bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of 9,9‐bis(4‐aminophenyl)fluorene‐based benzoxazine and properties of its high‐performance thermoset
Authors: Chang Hou Chien , Lin Ching Hsuan , Tian Yu Wei , Feng Yu Ren , Chan Li Hsin 
Published: February 2012

AbstractA benzoxazine (P‐bapf) based on 9,9‐bis(4‐aminophenyl)fluorene (BAPF), phenol, and formaldehyde was successfully prepared using two‐pot and one‐pot procedures. In the two‐pot approach, BAPF initially reacted with 2‐hydroxybenzaldehyde, leading to 9,9‐bis(4‐(2‐hydroxybenzylideneimino)phenyl)fluorene. The imine linkages of 9,9‐bis(4‐(2‐hydroxybenzylideneimino)phenyl)fluorene were then reduced by sodium borohydride, forming 9,9‐bis(4‐(2‐hydroxybenzylamino)phenyl)fluorene. Finally, paraformaldehyde was added to induce ring closure condensation, forming benzoxazine (P‐bapf). In the one‐pot approach, P‐bapf was obtained directly by reacting BAPF, phenol, and paraformaldehyde in various solvents. Among the solvents, we found that using toluene/ethanol (2/1, v/v) as a solvent leads to the best purity and yield. No gelation was observed in the preparation. The structure of the resulting benzoxazine was confirmed by 1H, 13C, 1H1H and 1H13C NMR spectra. P‐bapf exhibits a photoluminescent emission at 395 nm under an excitation of 275 nm. After curing, the resulting P‐bapf thermoset exhibits Tg as high as 236 °C, and the Tg can be further increased to 260 °C by copolymerization with an equal equivalent of cresol novolac epoxy. The 5% degradation temperature of the P‐bapf thermoset reaches as high as 413 °C (N2) and 431 °C (air). The refractive index at 589 nm is as high as 1.70, demonstrating a high refractive index characteristic of fluorene linkage. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Controlled random and alternating copolymerization of (meth)acrylates, acrylonitrile, and (meth)acrylamides with vinyl ethers by organotellurium‐, organostibine‐, and organobismuthine‐mediated living radical polymerization reactions
Authors: Mishima Eri , Yamago Shigeru 
Published: February 2012

AbstractRandom and alternating copolymerizations of acrylates, methacrylates, acrylonitorile, and acrylamides with vinyl ethers under organotellurium‐, organostibine‐, and organobismuthine‐mediated living radical polymerization (TERP, SBRP, and BIRP, respectively) have been studied. Structurally well‐controlled random and alternating copolymers with controlled molecular weights and polydispersities were synthesized. The highly alternating copolymerization occurred in a combination of acrylates and vinyl ethers and acrylonitorile and vinyl ethers by using excess amount of vinyl ethers over acrylates and acrylonitorile. On the contrary, alternating copolymerization did not occur in a combination of acrylamides and vinyl ethers even excess amount of vinyl ethers were used. The reactivity of polymer‐end radicals to a vinyl ether was estimated by the theoretical calculations, and it was suggested that the energy level of singly occupied molecular orbital (SOMO) of polymer‐end radical species determined the reactivity. By combining living random and alternating copolymerization with living radical or living cationic polymerization, new block copolymers, such as (PBA‐alt‐PIBVE)‐block‐(PtBA‐co‐PIBVE), PBA‐block‐(PBA‐alt‐PIBVE), and (PTFEA‐alt‐PIBVE)‐block‐PIBVE, with controlled macromolecular structures were successfully synthesized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Mechanical properties of glass continuous poly(cyclohexylethylene) block copolymers
Authors: Mansour Ameara S. , Lodge Timothy P. , Bates Frank S. 
Published: February 2012

AbstractThe bulk mechanical properties of linear triblock and pentablock copolymers that self‐assemble into hexagonally packed cylinders with glassy, unentangled matrices of poly(cyclohexylethylene) (PCHE for a homopolymer, C for a block copolymer) with rubbery poly(ethylene‐alt‐propylene) (P) and semicrystalline polyethylene (E) minority components are examined. The tensile properties of high C content CEC triblock copolymer could not be quantified; however, CPC can plastically deform under uniaxial strain, unlike brittle PCHE. Both CECEC and CPCPC pentablock copolymers exhibited ductile tensile behavior, but the tensile properties of blends of these two pentablock copolymers show that the addition of crystallinity in the minority phase prevents strain softening after yielding and necking, which indicates that these samples deform only via crazing. On the other hand, the white gage region of CPCPC and the ability of CPCPC to neck indicate that high C content materials deform via shear yielding and crazing when the minority component is a rubbery material. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Wrapping corrections beyond the 𝔰𝔩(2) sector in 𝒩 = 4 SYM
Authors: Beccaria M. , Macorini G. , Ratti C. 
Published: February 2012

AbstractThe 𝔰𝔩(2) sector of 𝒩 = 4 SYM theory has been much studied and the anomalous dimensions of those operators are well known. Nevertheless, many interesting operators are not included in this sector. We consider a class of twist operators beyond the 𝔰𝔩(2) subsector introduced by Freyhult, Rej and Zieme. They are spin n, length‐3 operators. At one‐loop they can be identified with three gluon operators. At strong coupling, they are associated with spinning strings with two spins in AdS space and charge in S5. We exploit the Y‐system to compute the leading weak‐coupling four loop wrapping correction to their anomalous dimension. The result is written in closed form as a function of the spin n. We combine the wrapping correction with the known four loop asymptotic Bethe Ansatz contribution and analyze special limits in the spin n. In particular, at large n, we prove that a generalized Gribov‐Lipatov reciprocity holds. At negative unphysical spin, we present a simple BFKL‐like equation predicting the rightmost leading poles.
Transport and response coefficients in the blackfold approach
Authors: Camps J. 
Published: February 2012

AbstractThe blackfold approach is an effective theory for higher dimensional black holes. In this approach, black holes are described as materials: they are characterised by speeds of sound, viscosities and elastic moduli. These can be computed from first principles in general relativity by generalising techniques developed in AdS/CFT contexts. Apart from its intrinsic interest, this approach is a dramatic simplification of the Einstein equations that can be used to tackle important open problems of higher dimensional gravity.
Quadratic deformation of Minkowski space
Authors: Cervantes D. , Cervantes R. , Lledó M.A. , Nadal F.A. 
Published: February 2012

AbstractWe present a deformation of the Minkowski space as embedded into the conformal space (in the formalism of twistors) based in the quantum versions of the corresponding kinematic groups. We compute explicitly the star product, whose Poisson bracket is quadratic. We show that the star product although defined on the polynomials can be extended differentiably. Finally we compute the Eucliden and Minkowskian real forms of the deformation.
A brief review on the problem of divergence in Krein space quantization
Authors: Payandeh F. , Moghaddam Z.Gh. , Fathi M. 
Published: February 2012

AbstractIn this paper we have a brief review on the problem of divergence in quantum field theory and its elimination using the method of Krein space quantization. In this method, the auxiliary negative frequency states have been utilized, the modes of which do not interact with the physical states and are not affected by the physical boundary conditions. It is remarkable that Krein space quantization is similar to Pauli‐Villars regularization, so we can call it the “Krein regularization”. Considering the QED in Krein space quantization, it could be shown that the theory is automatically regularized. Calculation of the three primitive divergent integrals, the vacuum polarization, electron self energy and vertex function using Krein space method leads to finite values, since the infrared and ultraviolet divergencies do not appear. For another example, the Casimir stress on a spherical shell in de Sitter spacetime for a massless scalar field could be calculated using Krein space quantization.
Quantum backreaction in string theory
Authors: Evnin O. 
Published: February 2012

AbstractThere are situations in string theory when a finite number of string quanta induce a significant backreaction upon the background and render the perturbation theory infrared‐divergent. The simplest example is D0‐brane recoil under an impact by closed strings. A more physically interesting case is backreaction on the evolution of a totally compact universe due to closed string gas. Such situations necessitate qualitative amendments to the traditional formulation of string theory in a fixed classical background. In this contribution to the proceedings of the XVII European Workshop on String Theory in Padua, I review solved problems and current investigations in relation to this kind of quantum backreaction effects.
From supersymmetric to non‐supersymmetric black holes
Authors: Galli P. , Ortín T. , Perz J. , Shahbazi C.S. 
Published: February 2012

AbstractMethods similar to those used for obtaining supersymmetric black hole solutions can be employed to find also non‐supersymmetric solutions. We briefly review some of them, with the emphasis on the non‐extremal deformation ansatz of [1].
Ohmic and rectifying contacts on bulk AlN for radiation detector applications
Authors: Erlbacher Tobias , Bickermann Matthias , Kallinger Birgit , Meissner Elke , Bauer Anton J. , Frey Lothar 
Published: February 2012

AbstractIn this paper we report on ohmic and rectifying contacts fabricated on undoped bulk AlN substrates for radiation detector applications. The ohmic Ni contacts exhibit negligible contact resistances. Current conduction is dominated by field enhanced thermal emission from traps 0.4 to 0.6 eV below the conduction band. The Pt Schottky contacts show excellent rectifying behaviour. In forward conduction, device current is again limited by the Poole‐Frenkel effect. The Schottky barrier features very low reverse leakage currents, and voltages of up to ‐200 V can be applied. The capability of bulk AlN for radiation detectors at room temperature is demonstrated. Suitability is deduced from both X‐ray absorption experiments and low reverse leakage currents of the fabricated Schottky diodes. Additionally, the AlN substrate is almost blind to sun light due to its wide band gap. Still, reduction of recombination sites in AlN is required to achieve maximum detector performance. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characteristics of AlN crystal growth depending on m‐ and a‐axis oriented off‐angle of c‐sapphire substrate
Authors: Maeda Noritoshi , Hirayama Hideki , Fugikawa Sachie 
Published: February 2012

AbstractFor the achievement of high‐efficiency AlGaN‐based deep‐ultraviolet (DUV) light‐emitting diodes (LEDs), we investigated the characteristics of AlN crystal growth depending on m‐ and a‐axis oriented off‐angle of c‐sapphire substrate. In order to reduce threading dislocation density (TDD) in AlN crystal growth, we used ammonia (NH3) pulse‐flow multilayer (ML) growth technique in the metal‐organic chemical vapor phase deposition (MOCVD). We found that a macrostep geometry (large step‐bunching) is generated on the surface of AlN template grown on m‐axis oriented (0001) sapphire substrate. On the other hand, macrostep‐free surface can be obtained for AlN grown on a‐axis oriented sapphire. We also found that cracks are easier generated in AlN grown on a‐axis oriented sapphire. It is considered that step‐flow growth is easily obtained for the growth of a‐axis oriented case due to that the atom site of the step edge in the growth is more stable. On the other hand, for m‐axis oriented case, step‐bunching is considered to occur because atoms are easily drifted during the growth due to that the atom site of the edge steps are more unstable. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current transport through an n‐doped, nearly lattice matched GaN/AlInN/GaN heterostructure
Authors: Corbett B. , Charash R. , Damilano B. , Kim‐Chauveau H. , Cordero N. , Shams H. , Lamy J.‐M. , Akhter M. , Maaskant P. P. , Frayssinet E. , Mierry P. de , Duboz J.‐Y. 
Published: February 2012

AbstractThe low refractive index of AlInN makes it a strong candidate as a waveguide cladding layer for lasers emitting from the blue to the green. A sequence of AlInN layers interfaced periodically with GaN is needed to provide a smooth surface for growth of quantum wells. The current transport across a highly doped single 54 nm thick layer of AlInN clad by GaN is analysed and is shown to be dominated by the heterointerfaces. Greater than 1 V is required to obtain current densities required in lasers of several kA/cm2. Frequency dependent electrical reflection measurements show that a 20 nm wide depletion zone is present at the interfaces even under bias and despite the high doping levels. A thermally activated resistive shunting of the interface is relevant at low voltages while the current is dominated by tunnelling at laser current densities. A low defect density AlInN/GaN multilayer structure requires > 10 V in order to drive current at levels needed in a laser diode. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ge(100) surfaces prepared in vapor phase epitaxy process ambient
Authors: Brückner Sebastian , Barrigón Enrique , Supplie Oliver , Kleinschmidt Peter , Dobrich Anja , Löbbel Claas , Rey‐Stolle Ignacio , Döscher Henning , Hannappel Thomas 
Published: February 2012

AbstractGe(100) substrates essential for subsequent III–V integration were studied in the hydrogen ambient of a metalorganic vapor phase epitaxy reactor. We confirmed thermal oxide and carbon removal by X‐ray photoelectron spectroscopy, characterized the (2 × 1)/(1 × 2) surface reconstruction by low energy electron diffraction, and employed reflection anisotropy spectroscopy for optical in situ analysis. Our Ge(100) spectra de‐ viate from reference data of clean surfaces prepared in ultra‐high vacuum, most probably due to the presence of hydrogen bonds. The observation was correlated with Fourier‐transform infrared spectroscopy showing coupled H–Ge–Ge–H stretch modes associated with a monohydride termination of the Ge(100) surface. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integration of the OpenIGTLink Network Protocol for image‐guided therapy with the medical platform MeVisLab
Authors: Egger Jan , Tokuda Junichi , Chauvin Laurent , Freisleben Bernd , Nimsky Christopher , Kapur Tina , Wells William 
Published: February 2012

AbstractBackgroundOpenIGTLink is a new, open, simple and extensible network communication protocol for image‐guided therapy (IGT). The protocol provides a standardized mechanism to connect hardware and software by the transfer of coordinate transforms, images, and status messages. MeVisLab is a framework for the development of image processing algorithms and visualization and interaction methods, with a focus on medical imaging.MethodsThe paper describes the integration of the OpenIGTLink network protocol for IGT with the medical prototyping platform MeVisLab. The integration of OpenIGTLink into MeVisLab has been realized by developing a software module using the C++ programming language.ResultsThe integration was evaluated with tracker clients that are available online. Furthermore, the integration was used to connect MeVisLab to Slicer and a NDI tracking system over the network. The latency time during navigation with a real instrument was measured to show that the integration can be used clinically.ConclusionsResearchers using MeVisLab can interface their software to hardware devices that already support the OpenIGTLink protocol, such as the NDI Aurora magnetic tracking system. In addition, the OpenIGTLink module can also be used to communicate directly with Slicer, a free, open source software package for visualization and image analysis. Copyright © 2012 John Wiley & Sons, Ltd.
Comparison of different reconstruction algorithms for three‐dimensional ultrasound imaging in a neurosurgical setting
Authors: Miller D. , Lippert C. , Vollmer F. , Bozinov O. , Benes L. , Schulte D.M. , Sure U. 
Published: February 2012

AbstractBackgroundFreehand three‐dimensional ultrasound imaging (3D‐US) is increasingly used in image‐guided surgery. During image acquisition, a set of B‐scans is acquired that is distributed in a non‐parallel manner over the area of interest. Reconstructing these images into a regular array allows 3D visualization. However, the reconstruction process may introduce artefacts and may therefore reduce image quality. The aim of the study is to compare different algorithms with respect to image quality and diagnostic value for image guidance in neurosurgery.Methods3D‐US data sets were acquired during surgery of various intracerebral lesions using an integrated ultrasound‐navigation device. They were stored for post‐hoc evaluation. Five different reconstruction algorithms, a standard multiplanar reconstruction with interpolation (MPR), a pixel nearest neighbour method (PNN), a voxel nearest neighbour method (VNN) and two voxel based distance‐weighted algorithms (VNN2 and DW) were tested with respect to image quality and artefact formation. The capability of the algorithm to fill gaps within the sample volume was investigated and a clinical evaluation with respect to the diagnostic value of the reconstructed images was performed.ResultsMPR was significantly worse than the other algorithms in filling gaps. In an image subtraction test, VNN2 and DW reliably reconstructed images even if large amounts of data were missing. However, the quality of the reconstruction improved, if data acquisition was performed in a structured manner. When evaluating the diagnostic value of reconstructed axial, sagittal and coronal views, VNN2 and DW were judged to be significantly better than MPR and VNN.ConclusionVNN2 and DW could be identified as robust algorithms that generate reconstructed US images with a high diagnostic value. These algorithms improve the utility and reliability of 3D‐US imaging during intraoperative navigation. Copyright © 2012 John Wiley & Sons, Ltd.
Sharp kernel clustering algorithms and their associated Grothendieck inequalities
Authors: Khot Subhash , Naor Assaf 
Published: February 2012

AbstractIn the kernel clustering problem we are given a (large) n × n symmetric positive semidefinite matrix A = (aij) with
\documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}\sum_{i=1}^n\sum_{j=1}^n a_{ij}=0\end{align*}\end{document}
and a (small) k × k symmetric positive semidefinite matrix B = (bij). The goal is to find a partition {S1,…,Sk} of {1,…n} which maximizes \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}\sum_{i=1}^k\sum_{j=1}^k \left(\sum_{(p,q)\in S_i\times S_j}a_{pq}\right)b_{ij}\end{align*}\end{document}. We design a polynomial time approximation algorithm that achieves an approximation ratio of \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}\frac{R(B)^2}{C(B)}\end{align*}\end{document}, where R(B) and C(B) are geometric parameters that depend only on the matrix B, defined as follows: if bij = 〈vi,vj〉 is the Gram matrix representation of B for some \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}v_1,\ldots,v_k\in \mathbb{R}^k\end{align*}\end{document}
then R(B) is the minimum radius of a Euclidean ball containing the points {v1,…,vk}. The parameter C(B) is defined as the maximum over all measurable partitions {A1,…,Ak} of \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}\mathbb{R}^{k-1}\end{align*}\end{document}
of the quantity \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}\sum_{i=1}^k\sum_{j=1}^k b_{ij}\langle z_i,z_j\rangle\end{align*}\end{document}, where for i∈{1,…,k} the vector \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}z_i\in \mathbb{R}^{k-1}\end{align*}\end{document}
is the Gaussian moment of Ai, i.e., \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}z_i=\frac{1}{(2\pi)^{(k-1)/2}}\int_{A_i}xe^{-\|x\|_2^2/2}dx\end{align*}\end{document}. We also show that for every ε > 0, achieving an approximation guarantee of \documentclass{article}\usepackage{mathrsfs, amsmath, amssymb}\pagestyle{empty}\begin{document}\begin{align*}(1-\varepsilon)\frac{R(B)^2}{C(B)}\end{align*}\end{document}
is Unique Games hard. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013
New approach to nonrepetitive sequences
Authors: Grytczuk Jarosław , Kozik Jakub , Micek Piotr 
Published: February 2012

AbstractA sequence is nonrepetitive if it does not contain two adjacent identical blocks. The remarkable construction of Thue asserts that three symbols are enough to build an arbitrarily long nonrepetitive sequence. It is still not settled whether the following extension holds: for every sequence of three‐element sets L1,…,Ln there exists a nonrepetitive sequence s1,…,sn with si∈Li. We propose a new non‐constructive way to build long nonrepetitive sequences and provide an elementary proof that sets of size 4 suffice confirming the best known bound. The simple double counting in the heart of the argument is inspired by the recent algorithmic proof of the Lovász local lemma due to Moser and Tardos. Furthermore we apply this approach and present game‐theoretic type results on nonrepetitive sequences. Nonrepetitive game is played by two players who pick, one by one, consecutive terms of a sequence over a given set of symbols. The first player tries to avoid repetitions, while the second player, in contrast, wants to create them. Of course, by simple imitation, the second player can force lots of repetitions of size 1. However, as proved by Pegden, there is a strategy for the first player to build an arbitrarily long sequence over 37 symbols with no repetitions of size greater than 1. Our techniques allow to reduce 37–6. Another game we consider is the erase‐repetition game. Here, whenever a repetition occurs, the repeated block is immediately erased and the next player to move continues the play. We prove that there is a strategy for the first player to build an arbitrarily long nonrepetitive sequence over 8 symbols. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2012