bluuebunny/crossref_metadata_2025_split huggingface dataset:
A robust numerical method for flow through a pipe driven by an oscillating pressure gradient
Authors: Ansari Ali R. , Miller John J. H. , Shishkin Grigori I. 
Published: August 2006

AbstractThe problem of periodic flow of an incompressible fluid through a pipe, which is driven by an oscillating pressure gradient (e.g. a reciprocating piston), is investigated in the case of a large Reynolds number. This process is described by a singularly perturbed parabolic equation with a periodic right‐hand side, where the singular perturbation parameter is the viscosity ν. The periodic solution of this problem is a solution of the Navier–Stokes equations with cylindrical symmetry. We are interested in constructing a parameter‐robust numerical method for this problem, i.e. a numerical method generating numerical approximations that converge uniformly with respect to the parameter ν and require a bounded time, independent of the value of ν, for their computation. Our method comprises a standard monotone discretization of the problem on non‐standard piecewise uniform meshes condensing in a neighbourhood of the boundary layer. The transition point between segments of the mesh with different step sizes is chosen in accordance with the behaviour of the analytic solution in the boundary layer region. In this paper we construct the numerical method and discuss the results of extensive numerical experiments, which show experimentally that the method is parameter‐robust. Copyright © 2006 John Wiley & Sons, Ltd.
Computational study of the axial instability of rimming flow using Arnoldi method
Authors: Bae Sun Hyuk , Kim Do Hyun 
Published: August 2006

AbstractAxial instability of rimming flow has been investigated by solving a linear generalized eigenvalue problem that governs the evolution of perturbations of two‐dimensional base flow. Using the Galerkin finite element method, full Navier–Stokes equations were solved to calculate base flow and this base flow was perturbed with three‐dimensional disturbances. The generalized eigenproblem formulated from these equations was solved by the implicitly restarted Arnoldi method using shift‐invert technique. This study presents instability curves to identify the critical wavelength of the neutral mode and the critical β, which measures the importance of gravity relative to viscosity. The axial instability of rimming flow is examined and three‐dimensional flow was reconstructed by using eigenvector and growth rate at a critical wave number. The critical β value in the axial instability analysis was observed to be comparable to the onset β value of the transition between the bump and the homogeneous film state in 2‐D base flow calculations. Copyright © 2006 John Wiley & Sons, Ltd.
Adaptive wall functions for the v2‐f turbulence model
Authors: Kalitzin Georgi , Medic Gorazd 
Published: August 2006

AbstractAdaptive wall functions for the v2‐f turbulence model have been derived for the flow over a flat plate at zero pressure gradient. These wall functions were implemented via tables for the turbulence quantities and the friction velocity uτ. A special treatment for the ε and f boundary conditions is proposed. On fine grids (y+<1) this approach yields results consistent with the wall integration solution. Detailed numerical results are presented for a zero pressure gradient boundary layer and separated flow over a ramp. Copyright © 2006 John Wiley & Sons, Ltd.
A two‐phase flow interface capturing finite element method
Authors: Devals C. , Heniche M. , Bertrand F. , Tanguy P. A. , Hayes R. E. 
Published: August 2006

AbstractA new interface capturing algorithm is proposed for the finite element simulation of two‐phase flows. It relies on the solution of an advection equation for the interface between the two phases by a streamline upwind Petrov–Galerkin (SUPG) scheme combined with an adaptive mesh refinement procedure and a filtering technique. This method is illustrated in the case of a Rayleigh–Taylor two‐phase flow problem governed by the Stokes equations. Copyright © 2006 John Wiley & Sons, Ltd.
Comparison of derivative free Newton‐based and evolutionary methods for shape optimization of flow problems
Authors: Harth Zerrin , Sun Hongtao , Schäfer Michael 
Published: August 2006

AbstractThe object of this study is to investigate two derivative free optimization techniques, i.e. Newton‐based method and an evolutionary method for shape optimization of flow geometry problems. The approaches are compared quantitatively with respect to efficiency and quality by using the minimization of the pressure drop of a pipe conjunction which can be considered as a representative test case for a practical three‐dimensional flow configuration. The comparison is performed by using CONDOR representing derivative free Newton‐based techniques and SIMPLIFIED NSGA‐II as the representative of evolutionary methods (EM).For the shape variation the computational grid employed by the flow solver is deformed. To do this, the displacement fields are scaled by design variables and added to the initial grid configuration. The displacement vectors are calculated once before the optimization procedure by means of a free form deformation (FFD) technique.The simulation tool employed is a parallel multi‐grid flow solver, which uses a fully conservative finite‐volume method for the solution of the incompressible Navier–Stokes equations on a non‐staggered, cell‐centred grid arrangement. For the coupling of pressure and velocity a pressure‐correction approach of SIMPLE type is used. The possibility of parallel computing and a multi‐grid technique allow for a high numerical efficiency. Copyright © 2006 John Wiley & Sons, Ltd.
Unsteady simulations of the flow around a short surface‐mounted cylinder
Authors: Pattenden R. J. , Bressloff N. W. , Turnock S. R. , Zhang X. 
Published: August 2006

AbstractThe flow around a surface‐mounted circular cylinder, of height/diameter ratio 1 with a free end, is simulated using large‐eddy simulation (LES) and detached‐eddy simulation (DES) at a Reynolds number based on diameter of 200 000. A comparison is made between the abilities of the two models to capture flow features observed in particle image velocimetry (PIV) experiments carried out by the authors. The flow contains three interacting features formed from the junction flow between the cylinder and the ground, separation from the cylinder wall and resultant turbulent wake, and the flow over the free‐end of the cylinder. Both LES and DES overpredict the length of the recirculation region by 30%, but the turbulence quantities are close to the measured values. The topology of the flow over the free‐end is confirmed as consisting of an arch or ‘mushroom’ vortex. Due to the high Reynolds number the grid resolution is insufficient to resolve the approaching ground‐plane boundary layer flow with LES, leading to inaccuracies in the horseshoe vortex system. The DES model improves this area, though still has grid induced separation effects. Copyright © 2006 John Wiley & Sons, Ltd.
Numerical identification of flow‐induced oscillation modes in rectangular cavities using large eddy simulation
Authors: Rubio G. , De Roeck W. , Baelmans M. , Desmet W. 
Published: August 2006

AbstractSelf‐sustained oscillations are present in a wide variety of flows. For flows passing cavities, acoustics can play a role in the physical mechanisms triggering and maintaining the oscillation phenomena. This is the case for the flow over rectangular cavities, which is studied in this paper. The compressible LES Navier–Stokes equations are solved for cavities with an upstream laminar boundary layer. The flow passing rectangular cavities is computed, varying two different parameters related to the physics of the problem, Mach number and length of the cavity divided by the momentum thickness of the boundary layer at the leading edge. This paper intends to prove that the switch between shear‐layer oscillation mode, characterized by an acoustic feedback process, and wake oscillation mode, characterized by a large‐scale vortex shedding with Strouhal number independent of Mach number, can be identified using large eddy simulation, and consequently, with much less computational effort than in other studies in literature, where direct numerical simulation has been applied. Copyright © 2006 John Wiley & Sons, Ltd.
A methodology for high performance computation of fully inhomogeneous turbulent flows
Authors: You Donghyun , Wang Meng , Mittal Rajat 
Published: August 2006

AbstractA large‐eddy simulation methodology for high performance parallel computation of statistically fully inhomogeneous turbulent flows on structured grids is presented. Strategies and algorithms to improve the memory efficiency as well as the parallel performance of the subgrid‐scale model, the factored scheme, and the Poisson solver on shared‐memory parallel platforms are proposed and evaluated. A novel combination of one‐dimensional red–black/line Gauss–Seidel and two‐dimensional red–black/line Gauss–Seidel methods is shown to provide high efficiency and performance for multigrid relaxation of the Poisson equation. Parallel speedups are measured on various shared‐distributed memory systems. Validations of the code are performed in large‐eddy simulations of turbulent flows through a straight channel and a square duct. Results obtained from the present solver employing a Lagrangian dynamic subgrid‐scale model show good agreements with other available data. The capability of the code for more complex flows is assessed by performing a large‐eddy simulation of the tip‐leakage flow in a linear cascade. Copyright © 2006 John Wiley & Sons, Ltd.
Efficiency of a POD‐based reduced second‐order adjoint model in 4D‐Var data assimilation
Authors: Daescu D. N. , Navon I. M. 
Published: August 2006

AbstractOrder reduction strategies aim to alleviate the computational burden of the four‐dimensional variational data assimilation by performing the optimization in a low‐order control space. The proper orthogonal decomposition (POD) approach to model reduction is used to identify a reduced‐order control space for a two‐dimensional global shallow water model. A reduced second‐order adjoint (SOA) model is developed and used to facilitate the implementation of a Hessian‐free truncated‐Newton (HFTN) minimization algorithm in the POD‐based space. The efficiency of the SOA/HFTN implementation is analysed by comparison with the quasi‐Newton BFGS and a nonlinear conjugate gradient algorithm. Several data assimilation experiments that differ only in the optimization algorithm employed are performed in the reduced control space. Numerical results indicate that first‐order derivative methods are effective during the initial stages of the assimilation; in the later stages, the use of second‐order derivative information is of benefit and HFTN provided significant CPU time savings when compared to the BFGS and CG algorithms. A comparison with data assimilation experiments in the full model space shows that with an appropriate selection of the basis functions the optimization in the POD space is able to provide accurate results at a reduced computational cost. The HFTN algorithm benefited most from the order reduction since computational savings were achieved both in the outer and inner iterations of the method. Further experiments are required to validate the approach for comprehensive global circulation models. Copyright © 2006 John Wiley & Sons, Ltd.
A piecewise linear approach to volume tracking a triple point
Authors: Choi Benjamin Y. , Bussmann Markus 
Published: August 2006

AbstractAn approach to volume tracking three materials is presented that, in contrast with the so‐called ‘onion‐skin’ methodology, assumes the existence of a ‘triple point’ at which two interfaces between three materials intersect. The reconstruction of any cell that contains three materials is iterative: the approach is to locate a point of intersection between two interfaces that minimizes a given error expression. The advantages and limitations of the algorithm are presented via a series of advection tests that demonstrate that triple points can be reconstructed and advected just as well as simpler interfaces in typical applications. Copyright © 2006 John Wiley & Sons, Ltd.
Tumor necrosis factor and its p55 and p75 receptors are not required for axonal lesion‐induced microgliosis in mouse fascia dentata
Authors: Fenger Christina , Drojdahl Nina , Wirenfeldt Martin , Sylvest Lene , Jorgensen Ole Steen , Meldgaard Michael , Lambertsen Kate L. , Finsen Bente 
Published: August 2006

AbstractTumor necrosis factor (TNF) is a potent pro‐inflammatory and neuromodulatory cytokine. In the CNS it is produced primarily by microglia and considered to regulate microglial activation. On the basis of previous observations of increased microglial TNF mRNA synthesis in areas of anterograde axonal and terminal degeneration in mice, we studied the effect of TNF and its p55 and p75 receptors on axonal lesion‐induced microglial activation in fascia dentata following transection of the perforant path (PP) projection. Unexpectedly, cell counting showed that the axonal lesion‐induced microglial response in TNF and TNF‐p55p75 receptor knock out mice and C57BL/6 mice was similar 5 days after the lesion. In addition, the microglial expression of the lysosomal‐associated antigen CD68, and the clearance of MBP+ myelin debris appeared similar in TNF and TNF‐p55p75 receptor knock out mice compared to C57BL/6 mice. Quantitative PCR and in situ hybridization showed the expression of TNF mRNA to be maximally upregulated 6 h after the lesion, and confirmed that TNF mRNA was still upregulated 5 days after lesion when microglial numbers, CD11b mRNA level, and cellular TNF‐p55 and ‐p75 receptor mRNA level reached maximum. However, in spite of the induction of TNF mRNA, TNF protein level remained at base‐line in fascia dentata using immunohistochemistry and ELISA. In conclusion, the results showed a lower than expected lesion‐induced increase in TNF protein, and that neither TNF nor its receptors were required for the axonal lesion‐induced microglial morphological transformation and proliferation or for the initial clearance of degenerated myelin in the PP‐deafferented fascia dentata. © 2006 Wiley‐Liss, Inc.
Rafts in oligodendrocytes: Evidence and structure–function relationship
Authors: Gielen Ellen , Baron Wia , Vandeven Martin , Steels Paul , Hoekstra Dick , Ameloot Marcel 
Published: August 2006

AbstractThe plasma membrane of eukaryotic cells exhibits lateral inhomogeneities, mainly containing cholesterol and sphingomyelin, which provide liquid‐ordered microdomains (lipid “rafts”) that segregate membrane components. Rafts are thought to modulate the biological functions of molecules that become associated with them, and as such, they appear to be involved in a variety of processes, including signal transduction, membrane sorting, cell adhesion and pathogen entry. Although still a matter of ongoing debate, evidence in favor of the presence of these microdomains is gradually accumulating but a consensus on issues like their size, lifetime, composition, and biological significance has yet to be reached. Here, we provide an overview of the evidence supporting the presence of rafts in oligodendrocytes, the myelin‐producing cells of the central nervous system, and discuss their functional significance. The myelin membrane differs fundamentally from the plasma membrane, both in lipid and protein composition. Moreover, since myelin membranes are unusually enriched in glycosphingolipids, questions concerning the biogenesis and functional relevance of microdomains thus appear of special interest in oligodendrocytes. The current picture of rafts in oligodendrocytes is mainly based on detergent methods. The robustness of such data is discussed and alternative methods that may provide complementary data are indicated. © 2006 Wiley‐Liss, Inc.
The impact of the CERAD‐NP on diagnosis of cognitive deficiencies in late onset depression and Alzheimer's disease
Authors: Künig Gabriella , Jäger Michael , Stief Volker , Kaldune Andreas , Urbaniok Frank , Endrass Jerome 
Published: August 2006

AbstractObjectivesTo identify the most appropriate test combination for distinguishing between late onset depression (LOD) and Alzheimer's disease (AD). To achieve this objective, the Consortium to Establish a Register for Alzheimer's Disease‐Neuropsychological Battery (CERAD‐NP) data of patients diagnosed with these two conditions were analyzed using multiple regression analysis.MethodsIn the first regression analysis, the following CERAD‐NP subtests were included: verbal fluency, Boston naming test, word list learning, constructional praxis, word list recall, and constructional praxis recall. In a second regression analysis, only CERAD‐NP memory parameters were included: word list learning, word list recall, word list intrusions, word list savings, word list recognition, word list false positive errors, constructional praxis recall, and constructional praxis savings.ResultsThe combination of word list recall and constructional praxis recall best distinguished between LOD and AD, with a ROC of 0.91. In the stepwise regression of memory measures, word list recall, word list savings, and constructional praxis recall was the best combination, resulting in a ROC of 0.92.ConclusionThe most efficacious combination of the CERAD‐NP battery for discriminating between LOD and AD consisted of word list recall and constructional praxis recall. Of the CERAD‐NP memory measures, word list recall, word list savings, and constructional praxis recall represented the best diagnostic combination. Copyright © 2006 John Wiley & Sons, Ltd.
Validation of a memory inventory for the assessment of awareness of memory deficits in Alzheimer's disease in Chinese elderly
Authors: Cheong Lui Victor Wing , Wa Lam Linda Chiu , Kum Chiu Helen Fung 
Published: August 2006

AbstractBackgroundThis paper describes the development and validation of the Memory Inventory for Chinese (MIC), for measuring the awareness of memory deficits in the Chinese population with Alzheimer's disease (AD).MethodsA combination of qualitative and quantitative approaches was adopted. The MIC was developed with focus group discussion and pilot testing. It has a patient and a caregiver version. A consecutive series of 79 new out‐patients with the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorder Association (NINCDS‐ADRDA) criteria of probable and possible AD and 20 non‐demented elderly subjects were recruited.ResultsA high internal consistency was found, with Cronbach alpha of 0.89 for the patient version and 0.90 for the caregiver version of MIC. The inter‐rater reliability was satisfactory. For validity assessment, the caregiver score of the MIC correlated significantly with cognitive score of the subject as assessed by the Mini‐Mental State Examination (rp = −0.37; p < 0.01). The Memory Deficit Awareness Score, calculated by subtracting the patient score from the caregiver score, correlated significantly with clinician ratings of awareness of memory impairment (rs = −0.67; p < 0.01).ConclusionsThe MIC appears to be a culturally appropriate and valid instrument for the measurement of awareness of memory deficits in Chinese patients with AD. Potential applications of the MIC should be further explored in other subtypes of dementia and in prospective studies. Copyright © 2006 John Wiley & Sons, Ltd.
Subjective complaints and self‐evaluation of memory test performance in Questionable dementia
Authors: Wong Candy Ho Yan , Lam Linda Chiu Wa , Lui Victor Wing Cheong , Chiu Helen Fung Kum , Chan Sandra Sau Man , Tam Cindy Woon Chi 
Published: August 2006

AbstractBackgroundThe clinical significance of subjective memory complaints in elderly subjects has been an area of active research. In this study, we evaluated subjective complaints and self‐evaluation of memory test performance in subjects with Questionable dementia (QD) and mild Alzheimer's disease (AD).MethodsNinety‐two subjects (35 cognitively intact normal controls NC, 33 QD, and 24 mild AD) were assessed. Subjective memory complaints were evaluated using a memory inventory for the Chinese (MIC); objective assessment of awareness was assessed by the self‐evaluation of own memory test performance. Cognitive function was assessed with the Alzheimer's Disease Assessment Scale—Cognitive subscale (ADAS‐Cog), Category Verbal Fluency Test (CVFT) and Executive Interview (EXIT‐25). Depressive symptoms were evaluated with the Cornell Scale for Depression in Dementia (CSDD).ResultsThe total number of subjective memory complaints (MI‐tol) were significantly different between different subject groups (Kruskal Wallis test, χ2 = 13.19, p = 0.001). Significant correlations between scores of the MI‐tol and CSDD (r = 0.33, p < 0.001), CMMSE (r = −0.33, p < 0.001), CDR (r = 0.36, p < 0.001) were found. In self‐evaluation of memory test performance, the NC group tended to under‐estimate while the AD subjects tended to over‐estimate their performance. Group differences in the discrepancies of self‐evaluation of memory performance were significant for both the immediate (Kruskal Wallis test, χ2 = 9.86, p = 0.007) and delayed recall (Kruskal Wallis test, χ2 = 10.55, p < 0.001) trials.ConclusionsSubjects with QD and mild AD showed higher frequency of subjective memory complaints, reflecting that the subjects still retain some ability to appreciate own memory function. However, the trend for over‐estimation of performance in AD subjects suggests that the precision of estimation may be suboptimal. Moreover, depressive symptoms may affect the presentation of memory complaints and this factor should be carefully considered in future prospective studies. Copyright © 2006 John Wiley & Sons, Ltd.
Sleep duration during the 24‐hour day is associated with the severity of dementia in nursing home patients
Authors: Fetveit Arne , Bjorvatn Bjørn 
Published: August 2006

AbstractStudy objectivesTo describe the characteristics of 24‐h sleep patterns in nursing home patients with dementia, and to determine whether various degrees of dementia have any influence on total sleep duration.Design and settingCross‐sectional study in a nursing home population (n = 23) consisting of patients with varying degree of dementia. Sleep was measured with actigraphy for a consecutive period of 14 days, based on individual bed and rising time, which was registered by nursing home staff.Measurements and resultsMean age ± standard deviation was 86.1 ± 7.0 (range 72–96) and mean Mini‐Mental Status Examination Score (MMSE) was 13.4 ± 5.3 (range 1–21). Ten patients had MMSE ≤ 12. Sleep was extremely fragmented, with frequent wake bouts during nighttime and frequent naps during daytime. During the 24‐h period, patients spent nearly 13 h asleep, distributed as more than 9 h of nighttime sleep and more than 3 h of daytime sleep. Patients with severe degree of dementia (MMSE ≤ 12) slept significantly longer during the 24‐h day than patients with lesser degree of dementia (MMSE > 12). There was no significant difference in age between the dementia sub‐groups.ConclusionSleep duration during the 24‐h day was positively correlated with the severity of dementia in nursing home patients. This is in contrast with total sleep time seen in healthy elderly, which shows a gradually decline with age. Changes in sleep patterns in dementia could be explained by co‐morbid and environmental factors, as well as unknown pathological changes related to dementing illnesses. Copyright © 2006 John Wiley & Sons, Ltd.