bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hyperelastic effects in brittle materials failure
Authors: Buehler Markus J. , Abraham Farid F. , Gao Huajian 
Published: April 2011

AbstractA fact that has been neglected in most theories of brittle fracture is that the elasticity of a solid clearly depends on its state of deformation. Metals will weaken, or soften, and polymers stiffen as the strain approaches the state of materials failure. It is only for infinitesimal deformation that the elastic moduli can be considered constant and the elasticity of the solid linear. We show by large-scale atomistic simulations that hyperelasticity, the elasticity of large strains, can play a governing role in the dynamics of fracture and that linear theory is incapable of capturing all phenomena. We introduce a new concept of a characteristic length scale ξ for the energy flux near the crack tip and demonstrate that the local hyperelastic wave speed governs the crack speed when the hyperelastic zone approaches this energy length scale. The new length scale ξ, heretofore missing in the existing theories of dynamic fracture, helps to form a comprehensive picture of crack dynamics, explaining super-Rayleigh and supersonic fracture. We further address the stability of cracks, and show agreement of the Yoffe criterion with the dynamics of cracks in harmonic systems. We find that softening hyperelastic effects lead to a decrease in critical instability speed, and stiffening hyperelastic effects leads to an increase in critical speed. The main conclusion is that hyperelasticity plays a critical role in forming a complete picture of dynamic fracture.
Extremely Thin Absorber Layers in Solid State Solar Cells
Authors: Bellaidi A. , Ernst K. , Könenkamp R. 
Published: April 2011

AbstractWe report on recent progress in fabricating an inorganic solid state solar cell based on a nano-structured substrate with an extremely thin absorber, the so-called eta-cell. The cell uses HgCdTe as an absorber layer and TiO2 as a substrate. By adjusting the Hg/Cd ratio the conduction band edges in these two materials can be brought into alignment. This tuning provides an ideal tool to optimize the optical and electrical properties of the cell. In qualitative agreement with earlier work we find a band offset of 0.25 eV to give maximum transfer rates across the interface. The optimized cell has a short circuit current of 15 mA/cm2 and an open-circuit voltage of 0.6 V. We discuss the optical and electrical properties of the cell, and outline ideas to further improve the performance.
Modifying Nafion with Nanostructured Inorganic Oxides for Proton Exchange Membrane Fuel Cells
Authors: Daiko Yusuke , Klein Lisa C. , Nogami Masayuki 
Published: April 2011

AbstractNafion, a perfluorosulfonate ionomer, was modified to increase its thermal stability and reduce its methanol permeability. Hybrid membranes of TiO2·SiO2/Nafion and TiO2·SiO2·P2O5/Nafion™ were prepared using an infiltration sol-gel method. Si(OC2H5)4and Ti(OC4H9)4were infiltrated into dry NafionTMmembranes, followed by hydrolysis and condensation reactions in first HCl and then NH4OH solutions. The level of inorganic content was controlled by the infiltration time, incorporating up to 50 wt%. Solvent uptake, swelling, water content and proton conductivity were measured at room temperature. Hybrid membranes of TiO2·SiO2/Nafion with ∼30 wt% of infiltrated oxides showed a significantly lower methanol uptake of ∼20wt% and a swelling ratio of 1.15, as compared to those of unmodified NafionTMmembrane, ∼60wt% for methanol uptake and 1.8 for swelling ratio. Proton conductivities for TiO2·SiO2/Nafion hybrid membranes decreased with increasing infiltrated oxides. However, infiltrated membranes treated in phosphoric acid solutions to increase the number of P-OH groups showed a six-fold increase in proton conductivity.
Hybrid Proton-Carrier Polymer Composites for High-Temperature FCPEM Applications
Authors: Pern F. J. , Turner J. A. , Herring A. M. 
Published: April 2011

AbstractHybrid proton-carrier polymer composites were fabricated in an effort to develop high-performance high-temperature proton exchange membranes (PEMs) for fuel cell applications in the 100°–200°C range. The solution-cast hybrid membranes comprise a polymer host and a SiO2-based proton-carrier composite that was synthesized via sol gel approach using a functional silane and tetraethoxysilane (TEOS) in acidic conditions. The primary H+-carrying component was either a heteropoly silicotungstic acid (STA) or a sulfonic acid (SFA) that was thermooxidatively converted from a mercapto (-SH) group. The embedding level of STA on the silane-modified SiO2 sol gel composites was strongly affected by the presence and the functional group of the silane. Ion exchange capacity (IEC) of the water-washed, SiO2-based STA and SFA proton-carrier composite powders is in the range of 1.8–3.5 mmol/g, two to three times higher than that for Nafion 117 (0.9 meq/mol). A glycidylmethacrylate-type copolymer, PEMAGMA, which is stable up to ∼225°C, was able to produce mechanically robust and flexible hybrid membranes. Upon curing, the PEMAGMA composite membranes showed a ∼75% gel under the present formulation and retained the "free" STA effectively with slight loss when extracted in an 85°C water. The W12-STA-containing PEMAGMA membranes followed the weight loss trends of water from STA and the SiO2-based sol gel composite, showing a 10 wt% loss at 150°C and a 15 wt% loss at 225°C. Fuel cell performance tests of the preliminary films gave a Voc in the 0.85–0.93 V range, but a low current density of <4 mA/cm2. The resistive characteristics were attributed to inhomogeneous distribution of the sol gel nanoparticles in the PEMAGMA matrix, a result of phase separation and particulate agglomeration during film forming.
Degradation Behavior of Novel Poly(α-hydroxy acid)-Derived Polyesters
Authors: Sy Jay , Xu Xiaojun , Lipski Anna Marie , Stevens Molly , Shastri V. Prasad 
Published: April 2011

AbstractDue to their bioresorbable characteristics biodegradable polyesters are attractive materials for sutures, fracture fixation devices, and drug delivery systems. These polymers degrade primarily through a bulk erosion mechanism. In many instances including drug delivery and fabrication of orthopaedic devices, surface erosion is desired as it confers linearity with respect to degradation and changes in modulus. We hypothesized that surface erosion could be achieved in poly(αΏ-hydroxy acids) by tuning the lipophilicity of the system and hence the water uptake. Toward this end, we used a modular design strategy to manipulate the hydrophilic-lipophilic balance (HLB) of a polymer chain at various stages by judicious choice of building blocks. Using this novel synthetic strategy we have synthesized a library of degradable polyesters derived from poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) that exhibit surface erosion behavior. Surface erosion was further verified by ultrastructure analysis of degraded polymer pellets and thin films by Scanning Electron Microscopy and tapping mode Atomic Force Microscopy respectively.
Collagen-Inspired Nano-fibrous Poly(L-lactic acid) Scaffolds for Bone Tissue Engineering Created from Reverse Solid Freeform Fabrication
Authors: Chen Victor J. , Smith Laura A. , Ma Peter X. 
Published: April 2011

AbstractReverse solid freeform (SFF) fabrication was used to create highly-controlled macroporous structures in nano-fibrous poly (L-lactic acid) (PLLA) scaffolds. By using a computer-aided design (CAD) program to create a negative template for the scaffold, the three-dimensional (3-D) mold was created on a 3-D printer using a wax. After the template was printed, a solution of PLLA in tetrahydrofuran (THF) was cast into the mold, and was subsequently phase separated at -70°C which gives the nano-fibrous morphology. This resulted in a 3-D nano-fibrous scaffold with a uniform fiber mesh throughout the entire matrix, and greatly increased the surface area within the scaffold. Fiber diameters in these scaffolds were 50-500 nm, similar to type I collagen, and the densities of the fiber meshes can be altered by changing the polymer concentration. To examine the scaffold's potential for tissue regeneration, MC3T3-E1 osteoblasts were seeded and cultured on the scaffolds. Results show that the osteoblasts attached and proliferated on the scaffolds. After 6 weeks in culture, bone-like tissue was evident within the nano-fibrous scaffolds. By having the ability to control the macroporous architecture, interconnectivity, orientation, and external shape of the scaffold, as well as the nanometer-scaled fibrous features in the pore walls, this SFF fabrication/phase separation technique has great potential to design and create ideal scaffolds for bone tissue engineering.
Fabrication of Super Water-Repellent Surfaces by Nanosphere Lithography
Authors: Shiu Jau-Ye , Kuo Chun-Wen , Chen Peilin , Mou Chung-Yuan 
Published: April 2011

Abstract: Inspired by the water-repellent behavior of the micro- and nano-structured plant surfaces, superhydrophobic materials, with a water contact larger than 150° superhydrophobic surfaces using a combination of nanosphere lithography and plasma etching. It has been found that the water contact angle on these surfaces can be systematically tuned from 132° to 168° by trimming the diameters of polystyrene nanospheres using oxygen plasma. The water contact angles measured on these surfaces can be modeled by the Cassie's formulation without any adjustable parameter.
Relationship Between Dip-Coating Fabrication Parameters and the Elastic Properties of Rubber Latex Prosthesis
Authors: Neves-Junior W.F.P. , Santos T. C. dos , Ferreira M. , Mulato M. , Coutinho-Netto J. 
Published: April 2011

AbstractIn the present work we are mainly interested in the use of the natural latex extract from the Hevea brasiliensis for medical applications. This presentation focuses on the influence of the fabrication parameters on the final elastic properties of the tubes obtained by dip-coating. The elastic properties of the prosthesis were investigated using tension-deformation experiments. The influence of important fabrication parameters were studied, such as: dip-coating velocity, final prosthesis thickness (which was varied as a function of the number of baths), and thermal treatment. Single and cycled tension-deformation experiments were performed with closed and opened samples considering longitudinal and axial directions. A model is proposed for the anisotropy of the elastic behavior, which involves the sulfur bonds between polymeric chains.
Self-Assembling Microspheres from Charged Functional Polyelectrolytes and Small-Molecule Counterions
Authors: Mckenna Brandon , Birkedal Henrik , Bartl Michael H. , Deming Timothy J. , Stucky Galen D. 
Published: April 2011

AbstractMicrometer-sized spheres have been found to assemble from homopolymer electrolytes and small, multivalent counterions in water. In contrast to previous efforts, these vesicles do not use preformed templates, do not require block copolymers, and do not necessarily employ nanoparticles. We have investigated the requirements for vesicle formation with regards to both components of the assembly. Self-assembly occurs with a variety of poly-amino acids and counterions, all of which require a minimum number of charged groups to promote non-covalent crosslinking. We show how the assembly process is controlled by pH and how, in consequence, the pKa's of the reactants can be used to reliably predict sphere formation. By varying the nature of the small counterions, we have determined the requirements for assemblies. The assemblies have been further investigated using confocal microscopy and fluorescent labeling of the different components.
Effects of Surface Texturing on Cell Adhesion for Artificial Joints
Authors: Shi B. , Fairchild A. , Kleine Z. , Kuhn T. , Liang H. 
Published: April 2011

AbstractOne of the major issues of joint implants is their loss (detachment) and subsequent failure after a limited number of years in application. Understanding and improving cell adhesion to implanting materials to extend lifespan, lubrication, and self-regeneration properties are therefore substantially important. In this research, we investigate effects of surface properties, such as wettabilty and texture on cell culture for the purpose of biotribological applications. Materials used are polyurethane, polyvinyl alcohol, and glass. Surface analysis indicates that surface structures have profound impact on cells growth.
Adsorption of Amelogenin Nanopheres onto Charged Surfaces, A Model for Tooth Enamel Matrix Re-construction
Authors: J. Moradian-Oldak , C. Gergely , N. Bouropoulos , F.J.G. Cuisinier 
Published: April 2011

AbstractAmelogenins are hydrophobic proteins that constitute more than 90% of the secretory stage enamel matrix. The assembly of amelogenin into nanospheres has been postulated to be a key factor in controlling the structural organization of the enamel extracellular matrix framework, which provides the scaffolding for the elongated and oriented growth of enamel apatite crystals. To get insight into the structure and function of amelogenin in controlling the process of crystal growth we have utilized two different approaches to investigate adsorption of amelogenin nanospheres onto charged surfaces: A) analysis of adsorption of amelogenin onto hydroxyapatite crystals by means of Langmuir Model for protein adsorption. B) analysis of amelogenin mono or multi-layer formation by sequential adsorption process onto auto-assembled polyelctrolytes films. Our data indicate that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. We found that amelogenin nanospheres are negatively charged and a monolayer of these nanospheres adsorbed in an irreversible way on positively ending polyelectrolyte multilayers most likely through electrostatic interactions.
Effects of Surface Roughness and Maximum Load on the Mechanical Properties of Cancellous Bone Measured by Nanoindentation
Authors: Donnelly Eve , Baker Shefford P. , Boskey Adele L. , Meulen Marjolein C. H. van der 
Published: April 2011

AbstractNanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250-3000 μN. As the ratio of indentation depth to surface roughness decreased below approximately 3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was approximately 20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that are consistent with microstructural observations of lamellar bone as more mineralized than interlamellar bone.
Regular, low density cellular structures - rapid prototyping, numerical simulation, mechanical testing
Authors: Stampfl J. , Seyr M.M. , Luxner M.H. , Pettermann H.E. , Woesz A. , Fratzl P. 
Published: April 2011

AbstractCellular solids form the basis of many biological and engineering structures. Most models use the relative density and the mechanical properties of the bulk material as the main parameter for the prediction of the mechanical properties of such structures. In this work the influence of the architecture of periodic cellular solids on the mechanical properties is investigated numerically and experimentally.Using computer aided design, structures with 8x8x8 base cells are designed and fabricated. The physical prototypes which are tested experimentally are made from thermosetting and thermoplastic polymers by employing Rapid Prototyping (RP) techniques. Various RP techniques are compared regarding their suitability for the fabrication of cellular materials.For numerical simulation of the cellular structures, linear Finite Element analysis is employed. Three-dimensional models are set up using higher order beam elements. In a first step, the structure is treated as an infinite medium and homogenization via a 'periodic micro-field approach' is used. The entire elastic tensors for different relative densities are evaluated, from which the directional dependencies of the Young's moduli are derived. In a second step, simulations of finite structures are performed for direct comparison with experiments. Samples consisting of several basic cells are modeled which leads to a better correspondence to the experimental setup. Finite structures of different numbers of cells are modeled to study the influence of the sample size.The experimental and numerical results correspond very well and form a consistent picture of the problem. The multi-disciplinary approach leads to a comprehensive view of effects which govern the mechanical behaviour of the investigated cellular structures.
Corrosion of Copper Nuclear Waste Containers In Aqueous Sulphide Solutions
Authors: Smith J. , Qin Z. , Shoesmitha D.W. , King F. , Werme L. 
Published: April 2011

AbstractElectrochemical and surface analytical techniques are being used to determine the mechanismand kinetics of Cu corrosion in the presence of sulphide, with the primary goal of developing a mixed potential model for Cu corrosion under disposal conditions. Corrosion potential (Ecorr) measurements indicate the formation of copper sulphide films is rapid leading to rate control by the cathodic reduction of water. Impedance spectroscopy suggests the anodic charge transfer process is rapid leading to film growth limited by diffusive transport. Experiments are underway to determine the current-potential relationships necessary in the development of a mixed potential model.
Reexamining the Dissolution of Spent Fuel: A Comparison of Different Methods for Calculating Rates
Authors: Hanson Brady D. , Stout Ray B. 
Published: April 2011

AbstractDissolution rates for spent fuel have typically been reported in terms of a rate normalized to the surface area of the specimen. Recent evidence has shown that neither the geometric surface area nor that measured with BET accurately predicts the effective surface area of spent fuel. Dissolution rates calculated from results obtained by flowthrough tests were reexamined comparing the cumulative releases and surface area normalized rates. While initial surface area is important for comparison of different rates, it appears that normalizing to the surface area introduces unnecessary uncertainty compared to using cumulative or fractional release rates. Discrepancies in past data analyses are mitigated using this alternative method.
Risk-Based Evaluation of Long-Term Safety for a Yucca Mountain Repository Using the IMARC TSPA Code
Authors: Kessler John , Apted Michael , Kozak Matthew , Zhou Wei 
Published: April 2011

AbstractThe Electric Power Research Institute (EPRI) has conducted independent total system performance assessments (TSPAs) of the proposed Yucca Mountain spent fuel and high-level radioactive waste repository for 15 years. EPRI uses its TSPA code, IMARC, currently in its eighth version. The major results of the IMARC-8 analyses are presented in this paper. In all of the situations evaluated by EPRI using IMARC-8, the results for the reference repository concept for Yucca Mountain are well within the regulatory criteria established in the applicable regulations, 10 CFR 63 and 40 CFR 197. Further analyses indicate that at least two of the repository barriers must fail to function as anticipated for dose risks to rise as much as one millirem per year (1/15th of the regulatory limit).
Self-Irradiation of Monazite Ceramics: Contrasting Behavior of PuPO4 and (La,Pu)PO4 Doped with Pu-238
Authors: Burakov Boris E. , Yagovkina Maria A. , Garbuzov Vladimir M. , Kitsay Alexander A. , Zirlin Vladimir A. 
Published: April 2011

AbstractTo investigate the behavior of monazite during accelerated radiation damage, which simulates effects of long term storage, 238Pu-doped polycrystalline samples of (La,Pu)PO4 and PuPO4 were synthesized for the first time ever and studied using powder X-ray diffraction (XRD) analysis and optical microscopy. The starting precursor materials were obtained by precipitation of La and (or) Pu from their aqueous nitrate solutions followed by calcination in air at 700°C for 1 hour, cold pressing, and sintering in air at 1200-1250°C for 2 hours. The 238Pu contents in ceramic samples measured using gamma spectrometry were (in wt.% el.): 8.1 for (La,Pu)PO4 and 7.2 for PuPO4. The (La,Pu)PO4 monazite remained crystalline at ambient temperature up to a cumulative dose of 1.19 × 1025 alpha decays/m3. In contrast, the PuPO4 monazite became nearly completely amorphous at a relatively low dose of 4.2 × 1024 alpha decays/m3. Swelling and crack formation due to the alpha decay damage was observed in the PuPO4 ceramic. Also, under self-irradiation this sample completely changed color from initial deep blue to black. The (La,Pu)PO4 monazite was characterized by a similar change in color from initial light blue to gray, however, no swelling or crack formation have so far been observed. The results of this study allow us to conclude that the radiation damage behavior of monazite strictly depends on the chemical composition. The justification of monazite-based ceramics as actinide waste forms requires additional investigation.
A Novel Equation for Prediction of Intrinsic Sorption Constants of Metal Cations at Mineral-Water Interfaces
Authors: Xu Huifang , Wang Yifeng 
Published: April 2011

AbstractThe sorption of radionuclides onto mineral-water interfaces is an important mechanism of radionuclide retardation in subsurface environments. Although a large body of data on metal sorption has been accumulated, the interaction of radionuclides at the mineral-water interface is still not well quantified. In this paper, we establish a linear free energy relationship that can correlate intrinsic metal sorption constants to the known thermodynamic properties of metal cations and mineral phases. This relationship can be used to predict the intrinsic sorption constants of metal cations adsorption on various mineral-water interfaces. Based on a surface complexation model, an adsorption constant of a cation Mn+ onto a mineral surface can be represented by the sum of “intrinsic” and coulombic terms, that is logKads, Mn+ = logKint, Mn+ - (nF/2.303RT)0. To construct our linear free energy relationship, we further decompose an intrinsic sorption constant into the solvation contribution, which characterizes the work to be done to move a cation from one dielectric medium (solution) to another (interface), and the chemical contribution, which characterizes the chemical bonding abilities of cations to mineral surface sites. The overall intrinsic sorption constant can be calculated by the equation of:2.303RTlogKint, Mn+ = -ΩMn+ (1/εk) - a* δG0n, Mn+ - b* - β*rMn+ + δG0f, Mn+, or2.303 RT logKint, Mn+ = -ΩMn+ (1/εk) + a* δG0s, Mn+ + (1 - a*)δG0f, Mn+ - b* - β* rMn+,where, ΩMn+ is interfacial Born solvation coefficient of cation M, εk is the dielectric constant of a mineral; δG0n, Mn+, δG0s, Mn+ and δG0f, Mn+ are the non-solvation energy, solvation energy and the Gibbs free energy formation of a cation, respectively; rMn+ is the ionic radius of a cation; and a*, β*, and b* are constants, which can be determined by fitting the equation to the existing experimental data. We have applied the equation to the sorption of divalent cations on oxide, hydroxide, and silicate minerals. In particular, based on additivity of molecular polarizabilities, we have used the equation to calculate the intrinsic sorption constants of divalent metals and radionuclides on interstratified clay minerals that are commonly found in the nature or are proposed as backfills for nuclear waste geologic repositories. The discrepancies between calculated and measured values are generally within 0.8 log unit.