bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrospinning of Ultrahigh-Molecular-Weight Polyethylene Nanofibers
Authors: Rein Dmitry M. , Cohen Yachin , Ronen Avner , Zussman Eyal , Shuster Kim 
Published: April 2011

ABSTRACTThe electrospinning method was employed to fabricate extremely fine nanofibers of ultra-high molecular weight polyethylene (UHMWPE) for the first time, using a mixture of solvents with different dielectric constant and conductivity. A novel experimental device for elevated temperature electrospinning of highly volatile and quickly crystallizing polymer solutions and melts was developed. The possibility to produce the highly oriented nanofibers from ultra-high molecular weight polymers suggests new ways for fabrication of ultra-strong, porous, surface modified fibers and single-component nanocomposite yarn with improved properties.
Nanoscale Elastic and Tribological Properties of Poly(Acrylic Acid) Superabsorbent Gels
Authors: Talavera Beatriz , Martínez Juan J. , Santiago Francisca , Cuberes M. Teresa 
Published: April 2011

ABSTRACTUltrasonic Force Microscopy and Friction Force Microscopy have been applied to the characterization of the elastic and tribological responses of poly(acrylic acid) hydrogels at ambient conditions. The gels were prepared by free radical polymerization of acrylic acid monomers partially neutralized by sodium hydroxide, using N, N'-methylen-bis-acrylamide as a crosslinker. Nanoscale domains with different stiffness and friction are observed. Increasing the amount of crosslinker leads to the formation of smaller, more densely packed domains. The domains with higher stiffness also exhibit higher friction and lower topographic high. The results can be understood by assuming that (i) neutralization by sodium hydroxide leads to the formation of both acrylic acid and sodium acrylate polymeric strands (ii) the observed domains differ in their acrylic acid / sodium acrylate content. In the acrylic acid rich domains, hydrogen bonding among the polymeric strands explains a higher stiffness and lower topography. In the sodium acrylate rich domains, lubrication by water molecules linked by solvation to the sodium counterions accounts for a lower friction.
Ultra-Thin Layer Activation as a Potential Tool for Nano-wear Characteriation
Authors: Popa-Simil Liviu 
Published: April 2011

ABSTRACTAn application of the nuclear kinematics selective reaction is the usage of the recoil nuclear reaction in generating radioactive ion beams which may de used for MEMS and fine machinery parts labeling used for ultra thin layer activation techniques. The classical Thin or Ultra Thin Layer method relies in creation of a very thin layer on the technologic surface that to exhibit radioactivity of short life radioisotopes. For classical material loss applications concentrations of the order of ppb of different material generated by nuclear reaction were offering plenty of gamma or X radiation to be easily detected over the natural background level directly by a radiation gauge placed above the entire functional mechanism, or by accumulating these in the third tribologic medium – a lubricant or a fluid. In the case of MEMS devices the material concentrations are required to be high enough in order to produce a good radioactive signal or other methods based on resonant energies on isotopic materials may be used such as particle activated prompt gamma, connected with the possibility of the MEMS device of removing from the spot of the dislocated material that becomes technologically useless but carrying out tracer material. There are various possibilities of applying tracer materials on the MEMS devices in order to clearly determine in-situ and in operation the material loss and to correlate with the operation regime.
Ab Initio DFT Study of Ideal Strength of Crystal and Surfaces in Covalent Systems
Authors: Umeno Yoshitaka 
Published: April 2011

AbstractAb initio density functional theory (DFT) calculations were performed to examine various factors which may influence the ideal strength, namely multiaxial loading condition and structure with low symmetry. First, the effect of normal stress on the ideal shear strength (ISS) in covalent crystals, Si, C, Ge and SiC, was evaluated. It was found that the response of ISS to normal stress differs depending on the material, while in metals the trend is unchanged. Obtained ISS as a function of normal stress is useful to understand criteria of dislocation nucleation in a pristine crystal because local lattices at the nucleation site undergo superimposed stress components in experiment. Secondly the ideal tensile strength of silicon surface was evaluated to examine how atomistic-level structure affects the mechanical property. The theoretical tensile strength of Si nanofilms with (100) surface, which is flat with dimer-row structures, shows only 20-30% reduction even though the thickness is down to 1 nm, meaning that the flat surface possesses high strength.
Simultaneous Improvement of Ductility and Strength by Minute Doping in Ultrafine Grained Au Wires-Experiment and First Principle Study
Authors: Chew Yeong Huey Effie , Wong Chee Cheong , Ferraris Cristiano , Kim Hui Hui 
Published: April 2011

AbstractAchieving both high strength and ductility is a common goal in the design of fine-grained materials. Here we report that with only ppm level of calcium doping, ductility and strength in ultrafine-grained gold wires can be concurrently improved by 108% and 65% respectively. Preferential segregation of calcium to stacking faults and grain boundaries in gold has reduced stacking fault energy of the system effectively, as shown by TEM and first principle simulation study. Through the modification of stacking fault energy, one can simultaneously increases the strength and ductility of a system.
Experimental Evidence that the Onset of Mechanical Softening in Nanocrystalline Metals is Strain Rate Dependent
Authors: Wang Liwei , Prorok Bart 
Published: April 2011

AbstractThis paper reports on the influence of strain rate on the onset of mechanical softening of nanocrystalline gold at room temperature. Micro-tensile testing was performed with applied strain rates on the order of 10−4 s−1 to 10−6 s−1. Our results defined a threshold strain rate, whereby plastic deformation at larger rates was dominated by dislocation processes and at smaller rates by one or more other deformation mechanisms. Furthermore, the data suggested that the critical grain size for inverse Hall-Petch behavior was strain rate sensitive.
The Effect of Surface Roughness on the Extinction Spectra and Electromagnetic Fields around Gold Nanoparticles
Authors: Li Shuzhou , Schatz George C. 
Published: April 2011

AbstractElectromagnetic enhancement arising from plasmon resonance excitation plays a major role in surface-enhanced Raman spectroscopy (SERS), and as a result nanoparticle morphology can significantly affect SERS intensities. In this paper we have calculated these enhancements as well as extinction spectra using the discrete dipole approximation for a system consisting of a dimer of gold disks that is made using on-wire lithography. Including surface roughness in the calculations leads to SERS enhancements for the disks whose dependence on disk spacing and thickness is in agreement with experimental measurements, with a maximum enhancement when the thickness of the disk and the disk-disk gap are 100 nm and 32 nm, respectively. These results are in better agreement with experiments than earlier estimates based on flat surfaces.
Atomistic Study of Creation of Bimetallic Clusters by Coalescence
Authors: Mizuno S. , Shintani K. 
Published: April 2011

AbstractMetallic clusters show excellent performance as catalysts because of their high surface-to-volume ratio. An inert-gas aggregation source is an experimental method by which clusters are produced. In such a method, cluster coalescence is one of growth modes of clusters. Bimetallic clusters also attract much attention of researchers because of their novel physical and chemical properties. At coalescence of two metallic clusters of different species, alloying or core-shell structuring tends to occur spontaneously. Resulting alloyed clusters or core-shell clusters will behave as unique catalysts. In this paper, morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics simulation. All pair combinations of the elements Au, Ag, Pt, and Pd are considered. The interactions between such metallic atoms are calculated by using generic embedded-atom method (GEAM) potential. Two clusters of icosahedral structure are equilibrated at specified temperature beforehand. The two clusters are put close to each other, where the nearest two atoms belonging to the two clusters, respectively, start to interact with each other. After coalescence the original surfaces of the two clusters decrease, and the surface energy is transformed into the kinetic energy. Consequently, the temperature of the united cluster rises. If this temperature is higher than the melting temperature, melting and local alloying at the interface occur. If alloying spreads into the united cluster, an alloyed bimetallic cluster is synthesized. If melting occurs only in one of the two clusters, and the atoms in liquid phase gradually cover the surface of the other cluster, a core-shell cluster appears. The morphological evolutions in the two modes of coalescence are followed, and under what conditions each mode of coalescence occurs is discussed.The results show that the surface energy and atom size of two clusters determine which mode is selected at coalescence.
Low Energy Electron Microscopy for Semiconductor Applications
Authors: Mankos Marian , Spasov Vassil , Han Liqun , Kojima Shinichi , Jiang Ximan , Harb Salam , Grella Luca , Czarnik Cory 
Published: April 2011

AbstractA novel low energy electron microscope (LEEM) aimed at improving the throughput and extending the applications for semiconductor devices has been developed. A dual beam approach, where two beams with different landing energies illuminate the field of view, is used to mitigate the charging effects when the LEEM is used to image semiconductor substrates with insulating or composite (insulator, semiconductor, metal) surfaces. We have experimentally demonstrated this phenomenon by imaging a variety of semiconductor device wafers without deleterious charging effects. Results from several important semiconductor device layers will be illustrated in detail.
Using the Focused Ion Beam to Perform Serial Sectioning of Micron-Sized Particles for Coordinated Nanoscale Analysis
Authors: Bassim Nabil D. , De Gregorio Bradley T. , Stroud Rhonda M. 
Published: April 2011

AbstractStandard Focused Ion Beam (FIB) lift-out methods for production of transmission electron microscopy (TEM) thin sections destroy many cubic microns of material in order to produce a single 100-nm thick section. Microtome sectioning, in contrast, allows serial sectioning of adjacent multiple 100-nm sections, without loss of materials between sections, but lacks site specificity. In order to maximize the yield of analyzable material in thin section form from valuableone-of-a kind- micron-sized samples, we have developed serial sectioning techniques that combine FIB lift-out with microtomy. In this paper, we show an example of sectioning and subsequent TEM analysis of simulated cometary residues which resemble impact craters collected during the NASA Stardust Mission. These techniques may be generalized to any one-of-a-kind sample for which preserving analyzable volume is critical, such as forensic analysis of dust particles, failure analysis and electronic device sectioning.
Cell Self Assembly of Intracellular Interface Using Cell Migration
Authors: Hoshino Takayuki , Konno Tomohiro , Ishihara Kazuhiko , Morishima Keisuke 
Published: April 2011

AbstractA cell-driven self-assembly of intracellular nano-device was proposed for bio-hybrid interface. This cells-driven self-assembly employed cell migration force to insert a conductive nanoneedle which would be worked as intracellular electrode. Such a nanoneedle was fabricated in the bottom of a microwell using focused ion beam induce deposition. The microwell structure with a coating of cell adhesion molecules was employed as the scaffold of the cell migration. A glass plate with the microwells had a non cell binding coating of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer as an anti-biofouling material. Thus a cell adhered only on the wall of a microwell then the cell migrated into the microwell. Adhesion force and migration force induced self-insertion of the nanoneedle into a live cell body using the cell's own migration force. The inserted nanoneedle was made of electrical conductive tungsten, so the intracellular nanoneedle might extract intracellular potential more precisely than extracellular electrode, while inducing much less damage to cells. In the future, the technique of cell-driven self-insertion of nanoneedle may be integrated with multi electrode arrays for developing long-lasting measurements device on cellular network researches, or the risk assessment of the nanomaterials on cellular activities.
The End Group Modification of Phospholipid Polymer Brush Grafted on Ferric Oxide Nanoparticles for Diagnostics
Authors: Matsuno Ryosuke , Ishihara Kazuhiko 
Published: April 2011

AbstractNanoparticles are widely applied as diagnostic reagents, drug-delivery carriers or bioaffinity beads. In particular, magnetic particles have been widely used in the study of biomedical applications. When we look ahead to the future, it is needed to construct precisely designed surface containing such as high bioaffinity and capability to capture of small amount protein or specific protein among various protein. As a method to construct precisely designed biocompatible polymer surface, atom transfer radical polymerization (ATRP) was widely used as a living free radical polymerization. ATRP has advantages such as control of molecular weight, narrow polydispersivity, easy synthesis of block copolymer, and preparation of high density polymer brush under mild condition. Previously, we have demonstrated synthesis of poly (2-methacryloyloxyethyl phosphorylcholine (MPC)) brush on ferric oxide (Fe3O4) by ATRP from immobilized initiator includes bromine that ATRP moiety. Here, it is known that poly(MPC) has been not affected for reduction of nonspecific binding, salt concentrations, pH and temperature. In this state, the poly(MPC)-grafted Fe3O4 could not be used for diagnostic material and collection material using magnetic interaction because poly(MPC) suppress protein adsorption. To introduce immobilization part for protein, p-nitrophenyloxycarbonyl polyethylene glycol methacrylate (MEONP) monomer that has active ester was polymerized as a block component. The poly(MPC-b-MEONP)-grafted Fe3O4 could capture proteins via active ester to amine of proteins. However, on careful consideration, this immobilization method had disadvantage for capture protein because immobilization part located in the side chain, not locate most outer surface. We focused on bromine (Br) located on end group of poly(MPC) brush, probably locate most outer surface. If the end group would be modified easily, the technique will be most effective modification. We adapted the reduction from azide (N3) to amine (NH2), after Br was exchanged to N3. This reduction has been called “staudinger reduction”. Generally, Click chemistry that reaction between N3 and alkyne is famous as a reaction of N3. On the other hand, the modification technique has wide application range due to amine group. At first, bromine was converted into azide, N3 using NaN3. Furthermore, the N3 was reduced to NH2 using PPh3 and H2O. The purification of magnetic nanoparticles with end group modified poly(MPC) brush was easy because of use of external magnetic interaction. The surface characterization at each step was estimated by XPS and FT-IR spectrum measurement. The absorbance signal attributed to N3 was appeared around 2000 cm-1 from FT-IR spectrum and N1s signal according to NH2 was observed at 399 eV from XPS measurement. The surface NH2 could react to carboxyl group or convert into other functional groups easily. The end group modification will be a useful for various bioaffinity bead applications.
Self-assembled Materials Containing Complementary Nucleobase Molecular Recognition
Authors: Smitthipong Wirasak , Chworos Arkadiusz , Lin Brian , Neumann Thorsten , Gajria Surekha , Jaeger Luc , Tirrell Matthew 
Published: April 2011

AbstractHere we report the nucleic acid/cationic amphiphile based-materials in which we exchange the counter-ions of the polyanionic backbone of the nucleic acids with the cationic amphiphiles to form self-assembled transparent films with the thickness of several microns. Predominantly, single stranded poly(A), poly(U) and double stranded poly(AU) were employed for these studies. Small-angle X-ray scattering (SAXS) experiments suggested lamellar-like structure for all the film samples. However, the molecule length as well as the molecular structure of nucleic acids can affect the topology and mechanical properties of these films. Complementary base-paring of poly(AU) is reported here with comparison to poly(A) and poly(U) complexes.
Collagen Matrix Alignment Using Inkjet Printer Technology
Authors: Deitch Sandra , Kunkle Catherine , Cui Xiaofeng , Boland Thomas , Dean Delphine 
Published: April 2011

AbstractCollagen fiber orientation plays an important role in many cell properties and actionsin vivo. Collagen and other matrix proteins are aligned in many tissues during normal functioning. For example, cardiomyocytes align in the heart to produce a synchronously beating tissue. The extra-cellular matrix environment, including collagen, is aligned along the cells. This matrix helps with cell adhesion and the alignment of the fibers also contributes to the anisotropic mechanical property of the tissue. While it is easy to replicate randomly oriented collagenin vitro, it is much more difficult to create aligned collagen matrices for cell culture. In this work, a novel inkjet printer-based collagen alignment technique was established. A 1 mg/ml rat tail collagen type I solution was printed, using a modified HP DeskJet 500 printer, onto plasma cleaned and UV sterilized glass slides. The collagen was printed in an eight line pattern, designed in Microsoft Word with 87.5 &#956;m by 23.1 mm lines. The pattern was printed three successive times on each slide to complete the alignment. Immunofluorescence imaging of primary antibodies specific to collagen type I indicated that the heat involved in the printing process was not great enough to denature the collagen. The extent of collagen alignment was quantified using atomic force microscopy and compared to random collagen films and collagen films aligned using a mechanical scraping method. Additionally, neonatal rat cardiomyocytes were cultured on the aligned matrices. These cells require extracellular matrix alignment to maintain their in vivo-like phenotype during in vitro culture. The cells grew along the lines of collagen and coordinated beating, indicating the success of the aligned matrix. This collagen alignment technique is cheap, fast, precise, and easy to use in comparison to other current techniques. It can be used to align collagen on any type of substrate, such as a gel, which makes it a useful tool in many applications. This technique may also be used to align other extra-cellular matrix proteins and could even be used to create a three dimensional construct with varying fiber orientations.
Biocompatibility, Bioactivity and Mechanical Properties of Portland Cement and Portland Cement-Metakaolin Blends for Bone Tissue Engineering Applications
Authors: Gallego Daniel , Higuita Natalia , Garcia Felipe , Posada Olga M. , Lopez Luis E. , Litsky Alan S. , Hansford Derek J. 
Published: April 2011

AbstractWe studied the potential applications of Portland cement and Portland cement-Metakaolin blends as scaffolding materials for load bearing bone tissue engineering. Cementitious pastes were prepared by mixing Portland cement and Metakaolin at different ratios (100:0, 85:15), and hydrated under a concentrated CO2 atmosphere (carbonated pastes). Pastes fabricated similarly, but hydrated under normal atmospheric conditions were used for comparison (non-carbonated pastes). Compressive tests were run to evaluate the mechanical properties of the pastes. The bioactivity of the samples was tested in a simulated body fluid (SBF) solution for 1 and 4 days. Sample morphology and chemistry were characterized via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The cytocompatibility was studied using human osteosarcoma (HOS) cell cultures and the direct contact assay. Mechanical characterization did not show significant differences in the compressive strength of the blends compared to pure cement controls. The bioactivity test revealed that the pastes induced surface precipitation of calcium phosphate (CaP) when exposed to the SBF solution (as confirmed by SEM and EDS). Non-carbonated pastes induced early CaP precipitation. Cytocompatibility experiments showed that the carbonated blends allowed adequate cell growth. Non-carbonated blends presented a highly cytotoxic behavior. The introduction of Metakaolin did not affect the cytocompatibility of the samples. These results show that Portland cement and Portland cement-Metakaolin blends could present suitable characteristics for applications as scaffolding materials in load bearing bone tissue engineering.
Electrospun Gelatin/Hydroxyapatite Nanocomposite Scaffolds for Bone Tissue Engineering
Authors: Catledge Shane , Tyagi Parul , Koopman Mark , Stanishevsky Andrei , Vohra Yogesh K. 
Published: April 2011

AbstractElectrospun composite scaffolds were prepared by mixing gelatin with nanoparticles of hydroxyapatite (nanoHA) in 2,2,2-trifluoroethanol (TFE) solution. The fibrous composite scaffolds with nanoHA content from 0 to 40 wt% were compared in terms of structure and morphology via x-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that dispersion of nanoHA in the scaffolds is uniform for 0%, 10%, 20%, and 30% nanoHA content, but significant nanoHA agglomeration can be observed for scaffolds with 40% nanoHA. In order to study the effect of nanoHA content on mechanical properties at the nanoscale level, the fibrous scaffolds were pressed into dense pellets and tested by nanoindentation to determine Young's modulus. Young's modulus was found to increase linearly with nanoHA content, reaching unexpectedly high values of 10.2 ± 0.8 GPa. Results are compared with other polymer/HA composites including those made with polycaprolactone or collagen.