bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mars pathfinder: New data and new model simulations
Authors: Savijärvi Hannu , Määttänen Anni , Kauhanen Janne , Harri Ari‐matti 
Published: March 2004

AbstractThe diurnal cycle in the temperature and wind speed of the Mars Pathfinder lander (MPF) is compared with the results from a one‐dimensional high‐solution boundary‐layer model. The radiation scheme of the model has been validated against line‐by‐line calculations in an average Martian case. The agreement with MPF observations is good. Strong daytime turbulent variability and steep vertical temperature gradients characterize the observations. A detailed look at the model physics reveals that the thin atmosphere responds strongly to thermal radiation. During the daytime, absorption of surface‐emitted thermal radiation by CO2, water vapour and dust is the main heating agent below 200 m despite the fact that the surface layer is strongly convective and dust absorbs solar radiation. The night‐time inversion is also transferred to the air mainly by long‐wave processes, although turbulent cooling dominates very near the surface (below 40 m). The near‐surface net heating/cooling displays a sensitive balance between several large and opposite physical processes, wherefore accurate algorithms and high resolution are needed for detailed model results. The modelled hydrologic cycle reveals a well‐mixed layer of up to 5 km with thin icy fog and frost forming in the night‐time. These sublimate back to the air soon after sunrise. Copyright © 2004 Royal Meteorological Society
The accuracy of stratospheric analyses in the northern hemisphere inferred from long‐duration balloon flights
Authors: Hertzog A. , Basdevant C. , Vial F. , Mechoso C. R. 
Published: March 2004

AbstractIn January and February 2002, six superpressure balloons (SPBs) were launched from Kiruna, Sweden (69°N,21°E). The balloons drifted in the polar lower stratosphere for up to 45 days. Temperature, wind and altitude observations were collected every 15 minutes during the flights. This dataset serves as a reference to assess the accuracy of the European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses in the lower stratosphere during the 2002 winter. In particular, it is found that both models succeeded in simulating the large temperature fluctuations observed during the SPB flights, which were induced by a geographical shift between the stratospheric vortex and the low temperature area. Furthermore, the model biases are found to be small for all variables (temperature, wind, height). Nevertheless, it is found that NCEP/NCAR reanalyses tend to be slightly warmer (0.8 K) than the observations, while the converse is true for ECMWF analyses (−0.3 K). The observations also exhibit small‐scale fluctuations that are presumably produced by (inertia‐)gravity waves and which induce some scatter in the analysis/observation comparisons. Finally, trajectory comparisons are performed. It is found that trajectories built with ECMWF winds are more accurate than those built with NCEP/NCAR winds. With both models, the trajectory errors increase with time upto about 15 days and then tend to fluctuate. Typical errors after 15 days are 1000 ± 1200 km for ECMWF and 2300 ± 1300 km for NCEP trajectories. Copyright © 2004 Royal Meteorological Society
Rapid Deletion of Mossy Cells Does Not Result in a Hyperexcitable Dentate Gyrus: Implications for Epileptogenesis
Authors: Ratzliff Anna d. H. , Howard Allyson L. , Santhakumar Vijayalakshmi , Osapay Imola , Soltesz Ivan 
Published: March 2004

Loss of cells from the hilus of the dentate gyrus is a major histological hallmark of human temporal lobe epilepsy. Hilar mossy cells, in particular, are thought to show dramatic numerical reductions in pathological conditions, and one prominent theory of epileptogenesis is based on the assumption that mossy cell loss directly results in granule cell hyperexcitability. However, whether it is the disappearance of hilar mossy cells from the dentate gyrus circuitry after various insults or the subsequent synaptic-cellular alterations (e.g., reactive axonal sprouting) that lead to dentate hyperexcitability has not been rigorously tested, because of the lack of available techniques to rapidly remove specific classes of nonprincipal cells from neuronal networks.We developed a fast, cell-specific ablation technique that allowed the targeted lesioning of either mossy cells or GABAergic interneurons in horizontal as well as axial (longitudinal) slices of the hippocampus. The results demonstrate that mossy cell deletion consistently decreased the excitability of granule cells to perforant path stimulation both within and outside of the lamella where the mossy cell ablation took place. In contrast, ablation of interneurons caused the expected increase in excitability, and control aspirations of the hilar neuropil or of interneurons in the presence of GABA receptor blockers caused no alteration in granule cell excitability.These data do not support the hypothesis that loss of mossy cells from the dentate hilus after seizures or traumatic brain injury directly results in hyperexcitability.
Real‐time identification of vehicle chassis dynamics using a novel reparameterization based on sensitivity invariance
Authors: Brennan S. , Alleyne A. 
Published: March 2004

AbstractThis work presents a novel methodology to identify model parameters using the concept of sensitivity invariance. Within many classical system representations, relationships between Bode parameter sensitivities may exist that are not explicitly accounted for by the formal system model. These relationships, called sensitivity invariances, will explicitly limit the possible parameter variation of the system model to a small subspace of the possible parameter gradients. By constraining the parameter identification or adaptation to a model structure with uncoupled parameter sensitivities, a more efficient identification can be obtained at a reduced computational and modelling cost. As illustration, an identification method of using sensitivity invariance is demonstrated on an experimental problem to identify, in real time, a time‐varying tire parameter associated with the chassis dynamics of passenger vehicles at highway speeds. The results are validated with simulations as well as an experimental implementation on a research vehicle driven under changing road conditions. Copyright © 2004 John Wiley & Sons, Ltd.
Probing small scale structure in the atmosphere of V471 Tauri
Authors: Walter F. M. 
Published: March 2004

AbstractThe white dwarf in the eclipsing binary system V471 Tau is viewed through the atmosphere of the active K star prior to ingress and after egress. In the far UV the surface brightness of the hot white dwarf far outshines the K star emission. We can use this to probe the structure of the extended K star atmosphere along one line of sight, in absorption, on spatial scales of the radius of the white dwarf (10,000 km). The time series of HST/STIS spectra which show a hot (>250,000 K) extended (>1 K star radius) atmosphere around the K star. We see discrete structures in the velocity‐resolved spectra, on spatial scales of less than 100,000 km. The mean velocity is that expected of gas in co‐rotation with the K star, but the discrete velocity structures have excursions of up to 70 km/s from the mean. The mean temperature seems to increase with height above the K star photosphere. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
What can we learn from accretion disc eclipse mapping experiments?
Authors: Baptista R. 
Published: March 2004

AbstractThe accretion disc eclipse mapping method is an astrotomographic inversion technique that makes use of the information contained in eclipse light curves to probe the structure, the spectrum and the time evolution of accretion discs in cataclysmic variables. This paper presents examples of eclipse mapping results that have been key to improve our understanding of accretion physics. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stokes imaging and Doppler mapping of the magnetic cataclysmic variable V834 Cen
Authors: Potter S. , Romero‐Colmenero E. , Buckley D. A. H. 
Published: March 2004

AbstractWe report on new phase resolved spectroscopic and polarimetric observations of the polar (AM Herculis star) V834 Cen during a high state of accretion. Strong emission lines and high levels of variable circular and linear polarization are observed over the orbital period.The polarization data is modelled using the Stokes imaging technique of Potter et al. The spectroscopic emission lines are investigated using the Doppler tomography technique of Marsh & Horne.Up to now both techniques have been used separately to investigate the geometry and accretion dynamics in Cataclysmic Variables. For the first time we apply both techniques to phase resolved spectroscopic and polarimetric observations: in this case to the polar V834 Cen. This allows us to compare and test each technique against each other and hence derive a better understanding of the geometry, dynamics and system parameters of V834 Cen.Both techniques are consistent with the interpretation that the ballistic stream extends for more than approximately 40 degrees in azimuth around the white dwarf before becoming, threaded by the magnetic field lines. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Doppler tomography of accretion in binaries
Authors: Steeghs D. 
Published: March 2004

AbstractSince its conception, Doppler tomography has matured into a versatile and widely used tool. It exploits the information contained in the highly‐structured spectral line‐profiles typically observed in mass‐transferring binaries. Using inversion techniques akin to medical imaging, it permits the reconstruction of Doppler maps that image the accretion flow on micro‐arcsecond scales. I summarise the basic concepts behind the technique and highlight two recent results; the use of donor star emission as a means to system parameter determination, and the real‐time movies of the evolving accretion flow in the cataclysmic variable WZ Sge during its 2001 outburst. I conclude with future opportunities in Doppler tomography by exploiting the combination of superior data sets, second generation reconstruction codes and simulated theoretical tomograms to delve deeper into the physics of accretion flows. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Doppler tomography of cataclysmic variables
Authors: Morales‐Rueda L. 
Published: March 2004

AbstractThe study of cataclysmic variables (CVs), and in particular of the evolution of their accretion discs throughout their different brightness states, has benefited largely from the use of indirect imaging techniques. I report on the latest results obtained from Doppler tomography of CVs concentrating mainly on results published since the 2000 Astrotomography meeting in Brussels. Emphasis is given to the spiral structures found in the accretion discs of some CVs, to the evolution of these structures throughout quiescence and outburst, and to our search for them in more systems. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approaching Supramolecular Functionality
Authors: Schalley Christoph A. , Lützen Arne , Albrecht Markus 
Published: March 2004

AbstractFunctional molecules require a high degree of complexity which is difficult to achieve by covalent synthesis. This article discusses supramolecular approaches to the creation of larger architectures through noncovalent bonds, self‐assembly, and template strategies. It highlights selected examples for the structural and conformational control of function and attempts to identify difficulties and challenges which may arise in future.
Selective Generation and Reactivity of 5′‐Adenosinyl and 2′‐Adenosinyl Radicals
Authors: Chatgilialoglu Chryssostomos , Duca Maria , Ferreri Carla , Guerra Maurizio , Ioele Marcella , Mulazzani Quinto G. , Strittmatter Harald , Giese Bernd 
Published: March 2004

AbstractThe reaction of hydrated electrons (e${{- \hfill \atop {\rm aq}\hfill}}$) with 8‐bromoadenosine 7 has been investigated by radiolytic methods coupled with product studies. Pulse radiolysis revealed that one‐electron reductive cleavage of the CBr bond gives the C8 radical 8 followed by a fast radical translocation to the sugar moiety. The reaction is partitioned between C5′ and C2′ positions in a 60:40 ratio leading to 5′‐adenosinyl radical 9 and 2′‐adenosinyl radical 11. This radical translocation from C8 to different sites of the sugar moiety has also been addressed computationally by means of DFT B3LYP calculations. In addition, ketone 21 was prepared and photolyzed providing an independent generation of C2′ radical 11. Both C5′ and C2′ radicals undergo unimolecular reactions. Radical 9 attacks adenine with a rate constant of 1.0×104 s−1 and gives the aromatic aminyl radical 10, whereas C2′ radical 11 liberates adenine with a rate constant of 1.1×105 s−1.
Pd‐Catalyzed Coupling Reactions Involving Propargylic/Allenylic Species
Authors: Ma Shengming 
Published: March 2004

AbstractIn this review, the Pd‐catalyzed coupling reaction involving propargylic/allenylic species is discussed. In these reactions, η1‐ and η3‐propargylic/allenylic species have been proposed as the key intermediates for the selective formation of either allenes or alkynes. It should be noted that, in most cases, allenes are formed as the major products. Electronic, steric, and ligand effects have been observed for the control of the regioselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Entropy‐Driven Asymmetric Synthesis with Chiral Tethers
Authors: Sugimura Takashi 
Published: March 2004

AbstractThe 2,4‐pentanediol (PD)‐tethered reaction is a stereocontrolled reaction having versatile applicability. When reactant and reagent elements are connected through a PD tether prior to their reaction, stereochemical purity of the product is very high for nine different types of reactions so far studied. Selectivity of one of the reactions shows temperature independency over a wide range from −78 to 150 °C, which indicates that the stereocontrol is driven by the entropy term. The strict stereocontrol of this reaction at high temperatures can be extended to vapor phase reactions performed above 250 °C. To understand how the two methyl groups on the PD tether stereocontrol the reaction, a new parameter, a chiral perturbation factor, is introduced. By this analysis, it is disclosed that the methyl groups promote an activation entropy change for both the diastereomeric processes, and the strict stereocontrol is achieved when the changes have opposite signs. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Total Synthesis without Protection: Three‐Step Synthesis of Optically Active Clavicipitic Acids by a Biomimetic Route
Authors: Yokoyama Yuusaku , Hikawa Hidemasa , Mitsuhashi Masaharu , Uyama Aki , Hiroki Yasuhiro , Murakami Yasuoki 
Published: March 2004

AbstractA three‐step synthesis of a mixture of optically active cis‐ and trans‐clavicipitic acids 6, which are ergot alkaloids, was achieved, starting from 4‐bromoindole (7) and dl‐serine (dl‐2). This short synthesis was made possible by omitting the protection and deprotection steps from the synthetic route. The key step was the spontaneous cyclization of 4‐vinyltryptophan (10) formed from the Heck reaction of 4‐bromotryptophan (8) with 2‐methyl‐3‐buten‐2‐ol (9) in aqueous media. During this investigation, we also found that the palladium‐catalyzed reaction of 8 with 9 showed an interesting pH dependence; under strongly basic conditions, the Heck reaction occurred to give a C4‐vinylated product 10, whereas an N‐allylated product 19b was formed under neutral or weakly basic conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Xyloketals, Natural Products from the Mangrove Fungus Xylaria sp
Authors: Krohn Karsten , Riaz Muhammad , Flörke Ulrich 
Published: March 2004

AbstractThe xyloketal family of compounds was synthesized by condensation of phloroglucinol (7) or 2,4‐dihydroxyacetophenone (15) with the enone 8a or 14 in multistep, one‐pot, domino reactions, leading to the xyloketals and 5‐demethylxyloketals, respectively. In the case of condensation with phloroglucinol (7), the mono‐, bis, and tris adducts 6/18, 2/19, 1/20 are formed; their ratios depend on the ratio of stating materials and reaction time. The ring junction of the pyran and furan rings B and C (at C‐2 and C‐6) is always cis. The cis orientation of the methyl groups at C‐2 and C‐5 is also predominant (8.5:1.5), as found in the natural products. In the bis and tris adducts (2/19, 1/20), the relative orientation of the rings B and C can be syn and anti, with the sterically less demanding anti orientation slightly favored statistically. Xyloketal D (4a) was obtained in the condensation of 15 with enantiomerically enriched enone 8a, confirming the absolute configuration of the natural product. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
3‐Tocopherylisoxazolines by [2+3] Cycloaddition
Authors: Rosenau Thomas , Adelwöhrer Christian , Hofinger Andreas , Mereiter Kurt , Kosma Paul 
Published: March 2004

AbstractNew isoxazoline derivatives of α‐tocopherol (1), the main component of vitamin E, were synthesized in a facile, two‐step sequence consisting of nitration followed by 1,3‐dipolar cycloaddition. 5‐Nitromethyl‐γ‐tocopheryl acetate (3), obtained from the cheap α‐tocopheryl acetate (2) by direct nitration in one step, acted as the nitrile oxide precursor in the reaction with various alkenes. The facile conversion proceeded in the presence of equimolar amounts of PhNCO and catalytic amounts of triethylamine. The NMR spectra of the product isoxazolines 5−13, showing strongly temperature‐dependent resonances of the 4′′‐CH, 4‐CH2 and the acetyl group, are discussed, and the crystal structures of model compounds containing a methyl group instead of the isoprenoid side chain are presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of a 3,4‐Di‐O‐substituted Heptose Structure: A Partial Oligosaccharide Expressed in Neisserial Lipooligosaccharide
Authors: Kubo Hiroyuki , Ishii Kazuyuki , Koshino Hiroyuki , Toubetto Kenji , Naruchi Kentarou , Yamasaki Ryohei 
Published: March 2004

AbstractWe have synthesized a tetrasaccharide containing a 3,4‐dibranched L‐glycero‐D‐manno‐heptose (Hep), β‐lactosyl‐(1⇄4)‐[L‐α‐D‐Hep‐(1⇄3)]‐L‐α‐D‐Hep 19, by using a mannose (Man) derivative as an acceptor. Prior to the construction of the branched Hep, we confirmed that the 3,4‐dibranched Man structure could be synthesized using a 3‐branched Man 6 as an acceptor. Glycosylation of the acceptor 6 using hepta‐O‐acetyl‐α‐lactosyl trichloroacetimidate (7) gave the desired 3,4‐dibranched structure, β‐lactosyl‐(1⇄4)‐[α‐Man‐(1⇄3)]‐α‐Man 8. As expected, β‐lactosyl‐(1⇄4)‐[L‐α‐D‐Hep‐(1⇄3)]‐α‐D‐Man 14 was also obtained by glycosylating the 4‐OH acceptor 13 with 7 in a similar manner. The Man residue of 14 was converted into the Hep unit by Swern oxidation, Grignard reaction, and oxidative cleavage followed by reduction. Thus, we constructed the 3,4‐dibranched Hep structure 19 by using the 3‐branched Man 13 as an acceptor. The current results demonstrate that the gauche orientation of the O‐3 and O‐4 units of the Man configuration does not prevent the formation of the 3,4‐di‐O‐substituted structure. This approach should provide an alternative method to synthesize the 3,4‐dibranched Hep structure expressed in LOS produced by pathogenic Gram‐negative bacteria such as the Neisserial and Haemophilus species. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of New Constrained Tricyclic Amines and Tricyclic Aminophosphonates Containing the 2‐Azatricyclo[3.3.0.03,6]octane Skeleton
Authors: Rammeloo Thomas , Stevens Christian V. , Soenen Bram 
Published: March 2004

AbstractA short and easy method for the preparation of the 2‐azatricyclo[3.3.0.03,6]octane skeleton is described. The key step consists of an intramolecular ring closure of an endo‐oriented amino group and an exo‐oriented bromine atom. The amines were prepared through reduction of a suitable bicyclic imine. Nucleophilic addition of phosphite to the imines gave the corresponding aminophosphonates, which could be ring‐closed to the tricyclic aminophosphonates through an analogous pathway. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Iron‐Catalyzed Transformations of 2‐Chloro‐1,6‐heptadienes
Authors: Nečas David , Kotora Martin , Císařová Ivana 
Published: March 2004

Abstract(Phosphane)iron complexes in the presence of excess trialkylaluminium reagents catalyze various transformations of 2‐chloro‐α,ψ‐dienes, depending on their structure. Most notably, in the cases of simple 2‐chloro‐1,6‐heptadienes, cyclization with transfer of the alkyl group (Me and Et) from the corresponding trialkylaluminium compound was observed to give 2‐alkyl‐1‐methylidenecyclopentanes. Reaction with 2‐chloro‐1,7‐octadiene afforded the product of reductive dehalogenation. In the case of 2‐chloro‐4‐aza‐1,6‐heptadiene a partial or complete hydrogenation of the double bonds was observed depending on the amount of trialkylaluminum reagent used. Interestingly, allyl(2‐chloroallyl)malonate underwent C−C bond cleavage with the loss of an allyl group to give (2‐chloroallyl)malonate. In the presence of ruthenium catalysts only reductive dehalogenation was observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The Structures of the Lipid A Moieties from the Lipopolysaccharides of Two Phytopathogenic Bacteria, Xanthomonas campestris pv. pruni and Xanthomonas fragariae
Authors: Silipo Alba , Molinaro Antonio , Lanzetta Rosa , Parrilli Michelangelo , Lindner Buko , Holst Otto 
Published: March 2004

AbstractLipopolysaccharides (LPSs) are vital and exclusive structural components of the outer membranes of all Gram‐negative bacteria. They play an important role in the communication between the pathogen and both animal and vegetal host cells. Structurally, they comprise in their smooth (S) form three regions, namely the O‐specific polysaccharide (or O‐antigen), the core region and the lipid A (the endotoxic active moiety). In this paper, the structure of the lipid A moieties from two lipopolysaccharides of two phytopathogenic bacteria, X. campestris pv. pruni and Xanthomonas fragariae, is described. The sugar backbone is constituted by the typical bis(phosphorylated)β‐(1′⇄6)‐linked D‐glucosamine disaccharide. Both lipid A fractions are remarkably heterogeneous with respect to the fatty acid chain length. The major species are hexacylated lipid A, with a symmetric [3+3] distribution in which the secondary fatty acids are exclusively ester‐linked. The primary structure of these two complex glycolipids is herein elucidated by means of chemical degradation, MS spectrometry and 2D NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Oxidative Fragmentation of the Bridged β‐Triketone Core of Hyperforin (Eur. J. Org. Chem. 6/2004)
Authors: Verotta Luisella , Lovaglio Erminio , Sterner Olov , Appendino Giovanni , Bombardelli Ezio 
Published: March 2004

AbstractThe cover picture shows Hypericum perforatum in full bloom, its bioactive compound hyperforin and the unusual structure of two oxidized products, whose mechanism of formation is discussed in the article by L. Verotta, O. Sterner et al. on p. 1193 ff.