117 research outputs found
Modelling mixed-mode fracture in poly(methylmethacrylate) using peridynamics
No full textAbstractPeridynamics (Silling (2000)) is a non-local continuum theory that is particularly suited to handle discontinuities in the displacement field, such as those arising during fracture. Peridynamics prescribes that each material point interacts with all its neighbors contained in a sphere of given radius; this assumption introduces a characteristic length scale in the continuum description. In a nutshell, the interactions between material points depend on their relative distance; in the peridynamics framework this distance is called the “bond length”. The equations of motion, holding at each material point, link the material point acceleration to the integral over the point neighborhood of a force density field, whose strength depend on bond-stretches, i.e. the ratio of the actual bond-length over the initial one. In these equations the displacement gradient does not appear, thus naturally allowing for discontinuities in the displacement field to occur. As to failure, the simplest possible damage description is provided by an interaction law prescribing the force to vanish when a critical bond-stretch threshold is crossed; this parameter can be related to the Mode I critical strain energy release rate. A single parameter is needed to describe failure, in principle under every possible loading condition.In this work the predictive abilities of peridynamics were checked against experimental results in the case of mixed-mode failure of brittle polymers. Pre-cracked poly(methylmethacrylate) (PMMA) samples were tested using different specimens, in order to obtain Mode I, Mixed-Mode and Mode II loading conditions. The material was assumed to behave according to a peridynamics brittle elastic material model; the parameters needed to calibrate the elastic behavior were determined from Mode I tests, as was the critical stretch.The peridynamics simulations of mixed-mode tests were able to catch the correct fracture initiation load and to provide a fair description of the crack path under different conditions. The peridynamics model was also able to qualitatively capture the typical “nail” shape assumed by the crack front during propagation
A review on graphene and graphene composites for application in electromagnetic shielding
No full text<p>This document is an author version of review paper ragarding new shielding materials. <span>To design an EMI shielding product, a compromise must be achieved between the electromagnetic shielding efficiency, the thickness of shielding materials, durability, mechanical strength, reduced volume and weight, and elasticity. Due to its ability to block EMWs, flexibility, lightweight, and chemical resistivity, graphene has been identified as a promising candidate material for efficient EMI shielding. Herein, we reviewed the studies that investigated various graphene-based composites as potential EMI shielding materials, with a focus on the composites based on graphene and silver nanowires due to their high EMI shielding efficiency, low production price, and favorable mechanical properties. </span></p>
Silymarin prevented 6-OHDA induced oxidative stress in the substantia nigra of Parkinsonian male rats
No full textMetellina haddadi Marusik & Larsen 2018, sp. n.
No full text<i>Metellina haddadi</i> sp. n. (figs 1–34) <p>urn:lsid:zoobank.org:pub: 65B0A77E-FA5E-487D-96DB-C266EE3071C0:</p> <p>T y p e s: Holotype ♂ (NCA) and paratypes 2 ♂, 3 ♀ (NCA), 1 ♂, 4 ♀ (SAMC) and 2 ♂, 2 ♀ 1 juv (ZMMU), <b>South Africa</b>, Western Cape, Cape Town, foothills of the Table Mountain, Newlands Forest, 33°58’14.2” S, 18°26’59.2” E, 250 m, 4.01.2014 (Y. M. Marusik & N. Larsen).</p> <p>Diagnosis. The males of this new species well differ from African congeners by having the cymbium as long as the palpal femur (shorter in other species) and the shape of paracymbium which has a bifid lateral process (<i>Lp</i>) (not bifid in other species). The epigyne of the new species resembles that of <i>M. merianopsis</i> by having a ventral projection of the median plate. The two species can be differentiated by the presence of the sclerotized plate (<i>Sp</i>) in front of the epigyne in the new species and lacking in <i>M. merianopsis</i>.</p> <p>D e s c r i p t i o n. Male (holotype). Total length 7.90. Carapace 3.75 long, 2.50 wide. General appearance as in figs 1–2, 32. Carapace light brown, with dark-brown broad median band and marginal stripes. Fovea deep, appears as inverted Y. Chelicera, endites and sternum brown. Chelicera with 3 pro- and 4 retromarginal teeth (figs 20–22). Legs light brown, with dark round spots around spines on femora I–II, tibiae I–II with 4 dark annulations; tibiae III–IV with 2 dark annulations; coxa II with gray prolateral spot distally; coxa IV with grey hue basally, and coxa III. Abdomen twice as long as wide, background formed by white guanine spots, median dark band located in Fig. 32–33. <i>Metellina haddadi</i> sp. n. in natural anterior part, posterior 1/3 with series of dark habitats: 32 — male and female; 33 — resting female, showing ventral abdominal pattern. transverse stripes; venter with wide dark median band bordered by whitish stripes and a pair of round spots near spinnerets.</p> <p>Leg segment lengths in male</p> <p>Fe Pt Ti Mt Ta Total</p> <p>Palp 1.07 0.4 0.5 1.07 3.13</p> <p>I 8.0 2.0 8.8 8.5 2.2 29.5</p> <p>II 7.0 1.8 7.0 7.6 1.7 25.1</p> <p>III 3.7 1.1 2.7 3.3 1.1 11.9</p> <p>IV 5.0 1.1 4.0 4.5 1.1 15.7</p> <p>Spination of leg I: femur d1p4r7 to10; patella d1; tibia d1or 2 p3 r3; metatarsus d1p1r1. Metatarsi and partly tibiae I–II with strong, erect, inflexible setae.</p> <p>Palp as in figs 5–15, 23–28. Femur as long as cymbium and slightly shorter than patella+tibia, tibia and cymbium and ventral part of paracymbium with long macrosetae. Cymbium long, more than3times longer than wide, paracymbium complex, with subconical, weakly sclerotized ventral part (<i>Pv</i>) covered with long setae and heavily sclerotized dorsolateral part (<i>Pl</i>), the latter with 2 processes: the bifid lateral process (<i>Lp</i>) and the dorsal process (<i>Dp</i>); the dorso-lateral part of the paracymbium and cymbium form a deep fovea (pocket) (<i>Pf</i>). The tegulum and sperm duct distinct, transverse; conductor (<i>Co</i>) wide at base, with parallel margins, tip (<i>Ct</i>) tapering, weakly sclerotized; embolic division with massive and complex base (<i>Eb</i>) comprising a main square part (<i>Mp</i>) with a deep cavity (<i>Dc</i>) and lamellate process (<i>Ll</i>) guiding the embolus (<i>Em</i>); embolus partly hidden by conductor.</p> <p>Female (paratype). Total length 9.3. Carapace 3.75 long, 2.65 wide. Prosoma coloured as in male (figs 4, 32). Abdomen lighter than male, with more guanine spots, long, light median band, running all over dorsum, mid part with short, dark stripe; median band bordered with wide sublateral bands, mid part of bands lighter than anterior and posterior parts; sides of abdomen white with slanted dark band anteriorly and series of broken slanted stripes.</p> <p>Leg segment lengths in female</p> <p>Fe Pt Ti Mt Ta Total</p> <p>Palp 1.1 0.4 08 1.25 3.55</p> <p>I 5.6 1.75 5.7 5.9 1.6 20.55</p> <p>II 4.5 1.5 4.05 4.5 1.25 15.8</p> <p>III 2.7 1.0 1.85 2.15 0.85 8.55</p> <p>IV 3.8 1.05 3.0 3.25 0.9 12.0</p> <p>Spination of leg I: femur d2 p4 or 5 r5; patella d1; tibia d2 p3 r3; metatarsus d1 p1 r1. Metatarsi and partly tibiae I–II as in male with erect, inflexible setae, but shorter and less dense in comparison to males.</p> <p>Epigyne as in figs 16–19, 29–31. Epigynal plate almost 3 times wider than long, median plate (<i>Me</i>) weakly sclerotized, slightly projected ventrally; anterior part of plate with distinct fovea (<i>Af</i>); in caudal view, median plate pentagonal, with pair of shallow pits (<i>Pi</i>). Small transverse rectangular sclerotized plate (<i>Sp</i>) located anterior to epigyne. Receptacles cylindrical, bent in mid part, basal part diverging, distal parts converging, distal part spaced by about 3.5 diameters.</p> <p>V a r i a t i o n s. Body length in males varies from 6.5 to 7.4 and in females from 7.0 to 9.3.</p> <p>Habitat. The species occur in large numbers in shaded places along mountain creeks with stony banks. During the daytime it is not easy to find specimens although webs are rather common. In the nighttime, spiders stay at the web hub and can be easily seen and collected.</p> <p>D i s t r i b u t i o n. Known only from the type locality (fig 34).</p> <p>Etymolog y. The specific name is a patronym in honour of our friend and colleague Charles Haddad (Bloemfontein, South Africa) who helped to organize YM’s trip to South Africa.</p> <p>Etymology. The specific name is a patronym in honour of our friend and colleague Charles Haddad (Bloemfontein, South Africa) who helped to organize YM’s trip to South Africa.</p> <p>We thank Seppo Koponen, who arranged stay of the senior author at Turku and the work carried out at the Zoological Museum and Charles Haddad (University of the Free State, South Africa) for his help in arranging of senior author’s trip to South Africa. Special thanks to Ansie Dippenaar-Schoeman (NCA, South Africa) for valuable comments that improved our manuscript. English of the final manuscript was kindly checked by Sarah Crews (Californian Academy of Sciences, USA).</p>Published as part of <i>Marusik, Yu. M. & Larsen, N., 2018, A Synopsis Of African Metellina (Aranei, Tetragnathidae, Metainae) With Description Of A New Species From South Africa, pp. 205-216 in Vestnik Zoologii (Vestn. Zool.) (Vestn. Zool.) 52 (3)</i> on pages 212-215, DOI: 10.2478/vzoo-2018-0021, <a href="http://zenodo.org/record/6454685">http://zenodo.org/record/6454685</a>
Modulation of Extracellular Matrix by Scrophularia striata Extract in Vitro: A Potential Antiscarring Agent
No full textSilymarin and neurodegenerative diseases: Therapeutic potential and basic molecular mechanisms
No full textFabrication and characterization of graphene-based carbon hollow spheres for encapsulation of organic corrosion inhibitors
No full textIn this work, we synthesized carbon hollow spheres (CHSs) using the silica templating method, encapsulated 2-mercaptobenzimidazole (MBI) inhibitor in the CHSs and evaluated their corrosion inhibition performance upon exposure of mild steel to a saline solution containing the released inhibitor. The effects of silica template surface modification on the CHS structure was evaluated, while the structure and morphology of the synthesized CHS was analyzed using field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), Raman spectroscopy and X-ray diffraction (XRD) spectroscopy. Furthermore, thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy mapping (EDS-mapping) and UV–vis were employed to evaluate the MBI release from carbon capsules at different pH values. Corrosion protection performance of the doped CHS was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed tunability of the shell structure between an amorphous carbon and graphene structure using surface modification of the silica templates. Moreover, the MBI release from the CHSs showed to be pH-dependent allowing smart protection of mild steel when exposed to corrosive conditions.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.(OLD) MSE-
Energy-Efficient SNN Implementation Using RRAM-Based Computation In-Memory (CIM)
No full textSpiking Neural Networks (SNNs) can drastically improve the energy efficiency of neuromorphic computing through network sparsity and event-driven execution. Thus, SNNs have the potential to support practical cognitive tasks on resource constrained platforms, such as edge devices. To realize this, SNN requires energy-efficient hardware which can run applications with a limited energy budget. However, the conventional CMOS implementations cannot achieve this goal due to the various architectural and technological challenges. In this work, we address these issues by developing an energy-efficient and accurate SNN hardware based on Computation In-Memory (CIM) architecture using Resistive Random Access Memory (RRAM) devices. The developed SNN architecture is based on unsupervised Spike Time Dependent Plasticity (STDP) learning algorithm with online learning capability. Simulation results show that the proposed architecture is energy-efficient with a consumption of ≈20 fJ per spike, while maintaining state-of-the-art inference accuracy of 95% when evaluated using the MNIST dataset.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Computer EngineeringQuantum & Computer Engineerin
Mechanical and Corrosion Protection Properties of a Smart Composite Epoxy Coating with Dual-Encapsulated Epoxy/Polyamine in Carbon Nanospheres
No full textCarbon nanocapsules doped separately with epoxy and polyamine were used to fabricate an epoxy nanocomposite coating. Carbon nanospheres with dual-encapsulated epoxy/polyamine were dispersed uniformly in the epoxy resin at concentrations of 2, 5, and 10 wt %. The mechanical properties of the nanocomposites were studied by tensile testing and scratch hardness measurements. Furthermore, nanocomposites were applied on mild steel substrates, and their corrosion protection and barrier performance were evaluated using electrochemical impedance spectroscopy (EIS). Adhesion loss measurements of coatings after 240 h exposure to 3.5 wt % NaCl solution were performed by pull-off adhesion testing. Also, the buried steel/polymer interface was studied in situ using attenuated total reflection Fourier transform infrared spectroscopy in the Kretschmann geometry. The results showed that both mechanical and corrosion protection properties of the prepared nanocomposites are enhanced as compared to the baseline epoxy coating and improved with the concentration of doped carbon nanocapsules. Maximum mechanical and corrosion protection properties were achieved in the case of 10 wt % doped carbon nanocapsules as a result of active intermolecular interactions between the epoxy and polyamine chains of the coating matrix and amine groups grafted on the surface of carbon capsules.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.(OLD) MSE-
Effect of WR-1065 on 6-hydroxydopamine-induced catalepsy and IL-6 level in rats
No full textObjective(s): Neuroinflammation and oxidative stress play a key role in pathogenesis of Parkinson’s disease (PD). In the present study we investigated the effect of reactive oxygen species (ROS) scavenger WR-1065 on catalepsy and cerebrospinal fluid (CSF) level of interleukin 6(IL-6) and striatum superoxide dismutase (SOD) activity in 6-hydroxydopamine (6-OHDA) induced experimental model of PD.
Materials and Methods: Seventy two male Wistar rats were divided into 9 equal groups and 6-OHDA (8 μg/2 μl/rat) was infused unilaterally into substantia nigra pars copmacta (SNc) to induce PD. Catalepsy was measured by standard bar test, CSF level of IL-6 was assessed by enzyme-linked immunosorbent assay (ELISA) method and SOD activity measured by spectrophotometric method. In pre-treatment groups WR-1065 (20, 40 and 80 μg/2 μl/rat/day, for 3 days) was infused into the SNc before 6-OHDA administration and 21 days later, as a recovery period, behavioral and molecular assay tests were done.
Results: Our results showed that pre-treatment with WR-1065 improved (
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