated silk fibroin (SF) solution (or dope) into tough insoluble threads. To investigate the interaction between SF and Cu(II), a series of regenerated SF (RSF) films with different mass ratios of Cu(II) to SF were prepared. X‐ray photoelectron spectroscopy (XPS) was employed to study the chemical interaction between Cu(II) and SF in these Cu(II)–RSF films. A significant change in the binding energy of Cu 2p3/2 demonstrated that the chemical state of Cu(II) in the Cu(II)–RSF films was affected by the interaction between Cu(II) and SF. Moreover, chemical shifts of N 1s and O 1s of SF were also detected, implying that Cu(II) may coordinate with both N and O atoms in the SF. In addition, Raman spectra of the same series of Cu(II)–RSF films recorded the conformation transition of SF that may occur by the coordination of Cu(II) and SF macromolecular chains. © 2006 Wiley Periodicals, Inc. Biopolymers 82: 144–151, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Staging of chronic myeloid leukemia in the imatinib era
Authors: Cortes Jorge E. , Talpaz Moshe , O'Brien Susan , Faderl Stefan , Garcia‐Manero Guillermo , Ferrajoli Alessandra , Verstovsek Srdan , Rios Mary B. , Shan Jenny , Kantarjian Hagop M.
Published: February 2006

BACKGROUND

Several staging classification systems, all of which were designed in the preimatinib era, are used for chronic myeloid leukemia (CML). The World Health Organization (WHO) recently proposed a new classification system that has not been validated clinically. The authors investigated the significance of the WHO classification system and compared it with the classification systems used to date in imatinib trials (“standard definition”) to determine its impact in establishing the outcome of patients after therapy with imatinib.

METHODS

In total, 809 patients who received imatinib for CML were classified into chronic phase (CP), accelerated phase (AP), and blast phase (BP) based on standard definitions and then were reclassified according to the new WHO classification system. Their outcomes with imatinib therapy were compared, and the value of individual components of these classification systems was determined.

RESULTS

With the WHO classification, 78 patients (10%) were reclassified: 45 patients (6%) were reclassified from CP to AP, 14 patients (2%) were reclassified from AP to CP, and 19 patients (2%) were reclassified from AP to BP. The rates of complete cytogenetic response for patients in CP, AP, and BP according to the standard definition were 72%, 45%, and 8%, respectively. After these patients were reclassified according to WHO criteria, the response rates were 77% (P = 0.07), 39% (P = 0.28), and 11% (P = 0.61), respectively. The 3‐year survival rates were 91%, 65%, and 10%, respectively, according to the standard classification and 95% (P = 0.05), 63% (P = 0.76), and 16% (P = 0.18), respectively, according to the WHO classification. Patients who had a blast percentage of 20–29%, which is considered CML‐BP according to the WHO classification, had a significantly better response rate (21% vs. 8%; P = 0.11) and 3‐year survival rate (42% vs. 10%; P = 0.0001) compared with patients who had blasts ≥ 30%.

CONCLUSIONS

Different classification systems had an impact on the outcome of patients, and some prognostic features had different prognostic implications in the imatinib era. The authors believe that a new, uniform staging system for CML is warranted, and they propose such a system. Cancer 2006. © 2006 American Cancer Society.
Homolysis of N‐alkoxyamines: A Computational Study
Authors: Gaudel‐Siri Anouk , Siri Didier , Tordo Paul
Published: February 2006

During nitroxide‐mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO., the reversible formation of N‐alkoxyamines [PON(R1)R2] reduces significantly the concentration of polymer radicals (P.) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the CON(R1)R2bond. In this study, theoretical BDEs of a large series of model N‐alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (Tc ), and the dissociation rate constant (kd ), of the N‐alkoxyamines are established. The homolytic cleavage of the NOC bond is also investigated at the B3P86/6‐311++G(d,p)//B3LYP/6‐31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N‐alkoxyamines with a OCON(R1)R2fragment, and the strengthening of their CON(R1)R2bond is interpreted in terms of stabilizing anomeric interactions.
A Theoretical Study of the Structure and Bonding of UOX4(X=F, Cl, Br, I) Molecules: The Importance of InverseTransInfluence
Authors: Kovács Attila , Konings Rudy J. M.
Published: February 2006

The structural and bonding properties of the uranium(VI) oxyhalides UOX4(X=F, Cl, Br, I) have been investigated by quantum chemical calculations at three different levels of theory: quasi‐relativistic density functional theory (DFT) in conjunction with a triple‐zeta all‐electron basis set, as well as MP2 and the Becke3–Perdew–Wang91 exchange‐correlation functional in conjunction with relativistic effective core potentials. The computations located four stationary points on the potential energy surface: a tetragonal pyramid with the O atom in the apical position (C4v ), a trigonal bipyramid with the O atom in the equatorial position (C2v ), a trigonal bipyramid with the O atom in the axial position (C3v ) and aCsstructure derived fromC3vby opening the XeqUXeqangle to near 180°. TheCsminimum, however, seems to be an artefact of the Becke–Perdew functional on the flat potential energy surface. In theC3vstructure, the linear XaxUO moieties show clearly the geometrical consequences of the inversetransinfluence (ITI) effect. This interaction can stabilise these sterically less favoured geometries. Two important trends are revealed by our computations: 1) UOX4with the small X=F prefers theC3vstructure, whereas with increasing halogen size the sterically less crowdedC2vstructure is more important; and 2) MP2 theory accounts to a lesser extent for the ITI effect with respect to DFT, which results in different structural preferences (MP2 forC2v , DFT forC3v ) in the heavier halides. In addition, an important bonding property of the UOX4molecules is the clear triple‐bond character of the formally double UO bonds.
Computational Studies on the Cyclization of Polycyclic Aromatic Hydrocarbons in the Synthesis of Curved Aromatic Derivatives
Authors: Buñuel Elena , Marco‐Martínez Juan , Díaz‐Tendero Sergio , Martín Fernando , Alcamí Manuel , Cárdenas Diego J.
Published: February 2006

Computational studies on the cyclization reactions of some polycyclic aromatic hydrocarbons (PAHs) were performed at the DFT level. Compounds C26H14 and C24H14, which show the connectivity of C60 fullerene fragments, were chosen as suitable models to study the formation of curved derivatives by six‐ or five‐membered ring formation, upon oxidation to their radical cations. Four possible pathways for the cyclization process were considered: a) initial CC bond formation to afford a curved derivative, followed by dehydrogenation; b) homolytic CH cleavage prior to cyclization; c) initial concerted H2 elimination and subsequent cyclization; and d) deprotonation of the radical cations prior to cyclization. Computed reaction and activation energies for these reactions show that direct cyclization from radical cations (pathway a) is the lowest‐energy mechanism. The formation of five‐membered rings is somewhat more favourable than benzannulation. After new cycle formation, homolytic CH dissociation to afford the corresponding cations is the most favourable process. These cations react with H. without barrier to give H2. Intermediate deprotonations are strongly disfavoured. The relatively low activation energies compared with carbon cage rearrangements suggest that ionization of PAHs can be used for the tailored preparation of nonplanar derivatives from suitable precursors.
A Kinetic Study of the Reaction between N,N‐Dimethyl‐p‐toluidine and its Electrogenerated Radical Cation in a Room Temperature Ionic Liquid
Authors: Evans Russell G. , Compton Richard G.
Published: February 2006

The reaction between N,N‐dimethyl‐p‐toluidine (DMT) and the radical cation generated through its one‐electron oxidation has been studied electrochemically in the room temperature ionic liquid N‐methyl‐N‐butylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [Py14][NTf2]. Kinetic information obtained as linear sweep and cyclic voltammetry collected at 5 μm, 10 μm and 0.3 mm diameter platinum disk electrodes over a range of initial substrate concentrations and scan rates spanning five orders of magnitude was complemented by chronoamperometric measurements designed to probe the rate of diffusion. At the fastest scan rates the homogeneous reactions following the initial electron transfer were effectively out‐run, facilitating an assessment of the electrode kinetics using DIGISIM®and a validated Nicholson′s method. Through digital simulation the voltammetry was then shown to be consistent with a mechanism established for the same reaction in acetonitrile, involving dimerisation of the DMT radicals following an initial and rate‐determining proton transfer step. After careful consideration of all parameters, a bimolecular rate constant of (3.4±1.1)×102dm3 mol−1s−1was deduced by fitting the data. This was compared to the equivalent value for acetonitrile and, in light of this, the implications on the viability of ionic liquids for use as alternative mainstream solvents briefly assessed.
Resonant X‐ray Scattering: A Tool for Structure Elucidation in Liquid Crystals
Authors: Gleeson Helen F. , Hirst Linda S.
Published: February 2006

The use of resonant X‐ray scattering to determine structures in liquid crystal systems is surveyed. This powerful experimental technique utilises “forbidden reflections” to determine the subtle differences in interlayer orientation that differentiate several smectic systems. The technique relies on the materials containing an atom to which the X‐ray energy can be tuned, usually sulphur or selenium. Experiments are often carried out on free‐standing films that provide a highly monodomain structure that allows high‐resolution measurements to be made, and, hence, structural details to be determined. Alternatively, resonant scattering has been demonstrated for materials contained in glass devices that permit the application of electric fields to the system, in a manner analogous to that used in liquid crystal devices. The resonant scattering technique provides unequivocal descriptions of the packing in smectic systems, and the way in which the packing is distorted in electric fields. This Minireview describes the principles behind resonant X‐ray scattering, its application to liquid crystals and some of the potential for the future.
Exploring Two‐State Reaction Pathways in the Photodimerization of Cyclohexadiene
Authors: Domingo Luis R. , Pérez‐Prieto Julia
Published: February 2006

The ground‐ (S0 ) and lowest triplet‐state (T1 ) pathways associated with dimerization of cyclohexadiene to give [2+2] and [4+2] cycloadducts have been theoretically studied at the UBLYP and UB3LYP levels of theory with the 6‐31G* basis set. The DFT energies were validated by CCSD(T) single‐point energy calculations. These cycloaddition reactions follow stepwise mechanisms with formation of bis‐allylic biradical (BB) intermediates. In the S0 ground state, the interaction between two cyclohexadiene molecules with formation of BB intermediate IN(S0 ) has a large activation enthalpy of 32.0 kcal mol−1. On the other hand, CC bond‐formation in the lowest triplet state (T1 ) leading to BB intermediate IN(T1 ) has a low activation enthalpy of 5.0 kcal mol−1, but the subsequent ring closure involves a very large activation enthalpy of 43.4 kcal mol−1. Triplet‐to‐singlet intersystem crossing from IN(T1 ) to IN(S0 ) favors cyclization to give the corresponding [2+2] and [4+2] cycloadducts.
Microwave Synthesis of Nanoporous Materials
Authors: Tompsett Geoffrey A. , Conner William Curtis , Yngvesson K. Sigfrid
Published: February 2006

Studies in the last decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented a significantly reduced time for fabricating zeolites, mixed oxide and mesoporous molecular sieves by employing microwave energy. In many cases, microwave syntheses have proven to synthesize new nanoporous structures. By reducing the times by over an order of magnitude, continuous production would be possible to replace batch synthesis. This lowering of the cost would make more nanoporous materials readily available for many chemical, environmental, and biological applications. Further, microwave syntheses have often proven to create more uniform (defect‐free) products than from conventional hydrothermal synthesis. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. We review the many studies that have demonstrated the enhanced syntheses of nanoporous oxides and analyze the proposals to explain differences in microwave reactions. Finally, the microwave reactor engineering is discussed, as it explains the discrepancies between many microwave studies.
Femtosecond Relaxation Dynamics of Solvated Electrons in Liquid Ammonia
Authors: Lindner Jörg , Unterreiner Andreas‐N. , Vöhringer Peter
Published: February 2006

The ultrafast relaxation dynamics of the well‐known solvated electron in liquid ammonia solutions are investigated with femtosecond near‐infrared pump–probe absorption spectroscopy. Immediately after photoexcitation, the dynamic absorption spectrum of the electron is substantially red‐shifted with respect to its stationary spectrum. A subsequent dynamic blue shift of the pump–probe spectrum occurs on a timescale of 150 fs. The data are understood in terms of ground‐state “cooling” and can be quantitatively simulated by an intuitive temperature‐jump model employing a dynamically evolving Kubo line shape for the electronic resonance. A simple estimate implies that, on average, the electron in the liquid is coordinated to six nearest‐neighbor ammonia molecules. An equivalent analysis of the data based on a bubble‐formation/cavity‐contraction mechanism is briefly outlined.
Theoretical Study on the Structures and Electronic Spectra of TCNE2−
Authors: Cuesta Inmaculada García , Sánchez‐Marín José , Sánchez de Merás Alfredo M. J.
Published: February 2006

Investigations into the charge‐separated states and electron‐transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2−has D2dsymmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved.
Enantiodiscrimination between an N‐Acetyl‐L‐cysteine SAM and Proline: An In Situ Spectroscopic and Computational Study
Authors: Bieri Marco , Bürgi Thomas
Published: February 2006

A combination of attenuated total reflection infrared (ATR‐IR) and modulation excitation spectroscopy (MES) is used to study the enantiodiscriminating interactions between proline and a chiral, self‐assembled monolayer (SAM) of N‐acetyl‐L‐cysteine on gold. The N‐acetyl‐L‐cysteine SAM consists of a mixture of protonated and deprotonated molecules. Whereas both species are influenced by adsorbed proline, only the deprotonated molecules are involved in enantiodiscrimination. Density functional theory (DFT) calculations reveal that electrostatics dominates the interaction between the two molecules. By modulating the absolute configuration of proline over the chiral SAM, and a subsequent phase‐sensitive detection of the periodically varying signals in the ATR‐IR spectra, the small spectral differences between the diastereomeric complexes are spotted. The resulting difference spectrum is in qualitative agreement with the spectrum predicted by the DFT calculations.
Defining and maximizing PPT—a novel performance parameter for IEEE 802.11 DCF
Authors: Li Yun , Long Ke‐Ping , Zhao Wei‐Liang
Published: February 2006

Much research has been conducted on saturation throughput of IEEE802.11 DCF, and has led to some improvement. But increasing the successful transmission probability of packet is also important for saving stations' battery energy and decreasing the packet delay. In this paper, we define a new performance parameter, named Product of successful transmission Probability and saturation Throughput (PPT), for 802.11 DCF, which binds successful transmission probability and saturation throughput together. An analysis is given to maximize PPT. An expression of optimal minimum contention windows (CWmin) is obtained analytically for maximizing PPT. For simplicity, we give a name DCF‐PPT to the 802.11 DCF that sets its CWminaccording to this expression. The performance of DCF‐PPT is simulated with different stations in terms of saturation throughput, successful transmission probability and PPT. The simulation results indicate that, compared to 802.11 DCF, DCF‐PPT can significantly increase the PPT and successful transmission probability (about 0.95) on condition that the saturation throughput is not decreased. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Properties of the Ordered Double Perovskite Sr2MnTeO6
Authors: Ortega‐San Martin Luis , Chapman Jon P. , Lezama Luis , Sánchez Marcos Jorge , Rodríguez‐Fernández Jesús , Arriortua María I. , Rojo Teófilo
Published: February 2006

The ordered double perovskite Sr2MnTeO6 was prepared by the freeze‐drying method. The nuclear and magnetic structures were determined by both X‐ray and neutron (D2B and D1B) powder diffraction. A distorted, double perovskite structure type described by the monoclinic P121/n1 space group is observed at room temperature and down to 4 K. The room temperature EPR spectrum shows an isotropic signal centered at a g value of 1.998 indicating that manganese ions are in the +2 oxidation state. At low temperature the EPR signal broadens as the exchange and dipolar interactions between Mn2+ cations increase. Below 25 K no signal is observed, indicating that the sample is magnetically ordered. The dc magnetic susceptibility shows the existence of antiferromagnetic interactions with an ordering temperature around 20 K. A sharp λ‐type anomaly observed at 19 K in the specific heat curve and refinement of low‐temperature neutron diffraction data confirm the presence of a three‐dimensional, antiferromagnetic ordered structure with an ordering temperature of ca. 23 K. The propagation vector of the magnetic structure is k = [0,0,0], yielding a type I antiferromagnetic ordering between Mn2+ (S = 5/2) cations. At 2 K, each manganese ion is antiferromagnetically aligned to 8 out of 12 nearest‐neighbors at an approximate distance of 5.6 Å. This magnetic structure can be viewed as being composed of ferromagnetic arrangement of Mn2+ moments in the ab plane, coupled antiferromagnetically along the c axis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Coordination Dependence of Magnetic Properties within a Family of Related [FeII2] Complexes of a Triazine‐Based Ligand
Authors: Quesada Manuel , de Hoog Paul , Gamez Patrick , Roubeau Olivier , Aromí Guillem , Donnadieu Bruno , Massera Chiara , Lutz Martin , Spek Anthony L. , Reedijk Jan
Published: February 2006

The coordination chemistry of the polydentate ligand 2,4,6‐tris(dipyridin‐2‐ylamino)‐1,3,5‐triazine (dpyatriz) with FeII has been explored, leading through variation of the counterion and the solvent system to the preparation of three different dinuclear complexes: [Fe2(dpyatriz)2(H2O)2(CH3CN)2](ClO4)4 (1), [Fe2(dpyatriz)2(H2O)2(CH3OH)2](BF4)4 (2) and [Fe2(dpyatriz)2Cl2](CF3SO3)2 (3). The X‐ray structure of these compounds has revealed that besides the difference in the noncoordinated anion, complex 1 differs from complex 2 only in the nature of the terminal ligands. Bulk magnetisation studies and Mössbauer spectroscopy have shown that such a subtle difference produces a change to the crystal field on the metal atoms, originating an important disparity of the magnetic behaviour. Thus, complex 1 experiences a partial spin crossover centred at approximately 265 K, whereas complex 2 shows two uncoupled high‐spin FeII centres over most of the studied temperature range, experiencing the effect of very weak antiferromagnetic coupling and/or single‐ion zero‐field splitting at low temperature. By contrast, complex 3, in which the triazine ring of dpyatriz is coordinated for the first time, displays (very uncommon) ferromagnetic coupling between both FeII ions within the molecule, leading to an S = 4 spin ground state. A fit of the experimental data led to a value of the coupling constant of J = +0.23 cm–1 (using H =–2JS1S2 as the convention for the exchange Hamiltonian) and provided an estimation of D = 0.63 cm–1 for the ground‐state axial zero‐field splitting parameter. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
The Influence of Ring Size on the Selectivity of Phosphorus Heterocycle Aminolysis in the Presence of Water or Alcohols – Case of 2‐Oxo‐ or 2‐Thioxo‐3‐sulfonyl‐1,3,2‐oxazaphosphorinanes
Authors: Dujols Frédéric , Mulliez Michel
Published: February 2006

Seven phosphorus heterocycles 2 were synthesized in one step by condensing PIV dichlorides 3 with N‐sulfonyl‐3‐aminopropanols 4. In the presence of water, they react selectively with the less bulky amines. No change in selectivity of aminolysis was observed when using these six‐membered heterocycles 2 instead of their five‐membered analogs 1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Influence of the Number and Geometry of Binding Sites on Host–Guest Affinity: Imidazolium‐Substituted Receptor Molecules for Small Inorganic Anions
Authors: Fahlbusch Tilmann , Frank Markus , Schatz Jürgen , Schmaderer Harald
Published: February 2006

The influence of the number and relative geometry of the binding sites on the binding of spherical and tetragonal inorganic anions (Cl–, Br–, H2PO4–, and HSO4–) has been studied by using imidazolium salts based on benzene and calix[4]arenes. Binding constants in DMSO were found to be in the range of 200–2000 L mol–1. Three or four binding sites (2b–4b) lead to the nonselective binding of all anions indicating the decisive influence of the number of possible binding positions; binding constants of approximately 2000 for H2PO4–, 1000 for HSO4–, 900 for Cl–, and 800 L mol–1 for Br– were obtained. Benzene‐ (1b) and calixarene‐based (5b) bis(imidazolium) salts exhibited a high selectivity towards H2PO4–/HSO4– and Cl–/Br– indicating that for the complexation of H2PO4– and Cl– two binding sites are necessary, and for Br– and HSO4– at least three. In this case, selectivity could be obtained by simple variation of the number of identical binding positions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Palladium‐Catalyzed Suzuki–Miyaura Cross‐Coupling Using Phosphinous Acids and Dialkyl(chloro)phosphane Ligands
Authors: Wolf Christian , Ekoue‐Kovi Kekeli
Published: February 2006

The use of eleven palladium complexes having monomeric and μ‐chloro‐bridged dimeric structures and either bulky dialkyl‐ and diarylphosphinous acid ligands (POPd, POPd‐Br, POPd1, POPd2, POPd6, POPd7, Ph1‐Phoxide) or dialkyl(chloro)phosphane ligands (PXPd, PXPd2, PXPd6, PXPd7) for Suzuki–Miyaura coupling reactions has been evaluated. Screening and optimization of catalyst loading, solvent, temperature, and base showed that excellent results can be obtained with electron‐deficient and electron‐rich aryl iodides, bromides, and chlorides in the presence of 2.5 mol‐% of palladium–phosphinous acid POPd, (tBu2POH)2PdCl2, in 1,4‐dioxane using cesium carbonate as base. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Recent Advances in Asymmetric Nitroso Diels–Alder Reactions
Authors: Yamamoto Yuhei , Yamamoto Hisashi
Published: February 2006

During the past decade, the nitroso Diels–Alder (NDA) reaction has become more practical tool for organic synthesis, and a numbers of important compounds have been synthesized using this method. Until recently, no reports on a catalytic asymmetric version of this reaction had been reported; the major issues were the high reactivity of nitroso compounds and their chemical properties. This microreview outlines recent advances in the area of asymmetric NDA reaction following the review by Streith and Defoin in 1994. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Evaluating probability forecasts in terms of refinement and strictly proper scoring rules
Authors: Krämer Walter
Published: February 2006

This note gives an easily verified necessary and sufficient condition for one probability forecaster to empirically outperform another one in terms of all strictly proper scoring rules. Copyright © 2006 John Wiley & Sons, Ltd.
Infiltration pattern in a regolith–fractured bedrock profile: field observation of a dye stain pattern
Authors: Kim Jae Gon , Lee Gyoo Ho , Lee Jin‐Soo , Chon Chul‐Min , Kim Tack Hyun , Ha Kyoochul
Published: February 2006

We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two overburdens (OB1 and OB2), a buried rice paddy soil (PS), two texturally distinctive weathered materials (WM1 and WM2) and a fractured sedimentary rock (BR), using a Brilliant Blue FCF dye tracer. A black‐coloured coating in conducting fractures in WM1, WM2 and BR was analysed by X‐ray diffraction and scanning electron microscopy. The dye tracer penetrated to greater than 2 m depth in the profile. The macropore flow and saturated interflow were the major infiltration patterns in the profile. Macropore flow and saturated interflow were observed along fractures in WM1, WM2 and BR and at the dipping interfaces of PS–WM1, PS–WM2 and PS–BR respectively. Heterogeneous matrix flow occurred in upper overburden (OB1) and PS. Compared with OB1, the coarser textured OB2 acted as a physical barrier for vertical flow of water. The PS with low bulk density and many fine roots was another major conducting route of water in the profile. Manganese oxide and iron oxide were positively identified in the black coating material and had low crystallinity and high surface area, indicating their high reactivity with conducting contaminants. Copyright © 2006 John Wiley & Sons, Ltd.