bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and characterization of CdTe nanoparticles attached to poly(4‐vinylpyridine) nanofibers
Authors: Wang Shugang , Li Yaoxian , Li Jun , Du Jianshi , Bai Jie , Yang Qingbiao , Chen Xuesi
Published: December 2007

The major objective of this work was to characterize the status of CdTe nanoparticles attached to the surface of poly(4‐vinylpyridine) (P4VP) nanofibers. Scanning electron microscopy and transmission electron microscopy images indicated that the attachment of CdTe nanoparticles enlarged the diameter of P4VP nanofibers. Moreover, the results of the energy‐dispersive X‐ray spectrum and the electron diffraction pattern revealed that the deposition on the surface of P4VP nanofibers was CdTe in a cubic lattice. Furthermore, CdTe existed in its optical style according to photoluminescence spectra. X‐ray photoelectron spectroscopy verified Cd in CdTe nanoparticles combined with the N atom in P4VP nanofibers. Therefore, the obtained results provide some references for preparing coaxial nanofibers attached by other nanoparticles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Study on the formation process of polyacrylonitrile as‐spun fiber
Authors: Ji Bao‐Hua , Wang Ji‐Hua , Wang Cheng‐Guo , Wang Yan‐Xiang
Published: December 2007

In this article, the coagulation rate of PAN/DMSO dope was studied by observing the boundary movement of the gelled rods in different coagulation bath. Then the effect of the nature of solvent and coagulant and the coagulation conditions on the coagulation rate was discussed. It was found that the molecular size and molecular structure of coagulants is the most significant variable affecting the coagulation rate. The intermolecular affinity between coagulant and solvent determines the activation energy of coagulants, whereas the molecular volume is not a dominant factor. The coagulation rate depends not only on the diffusion coefficient of coagulants but also the nature of solvents. A solvent with strong polarity usually leads to a low‐coagulation rate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
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

A 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

UV 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

An 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

In 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

Catalytic 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

The 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

Sequences 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

In 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

I 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

Neutron 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

We 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

We 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

Differential 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

To 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

Homogeneous 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

Inspired 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

We 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

The 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

We 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

From 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

We 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

The 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)
Zeeman‐Doppler imaging of late‐type stars: The surface magnetic field of II Peg
Authors: Carroll T. A. , Kopf M. , Ilyin I. , Strassmeier K. G.
Published: December 2007

Late‐type stars in general possess complicated magnetic surface fields which makes their detection and in particular their modeling and reconstruction challenging. In this work we present a new Zeeman‐Doppler imaging code which is especially designed for the application to late‐type stars. This code uses a new multi‐line cross‐correlation technique by means of a principal component analysis to extract and enhance the quality of individual polarized line profiles. It implements the full polarized radiative transfer equation and uses an inversion strategy that can incorporate prior knowledge based on solar analogies. Moreover, our code utilizes a new regularization scheme which is based on local maximum entropy to allow a more appropriate reproduction of complex surface fields as those expected for late‐type stars. In a first application we present Zeeman‐Doppler images of II Pegasi which reveal a surprisingly large scale surface structure with one predominant (unipolar) magnetic longitude which is mainly radially oriented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Search for relationship between duration of the extended solar cycles and amplitude of sunspot cycle
Authors: Tlatov A.G.
Published: December 2007

Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large‐scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n + 2. The connection between cycle duration and its amplitude is established. Duration of the “latent” period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent period of cycles evolution is connected with the next sunspot cycle amplitude and can be used for the prognosis of a level and time of a sunspot maximum. The 24th activity cycle prognosis is made. The found dependences correspond to transport dynamo model of generation of solar cyclicity, it is possible with various speed of meridional circulation. Long‐term behavior of extended cycle's lengths and connection with change of a climate of the Earth is considered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3‐D non‐linear evolution of a magnetic flux tube in a spherical shell: The isentropic case
Authors: Jouve L. , Brun A.S.
Published: December 2007

We present recent 3‐D MHD numerical simulations of the non‐linear dynamical evolution of magnetic flux tubes in an adiabatically stratified convection zone in spherical geometry, using the anelastic spherical harmonic (ASH) code.We seek to understand the mechanism of emergence of strong toroidal fields from the base of the solar convection zone to the solar surface as active regions. We confirm the results obtained in cartesian geometry that flux tubes that are not twisted split into two counter vortices before reaching the top of the convection zone. Moreover, we find that twisted tubes undergo the poleward‐slip instability due to an unbalanced magnetic curvature force which gives the tube a poleward motion both in the non‐rotating and in the rotating case. This poleward drift is found to be more pronounced on tubes originally located at high latitudes. Finally, rotation is found to decrease the rise velocity of the flux tubes through the convection zone, especially when the tube is introduced at low latitudes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimentelle und numerische Untersuchungen zum Brandverhalten von Brettsperrholzplatten
Authors: Frangi Andrea , Fontana Mario , Bochicchio Giovanna
Published: December 2007

Brettsperrholzplatten stellen ein technisch und wirtschaftlich interessantes Produkt für den “modernen” Massivholzbau dar und finden in den letzten Jahren einen vermehrten Einsatz als großformatige Wand‐ und Deckenelemente im Wohnungsbau. Im Rahmen von zwei am Institut für Baustatik und Konstruktion der ETH Zürich und am Institut CNR‐IVALSA in San Michele all'Adige, Italien, laufenden Forschungsprojekten wurde das Brandverhalten von Brettsperrholzplatten mit mehreren experimentellen und numerischen Untersuchungen analysiert. Der vorliegende Artikel stellt die brandschutztechnisch relevanten Erkenntnisse aus den Untersuchungen dar und analysiert die grundsätzliche Fragestellung, ob sich im Brandfall Brettsperrholzplatten ähnlich wie Vollholzplatten verhalten. Die durchgeführten Untersuchungen haben gezeigt, dass das Brandverhalten von Brettsperrholzplatten durch das Verhalten der einzelnen Bretterlagen charakterisiert ist. Falls sich die einzelnen verkohlten Schichten frühzeitig ablösen, geht die Schutzwirkung der sich bildenden Holzkohleschicht verloren. Nach der Verkohlung und dem Abfallen jeder einzelnen Schicht ist in diesem Fall wegen der steigenden Brandraumtemperatur mit einem erhöhten Abbrand zu rechnen, ähnlich wie für geschützte Holzbauteile nach dem Versagen der Brandschutzbekleidung. Das Brandverhalten von Brettsperrholzplatten kann somit durch die Plattenschichtigkeit und die Dicke der einzelnen Schichten stark beeinflusst werden. Das Ablösen der Holzkohleschicht könnte für horizontale Bauteile (Decken) kritischer sein als für vertikale Bauteile (Wände).
Fluorescence quenching method for the determination of bleomycins A5 and A2 with halofluorescein dyes
Authors: Liu Jiangtao , Liu Zhongfang , Hu Xiaoli , Kong Ling , Liu Shaopu
Published: December 2007

In weak acidic medium, the anticancer antibiotics bleomycin A5 (BLMA5) and bleomycin A2 (BLMA2) bind with halofluorescein dyes, such as erythrosin (Ery), eosin Y (EY) and eosin B (EB), to form ion‐association complexes, which causes fluorescence quenching of halofluorescein dyes. The quenching values (ΔF) are directly in proportional to the concentrations of bleomycins over the range 0.09–2.5 µg/mL. Based on this, a fluorescence quenching method for the determination of BLMA5 and BLMA2 has been developed. The dynamic range is 0.12–2.5 µg/mL for the determination of BLMA5 and 0.09–2.0 µg/mL for BLMA2, with detection limits (3σ) of 0.04 µg/mL for BLMA5, 0.03 µg/mL for BLMA2, respectively. It has been applied to determine the two antibiotics in human serum, urine and rabbit serum samples. The recovery is in the range 90–102%. In this work, the optimum reaction conditions and the spectral characteristics of the fluorescence are investigated. The reasons for fluorescence quenching are discussed, based on the fluorescence theory. Copyright © 2007 John Wiley & Sons, Ltd.
Late morbidity after duodenum-preserving pancreatic head resection with bile duct reinsertion into the resection cavity
Authors: Cataldegirmen G , Bogoevski D , Mann O , Kaifi J T , Izbicki J R , Yekebas E F
Published: December 2007

Background

Reinsertion of the distal common bile duct (CBD) into the pancreatic resection cavity during duodenum-preserving pancreatic head excision (DPPHE) may be an alternative option to Whipple resection or bilioenteric anastomosis when chronic pancreatitis is associated with CBD stenosis.

Methods

Outcome in 82 patients with chronic pancreatitis who underwent DPPHE with CBD reinsertion was compared with that in 432 who had DPPHE without reinsertion and 50 who had a Whipple procedure or pylorus-preserving pancreatoduodenectomy (PPPD).

Results

There were no deaths after DPPHE with CBD reinsertion, compared with four (0·9 per cent) after DPPHE without reinsertion and three (6 per cent) after classical resection. Overall morbidity rates were 30, 28·9 and 36 per cent respectively. Fifteen patients (18 per cent) who had DPPHE with CBD reinsertion developed a stricture at the reinsertion site, compared with a long-term stricture rate of 2·3 per cent (ten patients) after DPPHE without CBD reinsertion and 4 per cent (two patients) after PPPD/Whipple resection.

Conclusion

Although associated with a high incidence of anastomotic stricture, reinsertion of the CBD into the resection cavity as part of DPPHE can be used to preserve duodenal passage and offers an alternative to extended resection for chronic pancreatitis.
Randomized clinical trial evaluating elective laparoscopic appendicectomy for chronic right lower-quadrant pain
Authors: Roumen R M H , Groenendijk R P R , Sloots C E J , Duthoi K E S , Scheltinga M R M , Bruijninckx C M A
Published: December 2007

Background

It is questionable whether elective appendicectomy can effectively reduce persistent or recurrent right lower-quadrant abdominal pain due to chronic or recurrent appendicitis.

Methods

This single-centre double-blind randomized clinical trial studied the effects of elective laparoscopic appendicectomy on pain 6 months after operation in patients with persistent or recurrent lower-quadrant pain. A secondary outcome evaluated was the relationship between clinical response and appendiceal histopathology. The analysis was performed on an intention-to-treat basis.

Results

Forty patients were randomized to laparoscopic appendicectomy (18) or laparoscopic inspection only (22). Postoperative pain scores differed significantly between the groups, favouring appendicectomy (P = 0·005). Relative risk calculations indicated that there was a 2·4 (95 per cent confidence interval (c.i.) 1·3 to 4·0) times greater chance of improvement in pain after laparoscopic appendicectomy. The number needed to treat was 2·2 (95 per cent c.i. 1·5 to 6·5). There was no association between postoperative pain scores and histopathology findings.

Conclusion

Persistent or recurrent lower abdominal pain can be treated by elective appendicectomy with significant pain reduction in properly selected cases. Histopathology may not be abnormal. Registration number: ISRCTN48831122 (http://www.controlled-trials.com).
Exploring the Substrate Specificity of a Mycobacterial Polyprenol Monophosphomannose‐Dependent α‐(1→6)‐Mannosyltransferase
Authors: Tam Pui‐Hang , Besra Gurdyal S. , Lowary Todd L.
Published: December 2007

A series of synthetic α‐(1→6)‐linked octyl mannopyranoside oligomers was evaluated as potential acceptors of a polyprenol monophosphomannose‐dependent α‐(1→6)‐mannosyltransferase that is involved in the biosynthesis of the mannan core of mycobacterial lipoarabinomannan. Initial evaluation demonstrated that the enzyme recognizes di‐, tri‐ and tetramannosides (5, 6 and 7) as substrates with different activities. While the highest mannosyltransferase activities were observed when the di‐ and trisaccharide were used as substrates, diminished enzymatic activity was seen with the tetramannoside. As octyl α‐D‐mannopyranosyl‐(1→6)‐α‐D‐mannopyranoside (5) appears to be the minimum structural element required for mannosyltransferase catalysis, a panel of methoxy and deoxy disaccharide analogues (8–21) were used to probe the substrate specificity of the enzyme further. In terms of the steric requirements at the active site, the enzyme does not recognize either C2′‐ and C2‐methoxy analogues as substrates, a result that suggests that the α‐(1→2)‐mannopyranosyl branches, which are present in the mannan core of LAM must be added on a larger α‐(1→6)‐oligomannan intermediate. In contrast, the presence of a methoxy functionality at the C3′, C3, C4′ and C4 positions are somewhat tolerated by the enzyme, although diminished enzyme activities were observed with the C4′‐ and C4‐methoxy analogues. Moreover, the 2′‐ and 4‐hydroxyl groups appear not to be critical for substrate binding at the active site, as both 2′‐ and 4‐deoxy analogues are substrates for the enzyme. In contrast, replacement of the hydroxyl groups at other positions essentially abolished enzymatic activity. Further kinetic characterization of the enzyme by using the effective acceptor substrates gave apparent KM values ranging from 111 to 437 μM, which are within two‐fold higher or lower than that for the parent dimannoside (5). Although the KM values indicate that the enzyme binds those acceptors with comparable affinities, the C4′‐methoxy analogue (12) turns over more slowly than the others, as indicated by the apparent Vmax values.
Towards a Tunable Tautomeric Switch in Azobenzene Biomimetics: Implications for the Binding Affinity of 2‐(4′‐Hydroxyphenylazo)benzoic Acid to Streptavidin
Authors: Farrera Joan‐Antoni , Canal Ivan , Hidalgo‐Fernández Pedro , Pérez‐García M. Lluïsa , Huertas Oscar , Luque F. Javier
Published: December 2007

The tautomeric equilibria of 2‐(4′‐hydroxyphenylazo)benzoic acid (HABA) and 2‐(3′,5′‐dimethyl‐4′‐hydroxyphenylazo)benzoic acid (3′,5′‐dimethyl‐HABA) have been studied by a combination of spectroscopic and computational methods. For neutral HABA in solvents of different polarity (toluene, chloroform, DMSO, DMF, butanol, and ethanol) the azo tautomer (AT) is largely predominant. For monoanionic HABA, the hydrazone tautomer (HT) is the only detected species in apolar solvents such as toluene and chloroform, while the AT is the only detected species in water and a mixture of both tautomers is detected in ethanol. Comparison of the results obtained for HABA and its 3′,5′‐dimethylated derivative shows that dimethylation of the hydroxybenzene ring shifts the tautomeric preferences towards the hydrazone species. These findings have been used to examine the differences in binding affinity to streptavidin, as the lower affinity of HABA can be explained in terms of the larger energetic cost associated with the tautomeric shift to the bioactive hydrazone species. Overall, these results suggest that a balanced choice of chemical substituents, embedding environment, and pH can be valuable for exploitation of the azo–hydrazone tautomerism of HABA biomimetics in biotechnological applications.
Antiproliferative Agents That Interfere with the Cell Cycle at the G1→S Transition: Further Development and Characterization of a Small Library of Stilbene‐Derived Compounds
Authors: Pizzirani Daniela , Roberti Marinella , Cavalli Andrea , Grimaudo Stefania , Di Cristina Antonietta , Pipitone Rosaria Maria , Gebbia Nicola , Tolomeo Manlio , Recanatini Maurizio
Published: December 2007

In this continuation of our research on derivatives containing the stilbene privileged structure or that are derived from it, we report the results of further studies carried out on the previously initiated collection of compounds. We used a parallel synthetic approach to rapidly obtain small sets of compounds and started the annotation of the library in progress by calculating some physicochemical properties to be eventually correlated with biological activities. A pharmacophore for the antiproliferative activity was also built to summarize the features of the library. We evaluated the antiproliferative and pro‐apoptotic activities of all compounds as well as the cell‐cycle effects of some representative compounds. After in‐depth investigations, 3′‐phenyl‐[1,1′;4′,1′′]terphenyl‐4,3′′,5′′‐triol showed the most interesting biological profile, as it interferes with cell‐cycle progression at the G1→S transition, acting on retinoblastoma phosphorylation and inducing cell differentiation.
Second‐order explicit integrator via composition for coupled rotating rigid bodies applied to roller cone drill bits
Authors: Endres L. , Krysl P.
Published: December 2007

We present a derivation of the equations of motion of a roller cone bit as an example of coupled rotating rigid bodies and apply a state‐of‐the‐art numerical integrator to produce an algorithm for use in a bit dynamics software application. The equations are derived using the virtual power method, which naturally handles the constraint between the bit body and the cones. These equations are fully three‐dimensional (three degrees of freedom for the body, plus one degree of freedom for each cone) and nicely parallel to the equations of motion of a single rigid body. We apply the composition of adjoint first‐order integrators (reminiscent of the approach used earlier to derive an explicit midpoint Lie method (Int. J. Numer. Meth. Eng.2005;63:2171–2193) to produce an algorithm that maintains the properties of the original three degree‐of‐freedom integrator: second‐order convergence, symplecticness, remarkable accuracy, and momentum conservation. This algorithm can be applied to other applications where one or more rigid bodies with a single rotational degree of freedom are attached to another rotating rigid body. Copyright © 2007 John Wiley & Sons, Ltd.
Übersicht zum derzeitigen Stand der numerischen Modellierung
Authors: Jäger Wolfram
Published: December 2007

Der Baustoff Mauerwerk hat eine Jahrtausend alte Tradition und wurde früher nur auf der Basis von Erfahrung und handwerklichem Können angewendet. Er kam deshalb bis in die zweite Hälfte des vorigen Jahrhunderts fast ohne Berechnung aus. Die jedoch immer höheren Anforderungen, beispielsweise aus der Notwendigkeit der Energieeinsparung, haben zu einer raschen Entwicklung der Mauerwerksprodukte geführt. Die Berechnung und Bemessung versuchte mitzuhalten oder nachzuziehen. Die Mittel der Computertechnik zur realitätsnahen Abbildung des Baustoff‐ und Bauteilverhaltens ermöglichten es, Tragwerke aus Mauerwerk besser beurteilen zu können. Die neuen Erkenntnisse und Verfahren der Mechanik konnten und können immer nutzbringender für die Weiterentwicklung der Berechnungs‐ und Bemessungsmethoden im Mauerwerksbau eingesetzt und zur Klärung von Verhaltens‐ und Versagensphänomenen angewendet werden.

Aber auch Schäden an bestehenden Mauerwerksbauten veranlassten die Ingenieure, den mechanischen Ursachen unter Nutzung der modernen Methoden der Baumechanik auf den Grund zu kommen und geeignete Reparatur‐ oder Verstärkungstechnologien behutsam einzusetzen.

Heute ist die numerische Analyse integraler Bestandteil der Forschungsstrategie im Mauerwerksbau. Sie wird vorrangig zur Problemlösung und zur Ursachenklärung eingesetzt. Für die täglichen Planungsaufgaben reichen die bisherigen Mittel üblicher Ingenieurlösungen nach wie vor aus. Für Problemlösungen und Schadensabklärungen werden meist Mittel und Möglichkeiten der modernen Baumechanik eingesetzt, die jedoch i. d. R. umfangreiches Spezialwissen und entsprechende Erfahrungen erfordern. Die Überprüfung der Ergebnisse ist oft schwer möglich, muss bei bestehenden Bauwerken an der Realität vorgenommen und zusätzlich durch weitere Plausibilitäts‐ und Ingenieurkontrollen ergänzt werden.

Nachfolgend soll eine kurze Einführung zur numerischen Simulation und Modellierung von Mauerwerk gegeben werden. Die anschließenden Beiträge zeigen die Einsatzmöglichkeiten von numerischen Methoden im Mauerwerksbau, wobei nur neuere Ergebnisse und Beispiele gezeigt werden sollen. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ermittlung effektiver elastischer Eigenschaften von Hochlochziegeln mittels numerischer Simulation
Authors: Hannawald Joachim , Brameshuber Wolfgang
Published: December 2007

Hochlochziegel (HLz) können in einem dreidimensionalen Finite‐Elemente (FE)‐Modell ganzer Wände nicht detailliert mit ihrer meist sehr komplexen Lochstruktur abgebildet werden, weil dann die Zahl der Freiheitsgrade der Berechnung zu groß würde. Sie müssen stattdessen als homogenes Ersatzkontinuum betrachtet werden, dessen effektive mechanische Eigenschaften zunächst nicht bekannt sind.

In diesem Beitrag wird ein numerisches Homogenisierungsverfahren vorgestellt, mit dem die effektiven elastischen Eigenschaften von HLz ermittelt werden können. Das Verfahren wird auf drei unterschiedliche, praxisübliche HLz angewendet. Hierbei zeigt sich, dass alle drei HLz effektiv als orthotropes, elastisches Kontinuum zu beschreiben sind und daher jeweils neun elastische Konstanten zur vollständigen Charakterisierung erforderlich sind. Bei den messtechnisch relativ einfach zu bestimmenden E‐Moduln in Steinhoch‐ und Steinlängsrichtung stimmen die mit dem Homogenisierungsverfahren bestimmten Werte gut mit den experimentellen Beobachtungen überein. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diskrete FE‐Modellierung von Mauerwerk zur Bestimmung der Druckfestigkeit
Authors: Graubner Carl‐Alexander , Richter Lars
Published: December 2007

Die Finite‐Element‐Methode (FEM) dient zur Beschreibung des komplexen physikalischen Verhaltens von Festkörpern (ferner auch von Flüssigkeiten, Gasen, Feldern) und stellt ein Grundwerkzeug in den Ingenieurwissenschaften dar. Die Ergebnisse der FEM liefern trotz der Leistungsfähigkeit nur eine Näherungslösung, die häufig mit aus Versuchen gewonnenen Daten verifiziert werden muss und eine anschließende Kalibrierung der Modellparameter notwendig macht.

In diesem Beitrag wird die Anwendung der FEM auf das Mauerwerk am Beispiel eines auf Druck belasteten 4‐Stein‐Körpers aus Ziegelmauerwerk beschrieben und insbesondere auf die Problematik der Abbildung der Materialeigenschaften eingegangen. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Moesin helps to restrain synaptic growth at the Drosophila neuromuscular junction
Authors: Seabrooke Sara , Stewart Bryan A.
Published: December 2007

The precise role of actin and actin‐binding proteins in synaptic development is unclear. In Drosophila, overexpression of a dominant‐negative NSF2 construct perturbs filamentous actin, which is associated with overgrowth of the NMJ, while co‐expression of moesin, which encodes an actin binding protein, suppresses this overgrowth phenotype. These data suggest that Moesin may play a role in synaptic development at the Drosophila NMJ. To further investigate this possibility, we examined the influence of loss‐of‐function moesin alleles on the NSF2‐induced overgrowth phenotype. We found that flies carrying P‐element insertions that reduce moesin expression enhanced the NMJ overgrowth phenotype, indicating a role for Moesin in normal NMJ morphology. In addition to the NMJ overgrowth phenotype, expression of dominant‐negative NSF2 is known to reduce the frequency of miniature excitatory junctional potentials and the amplitude of excitatory junctional potentials. We found that moesin coexpression did not restore the physiology of the mutant NSF2 phenotype. Together, our results demonstrate a role for moesin in regulating synaptic growth in the Drosophila NMJ and suggest that the effect of dominant‐negative NSF2 on NMJ morphology and physiology may have different underlying molecular origins. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008.