bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coronal “wave”: A signature of the mechanism making CMEs largescale in the low corona?
Authors: Attrill G.D.R. , Harra L.K. , van Driel‐Gesztelyi L. , Démoulin P. , Wülser J.‐P. 
Published: September 2007

AbstractWe analyse one of the first coronal waves observed by STEREO/EUVI associated with a source region just behind the limb, NOAA 10940. We apply the coronal “wave” model proposed by Attrill et al. (2007) to explain the evolution of the observed bright fronts, thereby arguing that the bright fronts and dimmings are due to magnetic reconnections between the expanding CME core and surrounding magnetic structures. We offer a discussion showing that this model provides a mechanism via which CMEs, expanding from a small source region can naturally become large‐scale in the low corona. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulations of fast and slow coronal mass ejections
Authors: Török T. , Kliem B. 
Published: September 2007

AbstractSolar coronal mass ejections (CMEs) show a large variety in their kinematic properties. CMEs originating in active regions and accompanied by strong flares are usually faster and accelerated more impulsively than CMEs associated with filament eruptions outside active regions and weak flares. It has been proposed more than two decades ago that there are two separate types of CMEs, fast (impulsive) CMEs and slow (gradual) CMEs. However, this concept may not be valid, since the large data sets acquired in recent years do not show two distinct peaks in the CME velocity distribution and reveal that both fast and slow CMEs can be accompanied by both weak and strong flares. We present numerical simulations which confirm our earlier analytical result that a flux‐rope CME model permits describing fast and slow CMEs in a unified manner. We consider a force‐free coronal magnetic flux rope embedded in the potential field of model bipolar and quadrupolar active regions. The eruption is driven by the torus instability which occurs if the field overlying the flux rope decreases sufficiently rapidly with height. The acceleration profile depends on the steepness of this field decrease, corresponding to fast CMEs for rapid decrease, as is typical of active regions, and to slow CMEs for gentle decrease, as is typical of the quiet Sun. Complex (quadrupolar) active regions lead to the fastest CMEs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variability and evolution in various classes of post‐AGB stars
Authors: Şahin T. , Jeffery C.S. 
Published: September 2007

AbstractWe aim to compare properties of early‐type post‐asymptotic giant‐branch (post‐AGB) stars, including normal first‐time B‐type post‐AGB stars, and extreme helium stars (EHes). Hipparcos photometry for 12 post‐AGB stars and 7 EHe stars has been analyzed; 5 post‐AGB stars are clearly variable. The Hipparcos data are not sufficiently sensitive to detect variability in any of the EHes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Statistical technique to study the connection between large‐scale structures in the ISM and low‐mass star formation
Authors: Kiss Z.T. 
Published: September 2007

AbstractApplying a color index selection the Point Source Catalog of the Two Micron All Sky Survey (2MASS PSC) has been searched for Classical T Tauri (CTT) stars in the 2nd and 3rd Galactic quadrant based on their apparent KS excess. The selection resulted in 3872 reliable CTT candidates. The obtained CTT sample is extended enough for statistical examination of the inhomogeneities in their distribution due to correlation with structures in the ISM, like infrared loops. A correlation was observed between the presence of dust loops and the CTT density. The latter shows an excess on loops with respect to that expected from random fluctuation in a homogeneous distribution matching with the observed overall distribution. Monte Carlo simulations were used to show the significance of the excess. The results imply that the formation of a fraction of CTTs was triggered during the loop formation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pulsation and orbit of AU Pegasi
Authors: Jurkovic M. , Szabados L. , Vinkó J. , Csák B. 
Published: September 2007

AbstractAU Pegasi is a pulsating star in a spectroscopic binary system with an orbital period of 53.26 days. Between 1960 and 1990 an extremely rapid period increase was observed in the value of the pulsation period, but in the last 15 years the observation show that the period set in 2.411 days. Fourier analysis of photometric data obtained during the ASAS project and those taken at the Piszkéstető Mountain Station of the Konkoly Observatory during 1994–2005 indicate that AU Pegasi is pulsating in two modes simultaneously, and the ratio of the frequencies of the two modes is 0.706, a value common for double‐mode classical Cepheids. A careful analysis of other photometric observations obtained during the era of the strong period increase also revealed existence of a second mode. This may suggest that this star is not a Type II Cepheid, despite its galactic position. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
More frequencies of KUV 02464+3239
Authors: Bognár Zs. , Paparó M. , Már A. , Kerekes Gy. , Pápics P. , Molnár L. , Plachy E. , Sztankó N. , Bokor E. 
Published: September 2007

AbstractPreliminary results on KUV 02464+3239, a pulsating DA white dwarf are presented. Located near the red edge of the DAV instability strip, KUV 02464+3239 shows large amplitude and long period pulsation modes. Up to now only one mode was known from a 50‐minute‐long light curve. Our more extended observations allowed the identification of three additional frequencies. The presence of previously known harmonics were confirmed and weak subharmonics are also noticeable at some parts of the light curve. This suggests the dominance of nonlinear pulsation effects from time to time. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multidimensional indexing tools for the virtual observatory
Authors: Csabai I. , Dobos L. , Trencséni M. , Herczegh G. , Józsa P. , Purger N. , Budavári T. , Szalay A.S. 
Published: September 2007

AbstractThe last decade has seen a dramatic change in the way astronomy is carried out. The dawn of the the new microelectronic devices, like CCDs has dramatically extended the amount of observed data. Large, in some cases all sky surveys emerged in almost all the wavelength ranges of the observable spectrum of electromagnetic waves. This large amount of data has to be organized, published electronically and a new style of data retrieval is essential to exploit all the hidden information in the multiwavelength data. Many statistical algorithms required for these tasks run reasonably fast when using small sets of in‐memory data, but take noticeable performance hits when operating on large databases that do not fit into memory. We utilize new software technologies to develop and evaluate fast multidimensional indexing schemes that inherently follow the underlying, highly non‐uniform distribution of the data: they are layered uniform indices, hierarchical binary space partitioning, and sampled flat Voronoi tessellation of the data. These techniques can dramatically speed up operations such as finding similar objects by example, classifying objects or comparing extensive simulation sets with observations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
J1128+592: a highly variable IDV source
Authors: Gabányi K.É. , Marchili N. , Krichbaum T.P. , Britzen S. , Fuhrmann L. , Witzel A. , Zensus J.A. , Müller P. , Liu X. , Song H.G. , Han J.L. , Sun X.H. 
Published: September 2007

AbstractShort time‐scale radio variations of compact extragalactic radio quasars and blazars known as IntraDay Variability (IDV) can be explained in at least some sources as a propagation effect; the variations are interpreted as scintillation of radio waves in the turbulent interstellar medium of the Milky Way. One of the most convincing observational arguments in favor of a propagation‐induced variability scenario is the observed annual modulation in the characteristic time scale of the variation due to the Earth's orbital motion. So far there are only two sources known with a well‐constrained seasonal cycle. Annual modulation has been proposed for a few other less well‐documented objects. However, for some other IDV sources source‐intrinsic structural variations which cause drastic changes in the variability time scale were also suggested. J1128+592 is a recently discovered, highly variable IDV source. Previous, densely time‐sampled flux‐density measurements with the Effelsberg 100‐m radio telescope (Germany) and the Urumqi 25‐m radio telescope (China), strongly indicate an annual modulation of the time scale. The most recent 4 observations in 2006/7, however, do not fit well to the annual modulation model proposed before. In this paper, we investigate a possible explanation of this discrepancy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Front‐ vs. back‐illuminated CCD cameras for photometric surveys: a noise budget analysis
Authors: Crouzet N. , Guillot T. , Fressin F. , Blazit A. , the A STEP team  
Published: September 2007

AbstractExoplanetary transit and stellar oscillation surveys require a very high precision photometry. The instrumental noise has therefore to be minimized. First, we perform a semi‐analytical model of different noise sources. We show that the noise due the CCD electrodes can be overcome using a Gaussian PSF (Point Spread Function) of full width half maximum larger than 1.6 pixels. We also find that for a PSF size of a few pixels, the photometric aperture has to be at least 2.5 times larger than the PSF full width half maximum. Then, we compare a front‐ with a back‐illuminated CCD through a Monte‐Carlo simulation. Both cameras give the same results for a PSF full width half maximum larger than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica Search for Transiting Extrasolar Planets) project. As a result, we choose a front‐illuminated camera for A STEP because of its better resolution and lower price, and we will use a PSF larger than 1.6 pixels. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended X‐ray Absorption Fine Structure (EXAFS) Studies of Hydroxo(oxo)iron Aggregates and Minerals, and a Critique of their Use as Models for Ferritin
Authors: Heath Sarah L. , Charnock John M. , Garner C. David , Powell Annie K. 
Published: September 2007

AbstractStructural models for the hydroxo(oxo)iron core of ferritin include extended mineral structures and cluster systems such as [Fe11O6(OH)6(O2CPh)15] ( = Fe11) and two clusters that crystallise in the same lattice (compound 1), namely, [Fe17(μ3‐O)4(μ3‐OH) 6(μ2‐OH)10(heidi)8(H2O)12]3+and[Fe19(μ3‐O)6(μ3‐OH)6(μ2‐OH)8(heidi)10(H2O)12]1+. The suitability of these systems as models for the structure of the core of ferritin has been tested by comparing their Fe K‐edge EXAFS and X‐ray crystallographic results with the Fe K‐edge EXAFS data on horse spleen ferritin. The interpretative procedure for the EXAFS analysis was optimised by using the X‐ray crystallographic data for compound 1 as a basis. This protocol was then used to interpret the Fe K‐edge EXAFS spectra of α‐ and γ‐Fe(O)OH and to reinterpret that previously recorded for horse spleen ferritin. The published Fe K‐edge EXAFS data on Fe11 were also considered. The Fe ⃛Fe distances provide a clear indication of the nature of the hydroxo(oxo)iron assembly. It was found that the iron–iron interactions are the most reliable guide. Clusters are shown to be more appropriate than infinite lattices as structural models for the core of ferritin.
From Quinidine to new Enantiopure Materials–Tricyclic Allylic N,O‐Acetals and a Stereospecific, Onepot Conversion of 1,2‐Secondary, Tertiary Diols into Spiroepoxides
Authors: von Riesen Cornelius , Jones Peter G. , Hoffmann H. M. R. 
Published: September 2007

AbstractHydrobromination of quinidine (1) with fuming HBr furnished diastereomeric secondary bromides 2a and 2b in 82% yield. After acetylation the resulting bromides 2a–Ac and 2b–Ac could be separated and converted stereospecifically into ethylidene rubanes Z)‐4 and (E)‐4, respectively. cis‐Dihydroxylation of (Z)‐olefin 4 with OsO4 was shown to be feasible by two catalytic variants, giving the two diastereomeric diols 5a and 5b, separable by chromatography. A simple onepot procedure was developed for converting the sterically hindered 1,2‐secondary, tertiary diols stereospecifically into spiroepoxides (5a 6a‐Ac; 5b 6b‐Ac). Our procedure involves overall inversion of configuration. The procedure complements the Kolb–Sharpless route to epoxides from 1,2‐disecondary diols with overall retention of configuration. The other two diastereomeric spiroepoxides 6c and 6d were prepared in one pot under different conditions (chloramine T, then alkali). Two unprecedented tricyclic allylic N,O‐acetals (Z)‐7 and (E)‐7 were also obtained. The structure of spiroepoxide 6c (as a CH2Cl2 monosolvate) and of tricyclic olefinic N,O‐acetal (E)‐7 was corroborated by X‐ray crystallography.
A Tricyclic Dehydrorubanone and New Isomers of the Major Quinidine Metabolite
Authors: von Riesen Cornelius , Hoffmann H. M. R. 
Published: September 2007

AbstractSpiroepoxide 1 was prepared from quinidine and converted into β‐amino alcohol 3 (86% over two steps). Dihydroxylation of enantiopure oxazatricylic olefin (E)‐4 provided diastereomeric diols 5a and 5b. Stereospecific conversion of 1,2‐secondary, tertiary diol 5b into tetracyclic spiroepoxide 6 was accomplished in high yield by a one‐pot tosylation–cyclization procedure. 1,2‐Diol cleavage with NaIO4 in 80% acetic acid afforded the new tricyclic dehydrorubanone 7, containing the 4‐oxa‐7‐azatricyclo[4.3.1.03,7]‐decan‐2‐one core structure. Similarly, acetylated rubanone 9 was prepared on a 20 g scale. Reduction with NaBH4 in the presence of CeCl3 provided rubanols 10a and 10b (1:1.1). Horner–Wittig reaction of 9 with diethyl cyanomethylphosphonate was (Z)‐selective, furnishing unsaturated nitrile (Z)‐13. Conversion into the α,β‐unsaturated aldehyde (Z)‐14 and reduction afforded enartiopure allylic alcohol (Z)‐12, which is a new isomer of the key quinidine metabolite 15.
Stereoselective Transformations with Configurationally Labile α‐Phenylselenoalkyllithium Compounds
Authors: Hoffmann Reinhard W. , Klute Wolfgang 
Published: September 2007

AbstractComplexation of the configurationally labile α‐phenylselenoalkyllithium compound 8 with 1,2‐bisdimethylaminocyclohexane 15 led to two diastereomeric complexes 13 and 14 in a 7:3 ratio. Owing to ligand acceleration the complexes 13 and 14 added more rapidly to benzaldehyde than the uncomplexed organolithium compound 8. Trapping of complexes 13 and 14 by benzaldehyde was shown to occur more rapidly than their equilibration. This corresponds to non‐Curtin–Hammett kinetics, in which enantiomeric enrichment in the products reflects the equilibrium ratio of the complexes 13 and 14.
Bismuth(III) Complexes of the Tripeptide Glutathione (γ‐L‐Glu–L‐Cys–Gly)
Authors: Sadler Peter J. , Sun Hongzhe , Li Hongyan 
Published: September 2007

AbstractThe tripeptide glutathione (γ‐L‐Glu‐L‐Cys‐Gly, GSH) is thought to play an important role in the pharmacology of bismuth drugs, but to our knowledge no chemical studies of bismuth glutathione complexes have been reported. We report here studies of interactions of the antiulcer compound ranitidine bismuth citrate (1) and [Bi(edta)]− with glutathione in aqueous solution and in intact red blood cells by NMR spectroscopy. The deprotonated thiol group is shown to be the strongest binding site for BiIII, and a complex with the stoichiometry [Bi(GS)3] is formed, as determined by 13C NMR titrations. A remarkably large lowfield shift of approximately 1.37 ppm for the β‐CH2 1H NMR resonances of GSH was observed on binding to BiIII. The complex [Bi(GS)3] is stable over the pH* range 2–10 (pH* = pH meter reading in D2O solution). A formation constant log K of 29.6±0.4 (I = 0.1 M, 298 K) for [Bi(GS)3] was determined by displacement of edta by GSH. The rate of exchange of GSH between free and bound forms is pH‐dependent, ranging from slow exchange (on the 1H NMR timescale) at low pH (ca. 3 s−1 at pH 4.0) to intermediate exchange at biological pH (ca. 1500 s−1). Such facile exchange may be important in the transport and delivery of BiIII in vivo. Spin‐echo 1H NMR showed that 1 reacts with GSH in red cells both in vivo and in vitro. A first‐order reaction of 1 with red blood cells was observed in vitro (k = 0.20±0.04 h−1, t1/2 = 3 h, 310 K), and the rate‐determining step appeared to involve the passage of BiIII through the cell membrane.
A new nickel(III) oxide family: MSr3NiO6 (M = Sc, In, Tm, Yb and Lu)
Authors: James Michael , Attfield J. Paul 
Published: September 2007

AbstractThe new phases MIIISr3NiIIIO6 have been prepared for M = Sc, In, Tm, Yb and Lu. Thermogravimetric analysis indicates that these phases are stoichiometric nickel(III) oxides. Rietveld refinement of their crystal structures from powder X‐ray diffraction data confirms that they adopt the rhombohedral K4CdCl6‐ type structure (space group R\documentclass{article}\pagestyle{empty}\begin{document}$ \bar 3 $\end{document}c, a = 9.6595 (2) and c = 10.8546 (3) Å for ScSr3NiO6). The M site is fully occupied for M = Sc and In, but a deficiency of scattering for M = Tm, Yb and Lu is shown to be due to Ni substitution through a simultaneous refinement of the YbSr3NiO6 structure using X‐ray and time‐of‐flight neutron diffraction data. The refined composition is (Yb0.83Ni0.17)‐Sr3NiO6. The magnetic susceptibilities of the M = Sc, In and Lu samples show Curie–Weiss behaviour down to 6K; however, ScSr3NiO6 shows a broad transition between 250 and 290 K, with Curie–Weiss behaviour above and below this anomaly. This transition is thought to be between the statically and dynamically Jahn–Teller distorted regimes of octahedrally coordinated, low‐spin Ni3+.
N‐Heterocyclic Carbenes: Generation under Mild Conditions and Formation of Group 8–10 Transition Metal Complexes Relevant to Catalysis
Authors: Herrmann Wolfgang A. , Elison Martina , Fischer Jakob , Köcher Christian , Artus Georg R. J. 
Published: September 2007

AbstractStable mono‐ and dicarbene adducts of late transition metals are readily accessible either by reaction of imidazolium salts with metal complexes bearing basic ligands, or by the cleavage of chloro‐ and acetato‐bridged dinuclear metal complexes with the free carbenes (e.g., 1,3‐dimethylimidazoline‐2‐ylidene). A general novel method for the deprotonation of N‐substituted azolium salts in liquid ammonia–the liquid ammonia route–is described. This method yields not only the known free monimeric 1,3‐dimethylimidazoline‐2‐ylidene in quantitative yield, but also otherwise hardly accessible derivatives. For example, imidazoline‐2‐ylidenes with linear, branched, cyclic, heteroatom‐substituted and even chiral hydrocarbon residues can be obtained. The nucleophilic behaviour of 1,3‐dimethyl‐imidazoline‐2‐ylidene is reported and compared with that of other donor ligands. Novel carbene complexes of RuII, RhIPdII, OsIIand IrIare presented. Reaction of the potentially chelating ligand 1,1′‐(1,2‐ethylene)‐3,3′‐dimethyldiimidazoline‐2,2′‐diylidene with [(COD)‐RhCl]2yields a dinuclear complex, in which two rhodium centres are linked by the dicarbene bridge. Four single‐crystal X‐ray diffraction structures ofnewmetalcarbene complexes (Rh, Os) are reported. N‐Heterocyclic carbene complexes of Group 8–10 transition metals are both thermally and chemically very stable. They do not show the typical reactivity of metal–carbon double bonds. For a number of reasons, these complexes must be regarded as donor adducts of the Lewis‐basicimidazoline‐2‐ylidene ligand and the Lewis‐acidicorganometallic fragment.
Di(polyprenyl) Phosphates as Models for Primitive Membrane Constituents: Synthesis and Phase Properties
Authors: Birault Véronique , Pozzi Gianluca , Plobeck Niklas , Eifler Stéphane , Schmutz Marc , Palanché Tania , Raya Jesus , Brisson Alain , Nakatani Yoichi , Ourisson Guy 
Published: September 2007

AbstractIdentical‐ and mixed‐chain di(polyprenyl) phosphates, derived from 3‐methyl‐2‐buten‐1‐ol, (E)‐geraniol, (E,E)‐farnesol, (E,E,E)‐geranylgeraniol, (R)‐citronellol, or (R)‐tetrahydrogeraniol have been synthesized by phosphitylation and oxidation with iodine/water. These phosphates gave organized systems in water, in particular vesicles, the physical properties of which were studied by photon correlation spectroscopy, electron microscopy, entrapment of a fluorescent dye (calcein), 31P NMR, stopped‐flow/light‐scattering studies, and fluorescence polarization with lipophilic probes. Interdigitation of mixed‐length phosphates was not found to have any favorable effect on the stability of the vesicles. The C>15 vesicles were formed despite the fact that they are composed of only one molecular species and are devoid of any reinforcer, but those with two geranyl chains appeared to be rather fragile. Phosphates containing C5 chains are soluble in water. The results obtained lend weight to the hypothesis that polyprenyl phosphates might have been primitive membrane constituents, and stimulate the search for appropriate reinforcers.
Synthesis, Crystal Structure, Electronic Structure, and Properties of Hf2In5, a Metallic Hafnide with One‐Dimensional Hf‐Hf and Two‐Dimensional In‐In Bonding
Authors: Pöttgen Rainer , Dronskowski Richard 
Published: September 2007

AbstractHf2In5—previously reported with the tentative composition “Hf3In4”—was prepared from the elements in a tantalum tube at 970 K. The X‐ray diffractional characterization by means of single‐crystal refinement reveals the presence of a tetragonal structure (a = 1024.71 (9), c = 305.66 (3) pm, P4/mbm, Z = 2) of Mn2Hg5 type. Hf2In5 is Pauli‐paramagnetic and a good metallic conductor. Quasi‐relativistic semiempirical and scalar‐relativistic ab initio band structure calculations reveal Hf2In5 to be a hafnide, composed of a two‐dimensional indium network threaded by infinite hafnium chains. The amount of In–In bonding scales counterintuitively with the interatomic distances.
The Silaguanidinium Cation and the Search for a Stable Silylium Cation in Condensed Phases
Authors: Pidun Ulrich , Stahl Martin , Frenking Gernot 
Published: September 2007

AbstractQuantum mechanical calculations at the MP2/6‐31 G(d) level are reported for the silaguanidinium cation Si(NH2)(1) and derivatives thereof. The equilibrium structure1ahasD3symmetry with planar amino groups rotated out of the SiN3plane by 19.60. The Si–N bond length of1 a(1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation1 aby the amino groups (63.5 kcal mol−1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol−1), but1 ais clearly better stabilized than alkyl‐substituted silylium cations. The electronic stabilization of1 aby the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6‐ 31 G(d) is markedly lower for Si(NH2)3‐(H2O)+(6) (28.8 kcal mol−1) than for SiMe3(H2O)+(40.6 kcal mol−1). The tris(dimethylamino) silylium cation Si(N‐Me2)3+(8) is even more stable than1 a. The complexation energy of Si(NMe2)3‐(H2O)+(10) is only 17.3 kcal mol−1. IGLO calculations of the29Si N M R chemical shifts predict that1 aand8should not show the same extremely low shielding that is calculated for alkyl‐sub‐stituted silylium ions. The calculated29Si resonances for8are in reasonable agreement with the experimental N M R spectrum of (Me2N)3SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation12would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of12hastert‐butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.