bluuebunny/crossref_metadata_2025_split huggingface dataset:
Random Telegraph Noise in Individual Single-walled Carbon Nanotubes
Authors: Jhang SungHo , Lee SangWook , Lee DongSu , Campbell Eleanor E. B. , Roth Siegmar , Park YungWoo 
Published: April 2011

ABSTRACTThe switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with electrons.
Controlling (In,Ga)As quantum structures on high index GaAs surfaces
Authors: Seydmohamadi Sh. , Wen H. , Wang Zh. M. , Salamo G. J. 
Published: April 2011

ABSTRACTWe investigate the formation of (In, Ga) As self assembled quantum structures grown on different orientations of a GaAs substrate along one side of the stereographic triangle between (100) and (111)A surfaces. The samples were grown by Molecular Beam Epitaxy, monitored by Reflection High-Energy Electron Diffraction during the growth and characterized by in-situ Scanning Tunneling Microscopy and Atomic Force Microscopy. A systematic transition from zero dimensional (In, Ga) As quantum dots to one dimensional quantum wires was observed as the substrate was varied along the side of the triangle within 25° miscut from the (100) toward (111)A, which includes several high index surfaces. We propose an explanation for the role of the substrate in determining the type of the nanostructure that is formed.
A Multiscale Model of the Si LPCVD Process
Authors: Rondanini Maurizio , Masi Maurizio , Carrà Sergio , Cavallotti Carlo , Milano Politecnico di 
Published: April 2011

ABSTRACTThe Low Pressure Chemical Vapor Deposition of Si from SiH4 is an industrial process that can be used to deposit epitaxial Si at relatively low surface temperatures. Multiscale models are necessary in order to tune the operating conditions to optimize the quality of the deposited materials. In this work we present a multiscale approach meant to describe the film morphological evolution at different time and length scales. The reactor fluid dynamics and overall mass and temperature balances are solved with the finite element method. The morphological evolution of the film is investigated with 3D kinetic Monte Carlo. We have systematically investigated the dependence of the growth morphology from temperature, pressure and gas phase composition (SiH4/H2 ratio) with the aim of determining the operating parameters window that can lead to the best film morphology. We found that the presence of a significant amount of hydrogen on the surface can significantly influence the surface morphology. In particular hydrogen can be considered as the principal responsible of the transition from an order terrace step flow growth regime, which prevails at high temperatures, to a disordered 3 dimensional growth regime. It is also worth noting that our KMC simulations show that the hydrogen surface chemistry active at low temperatures is probably richer than expected, since the formation of a significant number of island on the surface dramatically increases the concentration of steps, and thus the variety of configurations by which two adsorbed H atoms can interact.
Materials Science and Technology: A curriculum that works
Authors: Stoebe Thomas G. , Rusin John M. 
Published: April 2011

Materials Science and Technology is a curriculum developed at Battelle Pacific Northwest National Laboratories, which emphasizes hands-on, minds-on studies of materials science and technology. This curriculum has been taught to over 1000 middle and high school teachers nationwide in a series of week-long institute programs, and is used in classrooms in 16 states. Evaluations have shown that the curriculum is highly effective in getting students interested in science and technology, and in encouraging them to study more science.This paper presents the basics of the curriculum and its approach, along with venues used for promoting the curriculum and the teaching methods used. Full evaluation results are discussed, including the assessment of increased student interest and increased student involvement their own learning. Means of adapting the program to a local situation are also presented.
Turning Cutting-Edge Research into Secondary Curriculum
Authors: Zenner Greta M. , Crone Wendy C. , Aura Gimm J. , Lux Ken W. , Voyles Paul M. , Abbott Nicholas L. , Cina Anthony P. , Comins Ann Pumper , Tabora Johan , Tuchscherer Pamela , Tuchscherer Tyson , John Whitsett P. , Widstrand Cindy G. 
Published: April 2011

ABSTRACTTraditional science classroom activities rely on topics and experiments that are distant from the forefront of scientific research. As a result, students view science as stagnant and far removed from real life. Through a National Science Foundation-funded Research Experiences for Teachers (RET) program, we at the University of Wisconsin-Madison (UW) Materials Research Science and Engineering Center (MRSEC) work with secondary teachers to transform cutting-edge research in nanoscale science and engineering into curriculum that is appropriate for middle- and high-school classrooms. This benefits everyone involved: teachers learn about innovative science and the process of research; UW MRSEC personnel learn about science education and the state of today's schools; and students get to test and engage with new curriculum about breakthrough research. This past summer our RET participants conducted research on and developed curriculum about “smart” papers with microencapsulation technology, fuel cells, nano biosensors and liquid crystals, glassy metals, and Wells models.
Research Experiences for Teachers in Materials Science: A Case Study
Authors: Strand Michelle A. , Wignall Steve , Leslie-Pelecky Diandra L. 
Published: April 2011

ABSTRACTThe National Science Education Standards encourage teachers to become involved in research as ‘representatives of science in the classroom’. The Research Experiences for Teachers program affiliated with the Materials Research Science and Engineering Center at the University of Nebraska involves teachers in research on nanoscale magnetic and electronic structures over a summer. Two teachers and a sponsoring researcher share their experiences and what they believe are necessary elements for successful RET experiences.
Materials Education for the 21ST Century Workforce a Report on the 18th Biennial Conference on National Materials Policy, Washington D.C.
Authors: Christou Aris 
Published: April 2011

ABSTRACTThis article presents a summary report of the 18th biennial conference on National Materials Policy, held May 24–25, 2004 at National Academies Keck Center, Washington DC. This conference addressed the educational needs in materials science for the 21st century through a series of presentations which focused on all aspects of materials education including elementary (K-12), undergraduate as well as graduate education and continuing education. The conference therefore contributed to the definition of the educational needs for the 21st century workforce.
A Study of Mechanical Effect of Simulated Fault Movement on Engineered Barrier System
Authors: Nishimura Mayuka , Hirai Takashi , Tanai Kenji , Yui Mikazu 
Published: April 2011

ABSTRACTThe objective of this study is to clarify the mechanical effect on the engineered barrier system (EBS) of a fault movement, presupposed to occur in a high-level radioactive waste repository. The plan of this study is; 1) to understand the mechanical behavior of the buffer material when shearing takes place during experimental tests, and 2) to make progress in numerical analysis techniques in order to estimate the effect of fault movement on the EBS at a disposal site.Accordingly, the first part of this paper reports tests, which were carried out on a 1:20 model of the EBS. The experimental results indicate that the increased total pressure is due, in part, to the increase of pore water pressure. The second part of this paper reports the results of finite element simulations of the experiments. The calculation results show that the permeability of the near-field rock, which influences the amount of water draining from the buffer material, affects the pressure increase in the buffer material. With appropriately set parameters, the calculation shows agreement with the experimental results.
Waste Package Scenario Modelling
Authors: Watson Sarah P , Hodgkinson David P , Robinson Peter C , Bailey Lucy EF , Poole Mike J 
Published: April 2011

ABSTRACTUK Nirex has supported a programme of work to develop models describing the postclosure evolution of intermediate-level waste packages with the objectives of:• providing support and justification for the parameters and representations used in performance assessment models;• informing future model development and packaging advice.Scenarios for the potential evolution of a waste package were developed and modelled taking explicit account of waste package heterogeneity and the time-dependence of the physical and chemical characteristics of the system. The modelling work highlighted the treatment of organic complexants and the representation of physical containment as two areas in which the impacts of time dependence and package scale heterogeneity might be particularly significant.A subsequent study of the impact of organic complexants emphasised the importance of heterogeneity in package inventory in determining the radionuclide release from the near field.The degree of containment afforded by the wasteform and the waste container has been investigated as part of a study to develop a preliminary understanding of the mixing scales within the repository. The study suggests that the most important control on the release of radionuclides from the waste packages is the integrity of the waste encapsulation grout. Interactions between neighbouring packages are to be expected, but the degree to which homogeneous (well mixed) conditions develop may be limited in both time and space.
Consolidation of Ethanol/Bentonite Slurry Injected in a Planar Fracture; Mathematical Modelling and Experiment
Authors: Takase Hiroyasu , Iwasa Kengo , Ishii Takashi , Ueda Hiroyoshi , Sakabe Yasushi , Ishiguro Katsuhiko 
Published: April 2011

ABSTRACTEthanol/bentonite slurry is an alternative to the conventional cement-based material that may cause chemical disturbances to the host rock and the buffer material. In this study we carried out an experiment in which the ethanol/bentonite slurry was injected into a planar synthetic fracture at a constant rate. The pressure build-up due to the increase in viscosity of the bentonite ethanol slurry was observed and, eventually, consolidation of the slurry led to termination of the injection. A mathematical model was also developed to simulate the advection, dispersion and matrix dispersion of ethanol that contributed to the increase in viscosity of the ethanol/bentonite slurry, together with a Stoke's flow of the slurry before consolidation. Furthermore, applicability of the ethanol/bentonite slurry as a grouting material in a range of geological settings is discussed based on the result of a case study using the same model.
Impact of iron released from steel components on the performance of the bentonite buffer: a preliminary assessment within the framework of the KBS-3H disposal concept
Authors: Wersin Paul , Johnson Lawrence H. , Snellman Margit 
Published: April 2011

ABSTRACTSteel components in the engineered barrier of HLW repositories have a potential to react with the clay buffer and induce adverse effects on its properties. These effects have been assessed within the KBS-3H disposal concept, which includes spent fuel in copper canisters surrounded by bentonite blocks and a steel supercontainer (SC), placed within tunnels in deep crystalline Olkiluoto-type host rock. Based on literature review and thermodynamic modeling, the SC is predicted to completely corrode within a minimum of a few thousand years. The resulting corrosion products are expected to be magnetite, and depending on groundwater compositions, also iron sulfide and perhaps siderite. Furthermore corrosion-derived Fe(II) may react with the clay to form non-swelling phyllosilicates, such as berthierine. From simple mass balance estimates and by applying a more realistic reactive transport model, it can be deduced, that the effect of iron from the SC on the integrity of the bentonite buffer is limited. However, large uncertainties in adequately quantifying this effect pertain due to limited process knowledge on Fe-bentonite interactions.
CORALUS: An Integrated In Situ Corrosion Test on α-Active HLW Glass
Authors: Valcke Elie , Smets Steven , Labat Serge , Lemmens Karel , Iseghem Pierre Van , Thomas Peter , Godon Nicole , Jollivet Patrick , Parisot Géraldine , Mestre Jean-Pierre , Jockwer Norbert , Wieczorek Klaus , Pozo Claudine 
Published: April 2011

ABSTRACTIntegrated in situ corrosion tests with α-doped SON68 glass samples have been and are still being performed in the HADES underground laboratory in Mol, Belgium. Two test tubes have been dismantled, and the glass and clay samples have been analysed (mass loss, SEM, EDS, SIMS,…). The results on glass corrosion largely respond to the expectations and agree very well with results from surface laboratory tests and modelling predictions. The glass alteration is about two orders of magnitude higher at 90 °C than at 30 °C. The addition of powdered glass frit to a Ca-bentonite backfill reduces the glass alteration by two orders of magnitude in comparison with another backfill, dried Boom Clay. The α-doped glass samples were shown to have slightly thicker alteration layers. The thickness seemed to increase with increasing αβγ-activity. Because of the lack of sufficient data on mass loss, we cannot conclude that also the degree of alteration is higher for these samples. Under the thermal gradient in the test tubes, the reaction of Cabentonite with the glass samples and the powdered glass frit dispersed within the bentonite results in the neo-formation of non-swelling 7 Å minerals.
Studies on Metal Gluconic Acid Complexes
Authors: Warwick Peter , Evans Nick , Vines Sarah 
Published: April 2011

ABSTRACTThe presence of organic complexants, such as gluconic acid, in an intermediate-level radioactive-waste (ILW) repository may have a detrimental effect on the sorption of radionuclides, by forming organic complexes in solution. In order to assess this, stability constants are required for the complexes formed with radionuclides at high pH. This study reports the stability constants for the reactions of some divalent metals with gluconic acid (Gl). The metals studied were Cd, Co, Fe(II), and U(VI) at pH 13.3; and Co and U(VI) at pH 7. The constants were measured by the Schubert (ion-exchange) or solubility product methods. Stoichiometries of the complexes were also determined. At pH 7 each complex was of the form M1Gl1, with log β values suggestive of salt formation. At high pH, log β values were between 13 and 20. The constants have enabled speciation calculations to be performed showing the effect of gluconic acid on the metal's solubility, with data for Ni included. Solubility is predicted to increase in the presence of Gl from pH 9 to 13.5, suggesting that it may have an impact on radionuclide behaviour. The largest solubility increases are for Cd and Co, the smallest, U(VI).
Creep performance of OFP copper for the overpack of repository canisters
Authors: Auerkari Pertti , Holmström Stefan , Salonen Jorma , Nenonen Pertti 
Published: April 2011

ABSTRACTTo experimentally assess the long term creep performance of oxygen-free phosphorus- doped (OFP) copper for the overpack of repository canisters, the combination of modestly elevated temperature and multi-axial stress state has been applied for accelerated testing. Multi-axiality was induced by using notched compact tension (CT) specimens, with interrupted testing to periodically inspect for creep damage. Uniaxial creep testing was also conducted to support creep analysis of the CT specimens. After about 10000 h of testing at 150°C/46 MPa (reference stress), the inspected CT specimens showed only marginal creep cavity indications near the notch tip. However, a distinct grain boundary zone with elevated Pcontent was observed to appear and widen during testing, mainly near the notch tip. The significance of the grain boundary zone is not well understood, but indicates stress-enhanced microstructural changes at relatively low temperatures. The predicted isothermal uniaxial creep life at 150°C/46 MPa agreed satisfactorily within a factor of two in time, when obtained independently from converted multi-axial testing results and directly from a creep model based on the available uniaxial data. Although the uncertainties in extended extrapolation remain large, the prediction would suggest safe long term service at leastagainst pure creep failure of intact parent material.
Development of a rapid screening test for SCC susceptibility of copper in disposal vault conditions
Authors: Betova Iva G. , Bojinov Martin S. , Heinonen Jussi , Kinnunen Petri , Lilja Christina , Saario Timo 
Published: April 2011

ABSTRACTStress corrosion cracking is a potential failure mechanism of the copper canister proposed to be the main corrosion barrier in the Scandinavian design of the final nuclear waste disposal vault. The main target in SCC-oriented research is to determine the limiting values for the critical concentration of harmful species, the potential range in which these species cause SCC and the threshold stress level required for SCC. The present paper attempts to redefine the criteria for SCC susceptibility of copper in acetate solutions through analysis of potentiodynamic curves using both rotating disc and thin plate electrodes insulated on one side. A potential range in which the current densities at a slow sweep rate are lower than those at a fast sweep rate exists for Cu in 0.001 M - 0.1 M acetate. However, the values of the current densities within this range are significantly smaller than those postulated for active anodic dissolution, implying dissolution mediated by a surface film. New criteria for the SCC susceptibility of pure copper in acetate solutions have been formulated through Stern-Geary analysis of the polarisation curves. Several electrochemical characteristics, such as the current density at the positive crossover potential, the ratio between the corrosion current densities determined from the slow and fast sweeps, as well as the anodic current density in a fast sweep show a clear jump for concentrations between 0.01 M and 0.05 M. This, however, cannot yet be considered as an indication of SCC susceptibility at higher acetate concentrations, as evidenced by complementary SSRT tests.
Direct alpha-recoil as a process to generate U-234/U-238 disequilibrium in groundwater
Authors: Rasilainen Kari , Nordman Henrik , Suksi Juhani , Marcos Nuria 
Published: April 2011

ABSTRACTWe discuss quantitatively the capability of direct α-recoil to create observable radioactive disequilibrium (U-234/U-238 activity ratio > 1) in flowing groundwater. Coupled equations for radioactive decay chain are formulated for the solid U source and for the corresponding groundwater receiving the recoiling U-234 atoms. U-rich fracture coating material and the water flowing in the fracture are discussed in detail.The novel modelling approach worked well and provides a useful tool for more detailed site-specific studies with more detailed input data. The approach appears feasible because the equations are based on straightforward mass balance considerations.α-recoil -induced enrichment of U-234 in groundwater is a slow process: the increase of U-234/U-238 activity ratio to notable values above unity will take hundreds to thousands of years. Strong groundwater flow prevents any local recoil-induced U-234 enrichment in the water.
Bituminised Waste Re-treatment: Replacement of the Bitumen Matrix by a Glass Matrix
Authors: Impens Nathalie R.E.N. , Tennstedt Isabelle M. , Lemmens Karel , Gielen Ben , Laer Jo M.P. Van , Fonteyne Alfons F. , Vos Liliane , Vos Ben , Leenaers Ann J.G. , Berghe Sven Van den , Bree Peter J.P. Van , Oost Guido Van 
Published: April 2011

ABSTRACTThe vitrification of nuclear waste salts similar to the salts present in Eurobitum produced by the former Eurochemic reprocessing plant, Mol-Dessel, Belgium, is investigated. In order to approach the composition of the high-level waste reference glass SON68, mixtures with different ratios of glass frit to waste salts have been prepared and vitrified. The concentration of the waste salts varied between 17 and 25 % by weight.To compare the short term corrosion behaviour with reference waste glass, leach tests have been performed. During 8 weeks, the glass samples were submitted to leach tests at 363 K using Milli Q water as leachant, at a glass exposed area over leachant volume ratio equal to 100 m−1.During this short period, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) showed no gel layer formation. This technique did not detect changes in the chemical composition. However, X-ray photoelectron spectroscopy (XPS) showed that the binding energy of the Zr 3d and Si 2p electrons decreased as a function of leaching time, indicating an increasing covalent character of the glass surface. Inductively coupled plasma-mass spectrometry (ICP-MS) of the leachate as a function of time shows that ionic species such as Na and K leach faster than e.g. Si and B. These results together with the XPS data suggest the onset of a gel layer formation. The effect of waste content in the glass on the leaching rate is also studied. The results are compared with similar leaching tests on R7T7 type SON68 glass. Most elements are better retained in the simulated Eurobitum glass than in the SON68 glass.
Immobilization of Simulant ILW Actinide Wastes Containing Halides: Effect of Process Parameters on Wasteform Properties
Authors: Metcalfe Brian L. , Fong Shirley K. , Donald Ian W. 
Published: April 2011

ABSTRACTThe applicability of a process, originally developed to immobilize a chloride-rich intermediate level waste (ILW) arising from the pyrochemical reprocessing of plutonium, to alternative ILW waste-streams containing a large variety of cations, present as oxides together with KCl and CaF2, has been investigated. Non-radioactive studies, using simulated wastes containing hafnium and samarium as surrogates for the actinides, have been performed to establish the optimum processing parameters for the manufacture of wasteforms suitable for long-term storage/disposal. It has been demonstrated that the wastes can be immobilized by calcining with either Ca3(PO4)2 or CaHPO4 as the host. In excess of 97.5 % of the chloride present in calcined wastes, containing up to 3.2 wt% halides as a mixture of F- and Cl-, is immobilized when using this process. Whereas in the original calcined waste, the Cl- (about 12 wt%) was immobilized as chlorapatite, Ca5(PO4)3Cl, and spodiosite, Ca2(PO4)Cl, in these current wastes fluorapatite is the predominant halide containing phase. Conversion of the immobilized waste powder into a monolithic wasteform was achieved by sintering the powder with the addition of a sodium aluminium phosphate based glass. Both the calcined powder and the sintered monolithic wasteforms showed excellent durability in aqueous solution.