bluuebunny/crossref_metadata_2025_split huggingface dataset:
Perturbed Amelogenin Protein Self-assembly Alters Nanosphere Properties Resulting in Defective Enamel Formation
Authors: Paine Michael L. , Lei YaPing , Luo Wen , Snead Malcolm L. 
Published: April 2011

AbstractDental enamel is a unique composite bioceramic material that is the hardest tissue in the vertebrate body, containing long-, thin-crystallites of substituted hydroxyapatite. Enamel functions under immense loads in a bacterial-laden environment, and generally without catastrophic failure over a lifetime for the organism. Unlike all other biogenerated hard tissues of mesodermal origin, such as bone and dentin, enamel is produced by ectoderm-derived cells called ameloblasts. Recent investigations on the formation of enamel using cell and molecular approaches have been coupled to biomechanical investigations at the nanoscale and mesoscale levels. For amelogenin, the principle protein of forming enamel, two domains have been identified that are required for the proper assembly of multimeric units of amelogenin to form nanospheres. One domain is at the amino-terminus and the other domain in the carboxyl-terminal region. Amelogenin nanospheres are believed to influence the hydroxyapatite crystal habit. Both the yeast two-hybrid assay and surface plasmon resonance have been used to examine the assembly properties of engineered amelogenin proteins. Amelogenin protein was engineered using recombinant DNA techniques to contain deletions to either of the two self-assembly domains. Amelogenin protein was also engineered to contain single amino-acid mutations/substitutions in the amino-terminal self-assembly domain; and these amino-acid changes are based upon point mutations observed in humans affected with a hereditary disturbance of enamel formation. All of these alterations reveal significant defects in amelogenin self-assembly into nanospheres in vitro. Transgenic animals containing these same amelogenin deletions illustrate the importance of a physiologically correct bio-fabrication of the enamel protein extracellular matrix to allow for the organization of the enamel prismatic structure.
Collagen-calcium Phosphate Composite Coatings by Electrolysis-induced Self-assembly and Mineralization
Authors: Fan Yuwei , Duan Ke , Wang Rizhi 
Published: April 2011

AbstractA bone-like composite coating of collagen protein and calcium phosphate minerals is considered to be bioactive and may enhance bone growth and fixation of metallic orthopedic implants. In this study, we have successfully prepared a uniform collagen fibril/octacalcium phosphate composite coating on silicon substrate by electrolytic deposition. Under a typical deposition condition, a thin (100 nm) layer of calcium phosphate coating would form on the cathode (Si) surface first, which was followed by a thick (∼100 μm) composite coating. The porous composite layer consists of a collagen fibril network on which clusters of octacalium phosphate crystals nucleate and grow. The results not only provide a novel bioactive coating for biomedical implants, but also establish a new experimental protocol for studying biomineralization mechanisms of collagen based biological tissues.
Biological Modification in the Brushite Crystallization
Authors: Tang Ruikang , Darragh Molly R. , Orme Christine A. , Hoyer John R. , Nancollas George H. 
Published: April 2011

AbstractThe crystallization of brushite has been investigated in the presence of typical ionic biological components, magnesium, fluoride and citrate and a natural protein, osteopontin, using a constant composition method capable of nano-mole sensitivity. While the simple ionic additives, magnesium and fluoride do not have a significant effect, citrate ions can adsorb on lateral faces due to electrostatic interactions involving the functional carboxylate groups, resulting in crystal morphology changes. Osteopontin was the most effective inhibitor influencing the growth of virtually all brushite crystal faces.
Development of Self-assembled Muscle-powered Microdevices
Authors: Xi Jianzhong , Schmidt Jacob J. , Montemagno Carlo D. 
Published: April 2011

AbstractAs microcomponents in engineered systems, biological muscles have unique advantages such as large force transduction, utilization of biochemical fuel, and self-assembly from single cells, over other inorganic actuators for biomedical engineering applications. Successful integration of muscles with inorganic fabricated structures and electronics promises the capability of precisely characterizing muscles' mechanical properties and fabricating self-assembled controllable autonomous structures powered by ubiquitous glucose. However, the use of extracted muscle tissue from animals on these devices is impractical and inefficient, as the tissues must be dissected and incorporated into each device by hand with crude interfaces between the biological tissue and inorganic materials. Integration of muscle with fabricated structures would be optimally achieved through self-assembling muscle cells on MEMS. The construction of self-assembled muscle-powered MEMS structures is complicated by the stringent requirements to spatially direct the cell growth, control the tight connection of these differentiated structures with MEMS structures, and enable the cells and the integrated hybrid freedom to move. Conventional and soft photolithography techniques have been extensively employed to pattern the growth of a variety of cell types and investigate their interaction with substrate in the micrometer level. However, all studies are only suitable for patterning static cells on an immobile surface, so a novel system of spatially patterning the contractible cells must be developed to enable the cells and the integrated hybrid devices to be free to move.We present a novel system of self-assembling myocytes on MEMS devices. This system has shown its capability of spatially and selectively directed growth and differentiation of myocytes into single muscle bundles, attachment of these functional bundles to MEMS structures, and the controlled partial release of the resultant hybrid devices. Two groups of self- assembled muscle-MEMS devices, force-measuring cantilevers and muscle-powered microrobots have been created. Here the further detailed studies of this system are discussed, especially the concept of the self-assembly and the material interfacial problems in this system.
Effect of Inhibiting Oxyanions on the Localized Corrosion Susceptibility of Waste Package Container Materials
Authors: Dunn D.S. , Yang L. , Wu C. , Cragnolino G.A. 
Published: April 2011

AbstractThe DOE is currently preparing a license application for the permanent disposal of high level radioactive waste at Yucca Mountain, Nevada. The proposed design of waste packages for the disposal of high level radioactive waste consists of an outer container made of Alloy 22, a corrosionresistant Ni-Cr-Mo-W alloy, surrounding an inner container made of Type 316 nuclear grade stainless steel. Under conditions where passivity is maintained, the uniform corrosion rate of Alloy 22 is slow and long waste package lifetimes are projected. However, the initiation of localized corrosion such as pitting or crevice corrosion may decrease waste package lifetimes. In this study the crevice corrosion susceptibility of Alloy22 was determined in chloride solutions with additions of oxyanions that are present in the groundwater at the potential repository site. When present in sufficient concentrations relative to chloride, nitrate, carbonate, bicarbonate, and sulfate inhibited pitting and crevice corrosion of Alloy 22.
Electron Microprobe Investigation of Ti-pyrochlore Doped with Pu-238
Authors: Zamoryanskaya Maria V. , Burakov Boris E. 
Published: April 2011

Abstractpolycrystalline sample of Ti-pyrochlore, (Ca,Gd,Hf,U,Pu)2Ti2O7, doped with approximately 8.7 wt.% 238Pu and 20.0 wt.% 238U, has been studied at different cumulative doses of alpha induced radiation damage using scanning electron microscopy (SEM) and quantitative electron probe microanalysis (EMPA). All analyses of 238Pu-doped Ti-pyrochlore were done for comparison with 239Pu-doped pyrochlore synthesized under similar conditions. Our results suggest that accelerated alpha-induced radiation damage affects not only the crystalline structure of 238Pu-doped pyrochlore, but also causes changes in the chemical composition of the pyrochlore, and as proposed, destruction of pyrochlore-U-Pu solid solution. Numerous inclusions of a separate U-oxide phase were found in the 238Pu-doped pyrochlore crystalline matrix. The inclusions were observed visually using SEM and increased as a function of the cumulative dose. Also, after a cumulative dose of 1.1 × 1025 alpha decays/m3 the pyrochlore became nearly amorphous and inclusions of Hf-Ti-Ca-O phase were found in the crystalline matrix. In all cases separate phases of U-oxide and Hf-Ti-Ca-O were localized in chemically inhomogeneous areas. The results obtained allow us to assume that under self-irradiation the amorphization of Ti-pyrochlore might be accompanied with destruction of single solid solution, (Ca,Gd,Hf,U,Pu)2Ti2O7, into several pyrochlore phases of different chemical composition and precipitation of some amount of Pu and U into separate oxide phases.
Correlation of Formation Enthalpies with Critical Amorphization Temperature for Pyrochlore and Monazite
Authors: Helean K.B. , Navrotsky A. , Lian J. , Ewing R.C. 
Published: April 2011

AbstractSystematic studies of a series of RE-titanate pyrochlore single crystals determined the formation enthalpies, ΔH0f-ox, and the critical amorphization temperature, Tc, the temperature above which the crystal can no longer be amorphized. A negative linear correlation was observed between ΔH0f-ox and Tc. In general as the cation radius ratio, RA/RB, decreases the formation enthalpy becomes less exothermic, i.e. the pyrochlore structure becomes less thermodynamically stable while the susceptibilty to ion beam-induced amorphization decreases. The opposite relation, i.e. a positive linear correlation between ΔH0f-ox and Tc was observed for a series of REPO4 single crystals with both the monazite and xenotime structures. Both relations can be understood in terms of pyrochlore and orthophosphate crystal chemistry, their formation of point defects, and the role of ion-irradiation induced phase transformations.
The immobilization of chloride-containing actinide waste in a calcium phosphate ceramic host: ageing studies
Authors: Metcalfe B. L. , Donald I. W. , Scheele R. D. , Strachan D. M. 
Published: April 2011

AbstractImmobilization of radioactive wastes arising from the pyrochemical reprocessing of Pu metal with calcium phosphate as the host material has been investigated. Initial studies in which non-active elements are substituted for the actinide elements present in the wastes demonstrated that effective immobilization of both the cations and chloride ions was achieved within the chlorapatite Ca5(PO4)3Cl, and spodiosite, Ca2(PO4)Cl, mineral phases produced during the solid state reaction between host and waste. Follow-up studies with radioactive simulated waste composed of CaCl2, PuCl3 and AmCl3have confirmed the viability of the process and the durability of the product in aqueous solution. More recently a study of the long-term radiological stability and chemical durability of the ceramic product has commenced in which accelerated ageing of the ceramic phases is being achieved through the replacement of the 239Pu (half life 24,360y) that is contained in the actual waste by the short lived isotope 238Pu (half life 86.4y). The preparation of non-active and active samples and the crystal phases formed in each system as determined with XRD are herein reported. Data are presented which show that there is no detectable change in the XRD pattern of the samples containing 238Pu after 532 days of ageing, corresponding to around 400 years of real time ageing employing 239Pu. The detailed effects of ageing on the crystal structure and on the chemical durability of samples in aqueous solution are reported.
Crystallisation Within Simulated High Level Waste Borosilicate Glass
Authors: Rose Peter B. , Ojovan Michael I. , Hyatt Neil C. , Lee William E. 
Published: April 2011

AbstractThe devitrification products of two simulated high level radioactive waste (HLW) glasses have been investigated. Magnox waste glass contained RuO2 as its primary crystal phase, Pd-Te inclusions, a Cr-, Fe- and Ni-rich spinel phase, a Si- and lanthanide-rich phase and also a Zr-rich phase which incorporated Ce and Gd. Upon heat treatment the glass developed a zektzerite-type phase, CeO2, a strontium molybdate (containing Nd and La) as well as a Si-rich phase. 75/25 glass, comprising a blend of reprocessing waste derived from UO2 and Magnox fuels, contained RuO2 as its primary crystalline phase, CeO2 and a Si- and Ru-rich phase. Heat treatment of this glass resulted in the growth of the CeO2 crystals, the development of a strontium molybdate (containing Nd and La) and a Si- and lanthanide-containing phase. A sodium lanthanum molybdate with a powellite-type structure formed on the surface of both glasses after heat treatment in air.
Long-term behavior of R7T7-type nuclear glass: Current state of knowledge and outlook
Authors: Gin S. , Godon N. , Ribet I. , Jollivet P. , Minet Y. , Frugier P. , Vernaz E. , Cavedon J.M. , Bonin B. , Quang R. Do 
Published: April 2011

AbstractThis article reviews current knowledge of the long-term behavior of R7T7-type glass during the thermal phase and in geological repository conditions (aqueous alteration). In interim storage R7T7 glass can be considered to conserve its integrity over time. In geological repository conditions, the mechanisms of glass alteration by water have been identified and parameter values have been assigned to the reaction kinetics for wide variations of the influential factors (temperature, pH, flow rate, S/V ratio, etc.). CEA has developed an operational model to obtain robust and reasonably conservative predictions of the glass quantities altered after disposal. Examples of applications of the operational model are discussed, future research topics are also proposed to consolidate this approach.
Fundamental Experiments on Permeability Change of Flow-path by Highly Alkaline Plume
Authors: Usui Hideo , Niibori Yuichi , Tanaka Koichi , Tochiyama Osamu , Mimura Hitoshi 
Published: April 2011

AbstractIn the geological disposal system, natural barrier contains many selective flow-paths. Since cement used for the repository construction alters the condition of groundwater to a highly alkaline pH of about 13, such hyperalkaline plume would affect permeabilities of the flow-paths. To obtain more reliable estimate on the migration of radionuclides released from the repository, we must consider the changes in flow-paths with time and/or in space.In this study, the influence of highly alkaline plume on the permeability has been examined, considering also the direction of flow. In order to simulate the flow-paths, the amorphous silica particles were packed in the column, and the NaOH solution (0.1 M) was injected continuously at a constant flow-rate into the column at room temperature. The change in the permeability was traced, and the concentration of silicic acid in the eluted solution was measured by using the silicomolybdenum-yellow method. It was confirmed that the difference of pH values at the inlet and outlet of the column was negligibly small (pH=13.0).The experimental results showed that the change in fraction dissolved with time strongly depended on a flow-rate and a flow-direction. However, in the relation between the permeability and the fraction dissolved, the permeability did not change in the range of up to 0.35 in fraction dissolved. The SEM images of particle surface showed that the inner pores of particle increased in size. This suggested that, in this range of fraction dissolved, the porosity between particles is almost retained, while each particle dissolves mainly through its inner pores. Moreover, the dissolution rate in the column flow system was considered as being remarkably limited by diffusion process, in comparison with that estimated from the batch test.
Initial Results From Dissolution Testing of Spent Fuel Under Acidic Conditions
Authors: Hanson Brady D. , Friese Judah I. , Soderquist Chuck Z. 
Published: April 2011

AbstractFlowthrough dissolution tests using solutions with pH in the range 2 to 7 have been conducted on a moderate burnup Light Water Reactor spent fuel. Such low pH conditions have been modeled as possibly occurring in a failed waste package at the proposed repository at Yucca Mountain. The release oftotal uranium, 99Tc, 90Sr, 137Cs, and 239&240Pu were measured for up to 90% total reaction of the specimens. The reaction rates, determined both from the cumulative release and the release normalized to surface area, were found to decrease with increasing pH and with increasing extent of reaction. The implications to instantaneous release and long-term behavior ina geologic repository are discussed.
Magnetic Properties of GaN Layers Implanted by Mn, Cr or V.
Authors: Guzenko Vitaliy A. , Thillosen Nicolas , Dahmen Andre , Calarco Raffaella , Schäpers Thomas , Luysberg Martina , Houben Lothar 
Published: April 2011

AbstractWe report on magnetic properties of the GaN layers implanted with 3d transition metal ions. GaN layers grown by MOVPE on sapphire substrates, p- or n-doped, were implanted by Mn, Cr or V ions with a dose of 5×1016 cm−2 and implantation energy of 200 keV. Subsequently, a rapid thermal annealing in nitrogen atmosphere for 5 minutes at different temperatures (700°C – 1050°C) was performed. The magnetization as a function of magnetic field as well as the dependence on temperature revealed paramagnetic behavior for all samples. In addition, an antiferromagnetic coupling between implanted ions was found.
Spin Lifetime Tuning in Zincblende Heterostructures and Tions to Spin Devices
Authors: Cartoixà X. , Ting D. Z.-Y. , Chang Y.-C. 
Published: April 2011

AbstractWe present analytical expressions for the D'yakonov-Perel' spin relaxation rates under the combined action of bulk and structural inversion asymmetry for [111] zincblende heterostructures when terms up to linear and third order in k are included in the Hamiltonian. We see for [111] heterostructures that, under the right conditions, the lowest-order-in-k component of the spin relaxation tensor can be made to vanish for all spin components at the same time. We study how the inclusion of terms of higher order in k affects these results. We finally discuss a proposal for a resonant spin lifetime transistor (RSLT) using the spin lifetime tuning concepts presented above, where the characteristics of the [111] device give the designer an added degree of freedom on the direction of the injected spins.
What Constitutes Successful Undergraduate Research?
Authors: Inglefield Colin , Johnston Adam 
Published: April 2011

AbstractResearch has become a point of much greater emphasis in the undergraduate science curriculum within the past few generations of undergraduate students. However, there is not universal agreement upon what constitutes a successful undergraduate research program, and how degrees of success should be measured. A model for a successful program based principally on student ownership of research projects will be presented here. This approach is an attempt to give undergraduate students the most holistic research experience possible, by involving them in all stages of a research project in a limited amount of time. A central goal for each student is a definable product of their particular project, which is disseminated to as wide an external audience as possible. Measures of success, from student perspectives, will be discussed. These measures include data from interviews of students before and after their research experience.
An Approach to the Teaching of Functional Materials for Materials Science and Engineering Undergraduate Courses
Authors: Finlayson Trevor R. , Muddle Barry C. 
Published: April 2011

AbstractTraditional materials science and engineering texts have, for the most part, focussed on instructing the undergraduate student on the physical properties of materials and providing a significant knowledge base from which, subsequently, to consider materials applications. With the increasing demand for professional materials scientists and engineers to embrace all classes of materials in their everyday applications, it is increasingly important for undergraduate teaching to increase the awareness of students to applications through a focus on functionality rather than just providing a thorough knowledge and understanding of material properties. This has become even more important in the area of “nanostructured” materials where functional devices are designed at the material fabrication stage. In this paper, recent experiences in the teaching of functional materials for electronic, thermal and optical applications, to a second level undergraduate student group, comprising both “science” and “engineering” students, are outlined and some initial outcomes from the assessment of the group discussed.
Near surface characteristics of highly sensitive metal oxide thin films
Authors: Kiriakidis G. 
Published: April 2011

ABSTRACTWe present the gas sensing properties of InOx thin films deposited by dc sputtering and ZnOx thin films deposited both by dc sputtering and PLD. The sensitivity of the films towards ozone is correlated with the deposition parameters like film thickness, substrate deposition temperature and growth rate. Secondary Ion Mass Spectrometry (SIMS) analysis showed a noticeable deficit in oxygen in the top 5 nm for films in the “conducting” state, i.e., after UV exposure. Analysis of the sensing response for alumina-based transducers of InOx thin films revealed high sensitivity (less than 25 ppb) with fast and stable response towards ozone while ultimate sensitivity levels down to 10 ppb for ozone and 50 ppb for NO2 were achieved. Surface topography study of ZnOx films utilizing optical, AFM and SEM analyses has shown a distinct surface morphology variation correlated to the growth technique It is demonstrated that PLD leads to very rough surfaces with characteristic non-coordinated columnar features in contrast with the rather smooth surfaces obtained by sputtering.
FTIR Analysis of the Mechanisms of NOx Detection by Semiconductor Metal Oxide Nanoparticles
Authors: Baraton Marie-Isabelle , Merhari Lhadi 
Published: April 2011

ABSTRACTThe chemical reactions occurring at the surface of tin oxide nanoparticles under NOx adsorption have been investigated by Fourier transform infrared spectroscopy and correlated with the variations of the electrical conductivity of tin oxide. These surface reactions have been found dependent on the particle size and on the presence of oxygen. The strong coordination of the newly formed chemical species onto the nanoparticle surface may result in a poor reversibility of the sensor response.