bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Polysaccharides In Molecular Architecture of Plant Cell Wallsfrom Algae to Hardwoods
Authors: Atalla R. H. , Hackney J. M. 
Published: March 2011

AbstractThe structural polysaccharides are a family of polymers of hexoses and pentoses that occur in all plant cell walls. The distinguishing characteristic of these polymers is a β-1,4-linked backbone. The most common among these is cellulose, which is the linear homopolymer of anhydroglucose. These polysaccharides are capable of aggregating into highly ordered structures that are the primary determinants of the mechanical and physical properties of cell walls. An overview of the variations in patterns. of structural-polysaccharide aggregation within cell walls is presented here. Among the majority of the algae cellulose is the dominant structural polysaccharide; thus the habit of aggregation is dominated by the patterns of cellulose. Among primitive plants, other structural polysaccharides represent a larger fraction of cell-wall mass and cellulose is less dominant. In woody tissues of higher plants, structural polysaccharides are the major components of the cell wall, and the patterns of aggregation are again dominated by the characteristic habits of cellulose. Within tile phylogenetic framework, higher levels of morphological development apparently involve greater complexity in the molecular architecture of the cell walls and a finer level of blending of the components of aggregates at the molecular level.
Self-Assembled α-Helical Polypeptide Films
Authors: Enriquez Erwin P. , Samulski Edward T. 
Published: March 2011

AbstractPoly(γ-benzyl-L-glutamate) (PBLG) derivatized at its N-terminus with lipoic acid, a disulfide-containing moiety, self-assembles on gold from helicogenic solvents to give a thin film with the polypeptide α-helices orientation distribution different from the planar orientation in the unlabeled, physisorbed PBLG films (control) and Langmuir-Blodgett monolayers. The SA films were studied by angle-dependent XPS, reflection-absorption FTIR spectroscopy, and ellipsometry. The IR dichroic properties of the amide I and amide II bands were used to infer the orientational distribution of the helices in the self-assembled film and lead to two extreme pictures of the helix axis distribution function: (a) random (hemispherical distribution) and (b) perfect order with a tilt of 53° from the surface normal. Additional characterization is necessary to differentiate between these two distributions.
Design of Protein-Producing Bioreactors for Self-Assembling Systems.
Authors: Furlong Clement E. , Humbert Richard 
Published: March 2011

AbstractProteins, due to their complex structures, possess infinite possibilities for assembling themselves as well as other biological and nonbiological materials into complex, multicomponent structures. Many examples from nature demonstrate the high degree of flexibility, strength and “intelligence” offered by protein-organized, self-assembling systems. However, several problems must be overcome before self-assembling protein-based products can become commercially feasible. One problem is the high cost of protein production. A second problem involves the question of producing nonidentical protein subunits in the proper stoichiometry for self-assembly. A third problem involves the stability of the protein components of larger structures.We have been developing protein-producing bioreactors to address the problems associated with the commercial production of proteins, both as individual products as well as components of self assembling systems. The approach that we have taken is to clone the gene or cDNA that encodes the desired protein(s) and tailor the expression of the protein so that it can be produced at high levels under conditions where cell division is blocked. This assures that supplied nutrients go into product and not biomass, and at the same time provides conditions where cells can be immobilized without fracturing the support matrix during division. The blocking of cell growth also allows for the adjustment of protein stoichiometry by setting the ratios of cells that produce different subunits of complex structures.To simplify downstream processing and purification, we have designed a system where nearly pure protein is secreted directly into the medium. This approach allows for automated downstream processing and separation of product from cells before it is degraded. The model system that we are using for the development of the protein-producing bioreactors utilizes genetically modified strains ofEscherichia colithat secrete proteins which are usually found in the periplasmic space directly into the medium. The phosphatebinding protein serves as an ideal model protein for bioreactor development, since the regulatory elements that control its production are turned on by phosphate limitation, which also arrests cell division. We are presently determining if these regulatory and secretory elements can be used to direct the synthesis and secretion of heterologous proteins.
Effects of Surface Treatment on Light Emission from Porous Silicon
Authors: Khan Babar A. , Pinker Ronald , Shahzad Khalid , Rossi Barbara 
Published: March 2011

ABSTRACTVisible light emission from porous silicon has recently been demonstrated by several groups. We have found that annealing of porous silicon samples in an inert atmosphere over 250C reduces the emission intensity, almost fully quenching it by 450C. We believe that this is due to the removal of passivating hydrogen, based on measurements of infrared absorption due to Si-H vibrational modes. We have also found that we can partially recover the emission intensity in these annealed porous silicon layers by passivation in a hydrogen plasma. We have therefore demonstrated that hydrogen passivation is necessary for the observation of visible emission from porous silicon. We have also shown that thermal oxidation of porous silicon over 200C reduces the PL emission. We propose that this reduction is also due to the loss of hydrogen passivation during the oxidation.
Optical Characterization of the Visible Photoluminescence from Porous Silicon
Authors: Fuchs H. D. , Brandt M. S. , Stutzmann M. , Weber J. 
Published: March 2011

ABSTRACTThe visible photoluminescence of electrochemically etched silicon wafers is studied by cw- and pulsed-laser excitation. Raman data and infrared transmission measurements on the same samples prove the presence of oxygen and hydrogen in different bonding configurations in the luminescent layers. Identical optical properties are found for chemically synthesized siloxene (Si6O3H6) and its derivates. We present evidence that the origin of the strong room temperature luminescence in “porous” silicon can be traced to siloxene derivates present in the samples.
Characterization of Microporous Silicon Fabricated by Immersion Scanning
Authors: Bassous E. , Freeman M. , Halbout J.-M. , lyer S. S. , Kesan V. P. , Munguia P. , Pesarcik S. F. , Williams B. L. 
Published: March 2011

ABSTRACTA novel immersion scanning technique for making microporous silicon has been successfully applied to blank and lithographically patterned Si substrates. The advantages of the method lie in its simplicity, speed and adaptability to large and odd-size substrates. The photoluminescence (PL) spectra of microporous Si show a continuous decrease in intensity between 200K and 2K, but are fully reversible. Thermal desorption spectroscopy on microporous Si shows a classic hydrogen desorption spectrum which coincides with a quenching of the PL intensity. Under constant excitation, a degradation of PL Intensity occurs in oxygen and wet nitrogen but is only partially reversible in dry N2. Microporous Si PN junctions exhibiting normal I-V characteristics have been successfully fabricated with standard Si VLSI processes. Visible light emission under forward bias is detected which increases linearly In Intensity with Input current. This is the first observation of electroluminescence in the visible region from microporous SI PN junctions.
Pore Formation and Propagation Mechanism in Porus Silicon
Authors: Lehmann V. , Cerva H. , Gosele U. 
Published: March 2011

ABSTRACTThis paper presents a model of the microporous silicon formation process which is based on hole depletion due to quantum confinement in the porous structure. This model is compared with the formation of larger porous structures (meso-, macroporous) where hole depletion is generated by a space charge region.
Photoluminescence Excitation Spectroscopy (PLE) of Porous Silicon
Authors: Wang Lei , Wilson M. T. , Goorsky M. S. , Haegel N. M. 
Published: March 2011

ABSTRACTPLE spectroscopy was performed on samples of porous Si at temperatures of 300 and 4.2 K. PLE provides information about the absorption coefficient in the limit of optically thin samples and is an alternative method for determining absorption data on porous Si without removal of the substrate. The spectra obtained correspond closely to the relative changes in absorption coefficient for bulk Si between 2.0 and 3.5 eV, with a strong increase above 3.0 eV which is due to the direct bandgap transition.
Effect of a Siliceous Additive in a Clay Engineered Barrier on Aqueous Corrosion of R7T7 Nuclear Waste Glass
Authors: Godon N. , Andriambololona Z. , Vernaz E. 
Published: March 2011

ABSTRACTPrevious tests have shown that glass is highly corroded in the presence of smectite 4a, a clay under consideration for use as a repository engineered barrier material. Alteration experiments with French R7T7 glass were therefore conducted in moist clay media containing 5 wt% of a siliceous additive. Five siliceous materials were tested: silica gel, pozzolana, window glass, R7T7 glass frit and R7T7 glass, all in powder form. Following an initial 28-day preconditioning period during which the clay/additive/leachant system was allowed to reach equilibrium, a glass specimen was placed for 7 or 28 days in the moist clay medium. Glass alteration was characterized by the mass loss and by surface analysis. After 28 days in contact with the silica gel and with the three glass powders the mean glass corrosion rate calculated from the mass loss values was about 0.01 g.m−2d−1, versus 1.4 g·m−2d−1 with clay alone and 0.3 g·m−2d−1 with pozzolana. The use of a suitable additive can thus considerably attenuate the corrosive effects of moist smectite in contact with R7T7 glass.
Effects of Noble Metal Elements on Viscosity and Electrical Resistivity of Simulated Vitrified Products for High-Level Liquid Waste
Authors: Igarashi Hiroshi , Kawamura Kazuhiro , Takahashi Takeshi 
Published: March 2011

ABSTRACTThe effects of noble metal elements such as ruthenium, rhodium and palladium on the viscosity and electrical resistivity of simulated nuclear waste glass were studied. The glass enriched with noble metals showed the viscosity of a non-Newtonian fluid. The viscosity of the waste glass with 10 wt% Ru0 2 was 3 to 7 times higher than that of glass without noble metals. The RuO2 was mainly responsible for the increase in viscosity for the glass enriched with noble metals. Electrical resistivity of the glass with 15 wt% RuO2 was one seventh to two orders of magnitude lower than that of glass without noble metals. The three noble metals contributed to the decrease in resistivity. The quantitative effects of noble metals on these properties were obtained.
The Platinum Metals in Hllw — Glass Products
Authors: Kelm Manfred , Oser Bernhard 
Published: March 2011

ABSTRACTThe behaviour of the platinum metals in nuclear waste glass produced in a lab scale liquid fed ceramic melter was investigated. The platinum metals form two kinds of metallic conductive particles in the glass melt: RuO2 (preferentially needle shaped) and a Pd—Rh—Te alloy (tear—shaped). These phases decrease the electrical resistivity of the glass melt. Resistivities were measured at 950º and 1150 ºC. Powdered glass was used as starting material. For the same temperatures resistivities were calculated applying an equation derived for an embedment structure of highly conductive particles in a matrix of low conductivity. To match calculated and measuredresistivities one must assume needle—shaped particles. This gives evidence that mainly RuO2 contributes to the observed decrease in resistivity. If the measurements are started with glass blocks instead of glass powder, remarkably lower resistivities are measured in the melt. A comparison of both results indicates a partial destruction of particles or particle contacts by grinding. Thus, resistivities measured with ground samples are not representative of those effective in a melter.The investigation of solid glass samples yielded the following results: Within a few hours, Pd—Rh—Te and RuO2 particles form fine sediments in the melter. The development of stable coarse sediments needs some 1000 h of melter operation. The Pd—Rh—Te alloy particles reach a mean diameter of 5 μm in the fine sediment and of 20 μm in the coarse one. With time, the alloy dissolves more Rhand Te. Finally, the alloy separates into two phases. RuO2 dissolves Cr and Rh.
Tellurium and Palladium Diffusion in the German Waste Glass Vg 98/12 Measured with the Rbs Method
Authors: Yamashita M. , Matzke Hj. , Linker G. 
Published: March 2011

ABSTRACTThe diffusion of Te and Pd was measured in the German waste glass VG 98/012 usingion implantation to introduce these elements, and the Rutherford backscattering (RBS) method to measure their diffusion. Both elements tend to precipitate during manufacture ofnuclear waste glasses, and the Te-content of the precipitates depends on the annealing time. Diffusion of these elements is a basic property of the separation phenomenon. Diffusion of both elements was found to be very slow. Te-diffusion coefficients were in the range of 10-17 to 10-15 cm2s-1 between 540 and 590 αC. Surface evaporation of Te was observed at all heat treatments. Pd diffusion was not observed in this study, most likely due to limited solubility of Pd and formation of metal precipitates.
Microstructure, Partitioning and Dissolution Behaviour of Synroc Containing Acrinides
Authors: Blackford M.G. , Smith K.L. , Hart K.P. 
Published: March 2011

ABSTRACTSynroc formulations containing 10 wt% simulated PW-4b type HLW in combination with a single transuranic dopant (Np, Pu, Am or Cm) were fabricated and characterised using alpha-track methods, SEM, AEM and dissolution testing. The Pu, Am and Cm-doped samples were calcined in 3.5%H2/96.5%N2. One of the Np-doped Synrocs was calcined in an atmosphere of pure H2, whilst another Np-doped Synroc was calcined in a mixture of 3.5%H2/96.5%N2. All the different formulations displayed microstructures similar to those of Synroc containing actinide-free simulated HLW. AEM derived phase compositions and phase distributions are given. All the Synrocs showed good durability when exposed to leachants (including doubly deionised water, and pH- and Eh-buffered solutions with pHs between 2 to 10). There were no obvious differences between the two Np-doped samples. The improved appearance and behaviour of allthe Synrocs in this study compared with similar formulations described by other authors is attributed to improved mixing techniques during fabrication.
The Pyrochlore Line in the System CaO—ZrO2—TiO2: Implications on Synroc Phase Assemblages
Authors: Figueiredo M. Ondina , Santos António Correia dos , Cortina Carmen Parada , Basto M. Joao 
Published: March 2011

ABSTRACTResults of further studies on phase equilibria in system CaO—ZrO2—TiO2along the “pyrochlore” line ( Ca ZrxTi3-x07) are reported concerning the possible substitution of cerium for either calcium or zirconium in nominal “Ca Zr2 Ti 07”. The dominant tetragonal phase in this composition was identified as calzirtite. The structural role of zirconium and its tendency towards 7—coordination environments are discussed. Possible implications on high—level nuclear waste immobilizers like SYNROC are brieflyconsidered.
Solubility of Simulated Hlw Elements in Pyrochlore Structure
Authors: Hayakawa Issei , Kamizono Hiroshi 
Published: March 2011

ABSTRACTWe have found that lanthanum zirconate (La2Zr2O7) with a pyrochlore structure can be used as a superior host phase for actinide and lantanide elements contained in high-level nuclear waste. The solubility of Ce, Nd and Sr in La2Zr2O7 is determined because Ce and Nd may simulate the segregation of actinide and lanthanide elements at the grain boundaries of polycrystalline La2Zr2O7. The results show that La2Zr2O7 is a promising material for confining actinide and lanthanide elements in its crystal structure.
Determination of Criteria for Selecting A UO2Fuel Dissolution Model for Nuclear Fuel Waste Management Concept Assessment
Authors: Sunder S. , Shoesmith D.W. , Miller N.H. , Wallace G.J. 
Published: March 2011

ABSTRACTAssessing the concept of direct disposal of used nuclear fuel in a geological vault requires a model to predict the dissolution rate of UO2in groundwater. A solubility-limited model can be used to calculate the dissolution rate of UO2fuel under non-oxidizing conditions. When the oxidative dissolution of UO2is an irreversible process, a kinetic model is more suitable to describe the dissolution of UO2under oxidizing conditions. Experimental studies were carried out using electrochemical techniques and X-ray photoelectron spectroscopy, XPS, to determine criteria for selecting the appropriate model for estimating used-fuel dissolution rates as a function of the redox conditions in the vault at the time of container failure. UO2electrodes were subjected to prolonged (>1000 min) potentiostatic oxidation, and the rate of oxidation and dissolution of UO2fuel was investigated as a function of the applied potential. UO2oxidation was also carried out by the products of water radiolysis and studied as a function of dose rate, total dose and solution chemistry.These studies show that significant oxidative dissolution of UO2appears possible for potentials more positive than -100 mV vs SCE in solutions with a pH close to that of the deep groundwaters, i.e., from 6 to 10. A kinetic model, which takes into account the mechanism of UO2oxidation, is more appropriate to estimate dissolution rates of UO2fuel for redox conditions more oxidizing than -100 mV vs SCE.
Gap and Grain-Boundary Inventories of Cs, Tc, and Sr in Spent LWR Fuel
Authors: Gray W. J. , Strachan D. M. , Wilson C. N. 
Published: March 2011

ABSTRACTSoluble radionuclides concentrated within the gap and grain-boundary regions of spent fuel could dissolve relatively rapidly were the waste container to fail and the fuel to be contacted by water in a geologic repository. To provide an estimate of the quantities of radionuclides that may be rapidly released, fractional inventories of Cs, Tc, and Sr concentrated within the fuel/cladding gap region have been measured for U.S. LWR spent fuels with fission gas release (FGR) values ranging from 0.25% to 18%. Separate measurements of the grain-boundary inventories of Cs, Tc, and Sr have been made for the same fuels. The Cs gap inventories were generally found to be about one fourth of the FGR values. The Cs grain-boundary inventories were generally less than 1% of the total Cs inventories and were not strongly correlated with FGR. Both the gap and grain-boundary inventories of Tc and Sr were near the detection limits of the methods used, less than 0.2% of the total inventories of these elements. However, some of the Tc may reside at the grain boundaries in the form of relatively insoluble metallic particles and not be detected by these experiments. Data obtained by comparing the dissolution behavior of fuel fragments with that of fuel grains were used to estimate the dissolution rate of Cs from the grain boundaries of one of the fuels. Surface-area normalized dissolution rates determined for fuel fragments in these same tests exceeded those determined for grains. A likely explanation is that the estimated fragment surface area did not take into account the “effective” grain-boundary surfaces.
Corrosion of Carbon-Steel Containers for Heat-Generating Nuclear Waste in Brine Environments Relevant for A Rock-Salt Repository
Authors: Smailos E. , Schwarzkopf W. , Kienzler B. , KÖster R. 
Published: March 2011

ABSTRACTIn previous corrosion studies, carbon steels, especially the fine-grained steel TStE355, were identified as promising materials for heat-generating nuclear waste containers acting as a barrier in a rock-salt repository. In the present study detailed investigations have been performed on fine-grained steel to determine the influence of important parameters on its corrosion behaviour in disposal-relevant salt brines. These parameters are: brine composition (Mg Cl2-rich and NaCI-rich brines), temperature (90°C, 170°C), and salt impurities, such as H2S concentrations of 25 mg/I-200 mg/I salt brine.Under the conditions of the tests used here, carbon steel was subjected to general corrosion. Pitting and crevice corrosion or stress-corrosion cracking were not observed. The increase in temperature from 90°C to 170°C strongly enhanced the corrosion rate of the steel. In the MgCl2-rich brines, considerably higher rates (37-70 μm/a at 90°C, 200-300 °m/a at 170°C) were observed than in the NaCI-rich brine (5 μm/a at 90°C, 46 μm/a at 170°C). H2S concentrations in the MgCl2-rich Qbrine of up to 200 mg/l did not influence significantly the corrosion rate of the steel. The corrosion rates determined imply corrosion allowances that are technically acceptable for thick-walled containers. In view of these results, fine-grained steel continues to be considered as a promising material for long-lived HLW containers.
In-Situ Corrosion Studies on Cast Steel High-Level Waste Containers Plated with Titanium/Nickel-Alloys
Authors: Schwarzkopf W. , Smailos E. , KÖster R. 
Published: March 2011

ABSTRACTPrevious corrosion studies have shown that the passive alloys Ti 99.8-Pd and Hastelloy C4 are the most promising corrosion protection materials for long-term resistant carbon-steel containers for the disposal of heat-generating wastes in rock salt formations. Consequently, these materials are subject to more detailed investigations. The influence of selected container manufacturing characteristics (sealing technique, application mode of the corrosion protecting layer on the steel) on the corrosion behaviour of Ti 99.8-Pd and Hastelloy C4was studied using in-situ experiments. The corrosion resistance of the materials was examined both in NaCI brine and MgCl2-rich brine, which might enter into an HLW borehole under certain disposal conditions. Four electron-beam welded cast-steel tubes plated with corrosion protection layers made of Ti 99.8-Pd and Hastelloy C4, respectively, were stored for 18 months in 2-m deep heated boreholes in the Asse salt mine. The annular gap between the tubes and the borehole wall was filled with saturated NaCl-brine or Qbrine (MgCl2-rich). The vertical temperature profile in the boreholes ranged from 90°C to 200°CIn the cast-steel tube with a corrosion protection of Ti 99.8-Pd, no indication of corrosion was observed on the EB-welds or on the explosion plated material in both brines. The cast-steel tube with a corrosion protection of Hastelloy C4 also was found to be resistant to any kind of corrosion in the NaCl-brine. In the MgCl2-rich brine, however, small pitting corrosion of 15 pm was observed after 1.5 years on the passive surface layer that was formed.On the basis of these results, Ti 99.8-Pd continues to be considered as a promising corrosion protection material for long-lived HLW containers.