bluuebunny/crossref_metadata_2025 huggingface dataset:
Statische und dynamische Berechnung von Turbinenfundamenten aus Stahlbeton
Authors: Hüffmann Günter , Nawrotzki Peter , Uzunoglu Timur
Published: October 2005

Der vorliegende Aufsatz gibt einen Abriß über den aktuellen Stand der Technik bei der Auslegung und Berechnung von Turbinenfundamenten aus Stahlbeton aus der Sicht des Bauingenieurs. Dabei werden mögliche Fundamenttypen sowie auftretende Lasten und die an Turbinenfundamente gestellten Anforderungen ausführlich diskutiert. Aktuelle Berechnungsmethoden zur Ermittlung der Eigenfrequenzen und Schwingamplituden sowie die Behandlung von Sonderfällen in Erdbebengebieten werden erläutert. Baupraktische Aspekte und Kenndaten von ausgeführten Gas‐ und Dampfturbinenfundamenten runden den Beitrag ab.
Effects of i and i+3 residue identity on Cis–Trans isomerism of the aromatici+1–prolyli+2 amide bond: Implications for type VI β‐turn formation
Authors: Meng Hai Yun , Thomas Krista M. , Lee Aaron E. , Zondlo Neal J.
Published: October 2005

Cis–trans isomerization of amide bonds plays critical roles in protein molecular recognition, protein folding, protein misfolding, and disease. Aromatic–proline sequences are particularly prone to exhibit cis amide bonds. The roles of residues adjacent to a tyrosine–proline residue pair on cis–trans isomerism were examined. A short series of peptides XYPZ was synthesized and cis–trans isomerism was analyzed. Based on these initial studies, a series of peptides XYPN, X = all 20 canonical amino acids, was synthesized and analyzed by NMR for i residue effects on cis–trans isomerization. The following effects were observed: (a) aromatic residues immediately preceding Tyr–Pro disfavor cis amide bonds, with Ktrans/cis= 5.7–8.0, W > Y > F; (b) proline residues preceding Tyr–Pro lead to multiple species, exhibiting cis–trans isomerization of either or both X–Pro amide bonds; and (c) other residues exhibit similar values of Ktrans/cis (= 2.9–4.2), with Thr and protonated His exhibiting the highest fraction cis. β‐Branched and short polar residues were somewhat more favorable in stabilizing the cis conformation. Phosphorylation of serine at the i position modestly increases the stability of the cis conformer. In addition, the effect of the i+3 residue was examined in a limited series of peptides TYPZ. NMR data indicated that aromatic residues, Pro, Asn, Ala, and Val at the i+3 residue all favor cis amide bonds, with aromatic residues and Asn favoring more compact ϕ at Tyrcis and Ala and Pro favoring more extended ϕ at Tyrcis. D‐Alanine at the i+3 position particularly disfavors cis amide bonds. © 2005 Wiley Periodicals, Inc. Biopolymers 84: 192–204, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Targeted chemotherapy with cytotoxic bombesin analogue AN‐215 can overcome chemoresistance in experimental renal cell carcinomas
Authors: Keller Gunhild , Schally Andrew V. , Nagy Attila , Halmos Gabor , Baker Benjamin , Engel Jorg B.
Published: October 2005

BACKGROUND

Multidrug resistance (MDR) mediated by membrane transporters, such as P‐glycoprotein (MDR‐1) and MDR‐associated protein (MRP), remains a challenge in the therapy of renal cell carcinoma (RCC). Chemotherapy targeted to hormone receptors may provide a new approach to overcome chemoresistance. The cytotoxic analogue of bombesin/gastrin‐releasing peptide (GRP), AN‐215, consists of a superactive derivative of doxorubicin, AN‐201, which is linked to a bombesin analogue carrier: RC‐3094.

METHODS

The authors examined the expression of bombesin/GRP receptors in 3 human RCC cell lines (A‐498, ACHN. and 786‐0) by using reverse‐transcriptase‐polymerase chain reaction (RT‐PCR) analysis and radioligand‐binding assays. They also evaluated the effects of AN‐215 and its cytotoxic radical AN‐201 in the same RCC models in vivo, and they studied the effects of AN‐215 and AN‐201 on the expression levels of MDR‐1 and subtype 1 of MRP (MRP‐1) by using real‐time PCR.

RESULTS

A N‐215 significantly (P < 0.05) inhibited the growth of A‐498, ACHN, and 786‐0 RCC xenografted into nude mice by 59.2–67.6%, whereas the cytotoxic radical AN‐201 alone had no significant antitumor effects. The efficacy of AN‐215 was independent of the expression patterns of MDR‐1 and MRP‐1 in these RCC cell lines. The induction of MDR‐1 by AN‐215 was similar (Experiment 2) or weaker (Experiment 1) compared with AN‐201. Both AN‐215 and AN‐201 caused only a minor induction of MRP‐1.

CONCLUSIONS

The current findings indicated that targeted chemotherapy with cytotoxic bombesin/GRP analogue AN‐215 can inhibit the growth of RCC, providing a new treatment modality for patients with advanced RCC. Cancer 2005. © 2005 American Cancer Society.
Differences in the quality of breast cancer care among vulnerable populations
Authors: Haggstrom David A. , Quale Chris , Smith‐Bindman Rebecca
Published: October 2005

BACKGROUND

It is unknown whether differences in the quality of breast cancer care among women from racial and ethnic minority groups, the elderly, and rural areas have changed over time across the continuum of care.

METHODS

The linked Surveillance, Epidemiology, and End Results‐Medicare database identified 22,701 women ages 66–79 years diagnosed with early stage breast cancer from 1992–1999. Multiple breast cancer processes of care were measured, including breast‐conserving surgery, radiation therapy, documentation of estrogen receptor status, surveillance mammography, and a combined measure of “adequate care”.

RESULTS

African‐American and Hispanic women were significantly less likely to receive adequate care than White women in unadjusted comparisons (54.7% and 58.0% vs. 68.4% for African‐American and Hispanic vs. White women) and adjusted comparisons (adjusted odds ratio [AOR] 0.67; 95% confidence interval [95% CI] 0.59–0.76, and AOR 0.77; 95% CI 0.66–0.90 for African‐American and Hispanic women, respectively). The proportion of Asian/Pacific Islander women receiving adequate care was similar to White women. When considering only women diagnosed with breast cancer from 1997–1999, African‐American women remained less likely than White women to receive adequate care (AOR 0.63; 95% CI 0.50–0.79). Women ages 75–79 years were less likely to receive adequate care compared with women ages 66–69 years (AOR 0.74; 95% CI 0.69–0.80), and women from rural (vs. metropolitan) areas were less likely to receive adequate care (AOR 0.81; 95% CI 0.73–0.89).

CONCLUSIONS

The quality of breast cancer care is lower among vulnerable populations across the continuum of care, and many of these differences have not improved in more recent years. Cancer 2005. © 2005 American Cancer Society.
A stabilized finite element formulation to solve high and low speed flows
Authors: Costa Gustavo K. , Lyra Paulo R. M.
Published: October 2005

It is well known that numerical methods designed to solve the compressible Euler equations, when written in terms of conservation variables behave poorly in the incompressible limit, that is, when density variations are negligible. However, a change to pressure based variables seem to, partly, eliminate the problem by making the Jacobian matrices fully invertible whatever the flow regime may be. Despite this apparent benefit, the stabilization matrix plus discontinuity capturing operator (for the compressible regime) still need attention, since they tend to be ill behaved for either conservation or pressure variables. In this paper, we introduce a simple way of balancing two stabilizing matrices, one of them suitable for low Mach flows and the other one for supersonic flows, so that a wide range of flow regimes are covered with only one formulation. Comparison between conservation and pressure variables is made and numerical examples are shown to validate the method. Copyright © 2005 John Wiley & Sons, Ltd.
Crystal Structure and Carbon Vacancy Hardening of (W0.5Al0.5)C1−x Prepared by a Solid‐State Reaction
Authors: Yan Junmin , Ma Xianfeng , Zhao Wei , Tang Huaguo , Zhu Changjun , Cai Shuguang
Published: October 2005

Novel solid solutions of aluminum in tungsten carbide (WC) with or without carbon vacancies, which can be expressed by the chemical formula (W0.5Al0.5)C1−x (x=0.0–0.5), have been synthesized by the solid‐state reaction of W0.5Al0.5 alloy and the proper amount of carbon at around 1673 K in vacuum. The reaction time decreases from 73 to 50 h on increasing the carbon vacancy concentration from 0 to 50 %. The formation of the intended products is certified, by X‐ray diffraction, environmental scanning electron microscopy–energy‐dispersive X‐ray analysis, and inductively coupled plasma–atomic emission spectroscopy, even though the carbon vacancy concentration reaches the astonishing value of 50 %. The as‐prepared (W0.5Al0.5)C1−x samples have been identified as the hexagonal WC‐type structure belonging to the space group P6m2 (Z=1). Moreover, the crystallographic results reveal that the substituting aluminum atoms in the WC are located in the 1a site (the W atom position of the WC structure) and the cell parameters decrease slightly with increasing vacancy concentration. The hardness of the (W0.5Al0.5)C1−x system increases up to a maximum 2659 kg mm−2 at a carbon vacancy concentration of about 35 %, and the density of (W0.5Al0.5)C1−x is far lower than that of WC.
Charge Trapping and Photoadsorption of O2 on Dehydroxylated TiO2 Nanocrystals—An Electron Paramagnetic Resonance Study
Authors: Berger Thomas , Sterrer Martin , Diwald Oliver , Knözinger Erich
Published: October 2005

The interaction of photogenerated charges with molecular oxygen was investigated on TiO2 nanocrystals by means of paramagnetic resonance (EPR) spectroscopy. Compared to photoactivation experiments in vacuum at P<10−6 mbar and T=140 K, the presence of O2 enhances the concentration of persistently trapped electron and hole centres—by a factor of ten—due to the formation of adsorbed O2− species. The photoadsorption of oxygen was also tracked quantitatively by pressure measurements, and the number of trapped charges, hole centres and O2− was found to correspond to ten electron–hole pairs per TiO2 nanocrystal. Conversely, in experiments at P<10−6 mbar with one trapped electron–hole pair per particle, charge separation is not persistent and completely reversible with respect to temperature. Heating to 298 K causes the total annihilation of photogenerated and trapped charges.
Apertureless Near‐Field Vibrational Imaging of Block‐Copolymer Nanostructures with Ultrahigh Spatial Resolution
Authors: Raschke Markus B. , Molina Leopoldo , Elsaesser Thomas , Kim Dong Ha , Knoll Wolfgang , Hinrichs Karsten
Published: October 2005

Nanodomains formed by microphase separation in thin films of the diblock copolymers poly(styrene‐b‐2‐vinylpyridine) (PS‐b‐P2VP) and poly(styrene‐b‐ethyleneoxide) (PS‐b‐PEO) were imaged by means of infrared scattering‐type near‐field microscopy. When probing at 3.39 μm (2950 cm−1), contrast is obtained due to spectral differences between the CH stretching vibrational resonances of the respective polymer constituents. An all‐optical spatial resolution better than 10 nm was achieved, which corresponds to a sensitivity of just several thousand CH groups facilitated by the local‐field enhancement at the sharp metallic probe tips. The results demonstrate that infrared spectroscopy with access to intramolecular dimensions is within reach.
Structure Determination of Resorcinol Rotamers by High‐Resolution UV Spectroscopy
Authors: Myszkiewicz Grzegorz , Meerts W. Leo , Ratzer Christian , Schmitt Michael
Published: October 2005

The rotationally resolved S1←S0 electronic origins of several deuterated resorcinol rotamers cooled in a molecular beam have been recorded. An automated assignment of the observed spectra has been performed using a genetic algorithm approach with an asymmetric rotor Hamiltonian. The structures of resorcinol A and resorcinol B were derived from the rotational constants of twenty deuterated species for both electronic states. The lifetimes of different resorcinol isotopomers in the S1 state are also reported. As is the case for phenol, these lifetimes mainly depend on the position of deuteration. A nearly perfect additivity of the zero‐point energies after successive deuterations in resorcinol rotamers has been discovered and subsequently used in the full assignment of the previously reported low‐resolution spectra of deuterated resorcinol A. An analogous spectrum is also predicted for the resorcinol B rotamer.
An algorithm for isentropic flow
Authors: Glaister P.
Published: October 2005

An efficient algorithm is presented for the solution of the equations of isentropic gas dynamics with a general convex gas law. The scheme is based on solving linearized Riemann problems approximately, and in more than one dimension incorporates operator splitting. In particular, only two function evaluations in each computational cell are required. The scheme is applied to a standard test problem in gas dynamics for a polytropic gas.
Locally mass‐conserving Taylor–Hood elements for two‐ and three‐dimensional flow
Authors: Thatcher R. W.
Published: October 2005

By supplementing the pressure space for Taylor–Hood elements, elements that satisfy continuity locally are produced. These elements are shown to satisfy the Babuska–Brezzi compatibility condition by using the patch argument.

Two examples are presented, one illustrating the convergence rates and the other illustrating a difficulty with a Taylor–Hood element that is overcome by the element presented here.
Transient flow past a circular cylinder: A benchmark solution
Authors: Engelman Michael S. , Jamnia Mohammad‐Ali
Published: October 2005

The simulation of the von Karman vortex street behind a circular cylinder has long been used as a benchmark problem to test the performance of numerical algorithms for solving the Navier‐Stokes equations. It is particularly suited for comparing different numerical outflow boundary conditions since the computational domain must necessarily be terminated in the vortex street itself. This paper presents detailed numerical results of the flow past a cylinder at a Reynolds number of 100 on a very fine mesh which has been purposely designed to extend past the typically used dimensions. Hopefully, these results can form a basis of a benchmark solution for the comparison of the effects of different outflow boundary conditions.
The thermoconvective instability of plane poiseuille flow heated from below: A proposed benchmark solution for open boundary flows
Authors: Evans G. , Paolucci S.
Published: October 2005

The transient two‐dimensional Navier‐Stokes and energy equations have been solved numerically for flow in a horizontal channel heated from below in the Boussinesq limit. For the set of dimensionless parameters chosen, the flow consists of periodic transverse travelling waves resulting from a convective instability. The solution is proposed as a benchmark for the application of outflow boundary conditions (OBC) in time‐dependent flows with strong buoyancy effects. Richardson extrapolation in both time and space is used in obtaining the solution. Field plots and profiles of velocity, temperature, vorticity and streamfunction at selected axial positions and times are also presented from the finest grid and smallest time step calculation. The calculations have been made on an extended domain so that the effects of OBC used in the present study would be negligible in the test region.
Computer‐aided spillway design using the boundary element method and non‐linear programming
Authors: Henderson H. C. , Kok M. , De Koning W. L.
Published: October 2005

The general context of this paper is to support the design of spillways by a direct mathematical approach instead of trial‐and‐error methods.

First, a two‐dimensional model is formulated to determine the free surface and the discharge for a stationary, incompressible, homogeneous, non‐viscous and irrotational flow over a fixed spillway. The flow satisfies the Laplace equation and the Bernoulli equation (potential flow). An important feature of the model is that it can be extended to design the spillway structure when the spillway is not fixed but the pressure on the spillway is described by a cavitation criterion.

Next, the continuous model is discretized by the boundary element method (BEM). We use a non‐linear programming algorithm to calculate the pressures and the shape of the spillway. A computer‐aided design package is developed on a PC using the equations describing the free surface, the BEM and standard optimization techniques. The input and output of the model are realized using graphical routines. Finally, we discuss the convergence and the computation time of the algorithms.
Large‐scale computer simulation of fully developed turbulent channel flow with heat transfer
Authors: Lyons Stephen L. , Hanratty Thomas J. , McLaughlin John B.
Published: October 2005

Recently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three‐dimensional time‐dependent Navier‐Stokes and advection‐diffusion equations without the use of subgrid‐scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here.

Results from a Cray‐2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first‐ and second‐order moments agree well with experimental measurements; the agreement is poor for higher‐order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow.
A finite difference analysis of the extrudate swell problem
Authors: Ahn Young‐Cheol , Ryan Michael E.
Published: October 2005

The extrudate swell phenomenon of a purely viscous fluid is analysed by solving simultaneously the Cauchy momentum equations along with the continuity equation by means of a finite difference method. The circular and planar jet flows of Newtonian and power‐law fluids are simulated using a control volume finite difference method suggested by Patankar called SIMPLER (semi‐implicit method for pressure‐linked equations). This method uses the velocity components and pressure as the primitive variables and employs a staggered grid and control volume for each separate variable. The numerical results show good agreement with the analytical solution of the axisymmetric stick‐slip problem and exhibit a Newtonian swelling ratio of 13.2% or 19.2% for a capillary or slit die respectively in accordance with previously reported experimental and numerical results. Shear thinning results in a decrease in swelling ratio, as does the introduction of gravity and surface tension.
Variational parameter estimation for a two‐dimensional numerical tidal model
Authors: Das S. K. , Lardner R. W.
Published: October 2005

It is shown that the parameters in a two‐dimensional (depth‐averaged) numerical tidal model can be estimated accurately by assimilation of data from tide gauges. The tidal model considered is a semi‐linearized one in which kinematical non‐linearities are neglected but non‐linear bottom friction is included. The parameters to be estimated (bottom friction coefficient and water depth) are assumed to be position‐dependent and are approximated by piecewise linear interpolations between certain nodal values. The numerical scheme consists of a two‐level leapfrog method. The adjoint scheme is constructed on the assumption that a certain norm of the difference between computed and observed elevations at the tide gauges should be minimized. It is shown that a satisfactory numerical minimization can be completed using either the Broyden‐Fletcher‐Goldfarb‐Shanno (BFGS) quasi‐Newton algorithm or Nash's truncated Newton algorithm. On the basis of a number of test problems, it is shown that very effective estimation of the nodal values of the parameters can be achieved provided the number of data stations is sufficiently large in relation to the number of nodes.
A finite difference technique for solving the Newtonian jet swell problem
Authors: Han Chin‐Tsu , Tsai Chin‐Chin , Yu Tsai‐An , Liu Ta‐Jo
Published: October 2005

A finite difference technique that incorporates a numerical mapping has been successfully applied to analyse both planar and axisymmetric Newtonian jets. A pressure gradient equation and a free‐surface slope equation have been derived for free‐surface iteration. The computation of pressure inside the jet surface using the pressure gradient equation is stable and accurate at high Reynolds numbers. The free‐surface slope equation is needed for updating the free surface and is applicable for jets with strong surface tension effects. The present development can simulate the Newtonian jets for Reynolds numbers as high as 2000 and capillary number as low as 10−5. Numerical predictions by the present technique are close to the results of previous finite element simulations.
A fully implicit direct Newton's method for the steady‐state Navier–Stokes equations
Authors: Knoll Dana A. , McHugh Paul R.
Published: October 2005

Newton's method and banded Gaussian elimination can be a CPU efficient method for steady‐state solutions to two‐dimensional Navier–Stokes equations. In this paper we look at techniques that increase the radius of convergence of Newton's method, reduce the number of times the Jacobian must be factored, and simplify evaluation of the Jacobian. The driven cavity and natural convection problems are used as test problems, and finite volume discretization is employed.
Preconditioned finite element algorithms for 3D Stokes flows
Authors: Zhou Richard Q. N.
Published: October 2005

Preconditioned conjugate gradient algorithms for solving 3D Stokes problems by stable piecewise discontinuous pressure finite elements are presented. The emphasis is on the preconditioning schemes and their numerical implementation for use with Hermitian based discontinuous pressure elements. For the piecewise constant discontinuous pressure elements, a variant implementation of the preconditioner proposed by Cahouet and Chabard for the continuous pressure elements is employed. For the piecewise linear discontinuous pressure elements, a new preconditioner is presented. Numerical examples are presented for the cubic lid‐driven cavity problem with two representative elements, i.e. the Q2‐PO and the Q2‐P1 brick elements. Numerical results show that the preconditioning schemes are very effective in reducing the number of pressure iterations at very reasonable costs. It is also shown that they are insensitive to the mesh Reynolds number except for nearly steady flows (Rem → 0) and are almost independent of mesh sizes. It is demonstrated that the schemes perform reasonably well on non‐uniform meshes.
Semi‐implicit Skew Upwind Method for problems in environmental hydraulics
Authors: Zhou Siping , McCorquodale J. A. , Ji Zhong
Published: October 2005

A new computational method is presented for reducing numerical diffusion in environmental fluid problems. This method, which is referred to as the Semi‐Implicit Skew Upwind Method (SISUM), is a robust solution procedure for the conditional convergence of the discretized transport equations. The method retains the advantage of the low numerical diffusion of the conventional skew upwind schemes but does not suffer from over‐ or under‐shooting often found in these methods due to the improved interpolation schemes. The effectiveness of SISUM is demonstrated in several examples. The comparison of the results of a hybrid scheme and SISUM with field observations of convection‐dominated pollutant transport in strongly curvilinear river flow shows that SISUM successfully eliminates the high numerical diffusion produced by the hybrid scheme. The robustness of the method was tested by solving the hydrodynamics of a circular clarifier model with a large density gravity source term in the vertical‐momentum equation.
Instability of uniform flow
Authors: Renardy Michael
Published: October 2005

We consider uniform flow of a Newtonian fluid trasverse to a domain bounded by parallel planes. We investigate the possibility of introducing instabilities in this flow by the choice of inflow and outflow conditions. Some instabilities of this kind are found.
Implementation and performance of the time integration of a 3D numerical transport model
Authors: Sommeijer B. P. , Kok J.
Published: October 2005

The total solution of a three‐dimensional model for computing the transport of salinity, pollutants, suspended material (such as sediment or mud), etc. in shallow seas involves many aspects, each of which has to be treated in an optimal way in order to cope with the tremendous computational task involved. In this paper we focus on one of these aspects, i.e. on the time integration, and discuss two numerical solution methods. The emphasis in this paper is on the performance of the methods when implemented on a vector/parallel, shared memory computer such as a Cray‐type machine. The first method is an explicit time integrator and can straightforwardly be vectorized and parallelized. Although a stabilizing technique has been applied to this method, it still suffers from a severe time step restriction. The second method is partly implicit, resulting in much beter stability characteristics; however, as a consequence of the implicitness, it requires in each step the solution of a large number of tridiagonal systems. When implemented in a standard way, the recursive nature would prevent vectorization, resulting in a very long solution time. Following a suggestion of Golub and Van Loan, this part of the algorithm has been tuned for use on the Cray C98/4256. On the basis of a large‐scale test problem, performance results will be presented for various implementations.
A vector‐parallel scheme for Navier‐Stokes computations at multi‐gigaflop performance rates
Authors: Lorber A. A. , Carey G. F.
Published: October 2005

A class of vector‐parallel schemes for solution of steady compressible or incompressible viscous flow is developed and performance studies carried out. The algorithms employ an artificial transient treatment that permits rapid integration to a steady state. In the present work a four‐stage explicit Runge‐Kutta scheme employing variable local step size is utilized for the ODE system integration. The RK‐4 scheme is restructured to allow vectorization and enhance concurrency in the calculation for a streamfunction‐vorticity formulation of the flow problem. The parameters of the resulting RK scheme can be selected to accelerate convergence of the RK recursion. Four main procedures are considered which permit vector‐parallel solution: a Jacobi update, a hybrid of the Jacobi and Gauss‐Seidel method, red‐black ordering and domain decomposition. Numerical performance studies are conducted with a representative viscous incompressible flow calculation. Results indicate that a scheme involving domain decomposition with a Gauss‐Seidel type of update for the RK four‐stage scheme is most effective and provides performance in excess of 8 Gflops on the Cray C‐90.
Simulations of the unsteady separated flow past a normal flat plate
Authors: Najjar Fady M. , Vanka S. P.
Published: October 2005

Well‐resolved two‐dimensional numerical simulations of the unsteady separated flow past a normal flat plate at low Reynolds numbers have been performed using a fractional step procedure with high‐order spatial discretization. A fifth‐order upwind‐biased scheme is used for the convective terms and the diffusive terms are represented by a fourth‐order central difference scheme. The pressure Poisson equation is solved using a direct method based on eigenvalue decomposition of the coefficient matrix. A systematic study of the flow has been conducted with high temporal and spatial resolutions for a series of Reynolds numbers. The interactions of the vortices shed form the shear layers in the near‐and far‐wake regions are studied. For Reynolds numbers less than 250 the vortices are observed to convect parallel to the freestream. However, at higher Reynolds numbers (500 and 1000), complex interactions including vortex pairing, tearing and deformations are seen to occur in the far‐wake region. Values of the drag coefficient and the wake closure length are presented and compared with previous experimental and numerical studies.
Microhardness and fracture toughness of dental materials by indentation method
Authors: Şakar‐Deliormanli Aylin , Güden Mustafa
Published: October 2005

The main objective of this study was to measure the fracture toughness of the human teeth enamel using the microindentation technique and to compare the results calculated from the equations developed for Palmqvist and radial‐median cracks. Vickers microhardness measurements of dental ceramic (alumina) and human teeth were performed using indentation fracture method. The fracture toughness of enamel was calculated using different equations reported in the literature. Vickers microhardness of the sintered alumina specimen (98.8% theoretical density) was measured to be 14.92 GPa under 9.8N indentation load. Three equations based on the radial‐median cracks were found to be applicable for the fracture toughness determination of the enamel. Results show that indentation fracture method is adequate to measure microhardness and fracture toughness of dental materials. However the calculation of fracture toughness depended on the nature of the cracks and also on the location of the indentation. Therefore, it is necessary to identify the crack profile and to select the appropriate equation for accurate fracture toughness values. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Structural analysis of dextran‐based hydrogels obtained chemoenzymatically
Authors: Ferreira L. , Figueiredo M. M. , Gil M. H. , Ramos M. A.
Published: October 2005

This work reports the results of structural analysis in novel dextran–acrylate (dexT70‐VA) hydrogels generated chemoenzymatically. Porous structure as well as hydrogel surface and interior morphologies were evaluated by mercury intrusion porosimetry (MIP), nitrogen adsorption (NA), and scanning electron microscopy (SEM) analyses, as a function of the degree of substitution (DS), and initial water content used in the preparation of the hydrogel. MIP analysis showed that the overall networks were clearly macroporous with pore sizes ranging from 0.065 to 10 μm. As expected, the average pore size decreased as DS increased and as initial water content decreased. Moreover, the porosity values ranged from 75 up 90%, which shows that these hydrogels present an interconnected pore structure. Nitrogen adsorption analyses showed that the specific surface area of dexT70‐VA hydrogels increased either by increasing the DS or by decreasing the initial water content of the hydrogel. SEM results revealed that the surface of hydrogels with lower DS presented either a porous structure or a polymeric “skin” covering the pores, whereas hydrogels with higher DS were totally porous. Furthermore, the interior morphology varied according to the DS and the initial water content of the hydrogels. Finally, the average pore size was also determined from the swelling of hydrogel using a theoretical model developed by Flory‐Rehner. The comparison of the SEM and MIP results with the ones obtained by the equilibrium swelling theory of Flory‐Rehner shows that this approach highly underestimates the average pore size. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Frequency effect in fretting wear of Co‐28Cr‐6Mo versus Ti‐6Al‐4V implant alloys
Authors: Schaaff Petra , Dalmiglio Matteo , Holzwarth Uwe
Published: October 2005

A piezo‐electrically driven fretting testing device has been constructed and fretting release and release rates have been determined with highest accuracy, using a radiotracer technique. First results on the fretting release and release rate of titanium alloy fretting pads against cobalt‐chrome alloy fatigue specimens are reported. The frequency dependency of fretting release has been determined between 1 and 8 Hz and shows higher release rates for low frequencies, thus indicating that accelerated testing of materials and components of artificial joints must be analyzed extremely carefully. The present experiments under simple conditions present a base‐line study for step‐wise applying more complex and realistic testing conditions and for using radiotracer methods to quantify fretting release in simulated testing of artificial hip‐ and knee‐prostheses. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Integrated Modeling Program, Applied Chemical Theory (IMPACT)
Authors: Banks Jay L. , Beard Hege S. , Cao Yixiang , Cho Art E. , Damm Wolfgang , Farid Ramy , Felts Anthony K. , Halgren Thomas A. , Mainz Daniel T. , Maple Jon R. , Murphy Robert , Philipp Dean M. , Repasky Matthew P. , Zhang Linda Y. , Berne Bruce J. , Friesner Richard A. , Gallicchio Emilio , Levy Ronald M.
Published: October 2005

We provide an overview of the IMPACT molecular mechanics program with an emphasis on recent developments and a description of its current functionality. With respect to core molecular mechanics technologies we include a status report for the fixed charge and polarizable force fields that can be used with the program and illustrate how the force fields, when used together with new atom typing and parameter assignment modules, have greatly expanded the coverage of organic compounds and medicinally relevant ligands. As we discuss in this review, explicit solvent simulations have been used to guide our design of implicit solvent models based on the generalized Born framework and a novel nonpolar estimator that have recently been incorporated into the program. With IMPACT it is possible to use several different advanced conformational sampling algorithms based on combining features of molecular dynamics and Monte Carlo simulations. The program includes two specialized molecular mechanics modules: Glide, a high‐throughput docking program, and QSite, a mixed quantum mechanics/molecular mechanics module. These modules employ the IMPACT infrastructure as a starting point for the construction of the protein model and assignment of molecular mechanics parameters, but have then been developed to meet specialized objectives with respect to sampling and the energy function. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1752–1780, 2005
Preparation and Characterisation of Thermoresponsive Poly[(N‐isopropylacrylamide‐co‐acrylamide‐co‐(hydroxyethyl acrylate)] Microspheres as a Matrix for the Pulsed Release of Drugs
Authors: Fundueanu Gheorghe , Constantin Marieta , Bortolotti Fabrizio , Ascenzi Paolo , Cortesi Rita , Menegatti Enea
Published: October 2005

Summary: Despite the large number of publications and patents concerning pH/thermoresponsive polymers, few data are available concerning the preparation of thermoresponsive cross‐linked microspheres from preformed polymers. Therefore, N‐isopropylacrylamide‐co‐acrylamide‐co‐(2‐hydroxyethyl acrylate) copolymers were obtained as a new thermoresponsive material with a lower critical solution temperature (LCST) around 36 °C, in phosphate buffer at pH 7.4, and with a cross‐linkable OH group in their structure. The LCST value was determined both by UV spectroscopy and microcalorimetric analysis. These copolymers were solubilised in acidified aqueous solution below their LCST, dispersed in mineral oil, and transformed into stable microspheres by cross‐linking with glutaraldehyde. The thermoresponsive microspheres were characterised by optical and scanning electron microscopy, degree of swelling, and water retention. The pore dimensions of the microspheres and the retention volumes of some drugs and typical compounds were evaluated at different temperatures by liquid chromatography. Indomethacin, as a model drug, was included in the microspheres by the solvent evaporation method. Finally, the influence of temperature and of temperature cycling on drug release was investigated.

Effect of temperature and temperature cycling on indomethacin release from poly(NIPAAm‐co‐AAm‐co‐HEA) microspheres.

magnified image

Effect of temperature and temperature cycling on indomethacin release from poly(NIPAAm‐co‐AAm‐co‐HEA) microspheres.
Nigral degeneration and striatal dopaminergic dysfunction in idiopathic and parkin‐linked Parkinson's disease
Authors: Hu Michele T.M. , Scherfler Christoph , Khan Naheed L. , Hajnal Jo V. , Lees Andrew J. , Quinn Niall , Wood Nicholas W. , Brooks David J.
Published: October 2005

We have used MR segmented inversion recovery ratio imaging (SIRRIM) of the substantia nigra pars compacta to detect and correlate nigral signal change in idiopathic Parkinson's disease (PD) and parkin patients with striatal 18F‐dopa uptake. Nine PD patients, nine parkin patients, and eight control subjects were studied with a combination of MR inversion recovery sequences sensitive to nigral cell loss. Blinded independent observer rating and quantified nigral signal analysis were performed on all subjects. Striatal regions of interest were defined on T1‐weighted MRI coregistered to 18F‐dopa positron emission tomography. On blinded observer rating of the SIRRIM dorsal and ventral nigral images, 25% (2/8) of control subjects, 44% (4/9) of PD patients, and 67% (6/9) of parkin patients were classified as abnormal. Quantified total nigral signal intensities were reduced to a greater extent in the parkin compared to PD patients. There was a greater predilection for signal reduction in the ventral nigral slice of the PD compared to the parkin patient group, who showed a more uniform involvement. All PD and parkin patients were discriminated from controls on the basis of caudate and putamen 18F‐dopa Ki reductions. Our results suggest that MR segmented inversion recovery ratio imaging shows poor sensitivity for discriminating parkin and idiopathic PD patients from normal controls. Where nigral signal abnormalities were seen, parkin patients manifested generalized nigral cell loss with widespread striatal dopamine terminal dysfunction compared with the lateral nigral targeting seen in PD and selective loss of putamen 18F‐dopa uptake. © 2005 Movement Disorder Society
Pergolide versus levodopa monotherapy in early Parkinson's disease patients: The PELMOPET study
Authors: Oertel Wolfgang H. , Wolters Erik , Sampaio Cristina , Gimenez‐Roldan Santiago , Bergamasco Bruno , Dujardin Max , Grosset Donald G. , Arnold Guy , Leenders Klaus L. , Hundemer Hans‐Peter , Lledó Alberto , Wood Andrew , Frewer Paul , Schwarz Johannes
Published: October 2005

Dopamine agonists are used as initial treatment in patients with Parkinson's disease (PD) to reduce incidence and severity of motor complications. This paradigm is based on long‐term studies, allowing “rescue” therapy with levodopa. The present strict monotherapy study (PELMOPET, the acronym for the pergolide‐versus‐L‐dopa‐monotherapy‐and‐positron‐emission‐tomography trial) evaluated the efficacy and safety of pergolide versus levodopa without levodopa “rescue” medication. This multicenter, double‐blind, randomized, 3‐year trial compared pergolide monotherapy (n = 148) with levodopa monotherapy (n = 146) in dopamine‐naive patients with early PD (Hoehn and Yahr stage 1–2.5). Primary efficacy measures were clinical efficacy, severity and time to onset of motor complications, and disease progression. During the 3 years, severity of motor complications was significantly lower and time to onset of dyskinesia was significantly delayed in the group receiving pergolide (3.23 mg/day) compared with those receiving levodopa (504 mg/day). However, time to onset of motor complications was not longer in patients receiving pergolide after 3 years. Symptomatic relief (assessed by Unified Parkinson's Disease Rating Scale [UPDRS], UPDRS II, and III, Clinical Global Impressions [CGI] severity, and CGI and Patient Global Impressions [PGI] improvement) was significantly greater in patients receiving levodopa. Adverse events led to discontinuation of therapy in 17.6% of pergolide patients and 9.6% of levodopa patients. This is the first study comparing strict monotherapy with a dopamine agonist versus levodopa in previously untreated early PD. In principle, both levodopa and a dopamine agonist such as pergolide seem to be suitable options as initial PD therapy. The choice remains with the treating physician based on the different efficacy and adverse event profiles. © 2005 Movement Disorder Society
Minimal‐energy splines: I. Plane curves with angle constraints
Authors: Jou Emery D. , Han Weimin
Published: October 2005

This is the first in a series of papers on minimal‐energy splines. The paper is devoted to plane minimal‐energy splines with angle constraints. We first consider minimal‐energy spline segments, then general minimal‐energy spline curves. We formulate problems for minimal‐energy spline segments and curves, prove the existence of solutions, justify the Lagrange multiplier rules, and obtain some nice properties (e.g., the infinite smoothness). Finally, we report our computational experience on minimal‐energy splines.
Taylor expansions for distributions
Authors: Estrada R. , Kanwal R. P.
Published: October 2005

We present the Taylor asymptotic expansion of a perturbed distribution of the form
equation image
is a smooth function defined in ℝn. First we present the one‐dimensional theory to illustrate the underlying concepts and then we discuss the multi‐dimensional case. We find that various known results follow as special limits of our results.
Parameter‐dependent operator equations of the Riccati type with application to transport theory
Authors: Kuiper Hendrik J. , Mazumdar Tapas
Published: October 2005

We obtain an existence result for global solutions to initial‐value problems for Riccati equations of the form R′(t) + TR(t) + R(t)T = Tρ A(t)T1−ρ + Tρ B(t)T1−ρ R(t) + R(t)TρC(t) T1−ρ + R(t)TρD(t)T1−ρ R(t), R(0)=R0, where 0 ⩽ ρ ⩽ 1 and where the functions R and A through D take on values in the cone of non‐negative bounded linear operators on L1 (0, W; μ). T is an unbounded multiplication operator. This problem is of particular interest in case ρ = 1 since it arisess in the theories of particle transport and radiative transfer in a slab. However, in this case there are some serious difficulties associated with this equation, which lead us to define a solution for the case ρ = 1 as the limit of solutions for the cases 0 < ρ < 1.
Weak solutions of the Vlasov–Poisson initial boundary value problem
Authors: Alexandre Radjesvarane
Published: October 2005

This paper deals with existence results for a Vlasov‐Poisson system, equipped with an absorbing‐type law for the Vlasov equation and a Dirichlet‐type boundary condition for the Poisson part. Using the ideas of Lions and Perthame [21], we prove the existence of a weak solution having good Lp estimates for moment and electric field, by a good control on the higher moments of the initial data. As an application, we establish a homogenization result in the Hilbertian framework for this type of problem in non‐homogeneous media, following the work by Alexandre and Hamdache [2] for general kinetic equations, and Cioranescu and Mural [11] for the Laplace problem.
Classical solutions of two‐dimensional stokes problems on non‐smooth domains. Part 2: Collocation method for the radon equation
Authors: Lubuma Jean Mbaro‐Saman
Published: October 2005

The non‐uniquely solvable Radon boundary integral equation for the two‐dimensional Stokes‐Dirichlet problem on a non‐smooth domain is transformed into a well posed one by a suitable compact perturbation of the velocity double‐layer potential operator. The solution to the modified equation is decomposed into a regular part and a finite linear combination of intrinsic singular functions whose coefficients are computed from explicit formulae. Using these formulae, the classical collocation method, defined by continuous piecewise linear vector‐valued basis functions, which converges slowly because of the lack of regularity of the solution, is improved into a collocation dual singular function method with optimal rates of convergence for the solution and for the coefficients of singularities.
On the averaging method for rod equations with quadratic non‐linearity
Authors: Buitelaar R. P.
Published: October 2005

The averaging method is used to approximate solutions of systems of linearly coupled, (quadratic) non‐linear dispersive wave equations, which describe extensional–torsional dynamics of a rod. Existence and uniqueness results are established. Error estimates confirm the asymptotic validity of the approximation method on a long time‐scale. The linear couplings between the equations imply that resonance can occur inside a single mode of the solution, but energy can also be transferred to other modes.
Periodic optimal control for parabolic Volterra‐Lotka type equations
Authors: He Feiyue , Leung Anthony , Stojanovic Srdjan
Published: October 2005

This paper considers the optimal harvesting control of a biological species, whose growth is governed by the parabolic diffusive Volterra‐Lotka equation. We prove that such equation with L∞ periodic coefficients has an unique positive periodic solution. We show the existence and uniqueness of an optimal control, and under certain conditions, we characterize the optimal control in terms of a parabolic optimality system. A monotone sequence which converges to the optimal control is constructed.
Convergence of alternating domain decomposition schemes for kinetic and aerodynamic equations
Authors: Klar Axel
Published: October 2005

A domain decomposition scheme linking linearized kinetic and aerodynamic equations is considered. Convergence of the alternating scheme is shown. Moreover the physical correctness of the obtained coupled solutions is discussed.
Similarity solutions of dispersive long‐wave equations in two space dimensions
Authors: Sen‐Yue Lou
Published: October 2005

In this paper, both the direct method and the non‐classical Lie approach are applied to reduce the (2 + 1)‐dimensional dispersive long wave equations. Nine types of two‐dimensional PDE reductions and 13 types of ODE reductions are given. All the known reductions obtained by the classical Lie approach are reobtained as some special cases. Similar to the (1 + 1)‐dimensional case, some types of reductions with essential and logarithmic singular characteristic manifolds are allowed although the model is integrable.
Quaternion non‐linear filter for estimation of rotating body attitude
Authors: Aramanovitch L. I.
Published: October 2005

A problem of optimal estimation of a rotating vehicle's attitude with both differential equations of motion and observations of stars by onboard equipment is considered. The problem is formulated like a determinate non‐linear Kalman filter problem in quaternion terms. An exact analytical solution of the problem is also found in quaternion terms. Various types of solutions in accordance with a mutual arrangement of observed stars are presented. An example of only one observed star is demonstrated to support the method. The method is also suited for geodetic applications, e.g. geodetic positioning and navigation systems.