bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of cerebral blood volume using quantitative susceptibility mapping, R2* relaxometry, and ferumoxytol‐enhanced MRI
Authors: Rivera‐Rivera Leonardo A. , Schubert Tilman , Johnson Kevin M. 
Published: September 2019

Ferumoxytol‐enhanced MRI holds potential for the non‐invasive assessment of vascular architecture using estimates of cerebral blood volume (CBV). Ferumoxytol specifically enables steady‐state imaging with extended acquisition times, for substantial improvements in resolution and contrast‐to‐noise ratio. With such data, quantitative susceptibility mapping (QSM) can be used to obtain images of local tissue magnetic susceptibility and hence estimate the increase in blood susceptibility after administration of a contrast agent, which in turn can be correlated to tissue CBV. Here, we explore the use of QSM for CBV estimation and compare it with R2* (1/T2*)‐based results. Institutional review board approval was obtained, and all subjects provided written informed consent. For this prospective study, MR images were acquired on a 3.0 T scanner in 19 healthy subjects using a multiple‐echo T2*‐weighted sequence. Scanning was performed before and after the administration of two doses of ferumoxytol (1 mg FE/kg and 4 mg FE/kg). Different QSM approaches were tested on numerical phantom simulations. Results showed that the accuracy of magnetic susceptibility measurements improved with increasing image resolution and decreasing vascular density. In vivo changes in magnetic susceptibility were measured after the administration of ferumoxytol utilizing QSM, and significantly higher QSM‐based CBV was measured in gray matter compared with white matter. QSM‐ and R2*‐based CBV estimates correlated well, with similar average values, but a larger variance was found in QSM‐based estimates.
Physicochemical Compatibility of Dexmedetomidine With Parenteral Nutrition
Authors: Campos‐Baeta Ylenia , Saavedra‐Mitjans Mar , Garin Noe , Cardenete Joana , Cardona Daniel , Riera Pau 
Published: September 2019

AbstractBackgroundDexmedetomidine is an α2‐agonist used as a sedative agent in the intensive care setting. Simultaneous administration of dexmedetomidine and parenteral nutrition (PN) may be required. The aim of this study was to evaluate the physicochemical compatibility of dexmedetomidine Y‐site administered with PN.MethodsThree PN and 3 dexmedetomidine solutions were compounded. The tested infusion rate for PN was 66 mL/h. For dexmedetomidine, we considered the initial and maximum infusion rates (0.7 and 1.4 µg/kg/h) detailed in the data sheet. Taking this into account and considering a weight range of 55–95 kg, we tested 2 dexmedetomidine infusion rates (10 and 36 mL/h). The samples obtained were examined visually against light. pH was analyzed with a pH meter. Mean fat droplet diameter was determined by dynamic light scattering. Quantification of dexmedetomidine concentration was carried out by ultraperformance liquid chromatography–high‐resolution mass spectrometry. For each PN‐dexmedetomidine admixture, tests were performed in triplicate.ResultsNo alterations were observed by visual inspection. Average pH was 6.25 ± 0.01. Droplet diameter remained below 500 nm (298 ± 10 nm for 10‐mL/h rate and 303 ± 5 nm for 36‐mL/h rate). Dexmedetomidine concentrations at t = 0 were 519 ± 31 ng/mL and 1391 ± 90 ng/mL for 10‐ and 36‐mL/h infusion rates, respectively. At t = 24 hours, the concentrations obtained were 494 ± 22 and 1332 ± 102 ng/mL, which translates into ≥90% of the initial concentrations.ConclusionDexmedetomidine is physicochemically compatible with PN during simulated Y‐site administration at the tested infusion rates.
Linear‐frictional contact model for 3D discrete element simulations of granular systems
Authors: Kuhn Matthew R. , Suzuki Kiichi , Daouadji Ali 
Published: September 2019

SummaryThe linear‐frictional contact model is the most commonly used contact mechanism for discrete element (DEM) simulations of granular materials. Linear springs with a frictional slider are used for modeling interactions in directions normal and tangential to the contact surface. Although the model is simple in two dimensions, its implementation in 3D faces certain subtle challenges, and the particle interactions that occur within a single time step require careful modeling with a robust algorithm. The paper details a three‐dimensional algorithm that accounts for the changing direction of the tangential force within a time step, the transition from elastic to slip behavior within a time step, possible contact sliding during only part of a time step, and twirling and rotation of the tangential force during a time step. Without three of these adjustments, errors are introduced in the incremental stiffness of an assembly. Without the fourth adjustment, the resulting stress tensor is not only incorrect but it is also no longer a tensor. The algorithm also computes the work increments during a time step, both elastic and dissipative.
Design and analysis adaptivity in multiresolution topology optimization
Authors: Gupta Deepak K. , van Keulen Fred , Langelaar Matthijs 
Published: September 2019

SummaryMultiresolution topology optimization (MTO) methods involve decoupling of the design and analysis discretizations, such that a high‐resolution design can be obtained at relatively low analysis costs. Recent studies have shown that the MTO method can be approximately 3 and 30 times faster than the traditional topology optimization method for two‐dimensional (2D) and three‐dimensional (3D) problems, respectively. To further exploit the potential of decoupling analysis and design, we propose a dp‐adaptive MTO method, which involves locally increasing/decreasing the polynomial degree of the shape functions (p) and the design resolution (d). The adaptive refinement/coarsening is performed using a composite refinement indicator that includes criteria based on analysis error, presence of intermediate densities, as well as the occurrence of design artifacts referred to as QR‐patterns. While standard MTO must rely on filtering to suppress QR‐patterns, the proposed adaptive method ensures efficiently that these artifacts are suppressed in the final design, without sacrificing the design resolution. The applicability of the dp‐adaptive MTO method is demonstrated on several 2D mechanical design problems. For all the cases, significant speedups in computational time are obtained. In particular for design problems involving low material volume fractions, speedups of up to a factor of 10 can be obtained over the conventional MTO method.
The capacity for oestrogen to influence obesity through brown adipose tissue thermogenesis in animal models: A systematic review and meta‐analysis
Authors: Sievers Will , Rathner Joseph A. , Kettle Christine , Zacharias Anita , Irving Helen R. , Green Rodney A. 
Published: September 2019

SummaryPharmacological interventions to aid weight loss have historically targeted either appetite suppression or increased metabolic rate. Brown adipose tissue (BAT) possesses the capacity to expend energy in a futile cycle, thus increasing basal metabolic rate. In animal models, oestrogen has been implicated in the regulation of body weight, and it is hypothesized that oestrogen is acting by modulating BAT metabolism. A systematic search was performed, to identify research articles implementing in vivo oestrogen‐related interventions and reporting outcome measures that provide direct or indirect measures of BAT metabolism. Meta‐analyses were conducted where sufficient data were available. The final library of 67 articles were predominantly in rodent models and provided mostly indirect measures of BAT metabolism. Results of this review found that oestrogen's effects on body weight, in rats and possibly mice, are likely facilitated by both metabolic and appetitive mechanisms but are largely only found in ovariectomized models. There is a need for further studies to clarify the potential effects of oestrogen on BAT metabolism in gonad‐intact and castrated male animal models.
On the formulation of anisotropic plasticity for polymeric composites‐ rate‐dependent models with non‐linear isotropic/kinematic hardening
Authors: G Nagaraja Swaroop , Schuecker Clara 
Published: September 2019

AbstractThe use of fiber‐reinforced composites as a primary structural component in automotive and aerospace industries has significantly increased over time, due to their great weight saving potential. Consequently, the predictive modeling of the non‐linear behavior of composites has been a topic of intensive research over the last years. Experimental data shows non‐linear response that is direction dependent due to the fibrous micro‐structure. Since typical fiber materials can be considered essentially as linear elastic, the non‐linearities are attributable to the inelastic deformation in the matrix, occurring at relatively small strains.This study presents a relatively general, homogenized formulation of anisotropic plasticity for application to (mainly) polymeric composites. A constitutive model has been developed to simulate the non‐linearities exhibited by the composite, generating the anisotropic elastic and plastic response functions with the aid of representation theorems. Rate‐independent versions using isotropic hardening have previously been proposed by the authors. The main focus of this work is the extension to include rate dependency and non‐linear kinematic hardening effects. Selected numerical simulations which serve the purpose of illustrating the formulation discussed herein, are presented at the end.
Implementing a microstructure model with self‐organization into a FEM Software
Authors: Oelsch Erik , Wulf Hans , Ihlemann Jörn 
Published: September 2019

AbstractExperimental investigation of filled rubber reveal several complex properties like hysteresis, permanent set, Mullins‐effect. The connection of these properties to the microstructure is still unclear. The theory of Self‐Organizing Linkage Patterns (SOLP) by Ihlemann is an approach that relies crucially on deviations from average distributions. Specifically, it states that deformed rubber develops a pattern based on physical linkages which is characterized by regions of high and low linkage density. On this basis, all complex material properties can be explained as result of an adaption of the linkage pattern to the applied deformation. The theory is verified by a simulation program which uses a very abstract model of the molecular structure of filled rubber. Furthermore a FEM software is used to mix serial and parallel connection of single SOLP systems.
Non‐material finite element rod model for out‐of‐plane bending of an elastic strip with natural curvature
Authors: Schmidrathner Christian , Vetyukov Yury 
Published: September 2019

AbstractA novel finite element formulation for elastic unshearable rods in three‐dimensional space is presented. Looking forward to future implementations of axially moving belts, we use a mixed Eulerian‐Lagrangian kinematic formulation, which has the advantage that the element nodes are fixed in one spatial coordinate and the material points are flowing through the mesh, hence it is possible to discretize the elements in the free spans coarser than the ones in contact with the pulleys. Here, we present the solution of hanging rods with a flat cross‐section including a natural curvature, which causes an out‐of‐plane bending as well as torsion of the rod. For validation purposes we limit ourselves to equilibrium solutions (for which purely Lagrangian elements would be also applicable) with clamped boundary conditions. The results are compared with a shell model of the hanging strip. Preliminary results concerning the frictionless contact problem for a steel belt hanging on two pulleys are discussed.
Polymorphic Uncertainty Quantification of Computational Soil and Earth Structure Simulations via the Variational Sensitivity Analysis
Authors: Henning Carla , Ricken Tim 
Published: September 2019

AbstractDue to the high natural variability of mechanical properties in soil, comparatively high safety factors are still used for the dimensioning of earth structures. Back in the 1970s, probabilistic concepts were recommended as the technical standard for geotechnical applications. However, their dissemination failed because of the high computation costs on one hand and, on the other hand, often not enough data being available to carry out such analyses.By means of increasing computing power and enhanced mathematical models, a better understanding of the nature and influence of the uncertainties and errors could help to develop a more reliable risk assessment and to reduce inefficient safety factors. For this reason, we perform a research project within the priority program SPP 1886, installed by the DFG and focused on polymorphic uncertainty quantification. In the present subproject (SP 12), the focus is driven on quantification and assessment of polymorphic uncertainties in computational simulations of earth structures, especially for fluid‐saturated soils. To describe the strongly coupled and transient solid‐fluid response behavior, the Theory of Porous Media (TPM) is used and solved via the Finite Element Method (FEM).The goal is to overcome the above mentioned two problems by providing suitable numerical methods. Motivated by structural optimization research, the Variational Sensitivity Analysis (VSA) provides detailed prior information about the current equilibrium state for subsequent analyzes. On its basis, the information for which parameters and in which areas of the simulation domain a more detailed investigation is required can be obtained in advance. The method enables an immediate decision support, e.g. for site investigators or researchers. Not only the computational effort but also the applicability to any arbitrary FE‐Model are great advantages of this approach.
Modeling of active multiphase materials
Authors: Sauerwein Malte , Steeb Holger 
Published: September 2019

AbstractIn this contribution, material modeling and experimental investigations towards a chemically‐active multiphase material are presented. The material under consideration consists of a solid skeleton, while the pore space is filled with multiple reactive pore fluids. Here, the pore space is simultaneously filled with a pore liquid and a hydrogel made of a granulate of superabsorbent polymers (SAP). The three‐phase material is modeled within a continuum mixture theory based on the Hybrid Mixture Theory (HMT). Due to the hydrophilic character, the hydrogel is able to absorb large amounts of the pore liquid and binds it to the polymer structure. As a consequence, the saturation of free liquid in the void space decreases during the absorption, which also affects the permeability with respect to seepage flow. Since the absorption dynamics as well as the maximum water capacity of the hydrogel depend highly on external stimuli, e.g. the pore fluid chemistry, temperature, electric and magnetic fields, hydrogels are usually called active or functional materials. The hydrogel material used in this study is sensitive with respect to the ion concentration of the surrounding pore liquid.
The role of degenerate mobilities in Cahn‐Hilliard models
Authors: Dziwnik Marion 
Published: September 2019

AbstractThe present work provides an insight into the role of degenerate mobilities in phase field models and in particular their influence on the evolution of the interface. The equation of interest is the Cahn‐Hilliard equation (in two space dimensions) with a polynomial double well free energy and different order‐parameter dependent, degenerate mobilities. According to the preliminary work [1], considering an anisotropic version of the equation, the asymptotic sharp interface limit subtly dependents on the degeneracy of the mobility. Whilst a quadratic degenerate mobility leads to a sharp interface model where bulk diffusion is present at the same asymptotic order as surface diffusion, a bi‐quadratic degenerate mobility leads to a sharp interface model where bulk diffusion is subdominant. The present study continues the preliminary work and shows that the type of the degeneracy has a qualitative impact on the evolution: Considering numerical simulations of the dewetting process of a thin solid film with four‐fold anisotropic surface energy, the evolution with bi‐quadratic degenerate mobility turns out to be more effective for film pinch‐off than with quadratic degenerate mobility. An extension to the isotropic Cahn‐Hilliard equation ensures that the characteristic difference in the pinch‐off behavior is in fact mobility‐dependent.
A coupled isogeometric boundary element and finite element method for electro‐mechanical interaction
Authors: Rajski Michal P. , Harmel Maximilian , Sauer Roger A. 
Published: September 2019

AbstractSolving multiphysical problems is a challenging task in computational engineering both in regard to accuracy and efficiency. Finite element methods (FEM) – while very popular and well established for standard problems – are less straightforward for problems involving interfaces moving due to the influence of external fields. Such problems are characterized by additional challenges, such as mesh dynamics, re‐meshing and possible unboundedness of the external field. The boundary element method (BEM) can help to overcome these challenges. In the BEM formulation, the problem is solved solely from the boundary of the domain. This property – in conjunction with finite element shell and membrane formulations – leads to a very interesting coupled method, requiring only the surface discretization to solve multiphysical interface problems. To show the underling idea of the formulation, the electro‐mechanical interaction between two charged shells is considered as an example.
Inverse dynamics of underactuated flexible mechanical systems
Authors: Ströhle Timo , Betsch Peter 
Published: September 2019

AbstractAn alternative approach to the inverse dynamics of flexible mechanical systems is presented. In contrast to a sequential discretization in space and time a simultaneous space‐time discretization is applied to the problem of inverse dynamics of underactuated systems. In particular, a space‐time finite element formulation will be compared with a formulation which is based on the method of characteristics. Numerical examples are presented which underline the importance of solving this class of problems in space and time simultaneously.
Modeling and Simulation of the Aqueous Humor Flow in the Human Eye
Authors: Dörsam Simon , Olkhovskiy Vladislav , Friedmann Elfriede 
Published: September 2019

AbstractA mathematical model for the physiology of the aqueous humor flow in the human eye is developed. The governing equations are the Stokes and Darcy equations with certain physical characteristic parameters. We extend the model to describe diseases like glaucoma and retinal diseases and model their treatment. The developed models are solved with the mixed Finite Element method and the flow is visualized in a three‐dimensional eye model. An individual physiology of a healthy eye or of an eye with glaucoma can be represented by adjusting the parameters. We calculate the intraocular pressure and quantify the pressure decrease after a certain treatment. In case of retinal diseases we calculate the drug distribution and quantify the drug amount at the location of action.
Validation of an administrative claims coding algorithm for serious opioid overdose: A medical chart review
Authors: Mountcastle Sally B. , Joyce Andrew R. , Sasinowski Maciek , Costello Nancy , Doshi Snehal , Zedler Barbara K. 
Published: September 2019

AbstractPurposeA standardized definition for serious opioid overdose has not been clearly established for disease surveillance or assessing the impact of risk mitigation strategies. The purpose of this study was to use medical chart review to clinically validate a claims‐based algorithm to identify serious opioid overdose events.MethodsThe algorithm for serious opioid overdose required an opioid poisoning or external cause ICD‐9‐CM code occurring within 1 day of (a) an adverse effect code for serious central nervous system or respiratory depression or (b) a mechanical ventilation or critical care CPT code. The claims coding algorithm identified a sample of 145 individuals 18 years or older among patients that presented to the emergency department of two large hospitals in metropolitan Atlanta, Georgia from January 2014 to August 2015. Claims‐defined cases were evaluated against rigorous clinical definitions for serious opioid overdose using (a) literature‐based criteria for typical clinical manifestations of opioid overdose and/or (b) clinical response to the opioid‐specific reversal agent naloxone. The positive predictive value (PPV) for a serious opioid overdose was calculated as the percentage of clinically confirmed cases (definite or probable).ResultsAmong 140 evaluable claims‐defined cases, 107 fulfilled clinical criteria for a serious opioid overdose [95 definite and 12 probable; PPV of 76.4% (95% CI 69.4%, 83.5%)]. Among 30 nonconfirmed cases, 20 were polyintoxications involving one or more nonopioid psychoactive agents.ConclusionsAn administrative claims coding algorithm for serious opioid overdose had high clinical predictive performance in a medical chart review.
Spatio‐temporal variability of cloud cover types in West Africa with satellite‐based and reanalysis data
Authors: Danso Derrick Kwadwo , Anquetin Sandrine , Diedhiou Arona , Lavaysse Christophe , Kobea Arsène , Touré N'Datchoh Evelyne 
Published: September 2019

AbstractThis study aims to understand and document the occurrence and variability of cloud cover types in West Africa (WA). Investigations are carried out with a 10‐year hourly record of two cloud data products: CERES passive satellite observations and ERA5 reanalysis. The seasonal evolutions of high (HCC), middle (MCC), low (LCC) and total (TCC) cloud cover are examined. Both products agree on the seasonal and spatial occurrence of cloud cover, although CERES presents lower values of cloud fraction than ERA5 which is partly attributed to the inability of the satellite sensor to detect optically thin clouds in the atmosphere. Southern WA is found to be cloudier than other parts of the region in all seasons with mean TCC fractions of 70 and 80% for CERES and ERA5 respectively during the monsoon season. In all seasons, the presence of LCC over large areas of the Sahel/Sahara region is noted in the CERES product. This could be due to a possible misinterpretation of Saharan dust as low clouds which may have thus, caused it to overestimate the occurrences and fractions of LCC over this region. Northern WA is associated with higher frequencies of no cloud occurrence events, unlike the south where cloudless skies are rarely observed. Furthermore, in southern WA, overcast conditions of LCC are observed for a significant number of times (up to 20% of the time during the rainy season in CERES and 40% in ERA5). The climatology of cloud cover presented in this study could be useful for the planning of solar energy projects.