bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Study of Uranium(6+) Sorption on the Zeolite Mineral Clinoptilolite
Authors: Pabalan Roberto T. , Prikryl J. D. , Muller P. M. , Dietrich T. B. 
Published: March 2011

ABSTRACTExperiments on the sorption of uranium(6+) on clinoptilolite from solutions in equilibrium with atmospheric CO2(g) were conducted to understand the fundamental controls on uranium sorption on zeolite minerals, including the effects of pH, aqueous uranium speciation, and uranium concentration in solution. The results indicate that uranium(6+) species are strongly sorbed on the zeolite mineral clinoptilolite at near-neutral pH. The amount of uranium sorbed is strongly dependent on pH and, to some extent, on the total concentration of uranium. Uranium sorption on clinoptilolite is important in the pH range where UO2(OH)2°(aq) is the predominant uranium aqueous species, whereas sorption is inhibited at pH's where carbonateand hydroxy-carbonate-complexes are the primary uranyl species. Surface adsorption appearsto be the main sorption mechanism, although at pH<4 the results suggest ion exchange may occur between the UO2+2 ions in solution and the cations in the intracrystalline cation exchange sites of clinoptilolite.The effectiveness of zeolite-rich horizons underneath Yucca Mountain, Nevada, as barriers to actinide transport through sorption processes will depend strongly on groundwater chemistry. Reliable predictions of radionuclide transport through these horizons will need to properly account for changes in solution chemistry.
The Influence of Non-Linear Sorption on Colloid Facilitated Radionuclide Transport Through Fractured Media
Authors: Smith Paul A. 
Published: March 2011

ABSTRACTIn the safety assessment of nuclear waste repositories, sorption of radionuclides on the surfaces of colloids may significantly modify transport behaviour where colloid concentration is sufficiently high. In the case of fractured geological media, colloids may be excluded from matrix pores, in which case radionuclides bound to them are not subject to the retarding effects of matrix diffusion and sorption onto matrix pore surfaces.A model is presented describing colloid facilitated transport through fractured media with non-linear sorption. A simple criterion is developed to predict when the presence of colloids will have a significant influence on transport and effects resulting from non-linearity of sorption are described. However, lack of comprehensive sorption data, as well as computational efficiency, mean that the use of a simplified transport model, with linear sorption both on pore surfaces and colloids, is desirable if it can be demonstrated to be conservative. A further criterion is developed to predict where such a model, with linear sorption calculated for the highest concentration encountered along the flow path, would be expected to yield conservative results.
Diffusivity and Porosity in Rock Matrix—Laboratory Methods Using Artificial and Natural Tracers
Authors: Valkiainen M. , Olin M. , Uusheimo K. , Kumpulainen H. , Lehikoinen J. , Muurinen A. 
Published: March 2011

ABSTRACTThe nature of diffusivity and porosity in crystalline rock was studied by electrical conductivity measurements, steady-state diffusion experiments, saturation-leaching of tracers with cylindrical rock samples and analysis of the concentrations of different elements from core samples or pore water near fractures. The phenomena of main interest were dead-end porosity, ion-exclusion, sorption, and the continuity of pore networks. The modelling of experimental results was based on a modified Fick's second law for diffusion, which was solved either by analytical or numerical methods. The measured De and ε were found to statistically follow an exponential presentation: Archie's law. The existence of ion-exclusion for anions was confirmed. The connectivity of the pore network extended in the laboratory experiments at least six centimetres, in coarse-grained granite in nature several metres but in fine-grained rock samples of a uranium deposit the element mobilization effects could be seen only to the depth of 2–3 centimetres.
Model Validation and Decision Making: An Example Using the Twin Lakes Tracer Test
Authors: Olague Natalie E. , Davis Paul A. , Smith Darrla , Feeney Tom 
Published: March 2011

ABSTRACTAn approach to the validation of ground-water flow and transport models that are used in support of licensing a radioactive waste site is proposed and demonstrated. The approach attempts to interpret modeling results in light of their intended purpose. Instead of trying to find the ‘best’ fit model to the experimental data, we attempt to determine the conservativeness or bias invoked by applying different models to simulate the same experiment. In this way we are able to provide guidance to the regulatory community on where they should expect model results to fall relative to actual data and provide some evidence that certain model approaches lead to conservative results while other modeling approaches lead to non-conservative results. Applying this approach to the Twin Lakes Tracer Test demonstrated that a simple one-dimensional flow and one-dimensional dispersion model consistently over-predicts the maximum concentration. A one-dimensional flow with three-dimensional dispersion and two dimensional flow with two dimensional advection-dispersion are conservative only if they employ laboratory scale dispersivities. Therefore, if a decision-maker were to accept a similar site based on results from these types of models, there would be a relatively low chance that he has accepted an unsafe site. However, if decision-makers were to reject a similar site based on these types of results, there would be a relatively large chance that they rejected a safe site.
Approaches to Long-Term Performance Assessment of Deep Underground Disposal of Radioactive Wastes: A European Perspective
Authors: Sumerling Trevor J. , Read David 
Published: March 2011

ABSTRACTThe aim of long-term performance assessment (PA) is generally to develop confidence that the disposal system will perform within certain bounds and give rise to acceptably low impacts or risks. The PA procedure must be able to deal with:- uncertainty due to incomplete understanding of the relevant processes;- uncertainty due to limited sampling of the structures and characteristics of the system and especially the geological media;- uncertainty about future conditions and processes leading to changes in the engineered barriers and natural environment that may affect radionuclide release, transport and exposure pathways.A number of approaches have been taken to solving the problem of how to deal with such uncertainties. The differences in approach may be due to the stage of project development, differences in national regulatory guidance and the different r6les of the implementor and the regulator. This paper examines the rôles of the implementor and regulator and discusses possible approaches appropriate to both points of view.
Scanning Tunneling Microscopy on Charge Density Waves in Layered Compounds
Authors: De Hosson J. Th. M. , Van Bakel G. P. E. M. 
Published: March 2011

AbstractDifferent layered transition metal dichalcogenides were subjected to scanning tunneling microscopy to reveal the electronic charge distribution associated with the charge density wave (CDW) part of the superstructure, in addition to the atomic corrugation. The observations presented display three regimes ranging from localized CDW centred around defects/impurities in the case of lT-TiS2, via an intermediate regime governed by overlapping envelope functions in 2H-NbSe2, to a fully developed CDW system in 1T-TaSe2 (as well in a large number of other compounds). The fact that these observations have been made in solids ranging from (dirty) semiconductor (1T-TiS2) to semimetal (1T-TaSe2) to metallic (2H-NbSe2) points at the general applicability of the phenomenological Ginzburg-Landau theory, employed to describe the various regimes in which the formation of charge density waves and the accompanying periodic lattice distortions appear to act.
Al Induced Reconstructions on the Si(111) Surfaces Studied by Scanning Tunneling Microscopy
Authors: Yoshimura Masamichi , Takaoka Katsuya , Yao Takafumi , Sato Tomoshige , Sueyoshi Takashi , Iwatsuki Masashi 
Published: March 2011

AbstractThe atomic arrangements of the α-7×7 phase and incommensurate phases of Al adsorbed Si(111) surface are investigated respectively by scanning tunneling microscopy (STM). STM images of α-7×7 surface reveal that characteristic triangular structures consisting of three Al adatoms situated on the center part of each half unit cell. The three Al adatoms form a triangular cluster and are bonded to the center adatoms. In this situation, the dangling bond of the center adatom is saturated, which would modify its electronic structure into non-metallic. The incommensurate phase is consists of approximately 9×9 structures, which are separated each other with misfit dislocations. In the “9×9” structure, individual Al atom is visible arranged in threefold symmetry.
Structure of the ∑=3 (111) Grain Boundary in Cu-1.5%Sb
Authors: Fonda Richard W. , Luzzi David E. 
Published: March 2011

AbstractGrain boundaries in quenched and aged Cu-i.5%Sb were examined with Auger electron microscopy, transmission electron microscopy, and high resolution electron microscopy. The ∑=3 grain boundaries are strongly faceted, with the facets lying primarily along the coincident (111) planes of the two grains. The grain boundaries are enriched in antimony, as demonstrated by both AES and HREM. HREM images of the ∑=3 (111) ║ (111) grain boundary differ from those of the Cu-Bi ∑ =3 (111) ║ (111) grain boundary in the lack of a significant grain boundary expansion to accommodate the excess solute at the boundary. A preliminary investigation of the atomic structure of the ∑=3 (111) ║ (111) facet by HREM and multislice calculations is presented.
Compositional Analysis and High Resolution Imaging of Grain Boundaries in Pr-DOPED ZnO Ceramics
Authors: Solorzano I. G. , Sande J. B. Vander , Baek K. K. , Tuller H. L. 
Published: March 2011

AbstractAn electron microscopy investigation has been conducted in ZnO:Pr:Co varistor structures prepared by a new in-diffusion method. It has been shown that some boundaries host intergranular precipitates of a Prx Oy-based phase. All observations lead to the conclusion that grain boundaries exhibit Pr segregation, while Co is homogeneously distributed in the ZnO matrix. No continuous intermediate layer is present at the ZnO/ZnO boundary nor at the Pr2O3/ZnO interfaces. This is consistent with a barrier model based solely on a space charge depletion region(s).
A Compact Nuclear Microprobe With a Liquid Metal Ion Source and a Toroidal Analyzer
Authors: Takai Mikio , Mimura Ryou , Sawaragi Hiroshi , Aihara Ryuso 
Published: March 2011

AbstractA nondestructive three-dimensional RBS/channeling analysis system with an atomic resolution has been designed and is being constructed in Osaka University for analysis of nanostructured surfaces and interfaces. An ultra high-vacuum sample-chamber with a threeaxis goniometer and a toroidal electrostatic analyzer for medium energy ion scattering (MEIS) was combined with a short acceleration column for a focused ion beam. A liquid metal ion source (LMIS) for light metal ions such as Li+ or Be+ was mounted on the short column.A minimum beam spot-size of about 10 nm with a current of 10 pA is estimated by optical property calculation for 200 keV Li+ LMIS. An energy resolution of 4 × 10-3 (AE/E) for the toroidal analyzer gives rise to atomic resolution in RBS spectra for Si and GaAs. This system seems feasible for atomic level analysis of localized crystalline/disorder structures and surfaces.
Low Energy Point Source Electron Microscopy
Authors: Kreuzer H. J. 
Published: March 2011

AbstractThe theory of the point source low energy electron microscope is reviewed. Images are calculated for a carbon fibre, a small cluster of MgO and a double helix of carbon atoms. A Kirchoff-Helmholtz transform is used for reconstruction. The importance of image size is stressed and the chemical specificity of the method is demonstrated
Dissociative Phase Transitions, Split Shock Waves, Rarefaction Shocks, and Detonations
Authors: White C. T. , Robertson D. H. , Elert M. L. , Mintmire J. W. , Brenner D. W. 
Published: March 2011

AbstractWe present a comparative study of two different chemically-sustained shock waves. One shows behavior expected from the Zel'dovich, von Neumann, and Doering (ZND) continuum theory of planar detonations. The other exhibits the complexity of a split shock wave resulting from the presence of a polymorphic phase transition. This comparative study demonstrates the importance of carefully considering the high-pressure characteristics of the model in developing potentials for simulating detonations. This comparative study also raises the fascinating possibility of a first-order phase transition accompanying a condensed-phase detonation.
Femtosecond Spectroscopy of Chemically Reactive Solids: a Methodology
Authors: Wang Weining , Wefers Marc M. , Nelson Keith A. 
Published: March 2011

AbstractAn experimental methodology for recording femtosecond time-resolved observations of irreversible change in solids is described. The central problem posed is that the trime-dependent evolution must be observed on a single-shot (i.e. real-time) basis since the sample may be permanently altered after each excitation event. Preliminary demonstrations of real-time femtosecond spectroscopic observations are presented. In addition, one-shot data acquisition techniques open up the possibility of excitation intensities that greatly exceed optical damage threshholds of most samples. Since only one excitation pulse is used, cumulative damage mechanisms may be circumvented. Even if the sample is damaged in a single shot, in some cases the events of interest may be observed before damage occurs. The use of timed sequences of high-intensity excitation pulses to drive large-amplitude, coherent lattice vibrations is discussed. If successful, such large-amplitude lattice vibrations could assist crystalline chemical reactions or structural phase transitions.
Molecular Level Study of Insensitive and Energetic Layered and Intercalated Materials
Authors: Bardo Richard D. 
Published: March 2011

AbstractAn important goal in the detonation physics and chemistry community is to design explosives with high-performance capabilities, yet sufficiently low impact and shock sensitivities. The traditional ways of developing increasingly energetic explosives have led to an increase in sensitivity. It is, therefore, of practical and theoretical importance to design, from molecular level considerations, polycrystalline explosive systems which clearly exhibit directional sensitivity and initiation properties, and which approach the insensitivity of homogeneous or single-crystal explosives. Theoretical studies indicate that such systems may be constructed from special materials such as high-quality pyrolytic, layered, hexagonal boron nitride (BN) crystals. Intercalation of the crystals with various oxidizing agents can yield an explosive system with the desired properties. Under ordinary laboratory conditions and with modest pressures, the intercalate molecules readily enter the host lattice by exploiting the weak bonding between the layers, resulting in denser, metastable crystals. High energy release is achieved when products containing B2O3 are formed.
Pressure/Temperature/Reaction Phase Diagrams for Several Nitramine Compounds
Authors: Russell T. P. , Miller P. J. , Piermarini G. J. , Block S. 
Published: March 2011

AbstractPressure/temperature/reaction phase diagrams for several nitramine compounds, including hexanitrohexaazaisowurtzitane (HNIW), 1,3,5-trinitrohexahydro-l,3,5-triazine (RDX), ammonium dinitramide (ADN), and p-nitroaniline (PNA) are presented. A diamond anvil cell was used in conjunction with optical polarizing light microscopy (OPLM), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray diffraction (EDXD), and micro FT-Raman spectroscopy to determine these diagrams. A description is given of the diamond anvil cell and the associated techniques employed.
The Growth and Perfection of Single Crystals of Trinitrotoluene (TNT)
Authors: Gallagher Hugh G. , Sherwood John N. 
Published: March 2011

AbstractA study has been made of the crystal growth behaviour and perfection of TNT. Depending on the purity and the solvent used, crystallisation from solution yields material of monoclinic, twinned monoclinic or orthorhombic forms. Of these only the monoclinic form was suitable for detailed study by X-ray topographic techniques. The crystals of the orthorhombic form were too small and imperfect for examination.Seeded growth from ethyl acetate solution yielded lamellar twinned crystals in which the twin density was low. Under ideal conditions, relatively perfect samples could be obtained in which the dominant residual growth defects were stacking faults of Burgers vector b ½ [001] and dislocations.
Molecular Structure and Performance of High Explosives
Authors: Stine James R. 
Published: March 2011

AbstractEmpirical methods have been developed to predict density and heat of formation of proposed high explosives. These methods are parameterized in terms of molecular constituents consisting of atoms in particular bonding environments. These methods, along with the atomic composition of the molecule, are then used in an empirically based method to predict the performance of the explosive.Together, these methods form a unified mechanism of relating molecular structure to explosive performance. Indeed, this effort, along with the synthesis effort at Los Alamos, have led to the identification of a new class of high-nitrogen molecules that may prove to be high performance explosives.
Energetic Materials in Ceramics Synthesis
Authors: Kingsley J. J. , Pederson L. R. 
Published: March 2011

AbstractCombustion of a proper combination of an oxidizer and a fuel can produce the exothermicity required for the simultaneous synthesis of oxide ceramic powders. Oxidizers include metal nitrates, ammonium nitrate, and ammonium perchlorate, while urea, carbohydrazide, glycine and others have been used successfully as fuels. Combustion methods are particularly well-suited to producing multicomponent metal oxides, yielding compositionally homogeneous, fine particles with low impurity content. Organic fuels, particularly those containing nitrogen, also serve as a complexant in the precursor, which inhibits inhomogeneous precipitation from occurring prior to combustion. The exothermic redox decomposition of these oxidizer-fuel mixtures is initiated at low temperatures, usually <250°C. Properties of the products are influenced by the nature of the fuel and the oxidizer/fuel ratio. Many technologically important oxide ceramics have been produced by these methods.
A Novel Structure of a-SiN:H/a-Si:H Multilayer Avalanche Photodiode (MAPD)
Authors: Lihong Jiao , Zhiguo Meng , Zhonglin Sun 
Published: March 2011

Because of the lower density of interface states in a-Si:H/a-SiN:H than that in a-Si:H/a-SiC:H, an a-Si:H/a-SiN multilayer reach-through avalanche photodiode is fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition (PECVD) . In order to improve the performance of the a-Si:H/a-SiN:H APD'S, a novel structure is used. By controlling the deposition ratio of silicon and nitrogen of amorphous SiN,the valence band top of a-Si:H is deeper than that of a-SiN:H, that is, the a-Si :H/a-SiN: H system has the electron potential well in a-Si:H, while the hole well is in a-SiN:H, thus we can successfully suppress the hole impact ionization, correspondingly enhance the electron impact ionization effectively.The measurement of current versus voltage is employed to study the multiplication factors and the impact ionization coefficients. The characteristics of a-Si:H/a-SiN:H APD's,such as I-V curves, optical gains, impact ionization rates, excess noise factors, the relative response and the relationship between the breakdown voltage and wavelength, are studied. The electron multiplication factor is Mc=4.5 at reverse bias V=12v. An optical gain of 3.7 at reverse bias VR=12v and an incident light power Pin=3μw is obtained. Homo junction a-Si:H reach-through APD's and homojunction a-Si:H APD's are also fabricated for comparison.The results show that the novel a-Si:H/a-SiN:H APD's is promising in high-gain, low-noise photodetectors.
Photoluminescence from Nanocrystalline Silicon Prepared by Plasma CVD and Oxidation
Authors: Veprek S. , Rückschloβ M. , Landkammer B. , Ambacher O. 
Published: March 2011

AbstractLight emitting nanocrystalline silicon has been prepared by a completely dry processing which uses standard silicon technology. This enables us to prepare compact films on various substrates and to control the crystallite size. Dependence of the photoluminescence intensity and its peak energy on the crystallite size is reported and compared with current theoretical models.
Reducing Dislocation Density by Sequential Implantation of Ge and C in Si
Authors: Im Seongil , Washburn Jack , Gronsky Ronald , Cheung Nathan W. , Yu Kin Man , Ager Joel W. 
Published: March 2011

AbstractCarbon implantation was performed after high dose(5 x 1016/cm2) Ge implantation into [100] oriented Si substrates to study the effect of sequential implantation on dislocation nucleation. When the nominal peak concentration of implanted C is over 0.55 at%, Dislocations in the SiGe layer containing C are considerably reduced in density after solid phase epitaxial(SPE) annealing at 800°C for 1 hour, compared to the SiGe layer without C. These results suggest that during annealing, C atoms compensate the Geinduced misfit strain which causes dislocation generation in the region of peak Ge concentration. Channeling spectra obtained by RBS analysis show only 5% to 6% minimum back scattering yield as C atoms suppress the dislocation generation.
The Structure and the Physical Properties of Si/C Grown by Laser Pyrolysis of Si(CH3)2Cl2
Authors: Chang Hua , Lee Long Jeng , Hwang Rong Li , Lin M. S. , Lou J. C. 
Published: March 2011

AbstractThe chemical kinetics of laser pyrolysis of Si(CH3)2Cl2 was studied. Besides Si/C deposited on substrate as a needle the main gaseous products were H2 and HCI. The decomposition rate constants of Si(CH3)2Cl2 and the formation rate constants of H2 and HCl were measured. The chemical and physical properties of the Si/C needles were studied by various methods, such as their outer features, elemental analysis, Auger depth profile spectra, X-ray diffraction. Other useful properties, such as electric resistivity, photovoltaic effect and hardness, were also reported. A model for the pyrolysis and the growth process of this Si/C needles was proposed. It should be emphasized that the samples with desired physical properties could be grown by controlling the growth conditions properly -- the laser power and the pressure of Si(CH3)2Cl2.
Can Oxidation and Other Treatments Help Us Understand the Nature of Light-Emitting Porous Silicon?
Authors: Fauchet P.M. , Ettedgui E. , Raisanen A. , Brillson L.J. , Seiferth F. , Kurinec S.K. , Gao Y. , Peng C. , Tsybeskov L. 
Published: March 2011

AbstractUsing a careful analysis of the properties of light-emitting porous silicon (LEpSi), we conclude that a version of the “smart” quantum confinement model which was first proposed by F. Koch et al [Mat. Res. Soc. Symp. Proc. 283, 197 (1993)] and allows for the existence of surface states and dangling bonds, is compatible with experimental results. Among the new results we present in support of this model, the most striking ones concern the strong infrared photoluminescence that dominates the room temperature cw spectrum after vacuum annealing above 600 K.