bluuebunny/crossref_metadata_2025_split huggingface dataset:
Robust Design of Advanced Thermoelectric Conversion Systems: Probabilistic Design Impacts on Specific Power and Power Flux Optimization
Authors: Hendricks Terry J , Karri Naveen K. 
Published: April 2011

AbstractAdvanced, direct thermal energy conversion technologies are receiving increased research attention in order to recover waste thermal energy in advanced vehicles and industrial processes. Advanced thermoelectric (TE) systems necessarily require integrated system-level analyses to establish accurate optimum system designs. Past system-level design and analysis has relied on well-defined deterministic input parameters even though many critically important environmental and system design parameters in the above mentioned applications are often randomly variable, sometimes according to complex relationships, rather than discrete, well-known deterministic variables. This work describes new research and development creating techniques and capabilities for probabilistic design and analysis of advanced TE power generation systems to quantify the effects of randomly uncertain design inputs in determining more robust optimum TE system designs and expected outputs. Selected case studies involving stochastic TE .material properties demonstrate key stochastic material impacts on power, optimum TE area, specific power, and power flux in the TE design optimization process. Magnitudes and directions of these design modifications are quantified for selected TE system design analysis cases.
Electronic Phase Transitions in F-electron Metals at High Pressures: Synchrotron X-ray Spectroscopic Studies on GD to 100 GPa
Authors: Yoo Choong-Shik , Maddox Brian , Iota Valentin 
Published: April 2011

AbstractUnusual phase transitions driven by electron correlation effects occur in many f-electron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in third-generation synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the f-electrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce.
Quantifying the Importance of Orbital Over Spin Correlations in δ-Pu Within Density-Functional Theory
Authors: Soderlind Per 
Published: April 2011

AbstractThe electronic structure of plutonium is studied within the density-functional theory (DFT) model. Key features of the electronic structure are correctly modeled and bonding, total energy, and electron density of states are all consistent with measure data, although the prediction of magnetism is not consistent with many observations. Here we analyze the contributions to the electronic structure arising from spin polarization, orbital polarization, and spin-orbit interaction. These effects give rise to spin and orbital moments that are of nearly equal magnitude, but anti-parallel, suggesting a magnetic-moment cancellation with a zero total moment. Quantifying the spin versus orbital effects on the bonding, total energy, and electron spectra it becomes clear that the spin polarization is much less important than the orbital correlations. Consequently, a restricted DFT approach with a non-spin polarized electronic structure can produce reasonable equation-of-state and electron spectra for δ-Pu when the orbital effects are accounted for. Hence, we present two non-magnetic models. One in which the spin moment is canceled by the orbital moment and another in which the spin moment (and therefore the orbital moment) is restricted to zero.
Theoretical Studies of Spectral Properties of Plutonium
Authors: Zhu Jian-Xin , McMahan A.K. , Jones M.D. , Durakiewicz T. , Joyce J.J. , Wills J.M. , Albers R.C. 
Published: April 2011

AbstractBy combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of δ-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the “open shell” 5f5 configuration gives the best agreement, resolving the controversy over 5f “open shell” versus “close shell” atomic configurations in δ-Pu.
Testing of Uranium Dioxide Containing Different Levels of Alpha Activity Under Anaerobic and Reducing Conditions
Authors: Ödegaard-Jensen Arvid , Oversby Virginia 
Published: April 2011

AbstractSweden plans to dispose of spent nuclear reactor fuel in a deep geologic repository in granitic rock. The conditions in the repository in the long term will be reducing and water is not expected to contact the fuel until after more than 1000 years. At that time, most of the beta- and gamma-active nuclides will have decayed away and the radiation will be dominated by alpha decay. In order to simulate the radiolysis field for dissolution of spent fuel with age more than 1000 years we have used uranium dioxide containing 5% U-235 and 0, 5, or 10% U-233. The 10% U-233 gives an alpha activity appropriate to about 3000 years after disposal. Samples were testied in a synthetic groundwater with low ionic strength and with the chemical composition dominated by sodium bicarbonate and calcium chloride. Tests were run in triplicate using an atmosphere of nitrogen (1atm), hydrogen (10 bar), hydrogen (10 bar) plus an iron strip in the solution, nitrogen (1 atm) plus an iron strip in the solution, hydrogen (10 bar) plus an iron strip in the solution, hydrogen (10 bar) without the iron strip. Each of these test conditions was run for 2 consecutive periods of at least 21 days. The results showed that the dissolution behavior of the samples was the same for both nitrogen atmosphere and hydrogen atmosphere. The amount of U dissolved under these conditions clearly showed the enhancement of dissolution due to oxidation of the sample surface by radiolysis products. When an iron strip was added to the solution, the amount of dissolution decreased dramatically indicating that the Fe(II) ions released from the corroding iron were able to react with most of the radiolysis products before they could oxidize the uranium dioxide surface.
Orbital Hybridization in Uranium Compounds and its Influence on Electronic Properties
Authors: Wang Wei , Zhang Hong , Liu Guokui 
Published: April 2011

AbstractComputational analysis and modeling of spectroscopic properties of trivalent uranium in crystals of hexagonal symmetry have been conducted with inclusion of the crystal-field induced orbital hybridization between the 5f3 and 5f26d configurations. It is shown that, in the absorption spectrum with energy above 20,000 cm-1, the mixing of 5f3 and 5f26d states is significant. The spectrum in this region cannot be interpreted by the conventional model of crystal field theory. The Judd-Ofelt theory is completely failed in predicating the intensities of optical absorption from the ground state to the configuration mixed excited states. A new Hamiltonian including the odd ranks of crystal field interaction is diagonalized on the bases of all 5f3 and 5f26d states. A simulation of absorption spectrum is optimized in comparison with the experimental spectrum for determination of the Hamiltonian parameters.
Spin-Orbit Coupling Versus Exchange Interaction in Actinide Metals
Authors: van der Laan Gerrit , Moore Kevin Thomas 
Published: April 2011

AbstractThe electronic structure of the actinide metals, Th, U, Np, Pu, Am, and Cm, is investigated using electron energy-loss spectroscopy (EELS) in a transmission electron microscope, together with many-electron spectral calculations. At theN4,5edge, sum rule analysis gives the angular part of the spin-orbit interaction per hole, showing that while light metals (Th and U) followLScoupling, heavier metals (Pu, Am, and Cm) follow intermediate coupling of the 5fstates. The intermediate coupling is near thejjlimit for Pu and Am, but strongly shifted towards theLScoupling limit for Cm. At theO4,5edge many-electron spectral calculations show that the prepeak corresponds to a “forbidden” transition.
Multi Scale Study of Self-irradiation Effects in Plutonium Alloys
Authors: Berlu Lilian , Rosa Gaëlle , Jomard Gérald 
Published: April 2011

AbstractExperimental measurements have shown that plutonium alloys exhibit changes of their macroscopic as well as microscopic properties. For example, a swelling of plutonium alloys was observed with aging with dilatometry and X-ray diffraction. The main idea to explain these changes rises in self irradiation undergoing by those materials. Plutonium α decay is at the origin of displacements cascades creating a large amount of structural defects. These later by anihilation and recombination give rise to larger defects such as voids and clusters. The aim of this work is to study the occurrence of such phenomena combining ab-initio, molecular dynamic and Monte Carlo methods in a coherent multi-scale approach which would help to understand long term behavior of structural defects and consequences of self irradiation. We show that plutonium does not seem to behave like other metals under ion irradiation. We discuss results obtained for high energy displacements cascade simulations. After parametric study of displacements cascade simulations combining temperature and cascade energy has been exposed, superposition of low energies displacements cascades is discussed as a method to construct realistic defect microstructures and to reach a rational use of computational time. At the end, we will present results of preliminary Monte Carlo simulations based on our molecular dynamic data which show that the spatial correlation of the stable defects populations created by the cascades seems to have a great influence on the predicted swelling.
Direct Energy Conversion Nano-hybrid Fuel
Authors: Popa-Simil Liviu 
Published: April 2011

AbstractMost of the exothermic nuclear reactions transfer the mass defect or binding and surplus energy into kinetic energy of the resulting particles. These particles are traveling through material lattices, interacting by ionization and nuclear collisions. Placing an assembly of conductive-insulating layers in the path of such radiation, the ionization energy is transformed into charge accumulation by polarization. The result is a super-capacitor charged by the moving particles and discharged electrically. Another more promising solution is to use bi-material nanoparticles organized such as to act like a serial connection and add the voltage. A spherical symmetry fission products source coated in several nano-layers is desired for such structures. The system may operate as dry or liquid-immersed battery, removing the fission products from the fissile material. There is a tremendous advantage over the current heat flow based thermal stabilization system allowing a power density up to 1000 times higher.
Recoil Based Fuel Breeding Fuel Structure
Authors: Popa-Simil Liviu 
Published: April 2011

AbstractNuclear transmutation reactions are based on the absorption of a smaller particle as neutron, proton, deuteron, alpha, etc. The resulting compound nucleus gets out of its initial lattice mainly by taking the recoil, also with help from its sudden change in chemical properties. The recoil implantation is used in correlation with thin and ultra thin materials mainly for producing radiopharmaceuticals and ultra-thin layer radioactive tracers. In nuclear reactors, the use of nano-particulate pellets could facilitate the recoil implantation for breeding, transmutation and partitioning purposes. Using enriched 238U or 232Th leads to 239Pu and 233U production while using other actinides as 240Pu, 241Am etc. leads to actinide burning. When such a lattice is immersed into a radiation resistant fluid (water, methanol, etc.), the recoiled product is transferred into the flowing fluid and removed from the hot area using a concentrator/purifier, preventing the occurrence of secondary transmutation reactions. The simulation of nuclear collision and energy transfer shows that the impacted nucleus recoils in the interstitial space creating a defect or lives small lattices. The defect diffuses, and if no recombination occurs it stops at the lattices boundaries. The nano-grains are coated in thin layer to get a hydrophilic shell to be washed by the collection liquid the particle is immersed in. The efficiency of collection depends on particle magnitude and nuclear reaction channel parameters. For 239Pu the direct recoil extraction rate is about 70% for 238UO2 grains of 5 nm diameters and is brought up to 95% by diffusion due to 239Neptunium incompatibility with Uranium dioxide lattice. Particles of 5 nm are hard to produce so a structure using particles of 100 nm have been tested. The particles were obtained by plasma sputtering in oxygen atmosphere. A novel effect as nanocluster radiation damage robustness and cluster amplified defects rejection will be discussed. The advantage of the method and device is its ability of producing small amount of isotopic materials easy to separate, using the nuclear reactors, with higher yield than the accelerator based methods and requiring less chemistry. It also represents a reliable candidate for nuclear fuel breeding reducing the cost of super-grade Plutonium and Thorium toward the price of urania and thoria.
Plutonium Elastic Moduli, Electron Localization, and Temperature
Authors: Migliori Albert , Mihut-Stroe Izabella , Betts Jon B. 
Published: April 2011

AbstractIn almost all materials, compression is accompanied naturally by stiffening. Even in materials with zero or negative thermal expansion, where warming is accompanied by volume contraction it is the volume change that primarily controls elastic stiffness. Not so in the metal plutonium. In plutonium, alloying with gallium can change the sign of thermal expansion, but for the positive-thermal-expansion monoclinic phase as well as the face-centered-cubic phase with either sign of thermal expansion, and the orthorhombic phase, recent measurements of elastic moduli show soften on warming by an order of magnitude more than expected, the shear and compressional moduli track, and volume seems irrelevant. These effects point toward a novel mechanism for electron localization, and have important implication for the pressure dependence of the bulk compressibility.
The Nanoscale Informal Science Education Network
Authors: Bell Larry 
Published: April 2011

AbstractThe Nanoscale Informal Science Education Network was formed by the Museum of Science in partnership with the Science Museum of Minnesota and the Exploratorium through a cooperative agreement with the National Science Foundation in the fall of 2005. Over the course of its first two years the NISE Net focused on developing prototype informal educational materials to engage the public in learning about nanoscale science and technology. Now the NISE Net if focusing on building the network and disseminating materials and knowledge broadly to facilitate capacity building, partnering, and getting nano education activities for the public to happen in over 100 sites nationwide. NanoDays in 2008 from March 29 through April 6 has been developed to focus these efforts.
European Nanotechnology Masters Recognition Scheme - Supporting Technical Higher Education
Authors: Singh Kshitij Aditeya 
Published: April 2011

AbstractEurope aspires to become a knowledge oriented economy by 2010 in which nanoscience and nanotechnologies play an important role. However, the development of skills and competencies in the workforce will be critical in realising the benefits offered by nanoscience and nanotechnologies. The Nanotechnology Masters Recognition Scheme aims to support technical higher education by addressing the challenges of education in nanoscience and nanotechnologies particularly at the masters' level. The paper provides an overview of the education and professional development systems in Europe with specific examples from the U.K. The paper also underlines how the scheme addresses the challenges of skills and competencies development within the European context through information dissemination, identifying gaps and professional needs, encouraging professional development, and supporting through various different measures.
Towards Terabit/in2 Magnetic Storage Media
Authors: Niarchos Dimitris , Manios E. , Panagiotopoulos I. 
Published: April 2011

AbstractIn modern society there is an almost insatiable demand for ever increasing storage capacities in computers and consumer electronics. Magnetic recording is the dominant storage technology and the hard disk, due to its versatility, is becoming a pervasive device in various applications. The soaring demand arises from data-intensive computer applications, including graphics, animation, multimedia and desktop publishing, to which can be added a growing market for non-PC consumer devices such as set-top boxes, cameras, mobile phones, laser printers and satellite navigation systems. In response to this demand the hard disk drive manufacturers have come forward with spectacular increase in storage capacities and densities over the last decade. It is currently projected that the evolution of conventional perpendicular recording storage density in the hard disk industry will reach a limit of 500 Gbit/in2, while further progress will require major breakthroughs and alternative technologies.
In this presentation we will review the state-of-the-art in magnetic recording media and we will discuss the future approaches to reach densities in excess of 1 Tbit/in2 densities along the three axes : a) self-assembled coercive nanoparticles, b) exchange spring media and percolated media, and c) bit-patterned media (nanoscale patterning). This entails resolving several conflicting requirements with regard to signal to noise ratio (SNR) , writability and thermal stability of these new promising systems.
Investigation on the Immobilisation of Carbon in OPC-BFS and OPC-PFA Systems
Authors: Kinoshita Hajime , Borges Paulo H. R. , Utton Claire A. , Milestone Neil B. , Lynsdale Cyril 
Published: April 2011

AbstractThe reaction of CO2 gas with OPC, OPC-BFS and OPC-PFA composite cement systems were studied using XRD, SEM and TG to investigate the applicability of these materials to immobilise carbon arising from graphite waste. XRD results suggested that calcite formed in OPC system after the carbonation reaction, whereas calcite and vaterite were observed in OPCBFS and OPC-PFA systems. In OPC system, nearly half of Ca(OH)2 was consumed to form CaCO3. In OPC-BFS and OPC-PFA systems, the amount of CaCO3 formed, corresponded to the consumption of greater than 100% of Ca(OH)2 initially present, suggesting that other hydration products e.g. C-S-H were also consumed, either directly or indirectly during the carbonation process. The OPC-BFS system became more porous after carbonation. OPC-PFA system indicated a high efficiency on the conversion of Ca in the system into CaCO3.
Changes to Alkali Ion Content Adjacent to Crystal-Glass Interfaces
Authors: Rushton Michael J. D. , Grimes Robin W. , Owens Scott L. 
Published: April 2011

AbstractAtomic scale molecular dynamics simulations have been used to predict the location of glass modifying Na, Li and Mg species in a borosilicate Magnox type waste glass adjacent to interfaces with the (100) and (110) surfaces of MgO, CaO and SrO crystals. These simulations show a considerable increase in alkali and alkali earth concentration adjacent to specific interfaces. In particular, there are significant, systematic changes in Na, Li and Mg position and concentration as a function of both the crystal's terminating surface and composition.
A Mössbauer Study of Iron in Vitrified Wastes
Authors: Hannant Oliver M. , Bingham Paul A. , Hand Russell J. , Forder Sue D. 
Published: April 2011

Abstract57Fe Mössbauer spectroscopy has been used to study the environment and oxidation state of iron in a series of vitrified sewage sludge ash (SSA) wastes, which are broadly similar in composition and variability to some intermediate-level legacy wastes (ILLW). The SSA wastes studied here are incapable of forming an homogeneous glass when melted at 1450 °C although increasing additions of CaO reduce the crystalline content, which consists of Ca3(PO4)2 and Ca3Mg3(PO4)4. Bulk glass transition temperatures of 670–850 °C have been measured, the value decreasing with increasing CaO content. Tetrahedrally coordinated Fe3+ appears to exist in vitrified SSA only at high CaO contents (> ∼ 29 mol. %) and whilst broadly similar to our previous results for simulated vitrified SSA, behavioural differences have been noted between fitted Mossbauer parameters for real and simulated vitrified SSA. We suggest that these could be attributable to the buffering action of carbon and other reducing agents in the real SSA wastes.
HIPed Tailored Ceramic Waste Forms for the Immobilisation of Cs and Sr
Authors: Carter Melody L. , Vance E. R. 
Published: April 2011

AbstractThis paper illustrates the benefits of hot isostatically pressed (HIPed) tailored ceramic waste forms for the immobilisation of Cs and Sr separated from spent nuclear fuel. Experimental data on microstructure and aqueous durability are presented for Cs- and Sr-bearing hollanditerich tailored ceramics prepared with 12-18 wt% waste (on an oxide basis). MCC-1 type leach testing, on the sample containing 12 wt% waste at 90°C for 28 days revealed extremely low normalised 7-28-day Cs and Sr release rates of 0.003 and 0.004 g/m2day respectively.
Neutron and Resonant X-ray Diffraction Studies of Zirconolite-2M
Authors: Whittle Karl R. , Smith Katherine L. , Hyatt Neil C. , Lumpkin Gregory R. 
Published: April 2011

AbstractZirconolite (nominally CaZrTi2O7) is a constituent phase of potential waste forms for the safe immobilisation of actinide wastes. Structural studies of such materials provide important information about cation ordering, lattice parameters, and strain effects, and provide input into the modelling of alpha decay damage and the development of future wasteform designs. A suite of zirconolites based on the replacement of Ti with Nb and Fe has been studied using high resolution neutron diffraction and resonant X-ray diffraction to determine the degree of disorder across the available cation sites. Resonant X-ray diffraction is a unique method which allows the location of certain cations to be determined accurately by taking advantage of the change in scattering power close to an absorption edge (e.g., Nb-K and Zr-K). Using standard X-ray diffraction alone this is not possible and there is little scattering difference between Nb and Zr.Raman spectroscopy and measured lattice parameters have shown that the exchange of Ti with Nb and Fe has a non-linear effect on the unit cell dimensions and Raman peak positions while retaining the 2M polytype. Mössbauer spectroscopy has shown that the Fe preferentially fills the Ti split (C2) site. The results from this study provide a more complete picture of the cation order-disorder problem and are generally consistent with the behaviour of lattice parameters across the series.