bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal singular control for systems involving parameters
Authors: Popescu Mihai 
Published: August 2008

AbstractWhat we shall take into consideration is represented by the problems of singular optimal control when the index of performance, the differential constraints and the final conditions contain parameters. What is determined is the trajectory of the neighboring extremal for the initial point perturbed at the constraints of the perturbed final manifold. The present study evaluates the variation of the command on the extremal. This one allows obtaining the second variation in the singular case. The sufficient conditions of minimum are a result of imposing the non‐negativity of the second variation. The application made analysis the optimality of the singular control for a system in the class of affine differential systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Qualitative response of interaction networks: application to the validation of biological models
Authors: Siegel Anne , Guziolowski Carito , Veber Philippe , Radulescu Ovidiu , Le Borgne Michel 
Published: August 2008

AbstractWe advocate the use of qualitative models for the analysis of shift equilibria in large biological systems. We present a mathematical method, allowing qualitative predictions to be made of the behaviour of a biological system. These predictions are not dependent on specific values of the kinetic constants. We show how these methods can be used to improve understanding of a complex regulatory system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spontaneous particle creation within the external field approximation of QED
Authors: Szpak Nikodem 
Published: August 2008

AbstractIt is expected that strong electromagnetic fields in QED may lead to destabilization of the vacuum, its decay and spontaneous production of an electron‐positron pair if the strength of the electric field exceeds some threshold. We study the problem within an external field approximation of QED in presence of time‐dependent external fields and define the spontaneous particle creation via the adiabatic limit. We consider some model fields, which we solve analytically or numerically, in order to explain the subtlety of the effect and to recognize problems appearing in its proof. We conclude by characterizing when the effect can exist in a stable way and when it becomes unstable w.r.t. small perturbations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Developments in matching and scaling algorithms
Authors: Duff Iain S. 
Published: August 2008

AbstractWe look at some recent work on scaling and matching algorithms. We show how these algorithms can be used as a preprocessor for direct methods for solving symmetric indefinite systems. We also discuss current work towards developing implementations for parallel machines. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Toward fast and accurate methods for dose calculation in radiotherapy
Authors: Frank Martin , Hensel Hartmut , Klar Axel 
Published: August 2008

AbstractThis paper represents a first step toward a moment method for dose calculations in radiotherapy. Starting from a deterministic transport model, a new macroscopic model is derived having two goals in mind: lower computation times on the one hand, high accuracy and model inherent incorporation of tissue inhomogeneities on the other hand. While being fast, the second property is lost in the often used pencil beam models. Some numerical results are presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carleman estimate for parabolic equation with memory effects and exact controllability
Authors: Kumarasamy Sakthivel 
Published: August 2008

AbstractA nonlinear parabolic problem with memory effect is considered. We first establish a Carleman type estimate for a linear problem which is the adjoint of a suitable linearization of the nonlinear problem. As a consequence of this estimate we obtain an observability estimate. Then we establish the exact controllability of the linearized system with distributed control over a subdomain. Finally, we arrive at the controllability of the nonlinear system via a classical fixed point theorem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modelling of turbulent flow over rough walls
Authors: Louda Petr , Příhoda Jaromír , Kozel Karel 
Published: August 2008

AbstractThe numerical simulation of turbulent flow over rough walls was carried out for various types of roughness. The mathematical model was based on the Reynolds averaged Navier‐Stokes equations for incompressible flow. The two‐equation SST and oneequation Spalart‐Allmaras turbulence models were used. Boundary conditions on rough walls were prescribed directly on the wall using the SST model modified to account for wall roughness by Hellsten and Laine (1997) and the SA model modified by Aupoix and Spalart (2003). Turbulence models were tested for the constant pressure turbulent boundary layer on the rough wall formed by commercial abrasive paper and by tightly packed spheres. The effect of wall roughness on the decelerated flow over a smoothly contoured ramp with flow separation was investigated. Obtained results were compared with experimental data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
How to discretize the Total Variation of an image?
Authors: Moisan Lionel 
Published: August 2008

AbstractBecause they are based on finite differences, usual discretizations of the Total Variation lead to aliased images. We propose a new discretization called spectral total variation that agrees with Shannon sampling principles and produces images that can be exactly interpolated. The quality improvement is illustrated experimentally in the case of image deblurring. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of a Joule–heating model related to resistance welding
Authors: González Montesinos María Teresa , Ortegón Gallego Francisco 
Published: August 2008

AbstractThe purpose of this work is to establish the existence of capacity solutions to the thermistor problem under certain weak assumptions on data. Also, some numerical results are shown. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis and characterization of sulfonated block copolymers by atom transfer radical polymerization
Authors: Baek Kyung‐Youl 
Published: August 2008

AbstractWell‐defined sulfonated polystyrene and block copolymers with n‐butyl acrylate (nBA) were synthesized by CuBr catalyzed living radical polymerization. Neopentyl p‐styrene sulfonate (NSS) was polymerized with ethyl‐2‐bromopropionate initiator and CuBr catalyst with N,N,N′,N′‐pentamethylethyleneamine to give poly(NSS) (PNSS) with a narrow molecular weight distribution (MWD < 1.12). PNSS was then acidified by thermolysis resulting in a polystyrene backbone with 100% sulfonic acid groups. Random copolymers of NSS and styrene with various composition ratios were also synthesized by copolymerization of NSS and styrene with different feed ratios (MWD < 1.11). Well defined block copolymers with nBA were synthesized by sequential polymerization of NSS from a poly(n‐butyl acrylate) (PnBA) precursor using CuBr catalyzed living radical polymerization (MWD < 1.29). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5991–5998, 2008
9‐Bromoanthracene photodimers as initiators in controlled radical polymerization: Silane radical atom abstraction coupled with nitroxide mediated polymerization
Authors: Thakur Sona , Smith Jenell R. , Tillman Eric S. , Cohen Nicole A. , Contrella Nathan D. 
Published: August 2008

AbstractSlow initiation relative to propagation has previously prevented photodimers of 9‐bromoanthracene or 9‐chloroanthracene, formed by [4 + 4] photocyclization reactions of the analogous 9‐haloanthracene, from being viable initiators in atom transfer radical polymerization (ATRP) reactions. The resulting polymers were found to possess high polydispersity index (PDI) values, much higher than expected number average molecular weight (Mn) values, with the reaction displaying a nonlinear relationship between monomer conversion and Mn. We report here the use of silane radical atom abstraction (SRAA) to create initiating bridgehead radicals in the presence of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) to mediate the polymerization. When using SRAA coupled with nitroxide mediated polymerization, a dramatic decrease in PDI values was observed compared with analogous ATRP reactions, with Mn values much closer to those anticipated based on monomer‐to‐initiator ratios. Analysis using UV‐Vis spectroscopy indicated only partial anthracene labeling (∼ 25%) on the polymers, consistent with thermolysis of the anthracene photodimer coupled with competition between initiation from the bridgehead photodimer radical and silane‐based radical. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6016–6022, 2008
A hybrid‐type, chiral π‐conjugated polymer wrapped with polyhedral oligomeric silsesquioxanes
Authors: Miyake Junpei , Chujo Yoshiki 
Published: August 2008

AbstractA novel hybrid‐type chiral binaphthyl‐based polyarylene derivative with polyhedral oligomeric silsesquioxanes (POSS) units 2a was prepared by Suzuki–Miyaura coupling polymerization from a chiral (R)‐6,6′‐dibromo‐2,2′‐diPOSS‐substituted 1,1′‐binaphthyl derivative 1a and p‐biphenylene diboronic acid. As a reference, a binaphthyl‐based polyarylene derivative without POSS unit 2b was also prepared. The obtained polymers were studied with thermogravimetric analysis, optical rotations, circular dichroism (CD), ultraviolet‐visible, and photoluminescence (PL) spectra. Gel permeation chromatography measurements of 2a and 2b showed that their number‐average molecular weights were 13,300 and 16,500, respectively. The thermal stability of POSS‐modified polymer 2a (temperature of 10% weight loss; T10 = 380 °C) was extremely high compared with that of polymer without POSS unit 2b (T10 = 335 °C) due to the siliceous bulky POSS segments on the side chains. The specific optical rotation [α]D was −66.7° (c 0.06, CHCl3) for 2a and −62.3° (c 0.06, CHCl3) for 2b. The CD spectra showed that these two polymers had very similar and strong Cotton effects. Film polymer 2a showed almost the same PL spectrum as that in dilute CHCl3 solution, indicating that bulky POSS units strongly suppressed intermolecular aggregation of the π‐conjugated polymer backbone. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6035–6040, 2008
Random terpolymers for electroluminescent devices: Synthesis and characterization of new cyano‐containing poly(fluorenylene‐vinylene)s
Authors: Grisorio Roberto , Piliego Claudia , Fini Paola , Cosma Pinalysa , Mastrorilli Piero , Gigli Giuseppe , Suranna Gian Paolo , Nobile Cosimo Francesco 
Published: August 2008

AbstractThe synthesis of new random poly(2,7‐fluorenylene‐vinylene)s was achieved by a Suzuki–Heck cascade polymerization reaction. The poly(fluorenylene‐vinylene) base structure was modified by the regio‐random incorporation of 1‐cyano‐2,5‐phenylene as electron withdrawing unit (CN‐PFV1) and its properties were compared with terpolymers also embodying 1,4‐dioctyloxy‐2,5‐phenylene (CN‐PFV2) or 3,6‐N‐octylcarbazole (CN‐PFV3) as electron‐donating moieties. Thermal analysis revealed a high thermal stability (Td > 389 °C) and the absence of glass transitions for all polymers. Cyclic voltammetry indicated a high electron affinity of the materials (2.96–3.21 eV) attributed to the presence of the cyano‐containing comonomer. In dilute solutions, the copolymers showed a broad green fluorescence with quantum yields ranging from 0.42 to 0.79, while in the solid state, a relatively narrow emission centered at ∼ 560 nm, governed by the low‐energy segments within the π‐conjugated backbone, was observed. The electroluminescence properties of the materials were tested in OLED devices of ITO/PEDOT‐PSS/CN‐PFV1‐3/Ca/Al or ITO/PEDOT‐PSS/CN‐PFV1‐3/Alq3/Ca/Al configurations, showing a bright green‐yellow emission that, in the case of CN‐PFV2, reached 1403 cd/m2 with efficiencies as high as 0.13 cd/A. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6051–6063, 2008
Electrospray ionization mass spectrometric study of end‐groups in peroxydicarbonate‐initiated radical polymerization
Authors: Buback Michael , Frauendorf Holm , Janssen Olaf , Vana Philipp 
Published: August 2008

AbstractInitiation by diethyl peroxydicarbonate (E‐PDC), di‐n‐tetradecyl peroxydicarbonate (nTD‐PDC), di‐n‐hexadecyl peroxydicarbonate (nHD‐PDC), and di‐2‐ethylhexyl peroxydicarbonate (2EH‐PDC) of free‐radical polymerizations of methyl methacrylate in benzene solution was studied by end‐group analysis via electrospray ionization mass spectrometry (ESI‐MS). Unambiguous assignment of ESI‐MS peaks allows for identification of the type of radical that starts chain growth. In case of initiation by dialkyl peroxydicarbonates with linear alkyl groups, almost exclusively alkoxy carbonyloxyl species, which are the primary fragments from initiator decomposition, occur as end‐groups. With 2EH‐PDC, however, both the primary 2‐ethylhexoxy carbonyloxyl fragment and a second moiety, which is formed by decarboxylation of the 2‐ethylhexoxy carbonyloxyl radical, are clearly observed as end‐groups. The decarboxylation process is described by a concerted mechanism which involves a 1,5‐hydrogen shift reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6071–6081, 2008
Compensation in boron‐doped CVD diamond
Authors: Gabrysch Markus , Majdi Saman , Hallén Anders , Linnarsson Margareta , Schöner Adolf , Twitchen Daniel , Isberg Jan 
Published: August 2008

AbstractHall‐effect measurements on single crystal boron‐doped CVD diamond in the temperature interval 80–450 K are presented together with SIMS measurements of the dopant concentration. Capacitance–voltage measurements on rectifying Schottky junctions manufactured on the boron‐doped structures are also presented in this context. Evaluation of the compensating donor (ND) and acceptor concentrations (NA) show that in certain samples very low compensation ratios (ND/NA below 10–4) have been achieved. The influence of compensating donors on majority carrier transport and the significance for diamond device performance are briefly discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band bending and quasi‐2DEG in the metallized β‐SiC(001) surface
Authors: Rurali R. , Wachowicz E. , Hyldgaard P. , Ordejón P. 
Published: August 2008

AbstractWe study the mechanism leading to the metallization of the β‐SiC(001) Si‐rich surface induced by hydrogen adsorption. We analyze the effects of band bending and demonstrate the existence of a quasi‐2D electron gas, which originates from the donation of electrons from adsorbed hydrogen to bulk conduction states. We also provide a simple model that captures the main features of the results of first‐principles calculations, and uncovers the basic physics of the process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of the antiobesity effects of the protopanaxadiol‐ and protopanaxatriol‐type saponins of red ginseng
Authors: Kim Ji Hyun , Kang Soon Ah , Han Seung‐Moo , Shim Insop 
Published: August 2008

AbstractA previous study demonstrated that ginseng crude saponins prevent obesity induced by a high‐fat diet in rats. Ginseng crude saponins are known to contain a variety of bioactive saponins. The present study investigated and compared the antiobesity activity of protopanaxadiol (PD) and protopanaxatriol (PT) type saponins, major active compounds isolated from crude saponins. Male 4‐week‐old Sprague‐Dawley rats were fed with normal diet (N) or high‐fat diet (HF). After 5 weeks, the HF diet group was subdivided into the control HF diet, HF diet‐PD and HF diet‐PT group (50 mg/kg/day, 3 weeks, i.p.). Treatment with PD and PT in the HF diet group reduced the body weight, total food intake, fat contents, serum total cholesterol and leptin to levels equal to or below the N diet group. The hypothalamic expression of orexigenic neuropeptide Y was significantly decreased with PD or PT treatment, whereas that of anorexigenic cholecystokinin was increased, compared with the control HF diet group. In addition, PD type saponins had more potent antiobesity properties than PT saponins, indicating that PD‐type saponins are the major components contributing to the antiobesity activities of ginseng crude saponins. The results suggest that the antiobesity activity of PD and PT type saponins may result from inhibiting energy gain, normalizing hypothalamic neuropeptides and serum biochemicals related to the control of obesity. Copyright © 2008 John Wiley & Sons, Ltd.
1D lead iodide crystals encapsulated within single walled carbon nanotubes
Authors: Kuganathan Navaratnarajah , Green Jennifer C. 
Published: August 2008

AbstractThe structure and binding energies of lead iodide crystals encapsulated within single‐walled carbon noanotubes are studied using density functional theory. Calculations were performed on the simulated PbI2 structure encapsulated within a (12,12) single‐walled nanotube, to investigate the perturbations on the PbI2 crystal and tube structure and electronic structure, and to estimate the binding energy. The calculation confirms the structure as a single chain of PbI6 octahedra bound by two chains of PbI5 square pyramids. The calculated binding energy shows that the encapsulation is noncovalent. Minimal charge transfer is observed between nanotube and the PbI2 crystals. The band gap is shown to increase from the bulk to the encapsulated structure. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Prediction of excited state energies for molecular nitrogen using quantum Monte Carlo methods
Authors: Fayton Floyd A. , Gibson Ainsley A. , Harkless John A. W. 
Published: August 2008

AbstractUsing the quantum Monte Carlo (QMC) method, we estimated electronic excitation energies for four low‐lying Frank–Condon states of dinitrogen. QMC trial function forms were examined, with single and multideterminant wave functions derived from configuration interaction (CI) and complete active space self‐consistent field theory (CASSCF) calculations. Variational Monte Carlo (VMC) and fixed‐node diffusion Monte Carlo (FN‐DMC) results compare favorably with TDHF, MRDCI, TDDFT, MR‐CCSD, EOM‐CCSD, and CASSCF which demonstrate the accuracy of QMC for these excited electronic states. The CASSCF constructed trial functions for QMC (QMC‐CAS) and MR‐CCSD deviate the least from the experimental values presented. Mean absolute deviation (MAD), or the difference between the calculated result and the experimental value divided by the total number of calculated results, is provided for each method. The least favorable MAD is obtained by the multideterminant and single determinant CISD trial function used for VMC calculations at 1.67 and 1.32, respectively. The lowest three MAD's are provided by the multideterminant CASSCF‐VMC (0.23), the multideterminant CASSCF‐DMC (0.14), and the MR‐CCSD (0.13) calculation. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Modeling enzymatic transition states by force field methods
Authors: Hansen M. B. , Jensen H. J. A. , Jensen F. 
Published: August 2008

AbstractThe SEAM method, which models a transition structure as a minimum on the seam of two diabatic surfaces represented by force field functions, has been used to generate 20 transition structures for the decarboxylation of orotidine by the orotidine‐5′‐monophosphate decarboxylase enzyme. The dependence of the TS geometry on the flexibility of the system has been probed by fixing layers of atoms around the active site and using increasingly larger nonbonded cutoffs. The variability over the 20 structures is found to decrease as the system is made more flexible. Relative energies have been calculated by various electronic structure methods, where part of the enzyme is represented by a force field description and the effects of the solvent are represented by a continuum model. The relative energies vary by several hundreds of kJ/mol between the transition structures, and tests showed that a large part of this variation is due to changes in the enzyme structure at distances more than 5 Å from the active site. There are significant differences between the results obtained by pure quantum methods and those from mixed quantum and molecular mechanics methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Proton transfer at the carboxylic sites of amino acids: A single water molecule catalyzed process
Authors: Yang Gang , Wu Xiaomin , Zu Yuangang , Liu Chengbu , Fu Yujie , Zhou Lijun 
Published: August 2008

AbstractAb initio calculations at MP2 level of theory were used to study the proton transfer at the carboxylic sites of amino acids, in the isolated, mono‐ and di‐hydrated forms. In the case of water dimer, two interaction modes with glycine neutral structures (see Fig. 3) were explored, corresponding to the concerted and stepwise reaction pathways. Their transition states can be described as (H2OHOH2)+ [Fig. 4(a)] and (H2O‐‐‐HOH2)+ [Fig. 4(b)], respectively. The energy analysis indicated that the concerted pathway is preferred. In the isolated, mono‐ and di‐hydrated glycine complexes, the activation barriers of the proton transfer at the carboxylic sites were calculated to be 34.49, 16.59, and 13.36 kcal mol−1, respectively. It was thus shown that the proton transfer is significantly assisted and catalyzed by water monomer so that it can take place at room temperature. Instead, the further addition of water molecules plays solvent effects rather than catalytic effects to this proton transfer process. The above results obtained with discrete water molecules were supported by the solvent continuum calculated data. It was also observed that the heavy dependence of the solvent continuum models on dipole moments may produce misleading results. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Theoretical study on the mechanism for the thermal rearrangement reactions of 2‐silylethyl acetate H3SiCH2CH2OCOCH3
Authors: Jia Zhongfeng , Feng Shengyu , Song Enfeng , Sun Wenyan , Cong Lixiao 
Published: August 2008

AbstractThe thermal rearrangement mechanisms of 2‐silylethylacetate H3SiCH2CH2OOCCH3 were investigated by ab initio molecular orbital theory for the first time. All structures of reactant, transition states, and products were located and fully optimized at the B3LYP/6‐311+G(d, p) levels, and harmonic vibrational frequencies for the involved stationary points on the potential energy surface were obtained. The reaction pathways were analyzed and confirmed by intrinsic reaction coordinate (IRC) calculations. Furthermore, atomic charges were determined by using the natural bond orbital (NBO) analysis. The calculational results show that H3SiCH2CH2OOCCH3 can rearrange thermally in two ways. One is [1,3] rearrangement (Reaction A), in which silyl group transfers from carbon to oxygen(in COC) via a four‐membered ring transition state, forming silyl acetate and ethylene, the other way, [1,5] rearrangement (Reaction B), happens with transferring of silyl group from carbon to oxygen (in CO) via a six‐membered ring transition state, forming the same products as in Reaction A. The energy barriers of the Reactions A and B were calculated to be 188.9 and 191.6 kJ/mol at the B3LYP/6‐311+G(d,p) levels, respectively. Changes in thermodynamic functions (ΔS, ΔH, and ΔG), equilibrium constant K(T), as well as preexponential factor A(T), and reaction rate constant k(T) in Eyring transition state theory were calculated over a temperature range of 200–1600 K, and then thermodynamic and kinetic properties of the reactions were analyzed. It can be suggested that Reactions A and B are noncompetitive, and both happen only at elevated temperature. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009