bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photocurable epoxy/cubic silsesquioxane hybrid materials for polythiourethane: Failure mechanism of adhesion under weathering
Authors: Mya Khine Yi , Nakayama Norio , Takaki Toshihiko , Xiao Yang , Lin Ting Ting , He Chaobin 
Published: December 2007

AbstractA new inorganic–organic hybrid coating containing epoxy‐functionalized cubic silsesquioxane (CSSQ) has been developed, which can be polymerized cationically by UV radiation. This solvent‐free solution can be used as hybrid coating for polythiourethane (PTU) substrate. The surface properties of the coating film were determined by adhesion and scratch resistance. The excellent adhesion of coating films on the substrate was observed at the initial stage before weathering, but deteriorated after exposure to the sunshine. The low viscosity of hybrid coating solution (∼ 15 mPa s) leads to fast curing and the formation of hybrid coating film during the photopolymerization reaction. The adhesion failure was evaluated by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS) analyses. AFM images showed that the surface is smooth at the initial stage, but a texture surface was developed after weathering. The shrinkage of the hybrid film due to the increase in crosslinking density by postpolymerization would affect the surface roughness after weathering. XPS analysis indicated that the adhesion failure occurred by photodegradation of the PTU substrate during weathering. The weathering resistance was significantly improved by adding UV absorbers, which protected the polymer substrate from the photodegradation. The advantages of the hybrid coating include fast cure speed, solvent‐free formulation, and improved surface properties of the coating film. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Application of benzotriazole reactive UV absorbers to cellulose and determining sun protection of treated fabric spectrophotometrically
Authors: Akrman Jiří , Přikryl Josef 
Published: December 2007

AbstractUV absorbers for treating cotton textiles with the aim of increased protection against harmful effects of UV component of solar radiation have been prepared by reactions of five different aminophenylsulfobenzotriazoles with the condensation product of 4‐aminophenyl‐sulfatoethylsulfone and cyanuric chloride. The UV absorbers with two different reactive groups (monochlorotriazine and aromatic vinylsulfone), capable of formation of covalent bonds with hydroxyl groups of cellulose, were applied to one cellophane foil and two cotton fabrics of different porosities. This treatment increased the ultraviolet protection factor from a value of UPF = 3 to UPF = 100 and above. For attaining a high UPF value, the cotton material should exhibit low porosity. The UV absorbers with 2‐hydroxyphenyl group are stable in light and do not fluoresce on the fabric on contrary to derivatives without 2‐hydroxyphenyl group or with 2‐methoxyphenyl group. The high photostability of absorbers is explained by the possibility to disperse the absorbed energy of UV radiation in the form of harmless energy such as IR radiation (heat) through the reversible hydrogen bond between phenolic hydroxyl group and triazine cycle. The UV filters block the effect of optical brightening agents on cotton by quenching the fluorescence. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Preparation of emulsifier‐free polystyrene by conventional emulsion polymerization with a hydrolysable emulsifier
Authors: Itoh Y. , Akasaka R. , Takahashi K. 
Published: December 2007

AbstractAn alkali‐hydrolyzable surfactant, (1‐tetradecyloxycarbonyl)trimethylammonium chloride, was used as an emulsifier for emulsion polymerization of styrene inwater. The polymerization yielded a high molecular‐weight polymer almost quantitatively. Addition of a small amount of NaOH to the resulting latex solution precipitated the polymer immediately. Analysis of the centrifuged solid indicated almost perfection of both recovery of the polymer and removal of surface‐active species from it. Minimization of ionic species in the polymer solid was confirmed by a high contact angle of the polymer film with water. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters
Authors: Ojha Satyajeet S. , Afshari Mehdi , Kotek Richard , Gorga Russell E. 
Published: December 2007

AbstractIn the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Chiral‐Catalyst‐Based Convergent Synthesis of HIV Protease Inhibitor GRL‐06579A
Authors: Mihara Hisashi , Sohtome Yoshihiro , Matsunaga Shigeki , Shibasaki Masakatsu 
Published: December 2007

AbstractCatalytic asymmetric synthesis of GRL‐06579A (1), an HIV‐1 protease inhibitor effective against multi‐protease‐inhibitor‐resistant viruses, is described. A convergent strategy that utilizes heterobimetallic multifunctional catalysts developed in our group is a key feature of the synthesis. The chirality of the bicyclic tetrahydrofuran unit of 1 was introduced through Al–Li–bis(binaphthoxide) (ALB) catalyst‐controlled Michael addition of dimethyl malonate to racemic 4‐O‐protected cyclopentenone. ALB afforded not only the trans adduct with up to 96 % ee from a matched substrate through kinetic resolution, but also the cis adduct with 99 % ee through a catalyst‐controlled Michael addition to a mismatched substrate. The Michael addition to produce the unusual cis adduct is described in detail. The framework of the bicyclic tetrahydrofuran was constructed by an intramolecular oxy‐Michael reaction. The amino alcohol unit was constructed by an La–Li3–tris(binaphthoxide) (LLB)‐catalyzed diastereoselective nitroaldol reaction of N‐Boc aldehyde (Boc=tert‐butoxycarbonyl) derived from L‐phenylalanine. LLB promoted the nitroaldol reaction without racemization of the chiral aldehyde to give the nitroaldol adduct in 85 % yield and with 93:7 diastereoselectivity and over 99 % ee.
Can variable meridional flows lead to false exoplanet detections?
Authors: Beckers J.M. 
Published: December 2007

AbstractThe search for habitable exoplanets centers on planets with Earth‐like conditions around late type stars. Radial velocity searches for these planets require precisions of 1 m/s and better. That is now being achieved. At these precisions stellar surface motions might lead to false detections. Of particular interest are variable meridional flows on stellar surfaces. I review the available observations of solar surface meridional flows using both Doppler shift and local helioseismology techniques. Interpretation in terms of Doppler shifts in integrated starlight leads to estimates of the likelihood of false detections. It is unlikely that these false detections occur in the habitability zones of exoplanets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling the time variation of the surface differential rotation in AB Doradus and LQ Hydrae
Authors: Lanza A.F. 
Published: December 2007

AbstractSequences of Doppler images of the young, rapidly rotating late‐type stars AB Dor and LQ Hya show that their equatorial angular velocity and the amplitude of their surface differential rotation vary versus time. Such variations can be modelled to obtain information on the intensity of the azimuthal magnetic stresses within stellar convection zones. We introduce a simple model in the framework of the mean‐field theory and discuss briefly the results of its application to those solar‐like stars. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differential rotation and meridional circulation in global models of solar convection
Authors: Miesch M.S. 
Published: December 2007

AbstractIn the outer envelope of the Sun and in other stars, differential rotation and meridional circulation are maintained via the redistribution of momentum and energy by convective motions. In order to properly capture such processes in a numerical model, the correct spherical geometry is essential. In this paper I review recent insights into the maintenance of mean flows in the solar interior obtained from high‐resolution simulations of solar convection in rotating spherical shells. The Coriolis force induces a Reynolds stress which transports angular momentum equatorward and also yields latitudinal variations in the convective heat flux. Meridional circulations induced by baroclinicity and rotational shear further redistribute angular momentum and alter the mean stratification. This gives rise to a complex nonlinear interplay between turbulent convection, differential rotation, meridional circulation, and the mean specific entropy profile. I will describe how this drama plays out in our simulations as well as in solar and stellar convection zones. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraints on angular momentum transport in the Sun from simulations of the tachocline
Authors: Garaud P. 
Published: December 2007

AbstractI present a new numerical tool for studying the interaction of meridional flows and magnetic fields, and study their role in establishing angular‐momentum balance in the solar radiative zone. Quantitative comparisons with helioseismic observations provide stringent constraints on existing models of the dynamics of the solar interior. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic field evolution in neutron stars
Authors: Reisenegger A. 
Published: December 2007

AbstractNeutron stars contain persistent, ordered magnetic fields that are the strongest known in the Universe. However, their magnetic fluxes are similar to those in magnetic A and B stars and white dwarfs, suggesting that flux conservation during gravitational collapse may play an important role in establishing the field, although it might also be modified substantially by early convection, differential rotation, and magnetic instabilities. The equilibrium field configuration, established within hours (at most) of the formation of the star, is likely to be roughly axisymmetric, involving both poloidal and toroidal components. The stable stratification of the neutron star matter (due to its radial composition gradient) probably plays a crucial role in holding this magnetic structure inside the star. The field can evolve on long time scales by processes that overcome the stable stratification, such as weak interactions changing the relative abundances and ambipolar diffusion of charged particles with respect to neutrons. These processes become more effective for stronger magnetic fields, thus naturally explaining the magnetic energy dissipation expected in magnetars, at the same time as the longer‐lived, weaker fields in classical and millisecond pulsars. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamo action in simulations of penetrative solar convection with an imposed tachocline
Authors: Browning M.K. , Brun A.S. , Miesch M.S. , Toomre J. 
Published: December 2007

AbstractWe summarize new and continuing three‐dimensional spherical shell simulations of dynamo action by convection allowed to penetrate downward into a tachocline of rotational shear. The inclusion of an imposed tachocline allows us to examine several processes believed to be essential in the operation of the global solar dynamo, including differential rotation, magnetic pumping, and the stretching and organization of fields within the tachocline. In the stably stratified core, our simulations reveal that strong axisymmetric magnetic fields (of ∼ 3000 G strength) can be built, and that those fields generally exhibit a striking antisymmetric parity, with fields in the northern hemisphere largely of opposite polarity to those in the southern hemisphere. In the convection zone above, fluctuating fields dominate over weaker mean fields. New calculations indicate that the tendency toward toroidal fields of antisymmetric parity is relatively insensitive to initial magnetic field configurations; they also reveal that on decade‐long timescales, the magnetic fields can briefly enter (and subsequently emerge from) states of symmetric parity.We have not yet observed any overall reversals of the field polarity, nor systematic latitudinal propagation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The azimuthal magnetorotational instability (AMRI)
Authors: Rüdiger G. , Hollerbach R. , Gellert M. , Schultz M. 
Published: December 2007

AbstractWe consider the flow of an electrically conducting fluid between differentially rotating cylinders, in the presence of an externally imposed current‐free toroidal field B0(Rin/R) êϕ . It is known that the classical, axisymmetric magnetorotational instability does not exist for such a purely toroidal imposed field.We show here that a nonaxisymmetric magnetorotational instability does exist, having properties very similar to the axisymmetric magnetorotational instability in the presence of an axial field. In the nonlinear regime the magnetic energy of the perturbances is shifted (in the sense of an inverse cascade) to the axisymmetric mode rather than to the modes with m > 1. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differential rotation in F stars
Authors: Reiners A. 
Published: December 2007

AbstractDifferential rotation can be detected in single line profiles of stars rotating more rapidly than about v sin i = 10km s‐1 with the Fourier transform technique. This allows to search for differential rotation in large samples to look for correlations between differential rotation and other stellar parameters. I analyze the fraction of differentially rotating stars as a function of color, rotation, and activity in a large sample of F‐type stars. Color and rotation exhibit a correlation with differential rotation in the sense that more stars are rotating differentially in the cooler, less rapidly rotating stars. Effects of rotation and color, however, cannot be disentangled in the underlying sample. No trend with activity is found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of polar starspots through meridional circulation
Authors: Holzwarth V. , Mackay D.H. , Jardine M. 
Published: December 2007

AbstractTo explain the observed intermingling of polarities in the magnetic field distributions of rapidly rotating stars, surface magnetic flux transport models demand the presence of fast meridional flows.We combine simulations of the pre‐eruptive and post‐eruptive magnetic flux transport in cool stars to investigate the influence of a fast meridional circulation on the latitudinal eruption pattern of magnetic flux tubes and on the polar magnetic field properties. Magnetic flux tubes rising through the convection zone experience an enhanced latitude‐dependent poleward deflection through meridional flows, which renders the wings of stellar butterfly diagrams convex. The larger amount of magnetic flux emerging at higher latitudes supports the intermingling of opposite polarities of polar magnetic fields and yields magnetic flux densities in the polar regions about 20% higher than in the case disregarding the pre‐eruptive deflection. Taking the pre‐eruptive evolution of magnetic flux into account therefore eases the need for the fast meridional flows predicted by previous investigations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Turbulent viscosity and Λ‐effect from numerical turbulence models
Authors: Käpylä P.J. , Brandenburg A. 
Published: December 2007

AbstractHomogeneous anisotropic turbulence simulations are used to determine off‐diagonal components of the Reynolds stress tensor and its parameterization in terms of turbulent viscosity and Λ‐effect. The turbulence is forced in an anisotropic fashion by enhancing the strength of the forcing in the vertical direction. The Coriolis force is included with a rotation axis inclined relative to the vertical direction. The system studied here is significantly simpler than that of turbulent stratified convection which has often been used to study Reynolds stresses. Certain puzzling features of the results for convection, such as sign changes or highly concentrated latitude distributions, are not present in the simpler system considered here. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
How can α 2‐dynamos generate axisymmetric magnetic fields?
Authors: Elstner D. , Rüdiger G. 
Published: December 2007

AbstractInspired by a recently observed axisymmetric field in a fully convective star we investigate the influence of an anisotropic diffusivity on the dynamo. We find that with reasonable assumptions for the anisotropy of the diffusivity and the α ‐effect the preference of axisymmetric modes is achieved. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled model of magnetic flux generation and transport in stars
Authors: Işık E. , Schmitt D. , Schüssler M. 
Published: December 2007

AbstractWe present a combined model for magnetic field generation and transport in cool stars with outer convection zones. The mean toroidal magnetic field, which is generated by a cyclic thin‐layer α Ω dynamo at the bottom of the convection zone is taken to determine the emergence probability of magnetic flux tubes in the photosphere. Following the nonlinear rise of the unstable thin flux tubes, emergence latitudes and tilt angles of bipolar magnetic regions are determined. These quantities are put into a surface flux transport model, which simulates the surface evolution of magnetic flux under the effects of large‐scale flows and turbulent diffusion. First results are discussed for the case of the Sun and for more rapidly rotating solar‐type stars. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the solar rotation and activity
Authors: Brajša R. , Wöhl H. , Ruždjak D. , Vršnak B. , Verbanac G. , Svalgaard L. , Hochedez J.‐F. 
Published: December 2007

AbstractThe interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set (1878–1981) and a series of full‐disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998–2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Meridional flow profile measurements with SOHO/MDI
Authors: Mitra‐Kraev U. , Thompson M.J. 
Published: December 2007

AbstractWe present meridional flow measurements of the Sun using a novel helioseismic approach for analyzing SOHO/MDI data in order to push the current limits in radial depth. Analyzing three consecutive months of data during solar minimum, we find that the meridional flow is as expected poleward in the upper convection zone, turns equatorward at a depth of around 40 Mm (∼ 0.95 R⊙), and possibly changes direction again in the lower convection zone. This may indicate two meridional circulation cells in each hemisphere, one beneath the other. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The differential rotation of ε Eri from MOST data
Authors: Fröhlich H.‐E. 
Published: December 2007

AbstractFrom high‐precision MOST photometry spanning 35 days the existence of two spots rotating with slightly differing periods is confirmed. From the marginal probability distribution of the derived differential rotation parameter k its expectation value as well as confidence limits are computed directly from the data. The result depends on the assumed range in inclination i, not on the shape of the prior distributions. Two cases have been considered: (a) The priors for angles, inclination i of the star and spot latitudes β 1,2, are assumed to be constant over i, β 1, and β 2; (b) the priors are assumed to be constant over cos i, sin β 1, and sin β 2. In both cases the full range of inclination is considered: 0° ≤ i ≤ 90°. Scalefree parameters, i. e. periods and spot areas (in case of small spots) are taken logarithmically. Irrespective of the shape of the prior, k is restricted to 0.03 ≤ k ≤ 0.10 (1 σ limits). The inclination i of the star is photometrically ill‐defined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anti‐solar differential rotation and surface flow pattern on UZ Libræ
Authors: Vida K. , Kőovári Zs. , Švanda M. , Oláh K. , Strassmeier K.G. , Bartus J. 
Published: December 2007

AbstractWe re‐investigate UZ Libræ spectra obtained at KPNO in 1998 and 2000. From the 1998 data we compose 11 consecutive Doppler images using the Ca I‐6439, Fe I‐6393 and Fe I‐6411 lines. Applying the method of average cross‐correlation of contiguous Doppler images we find anti‐solar differential rotation with a surface shear of α ≈ –0.03. The pilot application of the local correlation tracking technique for the same data qualitatively confirms this result and indicates complex flow pattern on the stellar surface. From the cross‐correlation of the two available Doppler images in 2000 we also get anti‐solar differential rotation but with a much weaker shear of α ≈ –0.004. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of the solar tachocline with magnetic fields
Authors: Arlt R. , Sule A. , Filter R. 
Published: December 2007

AbstractThe stability of magnetic fields in the solar tachocline is investigated. We present stability limits for higher azimuthal wave numbers and results on the dependence of the stability on the location of toroidal magnetic fields in latitude. While the dependence of the wave number with the largest growth rate on the magnetic field strength and the magnetic Prandtl number is small, the dependence on the magnetic Reynolds number Rm indicates that lowest azimuthal modes are excited for very high Rm. Upon varying the latitudinal position of the magnetic field belts, we find slightly lower stability limits for high latitudes, and very large stability limits at latitudes below 10°, with little dependence on latitude in between. An increase of the maximum possible field was achieved by adding a poloidal field. The upper limit for the toroidal field which can be stored in the radiative tachocline is then 1000 G, compared to about 100 G for a purely toroidal field as was found in an earlier work. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)