bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient modal analysis of systems with local stiffness uncertainties
Authors: Wojtkiewicz S. F. , Gaurav  
Published: June 2009

AbstractThe characterization of the uncertainty in modal quantities of an uncertain linear structural system is essential to the rapid determination of its response to arbitrary loadings. Although the size of many computational structural models used is extremely large, i.e. thousands of equations, the uncertainty to be analyzed is oftentimes localized to very small regions of the model. This paper addresses the development of an efficient, computational methodology for the modal analysis of linear structural systems with local stiffness uncertainties. The newly developed methodology utilizes an enriched basis that consists of the sub‐spectrum of a nominal structural system augmented with additional basis vectors generated from a knowledge of the structure of the stiffness uncertainty. In addition, methods for determining bounds on the approximate modal frequencies and mode shapes are discussed. Numerical results demonstrate that the algorithm produces highly accurate results with greatly reduced computational effort. Copyright © 2009 John Wiley & Sons, Ltd.
A quadratic equal‐order stabilized method for Stokes problem based on two local Gauss integrations
Authors: Zheng Haibiao , Shan Li , Hou Yanren 
Published: June 2009

AbstractIn this article, we analyze a quadratic equal‐order stabilized finite element approximation for the incompressible Stokes equations based on two local Gauss integrations. Our method only offsets the discrete pressure gradient space by the residual of the simple and symmetry term at element level to circumvent the inf‐sup condition. And this method does not require specification of a stabilization parameter, and always leads to a symmetric linear system. Furthermore, this method is unconditionally stable, and can be implemented at the element level with minimal additional cost. Finally, we give some numerical simulations to show good stability and accuracy properties of the method. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010
Single‐cell compact finite‐difference discretization of order two and four for multidimensional triharmonic problems
Authors: Mohanty R.K. 
Published: June 2009

AbstractIn this article, we discuss finite‐difference methods of order two and four for the solution of two‐and three‐dimensional triharmonic equations, where the values of u,(∂2u/∂n2) and (∂4u/∂n4) are prescribed on the boundary. For 2D case, we use 9‐ and for 3D case, we use 19‐ uniform grid points and a single computational cell. We introduce new ideas to handle the boundary conditions and do not require to discretize the boundary conditions at the boundary. The Laplacian and the biharmonic of the solution are obtained as byproduct of the methods. The resulting matrix system is solved by using the appropriate block iterative methods. Computational results are provided to demonstrate the fourth‐order accuracy of the proposed methods. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010
Maternal plasma pentraxin 3 at 11 to 13 weeks of gestation in hypertensive disorders of pregnancy
Authors: Akolekar Ranjit , Casagrandi Davide , Livanos Panagiotis , Tetteh Amos , Nicolaides Kypros H 
Published: June 2009

AbstractObjectiveTo investigate whether in pregnancies that subsequently develop preeclampsia (PE), the maternal plasma concentration of the inflammatory factor pentraxin 3 (PTX3) at 11–13 weeks of gestation is increased and whether such a possible increase is associated with uterine artery pulsatility index (PI).MethodsThe concentration of plasma PTX3 at 11–13 weeks was measured in a case‐control study from 120 pregnancies that developed PE, including 27 who required delivery before 34 weeks (early PE), 87 cases of gestational hypertension (GH) and 207 normal controls. The median PTX3 multiple of the median (MoM) in the control and hypertensive groups were compared. Regression analysis was used to determine the significance of the association between plasma PTX3 and uterine artery PI.ResultsPlasma PTX3 was significantly higher in the early PE group (1.44 MoM; p < 0.0083) but not in late PE (1.11 MoM) or GH (1.10 MoM) compared to the controls (0.97 MoM). There was no significant association between plasma PTX3 levels and uterine artery PI in either the PE group (p = 0.693) or in the controls (p = 0.209).ConclusionIncrease in maternal plasma PTX3 in pregnancies that subsequently develop early PE is evident from 11–13 weeks but the underlying mechanism for such an increase remains uncertain. Copyright © 2009 John Wiley & Sons, Ltd.
Dispersion, crystallization kinetics, and parameters of Hoffman–Lauritzen theory of polypropylene and nanoscale calcium carbonate composite
Authors: Huang Jiann‐Wen 
Published: June 2009

AbstractIsothermal and nonisothermal crystallization of polypropylene (PP)/calcium carbonate (CaCO3) with two particle sizes (250–300 nm and 20–25 nm) were studied by differential scanning calorimeter. Equilibrium melting temperature (T) determined from both linear and nonlinear Hoffman–Weeks relations showed that the composites had a lower T as a result of the CaCO3 particles destroying the crystal of PP. Kinetics of the isothermal and nonisothermal crystallization was described by Avrami equation. For the first time, without the assumption of a constant U* value, Lauritzen–Hoffman parameters (U* and Kg) were evaluated directly by data‐fitting method for isothermal crystallization, and by Vyazovkin's method for nonisothermal crystallization. Kg values obtained were similar with and without the assumption of a constant U*and comparable to those in the literature. Both U* and Kg indicate the dual role the CaCO3 particles as nucleating agents to enhance the crystallization and as obstacles to the chain movement to reduce the crystallization. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Modeling of the fracture mechanism of HDPE subjected to environmental stress crack resistance test
Authors: Choi Byoung‐Ho , Weinhold Jeffrey , Reuschle David , Kapur Mridula 
Published: June 2009

AbstractEnvironmental stress crack resistance (ESCR) is a commonly used test to characterize cracking failure of high‐density polyethylene in applications such as wires, cables, blow molded containers, and other rigid packaging applications. From a resin design standpoint, it is important to understand the mechanism of environmental stress cracking especially in the case of materials with significantly different ESCR values. Currently, two standard ESCR tests, ASTM D1693 and ASTM F2136, are commonly accepted to measure environmental stress crack resistance of HDPE. An accurate observation of ESC is important to understand the fracture mechanism of samples. In this study, the ESCR performance of six HDPE samples was determined per ASTM D1693. The failed specimens were further characterized by scanning electron microscopy and fractographic methodology to investigate the failure mechanism. HDPE resins with low ESCR values had crack surfaces characterized by shorter and fewer fibrils. A new empirical model to predict polymer ESCR using tie chain concentration with different integration range, and water vapor transmission rate, to characterize detergent diffusion in the crack, was developed. The proposed empirical parameter improves the prediction of ESCR. The ability to predict ESCR performance from resin properties is a beneficial tool for new product development. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Synthesis and characterization of radio‐opaque thermosensitive poly[N‐isopropylacrylamide‐2,2′‐(ethylenedioxy)bis(ethylamine)‐2,3,5‐triiodobenzamide]
Authors: Leon Christine M , Lee Bae Hoon , Preul Mark , McLemore Ryan , Vernon Brent L 
Published: June 2009

AbstractBACKGROUND: In situ gelling polymers, like poly(N‐isopropylacrylamide) (poly(NIPAAm)), have many potential medical applications due to their biocompatibility and thermosensitivity.RESULTS: Radio‐opaque thermosensitive poly(NIPAAm) grafted with 10.7 wt% 2,2′‐(ethylenedioxy)bis(ethylamine)‐2,3,5‐triiodobenzamide was successfully synthesized and characterized. The conjugated polymer showed good visibility with X‐ray fluoroscopy. The polymer had a lower critical solution temperature of 30 °C after conjugation with triiodobenzamide as determined by cloud point determination and a transition peak temperature of 33.3 ± 0.57 °C as determined by differential scanning calorimetry.CONCLUSION: The polymer synthesized was highly visible under X‐rays, based upon the percentage incorporation of triiodobenzamide. After conjugation of the NIPAAm to the triiodobenzamide through a bis(ethylamine) linkage, the resultant polymer retained lower critical solution temperature characteristics in a temperature region that makes it physiologically useful. Copyright © 2009 Society of Chemical Industry
Enhanced crystallization of the γ‐form of propylene–ethylene copolymer in its miscible blends with propylene homopolymer
Authors: Na Bing , Lv Ruihua , Xu Wenfei , Tian Nana , Li Zhujun , Zhang Zhijie , Fu Qiang 
Published: June 2009

AbstractBACKGROUND: How to promote the formation of the γ‐form in a certain propylene‐ethylene copolymer (PPR) under atmospheric conditions is significant for theoretical considerations and practical applications. Taking the epitaxial relationship between the α‐form and γ‐form into account, it is expected that incorporation of some extrinsic α‐crystals, developed by propylene homopolymer (PPH), can enhance the crystallization of the γ‐form of the PPR component in PPR/PPH blends.RESULTS: The PPH component in the blends first crystallizes from the melt, and its melting point and crystal growth rate decrease with increasing PPR fraction. On the other hand, first‐formed α‐crystals of the PPH component can induce the lateral growth of PPR chains on themselves, indicated by sheaf‐like crystal morphology and positive birefringence, which is in turn responsible for enhanced crystallization of the γ‐form of the PPR component.CONCLUSION: Crystalline/crystalline PPH/PPR blends are miscible and the crystallization of the γ‐form of the PPR component is largely enhanced due to the heterogeneous nucleation from the α‐crystals first developed by the PPH component. Our findings could provide an effective way in practice to obtain isotactic polypropylene copolymers rich in γ‐form. Copyright © 2009 Society of Chemical Industry
Theoretical prediction of size‐expansion effect on the C8‐site activity in the modified guanine‐cytosine analogs
Authors: Li Huifang , Zhang Laibin , Han Li , Cukier Robert I. , Bu Yuxiang 
Published: June 2009

AbstractHomo/hetero ring‐expanded DNA analogs have been shown to be rationally modified DNA motifs with improved physical or biological properties. In this work, using density functional theory, the stability of these artificial DNA base pairs was examined with regard to three aspects associated with DNA damage, namely deprotonation, H‐abstraction, and H‐radical addition. The effect of size expansion on C8 activity was investigated because C8‐oxidative guanine (G) is one of the most important products of DNA damage. Computational results indicate that the insertion of an aromatic spacer ring in G considerably decreases the electron density over the C8 site, leading to easier deprotonation or H‐abstraction from the C8 site and more difficult H.‐radical attack on the C8 site. However, the opposite phenomenon is observed if the spacer ring is antiaromatic, because of the increased electron density over the C8 site. Moreover, these effects are more prominent the larger the aromaticity or antiaromaticity of the spacer ring. Further analyses, using natural bond orbitals (NBOs) and the nucleus‐independent chemical shift (NICS) index of aromaticity, indicate that the changes of the electron distribution over the C8 site arise because the aromatic spacer ring, involved in the conjugation structure, increases the electron delocalization from the electron‐rich imidazole ring to the diatropic six‐membered rings, while the antiaromatic spacer ring acts as an electron‐donating group, not only inhibiting the above electron delocalization, but also slightly increasing the electron density over the C8 site. The improved stability of these size‐expanded base pairs in different DNA‐damaged environments may encourage their use in practical applications. Copyright © 2009 John Wiley & Sons, Ltd.
Effect of ortho substituents on carbonyl carbon 13C NMR chemical shifts in substituted phenyl benzoates
Authors: Nummert Vilve , Piirsalu Mare , Mäemets Vahur , Vahur Signe , Koppel Ilmar A. 
Published: June 2009

Abstract13C NMR spectra of 37 ortho‐, meta‐, and para‐substituted phenyl benzoates, containing substituents in benzoyl and phenyl moiety, 4 ortho‐substituted methyl and 5 ethyl benzoates as well as 9 R‐substituted alkyl benzoates have been recorded. The influence of the ortho substituents on the carbonyl carbon 13C NMR chemical shift, δCO, was found to be described by a linear multiple regression equation containing the inductive, σI, resonance, σ°R, and steric, E, or υ substituent constants. For all the ortho‐substituted esters containing substituents in the acyl part as well as the phenyl part, the substituent‐induced reverse inductive effect (ρI < 0), the normal resonance effect (ρR > 0), and the negative steric effect (δortho < 0) with the E were observed. In the case of ortho substituents in the phenyl part, the resonance effect was negligible. Due to inductive effect, the ortho electron‐withdrawing substituents showed an upfield shift or shielding of the carbonyl carbon, while the electron‐donating substituents had an opposite effect. Because of the sterical consequences, ortho substituents revealed a deshielding effect on the 13C NMR chemical shift of the carbonyl carbon. For all the meta‐ and para‐substituted esters, the reverse substituent‐induced inductive and resonance effects (ρI < 0, ρR < 0) were found to be significant. In alkyl benzoates, the alkyl substituents showed the reverse inductive and steric effects. The log k values for the alkaline hydrolysis in water, aqueous 0.5 M Bu4NBr and 2.25 M Bu4NBr, and the IR frequencies, νCO, for the ortho‐, meta‐, and para‐substituted phenyl benzoates and alkyl benzoates were correlated nicely with the corresponding 13C NMR substituent chemical shifts, ΔδCO. Copyright © 2009 John Wiley & Sons, Ltd.
Investigation of sorption phenomena by solid phase extraction and liquid chromatography for the determination of some ether derivatives of tetrabromobisphenol A
Authors: Jonsson Susanne , Hörsing Maritha 
Published: June 2009

AbstractObserved sorption and chromatographic behaviour served as a starting point for the examination of four ether derivatives of the flame retardant tetrabromobisphenol A (TBBPA): dihydroxyethyl (DHEE), dimethyl (DMe), diallyl (DAE) and dibromopropyl (DBPE). To date, there is little or no information about these compounds in the scientific literature. The targets in the present study had calculated log Kow values of 6.0–10. A broad range of different types of solvents were used in order to elucidate the mechanisms of sorption onto silica (glass) and two solid phase extraction cartridges based on polystyrene divinylbenzene polymers, hydroxylated (Isolute ENV+) and vinylpyrrolidone (Oasis HLB) containing units. Also, three chromatographic columns (C18, C8 and dual C18‐based, i.e. a polar ligand together with C18 on a silica surface) were evaluated. The following were observed: desorption of the targets from silica surface by 1‐propanol showed the best results and the yields were further improved by silylation of the surface. Regardless of the experimental test conditions applied, the lowest recovery was seen for the DMe derivative, followed by TBBPA itself, which had calculated log Kow values in between the other targets. A washing solution containing up to 70% methanol could be used without elution of the targets from the solid phase extraction cartridge . The dihydroxethyl ether derivative of TBBPA is most probably not affected by environmental relevant pH due to a likely high pKa (ca 15). Also, this study shows that the polar character of the dual‐phase column was not as pronounced as asserted by the manufacturer. Copyright © 2009 John Wiley & Sons, Ltd.
Intra‐ and intermolecular NH···O hydrogen bonds in pyrrolyl derivatives of indane‐1,3‐dione – experimental and theoretical study
Authors: Sigalov M. , Shainyan B. , Chipanina N. , Ushakov I. , Shulunova A. 
Published: June 2009

Abstract2‐(Pyrrol‐2‐ylmethylene)‐1,3‐indandione (4) and 2‐(pyrrol‐2‐ylmethylene)‐3‐dicyanomethylidene‐1‐indanone (5) were synthesized. Multinuclear and 2D‐NMR, IR, UV spectroscopic investigations as well as quantum chemical calculations showed the presence of strong hydrogen bonding in these molecules. For both molecules, the presence of two conformers, with and without H‐bond, was experimentally detected in the basic solvents (DMSO, acetone, pyridine) and the solvate complexes were theoretically calculated. Specific behavior of the intramolecular H‐bonded complexes different from that of the intermolecular H‐complexes is discussed. Copyright © 2009 John Wiley & Sons, Ltd.
Electrochemistry in tetrahydrofuran and at low temperature: protocol, procedures and methods
Authors: Baron Ronan , Kershaw Neil M. , Donohoe Timothy J. , Compton Richard G. 
Published: June 2009

AbstractThis review describes the protocol, procedures and methods for electrochemical studies in THF and at low temperature that have been developed in the course of the last 5 years in our laboratory. Electrochemical studies in THF benefit from a large accessible potential window. In practice, it is however necessary to avoid the presence of humidity in the electrochemical cell. A specific reference electrode had to be designed for those measurements. Microelectrodes, the voltammetric response of which is negligibly affected by the resistivity of the medium, were preferred to macroelectrodes. Moreover, a methodology has been developed for the quantitative analysis of both voltammetric and chronoamperometric curves obtained for the microelectrodes. The fitting of chronoamperometric measurements using the Shoup and Szabo's expression allows us to estimate the diffusion coefficient of the substrate. The modelling of the cyclic voltammograms measured over a large range of scan rates allows the confirmation of the diffusion coefficient of the substrate DA, the determination of the diffusion coefficient of the electrogenerated molecule DB, of the formal potential E, of the transfer coefficient α and of the standard heterogeneous rate constant for the electron transfer k0. Typically, systems are investigated at temperatures ranging from room temperature to 192 K. Parameters obtained at various temperatures are used to extract, through Arrhenius plots, the activation energies both for the diffusion coefficient EA(D) and for the electron transfer reaction EA(k0). Copyright © 2009 John Wiley & Sons, Ltd.
Theoretical calculations of the kinetics and mechanisms of the gas phase elimination of primary, secondary, and tertiary 2‐hydroxyalkylbenzenes
Authors: Mora Jose R. , Lezama Jesus , Albornoz José M. , Hernandez Antonio , Córdova Tania , Chuchani Gabriel 
Published: June 2009

AbstractTheoretical study of the elimination kinetics of 2‐phenylethanol, 1‐phenyl‐2‐propanol, and 2‐methyl‐1‐phenyl‐2‐propanol in the gas‐phase has been carried out at the MP2/6‐31G(d,p), B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p), PBEPBE/6‐31G(d,p), and PBEPBE/6‐31++G(d,p) levels of theory. The three substrates undergo two parallel elimination reactions. The first elimination appears to proceed through a six‐membered cyclic transition state to give toluene and the corresponding aldehyde or ketone. The second parallel elimination takes place through a four‐membered cyclic transition state producing water and the corresponding unsaturated aromatic hydrocarbon. Results from MP2/6‐31G(d,p) and MPW1PW91/6‐31++G(d,p) methods were found to be in good agreement with the experimental kinetic and thermodynamic parameters in the formation of toluene and the corresponding carbonyl compound. However, the results for PBEPBE/6‐31G(d,p) were in better agreement with the experimental data for the second parallel reaction yielding water and the corresponding unsaturated aromatic hydrocarbon. The charge distribution differences in the TS related to the substitution by methyl groups in the substrates can account for the observed reaction rate coefficients. The synchronicity parameters imply semi‐polar transition states for these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.
X‐ray section images of dislocations and dislocation barriers in Si
Authors: Novikov S. , Fodchuk I. , Fedortsov D. , Struk A. 
Published: June 2009

AbstractBy means of numerical solution of the Takagi equations, modeling of X‐ray topographic images of deformation fields of the Lomer–Cottrell dislocation loops and dislocation barriers is made depending on their spatial location for the thin and thick crystals. Diffraction images created by dislocation loops and barriers of different size and spatial location are complicated and versatile in their thin structure.
X‐ray investigation of CdSe nanowires
Authors: Kurtuluş Özgül , Li Zhen , Mews Alf , Pietsch Ullrich 
Published: June 2009

AbstractCdSe nanowires (NWs) have been prepared by a solution–liquid–solid (SLS) approach using Bi nanocatalysts. Structural characterization has been performed by X‐ray powder diffraction providing an admixture of wurtzite and zinc‐blende (ZB) structure units separated by different types of stacking faults. The relative contributions of ZB type stacking units within the NWs were determined to be in the order of 3–6% from a set of ratios of reflection intensities appearing in only wurtzite structure to those appearing in both ZB and wurtzite (W) structure. In addition, the anisotropy of domain size within the NWs was evaluated from the evolution of peak broadening for increasing scattering length. The coherence lengths along the growth direction are found to be changing between 16 and 21 nm, smaller than the results obtained from TEM measurement, while the NW diameters are determined to be between 5 and 8 nm which is in good agreement with TEM inspection.