bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unifying catalyst size dependencies in floating catalyst and supported catalyst carbon nanotube synthesis
Authors: Rümmeli M. H. , Schäffel F. , Löffler M. , Kramberger C. , Adebimpe D. , Gemming T. , Ayala P. , Rellinghaus B. , Schultz L. , Büchner B. , Pichler T. 
Published: May 2008

AbstractDetailed studies with floating catalyst systems, namely, laser evaporation and laser assisted chemical vapour deposition (CVD), enabled the development of a catalyst volume to surface area model which dictates if a single walled carbon nanotube (SWCNT) can emerge or not. The model predicts differences in the case of supported catalysts. It predicts multi‐walled carbon nanotubes (MWCNT) will also emerge. This difference arises due to the catalyst/support interaction. Further, the model says that for supported catalysts the catalyst volume to surface area ratio also regulates the tube diameter and the number of walls the nanotube will have. In this contribution, experimental CVD data using predefined catalyst particles on a support are presented and compared with floating catalyst data. The findings for supported catalysts are in full agreement with those predicted by the catalyst surface area to volume model. The data show unified catalyst size dependencies for floating catalyst and supported catalyst carbon nanotube synthesis routes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large‐scale “atomistic” approach to discrete‐dopant‐induced characteristic fluctuations in silicon nanowire transistors
Authors: Li Yiming , Hwang Chih‐Hong , Huang Hsuan‐Ming 
Published: May 2008

AbstractNanowire fin‐typed field effect transistors (FinFETs) are ultimate structures and potential candidates for next generation nanoelectronic devices. Due to the limitation of manufacturability, nanowire transistors with a perfect gate structure (i.e., a surrounding gate with 100% gate‐coverage ratio) theoretically are not always guaranteed. Impact of the discrete dopants on device performance is crucial in determining the behaviour of nanoscale semiconductor devices. The immunity of nanowire transistor against random discrete‐dopant‐induced fluctuation may suffer from the variation of gate‐coverage‐ratio. Therefore, in this paper, we for the fist time study the impact of non‐ideal gate coverage on immunity against random‐dopant‐induced fluctuations for nanowire FinFETs. A 3D statistically sound “atomistic” approach for analyzing random‐dopant effect in nanodevice is presented. Discrete dopants are statistically positioned into the channel region to examine associated carrier transportation characteristics, concurrently capturing “dopant concentration variation” and “dopant position fluctuation”. Our results confirm that the influence of non‐ideal gate coverage disturbs the channel controllability of nanowire FinFETs and thus decreases the immunity against discrete‐dopant‐induced fluctuation. This study provides an insight into the problem of fluctuation in nanowire transistors and shows the importance of gate‐coverage ratio on device's immunity against discrete‐dopant‐induced fluctuation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lifetime fluctuations of a single emitter in a disordered nanoscopic system: The influence of the transition dipole orientation
Authors: Froufe‐Pérez L. S. , Carminati R. 
Published: May 2008

AbstractWe study the fluctuations of the fluorescence decay rate of a single emitter in a random cluster of nanoparticles, in a regime dominated by near‐field scattering. Configurational changes of the environment induce statistical changes of the decay rate. Two regimes are considered which differ in terms of transition dipole orientation. In one regime, the orientation of the transition dipole is assumed to remain constant while the configuration of the cluster changes randomly. In another regime, the orientation of the transition dipole is assumed unknown and continuously averaged over the three directions of space. Using exact numerical simulations and a simple analytical model, we show that the statistical distributions of the spontaneous decay rate are substantially different in both regimes. In both cases, the decay rate fluctuations are strongly dependent on the level of absorption at the nanoscale. We discuss the impact of this result in terms of imaging in complex media. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low energy properties of even‐legged d ‐dimensional quantum spin systems: a variational approach
Authors: Richert Jean , Gühne Otfried 
Published: May 2008

AbstractWe develop a variational formalism in order to study the gap structure in the spectrum of frustrated quantum spin systems. We introduce a trial wave function of a two‐leg ladder with one spin 1/2 on each site. The domains in which the wave function behaves realistically are determined. In these domains the spectra show a finite energy gap between the ground state and excited states. Under some approximations which are discussed the result can be extended to 2d and higher dimensional systems with an even number of rows. The gap vanishes for specific values of the coupling strengths which correspond to the location of phase transitions. In a second step we introduce quantitative estimates of the relevance of the variational ansatz which rest on the entanglement concept. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ab initio study of indium clusters on the Ge(5 × 5) wetting layer of Si(111)‐7 × 7
Authors: Psiachos D. , Stott M. J. 
Published: May 2008

AbstractAn ab initio study of In adsorbed on the Ge(111)‐5 × 5 wetting layer, which forms on top of a Si(111)‐7 × 7 substrate, is reported. A recent experiment showed that small In clusters form on this surface with some regularity but their exact size and structure are still unknown. Results are presented of a detailed investigation of the structural and electronic properties of a single adsorbed In atom and small candidate In clusters, carried out using density‐functional calculations. Using density difference plots and population analysis, the mechanisms of bonding for different In structures are explained. Comparison of total energies shows that for a single In atom the faulted half cell is marginally preferred to the unfaulted half, and little tendency for clustering of In is found for low coverages. Both of these conclusions seem to be at odds with the experimental results and possible explanations are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐phonon Umklapp process in silicon nanowires with square cross sections
Authors: Lü Xiang 
Published: May 2008

AbstractWe have evaluated the relaxation rate of silicon (Si) nanowires with square cross sections by considering the three‐phonon Umklapp process. The calculated model takes into account the energy gap between the phonon modes due to acoustic phonon confinement. It is found that the relaxation rate increases with increasing nanowire side length at small side length, and shows a peak behavior at about 5 nm before falling off at large side length. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability conditions for the coupled cluster equations
Authors: Szakács Péter , Surján Péter R. 
Published: May 2008

AbstractThe coupled cluster (CC) equations are studied from the point of view of the stability of their solution. The nonlinear nature of these equations may lead to undesired iteration properties including chaotic solutions. Iterations of various types (convergent, oscillatory, chaotic or divergent) are identified by the eigenvalues of the stability (Jacobi) matrix at the fixed points. Explicit (orbital) form of the stability matrix is obtained for the CCSD case, and the various iteration domains are investigated as a function of the control (damping) parameter of the CC iteration. The case of the BeH2 molecule at various nuclear arrangements is chosen as a numerical example. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Towards a universal product ion mass spectral library – reproducibility of product ion spectra across eleven different mass spectrometers
Authors: Hopley Chris , Bristow Tony , Lubben Anneke , Simpson Alec , Bull Elaine , Klagkou Katerina , Herniman Julie , Langley John 
Published: May 2008

AbstractProduct ion spectra produced by collision‐induced dissociation (CID) in tandem mass spectrometry experiments can differ markedly between instruments. There have been a number of attempts to standardise the production of product ion spectra; however, a consensus on the most appropriate approach to the reproducible production of spectra has yet to be reached. We have previously reported the comparison of product ion spectra on a number of different types of instruments – a triple quadrupole, two ion traps and a Fourier transform ion cyclotron resonance mass spectrometer (Bristow AWT, Webb KS, Lubben AT, Halket JM. Rapid Commun. Mass Spectrom. 2004; 18: 1). The study showed that a high degree of reproducibility was achievable. The goal of this study was to improve the comparability and reproducibility of CID product ion mass spectra produced in different laboratories and using different instruments. This was carried out experimentally by defining a spectral calibration point on each mass spectrometer for product ion formation. The long‐term goal is the development of a universal (instrument independent) product ion mass spectral library for the identification of unknowns.The spectra of 48 compounds have been recorded on eleven mass spectrometers: six ion traps, two triple quadrupoles, a hybrid triple quadrupole, and two quadrupole time‐of‐flight instruments. Initially, 4371 spectral comparisons were carried out using the data from eleven instruments and the degree of reproducibility was evaluated. A blind trial has also been carried out to assess the reproducibility of spectra obtained during LC/MS/MS.The results suggest a degree of reproducibility across all instrument types using the tuning point technique. The reproducibility of the product ion spectra is increased when comparing the tandem in time type instruments and the tandem in space instruments as two separate groups. This may allow the production of a more limited, yet useful, screening library for LC/MS/MS identification using instruments of the same type from different manufacturers. Copyright © 2008 John Wiley & Sons, Ltd.
Interactions of nucleosides with CrO and Cr3+ as studied by electrospray ionization mass spectrometry
Authors: Frańska Magdalena , Gierczyk Karolina 
Published: May 2008

AbstractThe interactions of CrO and Cr3+ with nucleosides studied by electrospray ionization mass spectrometry (ESI‐MS) are reported. In water, the nucleosides which do not contain the NH2 group form the unstable [M+HCrO4]− anion. In the presence of a reducing agent, namely methanol, chromate anion forms stable complexes with nucleosides, [M+CH3CrO4]− anions. The fragmentation of [M+CH3CrO4]− anions involve elimination of the methanol molecule. Chromium cation‐nucleoside complexes were not observed in water. In methanol solutions, adenosine and cytidine form [(M−H)+CrOCH3]+ and [(M−H)2+Cr]+ ions. Most probably, deprotonated imine tautomers form complexes in which a metal cation is simultaneously coordinated by two nitrogen atoms. Complexes containing chloride anions and a few methanol molecules were observed for other nucleosides. Guanosine and inosine form doubly charged ions of the type [M2+CrOCH3]2+ that probably contain a bond between the oxygen atom and the chromium cation, (HN(1)C(6)O)Cr3+). Copyright © 2008 John Wiley & Sons, Ltd.
Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size
Authors: Wiedemann‐Bidlack Felicitas B. , Colman Albert S. , Fogel Marilyn L. 
Published: May 2008

AbstractModern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology‐based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag3PO4 crystals by using a strongly buffered, moderate‐temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as δ18O, V‐SMOW scale) is typically 0.2–0.3‰ (1 s.d.) on samples as small as 300 µg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen. Copyright © 2008 John Wiley & Sons, Ltd.
Characterization of metabolites of a novel histamine H2‐receptor antagonist, lafutidine, in human liver microsomes by liquid chromatography coupled with ion trap mass spectrometry
Authors: Wang Yuya , Chen Xiaoyan , Li Qiang , Zhong Dafang 
Published: May 2008

AbstractThe metabolism of lafutidine in human liver microsomes was studied using liquid chromatography/ion trap mass spectrometry with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources. A total of 14 metabolites were identified including hydroxylated lafutidine and sulfonyl lafutidine as the major metabolites. The chemical properties and the MSn behaviors of lafutidine and all of its identified metabolites were studied in detail. Lafutidine had a fragmentation pattern as a result of homolytic bond cleavage in the MS/MS spectrum. This cleavage can form an odd‐electron ion with the loss of furan‐2‐ylmethyl radical (−81 Da with a proton shift), which then sequentially loses neutral groups in the MS3 spectrum. This fragmentation sequence was also observed from the metabolites with the unchanged sulfinyl moiety. When the sulfinyl moiety was oxidized to the sulfonyl moiety, this fragmentation sequence did not exist, which could be used to identify S‐oxidation metabolites of lafutidine. In general, N‐oxides could produce distinct [M+H–O]+ ions under LC/APCI‐MS due to the thermal activation in the desolvation region of the API source, which could be used to identify N‐oxidation metabolites of lafutidine. In order to avoid the possibility of false positives, the MS/MS spectrum of the [M+H–O]+ ion was compared with that of the non‐N‐oxidation metabolites or parent drug in the APCI source. If they were consistent, the structure could be finally confirmed. The exact masses for lafutidine and lafutidine N‐oxide fragment ions were determined using an LTQ/Orbitrap mass spectrometer. Copyright © 2008 John Wiley & Sons, Ltd.
Characterization of compounds from the roots of Saposhnikovia divaricata by high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry
Authors: Kang Jie , Sun Jiang‐Hao , Zhou Lei , Ye Min , Han Jian , Wang Bao‐Rong , Guo De‐An 
Published: May 2008

AbstractIn this study, four types of compounds including coumarins, chromones, furoylmethyl amino acid derivative and benzofuran glycoside were isolated from the roots of Saposhnikovia divaricata. The electrospray ionization (ESI) mass spectral fragmentation pathways of these compounds were proposed. In particular, the ESI‐MSn fragmentation behavior of linear dihydrofurocoumarins, dihydrofuro‐ and dihydropyranochromones were deduced in detail. For the linear dihydrofurocoumarins, the fragmentation was triggered by the initial loss of the C‐4′ substituting group. Then, the characteristic ions were observed followed by the losses of 15, 18, 28 and 46 Da. It is noteworthy that the elimination of H2O (18 Da) from the cleavage of the dihydrofuran ring is reported for the first time. For the linear dihydrofurochromones, characteristic eliminations of 18, 48 and 72 Da were observed. The loss of 18 Da could arise from two different fragmentation pathways, and the observed ion was composed of a mixture of two different structural ions. For the linear dihydropyranochromones, it was found that the dihydropyran ring was converted into the pyran ring by the elimination of the C‐3′ substituting group. This fragmentation was followed by the diagnostic losses of 18, 28, 42 and 54 Da in tandem mass spectrometry. The above fragmentation rules were successfully applied for the analysis of the chemical constituents of the roots of Saposhnikovia divaricata. A total of 32 compounds were identified or tentatively characterized by HPLC/DAD/ESI‐MSn. Among them, eight compounds were new and seven compounds were reported from that genus for the first time. Copyright © 2008 John Wiley & Sons, Ltd.
New features on the fragmentation and differentiation of C‐glycosidic flavone isomers by positive electrospray ionization and triple quadrupole mass spectrometry
Authors: Abad‐García Beatriz , Garmón‐Lobato Sergio , Berrueta Luis A. , Gallo Blanca , Vicente Francisca 
Published: May 2008

AbstractSix flavone mono‐C‐glucosides, four standards (β‐D‐glucopyranosyl‐(1 → C‐6)‐ and ‐(1 → C‐8)‐ apigenin and luteolin) and two others from lemon juice (β‐D‐glucopyranosyl‐(1 → C‐6)‐ and ‐(1 → C‐8)‐diosmetin) have been studied in order to analyze their fragmentation patterns. Initial separation was carried out using high‐performance liquid chromatography with diode‐array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface and a triple quadrupole mass spectrometer. Several systematic differences between collision‐induced dissociation tandem mass (CID‐MS/MS) spectra of C‐6‐ and C‐8‐isomers have been found and some general guidelines and two new diagnostic product ions have been proposed for the differentiation of C‐6‐ and C‐8‐flavonoid glycosides. These results have been successfully applied to the characterization of two flavone C‐glycosides found in lemon juice, and mass spectra of a flavone di‐C‐glycoside detected in lemon juice have been studied and interpreted. Copyright © 2008 John Wiley & Sons, Ltd.
A simple and universal method for the separation and identification of phospholipid molecular species
Authors: Retra Kim , Bleijerveld Onno B. , van Gestel Renske A. , Tielens Aloysius G.M. , van Hellemond Jaap J. , Brouwers Jos F. 
Published: May 2008

AbstractOne of the major challenges in lipidomics is to obtain as much information about the lipidome as possible. Here, we present a simple yet universal high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method to separate molecular species of all phospholipid classes in one single run. The method is sensitive, robust and allows lipid profiling using full scan mass spectrometry, as well as lipid class specific scanning in positive and negative ionisation mode. This allows high‐throughput processing of samples for lipidomics, even if different types of MS analysis are required. Excellent separation of isobaric and even isomeric species is achieved, and original levels of lyso‐lipids can be determined without interference from lyso‐lipids formed from diacyl species by source fragmentation. As examples of application of this method, more than 400 phospholipid species were identified and quantified in crude phospholipid extracts from rat liver and the parasitic helminth Schistosoma mansoni. Copyright © 2008 John Wiley & Sons, Ltd.
Rapid screening of clenbuterol in urine samples by desorption electrospray ionization tandem mass spectrometry
Authors: Lin Ziqing , Zhang Sichun , Zhao Mengxia , Yang Chengdui , Chen Depu , Zhang Xinrong 
Published: May 2008

AbstractRapid screening of clenbuterol in urine was performed by combining desorption electrospray ionization (DESI) and tandem mass spectrometry (MS/MS). Optimization experiments were carried out including the selection of substrates, spray solutions, nebulizing gas pressures, high‐voltage power supplies and flow rates of spray solution. The limit of detection (LOD), defined as the lowest quantity that can be detected, was 5.0 pg for the pure compound. Using DESI coupled with solid‐phase extraction (SPE), the linear response range was from 10 to 400 ng/mL (R2 = 0.993) and the concentration LOD for urine sample was 2.0 ng/mL. The analysis for one spiked urine sample was achieved within 4 min. In addition to the fast analysis speed, MS/MS provided structural information for the confirmation of clenbuterol. Urine samples from different people were investigated and the recoveries were within 100 ± 20%. The developed method can potentially be used for screening of clenbuterol in doping control. Copyright © 2008 John Wiley & Sons, Ltd.
Composition of the seed bank in drawdown areas of Navigation Pool 8 of the Upper Mississippi River
Authors: Kenow Kevin P. , Lyon James E. 
Published: May 2008

AbstractIn an effort to enhance aquatic plant production and habitat diversity on the Upper Mississippi River (UMR), resource managers considered water level reduction as a management tool to increase the area of emergent and submersed aquatic vegetation by natural seed germination. To quantify the availability of seed, we assessed the potential seed bank of selected areas of Navigation Pool 8 of the UMR from substrate samples collected in spring 2000. We tested these samples for viable seed content under four hydrologic conditions: dry, moist, shallow flooded and submerged. Forty‐seven species were identified in the seed bank, including 27 obligate wetland, 10 facultative wetland and 7 upland species. Dominant taxa within the seed bank included Sagittaria spp., Lindernia dubia, Zosterella dubia, Cyperus spp., Eragrostis spp. and Leersia oryzoides. Of the four hydrologic treatments, moist substrates had the greatest species diversity and were the most productive, yielding an average density of 1420 seedlings m−2. Emergent and submersed aquatic species were widely distributed, each type occurring in more than 90% of the samples. Timing of seedling germination varied among species and has implications for scheduling drawdowns to promote establishment of desired species. Seed bank results were correlated with the vegetation response on substrates exposed during a reduction of water levels of Pool 8 during summer 2001. Experimentally determining the composition and viability of seed banks from drawdown areas provides information useful in predicting the types of vegetation that may develop on exposed substrates. Further, these findings provide resource managers a better understanding of the potential for achieving desired vegetation response through water level reductions. Published in 2008 by John Wiley & Sons, Ltd.