bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constitutive model for quasi‐static deformation of metallic sandwich cores
Authors: Xue Zhenyu , Hutchinson John W. 
Published: October 2004

AbstractAll‐metal sandwich construction holds promise for significant improvements in stiffness, strength and blast resistance for built‐up plate structures. Analysis of the performance of sandwich plates under various loads, static and dynamic, requires modelling of face sheets and core with some fidelity. While it is possible to model full geometric details of the core for a few selected problems, this is unnecessary and unrealistic for larger complex structures under general loadings. In this paper, a continuum constitutive model is proposed as an alternative means of modelling the core. The constitutive model falls within the framework of a compressible rate‐independent, anisotropic elastic–plastic solid. The general form of the model is presented, along with algorithmic aspects of its implementation in a finite element code, and selected problems are solved which benchmark the code against existing codes for limiting cases and which illustrate features specific to compressible cores. Three core geometries (pyramidal truss, folded plate, and square honeycomb) are considered in some detail. The validity of the approach is established by comparing numerical finite element simulations using the model with those obtained by a full three‐dimensional meshing of the core geometry for each of the three types of cores for a clamped sandwich plate subject to uniform pressure load. Limitations of the model are also discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Cracking particles: a simplified meshfree method for arbitrary evolving cracks
Authors: Rabczuk T. , Belytschko T. 
Published: October 2004

AbstractA new approach for modelling discrete cracks in meshfree methods is described. In this method, the crack can be arbitrarily oriented, but its growth is represented discretely by activation of crack surfaces at individual particles, so no representation of the crack's topology is needed. The crack is modelled by a local enrichment of the test and trial functions with a sign function (a variant of the Heaviside step function), so that the discontinuities are along the direction of the crack. The discontinuity consists of cylindrical planes centred at the particles in three dimensions, lines centred at the particles in two dimensions. The model is applied to several 2D problems and compared to experimental data. Copyright © 2004 John Wiley & Sons, Ltd.
Supersensitivity due to uncertain boundary conditions
Authors: Xiu Dongbin , Karniadakis George Em 
Published: October 2004

AbstractWe study the viscous Burgers' equation subject to perturbations on the boundary conditions. Two kinds of perturbations are considered: deterministic and random. For deterministic perturbations, we show that small perturbations can result in O(1) changes in the location of the transition layer. For random perturbations, we solve the stochastic Burgers' equation using different approaches. First, we employ the Jacobi‐polynomial‐chaos, which is a subset of the generalized polynomial chaos for stochastic modeling. Converged numerical results are reported (up to seven significant digits), and we observe similar ‘stochastic supersensitivity’ for the mean location of the transition layer. Subsequently, we employ up to fourth‐order perturbation expansions. We show that even with small random inputs, the resolution of the perturbation method is relatively poor due to the larger stochastic responses in the output. Two types of distributions are considered: uniform distribution and a ‘truncated’ Gaussian distribution with no tails. Various solution statistics, including the spatial evolution of probability density function at steady state, are studied. Copyright © 2004 John Wiley & Sons, Ltd.
The cytoskeleton in neurodegenerative diseases
Authors: Cairns Nigel J , Lee Virginia M‐Y , Trojanowski John Q 
Published: October 2004

AbstractAbundant abnormal aggregates of cytoskeletal proteins are neuropathological signatures of many neurodegenerative diseases that are broadly classified by filamentous aggregates of neuronal intermediate filament (IF) proteins, or by inclusions containing the microtubule‐associated protein (MAP) tau. The discovery of mutations in neuronal IF and tau genes firmly establishes the importance of neuronal IF proteins and tau in the pathogenesis of neurodegenerative diseases. Multiple IF gene mutations are pathogenic for Charcot–Marie–Tooth (CMT) disease and amyotrophic lateral sclerosis (ALS)—in addition to those in the copper/zinc superoxide dismutase‐1 (SOD1) gene. Tau gene mutations are pathogenic for frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP‐17), and tau polymorphisms are genetic risk factors for sporadic progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Thus, IF and tau abnormalities are linked directly to the aetiology and pathogenesis of neurodegenerative diseases. In vitro and transgenic animal models are being used to demonstrate that different mutations impair protein function, promote tau fibrilization, or perturb tau gene splicing, leading to aberrant and distinct tau aggregates. For recognition of these disorders at neuropathological examination, immunohistochemistry is needed, and this may be combined with biochemistry and molecular genetics to properly determine the nosology of a particular case. As reviewed here, the identification of molecular genetic defects and biochemical alterations in cytoskeletal proteins of human neurodegenerative diseases has facilitated experimental studies and will promote the development of assays of molecules which inhibit abnormal neuronal IF and tau protein inclusions. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Die lines in plastics extrusion: Film blowing experiments and numerical simulation
Authors: Ding Fan , Giacomin A. Jeffrey 
Published: October 2004

AbstractDie lines are annoying surface striations that can destroy extrudate aesthetics and compromise product properties. The available literature on die lines has been previously reviewed to explore how die lines arise and how to minimize them. Many factors have been found to influence die line formation. Some techniques are effective in suppressing die lines, mainly discovered through manufacturing experience. Here, we first briefly introduce how to measure and characterize die lines (die line metrology). Film blowing experiments are then conducted to study how various die defects, material properties and operating conditions affect die lines. The empirical relations between die lines and die defects, material properties and operating conditions are explored using dimensionless groups. We also investigate the fluid mechanics in die line formation. The free surface flow of polymer melt leaving the die lips is simulated. The qualitative relations between die defects and die lines are explored. The results are compared with film blowing experiments. Finally, new ways to suppress die lines and prospects for future studies are proposed. Polym. Eng. Sci. 44:1811–1827, 2004. © 2004 Society of Plastics Engineers.
Flow and heat transfer simulation of injection molding with microstructures
Authors: Yu Liyong , Lee L. James , Koelling Kurt W. 
Published: October 2004

AbstractInjection molding has been used for mass production of polymer products with microstructures. Conventional Hele‐Shaw 2.5D midplane simulation is unable to describe the flow pattern correctly. It tends to over‐predict the effects of microstructures on global flow patterns. For the unidirectional flow, an x‐z planar based on the general momentum equation is able to achieve better accuracy and to retrieve more detailed flow and heat transfer information around the microstructures. A hybrid numerical technique is developed, which can significantly reduce the nodes and computation time, and yet provide good flow simulation around the microstructures. The mold‐melt heat transfer coefficient and injection speed are shown to be very important factors in determining the filling depth in microstructures. A decrease of the heat transfer coefficient and the occurrence of wall‐slip are likely in microchannels. Polym. Eng. Sci. 44:1866–1876, 2004. © 2004 Society of Plastics Engineers.
A study on the characteristics of antiplasticized polycarbonates and their optical disk substrates
Authors: Ueda Masaya 
Published: October 2004

AbstractThe characteristics of antiplasticized polycarbonates (PC) and their optical disk substrates were investigated. Meta‐terphenyl (m‐tPh) was chosen as an antiplasticizer. Blends of PC with small amounts of added m‐tPh were injection molded to form optical disk substrates. The flow properties of the blends were significantly improved by the common plasticizing effect of antiplasticizer at the melt state. The effect also induced reduction in internal stress, causing birefringence of the substrate. The increased stiffness and decreased glass transition temperature of the antiplasticized PC caused better flatness of the substrate and better microreplication of the groove geometry, respectively. It also resulted in embrittlement of the substrates, known to be a typical characteristic of antiplasticization. The antiplasticizer decreased the water absorption of the blends and also caused increased stiffness of the blends. The increased stiffness was associated with the elimination of secondary mechanical loss transition at low temperatures. From these results, the ideal viscoelastic property behavior of a polymer for an optical disk substrate to achieve better microreplication, better flatness, and low birefringence was proposed; that is, exhibiting lower modulus above glass transition temperature and higher modulus at the regions below glass transition temperature for the polymer of interest. Polym. Eng. Sci. 44:1877–1884, 2004. © 2004 Society of Plastics Engineers.
Bubble nucleation and growth in polymer solutions
Authors: Kim Ki Young , Kang Sung Lin , Kwak Ho‐Young 
Published: October 2004

AbstractThe molecular cluster model for homogeneous bubble nucleation was extended to predict the bubble nucleation events in elastomers, polymers and polymer solutions. For nucleation in elastomers and polymers, the strain energy overcome by a critical bubble during growth period was also considered. The calculation results for the number of bubbles nucleated are in good agreement with observed results. Further, the growing of the critical bubble by the diffusion process in a viscoelastic medium was treated by an integral method for the concentration boundary layer. The calculated cell sizes depending on the initial saturation pressure are in close agreement with the observed sizes. The governing equations developed in this study may be used in polymer processing of microcellular foams. Polym. Eng. Sci. 44:1890–1899, 2004. © 2004 Society of Plastics Engineers.
Synthesis and gas barrier characterization of poly(ethylene isophthalate)
Authors: Kotek Richard , Pang Kyeong , Schmidt Ben , Tonelli Alan 
Published: October 2004

AbstractPoly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004
The Interaction between Otto Fuel II and Aqueous Hydroxylammonium Perchlorate (HAP), Part I: Initial Observations and Time‐to‐Event Measurements
Authors: Bellerby John M. , Blackman Christopher S. 
Published: October 2004

AbstractInvestigations have shown that a violent event (normally auto‐ignition) occurs after a relatively short period of time when the two immiscible liquids Otto Fuel II and 82% aqueous hydroxylammonium perchlorate (HAP) come into contact at temperatures between 30 °C and 50 °C. Under quiescent conditions the time from initial contact to an event (time‐to‐event) depends on the relative volumes of the liquids as well as the temperature but there is no significant difference between the time‐to‐event recorded in an open container and that recorded in a sealed container at the same temperature. It is concluded that key reactions in the build up to an event are taking place in both the Otto Fuel II and in the HAP solution.
Enantiomer discrimination of peptides by tandem mass spectrometry: influence of the peptide sequence on chiral recognition
Authors: Czerwenka Christoph , Lindner Wolfgang 
Published: October 2004

AbstractThe enantiomer discrimination of peptides by electrospray ionization tandem mass spectrometry is described. A cinchona alkaloid derivative, tert‐butylcarbamoylquinine, is used as chiral selector. The chiral selector forms diastereomeric complexes with the peptide enantiomers in the liquid phase (methanolic solution), which are then transferred to the gas phase, where their dissociation behaviour is studied in an ion‐trap mass spectrometer. Different degrees of dissociation of the diastereomeric complexes allow for the discrimination of the peptide enantiomers. The influence of the peptide sequence on enantiomer discrimination is discussed and molecular recognition information is derived by comparing the results obtained for related peptides. For dipeptides, small amino acid residues at the N‐terminus and bulky side chains at the C‐terminus were found to enhance chiral recognition, while for tripeptides the effects were rather irregular. Copyright © 2004 John Wiley & Sons, Ltd.
Sequence‐ and site‐specific photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue
Authors: Oh Joo Yeon , Moon Jeong Hee , Kim Myung Soo 
Published: October 2004

AbstractPhotodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue was investigated using a homebuilt tandem time‐of‐flight mass spectrometer equipped with a matrix‐assisted laser desorption/ionization source. Efficient photodissociation of the protonated peptides was demonstrated. Most of the intense peaks in the laser‐induced tandem mass spectra were sequence ions. Furthermore, sequence ions due to cleavages at all the peptide bonds were observed; this is a feature of the technique that is particularly useful for peptide sequencing. Fragmentations at both ends of the tryptophanyl residue were especially prevalent, which can be useful for location of the tryptophanyl chromophore in a peptide. Copyright © 2004 John Wiley & Sons, Ltd.
The cores of random hypergraphs with a given degree sequence
Authors: Cooper Colin 
Published: October 2004

AbstractWe study random r‐uniform n vertex hypergraphs with fixed degree sequence d = (d1…,dn), maximum degree Δ = o(n1/24) and total degree θn, where θ is bounded. We give the size, number of edges and degree sequence of the κ ≥ 2) up to a whp error of O(n2/3 Δ4/3 log n). In the case of graphs (r = 2) we give further structural details such as the number of tree components and, for the case of smooth degree sequences, the size of the mantle. We give various examples, such as the cores of r‐uniform hypergraphs with a near Poisson degree sequence, and an improved upper bound for the first linear dependence among the columns in the independent column model of random Boolean matrices. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 25, 2004
Bootstrap confidence intervals for medical costs with censored observations
Authors: Jiang Hongyu , Zhou Xiao‐Hua 
Published: October 2004

AbstractMedical costs data with administratively censored observations often arise in cost‐effectiveness studies of treatments for life‐threatening diseases. Mean of medical costs incurred from the start of a treatment until death or a certain time point after the implementation of treatment is frequently of interest. In many situations, due to the skewed nature of the cost distribution and non‐uniform rate of cost accumulation over time, the currently available normal approximation confidence interval has poor coverage accuracy. In this paper, we propose a bootstrap confidence interval for the mean of medical costs with censored observations. In simulation studies, we show that the proposed bootstrap confidence interval had much better coverage accuracy than the normal approximation one when medical costs had a skewed distribution. When there is light censoring on medical costs (≤25 per cent), we found that the bootstrap confidence interval based on the simple weighted estimator is preferred due to its simplicity and good coverage accuracy. For heavily censored cost data (censoring rate ≥30 per cent) with larger sample sizes (n≥200), the bootstrap confidence intervals based on the partitioned estimator has superior performance in terms of both efficiency and coverage accuracy. We also illustrate the use of our methods in a real example. Copyright © 2004 John Wiley & Sons, Ltd.
Accounting for leadtime in cohort studies: evaluating when to initiate HIV therapies
Authors: Cole Stephen R. , Li Rui , Anastos Kathryn , Detels Roger , Young Mary , Chmiel Joan S. , Muñoz Alvaro 
Published: October 2004

AbstractCommonly reported comparisons of differences in disease progression according to disease staging at therapy initiation may be subject to bias if they do not account for the time it took the deferred group to reach the latter stage (that is, leadtime) and for previous events in those who initiate therapy at late stage (that is, unseen fast progressors). To estimate the impact of deferring initiation of highly active antiretroviral therapies (HAART) on time to clinical AIDS in the context of data from observational cohort studies, we describe a method that capitalizes on data from a pre‐HAART period to multiply impute estimated leadtimes and the unseen events among fast progressors. After accounting for leadtime and the unseen events, data from two large cohort studies (N=739) indicate that deferring HAART initiation until CD4 is below 200 cells/mm3was detrimental compared to initiating between 201 and 350 (hazard ratio=1.97; 95 percent confidence interval [CI] 1.09, 3.54), and that failure to account for leadtime resulted in a 38 per cent higher hazard ratio. In contrast, initiating HAART between 201 and 350 did not increase the hazard of AIDS compared to initiating with CD4 between 351 and 500cells/mm3(hazard ratio=0.70; 95 per cent CI 0.35, 1.42). Methods presented here offer an approach to analysing prevalent cohort studies and provide procedures to maximize the usefulness of observational data. Copyright © 2004 John Wiley & Sons, Ltd.
Comparing regression methods for the two‐stage clonal expansion model of carcinogenesis
Authors: Kaiser J. C. , Heidenreich W. F. 
Published: October 2004

AbstractIn the statistical analysis of cohort data with risk estimation models, both Poisson and individual likelihood regressions are widely used methods of parameter estimation. In this paper, their performance has been tested with the biologically motivated two‐stage clonal expansion (TSCE) model of carcinogenesis. To exclude inevitable uncertainties of existing data, cohorts with simple individual exposure history have been created by Monte Carlo simulation. To generate some similar properties of atomic bomb survivors and radon‐exposed mine workers, both acute and protracted exposure patterns have been generated. Then the capacity of the two regression methods has been compared to retrieve a priori known model parameters from the simulated cohort data. For simple models with smooth hazard functions, the parameter estimates from both methods come close to their true values. However, for models with strongly discontinuous functions which are generated by the cell mutation process of transformation, the Poisson regression method fails to produce reliable estimates. This behaviour is explained by the construction of class averages during data stratification. Thereby, some indispensable information on the individual exposure history was destroyed. It could not be repaired by countermeasures such as the refinement of Poisson classes or a more adequate choice of Poisson groups. Although this choice might still exist we were unable to discover it. In contrast to this, the individual likelihood regression technique was found to work reliably for all considered versions of the TSCE model. Copyright © 2004 John Wiley & Sons, Ltd.
Residual analysis in linear regression models with an interval‐censored covariate
Authors: Topp Rebekka , Gómez Guadalupe 
Published: October 2004

AbstractResidual analysis is a useful class of techniques for the evaluation of the goodness of a fitted model. Checking the underlying assumptions is important since most linear regression estimators require a correctly specified regression function and independent and identically distributed errors to be consistent. For uncensored data, the examination of the residuals of the fitted model is a standard tool for checking whether or not the underlying model assumptions hold. Such analysis has not been widely developed for censored data. Hillis (Statistics in Medicine1995;14:2023–2036) developed a residual plot for model checking when the response variable of a linear model is right‐censored, and Gómezet al. (Statistics in Medicine2003;22:409–425) proposed residuals in models with interval‐censored covariates. In this paper, we propose a new definition of residuals for linear models that incorporate interval‐censored covariates. This definition can be also applied when the response variable is interval‐censored. These new residuals are shown to perform better in model checking than other types of residuals in this context. We illustrate them with a data set from an AIDS clinical trial study. Copyright © 2004 John Wiley & Sons, Ltd.