bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of damage parameters for Ti‐6Al‐4V titanium alloy using continuum damage mechanics
Authors: Allahverdizadeh N. , Manes A. , Giglio M. 
Published: May 2012

AbstractModelling ductile damage is one of the most important applications of continuum damage mechanics (CDM) models. Scientists have previously tried to identify the damage parameters and have calibrated the failure behaviour of different materials using CDM models. However, more comprehensive studies are still needed to investigate the capabilities of CDM models for different materials. It is possible to extend the methodology to titanium alloys that are, currently, an optimal solution for highly stressed mechanical components. Therefore Lemaitre's CDM model parameters for ti‐6Al‐4V titanium alloy have been identified and reported in this work. A series of experimental tests have been carried out to identify the CDM model's parameters by the method of degradation of elastic modulus. A subroutine has been written in ABAQUS to numerically simulate the behaviour of the simple specimen using Lemaitre's model.
Laser beam cutting of metallic hollow sphere structures
Authors: Riegel H. , Merkel M. , Öchsner A. 
Published: May 2012

AbstractMetallic hollow sphere structures (MHSS) represent a relatively new group of advanced composite materials characterised by high geometry reproduction leading to relatively constant mechanical and physical properties. The MHSS combine the well‐known advantages of cellular metals without major scattering of their material parameters. Various joining technologies such as sintering, soldering and adhering can be used to assemble single metallic hollow spheres to interdependent structures and allow adjusting different macroscopic properties. A machining process for MHSS has to reflect the special characteristic of the composite material. Classical mechanical cutting techniques like sawing or milling often fail. Spheres or large pieces are separated from the bulk structure and cause a rough surface at the cutting zone. Other cutting techniques like water jet cutting cannot be used for oxidising material. This paper presents laser beam cutting as a proper technique to cut composite materials like MHSS. The quality of the cutting zone strongly depends on the process parameter e. g. focal length, tool velocity and the structural characteristics of MHSS, e. g. density, sphere diameter and density. The experimental work was done using a CO2‐laser with a power of 1.5 kW. All investigations were done with sintered hollow sphere structures having different macroscopic properties. The maximum depth of a cut kerf was determined for four configurations of MHSS as function of laser velocities, gas pressure of the process gas, focal length of the lense. The depth was evaluated using a power balance of the laser input power on one side and the power needed to warm and melt the MHSS on the other side. A comparison between simulation and experiment of the width and the depth of the cut kerf shows, that the laser beam gets multiple reflections on the surfaces of the hollow spheres, enlarging the width of the cut kerf. The functional dependency between laser velocity and cut kerf depth can be estimated well. Theoretical and experimental results fit well together.
Finite element simulation of the macroscopic heat conductivity of syntactic perforated hollow sphere structures
Authors: Sulong M. A. , Öchsner A. 
Published: May 2012

AbstractThis work investigated the thermal properties of a new type of hollow sphere structures. For this new type, the sphere shell is perforated by several holes in order to open the inner sphere volume for a matrix material. The effective thermal conductivity of syntactic (i. e. spheres completely embedded in a matrix) perforated hollow sphere structures in a primitive cubic (PC) arrangement of unit cell models were numerically evaluated for different hole diameters, matrix volume fractions and different base materials. The results are compared to typical configurations without perforation. In the scope of this paper, three‐dimensional finite element analyses were used in order to investigate these unit cell models.
Approximating survivable networks with minimum number of steiner points
Authors: Kamma Lior , Nutov Zeev 
Published: May 2012

AbstractGiven a graph H = (U, E) and connectivity requirements r = {r(u,v) : u, v ∈ R ⊆ U}, we say that H satisfies r if it contains r(u, v) pairwise internally‐disjoint uv‐paths for all u, v ∈ R. We consider the Survivable Network with Minimum Number of Steiner Points (SN‐MSP) problem: given a finite set V of points in a normed space (M, ‖·‖) and connectivity requirements, find a minimum size set S ⊂ M \ V of additional points, such that the unit disc graph induced by U = V ∪ S satisfies the requirements. In the (node‐connectivity) Survivable Network Design Problem (SNDP) we are given a graph G = (V, E) with edge costs and connectivity requirements, and seek a minimum cost subgraph H of G that satisfies the requirements. Let k = maxu,v ∈ Vr(u, v) denote the maximum connectivity requirement. We will show a natural transformation of an SN‐MSP instance (V, r) into an SNDP instance (G = (V, E), c, r), such that an α‐approximation algorithm for the SNDP instance implies an α · O(k2)‐approximation algorithm for the SN‐MSP instance. In particular, for the case of uniform requirements r(u, v) = k for all u, v ∈ V, we obtain for SN‐MSP the ratio O(k2 ln k), which solves an open problem from (Bredin et al. Proceedings of the 6th ACM International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc) (2005), 309–319). © 2012 Wiley Periodicals, Inc. NETWORKS, 2012
Polycarbonate urethane films modified by heparin to enhance hemocompatibility and endothelialization
Authors: Lu Yue , Shen Li , Gong Feirong , Cui Jiayang , Rao Ju , Chen Jianding , Yang Wei 
Published: May 2012

AbstractPolyurethane with pendant carboxyl groups was synthesized by a two‐step reaction using methylene diphenyl diisocyanate as hard segments, polycarbonate diols as soft segments and 2,2‐bis(hydroxymethyl) propionic acid as chain extenders. The surfaces of the casting polymer films were further covalently conjugated with heparin as confirmed by Fourier transform infrared spectroscopy. The associated surface‐exposed heparin content was measured to be 1.92 µg cm−2 and was shown to be active. Meanwhile, surface hydrophobicity decreased after heparin modification. Heparin immobilization greatly improved the hemocompatibility of polyurethane films both in vitro and in vivo. The in vitro cell responses revealed that the expression of proinflammatory markers CD106 and CD62E of human vein endothelial cells was significantly suppressed on the surfaces of the heparinized polyurethane films, while the affinity and proliferation of the cells were improved. The in vivo performance of this material before and after heparin modification was evaluated as a stent coating material in a porcine coronary artery injury model. Histological analysis indicated that heparinized polyurethane induced mild foreign body reactions and inflammation, which were much lower than those induced by unmodified polyurethane. Heparin immobilization also accelerated the endothelialization process on the surface of the polymer‐coated stents when implanted in porcine coronary arteries. More detailed long‐term studies are needed to confirm the biostability of the heparin and the endothelialized surfaces. Copyright © 2012 Society of Chemical Industry
Preparation of polymer microspheres with a rosin moiety from rosin ester, styrene and divinylbenzene
Authors: Yu Caili , Chen Chuanwei , Gong Qinhai , Zhang Fa‐Ai 
Published: May 2012

AbstractRosin was reacted with hydroxyethyl methacrylate to produce a macromonomer. This macromonomer was used to partly replace styrene for the novel preparation of polymer microspheres with divinylbenzene via suspension polymerization. Orthogonal experiments were conducted to analyze the factors influencing the particle size, particle size distribution, swelling ratio and degree of crosslinking of the polymer microspheres. Fourier transform IR spectroscopy, thermogravimetry and scanning electron microscopy were used to examine the structures, thermal properties and morphologies, respectively, of the polymer microspheres. The results showed that the amount of dispersant had the greatest influence on particle size and distribution. On the other hand, the monomer ratio greatly influenced the swelling ratio and degree of crosslinking of the polymer microspheres. The decomposition temperature of the polymer microspheres increased upon introduction of the rosin moiety into the product. Open pores were abundant on the surface of the polymer microspheres due to the existence of the porogen, which provided a base for adsorption and separation. The present study opens a novel route for using naturally occurring rosin. Copyright © 2012 Society of Chemical Industry
Interfacial agent effect on rheological response and crystallite characteristics in germicidal polypropylene/titanium dioxide nanocomposites
Authors: Serrano Cristina , Ressia Jorge A , Vallés Enrique M , Fernández‐García Marta , Cerrada María L 
Published: May 2012

AbstractGermicidal nanocomposites based on metallocene isotactic polypropylene (iPP) and titanium dioxide (TiO2) nanoparticles have been prepared at a constant TiO2 content of 2 wt%. Different quantities of a polypropylene wax partially grafted with maleic anhydride (PP‐g‐MAH) are employed to improve the polymer‐nanoparticle compatibility. Remarkable biocidal capabilities of these TiO2 nanocomposites have been found and their crystalline structure and thermal and rheological responses explored. Several very interesting features have been found in these germicidal nanocomposites. On the one hand, rheological parameters do not change significantly with respect to those exhibited by pure iPP. This is extremely advantageous for the processing of these compounds since they can be transformed under similar conditions to those employed for iPP. On the other hand, the existence of two polymorphs is observed independent of the amount of compatibilizer used. The enhancement in polymer‐nanoparticle interactions by effect of the interfacial (PP‐g‐MAH) component is appraised looking at dynamical mechanical relaxations as a function of temperature and at crystallization processes of the various nanocomposites. Copyright © 2012 Society of Chemical Industry
Computer simulation of solitary waves in a common or auxetic elastic rod with both quadratic and cubic nonlinearities
Authors: Bui Dinh T. , Long V. Cao , Xuan K. Dinh , Wojciechowski K. W. 
Published: May 2012

AbstractResults of numerical simulations are presented for propagation of solitary waves in an elastic rod of positive or negative Poisson's ratio, i.e. of a common or auxetic material. Splitting of various initial pulses during propagation into a sequence of solitary waves is considered in frames of a model which contains both quadratic and cubic nonlinear terms. The obtained results are compared with some exact analytic solutions, called solitons, what leads to the conclusion that the solitons describe well the more complicated wave fields which are obtained by numerical simulations. This is because the analytic solutions reflect complete balance between various orders of nonlinearity and dispersion. Collisions between some obtained solitary waves are also presented.
Automated assessment of learners' understanding in complex dynamic systems
Authors: Kopainsky Birgit , Pirnay‐Dummer Pablo , Alessi Stephen M. 
Published: May 2012

AbstractResearch on learning via system‐dynamics based learning environments depends on accurate measurement of learning. Most such research considers at least two aspects of learning: participants' understanding of the models and problems; and participants' performance in the environment, i.e. quality of decision making. Understanding is much more difficult to measure than performance. Measurement of understanding is often done by eliciting verbal protocols from participants. Coding and analysis of verbal protocols are subjective and time consuming. To facilitate measurement and analysis of understanding via verbal protocols, we investigate the utility of a software application which performs such analysis automatically. We assess this automated analysis methodology using data from a system‐dynamics based learning environment. The results from the automated analysis are comparable to the results from a manual analysis when we analyze how participants' understanding compares to experts and how it changes over time. Additionally, the automated analysis facilitates investigating relationships between understanding and performance. Copyright © 2012 System Dynamics Society.
Assembly of Graphene Sheets into 3D Macroscopic Structures
Authors: Yin Shengyan , Niu Zhiqiang , Chen Xiaodong 
Published: May 2012

AbstractIntegration of graphene sheets, 2D nanoscale building blocks, into 3D macroscopic assemblies and ultimately into a functional system is essential to explore the advanced properties of individual graphene sheets for macroscopic applications. This Concept paper summarizes different ways, such as flow‐directed assembly, layer‐by‐layer deposition, template‐directed method, and leavening strategy to assemble graphene sheets into the layered and porous 3D macroscopic structures. The obtained structures show unique properties, such as flexible network, high specific surface area, and outstanding electrical and mechanical properties. Furthermore, the functional systems based on such graphene 3D macroscopic structures have shown enhanced performance in the applications of energy storage, catalysis, environmental remediation, and sensing.
M13 Bacteriophage‐Activated Superparamagnetic Beads for Affinity Separation
Authors: Muzard Julien , Platt Mark , Lee Gil U. 
Published: May 2012

AbstractThe growth of the biopharmaceutical industry has created a demand for new technologies for the purification of genetically engineered proteins.The efficiency of large‐scale, high‐gradient magnetic fishing could be improved if magnetic particles offering higher binding capacity and magnetization were available. This article describes several strategies for synthesizing microbeads that are composed of a M13 bacteriophage layer assembled on a superparamagnetic core. Chemical cross‐linking of the pVIII proteins to a carboxyl‐functionalized bead produces highly responsive superparamagnetic particles (SPM) with a side‐on oriented, adherent virus monolayer. Also, the genetic manipulation of the pIII proteins with a His6 peptide sequence allows reversible assembly of the bacteriophage on a nitrilotriacetic‐acid‐functionalized core in an end‐on configuration. These phage–magnetic particles are successfully used to separate antibodies from high‐protein concentration solutions in a single step with a >90% purity. The dense magnetic core of these particles makes them five times more responsive to magnetic fields than commercial materials composed of polymer–(iron oxide) composites and a monolayer of phage could produce a 1000 fold higher antibody binding capacity. These new bionanomaterials appear to be well‐suited to large‐scale high‐gradient magnetic fishing separation and promise to be cost effective as a result of the self‐assembling and self‐replicating properties of genetically engineered M13 bacteriophage.
Measuring True Young's Modulus of a Cantilevered Nanowire: Effect of Clamping on Resonance Frequency
Authors: Qin Qingquan , Xu Feng , Cao Yongqing , Ro Paul I. , Zhu Yong 
Published: May 2012

AbstractThe effect of clamping on resonance frequency and thus measured Young's modulus of nanowires (NWs) is systematically investigated via a combined experimental and simulation approach. ZnO NWs are used in this work as an example. The resonance tests are performed in situ inside a scanning electron microscope and the NWs are cantilevered on a tungsten probe by electron‐beam‐induced deposition (EBID) of hydrocarbon. EBID is repeated several times to deposit more hydrocarbons at the same location. The resonance frequency increases with the increasing clamp size until approaching that under the “fixed” boundary condition. The critical clamp size is identified as a function of NW diameter and NW Young's modulus. This work: 1) exemplifies the importance of considering the effect of clamping in measurements of Young's modulus using the resonance method, and 2) demonstrates that the true Young's modulus can be measured if the critical clamp size is reached. Design guidelines on the critical clamp size are provided. Such design guidelines can be extended to other one‐dimensional nanostructures such as carbon nanotubes.
Lateral‐torsional buckling checks of steel frames using second‐order analysis
Authors: Wieschollek Matthias , Schillo Nicole , Feldmann Markus , Sedlacek (dec.) Gerhard 
Published: May 2012

AbstractThis article summarizes the rules given in EN 1993‐1‐1 [2] for using second‐order analysis to check the flexural and lateral‐torsional buckling of members and systems loaded in the strong plane of their cross‐section which may not fail due to out‐of‐plane instability.The rules relevant in EN 1993‐1‐1 [2] are those for equivalent geometrical imperfections resulting from the elastic buckling modes with amplitudes derived from column buckling tests according to EN 1990 Annex D [1] plus those for the linear superposition of utilization rates in the strong and weak planes as used for evaluating tests to determine the amplitude of imperfections and the partial factors.Computer assistance is generally required for determining the elastic buckling modes; the computer outputs gives both modal out‐of‐plane displacements and modal out‐of‐plane bending moments for the relevant flanges of the sections. The use of out‐of‐ plane bending moments makes the assessment clear and simple. It leads to a magnification factor for the in‐plane‐utilization rate that allows the design point x = xd to be found along the length of the member or system where the cross‐sectional check is relevant. It also shows that the results of the second‐order analysis for this design point and the use of buckling curves for member checks at this design point are identical.The assessment procedure with second‐order analysis is generic and applicable to all design cases, whereas the member checks with buckling curves as specified in EN 1993‐1‐1 [2] are intended to be valid for specific loadings and boundary conditions only (object‐oriented rules). They should be consistent with the generic rules. In this respect, this article is a contribution towards the further evolution of EN 1993‐1‐1 [2].
Component method for end plate joints, modeling of 3D frames: literature review
Authors: Heinisuo Markku , Perttola Henri , Ronni Hilkka 
Published: May 2012

AbstractLiterature of modelling steel frames in 3D using beam finite elements is presented. The development of member modelling is described first followed by joint modelling. The review ends with a brief introduction of the 3D component model for end plate joints. The next part includes three examples of the 3D component method: base bolt joint, beam‐ to‐column joint and member splice joint.
Abnormal expression of stathmin 1 in brain tissue of patients with intractable temporal lobe epilepsy and a rat model
Authors: Zhao Fenghua , Hu Yida , Zhang Ying , Zhu Qiong , Zhang Xiaogang , Luo Jing , Xu Yali , Wang Xuefeng 
Published: May 2012

AbstractMicrotubule dynamics have been shown to contribute to neurite outgrowth, branching, and guidance. Stathmin 1 is a potent microtubule‐destabilizing factor that is involved in the regulation of microtubule dynamics and plays an essential role in neurite elongation and synaptic plasticity. Here, we investigate the expression of stathmin 1 in the brain tissues of patients with intractable temporal lobe epilepsy (TLE) and experimental animals using immunohistochemistry, immunofluorescence and western blotting. We obtained 32 temporal neocortex tissue samples from patients with intractable TLE and 12 histologically normal temporal lobe tissues as controls. In addition, 48 Sprague Dawley rats were randomly divided into six groups, including one control group and five groups with epilepsy induced by lithium chloride‐pilocarpine. Hippocampal and temporal lobe tissues were obtained from control and epileptic rats on Days 1, 7, 14, 30, and 60 after kindling. Stathmin 1 was mainly expressed in the neuronal membrane and cytoplasm in the human controls, and its expression levels were significantly higher in patients with intractable TLE. Moreover, stathmin 1 was also expressed in the neurons of both the control and the experimental rats. Stathmin 1 expression was decreased in the experimental animals from 1 to 14 days postseizure and then significantly increased at Days 30 and 60 compared with the control group. Many protruding neuronal processes were observed in the TLE patients and in the chronic stage epileptic rats. These data suggest that stathmin 1 may participate in the abnormal network reorganization of synapses and contribute to the pathogenesis of TLE. Synapse 66:781–791, 2012. © 2012 Wiley Periodicals, Inc.
Quantitative analysis of binding sites for 9‐fluoropropyl‐(+)‐dihydrotetrabenazine ([18F]AV‐133) in a MPTP‐lesioned PD mouse model
Authors: Chao Ko‐Ting , Tsao Hsin‐Hsin , Weng Yi‐Hsin , Hsiao Ing‐Tsung , Hsieh Chia‐Ju , Wey Shiaw‐Pyng , Yen Tzu‐Chen , Kung Mei‐Ping , Lin Kun‐Ju 
Published: May 2012

Abstract[18F]AV‐133 is a novel PET tracer for targeting the vesicular monoamine transporter 2 (VMAT2). The aim of this study is to characterize and quantify the loss of monoamine neurons with [18F]AV‐133 in the MPTP‐lesioned PD mouse model using animal PET imaging and ex vivo quantitative autoradiography (QARG). Methods: Optimal imaging time window of [18F]AV‐133 was first determined in normal C57BL/6 mice (n = 3) with a 90‐min dynamic scan. The reproducibility of [18F]AV‐133 PET imaging was evaluated by performing a test–retest study within 1 week for the normal group (n = 6). For MPTP‐lesioned studies, normal, and MPTP‐treated [25 mg mg/kg once (Group A) and twice (Group B), respectively, daily for 5 days, i.p., groups of four normal and MPTP‐treated] mice were used. PET imaging studies at baseline and at Day 4 post‐MPTP injections were performed at the optimal time window after injection of 11.1 MBq [18F]AV‐133. Specific uptake ratio (SUr) of [18F]AV‐133 was calculated by [(target uptake–cerebellar uptake)/cerebellar uptake] with cerebellum as the reference region. Ex vitro QARG and immunohistochemistry (IHC) studies with tyrosine hydroxylase antibody were carried out to confirm the abundance of dopaminergic neurons. Results: The variability between [18F]AV‐133 test–retest striatal SUr was 6.60 ± 3.61% with less than 5% standard deviation between animals (intervariability). The percentages of MPTP lesions were Group A 0.94 ± 0.29, −42.1% and Group B 0.65 ± 0.09, −60.4%. By QARG, specific binding of [18F]AV‐133 was reduced relative to the control groups by 50.6% and 60.7% in striatum and by 30.6% and 46.4% in substantia nigra (Groups A and B, respectively). Relatively small [18F]AV‐133 SUr decline was noted in the serotonin and norepinephrine‐enriched regions (7.9% and 9.4% in mid‐brain). Results obtained from IHC consistently confirmed the sensitivity and selectivity of dopaminergic neuron loss after MPTP treatment. Conclusions: [18F]AV‐133 PET SUr displayed a high test–retest stability. The SUr significantly declined in the caudate putamen but not in the hypothalamus and midbrain regions after MPTP treatment in the mouse brain. The results obtained for QARG and IHC were consistent and correlated well with the PET imaging studies. On the basis of these concordant results, we find that [18F]AV‐133 should serve as a useful and reliable PET tracer for evaluating nigrostriatal degeneration. Synapse 66:823–831, 2012. © 2012 Wiley Periodicals, Inc.